Vehicular electronic control unit Number:7,149,609 from the United States Patent and Trademark Office (PTO) owispatent

Title: Vehicular electronic control unit

Abstract: A voltage generated by a variable analog signal source is input to first and second input terminals of a multi-channel A/D converter via an analog signal input circuit including an analog switch and first and second amplifiers, and a resulting digital conversion value is written to a data memory via a microprocessor. Digital conversion values corresponding to voltages at the first and second input terminals that are obtained when the analog switch is opened are stored as first and second error voltages and used for producing first and second correction voltages, respectively. When the input voltage is low, a value obtained by dividing, by a compensation gain, a second correction voltage corresponding to a second input voltage that is produced by the second amplifier and input to the second input terminal as an enlarged range input terminal is selected.

Patent Number: 7,149,609 Issued on 12/12/2006 to Hashimoto

---

Inventors:	Hashimoto; Kohji (Tokyo, JP)
Assignee:	Mitsubishi Denki Kabushiki Kaisha (Tokyo, JP)
Appl. No.:	10/891,525
Filed:	July 15, 2004

---

Foreign Application Priority Data

---

Jan 15, 2004 [JP]			P2004-008439

Current U.S. Class:	701/1 ; 323/299; 701/102; 701/22
Current International Class:	G05D 1/00 (20060101); G05D 3/00 (20060101); G05F 5/00 (20060101); B60L 1/00 (20060101)
Field of Search:	323/266,268,271,299,303,350,351 701/1,22,36,102,115 191/2,6 123/319,396

---

References Cited [Referenced By]

---

U.S. Patent Documents

	4843555		June 1989		Hattori et al.
	4926330		May 1990		Abe et al.
	5757605		May 1998		Furukawa
	6789533		September 2004		Hashimoto et al.
	6985074		January 2006		Li
	7031822		April 2006		Hashimoto et al.

Foreign Patent Documents

	10-169500		Jun., 1998		JP
	11-214996		Aug., 1999		JP
	2000-013227		Jan., 2000		JP

Primary Examiner: Nguyen; Matthew V.
Attorney, Agent or Firm: Sughrue Mion, PLLC

---

Claims

---

What is claimed is:

1. A vehicular electronic control unit comprising: an analog signal input circuit for producing voltages corresponding to a voltage generated by a variable analog signal source; a multi-channel A/D converter for converting the voltages produced by the analog signal input circuit into a conversion digital value; a data memory; a microprocessor for writing a digital conversion value produced by the multi-channel A/D converter to the data memory, the microprocessor having a capability of handling digital data having a longer bit length than a bit length corresponding to a resolution of the multi-channel A/D converter; and a nonvolatile program memory that cooperates with the microprocessor, the analog signal input circuit comprising: a full-range input circuit that is an input circuit provided between the variable analog signal source and a first input terminal of the multi-channel A/D converter, for producing a first input voltage, the full-range input circuit being configured so that the first input voltage becomes approximately equal to a full-scale input voltage of the multi-channel A/D converter when the voltage generated by the variable analog signal source has a maximum value; and an enlarged range input circuit that is an input circuit provided between the variable analog signal source and a second input terminal of the multi-channel A/D converter, for producing a second input voltage, the enlarged range input circuit being configured so that the second input voltage becomes approximately equal to the full-scale input voltage of the multi-channel A/D converter when the first input voltage is equal to a prescribed intermediate voltage that is lower than a maximum voltage, wherein the nonvolatile program memory stores programs to serve as: error signal storing means activated when the voltage generated by the variable analog signal source is zero, for writing, as a first error voltage, a digital conversion value of a first input voltage to the data memory at a first address, and for writing, as a second error voltage, a digital conversion value of a second input voltage to the data memory at a second address; gain compensating means for producing a second compensation voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage and dividing the second correction voltage by a compensation gain or multiplying the second correction voltage by a compensation gain reciprocal, the compensation gain being set so that the second compensation voltage becomes approximately equal to a first correction voltage in a low voltage range obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage, the low voltage range being a range that is lower than the intermediate voltage; and selecting and switching means for selectively using the second compensation voltage if the first input voltage is in the low voltage range, selectively using the first correction voltage if the first input voltage is in a high voltage range that is a range higher than or equal to the intermediate voltage, and issuing an instruction to store a digital conversion value that is proportional to a selection result to the data memory at a prescribed address.

2. The vehicular electronic control unit according to claim 1, wherein: the analog signal input circuit further comprises a first analog switch provided in the full-range input circuit and the enlarged range input circuit, for disconnecting the multi-channel A/D converter from the variable analog signal source or short-circuiting an input circuit between the variable analog signal source and the multi-channel A/D converter to thereby forcibly establish the same state as the voltage generated by the variable analog signal source is zero; and the nonvolatile program memory further store programs to serve as: error signal input means for on/off-controlling the first analog switch in accordance with a first instruction signal supplied from the microprocessor, and for causing the error signal storing means to operate; and present status holding means for preventing data that was selected and stored in the data memory by the selecting and switching means from being changed and keeping the data at a value that was in storage immediately before a start of operation of the error signal input means while the error signal input means is in operation.

3. The vehicular electronic control unit according to claim 1, wherein: the nonvolatile program memory further stores reference gain data that was stored in advance as a reference gain or a reference gain reciprocal and that is a statistical value such as an average or a center value of a plurality of samples obtained by calculating, for a large number of samples, a ratio of a measured value of the second correction voltage to a measured value of the first correction voltage in a state that the first input voltage was approximately equal to the intermediate voltage; and the compensation gain that is used by the gain compensating means is the reference gain.

4. A vehicular electronic control unit comprising: an analog signal input circuit for producing voltages corresponding to a voltage generated by a variable analog signal source that is an exhaust gas sensor having an oxygen pump device and an oxygen concentration cell device; a multi-channel A/D converter for converting the voltages produced by the analog signal input circuit into a conversion digital value; a data memory; a microprocessor for writing a digital conversion value produced by the multi-channel A/D converter to the data memory, the microprocessor having a capability of handling digital data having a longer bit length than a bit length corresponding to a resolution of the multi-channel A/D converter; and a nonvolatile program memory that cooperates with the microprocessor, the analog signal input circuit comprising: a variable analog signal circuit comprising: a pump current supply circuit for supplying a positive or negative pump current to the oxygen pump device; a current detection resistor connected to the pump current supply circuit; and a bias voltage source for adding a bias voltage to a positive or negative signal voltage produced by differentially amplifying a voltage across the current detection resistor; a full-range input circuit that is an input circuit provided between the variable analog signal source and a first input terminal of the multi-channel A/D converter, for producing a first input voltage, the full-range input circuit being configured so that the first input voltage becomes approximately equal to a full-scale input voltage of the multi-channel A/D converter when the voltage generated by the variable analog signal source has a maximum value; and an enlarged range input circuit that is an input circuit provided between the variable analog signal source and a second input terminal of the multi-channel A/D converter, for producing a second input voltage, the enlarged range input circuit being configured so that the second input voltage becomes approximately equal to the full-scale input voltage of the multi-channel A/D converter when the first input voltage is equal to a prescribed intermediate voltage that is lower than a maximum voltage, wherein the nonvolatile program memory stores programs to serve as: error signal storing means activated when the voltage across the current detection resistor is zero and both of the first and second input voltages are equal to a prescribed bias voltage, for determining error voltages with respect to a reference bias voltage that is an intrinsic digital conversion value corresponding to a normal bias voltage that complies with a standard, the error signal storing means writing, as a first error voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a first input voltage to the data memory at a first address, and writing, as a second error voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a second input voltage to the data memory at a second address; gain compensating means for producing a second compensation voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage, dividing a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage by a compensation gain or multiplying the second increment voltage by a compensation gain reciprocal, and adding the reference bias voltage to a resulting product or quotient, the compensation gain being set so that the second compensation voltage becomes approximately equal to a first correction voltage in an intermediate range obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage, the intermediate range being a range that is lower than the intermediate voltage; and selecting and switching means for selectively using the second compensation voltage if the first input voltage is in the intermediate range, selectively using the first correction voltage if the first input voltage is in one of outside ranges that are outside the intermediate range, and issuing an instruction to store a digital conversion value that is proportional to a selection result to the data memory at a prescribed address.

5. The vehicular electronic control unit according to claim 4, wherein: the variable analog signal circuit further comprises a power shutoff analog switch for forcibly making an input signal voltage of the full-range input circuit and the enlarged range input circuit equal to a voltage corresponding to the prescribed bias voltage by preventing a current flow between the pump current supply circuit and the current detection resistor or short-circuiting the current detection resistor; the nonvolatile program memory further store programs to serve as: error signal input means for on/off-controlling the power shutoff analog switch in accordance with a first instruction signal supplied from the microprocessor, and for causing the error signal storing means to operate; and a fuel cutting detecting means for judging that a fuel cutting state is established if fuel supply is not being done though control power is supplied immediately before a start of a drive, during a descending/coasting drive, or a decelerating/coasting drive or present status holding means for preventing data that was selected and stored in the data memory by the selecting and switching means from being changed and keeping the data at a value that was in storage immediately before a start of operation of the error signal input means while the error signal input means is in operation; and the error signal input means causes the error signal storing means to operate if the fuel cutting detecting means is detecting a fuel cutting state or if the present status holding means is in operation.

6. The vehicular electronic control unit according to claim 4, wherein: the nonvolatile program memory further stores reference gain data that was stored in advance as a reference gain or a reference gain reciprocal and that is a statistical value such as an average or a center value of a plurality of samples obtained by calculating, for a large number of samples, a ratio of a measured value of a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage to a measured value of a first increment voltage obtained by subtracting the reference bias voltage from the first correction voltage in a state that the first input voltage was approximately equal to the intermediate voltage; and the compensation gain that is used by the gain compensating means is the reference gain.

7. The vehicular electronic control unit according to claim 3, wherein: the nonvolatile program memory further stores a program to serve as variable weighted averaging means for calculating a weighted average voltage in a range where a curve of the second compensation voltage and a curve of the first correction voltage overlap with each other in such a manner as to decrease a weight coefficient ranging from 1 to 0 by which to multiply the second compensation voltage and to increase the weight coefficient ranging from 0 to 1 by which to multiply the first correction voltage as an absolute value of a difference between the second compensation voltage and the first correction voltage increases, and for employing the weighted average voltage as a second average voltage; and the selecting and switching means selectively uses the second average voltage instead of the second compensation voltage.

8. The vehicular electronic control unit according to claim 6, wherein: the nonvolatile program memory further stores a program to serve as variable weighted averaging means for calculating a weighted average voltage in a range where a curve of the second compensation voltage and a curve of the first correction voltage overlap with each other in such a manner as to decrease a weight coefficient ranging from 1 to 0 by which to multiply the second compensation voltage and to increase the weight coefficient ranging from 0 to 1 by which to multiply the first correction voltage as an absolute value of a difference between the second compensation voltage and the first correction voltage increases, and for employing the weighted average voltage as a second average voltage; and the selecting and switching means selectively uses the second average voltage instead of the second compensation voltage.

9. The vehicular electronic control unit according to claim 1, wherein: the nonvolatile program memory further stores programs to serve as: intermediate signal storing means activated when the first input voltage is forcibly set at a value that is approximately equal to the intermediate voltage, for writing, as a first intermediate voltage, a digital conversion value of the first input voltage to the data memory at a third address, and for writing, as a second intermediate voltage, a digital conversion value of a second input voltage to the data memory at a fourth address; and gain calculating means for calculating and storing a compensation gain K that is a ratio of a difference between the second intermediate voltage and the second error voltage to a difference between the first intermediate voltage and the first error voltage or a compensation gain reciprocal H that is a reciprocal of the compensation gain K; and the compensation gain that is used by the gain compensating means is the compensation gain K or the compensation gain reciprocal H calculated by the gain calculating means.

10. The vehicular electronic control unit according to claim 9, wherein: the analog signal input circuit further comprises: intermediate voltage generation circuit for generating a prescribed intermediate signal voltage that is lower than the maximum value of the voltage generated by the variable analog signal source; and a second analog switch provided in the full-range input circuit and the enlarged range input circuit, for applying the intermediate signal voltage generated by the intermediate voltage generation circuit to the first and second input terminals of the multi-channel A/D converter via the full-range input circuit and the enlarged range input circuit instead of the voltage generated by the variable analog signal source; and the nonvolatile program memory further stores programs to serve as: intermediate signal input means for on/off-controlling the second analog switch in accordance with a second instruction signal supplied from the microprocessor, for and causing the intermediate signal storing means to operate; and present status holding means for preventing data that was selected and stored in the data memory by the selecting and switching means from being changed and keeps the data at a value that was in storage immediately before a start of operation of the intermediate signal input means while the intermediate signal input means is in operation.

11. The vehicular electronic control unit according to claim 4, wherein: the nonvolatile program memory further stores programs to serve as: intermediate signal storing means activated when the first input voltage is forcibly set at a value that is approximately equal to the intermediate voltage, for writing, as a first intermediate voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of the first input voltage to the data memory at a third address, and for writing, as a second intermediate voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a second input voltage to the data memory at a fourth address; and gain calculating means for calculating and storing a compensation gain K (second difference voltage/first difference voltage) that is a ratio of second difference voltage between the second intermediate voltage and the second error voltage to first difference voltage between the first intermediate voltage and the first error voltage or a compensation gain reciprocal H (first difference voltage/second difference voltage) that is a reciprocal of the compensation gain K; and the compensation gain that is used by the gain compensating means is the compensation gain K or the compensation gain reciprocal H calculated by the gain calculating means.

12. The vehicular electronic control unit according to claim 11, wherein: the variable analog signal circuit further comprises a current reduction detection analog switch connected in series to a resistor that is parallel with the current detection resistor, for forcibly making an input signal voltage of the full-range input circuit and the enlarged range input circuit equal to a voltage corresponding to the intermediate voltage by decreasing a combined current detection resistance when a maximum current is flowing; and the nonvolatile program memory further stores a program to serve as: a fuel cutting detecting means for judging that a fuel cutting state is established if fuel supply is not being done though control power is supplied immediately before a start of a drive, during a descending/coasting drive, or a decelerating/coasting drive; and current decrease detection instructing means for closing the current decrease detection analog switch using a second instruction signal supplied from the microprocessor and causing the intermediate signal storing means to operate when the fuel cutting detecting means is detecting a fuel cutting state.

13. The vehicular electronic control unit according to claim 12, wherein the nonvolatile program memory further stores a program to serve as intermediate signal checking means for judging whether a sum of the second intermediate voltage stored by the intermediate signal storing means and the reference bias voltage is within a designated range that is lower than or equal to a maximum output voltage of the multi-channel A/D converter and higher than or equal to a designated output voltage that is a little lower than the maximum output voltage, and for validating the first and second intermediate voltages stored by the intermediate signal storing means and causing the gain calculating means to calculate a gain if the sum is within the designated range.

14. The vehicular electronic control unit according to claim 1, wherein: the nonvolatile program memory further stores programs to serve as: intermediate signal storing means activated when the first input voltage is approximately equal to the intermediate voltage, for writing, as a first intermediate voltage, a digital conversion value of the first input voltage to the data memory at a third address, and for writing, as a second intermediate voltage, a digital conversion value of a second input voltage to the data memory at a fourth address; gain calculating means for calculating and storing a compensation gain K (second difference voltage/first difference voltage) that is a ratio of second difference voltage between the second intermediate voltage and the second error voltage to first difference voltage between the first intermediate voltage and the first error voltage or a compensation gain reciprocal H (first difference voltage/second difference voltage) that is a reciprocal of the compensation gain K; and intermediate signal checking means for judging whether the second intermediate voltage that was stored by the intermediate signal storing means is within a designated range that is lower than or equal to a maximum output voltage of the multi-channel A/D converter and higher than or equal to a designated output voltage that is a little lower than the maximum output voltage, and for validating the first and second intermediate voltages that were stored by the intermediate signal storing means and causing the gain calculating means to calculate a gain if the second intermediate voltage is within the designated range; and the compensation gain that is used by the gain compensating means is the compensation gain K or the compensation gain reciprocal H calculated by the gain calculating means.

15. The vehicular electronic control unit according to claim 14, wherein: the nonvolatile program memory further stores reference gain data that was stored in advance as a reference gain or a reference gain reciprocal and that is a statistical value such as an average or a center value of a plurality of samples obtained by calculating, for a large number of samples, a ratio of a measured value of the second correction voltage to a measured value of the first correction voltage in a state that the first input voltage was approximately equal to the intermediate voltage; and the nonvolatile program memory further stores programs to serve as: compensation storage judging means for judging whether the gain calculating means calculated and stored a compensation gain K or a compensation gain reciprocal H; tentative gain compensating means activated instead of the gain compensating means if a judgment result of the compensation storage judging means is negative, for calculating a second estimate voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage and dividing a resulting second correction voltage by the reference gain or multiplying the difference by the reference gain reciprocal; and tentative selecting and switching means activated instead of the selecting and switching means if the judgment result of the compensation storage judging means is negative, for selectively using the second estimate voltage if the first input voltage is in the low voltage range, and selectively using a first correction voltage obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage if the first input voltage is in the high voltage range, and for issuing an instruction to store a digital value that is proportional to a selection result to the data memory at the prescribed address.

16. The vehicular electronic control unit according to claim 4, wherein: the nonvolatile program memory further stores programs to serve as: intermediate signal storing means activated when the first input voltage is approximately equal to the intermediate voltage, for writing, as a first intermediate voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of the first input voltage to the data memory at a third address, and for writing, as a second intermediate voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a second input voltage to the data memory at a fourth address; gain calculating means for calculating and storing a compensation gain K (second difference voltage/first difference voltage) that is a ratio of second difference voltage between the second intermediate voltage and the second error voltage to first difference voltage between the first intermediate voltage and the first error voltage or a compensation gain reciprocal H (first difference voltage/second difference voltage) that is a reciprocal of the compensation gain K; and intermediate signal checking means for judging whether a sum of the second intermediate voltage stored by the intermediate signal storing means and the reference bias voltage is within a designated range that is lower than or equal to a maximum output voltage of the multi-channel A/D converter and higher than or equal to a designated output voltage that is a little lower than the maximum output voltage, and for validating the first and second intermediate voltages that were stored by the intermediate signal storing means and causing the gain calculating means to calculate a gain if the sum is within the designated range; and the compensation gain that is used by the gain compensating means is the compensation gain K or the compensation gain reciprocal H calculated by the gain calculating means.

17. The vehicular electronic control unit according to claim 13, wherein: the nonvolatile program memory further stores reference gain data that was stored in advance as a reference gain or a reference gain reciprocal and that is a statistical value such as an average or a center value of a plurality of samples obtained by calculating, for a large number of samples, a ratio of a measured value of a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage to a measured value of a first increment value obtained by subtracting the reference bias voltage from the first correction voltage in a state that the first input voltage was approximately equal to the intermediate voltage; and the nonvolatile program memory further stores programs to serve as: compensation storage judging means for judging whether the gain calculating means calculated and stored a compensation gain K or a compensation gain reciprocal H; tentative gain compensating means activated instead of the gain compensating means if a judgment result of the compensation storage judging means is negative, for calculating a second estimate voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage, dividing, by the reference gain, a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage or multiplying the second increment voltage by the reference gain reciprocal, and adding the reference bias voltage to a resulting quotient or product; and tentative selecting and switching means activated instead of the selecting and switching means if the judgment result of the compensation storage judging means is negative, for selectively using the second estimate voltage if the first input voltage is in the intermediate range, and selectively using a first correction voltage obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage if the first input voltage is in one of the outside ranges, and for issuing an instruction to store a digital value that is proportional to a selection result to the data memory at the prescribed address, selection-using the first correction voltage.

18. The vehicular electronic control unit according to claim 16, wherein: the nonvolatile program memory further stores reference gain data that was stored in advance as a reference gain or a reference gain reciprocal and that is a statistical value such as an average or a center value of a plurality of samples obtained by calculating, for a large number of samples, a ratio of a measured value of a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage to a measured value of a first increment value obtained by subtracting the reference bias voltage from the first correction voltage in a state that the first input voltage was approximately equal to the intermediate voltage; and the nonvolatile program memory further stores programs to serve as: compensation storage judging means for judging whether the gain calculating means calculated and stored a compensation gain K or a compensation gain reciprocal H; tentative gain compensating means activated instead of the gain compensating means if a judgment result of the compensation storage judging means is negative, for calculating a second estimate voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage, dividing, by the reference gain, a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage or multiplying the second increment voltage by the reference gain reciprocal, and adding the reference bias voltage to a resulting quotient or product; and tentative selecting and switching means activated instead of the selecting and switching means if the judgment result of the compensation storage judging means is negative, for selectively using the second estimate voltage if the first input voltage is in the intermediate range, and selectively using a first correction voltage obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage if the first input voltage is in one of the outside ranges, and for issuing an instruction to store a digital value that is proportional to a selection result to the data memory at the prescribed address, selection-using the first correction voltage.

19. The vehicular electronic control unit according to claim 16, wherein: the nonvolatile program memory further stores a program to serve as variable weighted averaging means for calculating a weighted average voltage in a range where a curve of the second estimate voltage and a curve of the first correction voltage overlap with each other in such a manner as to decrease a weight coefficient ranging from 1 to 0 by which to multiply the second estimate voltage and to increase the weight coefficient ranging from 0 to 1 by which to multiply the first correction voltage as an absolute value of a difference between the second estimate voltage and the first correction voltage increases, and for employing the weighted average voltage as a second average voltage; and the tentative selecting and switching means selectively uses the second average voltage instead of the second estimate voltage.

20. The vehicular electronic control unit according to claim 18, wherein: the nonvolatile program memory further stores a program to serve as variable weighted averaging means for calculating a weighted average voltage in a range where a curve of the second estimate voltage and a curve of the first correction voltage overlap with each other in such a manner as to decrease a weight coefficient ranging from 1 to 0 by which to multiply the second estimate voltage and to increase the weight coefficient ranging from 0 to 1 by which to multiply the first correction voltage as an absolute value of a difference between the second estimate voltage and the first correction voltage increases, and for employing the weighted average voltage as a second average voltage; and the tentative selecting and switching means selectively uses the second average voltage instead of the second estimate voltage.

---

Description

---

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicular electronic control unit for an automobile or the like. In particular, the invention relates to an improved vehicular electronic control unit in which the accuracy is increased in a low voltage range or a particular intermediate zone for part of many analog signals by using a multi-channel A/D converter having an ordinary resolution.

2. Description of the Related Art

Vehicular electronic control units handle many analog signals. For example, analog signals are converted by two 16-channel A/D converters having a resolution of 10 bits into digital signals, which are input to a microprocessor for 16-bit or 32-bit computation.

However, there is a problem that the resolution of 10 bits cannot provide sufficient accuracy for part of the analog signals. Using high-resolution multi-channel A/D converters to solve this problem is excessive for ordinary analog signals that do not require high accuracy, and is also costly.

To solve this problem, JP-A-2000-13227 (patent document 1, paragraphs 0006-0011 and FIGS. 1 7) discloses a technique of increasing the accuracy of A/D conversion efficiently by using both of a first A/D converter covering all the voltage range and a second A/D converter covering a low voltage range for the same analog signal. Supplied with a reference voltage 5 V, for example, the first A/D converter converts an input voltage of 0 to 5 V into a digital value of 0 to 1,023. Supplied with a reference voltage 1.25 V, the second A/D converter converts an input voltage in a low voltage range of 0 to 1.25 V into a digital value of 0 to 1,023.

In the technique of patent document 1, to secure continuity between digital conversion values in the low voltage range of 0 to 1.25 V and those in the high voltage range of 1.25 to 5 V, the reference signal 1.25 V for the second A/D converter is supplied, as an input signal, to the first A/D converter and its digital conversion value (1,024.times.1.25/5=256) is obtained. A variation in the reference voltage 1.25 V that is the intermediate voltage for connection of the low voltage range and the high voltage range can be compensated for by monitoring the digital conversion value of the reference voltage 1.25 V.

However, patent document 1 does not refer to the issue of zero point adjustment that should be considered in the low voltage range.

On the other hand, JP-A-11-214996 (patent document 2, paragraph 0005 and FIG. 1) discloses a technique in which outputs of a preamplifier and a main amplifier that cascade-connected to it are input to a microprocessor via a multi-channel A/D converter. An input circuit of the preamplifier is equipped with an analog switch SW1 for zero point adjustment, an analog switch SW2 for gain control, and a reference voltage source for gain control. The microprocessor acquires data for zero point adjustment and data for gain control by on/off-controlling the analog switches SW1 and SW2 and reading A/D conversion values at each time point.

JP-A-10-169500 (patent document 3, paragraphs 0009 and 0010 and FIG. 1) discloses a technique for compensating for a variation in the characteristic of an exhaust gas sensor by calibrating the detection output in a fuel-cut state that provides an atmospheric environment in the exhaust gas sensor that has an oxygen pump device and an oxygen concentration cell device and in which an air-fuel ratio is detected on the basis of a signal voltage that is obtained by differentially amplifying a voltage across a current detection resistor provided in a pump current supply circuit.

The technique of patent document 1 has problems that the second A/D converter serves only as the A/D converter for handling signal voltages in the low voltage range and that one analog signal occupies inputs of three channels in total.

The technique of patent document 2 is not intended for increase in the accuracy of A/D conversion in the low voltage range. Digital conversion values of outputs of the preamplifier and the main amplifier are fixed by the resolution of the multi-channel A/D converter used.

The technique of patent document 3 is not intended for increase in the accuracy of A/D conversion but for the variation compensation of the exhaust gas sensor for detecting the air-fuel ratio.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a simple means that is effective in increasing the A/D conversion accuracy in a low voltage range or a particular intermediate range for part of many analog signals to be handled by a vehicular electronic control unit for an automobile by using a multi-channel A/D converter having the same full-scale input voltage for those signals and having an ordinary resolution, and that uses a prescribed reference gain to maintain continuity between digital conversion values in a low voltage range and those in a high voltage range or between digital conversion values in a particular intermediate range and those in the ranges outside it.

A second object of the invention is to provide a means capable of calculating, with learning, a highly accurate compensation gain when necessary by adding a means for obtaining a prescribed intermediate voltage, to maintain continuity between digital conversion values in a low voltage range and those in a high voltage range or between digital conversion values in a particular intermediate range and those in the ranges outside it.

A third object of the invention is to provide a means capable of calculating, with learning, a highly accurate compensation gain without a means for obtaining a prescribed intermediate voltage, to maintain continuity between digital conversion values in a low voltage range and those in a high voltage range or between digital conversion values in a particular intermediate range and those in the ranges outside it.

The invention provides a vehicular electronic control unit comprising:

an analog signal input circuit for producing voltages corresponding to a voltage generated by at least one variable analog signal source;

a multi-channel A/D converter for converting the voltages produced by the analog signal input circuit into a conversion digital value;

a data memory;

a microprocessor for writing a digital conversion value produced by the multi-channel A/D converter to the data memory, the microprocessor having a capability of handling digital data having a longer bit length than a bit length corresponding to a resolution of the multi-channel A/D converter; and

a nonvolatile program memory that cooperates with the microprocessor, the analog signal input circuit comprising:

a full-range input circuit that is an input circuit provided between the variable analog signal source and a first input terminal of the multi-channel A/D converter, for producing a first input voltage, the full-range input circuit being configured so that the first input voltage becomes approximately equal to a full-scale input voltage of the multi-channel A/D converter when the voltage generated by the variable analog signal source has a maximum value; and

an enlarged range input circuit that is an input circuit provided between the variable analog signal source and a second input terminal of the multi-channel A/D converter, for producing a second input voltage, the enlarged range input circuit being configured so that the second input voltage becomes approximately equal to the full-scale input voltage of the multi-channel A/D converter when the first input voltage is equal to a prescribed intermediate voltage that is lower than a maximum voltage, wherein the nonvolatile program memory stores programs to serve as:

error signal storing means activated when the voltage generated by the variable analog signal source is zero, for writing, as a first error voltage, a digital conversion value of a first input voltage to the data memory at a first address, and for writing, as a second error voltage, a digital conversion value of a second input voltage to the data memory at a second address;

gain compensating means for producing a second compensation voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage and dividing the second correction voltage by a compensation gain or multiplying the second correction voltage by a compensation gain reciprocal, the compensation gain being set so that the second compensation voltage becomes approximately equal to a first correction voltage in a low voltage range obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage, the low voltage range being a range that is lower than the intermediate voltage; and

selecting and switching means for selectively using the second compensation voltage if the first input voltage is in the low voltage range, selectively using the first correction voltage if the first input voltage is in a high voltage range that is a range higher than or equal to the intermediate voltage, and issuing an instruction to store a digital conversion value that is proportional to a selection result to the data memory at a prescribed address.

The invention also provides a vehicular electronic control unit comprising:

an analog signal input circuit for producing voltages corresponding to a voltage generated by at least one variable analog signal source that is an exhaust gas sensor having an oxygen pump device and an oxygen concentration cell device;

a multi-channel A/D converter for converting the voltages produced by the analog signal input circuit into a conversion digital value;

a data memory;

a microprocessor for writing a digital conversion value produced by the multi-channel A/D converter to the data memory, the microprocessor having a capability of handling digital data having a longer bit length than a bit length corresponding to a resolution of the multi-channel A/D converter; and

a nonvolatile program memory that cooperates with the microprocessor, the analog signal input circuit comprising:

a variable analog signal circuit comprising: a pump current supply circuit for supplying a positive or negative pump current to the oxygen pump device; a current detection resistor connected to the pump current supply circuit; and a bias voltage source for adding a bias voltage to a positive or negative signal voltage produced by differentially amplifying a voltage across the current detection resistor;

a full-range input circuit that is an input circuit provided between the variable analog signal source and a first input terminal of the multi-channel A/D converter, for producing a first input voltage, the full-range input circuit being configured so that the first input voltage becomes approximately equal to a full-scale input voltage of the multi-channel A/D converter when the voltage generated by the variable analog signal source has a maximum value; and

an enlarged range input circuit that is an input circuit provided between the variable analog signal source and a second input terminal of the multi-channel A/D converter, for producing a second input voltage, the enlarged range input circuit being configured so that the second input voltage becomes approximately equal to the full-scale input voltage of the multi-channel A/D converter when the first input voltage is equal to a prescribed intermediate voltage that is lower than a maximum voltage, wherein the nonvolatile program memory stores programs to serve as:

error signal storing means activated when the voltage across the current detection resistor is zero and both of the first and second input voltages are equal to a prescribed bias voltage, for determining error voltages with respect to a reference bias voltage that is an intrinsic digital conversion value corresponding to a normal bias voltage that complies with a standard, the error signal storing means writing, as a first error voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a first input voltage to the data memory at a first address, and writing, as a second error voltage, a value obtained by subtracting the reference bias voltage from a digital conversion value of a second input voltage to the data memory at a second address;

gain compensating means for producing a second compensation voltage by calculating a second correction voltage by subtracting the second error voltage from a second present voltage that is a digital conversion value of a second input voltage, dividing a second increment voltage obtained by subtracting the reference bias voltage from the second correction voltage by a compensation gain or multiplying the second increment voltage by a compensation gain reciprocal, and adding the reference bias voltage to a resulting product or quotient, the compensation gain being set so that the second compensation voltage becomes approximately equal to a first correction voltage in an intermediate range obtained by subtracting the first error voltage from a first present voltage that is a digital conversion value of a first input voltage, the intermediate range being a range that is lower than the intermediate voltage; and

selecting and switching means for selectively using the second compensation voltage if the first input voltage is in the intermediate range, selectively using the first correction voltage if the first input voltage is in one of outside ranges that are outside the intermediate range, and issuing an instruction to store a digital conversion value that is proportional to a selection result to the data memory at a prescribed address.

According to the vehicular electronic control unit of the invention, even with an inexpensive A/D converter having a low resolution, the unit of stepwise variations of digital conversion values in a low voltage input state can be reduced and a fine output characteristic can be obtained. Since the error adjustment function is provided that can be performed when necessary during a drive, products need not be adjusted at the time of shipment and the A/D conversion accuracy of an actual product can be increased by making automatic compensation in accordance with its actual use environment.

Further, according to the invention, even with an inexpensive A/D converter having a low resolution, the resolution of digital conversion values by the exhaust gas sensor can be improved in an intermediate voltage range when the sensor is frequently used in the vicinity of a theoretical air-fuel ratio. Since the error adjustment function is provided that can be performed when necessary during a drive, products need not be adjusted at the time of shipment and the A/D conversion accuracy of an actual product can be increased by making automatic compensation in accordance with its actual use environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a first embodiment of the present invention;

FIGS. 2A and 2B are graphs showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 1;

FIG. 3 is a flowchart showing the operation of the vehicular electronic control unit according to the first embodiment;

FIG. 4 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a second embodiment of the invention;

FIG. 5 is a graph showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 4;

FIG. 6 is a flowchart showing the operation of the vehicular electronic control unit according to the second embodiment;

FIG. 7 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a third embodiment of the invention;

FIGS. 8A and 8B are graphs showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 7;

FIG. 9 is a flowchart showing the operation of the vehicular electronic control unit according to the third embodiment;

FIG. 10 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a fourth embodiment of the invention;

FIGS. 11A and 11B are graphs showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 10;

FIG. 12 is a flowchart showing the operation of the vehicular electronic control unit according to the fourth embodiment;

FIG. 13 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a fifth embodiment of the invention;

FIGS. 14A and 14B are graphs showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 13;

FIG. 15 is a flowchart showing the operation of the vehicular electronic control unit according to the fifth embodiment;

FIG. 16 is a circuit block diagram showing the entire configuration of a vehicular electronic control unit according to a sixth embodiment of the invention;

FIGS. 17A and 17B are graphs showing an input/output characteristic of a multi-channel A/D converter shown in FIG. 16; and

FIG. 18 is a flowchart showing the operation of the vehicular electronic control unit according to the sixth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

The entire configuration of a vehicular electronic control unit according to a first embodiment of the present invention will be described below with reference to a circuit block diagram of FIG. 1.

In FIG. 1, reference symbol 100a denotes a vehicular electronic control unit such as an engine control unit that is mounted on an automobile. A variable analog signal source 101a that is one of many analog sensors is connected to the electronic control unit 100a.

Reference numeral 102 denotes a multi-channel A/D converter having a resolution of 10 bits that is provided inside the electronic control unit 100a. A regulated DC voltage 5 V is applied to a voltage source terminal Vcc and a reference voltage terminal Vref of the electronic control unit 100a. A first input voltage V10 of 0 to 5 V and a second input voltage V20 of 0 to 5 V are applied to a first input terminal CH1 and a second input terminal CH2 of the multi-channel A/D converter 102, respectively.

Therefore, the minimum unit of the input voltage to be converted into a digital voltage is 5/1,023 V.apprxeq.5 mV (DC), which corresponds to approximately 0.1% of the maximum value of the input voltage.

Many other analog signal sources (not shown) are connected to the multi-channel A/D converter 102. Analog voltage values that are input to the respective input channels are sequentially converted into digital values, which are stored in a buffer memory that is provided in the multi-channel A/D converter 102.

Reference symbol 103a denotes a microprocessor capable of processing 32-bit data, for example, simultaneously, and symbol 104a denotes a nonvolatile program memory that is bus-connected to the microprocessor 103a. The program memory 104a stores not only various control programs and control constants for operation as a vehicular electronic control unit but also various programs and control data for various control means of this embodiment.

Reference numeral 105 denotes a RAM memory for computation that is bus-connected to the microprocessor 103a. The RAM memory 105 also serves as a data memory; digital data that are stored in the buffer memory of the multi-channel A/D converter 102 can be read out by the microprocessor 103a and written to the RAM memory 105 when necessary.

Reference symbol 110a denotes a voltage divider circuit that is a series circuit of an input resistor R10 and a pull-down resistor R11. Reference symbol 111a denotes a first analog switch that is connected in series to the input resistor R10 and is provided between the variable analog signal source 101a and the first input terminal CH1. The analog switch 111a is on/off-controlled by a first instruction signal SW1 that is generated by the microprocessor 103a. The first input voltage V10 has a value obtained by dividing the output voltage of the variable analog signal source 101a between the input resistor R10 and the pull-down resistor R11.

Reference symbol 120a denotes a second amplifier that is connected to a pull-down resistor R19 and that produces the above-mentioned second input voltage V20. The positive-side input terminal of the second amplifier 120a is connected to the first input terminal CH1 via an input resistor R16, and its negative-side input terminal is connected to the connecting point of a voltage division resistor R17 and a feedback resistor R18. The feedback resistor R18 is connected to the output terminal of the second amplifier 120a.

Therefore, a theoretical gain G relating to the ratio of the second input voltage V20 to the first input voltage V10 is given by G=V20/V10=(R17+R18)/R17. (1)

FIG. 2A is a graph showing an input/output characteristic of the multi-channel A/D converter 102 shown in FIG. 1. The horizontal axis represents the analog input voltage (first input voltage V10) and the vertical axis represents the digital conversion value corresponding to the first input voltage V10 or the second input voltage V20.

A full-scale voltage Vf which is the maximum value of the analog input voltage is the voltage that is applied to the reference voltage terminal Vref of the multi-channel A/D converter 102 and is DC 5V in this embodiment. A maximum output voltage Vb which is the maximum value of the digital conversion value is equal to a digital dedicated value 1,023 in this embodiment.

Reference numeral 200 denotes a curve representing a relationship between the first input voltage V10 and the corresponding digital conversion value, that is, the first present voltage. The first present voltage is equal to a first error voltage RAM11 when the first input voltage V10 is zero.

Reference numeral 201 denotes a curve representing a relationship between the first input voltage V10 and the first correction voltage that is obtained by digitally subtracting the first error voltage RAM11 from the first present voltage (200). Reference symbol 201a in FIG. 2B denotes a low voltage portion of the curve 201.

Reference symbol 210 denotes a curve representing a relationship between the first input voltage V10 and the digital conversion value (i.e., second present voltage) corresponding to the second input voltage V20. Since the second input voltage V20 is the voltage obtained by amplifying the first input voltage V10 at the theoretical gain G, the digital conversion value reaches the maximum output voltage Vb=1,023 when the first input voltage V10 becomes equal to an intermediate voltage of about 1.25 V, for example. The second present voltage (210) is equal to a second error voltage RAM21 when the first input voltage V10 is zero.

Reference numeral 211 denotes a curve representing a relationship between the first input voltage V10 and the second correction voltage that is obtained by digitally subtracting the second error voltage RAM21 from the second present voltage (210).

Reference symbol 212a denotes a curve representing a relationship between the first input voltage V10 and the second compensation voltage that is obtained by dividing the second correction voltage (211) by the theoretical gain G. If the amplification factor of the second amplifier 120a is equal to the theoretical gain G correctly, the curve 212a of the second compensation voltage coincides with the low voltage portion 201a of the curve 201 of the first correction voltage.

However, the following problem exists. The resistance values of the voltage division resistor R17 and the feedback resistor R18 shown in FIG. 1 have variations. For example, slight deviations occur even if they are high-accuracy resistors whose errors are within 0.1%, for example. Such errors are on the same level as the resolution of the multi-channel A/D converter 102. It is unlikely that the curve 212a of the second compensation voltage exactly coincides with the low voltage portion 201a of the curve 201 of the first correction voltage.

However, in practice, the error between the curve 212a and the low voltage portion 201a is reduced by using, instead of the theoretical gain G, a reference gain R that is a measured average based on a large number of product samples.

In FIG. 2B showing, in an enlarged manner, the region where the first input voltage V10 is low, reference symbol 201a denotes the above-mentioned low voltage portion of the curve 201 of the first corrected voltage 201, symbol 212a denotes the above-mentioned curve of the second compensation voltage, and symbol 214a denotes a curve of the second average voltage. The second average voltage is calculated according to the following equation: V214={V201.times..alpha.+V212(1-.alpha.)}/2 (2) .alpha.=V211/(Vb-RAM21) (3) where V201 is the first correction voltage, V212 is the second compensation voltage, V214 is the second average voltage, .alpha. is a weight coefficient, Vb is the maximum output voltage, and RAM21 is the second error voltage.

The operation of the vehicular electronic control unit 100a according to the first embodiment that is configured as shown in FIG. 1 will be described below with reference to a flowchart of FIG. 3.

In FIG. 3, at a start step 300, a calibration operation of the microprocessor 103a is started. The start step 300 is activated repeatedly, that is, every time an operation end step 315 (described later) is executed.

At step 301 which is executed after step 300, it is judged whether the current operation is the first one by monitoring whether an initial operation flag (not shown) was set at the next step 302a. At step 302a which is executed if the judgment result of step 301 is "yes," (i.e., the current operation is the first one), an initial value is written to the RAM memory 105 at a prescribed address RAM00 and the initial operation flag is set. The set state of the initial operation flag is stored and maintained until power-off of the electronic control unit 100a.

The address RAM00 is an address (of RAM memory) where a digital conversion value that is proportional to a voltage generated by the variable analog signal source 101a is written. When the microprocessor 103a needs a digital conversion value that is proportional to a voltage generated by the variable analog signal source 101a, the microprocessor 103a r