Title: Apparatus for controlling an electric power steering system
Abstract: An apparatus for controlling an electric power steering system is provided, which has a microcomputer for determining a signal for target current, the other microcomputer for determining a signal for motor control, a motor drive circuit for driving a brushless motor. The apparatus has a feature that the microcomputers can back up each other in controlling an electric power steering system even if failure occurs in one of the microcomputers.
Patent Number: 6,885,927 Issued on 04/26/2005 to Arimura
| Inventors:
|
Arimura; Yutaka (Wako, JP)
|
| Assignee:
|
Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
407495 |
| Filed:
|
April 4, 2003 |
Foreign Application Priority Data
| Apr 17, 2002[JP] | 2002-114806 |
| Apr 17, 2002[JP] | 2002-114807 |
| Apr 17, 2002[JP] | 2002-114808 |
| Current U.S. Class: |
701/41 |
| Intern'l Class: |
B62D 005//04 |
| Field of Search: |
701/41,43
180/443,446
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Thu V.
Attorney, Agent or Firm: Merchant & Gould P.C.
Claims
1. An apparatus for controlling an electric power steering system comprising:
a motor for providing assist steering torque for a steering line, said motor
comprising a brushless motor;
a sensor for detection of steering torque acting on said steering line and delivering
a signal of steering torque;
a device for detection of rotational phase of said motor and delivering a phase
signal;
a device for detection of current of said motor and delivering a signal of current;
a current control unit for determining a signal for target current based upon
at least said signal of steering torque, said current control unit comprising a
first microcomputer;
a drive control unit for determining a signal for motor control for controlling
said motor based upon a deviation between said signal for target current and said
signal of current, along with said phase signal, said drive control unit comprising
a second microcomputer and a motor drive circuit for driving said motor based upon
said signal for motor control; and
wires electrically connecting said current control unit and drive control unit,
wherein said drive control unit incorporates said signal of steering torque from
said sensor for detection of steering torque, and if said first microcomputer fails,
said second microcomputer determines a signal for target current based upon said
signal of steering torque.
2. An apparatus according to claim 1, wherein said first microcomputer incorporates
said phase signal, and if said second microcomputer fails, said first microcomputer
determines a signal for motor control for controlling said motor based upon said
phase signal and delivers said signal for motor control to said motor drive circuit
for driving said motor.
3. An apparatus according to claim 1, wherein said first microcomputer incorporates
said phase signal from said second microcomputer and performs damper control, and
if said first microcomputer can not receive said phase signal normally, said second
microcomputer performs damper control based upon said phase signal.
4. An apparatus according to claim 1, wherein said second microcomputer performs
damper control based upon said phase signal.
Description
FIELD OF THE INVENTION
The present invention relates to an apparatus for controlling an electric power
steering system, in which the apparatus directly exerts power generated by a brushless
motor on a steering line so as to reduce the steering torque required of a driver.
BACKGROUND OF THE INVENTION
A direct current motor with brushes has been generally used for an electric power
steering system. An electric power steering system with a brushless motor has also
been developed, which solves a problem of aged deterioration associated with a
direct current motor with brushes. A brushless motor uses a three phase winding
as an outer stator and plural permanent magnets as an inner rotor. When the three
phase winding is supplied with current depending upon the rotational phase of inner
rotor, the inner rotor will rotate. In this way, since a brushless motor does not
require a brush, it is free from degradation of steering feeling caused by the
abrasion of brush. A brushless motor, whose inner rotor is made of magnets, has
a small moment of inertia, thereby preventing degradation of steering feeling caused
by a big moment of inertia.
An apparatus for controlling an electric power steering system, which employs
a brushless motor, sends a signal for motor control to a motor drive circuit so
that the signal drives Field Effect Transistors (FET's) with Pulse Width Modulation
(PWM) or switches them off. The apparatus thus determines a signal for target current
based upon a signal of steering torque sent by a sensor for detection of steering
torque and also compensates this signal for target current by inertia and damper
control. These processes are performed so that assist steering torque generated
by the brushless motor, which corresponds to target current running through the
brushless motor, can be determined. Also the apparatus determines a signal for
motor control based upon both a deviation between a signal for target current and
a signal of motor current (actual current) sent by a device for detection of motor
current, and a phase signal of motor rotation (an actual rotational phase of inner
rotor) sent by a device for detection of rotational phase of motor, thereby supplying
a target current to the brushless motor. In a motor drive circuit, the FET's are
PWM driven based upon the signal for motor control, thereby rotating the brushless
motor in a positive or reverse direction.
In the motor drive circuit, the FET's generate heat as a result of some ten amperes
of current running therethrough. Also driving of a brushless motor requires accurate
control of current depending on the rotational phase of an inner rotor. Two of
relatively inexpensive and simple microcomputers, which share control of a brushless
motor, are used in an apparatus for controlling an electric power steering system.
A current control unit having a microcomputer which determines target current is
placed apart from a motor drive circuit. In this way the current control unit can
determine accurate target current since analogue circuits and the like for shaping
a signal for steering torque are free from the effect of heat. On the other hand,
a drive control unit having a microcomputer which determines a signal for motor
control is placed in the neighborhood of a brushless motor and device for detection
of rotational phase of motor. The drive control unit can thus perform accurate
current control for the brushless motor based upon a phase signal of motor rotation
which has a small amount of noise and no phase delay as a result of a short transmission
path of the signal. These current control and drive control units are electrically
coupled by wires, thereby communicating each other. For example, the current control
unit sends a signal for target current, and on the other hand the drive control
unit sends a phase signal of motor rotation to be used for damper control.
In a general control apparatus, in which plural microcomputers perform shared
computation, the microcomputers are electrically connected by wires and various
types of synchronization are adopted for mutual communication of data. An apparatus
for controlling an electric power steering system has two microcomputers which
share the drive control of a brushless motor and perform high-speed communication
by clock synchronization.
In this apparatus, a microcomputer for a current control unit serves as a master
microcomputer and the other microcomputer for a drive control unit serves as a
slave microcomputer. The microcomputer in the current control unit thereby generates
clock signals for communication by clock synchronization and transmits the signals
to the microcomputer in the drive control unit via wires for clock signals. In
this way, the two microcomputers transmit or receive data mutually via the wires.
However, when one of the two microcomputers fails, the apparatus cannot
continue a sequence of control which is required by an electric power steering
system. The apparatus is thus unable to perform drive control for a brushless motor,
thereby failing to exert assist steering torque on a steering line. Also, when
the current control unit cannot receive a phase signal of motor rotation due to
a disconnection of wires for communication between the current and drive control
units, the current control unit cannot perform damper control anymore, thereby
damaging steering feeling of a driver.
Further, the microcomputer in current control unit requires data associated
with a center value of steering torque, and on the other hand the microcomputer
in drive control unit needs an offset value of motor encoder. In this way, each
microcomputer reads out the data stored in an Electrically Erasable Programmable
Read Only Memory (hereinafter referred to as EEPROM), which is prepared for each
microcomputer. Then, the apparatus, which controls a brushless motor with two microcomputers,
requires an EEPROM for each microcomputer, thereby resulting in a costly configuration
with two EEPROM's.
Signals are transmitted or received by clock synchronization to perform high-speed
communication between the two microcomputers. In this communication by clock synchronization,
a master microcomputer (a microcomputer in current control unit) transmits data
in reference to clock signals generated therein, and on the other hand a slave
microcomputer (a microcomputer in drive control unit) receives the data in reference
to the clock signals transmitted by the master microcomputer. The slave microcomputer
will continue receiving unsynchronized data once a time lag occurs in the received
data. This results in a situation that the slave microcomputer cannot receive normal
data such as target current, and thereby the slave computer is unable to determine
a correct signal for motor control. As a result, the control apparatus for an electric
power steering system cannot exert assist steering torque on a steering line.
If the microcomputer in drive control unit is not ready to receive data, a time
lag will appear in received data. This type of phenomenon occurs, for example,
when components of the microcomputer in drive control unit are not electrically
initiated or the initial check of a Central Processing Unit (CPU) has not been
completed at starting of a vehicle (turning on of ignition switch). Also when a
noise is on a wire running from the microcomputer in current control unit to the
microcomputer in drive control unit while data is transmitted, a time lag appears
in the data. The microcomputer in drive control unit thus receives unsynchronized signals.
Further, when the slave microcomputer is unable to receive correct clock
signals due to a disconnection of wires for clock signals or failure of an interface
circuit (port and the like), the master and slave microcomputers cannot communicate
data by clock synchronization. In this way, the microcomputer in drive control
unit cannot receive correct data (target current and the like) and thereby the
apparatus for an electric power steering system cannot exert assist steering torque
on a steering line.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for controlling
an electric power steering system, which is capable of performing failsafe control,
even if a failure associated with the shared control of a brushless motor by two
control units occurs.
Another object of the present invention is to provide an apparatus for controlling
an electric power steering system, which enables sharing of a common memory by
the two control units, so that such a problem that each microcomputer requires
a memory can be solved.
Still another object of the present invention is to provide an apparatus for
controlling an electric power steering system, which enables continuous communication
between master and slave microcomputers even if normal communication by clock synchronization fails.
The present invention provides an apparatus for controlling an electric power
steering system having, a brushless motor, a sensor for detection of steering torque
acting on the steering line, a device for detection of rotation of the motor, a
device for detection of current of the motor, a current control unit with a first
microcomputer for determining a signal for target current, a drive control unit
with a second microcomputer for determining a signal for motor control and wires
electrically connecting the current control unit and drive control unit. The apparatus
has a feature that the drive control unit incorporates the signal of steering torque
from the sensor for detection of steering torque, and if the first microcomputer
fails, the second microcomputer determines a signal for target current based upon
the signal of steering torque.
According to the apparatus for controlling an electric power steering system,
the second microcomputer determines target current based upon a signal of steering
torque even if the second microcomputer fails to perform control. And the second
microcomputer is able to continue the control of a brushless motor independently
and thereby the apparatus can exert assist steering torque on a steering line.
The present invention also provides an apparatus for controlling an electric
power steering system, wherein the first microcomputer incorporates the phase signal,
and if the second microcomputer fails, the first microcomputer determines a signal
for motor control based upon the phase signal and delivers the signal for motor
control to the motor drive circuit.
Even if the failure of the second microcomputer occurs, the apparatus thus allows
the first microcomputer to determine a signal for motor control based upon a signal
for target current and a phase signal of motor rotation and delivers the signal
for motor control to a motor drive circuit. In this way, the apparatus continues
control for a brushless motor only with the first microcomputer, thereby keeping
exerting assist steering torque on a steering line.
The present invention still provides an apparatus, wherein the first microcomputer
incorporates a signal of motor rotation from the second microcomputer and performs
damper control, and if the first microcomputer can not receive the signal normally,
the second microcomputer performs damper control based upon the signal.
Even if the first microcomputer fails to receive the signal of motor rotation
correctly, the second microcomputer performs damper control based upon the signal.
The apparatus thus allows the second microcomputer to perform compensation for
a signal for target current without damper compensation sent by the first microcomputer,
thereby maintaining a desirable steering feeling of a driver.
The present invention yet provides an apparatus, wherein the second microcomputer
performs damper control based upon a signal of motor rotation.
The apparatus for controlling an electric power steering system allows the second
microcomputer to perform continuous damper control for a signal for target current
based upon the signal for motor rotation. In this way, even if the first microcomputer
fails to receive data, the apparatus allows the second microcomputer to perform
damper compensation for the signal for target current, thereby keeping excellent
steering feeling of a driver.
The present invention further provides an apparatus for controlling an electric
power steering system having a brushless motor, a sensor for detection of steering
torque, a device for detection of rotation of the motor, a device for detection
of current of the motor, a current control unit with a first microcomputer for
determining a signal for target current, a drive control unit with a second microcomputer
for determining a signal for motor control and wires electrically connecting the
current control unit and drive control unit. The apparatus has a feature that a
memory is connected to one of the first and second microcomputers and when the
memory is connected to the first microcomputer, data stored in the memory is transmitted
from the first microcomputer to the second microcomputer via the wires, and vice versa.
The apparatus makes it feasible for the first and second microcomputers to use
a memory in common, thereby allowing communication between the two microcomputers
with the data stored in the memory such as EEPROM. Thus, the apparatus does not
require a memory for each of the microcomputers, leading to a cost reduction.
The present invention still further provides an apparatus, wherein the second
microcomputer sends standby signals notifying the first microcomputer of a ready
status of data reception, and then the first microcomputer starts to send data
to the second microcomputer after receiving the standby signals.
In the apparatus, when the transmission of data is ready during a vehicular start
or after the recovery of a communication error, the second microcomputer sends
standby signals to the first microcomputer. And the first microcomputer starts
sending data to the second microcomputer after reception of the standby signals.
In this way, the apparatus achieves secure data reception by the second microcomputer
during a vehicular start, and also provides resumption of normal communication
by sending standby signals even if an error occurs during communication.
The present invention yet further provides an apparatus for controlling an electric
power steering system having a brushless motor, a sensor for detection of steering
torque, a device for detection of rotation of the motor, a device for detection
of current of the motor, a current control unit for determining a signal for target
current and a drive control unit for determining a signal for motor control. The
current control unit has a first microcomputer with a first clock serving as a
master microcomputer and the drive control unit has a second microcomputer with
a second clock serving as a slave microcomputer, respectively. The apparatus also
has first wires for transmitting clock signals and transmitting data between the
master and slave microcomputers. The apparatus has a feature that when one of the
master and slave microcomputers detects an error in communication therebetween
under clock synchronization, the master and slave microcomputers continue communication
each other by switching from clock synchronization to an asynchronous technique.
Even if the slave microcomputer cannot perform normal communication with clock
synchronization technique due to a problem associated with reception of clock signals
generated by the master microcomputer, the apparatus enables continuous communication
between the two microcomputers with asynchronous technique.
Abnormality of communication by clock synchronization includes the following
exemplary cases such as the failure of slave microcomputer in reception of clock
signals generated by the master microcomputer, the failure of master microcomputer
in confirmation of the readiness of data reception by slave computer, no data transmission
from the master to slave microcomputer in a given period of time and vice versa.
And the failure of slave microcomputer mentioned above has various causes such
as the disconnection of wires for clock signals, the failure of an interface circuit
(port) of transmission or reception side and the failure of an amplifier for amplifying
clock signals generated by the master microcomputer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a figure describing the overall structure of an apparatus for controlling
an electric power steering system according to the present invention. Related components
such as a steering wheel, rack & pinion mechanism and the like are also shown in
the figure.
FIG. 2 is a block diagram showing current and drive control units according
to the first embodiment.
FIG. 3 is a block diagram showing current and drive control units according
to the second embodiment.
FIG. 4 is a block diagram showing current and drive control units according
to the third embodiment.
FIG. 5 is a block diagram showing current and drive control units according
to the fourth embodiment.
FIG. 6 is a block diagram showing current and drive control units according
to the fifth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described referring
to the accompanying drawings.
a. Failsafe Control
An apparatus for controlling an electric power steering system, which has two
control means (microcomputers and the like) for controlling a brushless motor,
allocates at least basic functions to both of the means so that a means and the
other can back up each other to continue the control of brushless motor, even if
one of the two means fails. In this connection, the apparatus allows both means
to incorporate signals needed for the control.
The apparatus according to the embodiments to be described has a current control
unit for determination for target current for a brushless motor and a drive control
unit for driving the brushless motor based upon the target current, which are placed
apart and electrically connected by wires. The current control unit having a one-chip
microcomputer is placed along a pinion shaft. On the other hand, the drive control
unit having the other microcomputer and a motor drive circuit, is placed next to
the brushless motor. The embodiments to be described are categorized into three
different cases in terms of the microcomputers for the current control unit and
drive control unit: two microcomputers are fully redundant each other in a first
embodiment, both microcomputers have a function of damper control in a second embodiment
and only the microcomputer in drive control unit has a function of damper control
in a third embodiment.
First the overall structure of an apparatus for controlling an electric power
steering system is described with related components such as a steering wheel,
rack & pinion mechanism and the like referring to FIG.
1. FIG. 1 is a figure
describing the overall structure of the apparatus, which is applicable to all the
three embodiments and also two more embodiments to be described later.
An apparatus
1 for controlling an electrical power steering system, which
is provided in a steering line S including a steering wheel
3 to wheels
W, assists the steering torque generated by means
2 for generating manual
steering torque. A drive control unit
5 of the apparatus
1 generates
a motor voltage VM based upon a signal IMS for target current delivered by a current
control unit
4. The apparatus
1 further drives a brushless motor
6 based upon the motor voltage VM to generate assist steering torque, thereby
reducing the required manual steering torque exerted by the means
2.
The means
2 has a pinion shaft
7a of a rack & pinion mechanism
7 which is coupled to a steering shaft
2a via a connecting
rod
2b. The connecting rod
2b has universal joints
2c and
2d at both ends. The rack & pinion mechanism
7 converts the rotational motion of pinion shaft
7a to the
reciprocal motion of rack shaft
7c in a lateral direction or a direction
of vehicular width by engaging a pinion
7b with rack teeth
7d.
At both ends of rack shaft
7c, the right and left forward wheels
W are connected to via ball joints
8 and tie rods
9.
The apparatus
1 has the brushless motor
6 so as to generate assist
steering torque. The brushless motor
6 exerts assist steering torque on
the pinion shaft
7a via a torque limiter
10 and reduction
gears mechanism
11.
An electric power steering system, which transmits both steering torque exerted
by a driver on the steering wheel
3 and assist torque generated by the brushless
motor
6 depending on the steering torque to the pinion shaft
7a,
steers the wheels W with the rack & pinion mechanism
7.
The apparatus
1 is contained in a housing (not shown) extending in a direction
of vehicular width so that the rack shaft
7c is slidable in a longitudinal
direction thereof. The housing also contains the rack & pinion mechanism
7,
torque limiter
10 and reduction gears mechanism
11. An upper opening
of the housing is closed with a lid (not shown), the middle of which the pinion
shaft
7a penetrates and inside of which a torque sensor TS for detection
of steering torque is installed. Further, on the external circumferential surface
of lid, a container (not shown) for housing the current control unit
4 is disposed.
A side opening of the housing is closed with the other lid (not shown) and a
motor
case (not shown) is mounted on the surface of lid opposite to the housing. The
motor case houses the brushless motor
6 and a device
13 for detection
of motor rotation at an end of the brushless motor
6. And on the external
circumferential surface of motor case, a container (not shown) for the drive control
unit
5 is mounted. In this way, the drive control unit
5 is placed
next to the brushless motor
6 and device
13.
Inside the side opening of housing are housed the torque limiter
10.
The torque limiter
10 is a mechanism for restricting torque. An inner element
(not shown) which is male tapered and serration coupled to the shaft (not shown)
of brushless motor
6 is mated with an outer element (not shown) which is
female tapered (cup like) and serration coupled to the worm shaft (not shown) of
reduction gears mechanism
11. When torque exceeding a predetermined value
is exerted on the torque limiter
10, a slip will occur between the outer
circumferential surface of inner element and the inner circumferential surface
of outer element. In this way, the torque limiter
10 is able to control
assist steering torque transmitted from the brushless motor
6 to reduction
gears mechanism
11, thereby cutting off undesirably large torque. Therefore,
excessive torque does not occur in the brushless motor
6 or is not transmitted
downstream the torque limiter
10.
Further, the reduction gears mechanism
11 is housed in the housing.
The reduction gears mechanism
11, which transmits the assist steering torque
generated by brushless motor
6 to the pinion shaft
7a, is
made of a worm gear mechanism. The reduction gears mechanism
11 includes
a worm shaft (not shown) connected to the shaft of brushless motor
6 via
the torque limiter
10, a worm gear (not shown) formed on the worm shaft
and a worm wheel (not shown) connected to the pinion shaft
7a.
A signal V of vehicle speed detected by a speed sensor VS and a signal T of steering
torque detected by a torque sensor TS enter the current control unit
4.
The current control unit
4 determines a signal IMS for target current based
upon the signals V and T, and delivers this signal IMS, based on which a current
to be supplied to the brushless motor
6 is determined, to the drive control
unit
5. The current control unit
4 and drive control unit
5
are electrically connected by wire harnesses WH.
A signal IMO detected by a device
12 for detection of motor current and
a signal PMO detected by a device
13 for detection of motor rotation enter
the drive control unit
5. A microcomputer
50 of the drive control
unit
5 generates a signal VO for motor control based upon the signal IMS
along with the signals IMO and PMO. A motor drive circuit
51 then imposes
a motor voltage VM on the brushless motor
6 based on the signal VO (see
FIGS.
2-
4). The drive control unit
5, which is connected to
a battery BT via fuses FS and an ignition switch IG, is supplied with battery power
source (12 V). In this way, the drive control unit
5 generates a constant
voltage of 5 V by transforming the battery power source of 12 V, supplying the
current control unit
4 with this constant voltage.
The speed sensor VS, which detects the speed of a vehicle as a number of pulses
per time, sends pulse signals corresponding to the detected number of pulses to
the current control unit
4 as a signal V of vehicle speed. In this connection,
the speed sensor VS may be prepared as a dedicated sensor for the apparatus
1
or another existing sensor for detection of vehicle speed may alternatively be
adopted if it is available.
The torque sensor TS is a sensor of magneto striction, in which an electrical
coil electromagnetically detects the effect of magneto striction caused by the
steering torque manually exerted by a driver and acting on the pinion shaft
7a,
including the magnitude and direction. And the torque sensor TS sends an analogue
electric signal representative of detected steering torque to the current control
unit
4 as a signal T of steering torque. The signal T includes the magnitude
and direction of steering torque.
The device
12 for detection of motor current, which has a resistor or
Hall element connected in series to the brushless motor
6, detects motor
current IM actually running through the brushless motor
6. The device
12
feedbacks (negative feedback) a signal IMO of motor current to the drive control
unit
5. The signal IMO is a three-phase alternating signal, including a
motor current representing magnitude of actual current running through each of
three phase winding of brushless motor
6 and the information on which phase
of three phase winding the current runs through.
The device
13 for detection of motor rotation, which is a resolver placed
at an end of brushless motor
6, detects an angle PM of motor rotation. The
device
13 has a layered core rotor (not shown) secured to an end of the
shaft (not shown) of brushless motor
6 and a detection element, a combination
of exciting coil and detection coil (not shown), for magnetically detecting a rotational
angle of the layered core rotor. The device
13 sends a signal PMO of motor
rotation representative of the angle PM to the drive control unit
5. The
signal PMO, which includes the direction and angle of rotation of inner rotor (not
shown) of brushless motor
6, has two signals of excitation, two signals
of cosine and two signals of sine.
A first embodiment of the present invention is described referring to FIGS. 1
and
2. FIG. 2 is a block diagram showing current control and drive control units according
to the first embodiment. The object of the first embodiment is to provide an apparatus
for an electric power steering system, which is able to control a brushless motor
6 using at least one of microcomputers
40A and
50A, by adopting
redundant structure for the two microcomputers
40A and
50A.
A current control unit
4A according to the first embodiment is described
referring to FIG.
2.
The current control unit
4A and a drive control unit
5A are electrically
connected by wire harnesses WH and communicate signals therethrough (see FIG.
1).
The current control unit
4A includes the microcomputer
40A made of
one chip, an output circuit for signals (not shown), a memory (not shown) such
as Electrically Erasable Programmable Read Only Memory (EEPROM) and a watch dog
timer (not shown).
The current control unit
4A, which incorporates signals T and V from a
vehicle and a speed signal SMO of motor rotation from the drive control unit
5A,
determines target current to be supplied to a brushless motor
6 based upon
the signals T, V and SMO. Further, the current control unit
4A incorporates
a signal PMO′ (digital signal) of motor rotation and a signal IMO′
(digital signal) of motor current from the drive control unit
5A. If the
microcomputer
50A in the drive control unit
5A fails, the current
control unit
4A determines a signal VO for motor control for controlling
the brushless motor
6 based upon the target current and the acquired digital
signals PMO′ and IMO′, then sending the signal VO to a motor drive
circuit
51.
The current control unit
4A monitors the operation of microcomputer
40A
with a watch dog timer. The current control unit
4A thus performs self monitoring
and in addition sends a signal of failure to the drive control unit
5A (microcomputer
50A) if the current control unit
4A detects the failure of microcomputer
40A with the watch dog timer. Further, the current control unit
4A
sends watch dog pulses to the microcomputer
50A and checks the return of
pulses sent back by the microcomputer
50A. In this way, the current control
unit
4A also monitors the operation of microcomputer
50A.
I/F circuits
41 for torque sensor and
42 for speed sensor are described
before starting description of the structure of microcomputer
40A.
The I/F circuit
41 receives a signal T (analogue signal) of steering torque
from a torque sensor TS and converts the signal T into a signal T′ (digital
signal), delivering the signal T′ to a device
40a for target
current and a device
40d for inertia control. The I/F circuit
42
receives a signal V (pulse signal) of vehicle speed from a speed sensor VS and
converts the signal V into a signal V′ (digital signal), delivering the
signal T′ to the devices
40a and
40d. In this
connection, the signals T′ and V′ (digital signals) are sent to the
microcomputer
50A in the first embodiment but are not sent to a microcomputer
50B of the second embodiment or microcomputer
50C of the third embodiment
(see FIGS.
3 and
4).
The structure of microcomputer
40A is now described. The microcomputer
40A includes a device
40a for target current, a device
40b
for damper control, a device
40c for damper compensation, a device
40d for inertia control and a device
40e for inertia
compensation so that the microcomputer
40A can determine a signal IMS for
target current. The microcomputer
40A also includes a device
40f
for failure decision so as to decide an occurrence of failure of microcomputer
50A. The microcomputer
40A further includes the following devices
so as to back up microcomputer
50A, namely to determine a signal VO for
motor control, if the microcomputer
50A fails: a device
40g for
conversion of current, a device
40h for conversion of rotational
angle, a device
40i for computation of torque deviation, a device
40j for computation of magnetic field deviation, a device
40k
for torque proportional integral (PI) control, a device
40l for
magnetic field PI control, a device
40m for conversion of voltage
and a device
40n for conversion of pulse width modulation (PWM).
The microcomputer
40A, which generates clock signals, executes processes
based upon the clock signals and performs communication with the microcomputer
50A by clock synchronization. For this purpose, the microcomputer
40A
sends the clock signals to the microcomputer
50A.
When the microcomputer
50A is normal, the microcomputer
40A repeats
processes for each primary process time in both the devices
40a-
40e
for determining a signal IMS for target current and the device
40f
to decide if failure occurs in the microcomputer
50A. On the other hand
if the microcomputer
40A decides that the microcomputer
50A fails,
the microcomputer
40A executes additional processes for each failure process
time, which is a slot of vacant time relative to the primary process time, in the
devices
40g-
40n for determining a signal VO for motor
control. The failure process time is longer than the primary process time and the
number of processes performed in the devices
40g-
40n of
microcomputer
40A is smaller than that performed in the microcomputer
50A
while normal. In this connection, when the microcomputer
50A fails, it may
be possible to set a primary process time longer than that of normal operation
so that more process time can be allocated for processes in the devices
40g-
40n.
The device
40a for target current is described.
The device
40a receives the signal T′ (digital signal) of
steering torque from the I/F circuit
41 and the signal V′ (digital
signal) of vehicle speed from the I/F circuit
42, delivering the signal
IMS for target current to the device
40c for damper compensation.
The device
40a reads out a signal IMS from a map defining the relationship
between signals T′ and V′ vs. signal IMS, which is prepared in advance
based upon experimental data or design values. This signal IMS includes the information
of current to be used as a reference for determining target motor current supplied
to the brushless motor
6. In this connection, a large value of signal IMS
is selected for a small value of signal V′ when reaction force exerted by
road surface is large. On the other hand, while a vehicular is driving at high
speed, a small value of signal IMS is selected for a large value of signal V′
for the stability of vehicle. Also a signal IMS is so related to a signal T′
that the signal IMS is set to be zero when the signal T′ is around zero
and increases with the signal T′ after the signal T′ reaches a predetermined
value. A signal IMS for target current is set to be less than or equal to a maximum
target current, which is derived from an allowable maximum current to be supplied
to the brushless motor
6.
The device
40b for damper control is described.
The device
40b receives a speed signal SMO of motor rotation sent
by the microcomputer
50A or the other signal SMO from the device
40h
for conversion of rotational angle, delivering a signal for damper control
to the device
40c for damper compensation. The device
40b
reads out a speed signal SMO from a map defining the relationship between signal
for damper control and signal SMO, which is prepared in advance based upon experimental
data or design values. In order to improve the steering feeling of a driver by
damping excessive assist torque, the larger a speed signal SMO is, the larger a
signal for damper control is selected for. In this connection, the device
40b
may incorporate a signal V′ (digital signal) and determine a signal
for damper control taking into account the signal V′.
The device
40c for damper compensation is described.
The device
40c receives a signal IMS for target current from the
device
40a for target current and a signal for damper control from
the device
40b for damper control, delivering a signal (IMS)d for
target current (after damper compensation) to the device
40e for
inertia compensation. The control performed by devices
40b and
40c
damps excessive assist torque due to the inertia of rotational portions of
a brushless motor
6 when a large amount of motor drive current IM is supplied
to the brushless motor
6, thereby improving the steering feeling of a driver.
The rotational speed of brushless motor
6 will not decelerate immediately
due to its inertia when the brushless motor
6 rotates at high speed with
a large amount of motor current IM. The object of damper control is to restrict
the rotational speed of brushless motor
6. For this purpose, the device
40c subtracts a signal for damper control from a signal IMS for target
current to generate a signal (IMS)d (after damper compensation).
The device
40d for inertia control is described.
The device
40d receives a signal T′ (digital signal) of
steering torque from the I/F circuit
41 and signal V′ (digital signal)
of vehicle speed form the I/F circuit
42, delivering a signal for inertia
control to the device
40e for inertia compensation. The device
40d
differentiates a signal T′ with regard to time and delivers a time differential
of signal T′. The device
40d then reads out a signal for inertia
control from a map defining the relationship of time differential of steering torque
and signal V′ vs. signal for inertia control, which is in advance prepared
based upon experimental data or design values. In order to improve the response
to steering exerted by a driver, the larger a time differential is, the larger
a signal for inertia control will be.
The device
40e for inertia compensation is described.
The device
40e receives a signal (IMS)d for target current (after
damper compensation) from the device
40c of damper compensation and
a signal for inertia control from the device
40d for inertia control,
delivering a signal (IMS)di (after damper and inertia compensation) to the device
40f for failure decision. In this connection, the inertia control
performed by the devices
40d and
40e prevents deterioration
in the response to steering caused by the inertia of rotational portions of the
brushless motor
6, thereby improving the feeling of steering by a driver.
This control is required by the fact that the brushless motor
6 cannot switch
the direction of rotation immediately due to the inertia when the direction of
motor voltage VM is altered so as to switch the direction from a positive to reverse
direction or vice versa. The inertia control therefore synchronizes a timing of
switching the rotational direction of brushless motor
6 and that of switching
the rotational direction of a steering wheel
3. For this purpose, the device
40e adds a signal for inertia control to a signal (IMS)d (after damper
compensation) for target current, delivering a signal (IMS)di (after damper and
inertia compensation).
The device
40f for failure decision is described.
The device
40f receives the signal (IMS)di for target current (after
damper and inertia compensation) from the device
40e for inertia
compensation, transmitting the signal (IMS)di to the microcomputer
50A or
delivering the signal (IMS)di to the device
40i for torque deviation
computation. When the device
40f decides that the microcomputer
50A
is normal, the device
40f transmits the signal (IMS)di to the microcomputer
50A. On the other hand, when the device
40f decides that the
microcomputer
50A is not normal, the device
40f commands initiation
of processes executed in the devices
40g-
40n as backup
so as to determine a signal VO for motor control and delivers the signal (IMS)di
to the device
40i. For this purpose, the device
40f decides
whether or not the microcomputer
50A is normal based upon failure signals
sent by the drive control unit
5A and the return of signals for watch dog
pulses transmitted to the microcomputer
50A. In this connection, the device
40f decides that the microcomputer
50A fails if one of following
conditions is observed: indication of the failure of microcomputer
50A by
a failure signal, no return signal and a wrong return signal for a watch dog pulse.
The device
40g for current conversion is described.
The device
40g receives a signal IMO′ (digital signal) of
motor current transmitted by the drive control unit
5A and a phase signal
of motor rotation from the device
40h for conversion of rotational
angle, delivering a current signal for torque control to the device
40i
for computation of torque deviation and a current signal for magnetic field
control to the device
40j for computation of magnetic field deviation.
The device
40g performs the same processes as those of a device
50g
for current conversion in the microcomputer
50A.
The device
40h for conversion of rotational angle is described.
The device
40h receives a signal PMO′ (digital signal) of
motor rotation transmitted by the drive control unit
5A, delivering a phase
signal of motor rotation to both the device
40g for current conversion
and device
40m for voltage conversion and a speed signal SMO of motor
rotation to the device
40b for damper control. The device
40h
performs the same processes as those of a device
50h for conversion
of rotational angle in the microcomputer
50A.
The device
40i for computation of torque deviation is described.
The device
40i receives a signal (IMS)di for target current (after
damper and inertia compensation) from the device
40f for failure
decision and a current signal for torque control from the
40g for
current conversion, delivering a deviation signal for torque control to the device
40k for torque PI control. The device
40i performs
the same processes as those of a device
50i of the microcomputer
50A.
The device
40j for computation of magnetic field deviation is described below.
The device
40j receives a current signal for magnetic field control
from the device
40g for current conversion and delivers a deviation
signal for magnetic field control to the device
40l for magnetic
field PI control. The device
40j performs the same processes as those
of a device
50j for computation of magnetic field deviation.
The device
40k for torque PI control is described.
The device
40k receives a deviation signal for torque control from
the device
40i for computation of torque deviation and delivers a
signal for torque PI control (direct-current voltage) to the device
40m
for voltage conversion. The device
40k performs the same processes
as those of a device
50k for torque PI control of the microcomputer
50A.
The device
40l for magnetic field PI control is described.
The device
40l receives a deviation signal for magnetic field control
from the device
40j for computation of magnetic field deviation and
delivers a signal for magnetic field PI control (direct-current voltage) to the
device
40m for voltage conversion. The device
40l performs
the same processes as those of a device
50l for magnetic field PI
control of the microcomputer
50A.
The device
40m for voltage conversion is described.
The device
40m receives a phase signal of motor rotation from the
device
40h for conversion of rotational angle, a signal (direct-current
voltage) for torque PI control from the device
40k for torque PI
control and a signal (direct-current voltage) for magnetic field PI control from
the device
40l for magnetic field PI control, delivering a signal
(three-phase alternating-current voltage) for PI control to the device
40n
for PWM conversion. The device
40m performs the same processes
as those of a device
50m for voltage conversion of the microcomputer
50A.
The device
40n for PWM conversion is described.
The device
40n receives a signal (three-phase direct-current voltage)
for PI control from the device
40m for voltage conversion and transmits
a signal VO for motor control to the motor drive circuit
51 of drive control
unit
5A. The device
40n performs the same processes as those
of a device
50n for PWM conversion of the microcomputer
50A.
The drive control unit
5A according to the first embodiment is described
referring to FIG. 2
The drive control unit
5A communicates with the current control unit
4A
via the wire harnesses WH which connect the two units electrically (see FIG.
1).
The drive control unit
5A includes a microcomputer
50A of one microchip
for drive control, a motor drive circuit
51, an I/F circuit
52 for
motor current, a circuit for R/D conversion, an output circuit for signals (not
shown), a memory (not shown) such as EEPROM for storing data used by the microcomputer
50A and a watch dog timer (not shown).
The drive control unit
5A incorporates signals IMO and PMO from a vehicle
and a signal (IMS)di for target current (after damper and inertia compensation)
from the current control unit
4A, delivering a signal VO for motor control,
which is determined based upon the signals IMO, PMO and (IMS)di, to the motor drive
circuit
51 in order to drive the brushless motor
6. Further, the
microcomputer
50A incorporates signals T′ (digital signal) of steering
torque and V′ (digital signal) of vehicle speed from the current control
unit
4A. In this way, if the microcomputer
40A fails, the microcomputer
50A determines a target current to be supplied to the brushless motor
6
based upon a speed signal SMO of motor rotation in addition to the incorporated
signals T′ and V′.
The drive control unit
5A monitors the microcomputer
50A by a watch
dog timer. In addition to self monitoring, if the drive control unit
5A
detects the abnormal operation (failure) of microcomputer
50A, the drive
control unit
5A transmits failure signals to the current control unit
4A
(microcomputer
40A). Further, the drive control unit
5A, which transmits
watch dog pulses to the microcomputer
40A and monitors return pulses sent
back by the microcomputer
40A, performs mutual monitoring for the microcomputer
40A.
Before description of the micro computer
50A, the I/F circuit
52
for motor current and circuit
53 for R/D conversion are described.
The I/F circuit
52 receives a signal IMO (analogue signal) of motor current
from the device
12 for detection of motor current and converts the signal
IMO to a signal IMO′ (digital signal), delivering the signal IMO′
to the microcomputer
50A. On the other hand, the circuit
53 receives
a signal PMO (analogue signal) of motor rotation from the device
13 for
detection of motor rotation, delivering a signal PMO′ (digital signal) of
motor rotation to the microcomputer
50A. The circuit
53 converts
the analogue signal PMO of motor rotation into the digital signal PMO′ with
computation of the direction and angle of rotation. In this connection, the signals
(digital signals) IMO′ and PMO′ are transmitted to the microcomputer
40A in the first embodiment, but not transmitted to the microcomputers
40B
or
40C in the second or third embodiment (see FIGS.
3 and
4).
The microcomputer
50A for drive control is described.
The microcomputer
50A includes a device
50f for failure
decision in order to decide an occurrence of failure in the microcomputer
40A.
The microcomputer
50A also includes a device
50g for current
conversion, a device
50h for conversion of rotational angle, a device
50i for computation of torque deviation, a device
50j for
computation of magnetic field deviation, a device
50k for torque
PI control, a device
50l for magnetic field PI control, a device
50m for voltage conversion and a device
50n for PWM
conversion so as to determine a signal VO for motor control. The microcomputer
50A further includes a device
50a for target current, a device
50b for damper control, a device
50c for damper compensation,
a device
50d for inertia control and a device
50e for
inertia compensation so that the microcomputer
50A can back up the microcomputer
40A, namely determine a signal (IMS)di for target current (after damper
and inertia compensation) when the microcomputer
40A fails.
The microcomputer
50A, which generates clock signals, executes processes
based upon the signals. The microcomputer
50A communicates with the microcomputer
40A by clock synchronization using the clock signals transmitted by the
microcomputer
40A.
When the microcomputer
40A is normal, the microcomputer
50A repeats
processes in both the devices
50g-
50n for each primary
process time for determining a signal VO for motor control and the device
50f
to decide if failure occurs in the microcomputer
40A. On the other hand
when the microcomputer
40A fails, the microcomputer
50A repeats other
additional processes for each failure process time, which is a slot of vacant time
relative to the primary process time, in the devices
50a-
50e
for determining a signal (IMS)di for target current (after damper and inertia
compensation). The failure process time is longer than the primary process time
and the number of processes performed in the devices
50a-
50e
of microcomputer
50A is smaller than that performed in the microcomputer
40A while normal. In this connection, when the microcomputer
40A
fails, it may be possible to set a primary process time longer than that of normal
operation so that more process time can be allocated for processes in the devices
50a-
50e.
The device
50f for failure decision is described.
The device
50f receives a signal (IMS)di for target current (after
damper and inertia compensation) transmitted by the microcomputer
40A or
the other signal (IMS)di from the device
50e for inertia compensation,
and delivers either of the signals (IMS)di to the device
50i for
torque deviation computation. If the device
50f decides that the
microcomputer
40A is normal, the device
50f delivers a signal
(IMS)di transmitted by the microcomputer
40A to the device
50i.
On the other hand, if the device
50f decides that the microcomputer
40A fails, the device
50f commands initiation of processes
in the devices
50a-
50e so as to determine a signal
(IMS)di and delivers the signal (IMS)di to the device
50f. For this
purpose, the device
50f decides whether or not the microcomputer
40A is normal based upon failure signals sent by the current control unit
4A and the return of signals for watch dog pulses transmitted to the microcomputer
40A. In this connection, the device
50f decides that the microcomputer
40A fails if one of the following conditions is observed: indication of
the failure of microcomputer
40A by a failure signal, no return signal or
a wrong return signal for a watch dog pulse.
The device
50g for current conversion is described.
The device
50g receives a signal IMO′ (digital signal) of
motor current from the I/F circuit
52 for motor current and a phase signal
of motor rotation from the device
50h for conversion of rotational
angle, delivering a current signal for torque control to the device
50i
for compensation of torque deviation and a current signal for magnetic field
control to the device
50j for compensation of magnetic field deviation.
The device
50g determines a current signal for torque control by
sampling a current component, which generates the rotational torque of brushless
motor
6, from the motor current based upon a signal IMO of motor current
of three-phase alternating current, a phase signal of motor rotation and the like.
The device
50g also determines a current signal for magnetic field
control by sampling a current component which generates the magnetic field of brushless
motor
6 in the same manner as that of the current signal for torque control
described above.
The device
50h for conversion of rotational angle is described.
The device
50h receives a signal PMO′ (digital signal) of
motor rotation from the circuit
53 for R/D conversion and delivers a phase
signal of motor rotation to the devices
50g for current conversion
and
50m for voltage conversion. In addition the device
50h
transmits a speed signal SMO of motor rotation to the microcomputer
40A
and delivers the speed signal SMO to the device
50b for damper control.
The device
50h computes a rotational speed of the brushless motor
6 based upon an angle and direction of the signal PMO′, thereby determining
a speed signal SMO of motor rotation. The device
50h computes an
accurate phase of rotation based upon an angle,
