Title: Thermal expansion compensation shock absorber
Abstract: The present invention provides the art with a shock absorber which is capable of compensating for the differing thermal expansion between two materials. The shock absorber in its various embodiments includes a free floating pressure tube that is able to expand or contract axially without breaking a seal, a hybrid piston rod with a shaft of one material that compensates for differing thermal expansions and a cap of another material that absorbs axial forces, a unique rod guide assembly with a biasing member that compensates for differing thermal expansions, and a unique cylinder end assembly with a biasing member made from springs, a rubber block, or pressurized gas.
Patent Number: 7,004,293 Issued on 02/28/2006 to Schurmans
| Inventors:
|
Schurmans; Rudi (Woutervelo, BE)
|
| Assignee:
|
Tenneco Automotive Operating Company Inc. (Lake Forest, IL)
|
| Appl. No.:
|
671354 |
| Filed:
|
September 25, 2003 |
| Current U.S. Class: |
188/322.17; 188/315 |
| Current Intern'l Class: |
F16F 9/36 (20060101) |
| Field of Search: |
188/315,322.19,276,322.17
92/165.R
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Torres; Melanie
Attorney, Agent or Firm: Harness, Dickey & Pierce, PLC
Claims
What is claimed is:
1. A shock absorber which compensates for thermal expansion, said shock absorber comprising:
a rod guide assembly;
a floating pressure tube forming a compression chamber, said pressure tube slidingly
engaging said rod guide assembly;
a piston slidably disposed within said compression chamber;
a piston rod connected to said piston;
a reserve tube disposed around said pressure tube, said reserve tube and said
pressure tube defining a fluid reservoir;
a cylinder end assembly disposed between said compression chamber and said fluid
reservoir for controlling the flow of fluid between said compression chamber and
said fluid reservoir, said pressure tube slidingly engaging said cylinder end assembly; and
a first biasing member disposed between said pressure tube and said rod guide
assembly for urging said pressure tube axially away from said rod guide assembly;
said floating pressure tube being able to move freely relative to said rod guide
assembly and said cylinder end assembly.
2. The shock absorber according to claim 1, wherein said piston rod comprises:
a two-piece piston rod connected to said piston, said two-piece piston rod including
a shaft and a piston post, said piston post being secured to said piston.
3. The shock absorber according to claim 2, wherein said shaft is made from a
first material and said piston post is made from a second material.
4. The shock absorber according to claim 3, wherein said piston post is threaded
such that it screws onto said shaft.
5. The shock absorber according to claim 3, wherein said piston post is bonded
to said shaft.
6. The shock absorber according to claim 3, wherein said piston post is secured
to said shaft by a circle-clip.
7. The shock absorber according to claim 1, wherein said first biasing member
is at least one Belleville spring.
8. The shock absorber according to claim 1, wherein a retainer is disposed between
said rod guide assembly and said first biasing member.
9. The shock absorber according to claim 1, wherein a retainer for supporting
said first biasing member is disposed between said first biasing member and said
pressure tube.
10. The shock absorber according to claim 1, wherein said rod guide assembly
further includes a bushing for facilitating movement of said piston rod.
11. The shock absorber according to claim 10, wherein a retainer retains said bushing.
12. The shock absorber according to claim 1 further comprising:
a second biasing member disposed between said pressure tube and said cylinder
end assembly for urging said pressure tube away from said cylinder end assembly.
13. The shock absorber according to claim 12, wherein said second biasing member
is a Belleville spring.
14. The shock absorber according to claim 13, wherein said Belleville spring
is secured to said cylinder end assembly by a circle-clip.
15. The shock absorber according to claim 13, wherein said Belleville spring
is secured to said cylinder end assembly by a spring retainer.
16. The shock absorber according to claim 13, wherein said Belleville spring
is disposed between two radial retainers secured to the cylinder end assembly.
17. The shock absorber according to claim 12, wherein said cylinder end assembly
has two portions, a top portion connected to said pressure tube and a bottom portion
connected to said reserve tube, said top portion slidingly engaging said bottom portion.
18. The shock absorber according to claim 17, wherein said second biasing member
is disposed between said top portion and said bottom portion.
19. The shock absorber according to claim 12, wherein said second biasing member
and one end of said pressure tube are disposed within said cylinder end assembly.
20. The shock absorber according to claim 1 further comprising:
a base plate slidingly engaging said reserve tube adjacent said cylinder end
assembly; and
a second biasing member disposed between said base plate and an end of said reserve
tube for urging said base plate away from said end of said reserve tube.
21. The shock absorber according to claim 20, wherein said second biasing member
is a Belleville spring.
22. The shock absorber according to claim 20, wherein said second biasing member
is an elastomeric block.
23. The shock absorber according to claim 22, wherein said second biasing member
is a pressurized gas.
Description
FIELD OF THE INVENTION
Hydraulic dampers, such as shock absorbers, are used in connection with
motor vehicle suspension systems to absorb unwanted vibrations which occur during
the operation of the motor vehicle. The unwanted vibrations are dampened by shock
absorbers which are generally connected between the sprung portion (i.e., the vehicle
body) and the unsprung portion (i.e., the suspension) of the motor vehicle. A piston
assembly is located within the compression chamber of the shock absorber and is
usually connected to the body of the motor vehicle through a piston rod. The piston
assembly includes a valving arrangement that is able to limit the flow of damping
fluid within the compression chamber when the shock absorber is compressed or extended.
As such, the shock absorber is able to generate a damping force which "smooths"
or "dampens" the vibrations transmitted between the suspension and the vehicle body.
A prior art thermal expansion compensating twin tube shock absorber
100
is shown in FIG. 1. Shock absorber
100 comprises an elongated pressure tube
102 provided for defining a hydraulic fluid containing compression chamber
104 and an elongated reserve tube
106 provided for defining a hydraulic
fluid containing reservoir
108.
Disposed within compression chamber
104 is a reciprocal piston assembly
110 that is secured to one end of an axially extending piston rod
112.
Piston rod
112 is supported and guided for movement within pressure tube
102 by means of a combination seal and rod guide assembly
114 located
at the upper end of pressure tube
102 and having a centrally extending bore
116 through which piston rod
112 is reciprocally movable. Disposed
within bore
116 between rod guide assembly
114 and piston rod
112
is a bushing
118 which is used to facilitate movement of piston rod
112
with respect to rod guide assembly
114.
A compliant cylinder end assembly, generally designated at
120, is located
at the lower end of pressure tube
102. The compliant cylinder end assembly
120 includes a base valve assembly
122 that functions to control
the flow of hydraulic fluid between compression chamber
104 and fluid reservoir
108 as well as biasing member
124 that compensates for the differing
axial thermal expansion between the various components of shock absorber
100.
Fluid reservoir
108 is defined as the space between the outer peripheral
surface of pressure tube
102 and the inner peripheral surface of reserve
tube
106.
The upper and lower ends of shock absorber
100 are adapted for assembly
into a motor vehicle. Piston rod
112 is shown having a threaded portion
126 for securing the upper end of shock absorber
100 to the motor
vehicle while reserve tube
106 is shown incorporating a flange
128
having a pair of mounting holes
130 for securing the lower end of shock
absorber
100 to the motor vehicle (McPherson strut configuration). While
shock absorber
100 is shown in a McPherson strut configuration having threaded
portion
126 and flange
128 for securing it between the sprung and
unsprung portions of the motor vehicle, it is to be understood that this is merely
exemplary in nature and is only intended to illustrate one type of system for securing
shock absorber
100 to the motor vehicle. As will be appreciated by those
skilled in the art, upon reciprocal movement of piston rod
112 and piston
assembly
110, hydraulic fluid with compression chamber
104 will be
transferred between an upper portion
132 and a lower portion
134
of compression chamber
104 as well as between compression chamber
104
and fluid reservoir
108 through valve assembly
122 for damping relative
movement between the sprung portion and the unsprung portion of the motor vehicle.
This quick exchange of hydraulic fluid through valve assembly
122 and
piston assembly
110 as well as the friction between piston assembly
110
and pressure tube
102 and the friction between piston rod
112 and
rode guide
114 generates heat which is undesirable during prolonged operating conditions.
In addition to absorbing the heat generated while providing the damping function
for the motor vehicle, shock absorber
100 is also required to operate over
a broad range of temperatures ranging from severe cold temperatures of the winter
months to the extremely hot temperatures of the summer months. Prior art shock
absorbers are manufactured using steel for pressure tube
102 and reserve
tube
106. While steel has been proven to be an acceptable material for these
components, tubes manufactured from aluminum offer the advantages of weight savings
as well as improved heat dissipation. If the typical pressure tube
102 were
manufactured from steel while reservoir tube
106 were manufactured from
aluminum, the difference in their relative axial thermal expansion rates may present
problems for the shock absorber when operating over the necessary temperature extremes.
Specifically, structural failure may occur under extreme cold temperatures or loss
of pressure tube preload and sealing may occur under extreme hot temperatures.
Accordingly, continued development of shock absorbers with aluminum
tubes includes the further development of methods to compensate for differing thermal
expansion between aluminum and steel as well as the differing thermal expansion
between any other two materials.
SUMMARY OF THE INVENTION
The present invention provides the art with a shock absorber which is capable
of compensating for the differing thermal expansion between two materials and thus
eliminating the possibility of structural failure due to extreme cold temperatures
as well as the possibility of pressure tube preload loss and sealing failure under
extreme hot temperatures.
In one embodiment of the present invention, the shock absorber includes a free
floating pressure tube that is capable of compensating for differing thermal expansion
by freely moving between the rod guide assembly and the valve assembly.
In another embodiment of the present invention, a unique piston rod is provided
that includes an aluminum rod that eliminates the difference in thermal expansions.
The rod has a steel cap that absorbs compression forces.
In another embodiment of the present invention, a unique compensating rod guide
assembly is provided that includes a thermal compensation element capable of compensating
for the differing thermal expansion between the pressure tube and the reserve tube.
In still another embodiment of the present invention, a unique compensating cylinder
end assembly is provided that includes a thermal compensation element, and the
means for securing the element to the valve assembly. This compensating element
is either a spring, an elastomeric block, or gas pressure.
Other advantages and objects of the present invention will become apparent
to those skilled in the art from the subsequent detailed description, appended
claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings which illustrate the best mode presently contemplated for carrying
out the present invention:
FIG. 1 is a longitudinal cross-sectional view through a prior art thermal expansion
compensating shock absorber;
FIG. 2 is a longitudinal cross-sectional view of a shock absorber incorporating
a floating pressure tube;
FIG. 3 is a side view of a unique aluminum piston rod with a steel cap;
FIG. 4 is an enlarged side view of a threaded steel cap;
FIG. 5 is an enlarged side view of a bonded steel cap;
FIG. 6 is an enlarged cross-sectional view of a compensating rod guide assembly
with Belleville springs;
FIG. 7 is an enlarged cross-sectional view of a compensating rod guide assembly
with a bearing bush retainer;
FIG. 8 is an enlarged cross-sectional view of an alternate compensating rod
guide assembly with a bearing bush retainer;
FIG. 9 is an enlarged cross-sectional view of a compensating rod guide assembly
with a retainer;
FIG. 10 is an enlarged cross-sectional view of a compensating cylinder end assembly
with Belleville springs;
FIG. 11 is an enlarged cross-sectional view of the compensating cylinder end
assembly of FIG. 10 illustrating a circle-clip and retainer support for the compensating member;
FIG. 12 is an enlarged cross-sectional view of the compensating cylinder end
assembly of FIG. 10 illustrating a spring retainer for the compensating member;
FIG. 13 is an enlarged cross-sectional view of the compensating cylinder end
assembly of FIG. 10 illustrating a double ring retainer for a compensating member;
FIG. 14 is an enlarged cross-sectional view of an alternate compensating cylinder
end assembly having a two piece end assembly that sandwiches the compensating member;
FIG. 15 is an enlarged cross-sectional view of an alternate compensating cylinder
end assembly illustrating the pressure tube and compensating member disposed within
the valve assembly;
FIG. 16 is an enlarged cross-sectional view of a compensating cylinder end assembly
with Belleville springs at the base;
FIG. 17 is an enlarged cross-sectional view of a compensating cylinder end assembly
with an elastomeric block at the base;
FIG. 18 is an enlarged cross-sectional view of a compensating cylinder end assembly
with gas pressure at the base; and
FIG. 19 is an enlarged cross-sectional view of an alternate compensating cylinder
end assembly with gas pressure at the base.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Continued reference is made generally to FIG. 1 and specifically to the
components of shock absorber
100 throughout the subsequent description.
It is to be understood that the construction of shock absorber
100 is merely
exemplary in nature and is only intended to illustrate one type of hydraulic damping
apparatus within which the compensating elements of the present invention can be utilized.
Referring now to the drawings in which like reference numerals designate
like or corresponding parts throughout the several views, there is shown in FIG.
2 a unique compensating shock absorber
200 having a floating pressure tube
202 and a base valve assembly
222. Rod guide assembly
114
and base valve assembly
222 are mechanically secured to reserve tube
106.
As the relative length of reserve tube
106 changes due to thermal conditions,
the relative distance between rod guide assembly
114 and base valve assembly
222 changes. In the prior art, pressure tube
102 is fixed at one
end to one portion of rod guide assembly
114 and at the other end to base
valve assembly
122, such that changes in the length of pressure tube
102
due to thermal conditions were compensated for using a multi-piece valve assembly
122. In this embodiment of the present invention, a floating pressure tube
202 replaces pressure tube
102 of the prior art in order to compensate
for the different thermal expansions of reserve tube
106 and floating pressure
tube
202. Floating pressure tube
202 is sealed to rod guide assembly
114 and base valve assembly
222 using O-rings
204. Floating
pressure tube
202 is able to move freely between rod guide assembly
114
and base valve assembly
222 as the relative length of reserve tube
106
changes. Thus, both a standard valve guide assembly and a standard base valve assembly
can be easily modified to accept floating pressure tube
202.
In another embodiment of prior art shock absorber
100, a hybrid piston
rod
312 replaces the prior art piston rod
112 as shown in FIGS. 3-5.
Typically the prior art piston rod
112 is made from steel while rod guide
assembly
114 is made from aluminum. Under extreme thermal conditions the
seal between piston rod
112 and rod guide
114 can be broken by the
different thermal expansion of the two materials. Hybrid piston rod
312
includes an aluminum piston shaft
314 and a steel piston post
316.
As shown in FIG. 4, piston post
316 includes an internal bore
318
which slidingly receives the end of piston shaft
314. A circle-clip
320
retains the assembly of piston post
316 and piston shaft
316. As
shown in an alternative embodiment in FIG. 4, piston post
316 has an open
threaded bore
322 for receiving a threaded end of piston shaft
314.
Piston post
316 may be threaded on to piston shaft
314. Alternatively,
as seen in FIG. 5, a modified steel piston post
330 with a flat end
332
may be adhesively secured to the end of piston shaft
314. In operation,
aluminum piston shaft
314 expands and contracts at the same rate as aluminum
rod guide assembly
114 and thus prevents a break in the seal between the
two. Steel piston post
316, or alternately modified steel piston post
320,
absorbs the axial force on piston rod
312 when shock absorber
100
is in compression.
In still another embodiment of prior art shock absorber
100, various compensating
piston rod guide assemblies are shown in FIGS. 6-9. The compensating piston rod
guide assembly
414, as shown in FIG. 6, supports and guides the movement
of piston rod
112 and also compensates for the different thermal expansion
of pressure tube
102 and reserve tube
106. Compensating piston rod
guide assembly
414 includes bore
116 and bushing
118, as well
as a plurality, an even number in the preferred embodiment, of Belleville springs
424 disposed between rod guide
414 and pressure tube
102.
The difference in thermal expansion between steel pressure tube
102 and
aluminum reserve tube
106 is compensated for by the increase or decrease
in the compensation of Belleville springs
424.
On the left side of FIG. 7, an alternate compensating piston rod guide
414′
is shown. Alternate piston rod guide
414′ includes a bearing bush
retainer
450 disposed between Belleville springs
424 and rod guide
414′. Bearing bush retainer
450 seals rod guide
414′
and pressure tube
102 and retains bushing
118, and is further designed
to support Belleville springs
424. The thermal expansion of pressure tube
102 is directly compensated for by Belleville springs
424. On the
right side of FIG. 7, piston rod guide
414′ is shown with bearing
bush retainer
450 being replaced by compensation retainer
450′.
Compensation retainer
450′ functions the same as bearing bush retainer
450 in that it retains bushing
118 and it is designed to support
Belleville springs
424. The thermal expansion is directly compensated for
by Belleville springs
424.
In another embodiment, a compensating piston rod guide
414" is shown on
the left side of FIG. 8, wherein bearing bush retainer
452 is disposed between
the pressure tube
102 and Belleville springs
424. Bearing bush retainer
452 is similar to bearing bush retainer
450 in that it seals rod
guide
414" and pressure tube
102 and it supports Belleville springs
424. The difference between bearing bush retainer
452 and
450
is that Belleville springs
424 are disposed between rod guide
414"
and bearing bush
452 instead of between bearing bush retainer
450
and pressure tube
102 as shown in FIG. 7. The thermal expansion is directly
compensated for by Belleville springs
424. On the right side of FIG. 8,
piston rod guide
414" is shown with bearing bush retainer
452 being
replaced by compensation retainer
452′. Compensation retainer
450′
functions the same as bearing bush retainer
452′ in that it retains
bushing
118 and it is designed to support Belleville springs
424
with Belleville springs
424 being disposed between rod guide
414"
and bush retainer
452′. The thermal expansion is directly compensated
for by Belleville springs
424.
In still another embodiment, a compensating piston rod guide
414′"
is shown in FIG. 9, wherein bearing bush retainer
452 has been replaced
by a compensation spring support
460. Spring support
460 acts to
support Belleville springs
424 but it does not retain bushing
118.
Belleville springs
424 are disposed between rod guide
414′"
and spring support
460. The thermal expansion is directly compensated for
by Belleville springs
424.
In yet further embodiments of prior art shock absorber
100, various compensating
cylinder end assemblies are shown in FIGS. 10-19. In FIG. 10, a compensating cylinder
end assembly, generally designated as
520, is located at the lower end of
pressure tube
102 and functions to control the flow of hydraulic fluid between
compression chamber
104 and fluid reservoir
108. Compensating end
assembly
520 further acts to compensate for the differing axial thermal
expansion between the various components of shock absorber
100.
In FIG. 10, compensating cylinder end assembly
520 includes a base valve
assembly
522 and a plurality, an even number in the preferred embodiment,
of Belleville springs
524 disposed between pressure tube
102 and
base valve assembly
522. The difference in thermal expansion between the
steel pressure tube
102 and the aluminum reserve tube
106 is compensated
for by the increase or decrease in the compression of Belleville springs
524.
This embodiment differs from the prior art shown in FIG. 1 by eliminating the need
for the multi-piece base valve assembly
122 shown in FIG. 1.
Various methods for securing Belleville springs
524 to an end assembly
are shown in FIGS. 11-14. In FIG. 11, the compensating cylinder end assembly
520′
includes a reaction ring
550. Reaction ring
550 is retained to the
outside of pressure tube
102 by a circle-clip
552. Belleville springs
524 are disposed between ring
550 and compression valve assembly
522.
In FIG. 12, a compensating cylinder end assembly
520" includes an S-shaped
spring retainer
560. Spring retainer
560 is positioned between the
bottom of pressure tube
102 and the top of Belleville springs
524,
and acts to retain Belleville springs
524 between spring retainer
560
and valve assembly
522.
In FIG. 13, the compensating cylinder end assembly
520′" includes
a first retaining ring
570 and a second retaining ring
572. First
retaining ring
570 is positioned such that it is in contact with the bottom
of pressure tube
102. Second retaining ring
572 is secured to valve
assembly
522. Belleville springs
524 are disposed between first retaining
ring
570 and second retaining ring
572.
In FIG. 14, an alternate compensating cylinder end base valve assembly is designated
at
620. Compensating end base valve assembly
620 is divided into
two portions, an upper portion
650 and a lower portion
652, and includes
a plurality of Belleville springs
624 disposed between the two portions
650 and
652. Upper portion
650 is connected to pressure tube
102 and lower portion
652 is connected to or abuts reserve tube
106.
Upper portion
650 fits within lower portion
652 and is sealed by
an O-ring
654. Belleville springs
624 are disposed between the two
portions
650,
652 and act to compensate for the different thermal
expansion of pressure tube
102 and reserve tube
106 by moving upper
portion
650 and lower portion
652 towards or away from each other.
In FIG. 15, an alternate compensating cylinder end assembly is designated at
720.
Cylinder end assembly
720 includes a base valve assembly
722 having
a cylindrical wall
750 and a plurality of Belleville springs
724.
Cylindrical wall
750 is connected to and surrounds a base valve assembly
722 and further extends towards the opposite end of shock absorber
100.
Pressure tube
102 slides within cylindrical wall
750, and is sealed
by an O-ring
752. Belleville springs
724 are disposed between pressure
tube
102 and valve assembly
722 within cylindrical wall
750.
In another embodiment of shock absorber
100, compensating cylinder end
assembly
820 is shown in FIG. 16. Compensating end assembly
820 includes
a base valve assembly
822, a plurality of Belleville springs
824,
a base plate
850, an O-ring
852, and a bottom retainer
854.
Base plate
850 is capable of moving axially and is sealed to reserve tube
106 by O-ring
852. Bottom retainer
854 is fixed to reserve
tube
106 using a retaining ring
856 and provides a flat, stable bottom
for cylinder end assembly
820. Belleville springs
824, an even number
in the preferred embodiment, are disposed between base plate
850 and bottom
retainer
854. Belleville springs
824 act to compensate for the different
thermal expansion of the various components of shock absorber
100 through
base plate
850 and bottom retainer
854. In an alternate cylinder
end assembly
820′, as shown in FIG. 17, Belleville springs
824
are replaced with an elastomeric block
860. Elastomeric block
860
is disposed between base plate
850 and bottom retainer
854 and compensates
for the different thermal expansion of pressure tube
102 and reserve tube
106 by expanding or compressing as necessary.
In compressing cylinder end assembly
920, which includes a base valve
assembly
922 as shown in FIG. 18, pressurized gas
950, for example compressed
air, is disposed between a base plate
952 and a bottom retainer
954.
Bottom retainer
954 is sealed to reserve tube
106 by a weld
956
or other means known in the art such that the gas
950 remains pressurized.
Pressurized gas
950 compensates for the different thermal expansion of pressure
tube
102 and reserve tube
106 by expanding or compressing as necessary,
and also reduces the weight of the shock absorber. In alternate cylinder end assembly
920′ as shown in FIG. 19, bottom retainer
954 has been removed.
Pressurized gas
950 is disposed between base plate
952 and reserve
tube
106 and compensates directly for the different thermal expansion of
the pressure tube
102 and the reserve tube
106.
While the above detailed description describes the preferred embodiment of
the present invention, it should be understood that the present invention is susceptible
to modification, variation and alteration without deviating from the scope and
fair meaning of the subjoined claims.
*
