KR102401911B1 - Hydraulic control unit for a limited slip differential - Google Patents

Abstract

A hydraulic control unit for dispensing hydraulic fluid to a differential restrictor includes a hydraulic control unit housing, a sump and a motor. The hydraulic control unit housing has a bias assembly and an accumulator housing portion that houses the piston. A sump is formed within the hydraulic control unit housing and at least partially occupies a common space with a portion of the accumulator housing. The motor is configured to pump fluid into the interior of the accumulator housing portion. Fluid pumped into the accumulator housing portion causes the biasing assembly to at least partially collapse and initiates pre-filling into the hydraulic control unit. The biasing assembly is configured to expand and urge the piston in a first direction resulting in communication of fluid from the hydraulic control unit and into the differential restrictor.

Description

HYDRAULIC CONTROL UNIT FOR A LIMITED SLIP DIFFERENTIAL

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application Serial No. 61/978,413, filed April 11, 2014, and U.S. Patent Application Serial No. 29/508,563, filed November 7, 2014. The disclosure of the above application is incorporated herein by reference.

BACKGROUND This disclosure relates generally to differential limiters and more particularly to hydraulic control units that distribute hydraulic fluid to differential limiters.

A differential is provided on the vehicle to allow the outer drive wheels to rotate faster than the inner drive wheels while cornering while both drive wheels continue to receive power from the engine. While differentials are useful for cornering, differentials can cause the vehicle to lose traction in, for example, snow or mud or other slippery media. If one of the drive wheels loses traction, that drive wheel will rotate at a high rate and the other drive wheel may not rotate at all. In order to overcome this situation, a differential limiting device has been developed in which the non-rotating driving wheel rotates by shifting power from the driving wheel having lost traction.

The electronically controlled differential limiter may include a hydraulically-actuated clutch to limit differential rotation between the output shafts of the differential. In some configurations, the hydraulic distribution device may be located remote from the differential. In some instances, it is challenging to mount the hydraulic distribution device to the differential and/or the housing that houses the differential. It may also be challenging to connect a hydraulic coupling between the hydraulic distribution device and the differential limiter.

The background description provided herein is for the purpose of generally presenting the context of the disclosure. To the extent set forth in this background section, views of the presently named inventors' work as well as descriptions that may not otherwise qualify as prior art at the time of filing are not admitted, express or implied, as prior art contrary to the present disclosure. does not

A hydraulic control unit for dispensing hydraulic fluid to a differential restrictor includes a hydraulic control unit housing, a sump and a motor. The hydraulic control unit housing has a bias assembly and an accumulator housing portion that houses the piston. The accumulator housing portion defines an accumulator chamber with a piston. A sump is formed within the hydraulic control unit housing and at least partially occupies a common space with a portion of the accumulator housing. The motor is configured to pump a fluid into the accumulator chamber of the accumulator housing portion. Fluid pumped into the accumulator housing portion causes the biasing assembly to at least partially collapse and initiates pre-filling into the hydraulic control unit. The biasing assembly is configured to expand and urge the piston in a first direction resulting in communication of fluid from the hydraulic control unit and into the differential restrictor.

According to a further feature the hydraulic control unit housing further comprises a hydraulic control unit housing mounting structure having first and second receiving apertures both defining a first diameter. A first pair of first fasteners, all defining a second diameter less than the first diameter, couple the hydraulic control unit to an axle housing housing the differential limiter. The hydraulic coupling may have a first end received by a first receiving hole formed in the hydraulic control unit housing. The hydraulic coupling may have a second end configured to be received by a second receiving hole formed in a hydraulic port that engages the differential restrictor. At least one O-ring sealingly engaging the second receiving aperture may be disposed about the second end. The hydraulic coupling is configured to extend through a hydraulic coupler receiving hole formed in the axle housing.

According to another feature, the axle housing may have an inner diameter greater than the outer diameter of the hydraulic coupling. The hydraulic coupling is allowed to be positioned in a plurality of positions relative to the inner diameter of the axle housing during assembly of the hydraulic control unit to the differential limiter to provide a corresponding plurality of positions of the differential case relative to the axle housing. The first and second mounting members may include (i) third and fourth receiving holes, and (ii) first and second mounting passageways, respectively. A second pair of first fasteners may each extend through third and fourth receiving apertures coupling the hydraulic control unit to the axle housing.

According to another feature, the second fastener pair may extend through the first and second mounting passageways to engage the hydraulic control unit housing for coupling the first and second mounting members thereto. The hydraulic control unit may be pre-filled with hydraulic fluid prior to coupling to the axle housing. The biasing assembly may further include a first biasing member having a first modulus of elasticity and a second biasing member having a second modulus of elasticity. The first and second modulus of elasticity may be distinct.

A hydraulic control unit configured according to another example of the present disclosure and dispensing hydraulic fluid to a differential restrictor includes a hydraulic control unit housing, a sump, a motor, and a hydraulic coupling. The hydraulic control unit housing may have a bias assembly and a portion of the accumulator housing housing the piston. The accumulator housing portion defines an accumulator chamber with a piston. The sump may be formed in the hydraulic control unit housing. The sump may occupy a common space at least partially with the accumulator housing portion. The motor may be configured to pump a fluid into an accumulator chamber of the accumulator housing portion. The hydraulic coupling is configured to be received by (i) a first end received by a first receiving hole formed in the hydraulic control unit housing, and (ii) a second receiving hole formed in the hydraulic port engaging the differential limiter. It may have a second end that is Fluid pumped into the accumulator chamber of the accumulator housing portion causes the biasing assembly to at least partially collapse and initiates pre-filling into the hydraulic control unit. The biasing assembly is configured to expand and urge the piston in a first direction resulting in communication of fluid from the hydraulic control unit and into the differential restrictor.

According to a further feature, at least one O-ring sealingly engaging the second receiving aperture may be disposed around the second end. The hydraulic coupling may be configured to extend through a hydraulic coupler receiving hole formed in the axle housing. The axle housing may have an inner diameter greater than the outer diameter of the hydraulic coupling. The hydraulic coupling is allowed to be positioned in a plurality of positions relative to the inner diameter of the axle housing during assembly of the hydraulic control unit to the differential limiter to provide a corresponding plurality of positions of the differential case relative to the axle housing.

According to another feature, the hydraulic control unit housing may further include a hydraulic control unit housing mounting structure having first and second receiving apertures both defining a first diameter. A first pair of first fasteners, all defining a second diameter less than the first diameter, couple the hydraulic control unit to an axle housing housing the differential limiter. The first and second mounting members may include (i) third and fourth receiving holes, and (ii) first and second mounting passageways, respectively. A second pair of first fasteners extend through third and fourth receiving apertures respectively coupling the hydraulic control unit to the axle housing. The third receiving hole traverses the first mounting passageway. The fourth receiving hole traverses the second mounting passageway.

According to another feature, the second fastener pair may extend through the first and second mounting passageways to engage the hydraulic control unit housing for coupling the first and second mounting members thereto. The hydraulic control unit may be pre-filled with hydraulic fluid prior to coupling to the axle housing. The biasing assembly may further include a first biasing member having a first modulus of elasticity and a second biasing member having a second modulus of elasticity. The first and second modulus of elasticity may be distinct.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will be more fully understood from the detailed description and accompanying drawings.
1 is a front perspective view of a hydraulic control unit constructed in accordance with an example of the present disclosure and shown assembled on an axle housing;
Fig. 2 is a cross-sectional view of the hydraulic control unit of Fig. 1 taken along the line 2-2;
Fig. 3 is a cross-sectional view of the hydraulic control unit of Fig. 2 taken along line 3-3;
Fig. 4 is a detailed view of the attachment area of the hydraulic control unit of Fig. 1;
Fig. 5 is a cross-sectional view of the hydraulic control unit taken along line 5-5 of Fig. 2 and taken at the high pressure port illustrating the anti-rotation component;
6 is an exploded perspective view of the hydraulic control unit and axle housing;
Fig. 7 is a front perspective view of the hydraulic control unit of Fig. 1, shown with various fasteners disassembled for illustration;

Referring first to FIG. 1 , a hydraulic control unit constructed in accordance with an example of the present disclosure is shown and generally indicated by the reference numeral 10 . As can be appreciated herein, the hydraulic control unit 10 according to the present disclosure provides a single unit that can be mounted against or relative to the axle housing 12 . Its configuration allows for simple assembly and installation. In general, hydraulic control unit 10 may distribute hydraulic fluid to differential restrictor 14 received within axle housing 12 via hydraulic coupling 20 ( FIG. 5 ). The differential limiter 14 may be an electronic differential limiter having a clutch 22 and a piston (not specifically shown).

The differential limiter 14 is operable to drive a pair of axle shafts 30 , 32 connected to each pair of drive wheels (not shown). In general, the differential limiter 14 functions as a traditional open differential throughout normal operating conditions until an event requiring a bias torque occurs. When a loss of traction is detected or expected, the clutch 22 can be selectively actuated to generate an optimal rate of deflection for the situation.

The differential limiter 14 may further include a differential gear assembly 24 configured within a differential case 26 that acts to allow the axle shafts 30 , 32 to rotate at different speeds. Differential gear assembly 24 may include a pair of side gears (not specifically shown) mounted for rotation with axle shafts 30 and 32 (and drive wheels). In the open configuration described below, the differential gear assembly acts to allow the axle shafts 30 and 32 to rotate at different speeds.

Clutch 22 couples the drive shaft output to differential gear assembly 24 . Clutch 22 may include a clutch pack (not specifically shown) having a plurality of annular plates sandwiched between a plurality of annular friction disks. The plurality of annular plates and annular friction disks are sandwiched between each other and act to slide and rotate with each other in a substantially non-contact relationship when the clutch 22 is in its open position. However, it will be understood by those skilled in the art that the term "non-contact" as used herein is relative and does not necessarily indicate that the annular plate and the annular friction disk are absolutely not in contact when the clutch 22 is in the open state. will be. The annular plate and friction disk can move axially in frictional engagement with each other, thereby reducing relative rotation between the annular plate and the annular friction disk when clutch 22 is in a closed or partially closed configuration. In this way, when the clutch 22 is in its closed position, the side gear as well as the axle shaft and the drive wheel rotate together.

Clutch 22 may operate in an open configuration allowing the side gears to rotate independently of one another, for example at different speeds. Clutch 22 may also operate in a closed or partially closed configuration in which the side gears rotate together or partially together (ie, non-independently), eg, at substantially the same speed. Clutch 22 uses pressurized hydraulic fluid provided through hydraulic fluid coupling 20 from hydraulic control unit 10 to act on a piston to selectively actuate the clutch pack between open, closed and partially closed configurations. It is a hydraulic clutch. It will be appreciated that the differential limiter 14 described above is exemplary only. In this regard, hydraulic control unit 10 may be used to distribute hydraulic fluid to actuators (such as pistons) of any differential restrictor configuration.

With reference now generally to FIGS. 1 to 17 , the hydraulic control unit 10 will be described in greater detail. The hydraulic control unit 10 may generally include a hydraulic control unit housing 50 having an accumulator housing portion 54 and a housing manifold portion 56 . The accumulator housing portion 54 may form an accumulator chamber 64 having a piston 67 . The accumulator housing portion 54 houses the first and second biasing members 66A, 66B and the piston 67 . The first and second biasing members 66A, 66B may be collectively referred to herein as the biasing assembly 68 . The first biasing member 66A has a first modulus of elasticity while the second biasing member 66B has a second modulus of elasticity. The first and second modulus of elasticity cooperate together to provide a desired modulus of elasticity for the biasing assembly 68 . As can be appreciated herein, fluid is pumped into the accumulator chamber 64 behind the piston 67 causing the piston 67 to translate towards the first and second biasing members 66A, 66B.

In the hydraulic control unit 10 of the present disclosure, the accumulator chamber 64 houses the biasing members 66A, 66B and also provides a hydraulic sump 69 ( FIG. 3 ). Such a configuration allows for a reduction in packaging space. The housing manifold portion 56 may define various fluid passageways configured to provide access to the various sensors disclosed herein. The hydraulic control unit 10 may also include a motor 70 that may be coupled to the hydraulic control unit housing 50 .

The hydraulic control unit 10 may further include a clutch piston pressure sensor 72 ( FIG. 5 ), an accumulator pressure sensor 74 and a three-way proportional control valve 76 . The clutch piston pressure sensor 72 may be threaded or otherwise securely received by the hydraulic control unit housing 50 . Clutch piston pressure sensor 72 may be configured to measure pressure at the piston of differential limiter 14 . The accumulator pressure sensor 74 may be screwed or otherwise rigidly received in the hydraulic control unit housing 50 . The accumulator pressure sensor 74 may be configured to measure the pressure within the accumulator chamber 64 . The three-way proportional control valve 76 may be rigidly coupled to the hydraulic control unit housing 50 . The three-way proportional regulating valve 76 may be configured to regulate fluid pressure within a single hydraulic control unit housing 50 .

Motor 70 may operate a piston pump or gerotor gear assembly and may be conventionally configured. The gerotor gear assembly may include an inner gerotor gear and an outer gerotor gear. The operation of the gerotor gear assembly may be conventional where the relative rotation of the inner and outer gerotor gears may cause a pumping action on the fluid contained within the hydraulic control unit housing 50 . In the example where a piston pump is used, the piston pump may cause a pumping action on the fluid contained within the hydraulic control unit housing 50 . The pumping action ultimately causes fluid to be pumped into the accumulator chamber 64 (which shares a common space with the sump 69 ). The pumping action ultimately causes fluid to be pumped into the accumulator chamber 64 . In doing so, the biasing members 66A, 66B are at least partially folded to begin pre-filling into the system. In this regard, the motor 70 need not be continuously operated. Fluid pressure may be introduced into the differential limiter 12 by biasing members 66A, 66B acting on the piston 67 . A pressure relief valve 80 may be provided in the piston 67 . The pressure relief valve 80 can protect the system by releasing fluid in the event of an overpressure malfunction.

With specific reference to FIGS. 4 to 7 , further features of the hydraulic control unit housing 50 will be described. The hydraulic control unit housing 50 may define a receiving aperture 84 ( FIG. 5 ) configured to receive the hydraulic coupling 20 . The hydraulic control unit housing 50 may include a hydraulic control unit housing mounting structure generally designated 86 . The hydraulic control unit housing mounting structure 86 may generally include first, second, third and fourth receiving apertures 88A, 88B, 88C and 88D. The first, second, third and fourth receiving apertures 88A, 88B, 88C and 88D may define a first diameter D1 ( FIG. 7 ). In the illustrated example, the third and fourth receiving holes 88C and 88D may be formed in the mounting members 90A and 90B, respectively. Mounting members 90A and 90B may define mounting passages 92A and 92B, respectively, configured in a direction generally transverse to receiving holes 88C and 88D. Mounting passageways 92A and 92B may be aligned with connection holes 94A and 94B formed in housing manifold portion 56 .

The first fasteners 96A and 96B may extend through the mounting passageways 92A and 92B to threadly engage the connection holes 94A and 94B. First fasteners 96A and 96B couple mounting members 90A and 90B to housing manifold portion 56 . Second fasteners 100A, 100B, 100C and 100D may extend through receiving apertures 88A, 88B, 88C and 88D. The second fasteners 100A, 100B, 100C and 100D may have an outer diameter D2 ( FIG. 7 ). The outer diameter D2 is smaller than the first diameter D1 to allow for misalignment during assembly as will be understood herein.

With particular reference to FIG. 6 , the axle housing 12 includes a first mounting hole 126 , a second mounting hole 128 , a third mounting hole 130 , a fourth mounting hole 132 , and a hydraulic coupling receiving hole. (134). Generally, the hydraulic coupling receiving hole 134 is configured to receive the hydraulic coupling 20 . In the example shown, the hydraulic coupling receiving hole 134 allows the hydraulic coupling 20 to be suitably positioned in the receiving hole 140 formed in the hydraulic port 142 provided by the differential case 26 . To form a diameter (D3) larger than the diameter (D4) of the hydraulic coupling (20). Also, as will be described later, the differential case 26 may move into the axle housing 12 during shimming. In this regard, the inner diameter D5 formed in the axle housing 12 is larger than the outer diameter D6 of the hydraulic port 142 extending from the differential case 26 . In this regard, the hydraulic control unit 10 will automatically be positioned inside the hydraulic coupling receiving hole 134 and the receiving hole 140 . The second fastener 100A may be screwed with the first mounting hole 126 . The second fastener 100B may be screwed with the second mounting hole 128 . The second fastener 100C may be screw-coupled to the third mounting hole 130 . The second fastener 100D may be screw-coupled to the fourth mounting hole 132 .

During assembly of the differential assembly 14 to the inside of the axle housing 12 , the differential limiter 14 is seamed relative to the axle housing 12 to account for a predetermined amount of backlash. During seaming, the differential limiter 14 can move left and right (toward and away from the axle shafts 30 and 32 ). In this regard, the position of the receiving hole 140 formed in the hydraulic port 142 may not necessarily be at the same position. The dimensions of the hydraulic coupling receiving hole 134 (inner diameter D3) are properly aligned for receiving the hydraulic coupling 20 inside the receiving hole 140 while still connected to the hydraulic control unit housing 50 . make it possible The hydraulic coupling 20 is coupled to the axle housing 12 during assembly of the hydraulic control unit 10 to the differential limiter 14 to provide a corresponding plurality of positions of the differential case 26 relative to the axle housing 12. allowed to be positioned at a plurality of positions with respect to the inner diameter D3 of A first O-ring 144 may be sealably positioned between the hydraulic coupling 20 and the housing manifold portion 56 . The hydraulic coupling may further include a second O-ring 146 received within the groove 148 . The second O-ring 146 sealably engages the receiving aperture 140 .

Once the hydraulic coupling 20 is properly received by the hydraulic port 142 and acceptable alignment is achieved, the second fasteners 100A and 100B engage the first and second mounting holes ( 126 and 128). In particular, the receiving holes 88A and 88B have a larger diameter than the second fasteners 100A and 100B so that the second fasteners 100A and 100B are inside the first and second mounting holes 126 and 128, respectively. ) to allow lateral movement of the housing manifold portion 56 relative to the axle housing 12 prior to tightening. The second fasteners 100C and 100D may then be screwed into the third and fourth mounting holes 130 and 132 . Receiving holes 88C and 88D are provided to allow for misalignment resulting from second fasteners 100A and 100B securing housing manifold portion 56 relative to axle housing 12 , second fasteners 100C and 100D. It may have a larger diameter.

The hydraulic coupling 20 may provide an anti-rotation characteristic that inhibits rotation of the hydraulic coupling 20 about its axis in the installed position. In one configuration, the hydraulic control unit 10 may be pre-filled with hydraulic fluid prior to coupling to the axle housing 12 . A seal (not specifically shown) may be implemented at the interface between the hydraulic coupling 20 and the hydraulic coupling receiving hole 134 and/or the receiving hole 140 . Such a seal may rupture during the act of positioning the hydraulic coupling 20 into the hydraulic coupling receiving aperture 134 and/or into the receiving aperture 140 .

The foregoing description of examples has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular example are generally not limited to that particular example and, where applicable, may be substituted for each other and may be used in a selected example even if not specifically shown or described. The same can also be changed in a number of ways. Such changes are not to be regarded as a departure from the present disclosure and all such modifications are intended to be included within the scope of the present disclosure.

Claims (20)

A hydraulic control unit for dispensing hydraulic fluid to a differential limiter, comprising:
a hydraulic control unit housing having a biasing assembly and a portion of the accumulator housing housing the piston and defining an accumulator chamber with the piston;
a sump formed within the hydraulic control unit housing and occupying at least partially a common space with a portion of the accumulator housing; and
a motor configured to pump fluid into the accumulator chamber of the accumulator housing portion;
Fluid pumped into the accumulator housing portion at least partially collapses the biasing assembly and begins pre-filling the inside of a hydraulic control unit, the biasing assembly fluid from the hydraulic control unit and into the differential limiter. configured to expand and urge the piston in a first direction resulting in communication of
The hydraulic control unit housing comprises a hydraulic control unit housing mounting structure having first and second receiving apertures both defining a first diameter, (i) third and fourth receiving apertures, and (ii) first and second receiving apertures; first and second mounting members each comprising two mounting passageways;
A first pair of first fasteners, all defining a second diameter less than the first diameter, couple the hydraulic control unit to an axle housing housing a differential limiter, the second pair of first fasteners each having said extending through third and fourth receiving holes coupling the hydraulic control unit to the axle housing;
hydraulic control unit. delete The method of claim 1,
and a hydraulic coupling having a first end received by a first receiving hole formed in the hydraulic control unit housing.
hydraulic control unit. 4. The method of claim 3,
the hydraulic coupling having a second end configured to be received by a second receiving aperture formed in a hydraulic port that engages a differential limiter;
hydraulic control unit. 5. The method of claim 4,
at least one O-ring disposed about the second end sealingly engaging the second receiving aperture;
hydraulic control unit. 6. The method of claim 5,
wherein the hydraulic coupling is configured to extend through a hydraulic coupler receiving hole formed in the axle housing.
hydraulic control unit. 7. The method of claim 6,
The axle housing defines an inner diameter greater than the outer diameter of the hydraulic coupling, wherein the hydraulic coupling provides a corresponding plurality of positions of the differential case relative to the axle housing during assembly of the hydraulic control unit to the differential limiter. allowed to be positioned in multiple locations for the inner diameter of
hydraulic control unit. delete The method of claim 1,
and a second pair of fasteners extending through the first and second mounting passageways to engage the hydraulic control unit housing to couple the first and second mounting members to the hydraulic control unit housing.
hydraulic control unit. The method of claim 1,
The hydraulic control unit is pre-filled with hydraulic fluid prior to coupling to the axle housing.
hydraulic control unit. The method of claim 1,
The biasing assembly comprises:
a first biasing member having a first modulus of elasticity; and
a second biasing member having a second modulus of elasticity;
the first and second modulus of elasticity are separate
hydraulic control unit. A hydraulic control unit for dispensing hydraulic fluid to a differential limiter, comprising:
a hydraulic control unit housing having a biasing assembly and a portion of the accumulator housing housing the piston and defining an accumulator chamber with the piston;
a sump formed within the hydraulic control unit housing and occupying at least partially a common space with a portion of the accumulator housing;
a motor configured to pump a fluid into the accumulator chamber of the accumulator housing portion; and
(i) a first end configured to be received by a first receiving hole formed in the hydraulic control unit housing, and (ii) a second end configured to be received by a second receiving hole formed in a hydraulic port engaged with the differential limiter. a hydraulic coupling having a;
Fluid pumped into the accumulator chamber of the accumulator housing portion causes the biasing assembly to at least partially collapse and begins pre-filling into the hydraulic control unit, the biasing assembly being removed from the hydraulic control unit and the differential limiter. configured to expand and urge the piston in a first direction resulting in communication of the fluid into the interior of the
wherein the hydraulic coupling is configured to extend through a hydraulic coupler receiving hole formed in an axle housing receiving the differential limiter;
The hydraulic coupler receiving hole has a diameter larger than a diameter of the hydraulic coupling, and an inner diameter formed in the axle housing is larger than an outer diameter of the hydraulic port.
hydraulic control unit. 13. The method of claim 12,
at least one O-ring disposed about the second end sealingly engaging the second receiving aperture;
hydraulic control unit. delete 13. The method of claim 12,
The axle housing defines an inner diameter greater than the outer diameter of the hydraulic coupling, wherein the hydraulic coupling provides a corresponding plurality of positions of the differential case relative to the axle housing during assembly of the hydraulic control unit to the differential limiter. allowed to be positioned in multiple locations for the inner diameter of
hydraulic control unit. 13. The method of claim 12,
the hydraulic control unit housing further comprising a hydraulic control unit housing mounting structure having first and second receiving apertures both defining a first diameter;
a first pair of first fasteners all defining a second diameter less than the first diameter coupling the hydraulic control unit to an axle housing housing a differential limiter;
hydraulic control unit. 17. The method of claim 16,
first and second mounting members comprising (i) third and fourth receiving apertures, and (ii) first and second mounting passageways, respectively, respectively, wherein the second pair of first fasteners are each hydraulically controlled extending through third and fourth receiving apertures coupling the unit to the axle housing, the third receiving apertures traversing the first mounting passageway and the fourth receiving apertures traversing the second mounting passageways
hydraulic control unit. 18. The method of claim 17,
and a second pair of fasteners extending through the first and second mounting passageways to engage the hydraulic control unit housing to couple the first and second mounting members to the hydraulic control unit housing.
hydraulic control unit. 13. The method of claim 12,
The hydraulic control unit is pre-filled with hydraulic fluid prior to coupling to the axle housing.
hydraulic control unit. 13. The method of claim 12,
The biasing assembly comprises:
a first biasing member having a first modulus of elasticity; and
a second biasing member having a second modulus of elasticity;
the first and second modulus of elasticity are separate
hydraulic control unit.

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