Hydraulic control unit for a limited slip differential

Abstract

A hydraulic control unit that delivers hydraulic fluid to a limited slip differential includes a hydraulic control unit housing, a sump and a motor. The hydraulic control unit housing has an accumulator housing portion that houses a biasing assembly and a piston. The sump is defined in the hydraulic control unit housing and at least partially occupies a common space with the accumulator housing portion. The motor is configured to pump fluid into an accumulator chamber of the accumulator housing portion. The fluid pumped into the accumulator housing portion at least partially collapses the biasing assembly and introduces a pre-charge into the hydraulic control unit. The biasing assembly is configured to expand and urge the piston in a first direction resulting in fluid being communicated from the hydraulic control unit and into the limited slip differential.

What is claimed is: 
     
         1 . A hydraulic control unit that delivers hydraulic fluid to a limited slip differential, the hydraulic control unit comprising:
 a hydraulic control unit housing having an accumulator housing portion and a housing manifold portion that collectively house a biasing assembly and a piston, the housing manifold portion forming an accumulator chamber with the piston;   a vent hole defined in the hydraulic control unit housing;   a first passageway defined by the hydraulic control unit housing that is generally coaxial with the vent hole; and   a second passageway defined in the hydraulic control unit housing that intersects the vent hole and that is oriented at a different angle than the first passageway;   wherein the vent hole is dual purpose permitting hydraulic fluid entry into the accumulator chamber through the second passageway while air is permitted to escape the hydraulic control unit housing through the vent hole.   
     
     
         2 . The hydraulic control unit of  claim 1 , further comprising a vent insert disposed in the vent hole subsequent filling of the hydraulic fluid. 
     
     
         3 . The hydraulic control unit of  claim 2 , further comprising:
 a motor that is configured to pump fluid into the accumulator chamber of the accumulator housing portion.   
     
     
         4 . The hydraulic control unit of  claim 1  wherein the biasing assembly further comprises:
 a first biasing member having a first spring rate; 
 a second biasing member having a second spring rate, wherein the first and second spring rates are distinct; and 
 a guide rod that supports the first and second biasing members. 
 
     
     
         5 . The hydraulic control unit of  claim 4  wherein the fluid pumped into the accumulator housing portion at least partially collapses the biasing assembly and introduces a pre-charge into the hydraulic control unit, wherein the biasing assembly is configured to subsequently expand after the pre-charge and urge the piston in a first direction resulting in fluid being communicated from the hydraulic control unit and into the limited slip differential. 
     
     
         6 . The hydraulic control unit of  claim 1  wherein the hydraulic control unit housing further comprises:
 a hydraulic control unit housing mounting structure having first and second receiving bores that both define a first diameter and wherein a first pair of first fasteners that both define a second diameter, less than the first diameter, couple the hydraulic control unit to an axle housing that houses the limited slip differential. 
 
     
     
         7 . The hydraulic control unit of  claim 6 , further comprising a hydraulic coupling that has a first end that is received by a first receiving bore defined on the hydraulic control unit housing. 
     
     
         8 . The hydraulic control unit of  claim 7  wherein the hydraulic coupling has a second end that is configured to be received by a second receiving bore defined on the limited slip differential. 
     
     
         9 . The hydraulic control unit of  claim 8  wherein the hydraulic coupling is configured to extend through a hydraulic coupler receiving bore defined in the axle housing. 
     
     
         10 . The hydraulic control unit of  claim 9  wherein the axle housing defines an inner diameter that is greater than an outer diameter of the hydraulic coupling, wherein the hydraulic coupling is permitted to locate at a plurality of positions relative to the inner diameter of the axle housing during assembly of the hydraulic control unit to the limited slip differential to accommodate a corresponding plurality of positions of the differential relative to the axle housing. 
     
     
         11 . The hydraulic control unit of  claim 1 , further comprising a sleeve positioned between the piston and the accumulator housing portion, the sleeve formed of a dissimilar material than at least one of the piston and the accumulator housing portion. 
     
     
         12 . The hydraulic control unit of  claim 11  wherein the piston further comprises a first and second wear ring disposed on opposite ends of a seal, the wear rings configured to minimize the tendency of the piston to move off axis. 
     
     
         13 . The hydraulic control unit of  claim 12  wherein the piston further comprises a pressure relief valve that is configured to release fluid from the accumulator housing in the event of an over-pressure event. 
     
     
         14 . A hydraulic control unit that delivers hydraulic fluid to a limited slip differential, the hydraulic control unit comprising:
 a hydraulic control unit housing having an accumulator housing portion and a housing manifold portion that collectively house a biasing assembly and a piston, the housing manifold portion forming an accumulator chamber with the piston;   a vent hole defined in the hydraulic control unit housing;   a first passageway defined by the hydraulic control unit housing that is generally coaxial with the vent hole; and   a bypass fill port defined in the hydraulic control unit housing that intersects the vent hole;   wherein the vent hole is dual purpose permitting hydraulic fluid entry into the accumulator chamber through the second passageway while air is permitted to escape the hydraulic control unit housing through the vent hole.   
     
     
         15 . The hydraulic control unit of  claim 14 , further comprising a vent insert disposed in the vent hole subsequent filling of the hydraulic fluid. 
     
     
         16 . The hydraulic control unit of  claim 15 , further comprising:
 a motor that is configured to pump fluid into the accumulator chamber of the accumulator housing portion.   
     
     
         17 . A method of filling a hydraulic control unit that delivers hydraulic fluid to a limited slip differential with hydraulic fluid, the method comprising:
 providing a hydraulic control unit housing having an accumulator housing portion that houses a biasing assembly and a piston, the accumulator housing portion forming an accumulator chamber with the piston, the hydraulic control unit defining a vent hole and a first passageway;   inserting a filling needle into an opening of the vent hole;   advancing the needle along a second passageway, the second passageway intersecting the opening, the second passageway oriented at a different angle relative to the first passageway; and   passing fluid from the needle and into the accumulator housing while air within the hydraulic control unit escapes through the opening of the vent hole.   
     
     
         18 . The method of  claim 17 , further comprising:
 withdrawing the filling needle from the vent hole subsequent to the passing; and   inserting a vent insert into the vent hole subsequent to withdrawing the filling needle from the vent hole.