Land vehicles – Wheeled – Running gear
Reexamination Certificate
1999-03-26
2001-04-10
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Running gear
C092S128000, C280S005500, C280S006157
Reexamination Certificate
active
06213485
ABSTRACT:
STATEMENT REGARDING GOVERNMENT SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF THE INVENTION
This invention relates to a load distribution unit for a hydraulic vehicle suspension system.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,601,307 discloses a vehicle suspension system in which a double-acting hydraulic ram supports the vehicle at each wheel with the ram chambers at opposite diagonal comers of the vehicle cross-connected so as to provide four discrete hydraulic wheel circuits. A load distribution unit is connected to the four hydraulic circuits for hydraulically equalizing the pressures in the circuits. FIG. 5 of U.S. Pat. No. 5,601,307 discloses a load distribution unit (LDU) 140 which includes a pair of cylinders, each containing a double-acting ram that divides the cylinder which contains it into four variable volume chambers, one chamber at each end of the ram and two chambers inward of the two end chambers, each chamber being isolated from all the others. Each of the inward chambers communicates with a different one of the wheel circuits, with each LDU cylinder being connected to the same chambers of the wheel cylinders on opposite sides of the vehicle, i.e. one of the inward chambers of one of the LDU cylinders is connected to the wheel cylinder circuit that connects the front left bore side (upper) wheel cylinder chamber with the rear right rod side (lower) wheel cylinder chamber, and the other inward chamber of the same LDU cylinder is connected to the wheel circuit that connects the front right bore side wheel cylinder chamber with the rear left rod side wheel cylinder chamber. In the same manner, the inward chambers of the other LDU cylinder are connected to the two wheel circuits that connect the front rod side wheel cylinder chambers with the rear bore side wheel cylinder chambers. A total of six solenoid-operated pressure supply valves 204 are supplied for providing hydraulic fluid under pressure to the various chambers of the LDU, and a total of six pressure relief or drain valves 215 are provided for relieving pressure from the various chambers. Six valves are needed in each valve bank because the two end chambers (sometimes referred to as “bump” chambers) of each LDU cylinder are connected to the corresponding two end (bump) chambers of the other LDU cylinder. As a result, a pressure-tank valve pair is needed for each of the four wheel cylinder circuits and a pair is needed for each of the two connected end (bump) chambers, for a total of six pressure-tank valve pairs (12 valves total). In addition, a reservoir 66 is provided for the hydraulic fluid, together with a pump 65 and gas-charged accumulators 202 for maintaining pressure in the system.
The LDU equalizes pressures between the various wheel circuits, and also provides a means of adding fluid to the various discrete circuits or taking it away, for load leveling and raising or lowering of the vehicle relative to the wheels. The LDU contains two pistons, which have sliding seals and must be very low leak and low friction. Excess leakage in the seals or valves results in having to run the pump excessively, or the vehicle losing pressure too quickly when parked, with consequent unintended changes in attitude or level of the vehicle relative to the wheels. Competing with the need to make the seals tight and therefore with good leakage characteristics is the need to provide low friction in the movement of the LDU pistons. High friction results in poor performance of the LDU, and unintended and unpredictable differences in the pressures between the circuits of the system, and sudden changes in pressures occurring when the LDU pistons break lose of static friction binding them and start moving.
In addition, the linear position of the LDU pistons is monitored by the onboard computer. A linear position transducer must be provided for this purpose for each LDU piston, which provides a challenge to fit it into the envelope provided and to contain the pressures required.
SUMMARY OF THE INVENTION
The invention provides an LDU for a hydraulic vehicle suspension system in which the friction of the pistons is minimized. In one aspect, the cylinder sleeves in which the pistons reciprocate are fixed to the block of the LDU by a connection and assembly procedure which permits self alignment and negates the effects of gravity which misalign the parts. The result is consistently low friction in the movement of the piston.
In this aspect, the ends of the cylinder sleeves are sealed against the block with an o-ring seal, and bolts extending from an end cap at the opposite end of the sleeve fix the sleeve to the block. The end cap is also sealed to the cylinder sleeve by an o-ring. Preferably, the ends of the cylinder sleeves are beveled on their inner surfaces and the block and end cap are grooved to receive the ends so that the bevel seats on the o-ring and wedges it into the inside corner of the groove. Clearances between the cylinder outside diameter and inside diameter and the center block and end cap grooves allow the cylinder to “float” radially during assembly and achieve an optimum concentric location relative to the mating components of the LDU.
This assembly is performed with the cylinder axes vertical so that the weight of the parts resting against one another does not create misalignments. It is also performed after the piston rod is inserted through the block bore and sliding seal in which the piston rod slides and a removable piston head is attached to the piston rod.
In another aspect contributing to low friction operation, the cylinder sleeves and end caps are cantilevered from the block. The block is bolted to the vehicle, for example to a skid plate which is fixed to the vehicle. It is also desirable to add a third mounting bolt, positioned away from the block so as to react against tipping of the LDU about the block, and this may be affixed to the valve manifold which is bolted to the block. Thereby, a three point mounting is created without mounting the cylinders or end caps to the vehicle, which can result in misalignments of the pistons in the LDU cylinders and consequently increased friction.
In another feature of an LDU of the invention, a linear position transducer is contained within a clam shell compartment, which extends inside the tubular piston rod, keeps the transducer dry and is accessible from outside of the LDU and without exposing the fluid in the LDU to contaminants.
These and other objects and advantages of the invention will become apparent from the detailed description and drawings.
REFERENCES:
patent: 5447332 (1995-09-01), Heyring
patent: 5562305 (1996-10-01), Heyring
patent: 5601306 (1997-02-01), Heyring
patent: 5601307 (1997-02-01), Heyring et al.
“Position Sensing,” brochure, 6 pgs. (Apr. 1999), Milwaukee Cylinder, 5877 S. Pennsylvania Avenue, Cudahy, WI 53110.
“Design Engineer's Cylinder Guide,” brochure, 19 pgs. (Mar. 1999), Milwaukee Cylinder, 5877 S. Pennsylvania Avenue, Cudahy, WI 53110.
Abhold Timothy J.
Bucheger Terence A.
Doll Robert A.
Applied Power Inc.
Culbreth Eric
Quarles & Brady LLP
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