Land vehicles – Wheeled – Running gear
Reexamination Certificate
2001-02-13
2001-11-20
Mai, Lanna (Department: 3619)
Land vehicles
Wheeled
Running gear
C280S124159, C280S005505, C280S005506
Reexamination Certificate
active
06318742
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hydro-pneumatic vehicle suspension systems, and in particular to such systems having discrete hydraulic circuits, each of which is pressurized with a gas-charged accumulator.
2. Discussion of the Prior Art
Hydro-pneumatic vehicle suspension systems are well known. Typically, one or more single or double acting hydraulic cylinders are provided at each wheel to support the vehicle, with hydraulic circuits interconnecting the cylinders. A gas-charged accumulator is typically used to pressurize the hydraulic circuits and therefore, provide resilient displacement of the cylinders and consequently springing of the vehicle.
One hydro-pneumatic vehicle suspension system has come to be known as the “X”-type. In such a system, the cylinders of diagonally opposite wheels of a vehicle are connected with discrete hydraulic circuits, each circuit connecting the bore side of one of the cylinders with the rod side of the diagonally opposite cylinder. As used herein, “discrete” as referring to a hydraulic circuit means that the hydraulic circuit is closed against hydraulic fluid flow to or from another circuit, except for normal leakage, and includes a hydraulic circuit which is normally closed from external communication by 5 a valve, but can be opened by the valve to an external source or depository of hydraulic fluid. Such an X-system is known, for example, from patents such as French Patent No. 1,535,641 and U.S. Pat. Nos. 4,270,771; 5,447,332; 5,562,305; 5,601,306; and
5,601,307.
Thus, in an X-system, there are four discrete hydraulic circuits, with one pair of circuits associated with one set of diagonally opposite wheel support cylinders and the other pair associated with the other set of diagonally opposite wheel support cylinders.
Neglecting friction of the cylinders, the two circuits of each pair are at substantially the same pressure since that pressure is communicated from one discrete hydraulic circuit to the other through the pistons of the cylinders.
It is also known that it is desirable to equalize the pressures between the two pairs of discrete hydraulic circuits so that the wheel loading is kept substantially constant. In U.S. Pat. No. 4,270,771, pressure equalization between the two pairs of discrete hydraulic circuits is obtained by making the cylinders identical and by providing inlet/outlet check valves for each cylinder which supply all the cylinders with the same pressure or exhaust all the cylinders to the same tank pressure. In U.S. Pat. No. 5,447,332 and other patents listed above, pressure is equalized from one pair of circuits to the other by use of a “load distribution unit” (or “LDU”) which has four chambers separated from fluid communication with one another by pistons, and each discrete hydraulic circuit is communicated with one of the chambers so as to substantially equalize the pressures among the four discrete hydraulic circuits.
SUMMARY OF THE INVENTION
It is an object of the invention to provide for pressure equalization among all four wheel support cylinders in a hydro-pneumatic suspension system without the need for spring-operated inlet or outlet valves or for an LDU. This is accomplished by communicating gas pressures of the two pairs of circuits with one another.
A system of the invention has the benefit that it does not add substantially to the weight of an X-type system. In addition, the invention materially reduces the number of hydraulic fluid leak paths of an X-type with LDU system, since the LDU is eliminated. Reducing the weight of the suspension system has cost savings, requires less power to start and stop the vehicle and makes the vehicle more agile, for example, in cornering.
Eliminating the LDU also has the benefit of reducing the inertia of the suspension system. Since the LDU has pistons and a substantial volume of hydraulic fluid, all of which moves back and forth in normal operation, eliminating the moving pistons and hydraulic fluid reduces the inertia of the system, thereby making it more responsive to the forces exerted on the wheels of the vehicle in operation.
The foregoing and other objects and advantages of the invention will be apparent from the drawings and the detailed description.
REFERENCES:
patent: 2926023 (1960-02-01), Kraus
patent: 4270771 (1981-06-01), Fujii
patent: 4606551 (1986-08-01), Toti et al.
patent: 4625994 (1986-12-01), Tanaka et al.
patent: 4861066 (1989-08-01), Dernie
patent: 4930807 (1990-06-01), Lachaize
patent: 5447332 (1995-09-01), Heyring
patent: 5556115 (1996-09-01), Heyring
patent: 5562305 (1996-10-01), Heyring
patent: 5566970 (1996-10-01), Lin
patent: 5601306 (1997-02-01), Heyring
patent: 5601307 (1997-02-01), Heyring et al.
patent: 5794966 (1998-08-01), Macleod
patent: 5915701 (1999-06-01), Heyring
patent: 6010139 (2000-01-01), Heyring et al.
patent: 1535641 (1968-07-01), None
patent: 01078912-A (1989-03-01), None
patent: WO-84/02887 (1984-08-01), None
Actuant Corporation
Lan Ruth
Mai Lanna
Quarles & Brady LLP
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