Land vehicles – Wheeled – Running gear
Reexamination Certificate
1999-02-10
2001-10-30
Culbreth, Eric (Department: 3611)
Land vehicles
Wheeled
Running gear
C280S124158, C280S005502
Reexamination Certificate
active
06308973
ABSTRACT:
TECHNICAL FIELD
The present invention relates to suspension of a vehicle, and more particularly to a suspension for a heavy duty, mobile working vehicle, such as a crane or excavator, wherein a hydraulic oscillation circuit allows a cushioned ride during the travel mode of operation, and a stabilized platform by fluid trapped in the cylinders during a working mode of operation.
BACKGROUND OF THE INVENTION
For heavy duty material handling vehicles, it is known to provide suspension systems utilizing hydraulic support cylinders, either in an independent or semi-independent mounting arrangement. The objective is to provide a cushioned ride during the traveling mode of operation through the use of the cylinders and a stabilized suspension for the vehicle during the working mode of operation. For the traveling mode, it is known to provide pneumatic/hydraulic accumulators to provide a cushioning effect. Typically, the cylinders are coupled with transfer lines for moving the hydraulic oil between the extend and retract sides of the individual cylinders. It is also common to trap oil in the extend sides of the cylinder in order to provide a stabilized vehicle platform during the working mode of operation, such as during lifting a load by a crane or the use of a bucket on an excavator to dig.
One of the earliest examples of the suspension system of the type described is found in the Peiffer U.S. Pat. No. 3,550,993, issued Dec. 29, 1970. In this arrangement, the hydraulic circuit is capable of trapping fluid in the cylinders on the extend side for working. During the travel mode, fluid is exchanged between the extend and retract sides of each individual cylinder. However, a true oscillating motion is not possible since each pair of cylinders for either the front or rear axles are not coupled together. With such an arrangement, maintaining a level positioning of the vehicle is more difficult, and to compensate for this shortcoming, the use of level regulation valves operating continuously to modify the supply of hydraulic oil to all four cylinders of both axles is required. The complexity of the suspension system of the type in the '993 patent leaves much to be desired.
A later approach set forth in U.S. Pat. No. 4,174,854, issued Nov. 20, 1979, provides an advance in that an oscillation of the front and/or rear axle is provided through a modified hydraulic circuit. However, as in the '993 patent, constant monitoring of the height and the attitude of the vehicle is required to operate level regulation valves. In order to provide a stabilized suspension system for the working mode of operation, the '854 patent teaches rigidly locking the frame to the axle. A similar arrangement is found in the U.S. Pat. No. 5,368,322 issued Nov. 29, 1994, and this patent is one of the first to teach the use of a 4-bar assembly in the suspension to limit lateral axle movement in a hydraulic cylinder suspension system.
In more recent years, there have been several hydraulic circuits for automotive suspension systems designed to work as helpers for a basic mechanical spring system, such as U.S. Pat. No. 5,449,194, issued Sep. 11, 1995. These patents follow a reasonably long line of developments in this particular field and are directed in large part to combined systems, such as for working in concert with the brakes of the vehicle. For a proper operation, an even more complex system, such as with multiple pneumatic supply reservoirs and control valves, are required.
In each of the above described suspension systems, the nature of the operation requires extra complexity in terms of the mechanical structure, as well as the hydraulic and pneumatic circuits to control the support cylinders. Furthermore, even with the more complex circuitry, the operation of the system has been found to need improvement. In particular, there has been little progress in the development of a suspension system for the rear axle of a heavy duty vehicle that matches a superior cushioned ride in one mode, with a more stabilized working platform in the other mode. An arrangement that provides a more cushioned ride in the traveling mode of operation is needed in order to relieve the stress and fatigue of the operator. This system should also minimize the mechanical stress on the frame and the other vulnerable components of the vehicle. It would be desirable to maintain a simulated oscillating movement. This allows elimination of the center pin, bolster and the reinforced axle frame. The center of the vehicle would be opened with free space. Not only would there be a considerable initial cost savings and significant weight savings, but also better access to the engine of the vehicle and other components would result. Thus, the need for the present improved suspension system combinating these changes is apparent.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a suspension system simulating the bolster and pin type oscillation, but the system is provided with an enhanced cushioning effect in the traveling mode of operation, and a more stabilized platform during the working mode of operation.
It is another object of the present invention to provide a suspension system wherein semi-independent support of the rear axle of a heavy duty, working vehicle simulates the center pinned bolster arrangement, but provides for enhanced performance at a lower initial cost, a substantial weight savings and better access to the vehicle engine and other components, along with other benefits.
It is still another object of the present invention to provide an improved suspension system wherein the interaction between the hydraulic circuit and the electrical control circuit assures efficient operation in either mode, as well as switching from one to the other.
It is still another object of the present invention to improve the cushioning capability of the system in the travel mode, by utilizing less components in the hydraulic oscillation circuit. For example, in a preferred embodiment, a single accumulator and a return line bypass to the hydraulic oil reservoir eliminates the need for a second accumulator. Furthermore, using a piston and cylinder type accumulator provides a lower spring rate to extend the performance range in the traveling mode of operation for maximizing stress relief.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved suspension system with an axle oscillation circuit that simulates bolster center pinned oscillation motion is provided. The suspension is best adapted for use on a heavy duty crane, excavator or other material handling vehicle that requires cushioning of the ride in the traveling mode of operation, and then stabilizing of the vehicle to form a secure platform during a working mode. The system of the present invention is best adapted for a wheeled vehicle and is usually applied to the rear axle. During traveling, such as from job site to job site, or even for a pick and move operation at a job site, the rear axle can oscillate when uneven terrain is encountered. Not only is the ride cushioned to relieve stress and fatigue of the operator, but also to minimize the stress of the mechanical parts of the vehicle.
A hydraulic pressure source is connected through a set up valve to provide hydraulic control of the level of the vehicle frame with respect to the wheels. The set up valve includes a pressure feed line connected to the extend side of the hydraulic cylinders and a return line connected to the retract side and a reservoir. A standard
Gamble Olen H.
Griebel Francis J.
Harrington Daniel L.
Culbreth Eric
King and Schickli PLLC
Link-Belt Construction Equipment Company, L.P., LLLP
Lum L.
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