Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
2000-06-14
2003-12-16
Vanaman, Frank (Department: 3618)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
Reexamination Certificate
active
06662895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to hydraulic drive systems for self-propelled turf care equipment, and more particularly to a dual-path reversible hydrostatic drive system for a steerable turf care machine having a single variable volume hydraulic pump as a source of hydraulic drive power.
2. Discussion
Commercial turf care machines are typically self-propelled and are often equipped with drive mechanisms for both driving and steering the wheels of the machines. These drive mechanisms typically include a mechanism for transferring the driving torque from a source of power such as an internal combustion engine to at least two of the machine wheels, thereby turning the machine wheels and assisting the machine operator in both propelling and maneuvering the piece of equipment.
While both hydraulic and mechanical drive mechanisms have been commonly used in the past, hydraulic drive mechanisms are being implemented in turf care machines on an ever increasing basis due to decreases in the price of such systems. Specifically, hydrostatic drive mechanisms have long been known to exhibit desirable characteristics such as allowing a machine operator to quickly switch between forward, neutral and reverse modes of operation, and to provide for efficient steering of the machines as well. Dual path hydrostatic drives are used on both zero-turn riding mowers and zero-turn walk-behind mowers for a number of years, as is shown in U.S. Pat. No. 3,616,869 to Rilling and U.S. Pat. No. 4,920,733 to Berrios, which are both hereby incorporated by reference. These drive systems feature a dedicated hydraulic pump and hydraulic motor combination for each of the two driving wheels. Typically, the pumps and motors are located near the driving wheels, and the two pumps are driven by a belt powered by a pulley mounted to the output shaft of the internal combustion engine.
One desirable feature of these dual path machines is their ability to turn and maneuver with considerable agility. This is a direct result of each driving wheel being controlled by the operator independently of the other driving wheel. So, while one wheel is being driven forward at a desired speed, the other wheel can be driven, for example, in the opposite direction at the same speed, thereby allowing the turf care machine to turn on its own axis. Commercial riding and walk-behind mowers having a dual path hydrostatic drive system are available from more than a half-dozen different companies.
A turf care machine operator manipulates a typical dual path hydrostatic drive mechanism through a plurality of levers located on an operator/turf machine interface such as a handle bar structure. These operator control systems typically include both traction controls and speed controls to enhance machine operability and maneuverability. A typical traction control for a dual path hydrostatically-driven machine provides the machine operator with selective control between forward, neutral and reverse modes of operation for each driven wheel, while a typical speed control provides the operator with an overall control for regulating the maximum forward speed at which the machine can be operated. State-of-the art traction and speed controls are disclosed in U.S. Pat. No. 5,343,678 to Stuart and U.S. Pat. No. 5,651,241 to Wegner, which are both hereby incorporated by reference. They are also available on various mid-size commercial mowers including those from Textron Turf Care & Specialty Products of Johnson Creek, Wis., such as the Ransomes® Bob-Cat® mid-size mowers Model No. 942215 (a riding mower) and Model No. 930301 (a walk-behind mower), the operations and details of which are respectively described in publicly available Ransomes operator and service manuals.
While the present dual path hydrostatic drive systems that are presently available on commercial turf care machines typically exhibit sufficient performance characteristics, such systems normally require a hydraulic fluid reservoir as well as a pair of reversible variable displacement pumps, thus increasing turf care machine cost. It would therefore be desirable to provide more economic arrangements for the hydraulic drive system which facilitates ease of operation, improves efficiency and/or reduces manufacturing costs.
As such, a first object of the present invention is to provide an improved system for regulating/controlling a hydrostatic drive mechanism of a conventional turf care machine.
A second object of the present invention is to provide an improved system for regulating/controlling the hydrostatic drive system of a turf care machine that allows the operator to adjust the power to the drive system in a way which helps reduce heating of the hydraulic fluid and improves system efficiency.
A third object of the present invention is to provide a system and method for regulating/controlling the hydrostatic drive of a turf care machine that requires only one single pump for driving both drive wheels in a seemingly independent dual path mode of operation, thereby minimizing cost and the number of fluid linkages and parts in such a system.
A fourth object of the present invention is to provide an economically efficient dual-path hydrostatic drive system which has a reduced number of external hydraulic connections for improved system reliability.
SUMMARY OF THE INVENTION
To achieve one or more of the foregoing objects, and in accordance with the teachings of the present invention, a single-pump hydraulic drive system for a steerable, self-propelled wheeled vehicle is provided that is designed and adapted for regulating the operation of a self-propelled mower or other piece of turf care equipment or similar kind of the machine. The system of the present invention finds particular utility for midsize commercial mowers and similar kinds of steerable self-propelled wheeled equipment, typically having a net weight of about 140 kg (about 310 pounds) to about 500 kg (about 1100 pounds), which are manually steered and must often be manipulated around obstacles during operation.
A manually-steered self-propelled wheeled vehicle, such as a commercial mower, according to one embodiment of the present invention, is implemented with a single-pump hydraulic drive system having a pair of control valve sets for controlling the volume and direction of fluid from the single hydrostatic pump to a pair of wheel drive motors. The single hydraulic pump, which is preferably a variable volume pump, functions to provide hydraulic fluid power required to drive the wheels. The pump preferably includes a manually-operated maximum volume adjustment mechanism, such as a movable machine speed lever connected to a rotatable trunnion shaft or other volume control input means on the pump, for selectively setting the desired maximum pump displacement at any desired level, from a fraction of the pump's output, such 20%, all the way up to 100%. Via this machine speed lever, an operator can select the maximum drive speed at which the mower will operate. If desired, this speed control mechanism can be operatively connected in a combined manner on the turf machine so that the speed control lever limits the top speed of the traction controls. The operator traction controls typically include independently-actuated left and right control levers, typically operated by the user's left and right hands, which are mechanically connected via independent linkages to the conventional control valve operators mounted on the first and second valve sets, which valve sets will shortly be described.
The hydraulic pump is connected to a first valve set, which regulates the volume and direction of fluid to the left hydraulic wheel motor. The left wheel motor mechanically drives the mower's left driving wheel, and thus controls the direction and speed of rotation of the left driving wheel. Hydraulic fluid may also be partially or completely shunted or bypassed around the left hydraulic wheel motor by the first valve set, in those operating situations where the left driving wheel is
Harness & Dickey & Pierce P.L.C.
Textron Inc.
Vanaman Frank
LandOfFree
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