Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Patent
1979-02-08
1982-07-20
Peters, Jr., Joseph F.
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
180197, B60K 1710
Patent
active
043401260
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to hydraulic wheel drive systems for vehicles, and more particularly, to the prevention of the development of an overspeed condition in such systems.
2. Background Art
Prior art of possible relevance includes U.S. Pat. No. 3,984,978 issued Oct. 12, 1976 to Alderson.
The above identified Alderson patent discloses a vehicle wheel drive system wherein a wheel is driven by a hydraulic motor which in turn is provided with pressurized fluid by a pump. The motor is of the variable displacement type and control over the same is maintained by three valves including a flow control valve, a pressure control valve, and a direction control valve.
While the system works well for its intended purpose, as disclosed by Alderson, certain defects exist. The usual rotary output hydraulic motor typically has a maximum speed rating which cannot be safely exceeded without damaging or destroying the motor. And in a system such as that proposed by Alderson where a variable displacement motor is used, when there is no resistance to rotation of the wheel, the resulting drop in system pressure will tend to cause the pressure control valve therein to stroke back the motor, that is, reduce its displacement. This in turn causes an increase in the rotational output speed of the motor with the consequence that its safe speed limit may be exceeded.
Depending upon the application in which the system is used, the possibility of the lack of application of resistance to the wheel varies. When used in, for example, a motor grader as an auxiliary front wheel drive as proposed by Alderson, the possibility is quite real. It will typically occur when one or the other of the front wheels loses contact with the underlying terrain. This, in turn, can occur with a fair degree of frequency in a motor grader. For example, when the motor grader is being utilized to smooth uneven terrain, the fact that the terrain is uneven may cause one of the wheels to lose contact with it. Alternately, if the motor grader mold board is driven with considerable force into the underlying terrain to achieve the desired bite for grading purposes, it may lift one or the other or both of the front wheels off the ground since weight distribution in a typical motor grader usually results in the center of gravity being located well toward the rear of the vehicle.
To solve this problem, the prior art has utilized flow limiting devices in the flow paths to the motors. The flow limiters preclude sufficient flow to the motors to cause an overspeed condition of the motors to come into existence. However, such flow limiters add appreciably to the cost of the vehicle and because there will typically be a 200 to 250 psi pressure drop across each flow limiter, the size of the prime mover for the hydraulic pump must be increased to attain the same system pressure that would be obtainable at the motors without the flow limiters.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, there is provided a vehicle drive system including a wheel to be driven, a hydraulic rotary output motor connected to the wheel for driving the wheel, a hydraulic pump for providing hydraulic fluid under pressure to the motor, and a flow control valve for controlling the flow of hydraulic fluid between the motor and the pump. The invention contemplates the improvement wherein means are provided for sensing when the wheel loses contact with the underlying terrain and means responsive to the sensing means for halting the flow of hydraulic fluid between the pump and the motor.
As a consequence, the use of flow limiters is avoided in favor of simple sensing means and the undesirable overspeed condition is prevented from coming into existence whenever the condition that might lead to an undesirable overspeed condition is sensed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of an embodiment of a vehicle drive system made according to the invention;
FIG. 2 is a partial schematic of a modified embodiment of the vehicle drive system.
REFERENCES:
patent: 3177964 (1965-04-01), Anderson
patent: 3183015 (1965-05-01), Al linquant
patent: 3656570 (1972-04-01), Gortnar et al.
patent: 3666286 (1972-05-01), Engfer
patent: 3714999 (1973-02-01), Fletcher
patent: 3984978 (1976-10-01), Alderson
Caterpillar Tractor Co.
Peters Jr. Joseph F.
Smith Milton L.
LandOfFree
Overspeed control for a vehicle drive system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Overspeed control for a vehicle drive system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Overspeed control for a vehicle drive system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-246291