Motor vehicles – With means responsive to speed of vehicle for maintaining... – Including electrically actuated servomechanism
Reexamination Certificate
1999-08-30
2001-07-17
Mar, Michael (Department: 3619)
Motor vehicles
With means responsive to speed of vehicle for maintaining...
Including electrically actuated servomechanism
C180S242000, C180S308000, C123S350000, C701S093000
Reexamination Certificate
active
06260647
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to electronically controlling engine speed for a work machine and more particularly to the ability to electronically set and maintain the engine speed independent from the ground speed of the work machine so that various implements may be operated without continuous operator control of the engine speed.
BACKGROUND ART
Present work machines, such as wheel loaders, may utilize a hydrostatic transmission to assist in controlling ground speed. Typically, a plurality of variable displacement motors that drive the wheels of the work machine are displaced by a pressure signal within a signal line that is generated from a fixed displacement pump linked directly with an engine. Therefore, the ground speed is engine speed dependent so that as the engine speed increases the signal pressure increases to further displace the motor, increasing the ground speed. However, a “ball valve” is located in the signal line that can be opened to bleed off a volume of hydraulic fluid from the signal line to a tank, which subsequently reduces the signal pressure controlling the motor, slowing or even stopping the machine. Generally, this is referred to as the neutralization of the hydrostatic transmission so that the ground speed of the work machine is controlled substantially independent of the engine speed, allowing for increased power availability to the implement. However, during neutralization of the hydrostatic transmission, it is important to reach an engine speed that is high enough to operate an implement and maintain that engine speed throughout various loading conditions. Generally, this requires that an operator must continuously monitor and compensate for changes in the engine speed during operation of the implement, such as through the manual control of a governor pedal.
An approach for simultaneously controlling ground and engine speeds is disclosed in U.S. Pat. No. 4,157,124 issued to Bernard B. Poore on Jun. 5, 1979. This patent utilizes a vehicular gas turbine engine power system with an engine, an automatic clutch, a service clutch and an infinitely variable transmission coupled along a power train. A control system is utilized to control and vary the engine speed for maximum fuel efficiency in response to operator selected ground and engine speed commands. The engine speed is controlled substantially through exhaust gas temperature and engine speed feedback, reducing the ground speed, if necessary, to obtain the desired engine speed. The control system disclosed utilizes an advanced system for engine and ground speed control that functions with an infinitely variable transmission. The use of the disclosed control system would not be feasible on a work machine utilizing a hydrostatic transmission because of the need to control the engine speed independently from the ground speed. Preferably, the ability to control the engine speed independently from the ground speed control would utilize a separate electronic engine speed controller. Therefore, the engine could be set at any desired speed independent of the ground speed to efficiently drive a hydraulic implement pump for operating the implement and maintain the desired speed substantially throughout the implement operation. This ability would ensure efficient use of the engine, increase operator flexibility and control, and minimize operator fatigue. The engine speed controller should be relatively simple and inexpensive so that it may be easily added to an existing work machine already utilizing the hydrostatic transmission for controlling ground speed.
The present invention is directed to overcoming the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, an electronic engine speed control system is disclosed for a work machine. The work machine has an engine with a governor control that is movable between a plurality of positions so that a desired engine speed may be selected and utilized for driving a plurality of wheels through a hydrostatic transmission. The hydrostatic transmission is capable of controlling the plurality of wheels to obtain a desired ground speed of the work machine independent of the selected engine speed. The electronic engine speed control system comprises an electronic control module. An operator switch is connected to the control module and is movable to a set position which sends an input signal with a desired engine speed value to the control module. An engine sensor is connectable between the engine and the control module for sensing the speed of the engine and sending an input signal with an actual engine speed value to the control module. An actuator is connectable between the control module and the governor control and responsive to a control signal from the control module for moving the governor control to any one of the plurality of positions. The control signal is delivered to the actuator as a function of the desired and actual values so that the engine speed is electronically set and maintained at the desired value. Means are used for disrupting the control signal so that the engine speed is no longer electronically set and maintained at the desired value.
In another aspect of the present invention, a work machine comprises an engine, a plurality of wheels, a source of hydraulic fluid, a hydrostatic transmission, and an electronic engine speed control system. The hydrostatic transmission includes a hydraulic pump connected with the engine, a motor, a pressure signal line connected between the pump and the motor for transferring hydraulic fluid at various flows therebetween so that the motor drives the plurality of wheels at various speeds responsive to the flow of the hydraulic fluid, and a valve disposed within the signal line and movable from a closed position to a plurality of open positions for selectively neutralizing the hydraulic fluid flow to control the ground speed of the work machine independent from the engine speed. The electronic engine speed control system is operatively associated with and located remotely from the hydrostatic transmission for setting and maintaining the engine at any desired speed during neutralization of the hydrostatic transmission.
In yet another aspect of the present invention, an electronic engine speed control system is disclosed for a work machine. The work machine utilizes an engine with a governor control movable between a plurality of positions so that a desired engine speed may be selected and utilized for driving a plurality of wheels through a transmission. The transmission is controllable to obtain a desired ground speed independent of the selected engine speed. The electronic engine speed control system comprises an electronic control module. An operator switch is connected to the control module and is movable to a set position which sends an input signal with a desired engine speed value to the control module. An engine sensor is connectable between the engine and the control module for sensing the speed of the engine and sending an input signal with an actual engine speed value to the control module. An actuator is connectable between the control module and the governor control and responsive to a control signal from the control module for moving the governor control to any one of the plurality of positions. The control signal is delivered to the actuator as a function of the desired and actual values so that the engine speed is electronically set and maintained at the desired value. Means are used for disrupting the input signal between the operator switch and the control module so that the engine speed is no longer electronically set and maintained at the desired value.
In yet another aspect of the present invention, a method of setting and maintaining an engine speed for a work machine independent from the ground speed of the work machine is disclosed. The method comprises the steps of providing an engine with a governor control movable to a plurality of positions for controlling the engine speed. Then, selecting the engine speed by moving the gover
Calamari Michael A.
Fuller Paul D.
Mistry Bhikhubhai S.
Thomas Dante T.
Watson J. Roger
Caterpillar Inc.
Charlton Diana L.
Mar Michael
LandOfFree
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