Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission
Reexamination Certificate
1999-11-29
2001-07-03
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Engine controlled by transmission
C477S111000
Reexamination Certificate
active
06254509
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle powershift transmission and engine control system.
Powershift transmissions change speeds by disengaging one or more clutches and then engaging one or more clutches, with no interruption of power during the shift. Shift smoothness is obtained by modulating the pressure of the oncoming clutches, i.e. engaging them at low pressure. Shift smoothness is very sensitive to having the optimum engagement pressure in relation to the load being transmitted by the transmission. If the engagement pressure is too low, the vehicle may drop load or speed during the shift, if the engagement pressure is too high, the shift will be aggressive, jumpy and harsh. Under lightly loaded conditions, the typical engine governor response contributes to the poor shift. For example, during an upshift, if the engaging clutch locks up quickly, it will bring the engine speed down rapidly. The engine governor typically over-reacts to this drop in speed by quickly increasing fuel to the engine. An excess amount of fuel may then cause the engine to quickly overshoot the commanded speed. The resulting acceleration-deceleration causes the vehicle to pitch fore and aft, and produces a “jumpy” feel.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide a transmission and engine control system which prevents such engine governor-caused rough shifts.
Accordingly, another object of this invention is to provide a transmission and engine control system which makes shift smoothness less sensitive to modulating the oncoming clutch at the optimum pressure.
These and other objects are achieved by the present invention, wherein a control system for a vehicle is provided. The vehicle includes an engine which drives a powershift transmission. The powershift transmission has a gear box which is operated by a set of pressure operated clutches which are controlled by a corresponding set of solenoid operated shift control valves. The valves are controlled by an electronic vehicle control unit (VCU) in response to the shift command signals generated by an operator controlled shift control lever mechanism. The engine is controlled by an electronic engine control unit (ECU) which receives a throttle command signal from the VCU. During an upshift the control system depressurizes at least one off-going clutch and later pressurizes at least one on-going clutch. The VCU, during a shift, abruptly modifies the magnitude of the throttle command signal while the off-going clutch is being de-pressurized, and then gradually returns the magnitude of the throttle command signal back to its original magnitude when the on-going clutch is fully pressurized. During an upshift, the throttle command signal TC is similarly momentarily decreased at the start of the clutch swap, and is then gradually increased or ramped up. During a downshift, the throttle command signal TC is similarly momentarily increased at the start of the clutch swap, and is then gradually decreased or ramped down. This strategy allows the engine to accomplish most of the change in vehicle speed, and is less dependent on proper slipping of the oncoming clutch. This also causes the engine governor to react properly to the shift, and avoids governor over-reaction.
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Deere & Company
Estremsky Sherry
Ho Ha
LandOfFree
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