Interrelated power delivery controls – including engine control – Transmission control – Including fluid drive
Patent
1992-07-28
1994-08-16
Braun, Leslie A.
Interrelated power delivery controls, including engine control
Transmission control
Including fluid drive
475 72, 60487, 3644241, F16H 4704, F16H 6142
Patent
active
053376293
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
This invention relates to improvement in the starting characteristic of continuously variable transmissions of both the hydrostatic type adapted for a low to medium vehicle speed range and the hydro-mechanical type adapted for a low to high vehicle speed range.
BACKGROUND ART
In vehicles provided with a gasoline engine, it has been customary to determine the optimum engine speed for throttle position in view of improvement of fuel consumption and/or purification of exhaust gas. With a continuously variable transmission it is possible to run an engine at a desired speed regardless of the vehicle speed. To this end, it has been customary to control a continuously variable transmission by a speed-ratio controller so as to realize the above-mentioned desirable correspondence between throttle position and engine speed.
In particular, the conventional standard hydrostatic continuously variable transmission includes a variable speed hydraulic transmitting system between a pair of hydraulic pump/motors at least one of which at the input side is of a variable displacement type, and is so designed that the speed ratio of the output speed to the input speed can be rendered nearly zero with the displacement of the input hydraulic pump/motor acting as a pump being kept zero.
The conventional hydro-mechanical continuously variable transmission comprises: a differential mechanism having a first, a second and a third input/output terminal, a low-speed mechanical transmitting system between the first and second input/output terminals, and a high-speed mechanical transmitting system between the first and third input/output terminals; a hydraulic transmitting mechanism comprising a first hydraulic pump/motor of a variable displacement type the input/output shaft of which is connected to the second input/output terminal of the differential mechanism and a second hydraulic pump/motor of a variable displacement type the input/output shaft of which is connected to the third input/output terminal thereof thereby to form a variable speed hydraulic transmitting system; a low-speed clutch for connecting and disconnecting the transmitting terminal of the above-mentioned low-speed mechanical transmitting system to and from a rotary element provided at the output side; and a high-speed clutch for connecting and disconnecting the transmitting terminal of the above-mentioned high-speed mechanical transmitting system to and from another rotary element provided at the output side, whereby either a low-speed or a high-speed mode can be selected by operating either one of the above-mentioned clutches; the first input/output terminal being connected to an engine and the rotary elements, to an axle of the vehicle.
The speed-ratio controller that is composed chiefly of an ECU (electronic control unit) detects throttle position or accelerator pedal position and engine speed and controls the displacement of the hydraulic pump/motor so that the engine speed is kept at a desired value in accordance with the throttle position.
The above control will be described in detail. As the driver steps on the accelerator pedal, the throttle valve is opened, and the desired engine speed corresponding to the throttle position is obtained from a chart of throttle position/desired engine speed, and the displacement of the hydraulic pump/motor, that is, the speed ratio of the continuously variable transmission is controlled so as to keep the actual engine speed at the desired value.
The vehicle provided with the conventional continuously variable transmission has the following three problems:
First, a time delay exists between the time the accelerator pedal is stepped on to start the vehicle and the time the vehicle begins to start, with resulting deterioration of response. In particular, if the throttle position is subjected to a stepwise increase as the driver steps on the accelerator pedal, the desired engine speed SD greatly increases stepwise. The actual engine speed SE, however, increases with the first order lag accompanied with loss ti
REFERENCES:
patent: 3901031 (1975-08-01), Knapp et al.
patent: 4261229 (1981-04-01), Mizuno et al.
patent: 5214983 (1993-06-01), Kobayashi et al.
Braun Leslie A.
Shimadzu Corporation
Ta Khoi
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