Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2000-03-14
2001-07-10
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S131000, C477S138000
Reexamination Certificate
active
06258010
ABSTRACT:
TECHNICAL FIELD
This invention relates to hydraulic control mechanisms and more particularly to hydraulic systems for controlling the shift sequence of a power transmission.
BACKGROUND OF THE INVENTION
One-way torque transmitting mechanisms have been employed in many automatic shifting transmissions to accommodate the ratio interchange in the transmission. The one-way torque transmitting mechanism is provided to either transmit torque from the engine to a gear member or transmit torque from the gear member to ground. As is well-known, the one way torque transmitting mechanism will release the controlled gear member upon a reversal of torque that occurs during the ratio interchange. This permits a smooth transition between ratios. The one-way mechanisms are mechanical devices that require space in the transmission and also add weight to the transmission.
To eliminate the use of one-way torque transmitting mechanisms, some transmission control systems have incorporated electrohydraulic control systems with “clutch to clutch” shift technology. The control systems have utilized two strategies, open loop control and closed loop control. During open loop control, the oncoming friction torque transmitting mechanism (clutch or brake) is filled with fluid and the pressure is ramped up to the inertial pressure required during the shift. The release timing of the pressure in the offgoing friction torque transmitting mechanism is based on an estimation of the oncoming torque transmitting mechanism fill time. The fill time of the oncoming torque transmitting mechanism varies due to many design and assembly factors such that the release of the offgoing torque transmitting mechanism can be early, causing a flare, or late, causing a tie-up. Some control algorithms have been developed to detect the oncoming clutch fill using an input or output speed signal. However, these have not proved reliable for practical use.
During closed loop control, the offgoing torque transmitting mechanism capacity is reduced to its critical point by generating a predetermined slip speed in the offgoing torque transmitting mechanism. The oncoming torque transmitting mechanism is filled and ramped up to the inertial pressure. As the oncoming torque transmitting mechanism gains capacity, the input speed will drop. As the input speed drop is detected by the microprocessor, the offgoing torque transmitting mechanism capacity is reduced to zero. In the closed loop control, there is a controlled engine flare at the beginning of the interchange causing an output torque dip. Also since the offgoing torque transmitting mechanism is not released until the input speed drop is detected, a tie-up is present during the ratio interchange.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved transmission control system.
In one aspect of the present invention, a plurality of shift logic valves and pressure control valves are interconnected to control the interchange and continuous engagement of a plurality of torque transmitting mechanisms. In another aspect of the present invention, the pressure control valves are comprised of two oncoming torque transmitting mechanism control valves and two offgoing torque transmitting mechanism control valves. In yet another aspect of the present invention, the oncoming torque transmitting mechanism control valves and the offgoing torque transmitting mechanism control valves are arranged in operative pairs with an oncoming torque transmitting mechanism control valve and an offgoing torque transmitting mechanism control valve in each pair.
In still another aspect of the present invention, an interlock passage is connected between each offgoing torque transmitting mechanism control valve and the output pressure of the paired oncoming torque transmitting mechanism control valve. In a further aspect of the present invention, the output pressure of the oncoming torque transmitting mechanism control valve will cause the output pressure of the offgoing torque transmitting mechanism control valve to be reduced below the critical capacity of the offgoing torque transmitting mechanism during an upshift ratio interchange.
REFERENCES:
patent: 4827806 (1989-05-01), Long et al.
patent: 5913916 (1999-06-01), Bai et al.
patent: 6110071 (2000-08-01), Kozan et al.
Bai Shushan
Moses Robert Lowell
Estremsky Sherry
General Motors Corporation
Hargitt Laura C.
Lewis Tisha D.
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