Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1982-08-04
1985-01-22
Braun, Leslie A.
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
74752C, 74867, 74868, B60K 4104
Patent
active
044944233
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a hydraulic control system for an automatic transmission and more particularly to such a system, which upon sensing an unacceptable combination of pressurized clutches and servos reverts to the combination that produces a predetermined speed ratio.
2. Description of the Prior Art
Automatic transmissions for automotive use include planetary gearsets, whose elements are hydraulically engaged or braked in order to produce selected speed ratios between the engine crankshaft and the output shaft of the transmission. Automatic gear change transmissions may be controlled by electronic means which produce digital voltage signals that are converted to analog signals to operate solenoid valves. These valves connect hydraulic line pressure to the selected clutches and brakes or vent the hydraulic cylinder of these elements to atmosphere. The control system should operate such that in the event of a control system failure the transmission may operate in at least one forward drive range and in the reverse drive range in order to permit driving the vehicle to a service or repair station.
SUMMARY OF THE INVENTION
It is an object of this invention that the transmission be automatically set for operation in a predetermined gear ratio if a malfunction is sensed that causes the clutches and brakes to be operated so as to prevent rotational movement of the engine or driveshaft. The hydraulic control system according to the invention senses a concurrent application of three or more clutch or brake elements, concurrent application of the low-reverse band and the intermediate clutch, and concurrent application of the low-reverse band and the direct clutch.
The hydraulic control circuitry for realizing this objective includes a detector valve having four differential areas each of which communicates with hydraulic lines that pressurize each of the friction elements. When the combination of differential areas are pressurized so as to correspond to one of the malfunctions sensed by the circuit, a pressure force is developed on a transfer valve causing it to move to a second state. Opposing the force on the detector valve is a transfer valve that performs several functions.
The transfer valve produces a force opposite that of the detector valve. These forces vary linearly with the line pressure thereby maintaining equilibrium with the hydraulic fail-safe system despite changes in line pressure. If a malfunction is sensed, during the resultant fail-safe operation, the detector valve directs line pressure to the forward clutch and intermediate clutch thus causing the transmission to operate in second gear. In the fail-safe mode, the transfer valve disconnects line pressure from the solenoid-operated valves through which the various clutches and brake elements of the transmission are normally pressurized. This is done to prevent a malfunctioning solenoid circuit from pressurizing friction elements other than those required to be pressurized for operation in the second gear ratio. The friction elements other than those required for second gear operation are vented through the transfer valve if a malfunction is sensed. The transfer valve maintains the hydraulic control system in the second gear ratio through action of the transfer valve that shuttles to the fail-safe position. In the second state line pressure applied to an area of the transfer valve larger than that which creates the detector valve opposing force maintains the transfer valve in the fail-safe condition until the manual valve is moved out of the Overdrive, Drive, or one-range and into Park, Reverse or Neutral. This action permits an easy resetting of the transfer and detector valves if this valve combination incorrectly senses a malfunction or following a malfunction that has been rectified. However, these valves will immediately return to the fail-safe position if another malfunction is sensed.
The detector valve has four pressure areas formed on a spindle that moves between a first, or
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Byler Richard E.
McCarthy James P.
Braun Leslie A.
Diehl Dwight G.
Ford Motor Company
Harrington Donald J.
McKenzie Frank G.
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