Saturn Corporation

Susan L Rees

Larry T Nitz

Rimas S Milunas

Nader Motamedi

William J Bolander

Glenn P O'Connell

A motor vehicle has a multi-speed automatic transmission and a cruise control system. A method of shift control when the cruise control system is enabled infers from a plurality of factors based on cruise control error quantities the desirability of forcing a downshift to a lower speed ratio.

Cruise control inference based shift pattern control

A shift pattern control for a multiple speed ratio transmission wherein an inference-based control overrides the normal shift pattern to automatically achieve manual pulldown operation under conditions for which such operation would be advised and expected. The inference-based control is achieved with a fuzzy logic technique by which vehicle parameters influencing the desirability of manual pulldown operation are measured or estimated, and used to establish an aggregate measure of the overall need for engine braking and downshifting. In the preferred embodiment, the fuzzy logic parameters include vehicle speed, grade load, engine throttle position, time of braking and time of deceleration. The parameters are applied to membership functions to indicate the truthfulness of the specified conditions, and logical combinations of the truth indications are formed, weighted to reflect their criticality, and combined to form an aggregate measure of the overall need for pulldown operation.

Inference-based manual pulldown control of an automatic transmission

A traction control system provides coordinated use of axle torque management via engine spark, engine fuel, and transmission gear ratio. Primary torque management is provided by retarding the ignition timing to reduce engine torque. When the spark retard reaches a determined limit value, the vehicle automatic transmission is upshifted which reduces axle torque and engine speed, thus reducing the amount of spark retard required to control a slip condition, thereby increasing the authority of the spark retard system. The limit spark retard threshold is established as a function of the temperature of the catalytic converter so as to prevent an overtemperature condition. Further, fuel control is ultimately used if control of ignition timing is incapable of bringing the acceleration slip under control. This condition may exist, for example, when the spark system authority of control is insufficient due to limitations placed upon its authority in response to a sensed hot catalytic converter condition.

Integrated traction control system

An improved torque converter clutch (TCC) engagement control method utilizing a combination of pressure control and flow control methodologies to ensure consistently smooth and timely TCC engagement. The engagement is initiated with a pressure control methodology in which the duty cycle of a PWM actuator is selected to produce a desired pressure differential across the TCC clutch plate. However, if the flow conditions are such that the pressure control methodology fails to promptly initiate engagement of the TCC, as detected in relation to the speed difference across the torque converter, a flow control methodology is substituted for the pressure control to initiate clutch engagement. In this case, the duty cycle of the actuator is adjusted to a value which provides full or near-full fluid flow. This control is maintained for a predetermined period, or until the speed difference across the torque converter indicates initiation of TCC engagement. At such point, the pressure control methodology is resumed to complete the TCC engagement.

Control method for the engagement of a torque converter clutch

An improved shift pattern control in which successive upshifting and downshifting is avoided in conditions of above normal loading by inhibiting upshifting to a speed ratio having insufficient gradeability in relation to a measure of the actual loading. In essence, the control continually monitors the gradeability of the various forward speed ratios of the transmission in relation to a measure of the actual grade load to determine their excess gradeability, and removes from the shift pattern those speed ratios having insufficient excess gradeability. This ensures that the transmission will never be upshifted to a speed ratio that has insufficient gradeability for the given driving condition, thereby eliminating the successive upshifting and downshifting which occurs with conventional shift controls.

Gradeability-based shift pattern control for an automatic transmission

An improved method of scheduling ratio shifting in a vehicle transmission adaptively adjusts the normal shift schedule to avoid shift-related overheating of the torque transmitting devices of the transmission. In normal operation, transmission shifting is scheduled by comparing measured vehicle speed and engine throttle position values with predefined load data. In the background, the transmission controller determines the cumulative thermal energy stored in the torque transmitting devices. If excessive energy is indicated, the normal shift schedule is modified to allow extended operation in the lower speed ratios. When the cumulative energy indication returns to a normal level, normal shift scheduling is resumed.

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Clawson, MI, United States of America

Susan L Rees