Abstract: The system provides an improved clutch control system for use in a continuously variable transmission system. The system provides for generation of a clutch pressure setpoint to re-engage the clutch during special conditions in which the torque created by the vehicle inertia would tend to drive the engine to an undesirable operating point. Clutch slip speed is monitored as a difference value and integrated to provide a gradually decreasing error signal to return the clutch input speed to the clutch output speed, at which time clutch lockup will occur. Additionally, throttle position is monitored and a maximum torque schedule used to provide a maximum torque signal to prevent driver demand from undesirably racing the engine in similar conditions. A filtered output of the maximum torque schedule provides a pressure setpoint signal representative of actual driver demand which may be added to the clutch slip speed error signal to generate the clutch pressure setpoint.

Abstract: Temperature compensation techniques are utilized to provide consistent system response in a continuously variable transmission system or other control system over a range of expected operating temperatures. Variations in the independent transfer functions for various control functions, such as ratio control, line pressure control and clutch control are monitored or measured. Appropriate modifications to system operating parameters are scheduled based upon the measured, simulated or predicted variations in the transfer functions as previously determined. In operation, the disclosed system senses temperature and provides the appropriate compensation and gain parameter modifications in accordance with the selected schedules.

Abstract: Improved pulse width modulation technique provides for an increased sampling rate without an increased ON/OFF rate at associated control devices. Both ON/OFF and OFF/ON edges in a PWM signal are modulated. The system then samples at twice the pulse turn-on rate to provide more frequent sampling. System response time may be decreased without an increase in the operating frequency for the associated control device. Particular application of the present invention may be found in continuously variable transmission systems which utilize PWM-controlled electrohydraulic valves for ratio control, line pressure control and clutch control. A system for implementing the PWM signal has a duty-cycle calculator coupled with timing circuits to control input data reading functions and circuit enabling, leading edge and trailing edge regulators and an output pulse generator.

Abstract: Improved pulse width modulation technique provides for an increased sampling rate without an increased ON/OFF rate at associated control devices. Both ON/OFF and OFF/ON edges in a PWM signal are modulated. The system then samples at twice the pulse turn-on rate to provide more frequent sampling. System response time may be decreased without an increase in the operating frequency for the associated control device. Particular application of the present invention may be found in continuously variable transmission systems which utilize PWM-controlled electohydraulic valves for ratio control, line pressure control and clutch control. A system for implementing the PWM signal has a duty-cycle calculator coupled with timing circuits to control input data reading functions and circuit enabling, leading edge and trailing edge regulators and an output pulse generator.

Abstract: A line pressure control system for a continuously variable transmission which includes a continuously variable member, a clutch and a pressure transducer for providing a feedback signal for both closed loop line pressure and closed loop clutch control. The line pressure control system includes a closed loop control strategy and an open loop control strategy which operate independently, and initial conditions are determined and set to prevent discontinuities in the output. The closed loop control strategy includes proportional and integral gain terms. The control system is adaptable to utilize of a variety of different open loop control strategies to provide a schedule response to a desired line pressure or a maximum or minimum line pressure when appropriate. The control system also optionally provides for a transition from closed loop control to open loop control and vice versa in response to the output parameters generated.

Abstract: An improved clutch control system in a continuously variable transmission driven vehicle monitors driver selection of forward or reverse and implements the specific parameters for each. The control logic provides a preselected time interval for sensing of a pressure drop associated with the transition from one operating mode to another, such as from neutral to forward. The system provides for sensing that pressure drop and providing a desired fluid flow rate for clutch actuation consistent with the desired performance. The system also monitors pressure in the fluid actuation system at the end of the predetermined interval to ascertain when the pressure reaches a desired higher level indicative of a control characteristic to provide desired vehicle response to driver demand. Fluid flow to the clutch is controlled at a corresponding rate to provide a desired operating characteristic and to facilitate transition into a subsequent vehicle operating mode.

Abstract: A pressure transducer, which senses clutch pressure and effects closed loop clutch control in a continuously variable transmission, is used after the clutch is fully engaged to provide closed loop line pressure control to a desired setpoint, which line pressure regulates the tension on the belt in the transmission. Only a single transducer is needed since there is a known relationship between the clutch and line pressures when the clutch is locked up. Prior to lockup, the line pressure is governed by an open loop controller which establishes the line pressure at a level higher than that called for by the setpoint. This ensures that the line pressure will be high enough to provide the required tension on the belt so that it will not slip. After the clutch is engaged, the closed loop line pressure controller (which includes both the open loop line pressure controller and the closed loop clutch controller) establishes the line pressure at the setpoint.

Abstract: A ratio control system for use in a continuously variable transmission is disclosed in conjunction with an improved technique for operation thereof. Individual gain schedules provide proportional gain in response to a selected one of a number of modes dependent upon clutch input speed, transmission belt ratio, or engine set point. Engine speed set point is determined as a function of a set point schedule in conjunction with a limiter and a filter to provide a gradual response to rapid changes in a throttle input or driver demand signal and vehicle speed. The error signal generated as an output of any of the proportional gain loops is integrated and combined with a null signal to provide a signal to generate a duty cycle for a pulse width modulation controlled electrohydraulic control valve to control the pressure to the primary sheave in a continuously variable transmission system for modifying the belt ratio.

Abstract: A clutch control system provides and regulates pressure at a clutch for transmitting torque from an engine to a drive train through a continuously variable transmission. A positive torque value is determined for each throttle setting and provided as a pressure input signal. Engine speed is monitored through a closed loop feedback system to provide an error signal to the desired pressure setting. A pressure control loop monitors pressure at the clutch through a closed loop feedback system to maintain the pressure at the clutch at a desired level. Filtering is provided in the torque and engine speed loops to provide for a more realistic response to driver demand. Incorporation of belt ratio factor in the engine speed control loop further provides for consistent and accurate response to driver demand variations at differing transmission drive levels. Overall line pressure within the associated hydraulic system further controls a proportional gain in the pressure control loop to provide appropriate response.

Abstract: A clutch control system for a continuously variable transmission includes a mode determination system which samples input signals including position of the neutral-drive selector, driver demand, engine speed, vehicle speed, and clutch input speed. From these signals the operating mode is determined and the clutch control system operating mode is set. In starting the vehicle, a minor pressure feedback loop and a major engine speed feedback loop are used. When the clutch is locked up, these control loops are not employed in regulating the vehicle operation.

Abstract: An upshift gear ratio change is made in an automatic transmission by monitoring the driveline torque and operating a closed loop control system in response to that torque to in turn control the torque to obtain a desired shift. Shift quality is optimized, while torque transients are minimized, by initially closing the loop at the end of the static phase of the upshift when the driveline torque drops to its minimum turnaround point, the torque thereafter being controlled such that it increases from the turnaround point at a specified rate and in accordance with a predetermined first ramp command. As the increasing driveline torque then reaches a prescribed reset level, at an early stage in the dynamic phase, the closed loop control system is released and reset in order to control the torque in accordance with a second ramp command, the second ramp, that the torque is made to follow, thereby starting at a higher level than the first ramp.