A friction clutch coupling an engine and a gear transmission of a vehicle is controlled by a microprocessor based circuit using logic which defines operating modes according to engine and clutch conditions. During the time of clutch closure, when the vehicle is starting from rest in a startup or launch mode, the throttle or other engine control signal is restrained from quickly responding to the accelerator pedal. This avoids engine overspeeding which results from generating high torque before sufficient clutch capacity has been achieved. The control signal is developed as a function of the pedal position under control of throttle logic which, in turn, is dependent on clutch operating modes defined by the clutch logic. The clutch operating modes are four modes for automatic clutch operation comprising touch point approach mode which prohibits a throttle signal during initial clutch movement, creep mode or startup mode after touch point occurs, and lockup mode for completing clutch closing when low clutch slip is attained. A non-automatic mode is entered before the accelerator pedal is depressed or when engine stall conditions are detected.

Clutch Mode Control Logic

An electronically controlled continuously variable transmission system is provided with a driving belt trained over a primary and secondary pulley. The primary pulley is provided on a primary shaft and the secondary pulley is provided on a secondary shaft. Each pulley has corresponding spaced, conical pulley halves and at least one of the corresponding pulley halves is axially movable by respective primary and secondary moving devices. The transmission further includes a primary electronic control system for controlling the transmission ratio and a secondary electronic control system for controlling the belt tension. The primary electronic control system permits the operator to select from fuel economy, sporting, and maximum comfort performance modes. The primary electronic control means controls the transmission ratio in accordance with the performance mode selected. The moving devices include standby operating valves to permit continued operation of the transmission in case of power failure.

Electronically controlled continuously variable transmission

A method of controlling speed reduction ratio in a continuously variable speed transmission comprises the steps of setting a prescribed value of a parameter representing a driver's intention of acceleration and corresponding to an accelerator opening which is opened to a certain extent from a fully closed condition, setting a reference engine speed corresponding to the parameter so as to increase as said parameter increases from said prescribed parameter value when said parameter is in a range higher than said prescribed parameter value, setting said reference engine speed so as to increase as said parameter decreases from said prescribed parameter value when said parameter is in a range lower than said prescribed parameter value, and controlling said speed reduction ratio so that the engine speed coincides with said reference engine speed.

Method of controlling speed reduction ratio in a continuously variable speed transmission

A continuously-variable transmission (CVT) assembly is employed for transmitting a torque from an external power-source The CVT includes a variable-diameter input pulley and a variable-diameter output pulley, each having a respective range of adjustment The CVT also includes a continuous torque-transmitting element extending between the variable-diameter input pulley and the variable-diameter output pulley, and thereby operatively connecting the input pulley to the output pulley The CVT additionally includes a first elastic element having a first zero stiffness over the range of adjustment of the variable-diameter input pulley and configured to apply a first constant spring clamping force via the input pulley to the continuous torque-transmitting element Furthermore, the CVT includes a second elastic element having a second zero stiffness over the range of adjustment of the variable-diameter input pulley and configured to apply a second constant spring clamping force via the output pulley to the continuous torque-transmitting element

Continuously-variable transmission

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.

Continuously variable transmission line pressure control

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. For stable operation, the closed loop controller responds only to relatively slow changes of the setpoint. In response to fast changes, the closed loop controller is made ineffective so that the line pressure will be determined only by the open loop controller and will be greater than the level called for by the setpoint.

Control system for controlling the line pressure in a continuously variable transmission

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 (114) in conjunction with a limiter (116) and a filter (120) 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 (154) and combined (in 104) with a null signal (N0) to provide a signal (e4) 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. The integration function (154) may be used or bypassed at appropriate times to account for physical limitations in the possible range for the belt ratio. Full low and full overdrive conditions are provided through an open loop gain corresponding to maximum and minimum duty cycle signals.

Ratio control technique for continuously variable transmission

The system provides an improved clutch control system for use in a continuously variable transmission (18) system The system provides for generation of a clutch pressure setpoint (on 412) 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 (382) is monitored as a difference value and integrated (388) 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 (396) is monitored and a maximum torque schedule (398) used to provide a maximum torque signal to prevent driver demand from undesirably racing the engine in similar conditions A filtered output (406) of the maximum torque schedule provides a pressure setpoint signal (410) repre­sentative of actual driver demand which may be added to the clutch slip speed error signal (392) to generate the clutch pressure setpoint In this fashion, an engine may be loaded by an increase in the clutch pressure at the same time that the clutch input speed is returned to the clutch output speed to restore clutch lock up Addition of a constant value (388) to the clutch slip speed error signal ensures positive clutch lockup

Special start technique for continuously variable transmission clutch control

A pressure transducer (49), which senses clutch pressure and effects closed loop clutch control in a continuously variable transmission (25), 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 (29) in the transmission. Only a single transducer (49) 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 (86,75,74) 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 (86,93,75,74,78,49,79,88,89,91,92,94,95,96,97) establishes the line pressure at the setpoint. For stable operation, the closed loop controller responds only to relatively slow changes of the setpoint. In response to fast changes, the closed loop controller is made ineffective so that the line pressure will be determined only by the open loop controller and will be greater than the level called for by the setpoint.

William Paul Umlauf

Papers

Control system for controlling the line pressure in a continuously variable transmission

Ratio control technique for continuously variable transmission

Special start technique for continuously variable transmission clutch control

Control system for controlling line pressure in continuously variable transmission