A control system for a continuously variable transmission has a transmission ratio control valve having a spool for controlling oil supplied to a cylinder of a drive pulley to change the transmission ratio. The control system operates to control the transmission ratio in accordance with a desired ratio including a desired overdrive ratio for providing an overdrive transmission ratio. In a low vehicle speed range, the overdrive transmission ratio is controlled to a value slightly larger than the overdrive transmission ratio.

Transmission ratio control system for a continuously variable transmission

A control system and method for a power delivery system, such as in an automotive vehicle, having an engine coupled to a continuously variable ratio transmission (CVT). Totally independent control of engine and transmission enable the engine to precisely follow a desired operating characteristic, such as the ideal operating line for low fuel consumption. CVT ratio is controlled as a function of commanded desired system performance (e.g., power or torque) and measured actual system performance, such as CVT torque output, while engine fuel requirements (e.g., throttle position) are strictly a function of measured engine speed. Fuel requirements are therefore precisely adjusted in accordance with the ideal characteristics for any load placed on the engine. Appropriate controls prevent anomalous engine and vehicle behavior, and allow for transient start-up from rest.

Control system and method for a power delivery system having a continuously variable ratio transmission

A method and apparatus for controlling a plurality of subsystems (66, 70) associated with an agricultural vehicle such as a tractor. Examples of such subsystems in a tractor are hitch positioning, power take off (PTO), multiple range transmissions, differential lock, diesel fuel injection, and the like. A unified control system is provided including a central control unit having a first microprocessor (56) and a plurality of subservient control units each having a microprocessor (58, 60). Each of the subservient control unit microprocessors (58, 60) are connected for controlling at least one subsystem (66, 70) and for sensing the operating conditions of at least a single subsystem (66, 70) using sensors (68, 72). The subservient control unit microprocessors (58, 60) are also connected to the central control unit microprocessor (56) which controls communication between the subservient control unit microprocessors (58, 60). Various control criteria, including desired relationships among various subsets of the conditions, are stored in memories associated with the microprocessors. The microprocessors cycle through a series of subroutines in which various subsets of conditions are compared with the target, or desired relationships. Control signals are generated by the microprocessors for controlling the individual subsystems to bring the conditions thereof to the targeted relationships. Such relationships include, but are not limited to engine advance characteristics as a function of engine RPM and torque, transmission shift points, criteria for overriding a draft control for hitch positioning, and the like.

Electronic tractor control

A continuously variable transmission (CVT) with adjustable width pulleys has its belt tension and ratio controlled by an electronic-hydraulic system. The CVT also has a fluid-cooled clutch on the output pulley shaft. The engine speed, transmission output speed, throttle position, and gearshift position are sensed, and signals representing this information are passed to a computer. The computer provides set point signals denoting desired engine speed, line pressure, and clutch cooling condition to a control system. An electromechanical valve assembly regulates fluid flow to the CVT primary sheave, to control CVT ratio as a function of the computer provided set engine speed signal. A second electromechanical valve assembly controls the line pressure in the hydraulic system, which is applied to the secondary pulley to maintain belt tension, as a function of the set pressure signal provided by the computer. A solenoid-operated valve, regulated by the control system, either returns waste fluid from the second valve assembly directly to sump, or passes the fluid to the clutch when cooling is indicated.

Control arrangement for a variable pulley transmission

A function generator circuit is provided which generates a target engine revolution speed electric signal indicative of a target engine revolution speed which is a first predetermined function of an accelerator pedal stroke electric signal indicative of a depression degree of an accelerator pedal. There is also provided another function generator circuit which generates a target engine torque electric signal indicative of a target engine torque which is a second predetermined function of the accelerator pedal stroke electric signal. A comparator compares the actual and target engine revolution speed electric signals and generates a deviation signal indicative of a difference between these signals. A shift control varies a reduction ratio in the continuously variable transmission to vary the revolution speed of the engine in a direction to reduce the deviation signal. A fuel supply device is controlled in response to the target engine torque electric signal so as to supply a fuel enough for production of the target engine torque.

Control apparatus and method for engine-continuously variable transmission

An automatic speed ratio control system of the integration servo mechanism type for a stepless transmission of an automotive vehicle. Speed ratio is controlled by a hydraulic pump motor of variable displacement type, which in turn is controlled by an actuator having a piston and a cylinder to which hydraulic oil is supplied. The system comprises a target value generator which produces a target value for an engine speed corresponding to a throttle opening or an output torque of an engine, or which produces a target value for an engine output torque corresponding to a throttle opening or an engine speed; a detector for producing a signal indicative of an engine speed or an output torque of an engine; a control signal generator for comparing the signal from the detector against the signal from the target value generator to produce a control signal in accordance with a deviation therebetween; and a controller responsive to the control signal to drive the actuator to change a speed ratio of the stepless transmission. The system is characterized by further comprising means for controlling a gain of the alteration rate of the speed ratio in response to a rotational speed of an output shaft of the stepless transmission to increase the alteration rate when the rotational speed of the output shaft is low and decrease the alteration rate when the rotational speed of the output shaft is high.

Automatic speed ratio control system for stepless transmission of automotive vehicles

A speed ratio control system for a stepless variable speed transmission of vehicles having an electronic fuel injection control system. A speed ratio control signal for controlling the speed ratio of the stepless variable speed transmission is produced from the output fuel injection control signal from the electronic fuel injection control system and a target fuel injection quantity signal from an electronic arithmetic unit which generates the target fuel injection quantity signal in response to a throttle opening indication signal. The output fuel injection control signal is compared with the target fuel injection quantity signal to generate the speed ratio control signal which controls the speed ratio of the stepless variable speed transmission until the fuel injection indicated by the fuel injection from the electronic fuel injection system becomes equal to the target fuel injection quantity.

Speed ratio control system for stepless transmission of vehicles

A control system for a stepless variable speed transmission of power splitting type for use in a vehicle in which the power from an engine is transmitted with a controllable speed and wherein part of the power is converted into hydraulic power by means of hydraulic pump motor. The system comprises an up shift valve which switches a hydraulic pressure of a clutch and brake in the transmission to change the transmission to a high speed ratio range when a speed ratio increasing hydraulic pressure in a speed ratio control actuator exceeds a given value, a down shift valve which switches the hydraulic pressure of the clutch and brake to change the transmission to a low speed ratio range when a speed ratio decreasing hydraulic pressure exceeds a given value and a directional control valve which reverse the direction of the speed ratio increasing and the speed ratio decreasing hydraulic pressure to the actuator in accordance with a pressure difference between the hydraulic pressure of the clutch and brake in the low speed ratio range and the hydraulic pressure of the clutch and brake in the high speed range.

Kiyofumi Mizuno

Papers

Automatic speed ratio control system for stepless transmission of automotive vehicles

Speed ratio control system for stepless transmission of vehicles

Control system for a stepless variable speed transmission