Caterpillar Inc.

Philip C McKenzie

Noel J Rytter

Randall M Mitchell

Tony L Marcott

Lowell E Johnson

Michael F Coffman

Ashok K Kajjam

Dwight S Holloway

David W Bump, Deceased

Clutches in multi-speed transmission have been initially calibrated in an attempt to determine the point at which the clutch is filled and thus reduce the harshness of engagement of the elements within the clutches during future gear ratio changes in the transmission when being worked under normal conditions. In these earlier attempts at calibrating the clutches, the desired pressure level needed to fill the clutch was either empirically derived or calibrated by incrementally increasing or stepping the pressure level from a minimum value to the required value. In the subject invention, the clutches are calibrated by using a method of calibration that is substantially the same method that is used during normal operating conditions. By using substantially the same method, any effects of 'hysteresis' of the associated valving is basically eliminated.

Method of calibrating clutches in a transmission

A vehicle such as an earthmoving wheel loader has an engine, a torque converter having an impeller element, a reactor element and a turbine element, and an input clutch connected between the engine and the impeller element. An electrohydraulic control device is provided to controllably engage the input clutch and that includes a microprocessor-based electronic control module, an actuator mechanism having a control member that is progressively movable between first, second and third positions to deliver a first electrical signal to the electronic control module, and a valve for directing fluid to the input clutch at a decreasing pressure level when the control member is moved from the first to the second positions in response to another signal from the electronic control module. The electronic control module is programmed to maintain at least a minimal pressure level to the actuating piston of the input clutch when the control member is between the second and third positions. Moreover, a service brake is increasingly engaged by a service brake mechanism in response to the control member moving between the second and third positions. Other logic functions are included to control the input clutch and a lockup clutch connected between the engine and the turbine element.

Electrohydraulic control device for a drive train of a vehicle

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Peoria, IL, United States of America

Philip C McKenzie