New Control Concept for Haldex Limited Slip Coupling

Sammanfattning: The aim of this master thesis is to investigate a new control principal for Haldex Limited Slip Coupling. HLSC can be characterized as a hydraulic slip coupling intended to be part of a 4WD-system for passenger vehicles fitted between the front and rear axle. The investigation is to be both theoretical and practical. The current system can be described with the three following functional blocks:

A pump which delivers an even flow proportional to the number of differential revolutions. A controllable throttle valve with an Electronic Control Unit. A wet multi-plate clutch which transfers the torque.

This solution has several advantages and one disadvantage, it's temperature dependency. The effect is today compensated by the throttle's position via the ECU. The new control principal to be examined is made by replacing the throttle valve, including its ECU, by a system containing:

A proportional pressure relief valve, measurement of the rotational and a new ECU.

Tests have been performed on three different proportional valves (p.v.) along with reference testing with the throttle valve (t.v.). The general conclusions from the testing and the time delay simulation are:

The p.v. have a stable behaviour during most of the temperature range, with smaller variation than the t.v. The deviation becomes significant in the neighborhood of temperatures below -10C. The p.v. have a large number of parameters to be optimized for maximum performance, such as feeding current, system dependency and internal construction. The delays in the information of the numbers of differential revolutions are acceptable. The tested control principle works and shows potential to be as fast as the current system. The new principle offers a number of new approached in HLSC, i.e. one can change the control characteristics to being more flexible or make changes in the pump without loss of performance.