New Concept of Automatic Control for a Passenger Car Clutch

Abstract

This paper highlights the main functions of clutch automatic control systems. These are: forced clutch disengagement during gear shifting and when the engine falls below its minimum operating speed; forced clutch engagement under conditions of increasing engine speed or vehicle speed at a preset level or at a definite throttle position; adjustment of clutch friction torque, depending on the control parameter used. To achieve this, a closed-loop automatic control system is required. The system compares control signals with feedback from a selected parameter and generates commands for changing clutch friction torque. At present some automatic clutch systems use either the position of the accelerator pedal (‘Drivematic’ and ‘Guidosimplex’) or engine speed (ACTS) as the control parameter. The feedback parameter in these systems is the position of the clutch drive element. Comparison of the two systems shows that those using engine speed as the control parameter are more advanced, although their design is more complex. Engine speed is also used in the system of automatic electrovacuum friction clutch control (EPS) designed at the Central Automobile and Automobile Engine Scientific Research Institute (NAMI), but the principle of operation is totally different from existing systems. Particular features of this system are as follows: all necessary modes of automatic control are provided by only one multi-function electromagnet acting on the vacuum valve in the clutch actuating servo chamber; the feedback is dependent on the position of the clutch actuator and is provided by a spring acting on the armature of the valve drive electromagnet—the force of this spring changes in proportion to the position of the clutch actuator; clutch friction torque control as a function of engine speed is provided by changing the current strength in the electromagnetic winding—these changes are initiated by the electronic control unit of the automatic control system. To achieve the optimal performance of modern high-speed engines in combination with an automatic clutch system, all elements of the clutch control system must have minimal delay in converting input signals into control signals. This requirement resulted from an investigation of the EPS mathematical model comprising three non-periodic dynamic elements. The same results were experimentally proved when amplitude and phase frequency characteristics of the control system were measured. It was shown in particular that the time constants of dynamic elements must not exceed 0.04–0.06 s. This required the application of a brand new engineering circuit for designing the EPS electronic unit. The EPS system is now in mass production and is standard equipment for some models of small passenger cars manufactured in the former Soviet Union. The system has been patented in the United States, Japan, Germany, Great Britain, France and Italy.