Hydraulic Clutch Actuation Systems for Light Trucks

Abstract

ABSTRACT The clutch actuation system is directly linked to vehicle easy of operation and ergonomics. For passenger cars, a comfortable pedal force is considered light when it is under 100 N and hard if over 130 N. For Commercial vehicles, about 170 N are considered acceptable. This work looks forward to obtain a pedal curve in Excel which simulates the real one and can low down actuation systems developing time. For in such way, it points to cares about master cylinder actuation geometry, stroke and pedal effort variations in the way that it is comfortable for the driver, works on low hydraulic pressure and is able to keep functionality during whole clutch plate and disc life. Some calculations about lever and master cylinder push rod dimensions are realized in the way of keeping actuation angles drawing limits. Empirical evaluations about losses in components (hydraulic and mechanical) for determination of stroke of pedal and pedal effort actuation are also done. The need of an over center spring to low down pedal effort is also point of discussion, determining compromise between product costs and easy of operation. This paper leads to a virtual curve which relates pedal effort with pedal stroke and is composed from system and over center spring curve. INTRODUCTION This work came up with the need of increasing project effectiveness in the way of increasing durability, reducing costs and communization of components spending the lowest time as possible in practical verifications and measures. The objective of this work is generating a theoretical pedal curve which represents the real one. The validation is made using practical measurements Nowadays, one of the biggest companies’ worries is about cost of product. The components communization and after market cost reduction are focused. For getting those targets, the project conception must be based on acquired experiences, risk methods analysis [1] and tests which represent the real application. The actual innovation speed increases the hardness of this process. New vehicle launches come up with high frequency. A project that, ten years ago, would take two years to be finished must, nowadays, go through in six months or even less when it is about after sales problems. When the theme is about wearing components like springs, dampers brake and clutch systems, the problem is more critical because they depend directly from the way the drives run the vehicle. Even severe test cannot always detect failure modes. At the project conception, beyond quality cares, its necessary to give special attention for ergonomics and easy of operation The maximum force during pedal actuation is named pedal force. It direct function from cover assembly pressure and system lever relations including pedal itself. It means that for a more powerful vehicle, the pedal force will increase. Growing the system relations can decrease pedal force, but will affect pedal stroke. [2] says that a comfortable passenger car pedal force must be between 100N and 130. For light commercial vehicle values between 150N and 180N are acceptable. The clutch pedal lever conception says that it must be operated for the driver left leg. It must be located about 80 mm from the middle of the driver seat to the right