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          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

  Electric-hydraulic actuator




This is an electric-hydraulic control element, which is controlled through the CAN-Bus and which operates the clutch in heavy utility vehicles. A 24V, up to 350 W powerful electric motor provides more than 6000 N through the suitable hydraulics, to move a slave cylinder more than 20 centimeters. Thus, in the end, brake-, clutch fluid or mineral oil is passed through, e.g., the clutch system for the purpose of disengaging it.

Corresponding to the size of the trucks, this component is 33 centimeters long and weighs 8 kilogramms. It can also be flanged onto the outside of an internal cumbustion engine because it can withstand temperatures of up to 110C. As it is shown here, it can not only be applied to hydraulically operated clutches, it can basically, manage all setting-tasks which are electrically controlled.

This could then could also be the engaging of a switchable locking differential or the clutching of automated transmissions, in models with two pistons also in twin-clutch gearboxes. It is important here, that controlled pressure is built up, which e.g., predestines this actuator for use in traction control. Pressures of up to 200 bar are possible.

The DC-motor functions without brushes, which benefits it's service life and it's construction length. Internally, through a type of ball-bearinged spindle and a certain gear ratio, it drives a hydraulic piston. The pressure build-up takes place in a plastic casing and is supervised by a sensor. The regulation-electronics are accomodated in a space-saving manner.

The drive-motor is also called a BrushLess Direct Current-motor. In the meantime it is wdely used in motor vehicles, indeed, mostly as a small power unit with less performance. With the increasing amount of power saving and the turning to electric power units, it's number will increase even more. Of course, the small motors also play a very important role as far as comfort is concerned and are less important in the safety area.

The electric unit in action here is a typical short period drive. Indeed, during these short phases, it must apply a high amount of precisely regulated torque. Even learner-drivers learn, discover that being able to let the clutch in and out, is one of the more difficult tasks, because it shouldn't carried out be either too quickly or too slowly.

This could be quite clearly seen, when the first vehicles with an electric clutch were parking in reverse gear. Generally speaking, the actuators have a harder time than those running continuously, even moreso, when trucks carrying heavy loads are to be moved. In this case by the way, the hydraulics do have a certain amount of dampening effect.

The brushless electric motor is not possible without the help from electronics. They control, through suitable switching, the coils which are to be electrified by power-transistors as part of the stator-winding. The thereby occurring alternating-current portions are eliminated by a condenser. The stator-field differs depending on whether it's dealing with a continuous-, or a short period drive. A current limitation, through a certain length of serial switch on/switch off operations (pulse width modulation) is also often necessary.

One essential disadvantage of the high-performance DC-motor is it's high price. This alone is shown clearly by the fact that e.g., the Bosch Company also manufactures modern, small starters with customary commutators in the price-sensitive field. 01/14






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Translator: Don Leslie - Email: lesdon@t-online.de

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