After reliability and safety, flexibility and adaptability are the most important requirements of the electromechanical clutch – the new generation of commercial vehicle transmission system. These requirements are core values for thread specialist Eichenberger Gewinde, who are leading the way in the rolling (cold forming) of threads in the manufacture of ballscrews, leadscrews and nuts for use in electromechanical clutches. Using their expert knowledge and cutting edge production methods, Eichenberger’s technicians work closely with clients to achieve innovative, individual solutions.
Never before have we, as engineers, and in the wider society, been so aware of the importance of conserving scarce natural resources. But how do you preserve resources, conserve energy, systemise procedures, optimise processes and reduce operating costs when customer requirements are becoming more and more demanding? New technologies are clearly the answer to meet all of these demands.
Using a ballscrew in optimised applications
In one of the first automated transmission systems on the market, Eichenberger has developed the critical structural element for a cutting edge, automatic version of the clutch, taking it from a one-off prototype to series production. Using a cold-formed steel ballscrew of diameter 12mm and pitch 3mm, this novel clutch is able to fully engage even at low motor rotation speeds by merely pressing a switch. Operating the clutch is also adapted according to information supplied by a tilt sensor and the required starting gear, while the motor rotation speed can be increased for a smooth start if required. The clutch does not slip when it is used, meaning the speed of the mechanisms in frictional contact does not deviate. The clutch, therefore, is a hundred percent efficient at disconnecting the transmission from the engine. This efficiency effectively protects the clutch and other drive train components against mechanical overloading.
Frequent gear shifting is unavoidable with commercial vehicles in urban environments. Normally this increases clutch plate wear, and the necessity for subsequent replacement. However, Eichenberger’s novel clutch system reduces wear, increasing its service life and positively impacting maintenance and fuel costs.
Nothing is impossible
The smoothly coordinated shifting process, that moves a load of 3500 N in 0.02 seconds, demands the ultimate in terms of dynamic response. This took fully six years of fundamental research and development time in drive and lubrication fields, and it was found that only a ballscrew can stand up to these incisive demands between dynamic forces and momentum. Eichenberger’s robust Carry ballscrew meets these demands impressively. Moreover, thread rolling has an extremely positive impact on the roughness value of the thread flanks and the base radius, resulting in very low notch sensitivity.
Lifetime lubrication is demanding and difficult to guarantee. With seven-digit load changes at around 4000 RPM, achieving the impressive 90% efficiency factor of the Carry ballscrew for the entire service life required extensive tests. Some of the endurance tests lasted nine months, while lubrication tests to achieve the service life took more than two years. Eichenberger used their proven steel tube type ball return system for the 12 x 3 ballscrew, and a highly efficient connection of the deflection pipe was realised as a result of the developments.
Optimum interplay of spindles, nuts, balls and lubrication
Solution-oriented dialogue with the customer is, for Eichenberger, one the most important of all success factors. Customer-specific requirements regarding dynamic response, precision, load, speed, and service life are challenging, but, through teamwork, the perfect interplay of spindles, nuts, balls and lubrication achieved the desired results. A hundred percent inspection is performed on a special test stand due to the tight tolerances for torque, axial play and concentricity. The ballscrew unit with the special “inner life of the nut” is marked with a laser, and a registered data matrix code makes the contents of the final inspection traceable in a perfect ratio of one to one.
