The Optimized Design of the Exhaust Brake of the Automotive Diesel Engine

Exhaust brake performance is an important factor in the design of the automotive diesel engine. Many devices have been developed to achieve a higher exhaust brake force; however, most of these are complicated and expensive. This paper deals with an optimised design method for the exhaust brake system based on conventional engine components. The component design was optimised by use of a simulation program for exhaust valve behaviour and pulsating pressure waves in the exhaust pipe, which was developed at Isuzu Motors Ltd. based on an existing program.

It was found that the predictions from the computer simulation agreed well with the measured data, not only in respect of exhaust brake force but also valve bounce, exhaust port pressure and so on. The simulation program proved to be a useful means of predicting the effect of various brake design parameters, and enabled an optimised exhaust brake system to be achieved at the design stage. The original exhaust brake force obtained on a particular turbocharged diesel engine was a mean effective pressure of 0.56MPa at rated speed. Modification of the existing exhaust manifold configuration, which took better account of the pulsating pressure available therein, increased braking mean effective pressure to 0.74MPa. A braking mean effective pressure of 0.90MPa, corresponding to 103% of the rated power, was achieved by adopting a specially designed valve spring.