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The conventional diesel engine retarder is an add-on system that converts the power producing diesel engine into a power absorber by altering engine valve timing when vehicle retarding is desired. The retarding effect is achieved by releasing the compressed air charge near TDC compression to prevent energy from returning to the engine during expansion. Retarding performance is optimized only at one engine speed and the increased height due to the add-on approach is a disadvantage for some vehicle applications. This study introduces an integrated Variable Valve Timing (VVT) engine retarder (Figure 1) by applying the lost motion principle. The integrated retarding system has significant dimensional advantage over the conventional add-on engine retarder. The lost motion VVT retarder also provides optimized retarding performance over the entire engine operating range.

Variable Valve Actuation has been researched and applied to improve engine fuel economy and emissions. The effect on compression release engine retarding has not been considered. Heavy duty diesel engines are recognized for their ability to function as effective vehicle retarders. Many approaches have been taken to convert the power producing diesel engine into a power absorber by altering air flow management. Compression release diesel engine retarding is generated by altering engine valve timing when braking is desired. By releasing the compressed air charge at near TDC compression, the energy absorbed is prevented from returning to the engine during expansion. The net energy loss provides the braking effect. This study discusses the parameters used in system design to achieve maximum performance by using variable valve actuation, VVA, to produce the brake event. Retarding power potential is evaluated by cycle analysis for each system and supported by engine test data.

Diesel engine retarder performance varies as environment conditions change. An understanding of the mechanisms that produce this variance is gained through analytical consideration of ambient temperature, pressure and air moisture content. Retarding performance is quantified in an analytical model sensitive to these ambient parameters and their effect on system operating efficiency. Computer simulation is used to study the impact of ambient parameters on the turbocharged diesel engine and the compression release engine brake for a wide range of operating environments. Correlation with road performance is made to illustrate environment impact on maintained heavy vehicle downhill road speed.