Experimental Investigation of Power Hop in Passenger Cars 2015-01-2185

In this paper the power hop phenomenon is analyzed and important influencing factors are investigated. The results of driving tests on various road surfaces with different types of cars with longitudinal and transversal mounted engines as well as with front and rear wheel drive are presented. In order to understand and quantify the power hop effect the rotational speed of the individual wheels and the engine are measured. Additionally, the drive shaft torque, the engine movement in its bearings and the vertical deflection of the wheel with respect to the chassis are determined to get detailed knowledge about physical dependencies. It is shown that the rotational speed of the driven wheels is not a sufficient indicator to assess the occurrence of power hop by measurements. Alternatively, the measured longitudinal acceleration at the seat rail provides a good quantification. Nevertheless a detailed analysis of the rotational speed of the driven wheels points out great variations of the amplitude and frequency in dependence of the car. In case of power hop, the sensor information of the engine displacement as well as the drive shaft torque and the rotational speed of the driven wheels show the same frequencies. It is illustrated that the absolute value of the engine torque during acceleration has smaller effect on the power hop frequency but greater impact on the intensity and duration of the oscillations. As a result, it is concluded that a suitable control of the engine torque during acceleration might reduce the phenomenon of power hop.