Application of Hydraulically Controlled Rear Mount to Mitigate Key on/off Requirement of Passenger Car

Key on/off (KOKO) Vibration plays a vital role in the quality of NVH (Noise Vibration and Harshness) on a vehicle. A good KOKO experience on the vehicle is desirable for every customer. The vibration transfer to the vehicle can be refined either by reducing the source vibrations or improving isolation efficiency. For the engine mounting system of passenger cars, the mounts are an isolating element between the powertrain and receiver. Various noise, Vibration, and harshness criteria must be fulfilled by mounting system performance like driver seat rail vibration (DSR), tip-in/tip-out, judder performance, DSR at idle and Key on/off Vibration. Out of these requirements, in the paper, the investigation is done on KOKO improvement without affecting other NVH parameters related to mount performance. Higher damping is required to isolate Vibration generated during the Key-on event, and lower damping is required during the idle condition of the vehicle. These contradictory damping requirements can only be fulfilled by something other than conventional rubber mounts. The proposed solution is designed to have different damping during Key on and idle vehicle conditions. Increasing the mounting system damping can decrease the KOKO vibration by absorbing the energy during the event. As a result, the hydraulically controlled switchable rear mount is proposed, which can provide high damping during KOKO events but switches to lower damping to isolate vibrations under idle conditions. The level of damping is controlled by the proper design of the bypass channel and piston movement. The effect of damping is validated at the rig level to get the required performance at the vehicle level. The physically prototyped performance is demonstrated on the vehicle, which this paper explains.