Drive unit vibration damping support for electric motor-driven vehicle

1. A drive unit vibration damping support for use in an electric motor-driven vehicle to provide vibration damped support of a drive unit including an electric motor on a vehicle body, comprising:

a first vibration damping device being adapted to support the drive unit in vibration damping fashion on a subframe; and

a second vibration damping device being adapted to support the subframe in vibration damping fashion on the vehicle body,

wherein a spring constant of the first vibration damping device in a direction of input of torque reaction force of the electric motor is set to a greater value than a spring constant of the second vibration damping device; and

wherein an average of a distance between a torque roll axis of the drive unit and the second vibration damping device is set to a greater value as compared with an average of a distance between the torque roll axis and the first vibration damping device.

2. The drive unit vibration damping support for an electric motor-driven vehicle according to claim 1 , wherein:

the subframe is supported in vibration damping fashion on the vehicle body by a plurality of the second vibration damping devices situated towards a front end and towards a rear end of the vehicle;

support spring characteristics of the drive unit by the second vibration damping devices situated towards the front end differ from support spring characteristics of the drive unit by the second vibration damping devices situated towards the rear end; and

pitching resonance and bouncing resonance in the subframe are generated in coupled fashion.

3. The drive unit vibration damping support for an electric motor-driven vehicle according to claim 2 , wherein:

in a fundamental mode of vibration arising from coupling of pitching vibration and bouncing vibration in the subframe, a node of a vibration mode is biased towards either one of the front end and the rear end of the vehicle; and

of the plurality of second vibration damping devices situated towards the front end and the rear end of the vehicle, one of the second vibration damping devices situated a longer distance away from the node of the vibration mode have higher attenuation characteristics in a direction of input of pitching vibration and bouncing vibration, than another of the second vibration damping devices situated a shorter distance away from the node of the vibration mode.

4. The drive unit vibration damping support for an electric motor-driven vehicle according to claim 1 , wherein the drive unit is loaded onto the subframe via the first vibration damping device, and the subframe is subjected to a weight of the drive unit in addition to the drive torque reaction force of the drive unit.

5. The drive unit vibration damping support for an electric motor-driven vehicle according to claim 1 , wherein:

the drive unit is installed inside a rim of a vehicle wheel to constitute an in-wheel motor structure; and

the drive unit is connected to and supported on the subframe via a wheel assembly suspension member, and the first vibration damping device is constituted by a suspension vibration damping device disposed in a zone of transmission of the torque reaction force of the drive unit from the wheel assembly suspension member to the subframe.

6. The drive unit vibration damping support for an electric motor-driven vehicle according to claim 5 , wherein at least one of a shock absorber and a spring installed between the vehicle wheel and the vehicle body is attached to the vehicle body via the subframe.