Cylinder reducing downsizing engine has an effective means for fuel efficiency. However replacing a V6 cylinder with an in-line 4cylinder while maintaining engine torque performance, higher compression ratio per cylinder is required and increase engine vibration which will effect NVH vehicle performance in high frequency band (Fig.1). Weight will be needed with current technology to recover NVH performance and is a tradeoff to fuel efficiency.
Fig.1 Vibration increase by FE improvement
The world first Active Torque Rod was develop to recover high frequency band NVH performance applied with a light weight engine mount system, designing the torque rod Eigen frequency to a lower frequency band and using active control technology. For the active control function a world first liner characteristic inertia mass actuator was develop. This actuator is equipped with a function which converts a G-sensor acceleration signal to a velocity signal, and this function will realize a proportional-speed damping control system with an acceleration signal.
2. Technology details
2.1 System construction and vibration reduction theory
Pendulum engine mounting system is which right and left engine mounts are to support the engine weight and torque rod to support the engine torque. Pendulum engine mounting system has advantage with weight saving, however disadvantage in NVH performance in high drive torque load condition. To support a V6 cylinder like torque, Eigen frequency is drop to a lower frequency band under 200Hz, extending the isolation area to improve acceleration noise (Fig.2). 200Hz is an in-line 4cylinder 2nd order excitation range and this Eigen frequency will increase the vibration path in the booming noise. To prevent this, an inertia mass actuator is implanted inside the torque rod with a G-senor fixed on the side of torque rod body to feed back control damping force and lower level of Eigen frequency to improve booming noise. Using the actuator as an integrator to convert acceleration signal to a velocity signal, this system can be controlled by a simple function controller. (Fig.3).
Fig.2 Required function for mount system
Fig.3 Balancing damping and isolation with Active Torque Rod
2.2 Development of new inertia mass actuator
Torque rod Eigen frequency level can be lowered by increasing a bush damping factor, however this is a trade-off between isolation area in high frequency band. Therefore applying a proportional-speed damping force to the Eigen frequency, level can be lowered without affecting the isolation area. Even though the Eigen frequency is shift around 170Hz it is still a high frequency to control with a Non-linier characteristic solenoid type actuator used in a current active control mounts. A liner characteristic inertia mass actuator was develop based on new drive theory. The actuator moving mass is supported by a leaf spring and magnetic spring compactly constituted, using electrical steel sheet for a magnetic field to maintain a liner characteristic up to a high frequency band (Fig.4).
Fig.4 New inertia mass actuator
2.3 Adapting Axiomatic design
Axiomatic design is a design method to solve a conflict related function posited by Dr. Nam Pyo Suh (MIT) and used in this development.
A torque rod has two main function. One is to support an engine torque with a hard stiffness and second is to decrees stiffness to isolate engine vibration which is a conflict relation. First function is a static stiffness formed by a series bush stiffness and the second function is a parallel bush stiffness forming the rod Eigen frequency. Defining this relationship of the torque rod the two functions can be independently designed between the conflict function
2.4 Noise reduction effect
Acceleration noise level of in-line 4cylinder downsizing turbo with Active Torque Rod is shown in Fig5. compared with V6 cylinder vehicle.
Not only accomplishing a high quietness level in 250Hz~800Hz band but also saving 40% of system weight compared with current technology engine mount systems.
Fig5. Activing a V6 level NVH performance
To prevent global warming, improvement of engine thermal efficiency will cause engine vibration to increase, however Active Torque Rod prove that the two performance can balance. This technology can cover a wide band of booming noise and acceleration noise with one system and increase the possibility of multi-performance compatibility in a high level like weight reduction and fuel efficiency.
Masahiko Kondo *1
Koji Tanimura *2
Ryosuke Yamauchi *3
Akira Ueki *4
*1 Member, Nissan Motor Co., Ltd. Powertrain & EV Performance Engineering Dept.（560-2 Okatsukoku, Atsugi 243-0192）
*2 Nissan Motor Co., Ltd. Chassis Engineering Dept.（560-2 Okatsukoku, Atsugi 243-0192）
*3 Nissan Motor Co., Ltd. Powertrain & EV Performance Engineering Dept.（560-2 Okatsukoku, Atsugi 243-0192）
*4 Bridgestone Corporation Anti Vibration Products Development Dept. 1(1, Kashio-cho Totsuka-Ku 244-8510)
*5 Regular member, Sinfonia Technology Co., Ltd. R&D Center New Products Development Lab.(100 Takegahana-cho 516-8550)