THE RIGHT SENSORS IN THE ELECTRIC CAR
An ever-increasing demand for torque information is needed not only in internal combustion engines for map control, but also in electric vehicles. On the one hand, torque is the power factor for the vehicle, but on the other hand it is also a decisive factor when it comes to driving comfort.
Why sensors are important in electric cars
In electric drives for cars, in the future the output of the electric motor will be almost directly connected to the drive axle. Thus, in many cases there is no gear or only a very rudimentary one in between. This direct connection results in the torque delivered by the electric motor acting directly on the drive shaft, i.e. resulting in a direct flow of power. This direct force flow must be considered with regard to safety aspects. A failure of the electric motor or an unwanted power output has a direct effect on the driving behaviour of the vehicle. It is therefore necessary to install many additional sensors for series use in order to intercept or check the validity of faults in order to initiate suitable emergency shutdowns. Not only from the electric motor to the drive, but also force effects from the road have a direct effect on the electric motor. These bidirectional force flows have to be measured, controlled and evaluated in the functional safety circuits in series applications. With a torque sensor that can measure the power directly on the drive shaft, it is possible to
collect this safety-relevant information and pass it on to the controller.
How to use torque sensors in cars?
- Transmission: Electric transmissions are often controlled by torque
- Axle drive: electric motors are placed on the front or rear axle
- ABS: The torque sensor can also measure the resulting force
- Direct drive: there are already electric drives in wheels for driving and braking
How torque sensors can also measure wheel drives
This is still easy when electric motors are used for the entire vehicle. When wheel drives are used, it becomes more difficult. Each drive on each wheel
has its own performance behavior, which can be calibrated to each other, but can be detuned by aging effects. The tuning of these electric motors determines the driving behaviour of the vehicle. Without a direct measurement of parameters at the electric motor output, it is almost impossible to determine the driving behavior of the vehicle. With the use of torque sensors on these electric motors, the behaviour of each individual electric motor can be measured instantaneously and used as a setpoint input into the control unit to regulate the motors.
The sensors are also relevant in these areas
Not only the direct drive, but also the driving comfort can be improved by means of force sensors. For example, torque sensors on the limited slip differential can be used to precisely regulate the torque on the individual wheel, resulting in optimum cornering performance for the car. The information required for torque vectoring can not only improve driving dynamics. In principle, they can also be used to measure wheel slip and serve as a control variable for anti-slip control. In addition to these classic applications for torque sensors, there are other areas of application in e-mobility. For example, sensors can be used to directly measure the vehicle‘s weight and determine how much additional load has been absorbed. This information is important for determining consumption or as an input variable for the acceleration and deceleration behaviour of the vehicle. There are other possible applications in the area of steering for measuring steering forces.
