Introduction to the Anti-jerk function of new energy vehicle speed

Anti-jerk function is used in both new energy vehicles and traditional engine vehicles. However, the anti-jerk function of traditional vehicles is implemented in VCU or ECU, while that of new energy vehicles is implemented in MCU or VCU. For new energy vehicles, most OEMs require MCU to have anti-jerk function. When the car is driving, the driving torque is generated from the power system and transmitted to the wheel side of the vehicle, which goes through multiple links.

Due to the existence of elastic elements and transmission chain gaps in some links, the originally complex power output becomes even more confusing. During the vehicle driving calibration process, many driving problems are often encountered, such as Tip in Bump, Tip in Shock, Tip in Hesitation, Tip in surge, Tip in Stumble, Tip in retard, Tip out Shock, Tip out Surge, etc. These problems are more likely to occur on roads with low adhesion coefficients, such as ice.

However, these problems are more or less related to the anti-jerk function, which is a magical function that can suppress all kinds of disobedience. However, if you are not familiar with its temper, it will bring you all kinds of disobedience and all kinds of unexpected shocks. Let's introduce the Anti-jerk function below.

1. The concept of image stabilization

The sudden change of the output torque of the power transmission system causes the vehicle speed to fluctuate. In order to understand how the vehicle speed fluctuates, we make the following analysis. As shown in Figure 1, the vehicle speed is divided into: constant speed, acceleration, and speed fluctuation.

Figure 1. Components of vehicle speed

If you still don't understand the components of vehicle speed, then think of vehicle speed as a wave, which is composed of three waveforms: vehicle speed constant wave, acceleration wave and vehicle speed oscillation wave. See Figure 2.

Figure 2. Schematic diagram of vehicle speed components

When the anti-shake function detects the jitter of the vehicle speed, it will filter out the jitter of the vehicle speed, and then add a certain amount of anti-shake torque to the reference torque according to the magnitude of the vehicle speed jitter, so as to eliminate the speed jitter. As shown in Figure 3.

Based on the above block diagram, the anti-shake function can be understood as: filtering the vehicle speed and then multiplying it by the coefficient K to obtain the "anti-shake torque". Therefore, the key points of the anti-shake function are:

• Filter the vehicle speed and extract the “vehicle speed jitter”;

• The coefficient K that converts the “vehicle speed vibration” into the “anti-vibration torque”.

2. Modules of the anti-shake function

Based on the above concept of anti-shake function, we further subdivide it and obtain the modules of anti-shake function, as shown in Figure 4.

1). **Low-pass filter_1 ** is used to filter out the random noise of the measurement signal (i.e., vehicle speed signal), which is also a common method of low-pass filtering;

2). High-pass filter_1 is used to filter out the constant component of vehicle speed;

3). **High-pass filter_2 ** is used to filter out the acceleration component of vehicle speed;

4). The converter is used to convert the speed jitter into the jitter-eliminating torque. The unit of the conversion coefficient K is: Nm/rpm;

5). **Low-pass filter_2 ** is used to make the signal smoother after high-pass filtering, avoiding the peak wave caused by the high-pass filter;

6). The delay trigger is to ensure that the de-jitter torque takes effect at the right time, and to avoid time delays caused by sampling, calculation, etc. In layman's terms: it is to make the maximum de-jitter torque take effect as close to the peak of the speed waveform as possible each time, so as to achieve a better de-jitter effect.

7). The torque limit module is based on safety considerations and sets the maximum threshold of the de-jitter torque to avoid safety accidents caused by a large difference between the reference torque and the target torque under certain extremely special working conditions.

In addition, the following factors need to be considered when modeling:

Different gears have different speed ratios and gear gaps; factors such as the speed difference caused by clutch slip contact will cause the input signal (i.e., speed signal) to be amplified or reduced by different ratios, and at the same time, the speed jitter will be amplified or reduced by different ratios. Therefore, the amplification or reduction ratio of the high-pass filter input signal needs to be adjusted accordingly.

**3. **Example

Here is a speed jitter condition we encountered: the vehicle was driving on a low-adhesion road, the driver stepped on the accelerator suddenly, the TCS system detected tire slippage, and immediately limited the requested torque. During this process, the vehicle speed jittered greatly, as shown in Figure 5. After a little calibration, the speed jitter was greatly improved.

Items slightly calibrated for anti-jerk function:

• Adjust the coefficient of the amplification of the high-pass filter input signal;

• Adjusts the point in time when the debounce torque in the trigger intervenes.

Figure 5. Example before and after stabilization calibration

As mentioned at the beginning of the article: Anti-jerk function is a magical function. If you are not familiar with its temper, it will bring you all kinds of disobedience and unexpected shocks. If it is not used properly, it will have a negative effect under certain working conditions, as shown in Figure 5 before calibration.