A brief analysis of the impact of CLTC on new energy three-in-one electric drive systems (Part 1)

Introduction: This paper compares and analyzes the characteristic parameters of NEDC/WLTP/CLTC cycle conditions, and based on the vehicle parameters of a pure electric passenger car, compares and analyzes the characteristics of different cycle conditions from the dimensions of power distribution, high-efficiency area distribution, average efficiency, power consumption, and brake energy recovery ratio. Combined with the working principle and key technical indicators of the three-in-one electric drive system, this paper analyzes the impact of the application of CLTC on the electric drive system from an economic perspective, providing a theoretical basis for the direction of product design and development.

With the gradual implementation of the National VI standard in Shanghai and even across the country, my colleagues and friends are constantly discussing and complaining about automobile energy consumption and standard operating conditions.

The government has also considered this issue. Considering the lack of energy consumption and emission standards suitable for China, in March 2015, the Ministry of Industry and Information Technology issued a project demand, and China Automotive Research Institute took the lead and organized industry experts to carry out a three-year research and development of China's working conditions. In August 2018, the draft for comments was completed and published; the official standard was released on October 25, 2019:

▲ "China Vehicle Driving Conditions Part 1: Light Vehicles" (GBT38146.1-2019)

▲ "China Vehicle Driving Conditions Part 2: Heavy Commercial Vehicles" (GBT38146.2-2019)

Here is one more thing, is the correct abbreviation CATC? Or CLTC? Many people may be confused about this. A picture clearly explains this problem:

Figure 1 China's automobile driving conditions CATC

Let's get back to the point. In short, CLTC-P (China light-duty vehicle test cycle-passenger) is the passenger car part of CATC (China Automotive Test Cycle). It is a standard operating condition defined based on 41 cities, 3,832 vehicles, 32.78 million kilometers of accumulated GIS traffic low-frequency dynamic big data. (#Who else?...#)

So, what’s so great about this standard?

So, facing such an awesome CLTC, how can we develop matching from the perspective of three-in-one electric drive system to improve the range of electric vehicles, save energy and reduce emissions?

Regarding the above issues, we analyze them in three parts according to the following logic:

1. NEDC/WLTP/CLTC cycle operating condition characteristic data

2. Comparative analysis of cycle conditions based on a pure electric vehicle

3. Impact of CLTC Application on Three-in-One Electric Drive System

This article is an analysis of the first part.

1. NEDC/WLTP/CLTC cycle operating condition characteristic data

Figure 2 is a comparison chart of NEDC/WLTP/CLTC cycle conditions, and Table 2 describes the characteristic data corresponding to the cycle conditions. As can be seen from Figure 1, CLTC has added a wider range of road conditions information compared to NEDC: urban conditions, suburban conditions and highway conditions. The cycle time is still consistent with WLTP, which is 1800s; however, compared with WLTP, it lacks the definition of the ultra-high-speed section, and the maximum speed and average speed are the lowest of the three, which is more in line with the current highway regulations and the big data collected by traffic GIS.

Figure 2 NEDC/WLTP/CLTC cycle operating curve

Table 1 NEDC/WLTP/CLTC cycle condition characteristics data

Figure 3 shows the distribution of NEDC/WLTP/CLTC under four driving modes: acceleration, deceleration, constant speed and parking. It can be seen that the acceleration and deceleration ratio of WLTP/CLTC is significantly higher than that of NEDC, up to 35%~43%, which reflects the increase in the severity of the two cycle conditions; at the same time, the parking ratio of CLTC is higher than that of WLTP, which is 23.33%, which is consistent with the big data collected by traffic GIS, such as frequent traffic light parking conditions.

Figure 3 NEDC/WLTP/CLTC cycle driving mode time ratio comparison

Figure 4 shows the acceleration distribution of NEDC/WLTP/CLTC cycle conditions. It can be seen that for the working point a=0, the proportion of the three conditions is ranked as follows: NEDC>CLTC>WLTP, among which the proportion of NEDC at point 0 is as high as about 64%, and only includes uniform acceleration and deceleration driving modes.

Figure 4 shows the acceleration distribution of NEDC/WLTP/CLTC cycle conditions

Figure 5 shows the scatter distribution of acceleration in the NEDC/WLTP/CLTC cycle conditions in the vehicle speed domain. It can be qualitatively seen that the acceleration and deceleration of CLTC occurs more in the medium and low speed area (<80km/h) and there is no scatter distribution above 120km/h; at the same time, in the medium and low speed section, CLTC reduces the acceleration demand and increases the deceleration ratio compared to WLTP, that is, it enhances the impact of the braking energy recovery condition, which will be quantitatively analyzed later.

Figure 5 Scatter distribution of NEDC/WLTP/CLTC cycle acceleration in the vehicle speed domain

In summary, CLTC more truly reflects the working conditions with Chinese characteristics, specifically from the following aspects:

→More reasonable definition of average speed and maximum speed

→ Wider range of driving conditions

→More reasonable parking mode ratio

→More dynamic acceleration and deceleration conditions

In conclusion:

This article mainly compares and analyzes the characteristic data of the three cycle conditions of NEDC/WLTP/CLTC. In the subsequent (II), the vehicle parameters of a pure electric passenger car will be taken as an example to further compare and analyze its characteristics from multiple angles such as power distribution, high-efficiency area distribution, average efficiency, power consumption and brake energy recovery ratio. In (III), based on the working principle of the three-in-one electric drive system and with the economy of the whole vehicle as the design goal, the application of the CLTC cycle condition will be analyzed. The impact of the design and development of the electric drive system. Please stay tuned.