Characteristic analysis of driving cycles
Some parameters such as vehicle speed, acceleration/deceleration, running time, etc., can be used to reflect the characteristics of the vehicle’s movement on the road. Through the investigation and analysis of these motion characteristics, a driving condition that can represent the motion characteristics is developed. Regardless of whether it is expressed in modal or transient state, the driving cycles are ultimately expressed as a speed-time curve, and the time step is usually 1s.
Under the same control conditions (such as ambient temperature, wind speed, rolling resistance coefficient, etc.), the driving cycles of the test vehicle can be reproduced on the chassis dynamometer, and the vehicle’s power, economy, and vehicle emission performance can be tested. And compare. Since various driving cycles have different motion characteristics, the proportions of the four modes (idling, constant speed, acceleration and deceleration) are different, so the test results of the same car under different driving cycles are different.
Statistical analysis of driving cycles requires the introduction of a set of statistical characteristic values. These characteristic values mainly include: time (s), distance (km), average speed (km/h), average driving speed (km/h), maximum speed (km/h), maximum acceleration (m/s2), average Acceleration (m/s2), maximum deceleration (m/s2), average deceleration (m/s2), idling time ratio (%), constant speed time ratio (%), acceleration time ratio (%), deceleration time ratio ( %) and the maximum specific power Kmax (m2/s3), etc. The specific power K (m2/s3) is defined as 2va (v-vehicle speed, m/s; a-acceleration, m/s2), and the maximum specific power (Kmax) is taken as the characteristic value. Table 1 gives a comparative analysis of some characteristic values of some typical driving cycles at home and abroad, mainly including time, distance, average vehicle speed, maximum acceleration and maximum specific power and other parameters.
Through the comparative analysis in Table 1, it can be seen that when the Kmax value is low and the average vehicle speed is high, that is, when the vehicle runs at a relatively low power and maintains a high speed, the vehicle is operating in a relatively ideal state. The working conditions are ideal. Generally speaking, the operating conditions of vehicles on unobstructed roads such as highways or suburban roads are like this, such as commuting (COMMUT-ER), expressways (HWFET) and interstate expressways (WVUINTER). When the values of va, a and Kmax are all low, the working conditions are the most appropriate, such as FTP72, NEDC, etc. When the values of a and Kmax are both high, the vehicle needs more power to maintain operation under this kind of working condition, which is a more powerful working condition, such as LA-92 and SC03. When the average speed is below 20km/h, it can best represent city driving, such as NYCC, WVUCITY and other working conditions. It can also be seen from the table that US06 is the most powerful working condition, and its various parameters are almost 2.5 times the FTP value. From a pure specific power point of view, since the driving cycles in the United States are basically transient conditions, including a variety of transient changes in acceleration and load, its specific power is higher than European and Japanese operating conditions (which are modal operating conditions). ) Is much larger, so the requirements for vehicle power performance are more stringent. When selecting and using various driving cycles, these characteristic values can be studied to select operating conditions suitable for various needs.
On the basis of the basic characteristic parameters in Table 1, further study the probability distribution characteristics of each operating condition speed interval (such as dividing by 10km/h), and analyze the differences between various operating conditions statistically. Generally speaking, the probability distribution range of the speed interval of the certified working condition is relatively wide; while the research working condition focuses on the performance of the two extreme operating conditions of the vehicle, namely the low-speed interval (central city) and the high-speed interval (suburban or expressway). Both are larger operating conditions.