Load setting method for low temperature vehicles on chassis dynamometer

Abstract

The present invention provides a method for setting the load of a low-temperature vehicle on a chassis dynamometer, which includes the following steps: S1, performing a drum resistance fitting under normal temperature environment to obtain the fitting coefficients A d23 , B d23 , C d23 ; S2, measuring the drum force under normal temperature environment and low-temperature environment respectively; S3, after obtaining the drum forces in the normal temperature environment and the low-temperature environment, calculating the resistance fitting result of the vehicle on the chassis dynamometer under the low-temperature environment. The present invention can simulate the resistance situation of the vehicle under low-temperature conditions so as to obtain the low-temperature endurance performance of the vehicle, greatly reducing the research cost of vehicle enterprises for low-temperature working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of automobile measurement and testing, and in particular to a method for setting the load of a low-temperature vehicle on a chassis dynamometer. Background Art

[0002] The current international standards still lack effective test methods for vehicle sliding resistance in low-temperature environments; the existing whole-vehicle road resistance sliding test or wind tunnel sliding resistance test is difficult. Under extreme low temperature conditions, such as -20°C, the road surface is frozen, which not only destroys the flatness of the road surface, but also causes the road adhesion coefficient to decrease, making it difficult to maintain a stable and dry good adhesion condition. In addition, in the winter in the north, strong wind speeds may also interfere with the test, making it difficult for wind speed conditions to meet the test requirements. These factors work together to make vehicle sliding resistance testing in low-temperature environments challenging, resulting in low feasibility. Summary of the invention

[0003] The present invention aims to at least solve the technical problems existing in the prior art, and in particular innovatively proposes a method for setting the load of a low-temperature vehicle on a chassis dynamometer.

[0004] In order to achieve the above-mentioned object of the present invention, the present invention provides a method for setting the load of a low-temperature vehicle on a chassis dynamometer, comprising the following steps:

[0005] S1, refer to Appendix CC of GB 18352.6-2016 to fit the drum resistance at room temperature and obtain the fitting coefficient A d23 , B d23 , C d23 ;

[0006] S2, measuring the drum force at room temperature and low temperature respectively;

[0007] S3, after obtaining the drum forces in the normal temperature environment and the low temperature environment, calculate the resistance fitting result of the vehicle on the chassis dynamometer in the low temperature environment.

[0008] Furthermore, the normal temperature is 23°C and the low temperature is -7°C to -35°C.

[0009] Further, the determination of the drum force comprises the following steps:

[0010] S2-1, set the temperature of the environmental chamber or immersion chamber, and then place the vehicle in the environmental chamber for 12 hours;

[0011] S2-2, preheating the chassis dynamometer;

[0012] S2-3, check the vehicle status, and then fix the vehicle on the chassis dynamometer;

[0013] S2-4, set the resistance of the chassis dynamometer;

[0014] S2-5, preheating the vehicle;

[0015] S2-6, start the vehicle and put it in neutral (N gear); the chassis dynamometer is used for resistance measurement in constant speed mode. During the resistance measurement, the speed of the chassis dynamometer starts from 10 km / h and increases in steps of 10 km / h to the maximum value V j,max , V j,max It is the maximum reference speed for vehicle road gliding; and each speed is maintained for no less than 20 seconds in a stable state.

[0016] Furthermore, the chassis dynamometer preheating includes: the chassis dynamometer is at a speed of 100 km / h and lasts for 20 minutes.

[0017] Further, vehicle preheating includes: placing the vehicle in a clutch-disconnected or automatic neutral position; at this time, braking the vehicle to gradually reduce the vehicle speed from 80 km / h to 20 km / h over a period of 5 to 10 seconds, and then Vmax Drive at 90% of the speed for at least 20 minutes.

[0018] Furthermore, before setting the resistance of the chassis dynamometer, a zero drift measurement of the chassis dynamometer is performed.

[0019] Furthermore, setting the resistance of the chassis dynamometer includes:

[0020] The fitting coefficient of the normal temperature drum resistance A d23 , B d23 , C d23 As the Dyno set factor of the chassis dynamometer.

[0021] Furthermore, the resistance fitting of the chassis dynamometer includes:

[0022] F D_-20 =A d +B d *V+C d *V 2

[0023] Among them, A d , B d、 C d All are Dyno set coefficients configured on chassis dynamometer at low temperature;

[0024] V is the vehicle speed;

[0025] Furthermore, A d , B d , C d The calculation formula is as follows:

[0026] A d =X*A d23

[0027] B d =X*B d23

[0028] C d =C d23 *(T T' +273) / (T T +273);

[0029]

[0030] Where: k is the working condition sequence number; N is the total number of working conditions;

[0031] is the drum force measured under the kth working condition in low temperature environment;

[0032] is the drum force measured at the kth working condition under normal temperature;

[0033] A d23 , B d23 , C d23 is the Dyno set coefficient under normal temperature;

[0034] T T' is the temperature value of the normal temperature environment, unit: ℃;

[0035] T T It is the temperature value of low temperature environment, unit: ℃.

[0036] X is the ratio of the average force at each speed point at different temperatures.

[0037] In summary, due to the adoption of the above technical solution, the present invention can simulate the resistance of the vehicle under low temperature conditions to obtain the low-temperature endurance performance of the vehicle, which greatly reduces the research cost of automobile companies on low-temperature working conditions.

[0038] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0040] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0041] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0042] This method uses a drum and environmental chamber simulation method to perform an equivalent fitting test of the vehicle drum resistance at a low temperature of -20°C. The specific steps are as follows: Figure 1 shown.

[0043] S1, perform drum resistance fitting at room temperature and obtain the fitting coefficient A d23 , B d23 , C d23 ;

[0044] S2, drum force F at room temperature 23 The determination of the drum force F at low temperature -20 In national standard testing, the normal temperature is usually 23℃.

[0045] 1. Test the drum force F at room temperature 23 Determination of.

[0046] 1.1 Temperature setting: Set the temperature of the environmental chamber or immersion chamber to 23℃ (actual value 23℃±3℃), and immerse the vehicle for 12 hours; 1.2 Chassis dynamometer (drum) preheating: Drum 100km / h, after 20min preheating, perform chassis dynamometer zero drift measurement; drum preheating can eliminate the influence of the internal transmission system of the drum on the vehicle resistance as much as possible.

[0047] 1.3 Vehicle status check: Check the vehicle status and fix the vehicle on the chassis dynamometer;

[0048] 1.4 Resistance preset:

[0049] Use the existing drum sliding result A d23 , B d23 , C d23 or A d0 =0.1A t , B d0 =0.2B t , 、 C d0 =C t Among them, A t、 B t、 C t It is obtained under the condition of actual road sliding, which requires that the road surface is flat with zero slope, dry, the 5s average wind speed is lower than 5m / S, the 2s peak wind speed is lower than 8m / s, the crosswind vector is less than 2m / s, and the vehicle slides in neutral gear.

[0050] 1.5 Vehicle preheating: refer to the national standard GB18352.6-2016CC4.2.4. In addition, vehicle preheating also includes that the vehicle should be braked to reduce the speed from 80km / h to 20km / h steadily within 5 to 10 seconds when the clutch is disengaged or the automatic gear is in neutral. The brake pads are run-in to make the preheating more complete, so that the test results are more reasonable. Then, in the WLTC test cycle with the highest speed V max The WLTC (World Light Vehicle Test Cycle) test cycle is an internationally used light vehicle test standard that is designed to more accurately simulate real-world driving conditions, including different speeds and driving stages.

[0051] 1.6 Drum force F 23 Measurement: Vehicle READY ON, N gear, chassis dynamometer constant speed mode to measure resistance, starting at 10km / h, increase in steps of 10km / h to the highest reference point V j,max , V j,max The maximum reference speed for vehicle road coasting. (Refer to Appendix CC.2.2 of GB 18352.6-2016 for the method of determining the reference point), then reduce to 10km / h, with each 10km / h interval as shown in Table 1. And each speed is maintained at a stable state for no less than 20s.

[0052] 2. Drum force F at low temperature 23 The specific test steps are the same as those at normal temperature, but the ambient temperature can be changed to -20°.

[0053] Table 1 Test matrix

[0054] Working condition number k Vehicle speed V (km / h) time <![CDATA[F 23 (N)]]> <![CDATA[F -20 (N)]]> 1 10 20s 2 20 20s 3 30 20s 4 40 20s 5 50 20s 6 60 20s 7 70 20s 8 80 20s 9 90 20s 10 100 20s 11 110 20s 12 120 20s 13 130 20s 14 120 20s 15 110 20s 16 100 20s 17 90 20s 18 80 20s 19 70 20s 20 60 20s 21 50 20s 22 40 20s 23 30 20s 24 20 20s 25 10 20s

[0055] S3, calculate the resistance fitting result of the vehicle on the chassis dynamometer at -20℃

[0056] Before the implementation of this method, the vehicle will be subjected to actual road sliding at a normal temperature of 23°C according to Appendix CC of National Standard 18352.6 to obtain the sliding resistance curve of the vehicle at normal temperature:

[0057] F road_23 =A t +B t *V+C t *V2 (1)

[0058] When a vehicle is sliding in neutral on the road, the resistance of the vehicle is mainly composed of air resistance, inertial resistance, mechanical resistance (internal resistance + rolling resistance) and slope resistance.

[0059] F j =F aero +F i +F m +F grav (2)

[0060] Among them, F j is the vehicle resistance, F aero is the air resistance, F i is the inertial resistance, F m is the mechanical resistance, F grav is the slope resistance.

[0061] This method will be studied for flat roads, neutral gear and constant speed conditions. When the vehicle is on a flat road, the inertial resistance F i =0, ramp resistance F grav =0. The above formula is simplified to

[0062] F j =F aero +F m (3)

[0063] The air resistance F aero It has a quadratic relationship with speed, expressed as C t *v2, mechanical resistance is approximately linearly related to speed, expressed as (A t +B t *v). Where A t , B t , C t is the coefficient obtained from actual road sliding, and v represents the vehicle speed.

[0064] When the vehicle is in neutral and at a constant speed, the vehicle runs at a constant speed on the drum. The resistance of the whole vehicle is the resistance F exerted by the drum. d And the internal transmission resistance of the whole vehicle.

[0065] F j =F d +F f (4)

[0066] Among them, F f is the internal transmission resistance of the vehicle, F d is the chassis dynamometer resistance, expressed as a quadratic function of the vehicle speed V,

[0067] F d =A d +B d *V+C d *V 2

[0068] Among them, Ad , B d、 C d Dyno set coefficients configured for chassis dynamometer (drum);

[0069] When the vehicle and the drum are fully preheated, the vehicle is in a force balance state when the drum drags the vehicle at a constant speed. At this time, it can be understood that the force exerted by the drum is equivalent to the vehicle's wind resistance C d *V 2 and rolling resistance (A d +B d *V). When fitting at low temperature -20℃, this method has no significant effect on F d C d *V 2 and (A d +B d *V) are revised separately. Details are as follows:

[0070] Quadratic coefficient C d Determine method:

[0071] The factors affecting wind resistance depend on the air tightness, and the European standard R154-3.4.1 has a method to determine the quadratic coefficient C at different temperatures: C d =C*(T 23 +273) / (T T +273). In this method, T T =-20℃.

[0072] The above method is used to calculate the quadratic coefficient C d The correction is based on theoretical deduction of the universal gas state equation to obtain the air resistance at low temperatures without actual experimental testing.

[0073] (A d +B d *V) Determination method:

[0074] Since the drum force collected by the drum may not be the wheel force of the vehicle, it needs to be converted through an unknown lever arm, so it is determined by ratio. This method designs the test matrix in Table 1, and can measure the force F at each speed balance point at room temperature and low temperature 23 and F -20 , so we calculate the ratio of each speed point and finally take the average value to get the final ratio X:

[0075]

[0076] Where: k is the operating condition number, N is the total number of operating conditions, F -20 F is the drum force measured at -20℃ 23It is the drum force measured at 23°C. The drum force is obtained by a chassis dynamometer, on which the vehicle is located.

[0077] Through the above method (A d +B d *V) correction, when the existing objective conditions (test environment and site) do not meet the conditions for direct measurement, the increase rate of rolling resistance at low temperature can be indirectly obtained through ratio conversion.

[0078] Finally, the resistance fitting result at -20℃ low temperature is obtained:

[0079] F D_-20 =C d23 *(23+273) / (-20+273)*V 2 +X*(A d23 +B d23 *V)

[0080] Among them, A d =X*A d23 , B d =X*B d23 .

[0081] A d23 , B d23 , C d23 It is the Dyno set coefficient under normal temperature environment, which is obtained through the coasting test on the chassis dynamometer. The specific process is as follows:

[0082] First, set the normal temperature environment (the temperature of the environmental chamber or immersion chamber, and then place the vehicle in the environmental chamber for 12 hours;), and then perform the coasting test on the chassis dynamometer in accordance with CC.4.3.1.3.1-CC.43.1.3.2.

[0083] (1) The coasting test should be started within 120 seconds after the preheating is completed. If the iterative method is used, the time interval between the dynamometer preheating and the start of the coasting test can be extended until the vehicle is set up in the dynamometer coasting mode.

[0084] (2) Set an initial Dyno set coefficient for the chassis dynamometer and set the corresponding drum force on the chassis dynamometer; accelerate the vehicle to the set target speed, for example, 130 km / h.

[0085] (3) When the vehicle reaches the target speed, the chassis dynamometer eliminates the drum force to simulate the situation where the vehicle is sliding on the road without the driving force of the engine. At this time, the vehicle continues to slide by inertia, and the chassis dynamometer measures the resistance and sliding distance of the vehicle in the sliding state. During the sliding process, the chassis dynamometer records key data such as vehicle speed and sliding distance.

[0086] (4) After the coasting test is completed, the Dyno set coefficient is gradually adjusted using the iteration method to obtain the Dyno set coefficient under normal temperature environment.

[0087] By changing the Dyno set coefficient A of the chassis dynamometer d , B d , C d Configuration is performed to achieve vehicle sliding resistance testing in low temperature environments.

[0088] For the commonly used load setting method on chassis dynamometer in -7℃ low temperature environment, only the influence of air resistance on the vehicle is often considered. The resistance is set by shortening the vehicle's coasting time by 10%, that is, using a 1.1 times dynoset configuration drum. However, the change of the vehicle's own mechanical resistance under low temperature is also one of the important factors affecting the vehicle's coasting resistance. Ignoring the influence of the vehicle's own mechanical resistance under low temperature conditions may lead to inaccurate and incomplete evaluation of vehicle performance.

[0089] In addition, after the vehicle sliding resistance is obtained through the existing whole vehicle road resistance sliding test or wind tunnel sliding resistance test, it is still necessary to obtain the dyno set through drum sliding and then measure the vehicle endurance. The method of the present invention not only takes into account the mechanical resistance and wind resistance, but also directly obtains the dyno set coefficient and inputs it into the drum for vehicle endurance measurement. It has the following advantages: (1) It eliminates the intermediate step of calculating the vehicle sliding resistance, greatly simplifying the test process. This can improve test efficiency and shorten test time. (2) It can more accurately evaluate the vehicle's cruising range. By directly testing and obtaining the drum coefficient, the vehicle's power performance and energy consumption on the drum can be more directly reflected. Since the errors that may be introduced in the intermediate calculation link are avoided, the accuracy of the test results can be further improved.

[0090] In summary, by analyzing the resistance of the drum configuration, the performance of the vehicle under different working conditions can be evaluated, providing an important reference for the design, production and identification of the vehicle. In particular, low temperature has a huge impact on the range attenuation of pure electric vehicles, which has always been a pain point for companies and consumers. Through the method of the present invention, the research results show that extreme low temperatures (below -20°C) can cause the range attenuation of pure electric vehicles to reach about 70%.

[0091] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for setting the load of a low-temperature vehicle on a chassis dynamometer, characterized in that: The following steps are involved: S1, perform drum resistance fitting at room temperature and obtain the fitting coefficient A d23 , B d23 , C d23 ; A d , B d , C d The calculation formula is as follows: A d =X*A d23 B d =X*B d23 C d =C d23 *(T T' +273) / (T T +273); Where: k is the working condition sequence number; N is the total number of working conditions; is the drum force measured under the kth working condition in low temperature environment; is the drum force measured at the kth working condition under normal temperature; A d23 , B d23 , C d23 is the Dyno set coefficient under normal temperature; X is the ratio of the average force at each speed point at different temperatures; T T' is the temperature value of the normal temperature environment; T T is the temperature value of the low temperature environment; S2, measuring the drum force at room temperature and low temperature respectively; S3, after obtaining the drum forces in the normal temperature environment and the low temperature environment, calculate the resistance fitting result of the vehicle on the chassis dynamometer in the low temperature environment; The calculation formula of the resistance fitting result of the chassis dynamometer is as follows: F D_-20 =A d +B d *V+C d *V 2 Among them, A d , B d、 C d All are Dyno set coefficients configured on chassis dynamometer at low temperature; V is the vehicle speed.

2. A method for setting load on a chassis dynamometer for a low-temperature vehicle according to claim 1, characterized in that: The normal temperature is 23°C and the low temperature is -7°C to -35°C.

3. The method for setting the load of a low-temperature vehicle on a chassis dynamometer according to claim 1, characterized in that: The determination of drum force includes the following steps: S2-1, set the temperature of the environmental chamber or immersion chamber, and then place the vehicle in the environmental chamber for 12 hours; S2-2, preheating the chassis dynamometer; S2-3, check the vehicle status, and then fix the vehicle on the chassis dynamometer; S2-4, set the resistance of the chassis dynamometer; S2-5, preheating the vehicle; S2-6, start the vehicle and put it in neutral; the chassis dynamometer is used to measure the resistance in constant speed mode. During the resistance measurement, the speed of the chassis dynamometer starts from 10 km / h and increases in steps of 10 km / h to V j,max , V j,max It is the maximum reference speed for vehicle road gliding; and each speed is maintained for no less than 20 seconds in a stable state.

4. A method for setting the load of a low-temperature vehicle on a chassis dynamometer according to claim 3, characterized in that: Chassis dynamometer preheating includes: the chassis dynamometer is at a speed of 100km / h and lasts for 20 minutes.

5. The method for setting the load of a low-temperature vehicle on a chassis dynamometer according to claim 3, characterized in that: Vehicle warm-up includes: putting the vehicle in the clutch disengaged or automatic neutral gear; at this time, by braking, the vehicle speed is gradually reduced from 80km / h to 20km / h within 5 to 10 seconds, and then at the maximum speed V of the WLTC test cycle max Drive at 90% of the speed for at least 20 minutes.

6. The method for setting the load of a low-temperature vehicle on a chassis dynamometer according to claim 3, characterized in that: Before setting the resistance of the chassis dynamometer, perform a zero drift measurement of the chassis dynamometer.

7. The method for setting the load of a low-temperature vehicle on a chassis dynamometer according to claim 1, characterized in that: Setting the resistance of a chassis dynamometer involves: The fitting coefficient of the normal temperature drum resistance A d23 , B d23 , C d23 As the Dyno set factor of the chassis dynamometer.

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