A start-stop control method for a vehicle brake auxiliary vacuum pump

Abstract

The present invention provides a method for calibrating the start and stop of a vehicle brake assist vacuum pump, comprising: A. setting a vacuum start value P1 and a vacuum stop value P2 of the vacuum pump, where P1 = P2-X kPa, requiring the pumping time from P1 to P2 to satisfy a vacuum pump load rate of no more than 30%, and the value of X to satisfy the requirement of at least one full-stroke braking operation; B. monitoring the vacuum rise rate in the vacuum tank when the vacuum pump is operating, and recording the vacuum rise rate when the vacuum reaches the stop value P2, setting the vacuum rise rate as a control signal that triggers the vacuum pump to stop, and P1 as the signal that triggers the vacuum pump to operate; C. setting a minimum vacuum pump start value P3 to ensure vehicle braking performance, requiring the vacuum pump start value P1 to be no less than P3. This method solves the problem of calibrating the start and stop conditions of a vacuum pump even when the vehicle does not have an atmospheric pressure sensor (or the atmospheric pressure sensor fails).

Description

Technical Field

[0001] The present invention relates to a vacuum pump for assisting vehicle braking, in particular to a method for calibrating signals of starting and stopping the vacuum pump, and a method for controlling the brake assisting vacuum pump based on the method. Background Art

[0002] Braking performance is a critical aspect of vehicle performance, crucial to the safety of drivers and passengers. China's national standards GB / T 7258-2017, Technical Requirements for Motor Vehicle Operational Safety, and GB / T 12676-2014, Technical Requirements and Test Methods for Braking Systems of Commercial Vehicles and Trailers, regulate the braking performance and testing methods of motor vehicles. A vacuum pump is a motor-driven vacuum generator that provides an independent or auxiliary vacuum source for the vacuum booster servo in a vehicle's braking system.

[0003] Improving the performance of vehicle braking systems is a key task for production design departments. The vacuum booster is a crucial component of the braking system. Prior art discloses the matching design of vacuum boosters in passenger vehicle braking systems, such as "Matching Design of Vacuum Booster in Passenger Vehicle Braking Systems" (https: / / zhuanlan.zhihu.com / p / 100334607). To ensure an appropriate vacuum level in the vacuum booster, an electric vacuum pump can be used. The electric vacuum pump's control strategy involves setting start and stop vacuum levels. When the booster's vacuum level falls below the start vacuum level, the vacuum pump starts; when the booster's vacuum level exceeds the stop vacuum level, the vacuum pump stops. For example, if the start and stop vacuum levels of the vacuum pump in a pure electric vehicle are set to 45 kPa and 60 kPa, the vacuum range in the vacuum booster of that vehicle is 45 kPa to 60 kPa. It is desirable to achieve the desired effect by braking as many times as possible during the process of decreasing the vacuum level from 60 kPa to 45 kPa. This ensures that the brake pedal feel does not change noticeably with repeated application of the brake pedal. This also reduces the number of times the electric vacuum pump starts, significantly extending its lifespan.

[0004] To detect the vacuum level within the vacuum tank, existing technologies can directly measure the absolute air pressure or vacuum level within the tank. However, when a vehicle is traveling at different altitudes, this pressure measurement fails to reflect the atmospheric pressure environment in which the vehicle is located, and the vacuum pump control strategy cannot automatically adjust to the atmospheric pressure environment. Therefore, existing technologies have proposed improving the system by adding an atmospheric pressure sensor to achieve calibration.

[0005] The current problems are:

[0006] On the one hand, an external atmospheric pressure sensor is connected to the vehicle, which can malfunction. When diagnosing the ambient pressure sensor, only electrical fault detection is performed, resulting in low reliability. Furthermore, if the ambient pressure sensor fails, reliable operation of the vehicle's braking system cannot be guaranteed. To address this issue, prior art CN117087633 A controls the operation of the vacuum pump by monitoring its operating time, the tank's internal air pressure, and the brake signal.

[0007] On the other hand, if the VCU pin resources of electric vehicles are insufficient, it is impossible to add an atmospheric pressure sensor. Currently, many electric vehicles do not have an atmospheric pressure sensor. Summary of the Invention

[0008] The purpose of the present invention is to provide a calibration method for a brake auxiliary vacuum pump used in a vehicle without an atmospheric pressure sensor, so as to solve the problem that the vacuum pump can be calibrated to its start and stop conditions when the vehicle does not have an atmospheric pressure sensor (or the atmospheric pressure sensor fails).

[0009] Another object of the present invention is to control the start and stop of the vacuum pump based on the vacuum pump start and stop conditions obtained by the above-mentioned vacuum pump calibration method, thereby achieving the purpose of ensuring the braking effect.

[0010] The present invention provides a method for calibrating the start and stop of a vehicle brake auxiliary vacuum pump, comprising the following steps:

[0011] A. Set the vacuum pump's vacuum start value P1 and vacuum pump stop value P2, P1 = P2 - X kPa. The pumping time from P1 to P2 must ensure that the vacuum pump load rate is no more than 30%. The value of X must meet the requirement of at least one full-stroke braking.

[0012] B. Monitor the rate of increase of vacuum degree in the vacuum tank when the vacuum pump is working, and record the rate of increase of vacuum degree when the vacuum pump reaches the stop value P2. Set the rate of increase of vacuum degree as the control signal to trigger the vacuum pump to stop working, and P1 is the signal to trigger the vacuum pump to work.

[0013] C. To ensure the vehicle's braking performance, set the vacuum pump minimum starting value P3, requiring the vacuum pump starting value P1 to be no less than P3.

[0014] The present invention adopts a new calibration method for the brake assist vacuum pump, that is, the corresponding vacuum degree rising rate when the vacuum pump stops is set as the control signal for the vacuum pump to stop working, thereby getting rid of the dependence on ambient atmospheric pressure monitoring.

[0015] Regarding the start and stop values ​​P1 and P2 of the vacuum pump, those skilled in the art determine, based on the vacuum pumping efficiency curve of the vacuum pump, that the vacuum pumping time meets the requirement that the vacuum pump load rate is no higher than 30%, and that the vacuum degree drops from P2 to P1 after at least one full-stroke braking.

[0016] Regarding the minimum starting value P3 of the vacuum pump, those skilled in the art can determine it based on the performance data and standard requirements of the vacuum pump and the relationship between the pedal force and the braking deceleration under different vacuum degrees.

[0017] First, based on theoretical calculations of pedal force at different vacuum levels, the pedal force must meet the requirements of GB1267, while the braking deceleration and braking distance must meet those of GB12676 and GB7258. The vacuum level that meets the minimum regulatory performance requirements is used as the vacuum pump's minimum starting value, P3. Then, based on the vacuum pump bench test's vacuum efficiency curve and the pumping time from P1 (design stop value - X kPa) to P2 (design stop value), the vacuum pump load factor must be below 30%. The value of X must meet the requirement of at least one full-stroke braking operation.

[0018] For the vacuum measurement method, please refer to “Vacuum Test of Automobile Braking System” in Engineering Technology and Management, Huang Qi and Cao Zhiyu, 2017 / 11 / 26-211.

[0019] The definition of vacuum degree rise rate is: the vacuum degree rise value within the set time, such as the vacuum degree increase value within 0.2s.

[0020] Vehicle braking performance test can refer to standard GB / T12676.

[0021] The vacuum pump load factor is set at no more than 30% during measurement to extend the life of the vacuum pump. Therefore, the 30% load factor is not a critical value. The so-called vacuum pump load factor refers to the percentage of the vacuum pump's operating time. For example, if the vacuum pump operates for 12 seconds per minute, the load factor is 20%.

[0022] According to an embodiment of the present invention, the following steps are added after the aforementioned step A:

[0023] A1. Conduct a real-vehicle vacuum pump test to obtain the pumping time and full-stroke brake vacuum consumption values ​​at different vacuum start and stop values.

[0024] A2. Based on the data obtained in step A1, adjust the vacuum pump starting values ​​P1' and P2'. The vacuum pump pumping time from P1' to P2' must be less than 30% load, and the vacuum level must drop from P2' to P1' after at least one full-stroke braking cycle.

[0025] When designing brakes, a rule of thumb is to perform six braking cycles per minute, equivalent to three full-stroke braking cycles. The vacuum generated by these three full-stroke braking cycles is replenished by the vacuum pump, and the pumping time must ensure that the vacuum pump load factor is below 30%. For example, if the value of X meets the requirement of 1.5 full braking cycles, then during these three full braking cycles, the vacuum pump will operate twice, from P1 to P2. The duration of these two cycles cannot exceed 18 seconds, meaning that the single pumping time cannot exceed 9 seconds. If this exceeds 9 seconds, the values ​​of P1 and P2 need to be adjusted.

[0026] According to an embodiment of the present invention, tests are conducted at different altitudes, and the above process is repeated to obtain braking distance, braking deceleration, pedal force data and vacuum pump exhaust time at different altitudes and different vacuum levels. Based on the aforementioned P1' and P2', the start-stop control setting value is adjusted.

[0027] The altitudes at which tests and calibrations are performed depend on the application scenario and control requirements of the vacuum pump.

[0028] After obtaining the vacuum pump calibrated by the above-mentioned new method, a new control method for starting and stopping the vacuum pump is obtained accordingly. The difference between the new method and the existing vacuum pump control method is that the control signal for stopping the vacuum pump is triggered by the vacuum degree rising rate when the vacuum pump reaches the stop value P2.

[0029] Further according to an embodiment of the present invention, the vacuum pump stop value P2 is obtained by the vacuum pump start-stop calibration method described in any one of claims 1-3.

[0030] Based on the aforementioned vacuum pump calibration method, the present invention also provides a vehicle brake auxiliary vacuum pump start-stop control method, wherein the control signal for stopping the vacuum pump is triggered by the vacuum degree rising rate when the vacuum pump reaches the stop value P2 or P2'.

[0031] The stop value P2 or P2' is determined according to the vacuum pump calibration method described above.

[0032] The present invention also provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute any one of the aforementioned vehicle brake auxiliary vacuum pump start-stop control methods.

[0033] The technical solution provided by this invention does not utilize an atmospheric pressure sensor. Instead, it calibrates the vacuum pump's start and stop functions solely through the vacuum signal and its corresponding rate of vacuum rise. The same method is employed for calibration at different altitudes. Once calibrated, the vacuum pump used by a specific vehicle model can directly utilize the calibration results, incorporating the values ​​into the vehicle's vacuum pump start and stop control. This reduces VCU pin usage and avoids control inaccuracies caused by atmospheric pressure sensor failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Vacuuming efficiency curve of a single vacuum pump at a volume of 4L

[0035] Figure 2 Actual vehicle vacuum efficiency curve

[0036] Figure 3 Theoretical curve of vacuum booster input-output characteristics DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the embodiments. It should be noted that, unless otherwise specified, the embodiments and features of the embodiments of the present invention may be combined with each other. Unless otherwise specified, the percentages below are all weight percentages.

[0038] 1. Preliminary setting of the vacuum pump’s start value P1 and stop value P2

[0039] According to the vacuum pump manufacturer's test, the vacuum efficiency curve data of a single vacuum pump at a volume of 4L is as follows Figure 1 The actual vehicle braking system solution matches an 8L vacuum tank and two vacuum pumps of this model. You can refer to this curve to make preliminary settings for the start value P1 and stop value P2.

[0040] Vacuum degree = absolute pressure inside the atmospheric vacuum tank, such as Figure 1 As shown, as the absolute pressure in the tank decreases, the vacuum increases, and the rate of vacuum rise slows. Set the start value P1 to a vacuum below 55 kPa, and the stop value P2 to a vacuum of 80 kPa. Verify that the pumping time from P1 to P2 satisfies the vacuum pump load factor of no more than 30% and that it meets the requirement of at least one full-stroke braking.

[0041] Theoretical calibration of the vehicle vacuum booster's full-stroke braking intake volume is about 3L. Calculation shows that the vacuum drops to 57kpa after one full brake at a vacuum of 80kpa, which is higher than 55kpa. The start-stop value meets the requirement of at least one full-stroke braking. Braking design experience is that 6 brakings are performed in 1 minute, which is equivalent to 3 full-stroke brakings. The vacuum consumed by 3 full brakes is replenished by vacuum pump exhaust. The exhaust time needs to meet the requirement that the vacuum pump load rate is less than 30%, that is, the total exhaust time of the vacuum pump is less than 18s under 3 full brakes within 1 minute. Figure 1 From the vacuum efficiency curve, it can be seen that the time for pumping from a vacuum degree of 55kPa to 80kPa is about 5s, and the total pumping time under three full braking operations is 15s, which is lower than 18s, meeting the requirement that the vacuum pump load rate is lower than 30%.

[0042] 2. Calibrate the start and stop values ​​P1' and P2' of the vacuum pump on the actual vehicle

[0043] The calibration location is Zhuzhou, and the atmospheric pressure in Zhuzhou is 101.7kpa. Figure 1 The manufacturer tests the data of a single vacuum pump at a volume of 4L. The actual vehicle is affected by the local atmospheric pressure, vacuum pipeline and vacuum booster, and there are differences with the bench data. It is necessary to test the actual vacuum pump exhaust efficiency of the brake system. The vacuum degree in the brake system is reduced to 0kPa, and the vehicle is started to monitor the vacuum degree rise time. The actual vehicle vacuum efficiency curve is obtained as shown below. Figure 2 The curve shows that the actual time for pumping from 55kPa to 80kPa is 6.5s. The total pumping time under three full braking is 19.5s, which is higher than 18s and does not meet the requirement that the vacuum pump load rate is less than 30%. The start and stop values ​​P1' and P2' need to be redesigned.

[0044] The actual vehicle test shows the change in vacuum degree after the full-stroke brake pedal is pressed once under different vacuum degrees. The change value and the corresponding recovery of the exhaust vacuum degree are recorded in the following table.

[0045]

[0046] Based on the test data, the starting value P1' of the vacuum pump is set to 58kPa and the stopping value P2' is set to 78kPa. Under this setting value, the vacuum recovery time is 4.6s, the vacuum pump load rate is 23%, and it meets the requirement of one full-stroke braking.

[0047] 3. Adjustment of vacuum pump start and stop control logic

[0048] Because atmospheric pressure gradually decreases with altitude, the vacuum limit decreases with altitude. For example, if the vacuum pump can reach a maximum tank pressure of 20 kPa at an atmospheric pressure of 100 kPa, the vacuum level is 80 kPa. However, when the vehicle is located in a high altitude area with an atmospheric pressure of only 80 kPa, the absolute pressure inside the tank remains unchanged at 20 kPa, and the maximum vacuum level drops to 60 kPa. To ensure that the vacuum start and stop values ​​can be adjusted according to the vehicle's altitude, the control logic for stopping the vacuum pump when the vacuum reaches P2' is adjusted to stop when the VCU monitors the vacuum rising rate, which reaches a set value. Testing shows that when the vacuum reaches P2', it is 0.42 kPa higher than the vacuum level 0.2 seconds prior. Therefore, the vacuum pump stop control logic is adjusted to P(t) - P(t - 0.2) ≤ 0.42 kPa. The vacuum pump start control logic is P(t) - 20 kPa.

[0049] After adjusting the control logic, the test results showed that the vacuum pump started working when the instrument displayed a vacuum degree below 58kPa, and stopped working when the instrument displayed 78kPa. The values ​​were consistent with the design logic.

[0050] 4. Calibration of vacuum pump minimum starting value P3

[0051] Since the hydraulic inflection point of the boost curve of the vacuum booster decreases with the decrease of vacuum degree, see Figure 3 To ensure that the vehicle's braking performance meets the requirements of GB12676 and GB7258 regulations, it is necessary to measure the vacuum level at which both the front and rear wheels can reach a locked state under the maximum foot force of 700N when the vehicle is fully loaded. This vacuum level is set as the minimum starting value P3.

[0052] Braking tests were conducted at varying vacuum levels on a road surface with a road adhesion coefficient greater than 0.7. A pedal force sensor was used to measure foot force, and the VCU monitored vehicle and wheel speeds. The tests determined whether the wheels locked when a pedal force of less than 700N was applied at these vacuum levels. The test results showed that at a vacuum of 40kPa, a pedal force of 682N was required to achieve wheel lock. This indicates that the vacuum pump's minimum activation value, P3, is 40kPa, requiring that P(t) - 20kPa not fall below 40kPa. If the vacuum pump falls below 40kPa, the vacuum pump's activation value is 40kPa.

[0053] 5. Calibration result verification

[0054] The vehicle was tested in Anshun, with atmospheric pressure at the test point at 85.3 kPa. The data showed that the vacuum pump started operating when the instrument displayed a vacuum level below 43 kPa and stopped operating when the instrument displayed 63 kPa. These values ​​are consistent with the design logic.

[0055] The vacuum pump takes 4.5 seconds to pump air from a vacuum degree of 43kPa to 63kPa. After full-stroke braking at a vacuum degree of 63kPa, the instrument shows that the vacuum degree drops to 47kPa, which meets the design requirements.

Claims

1. A vehicle brake auxiliary vacuum pump start-stop calibration method, characterized in that A. Set the vacuum pump's vacuum start value (P1) and vacuum pump stop value (P2). P1 = P2 - X kPa. The pumping time from P1 to P2 must ensure that the vacuum pump load rate is no more than 30%. The value of X must meet the requirement of at least one full-stroke braking. A1. Perform a vehicle vacuum pump performance test to obtain the pumping time and full-stroke brake vacuum consumption values ​​at different vacuum start and stop values. A2. Based on the data obtained in step A1, adjust the vacuum pump start and stop values ​​P1' and P2'. The pumping time from P1' to P2' must be such that the vacuum pump load factor is no greater than 30%, and the vacuum level must drop from P2' to P1' after at least one full-stroke braking cycle. B. Monitor the rate of vacuum increase in the vacuum tank while the vacuum pump is operating, and record the rate of vacuum increase when the vacuum pump reaches the stop value P2'. Record this rate of vacuum increase and set it as the control signal to trigger the vacuum pump to stop, while P1' is the signal to trigger the vacuum pump to operate. B1. Conduct vehicle braking performance tests to obtain braking distance, braking deceleration, and pedal force data at different vacuum levels. C. To ensure vehicle braking performance, adjust the vacuum pump minimum starting value P3' based on the braking test data. The vacuum pump starting value P1' must not be less than P3'. D. Conduct verification at different altitudes to verify whether the vacuum pump start and stop values ​​are adjusted according to the altitude. Test braking performance, pedal force, and the pumping time between the vacuum pump start and stop values. Adjust the start and stop values ​​appropriately based on the test data. E. Repeat step B and record the stop value P2' when the calibrated vacuum rise rate is reached at different altitudes.

2. A vehicle brake auxiliary vacuum pump start-stop control method, characterized in that The control signal for stopping the vacuum pump is triggered by the rate of increase of the vacuum degree when the vacuum pump reaches the stop value P2', and the vacuum pump stop value P2' is obtained by the vacuum pump start-stop calibration method described in right 1.

3. A computer-readable storage medium, characterized in that The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute the method according to claim 2.

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