Master cylinder pressure estimation method and system based on wheel state

Abstract

The application discloses a master cylinder pressure estimation method and system based on wheel states, which is applied to an electronic stability control system and comprises the following steps: detecting the effectiveness of a master cylinder pressure sensor signal; if the master cylinder pressure sensor signal is effective, using the collected value of the master cylinder pressure sensor as a current master cylinder pressure estimation value; if the master cylinder pressure sensor signal is ineffective, judging whether antilock braking control is triggered; if the antilock braking control is not triggered, estimating the master cylinder pressure based on the whole vehicle deceleration; if the antilock braking control is triggered, judging whether the current is in the first antilock braking control cycle; if the current is in the first antilock braking control cycle, estimating the master cylinder pressure based on the maximum wheel deceleration of the current cycle; if the current is not in the first antilock braking control cycle, judging the wheel braking state based on at least one wheel state parameter of the current cycle, correcting the master cylinder pressure estimation value according to the judgment result, using the corrected master cylinder pressure estimation value as the current master cylinder pressure estimation value; and outputting the current master cylinder pressure estimation value for brake control.

Description

Technical Field

[0001] This application relates to the field of automotive electronic control technology, and more specifically, to a master cylinder pressure estimation method and system based on wheel conditions, for use in electronic stability control (ESC) systems, particularly suitable for fault-tolerant control when the master cylinder pressure sensor fails. Background Technology

[0002] With the continuous increase in the number of cars in my country, traffic safety has become a major concern for consumers and car manufacturers. To improve active safety, systems such as Anti-lock Braking System (ABS), Traction Control System (TCS), and Active Yaw Control (AYC) have emerged. These three systems—ABS, TCS, and AYC—comprise Electronic Stability Control (ESC), and all three components of the ESC system rely on brake pressure control.

[0003] Meanwhile, with the increasing prevalence of ESC systems, the requirements for precise control of braking pressure are becoming increasingly stringent. ESC systems typically obtain master cylinder pressure values ​​through master cylinder pressure sensors to achieve closed-loop control of wheel cylinder pressure. However, master cylinder pressure sensors may fail due to malfunctions, wiring harness issues, or other reasons. Once these sensors fail, the wheel cylinder pressure control algorithm of the ESC system will not function properly, seriously threatening driving safety. To improve system reliability, existing technologies have proposed sensorless ESC control schemes. For example, Chinese patent CN106218616A discloses a scheme: when the brake pedal is depressed, if the wheel slip ratio has not reached a predetermined threshold, the master cylinder pressure is estimated based on wheel deceleration information as a first estimate, and the braking pressure is controlled based on this first estimate. When the brake pedal is depressed, if the wheel slip ratio exceeds the predetermined threshold, the master cylinder pressure is estimated based on the wheel deceleration gradient as a second estimate. Upon triggering the ABS module's control program, the second estimate of the master cylinder pressure is used to control the brake pressure.

[0004] However, existing technologies have the following drawbacks:

[0005] First, when the slip ratio does not exceed the threshold, the estimation is made using only the wheel deceleration of a single wheel, without considering the influence of ground friction, resulting in insufficient estimation accuracy.

[0006] Second, after the slip ratio exceeds the threshold, correction is made based on the change characteristics of the wheel slip ratio. Since the vehicle speed is an estimated value and the wheel speed is easily affected by road surface unevenness (such as speed bumps and unpaved roads), and the slip ratio characteristics on roads with different adhesion coefficients are significantly different, the reliability and robustness of this correction method are poor.

[0007] Therefore, there is an urgent need for a more reliable and accurate master cylinder pressure estimation method to ensure the normal functioning of ESC systems, especially anti-lock braking systems (ABS), when the master cylinder pressure sensor fails. Summary of the Invention

[0008] This application provides a master cylinder pressure estimation method and system based on wheel status to solve the problems of inaccurate master cylinder pressure estimation and low reliability in the prior art after the master cylinder pressure sensor fails, so that the requirements of vehicle anti-lock braking control can still be met when the master cylinder pressure sensor fails.

[0009] The specific technical solution is as follows:

[0010] In a first aspect, embodiments of this application provide a master cylinder pressure estimation method based on wheel state, applied to an electronic stability control system (ESC). The master cylinder pressure estimation method includes:

[0011] Detect the validity of the master cylinder pressure sensor signal;

[0012] If the master cylinder pressure sensor signal is valid, the collected value of the master cylinder pressure sensor is used as the current estimated value of the master cylinder pressure.

[0013] If the master cylinder pressure sensor signal fails, determine whether to trigger anti-lock braking control;

[0014] If anti-lock braking system is not triggered, the master cylinder pressure is estimated based on the vehicle deceleration to obtain the current master cylinder pressure estimate.

[0015] If anti-lock braking control has been triggered, determine whether the current state is the first anti-lock braking control cycle;

[0016] If it is in the first anti-lock braking control cycle, the master cylinder pressure is estimated based on the maximum wheel deceleration of the current cycle to obtain the current master cylinder pressure estimate;

[0017] If it is not in the first anti-lock braking control cycle, the wheel braking state is determined based on at least one wheel state parameter of the current cycle, and the master cylinder pressure estimate is corrected according to the judgment result. The corrected master cylinder pressure estimate is used as the current master cylinder pressure estimate.

[0018] Output the current master cylinder pressure estimate for braking control.

[0019] In some embodiments of this application, estimating the master cylinder pressure based on the maximum wheel deceleration of the current cycle to obtain a current master cylinder pressure estimate specifically includes:

[0020] Based on the maximum wheel deceleration of the current cycle, and according to the preset mapping relationship between the maximum wheel deceleration and the master cylinder pressure, the estimated value of the current master cylinder pressure is obtained. The mapped estimated value of the current master cylinder pressure is not lower than the actual pressure value measured by a high-precision pressure sensor under standard test conditions.

[0021] In some embodiments of this application, the step of determining the wheel braking state based on at least one wheel state parameter of the current period and correcting the master cylinder pressure estimate based on the determination result specifically includes:

[0022] Determine if under-braking occurs;

[0023] If the system is under-braking, the estimated master cylinder pressure will be corrected downwards based on the degree of under-braking.

[0024] In some embodiments of this application, after the master cylinder pressure estimate is corrected downward based on the degree of underbraking, the method further includes: lowering the detection threshold for overbraking.

[0025] In some embodiments of this application, determining whether an under-braking state has occurred specifically includes:

[0026] Determine whether the road surface adhesion coefficient experiences a step change;

[0027] If no step occurs, the under-braking condition is determined based on the difference in locking pressure between the current anti-lock braking cycle and the previous anti-lock braking cycle and / or the difference in the boost phase time.

[0028] If the number of wheels that meet the under-braking conditions exceeds the first preset threshold, the vehicle is determined to be in an under-braking state.

[0029] In some embodiments of this application, the underbraking condition includes:

[0030] The difference between the locking pressure of this anti-lock braking cycle and the locking pressure of the previous anti-lock braking cycle is greater than the first pressure threshold; and / or

[0031] The difference between the boost phase time of this anti-lock braking cycle and the boost phase time of the previous anti-lock braking cycle is greater than the first time threshold.

[0032] In some embodiments of this application, the step of determining the wheel braking state based on at least one wheel state parameter of the current cycle and correcting the master cylinder pressure estimate based on the determination result further includes:

[0033] If it is not in an under-braking state, then determine whether an over-braking state has occurred;

[0034] If the vehicle is in an over-braking state, the master cylinder pressure estimate will be continuously corrected upwards based on the degree of over-braking until an under-braking state is detected.

[0035] In some embodiments of this application, determining whether a braking state has occurred specifically includes:

[0036] Determine whether the road surface adhesion coefficient experiences a step change;

[0037] If no step occurs, the over-braking condition is determined based on the difference in locking pressure, the time difference in the boost phase, and the time difference in the depressurization phase between the current anti-lock braking cycle and the previous anti-lock braking cycle.

[0038] If the number of wheels that meet the over-braking conditions exceeds the second preset threshold, the vehicle is determined to be in an over-braking state.

[0039] In some embodiments of this application, the over-braking condition includes:

[0040] The difference between the locking pressure of this anti-lock braking cycle and the locking pressure of the previous anti-lock braking cycle is less than the second pressure threshold, and the difference between the pressurization phase time of this anti-lock braking cycle and the pressurization phase time of the previous anti-lock braking cycle is less than the second time threshold. At the same time, the difference between the decompression phase time of this anti-lock braking cycle and the decompression phase time of the previous anti-lock braking cycle is greater than the third time threshold.

[0041] Secondly, embodiments of this application provide a master cylinder pressure estimation system based on wheel state, comprising: a processor and a memory, wherein the processor is coupled to the memory, and the memory is used to store a computer program, wherein when the computer program is executed by the processor, the master cylinder pressure estimation method based on wheel state as described in the first aspect is implemented.

[0042] The beneficial effects of the embodiments of this application are as follows:

[0043] This master cylinder pressure estimation method does not rely on easily disturbed wheel slip ratio characteristics or single wheel speed signals for master cylinder pressure estimation. Instead, it utilizes inherent and relatively stable observations (lock-up pressure, boost time, and depressurization time) in the ABS control cycle as the judgment basis, effectively overcoming the influence of road interference and vehicle speed estimation errors, resulting in high reliability and robustness. Furthermore, by detecting under-braking and over-braking states and performing real-time, feedback-based correction on the master cylinder pressure estimate, the estimated value can quickly converge to near the actual value, achieving adaptive correction and ensuring the accuracy of pressure control. In addition, a conservatively high estimate is used in the first ABS cycle, and the over-braking detection threshold is actively lowered after under-braking is detected. During over-braking, the threshold is continuously corrected upwards until under-braking is triggered, effectively preventing dangerous situations such as wheel lock-up and improving the system's failure safety. Moreover, this application is based on sensor signals (wheel speed sensors, etc.) of existing ESC systems, requiring no additional hardware costs and easily integrated and applied to existing products. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the hydraulic pipeline principle of the ESC system to which the embodiments of this application apply;

[0046] Figure 2 A schematic diagram of the anti-lock control process;

[0047] Figure 3 This is a schematic diagram of the hydraulic principle during the decompression phase after ABS is triggered.

[0048] Figure 4 Flowchart for calculating the opening time of the pressure reducing valve;

[0049] Figure 5 This is a schematic diagram of the hydraulic principle during the pressure holding phase after ABS is triggered.

[0050] Figure 6 This is a schematic diagram of the hydraulic principle during the pressurization phase after ABS is triggered.

[0051] Figure 7 Flowchart for calculating the opening time of the booster valve;

[0052] Figure 8 A schematic diagram of the hydraulic principle when ESC triggers active boost;

[0053] Figure 9 A graph showing the change in wheel cylinder pressure when the estimated pressure of the master cylinder is too high.

[0054] Figure 10 A graph showing the pressure change in the wheel cylinder when the estimated pressure of the master cylinder is too low.

[0055] Figure 11 A schematic diagram of the overall process for estimating master cylinder pressure based on wheel state, provided in an embodiment of this application;

[0056] Figure 12 This application provides a schematic diagram of a sub-process for detecting under-braking of wheels.

[0057] Figure 13 This is a schematic diagram of a wheel over-braking detection sub-process provided in an embodiment of this application. Detailed Implementation

[0058] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0059] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The terms "comprising" and "having," and any variations thereof, in the embodiments and drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0060] This application is based on the ESC system, and its hydraulic pipeline principle is as follows: Figure 1 As shown, HSV1 and HSV2 represent two suction valves, USV1 and USV2 represent two isolation valves, EV1, EV2, EV3, and EV4 represent four booster valves, and AV1, AV2, AV3, and AV4 represent four pressure reducing valves.

[0061] like Figure 2 As shown, anti-lock braking system (ABS) determines whether the wheel is in a stable state based on the wheel deceleration and slip ratio, and repeatedly performs depressurization-holding-increasing operations until the vehicle stops.

[0062] During normal braking, the ABS does not trigger, and no drive control is involved at this time. For example... Figure 1As shown, neither the motor nor the valves are energized. When the brake pedal is depressed, the high-pressure brake fluid in the master cylinder enters the four wheel cylinders through the isolation valve (USV) and the booster valve (EV), generating braking force on the wheels. At this time, the wheel state is stable, and the wheel slip ratio and wheel acceleration do not exceed the ABS intervention threshold, so no control is made on the wheel cylinder pressure.

[0063] After ABS is triggered, the decompression phase is as follows: Figure 3 As shown. When the wheels are in the decompression phase, the boost valve (EV) is energized and closes, isolating the master cylinder pressure from the wheel cylinder pressure. Simultaneously, the decompression valve is energized and opens, allowing brake fluid in the wheel cylinders to flow into the accumulator, causing a rapid drop in wheel cylinder pressure. To prevent the accumulator from becoming fully charged, the motor starts working, driving a plunger pump to pump brake fluid from the accumulator back into the master cylinder, ensuring sufficient brake fluid in the master cylinder.

[0064] When the anti-lock braking system (ABS) controller is in the decompression phase, the target wheel cylinder pressure value given by the upper-level controller is lower than the current wheel cylinder pressure. At this time, the booster valve closes and the decompression valve opens. The decrease in wheel cylinder pressure during the decompression phase is achieved by controlling the opening time of the decompression valve. The calculation process for the decompression valve opening time is as follows: Figure 4 As shown in the diagram. First, based on the wheel cylinder PV curve, the volume of brake fluid that needs to flow out of the wheel cylinder through the pressure reducing valve to reduce the pressure from the current wheel cylinder pressure to the target wheel cylinder pressure is calculated. Then, the pressure difference between the inlet and outlet of the pressure reducing valve is calculated. Next, the valve flow rate at the pressure reducing valve is calculated using the valve flow rate formula under the current pressure difference. Finally, dividing the volume of brake fluid that needs to flow out of the wheel cylinder through the pressure reducing valve by the valve flow rate at this time gives the theoretical opening time of the pressure reducing valve. From the control method of the pressure reducing valve, we can see that the opening time of the pressure reducing valve is related to the decrease in wheel cylinder pressure; the higher the actual wheel cylinder pressure, the longer the wheel remains in the pressure reduction phase.

[0065] After ABS is triggered, the pressure holding phase is as follows: Figure 5 As shown. When the pressure reducing valve opens, the wheel cylinder pressure begins to decrease, and the rate of wheel speed decrease slows down. Because the recovery of wheel slip ratio and wheel deceleration takes time, a pressure holding process is added during the pressurization and depressurization processes. When the wheel deceleration becomes positive, it means that the wheel speed begins to recover. At this time, the pressure reducing valve coil is de-energized, the valve port closes, and the wheel cylinder pressure stops decreasing.

[0066] After ABS is triggered, the boost phase is as follows: Figure 6 As shown, as wheel speed recovers, wheel slip ratio continues to decrease. When both wheel deceleration and slip ratio exceed the wheel deceleration stability threshold and slip ratio stability threshold, the wheel is considered to be in a stable state, and wheel pressure begins to increase. At this time, the pressure reducing valve remains closed, the pressure boosting valve coil is de-energized, the valve port opens, and high-pressure brake fluid in the master cylinder flows into the wheel cylinder, causing the wheel cylinder pressure to rise.

[0067] Similar to the control strategy for the decompression phase, the wheel cylinder pressure control strategy for the boost phase also transforms the pressure control problem into a valve opening time problem. When the wheel is in the boost phase, the boost valve opens and the decompression valve closes. The calculation process for the boost valve opening time is as follows: Figure 7 As shown. After receiving the target wheel cylinder pressure from the upper controller, the system first calculates the volume of brake fluid that needs to flow into the wheel cylinder through the booster valve based on the wheel cylinder PV curve. Then, it calculates the flow rate of the booster valve based on the pressure difference across the booster valve. Dividing the required brake fluid volume into the wheel cylinder by the booster valve flow rate under the current pressure difference yields the theoretical opening time of the booster valve. The wheel cylinder PV curve used in the above control strategy can be obtained through testing on a wheel cylinder stiffness test bench. The booster valve flow rate can be calculated using the orifice flow rate formula. Since the orifice flow rate is related to the pressure difference across the booster valve, it is necessary to calculate the pressure difference across the booster valve. The wheel cylinder pressure is obtained by accumulating the changes in wheel cylinder pressure during each depressurization and boosting phase, thus ensuring stable tracking of the target pressure. The booster valve inlet pressure is generally obtained using a master cylinder pressure sensor.

[0068] ESC triggers the active boost phase, such as Figure 8 As shown. When the vehicle's ESC is triggered, it actively boosts pressure on one side of the wheels. Taking the right front and right rear wheels as an example, when active boosting begins, since the driver is not pressing the pedal, the master cylinder has no pressure build-up. At this time, the motor drives the return pump to actively build up pressure. First, the isolation valve (USV) closes, the suction valve (HSV) opens, and the boost valve (EV) opens. The brake fluid in the master cylinder, driven by the motor pump, enters the wheel cylinder through the suction valve and the boost valve, and the wheel cylinder pressure begins to rise, completing the active pressure build-up process.

[0069] The ESC system described in this application installs a pressure sensor at the master cylinder location to collect master cylinder pressure. During anti-lock braking, if the master cylinder pressure sensor fails, the boost phase cannot be controlled, leading to two possible outcomes:

[0070] (1) The estimated master cylinder pressure is greater than the actual master cylinder pressure.

[0071] The boosting state when the estimated pressure of the master cylinder is too high is as follows: Figure 9 As shown. When the estimated master cylinder pressure is greater than the actual master cylinder pressure, the pressure difference across the booster valve is too large, leading to an overestimation of the booster valve flow rate calculated using the valve flow rate formula. When the target wheel cylinder pressure is determined, the volume of brake fluid flowing into the wheel cylinder through the booster valve can also be determined by referring to the table based on the wheel cylinder PV curve. In this case, the booster valve flow rate calculated based on the estimated master cylinder pressure is too large, resulting in a shorter booster valve opening time. This leads to a slower wheel cylinder pressure rise and a longer boosting period. After multiple boosting cycles, the calculated wheel cylinder lock-up pressure is too high.

[0072] (2) The estimated master cylinder pressure is less than the actual master cylinder pressure.

[0073] When the estimated pressure of the master cylinder is low, the boosting state is as follows: Figure 10 As shown, when the estimated master cylinder pressure is less than the actual master cylinder pressure, the calculated pressure difference at the booster valve orifice will be too small. The booster valve flow rate calculated from this smaller pressure difference will also be too small. When the volume of brake fluid needing to flow into the wheel cylinder through the booster valve is constant, the calculated booster valve opening time will be too long, leading to pressure overshoot during the boosting phase. Therefore, when the estimated master cylinder pressure is less than the actual master cylinder pressure, the wheel cylinder pressure rises rapidly, and the wheel quickly reaches the unstable region and begins to depressurize. Consequently, the boosting phase is shorter, and the calculated wheel cylinder lock-up pressure is lower. Because the wheel cylinder pressure rises rapidly with significant overshoot, the depressurization time in the unstable region is also longer.

[0074] Based on the above analysis of whether the estimated master cylinder pressure is too high or too low compared to the actual master cylinder pressure, the following conclusions can be drawn:

[0075] When the estimated master cylinder pressure is too high, the wheel cylinder pressure rises slowly and cannot keep up with the target wheel cylinder pressure, resulting in under-braking. In this case, the boosting phase lasts longer and the calculated wheel cylinder lock-up pressure is higher. When the estimated master cylinder pressure is too low, the wheel cylinder pressure rises too quickly and the boosting magnitude exceeds the given target wheel cylinder pressure, resulting in over-braking. In this case, the boosting phase lasts shorter and the calculated lock-up pressure is lower, while the decompression phase lasts longer.

[0076] If the wheel cylinder pressure rises slowly, the vehicle loses deceleration and the braking distance increases. If the wheel cylinder pressure rises rapidly, the wheel speed decreases quickly, which can easily lead to wheel lock-up and cause a safety accident.

[0077] Based on the above analysis, this application discloses a master cylinder pressure estimation method based on wheel status, applied to an ESC system. It utilizes the dynamic characteristics of the wheels exhibited during ABS control (such as lock-up pressure, boost time, and depressurization time) to indirectly infer the accuracy of the master cylinder pressure, and continuously corrects the estimated master cylinder pressure value through a closed-loop feedback mechanism. Detailed explanations follow.

[0078] Figure 11 A master cylinder pressure estimation method based on wheel conditions, according to an embodiment of this application, is illustrated. Figure 11 As shown, the master cylinder pressure estimation method includes the following steps:

[0079] Step S101: Detect the validity of the master cylinder pressure sensor signal.

[0080] If the master cylinder pressure sensor signal is valid, proceed from step S101 to step S102; if the master cylinder pressure sensor signal is invalid, proceed from step S101 to step S103.

[0081] In this application, the master cylinder pressure sensor signal acquired at the bottom layer is first detected, and the validity of the master cylinder pressure sensor signal is determined based on the signal quality of the master cylinder pressure sensor.

[0082] Step S102: Use the value collected by the master cylinder pressure sensor as the current master cylinder pressure estimate.

[0083] In this application, after determining that the master cylinder pressure sensor is valid, the collected value of the master cylinder pressure sensor is subjected to PT filtering processing, and the processed collected value of the master cylinder pressure sensor is assigned to the master cylinder pressure in the algorithm.

[0084] Step S103: Determine whether anti-lock braking control is triggered.

[0085] If the anti-lock braking system is not triggered, proceed from step S103 to step S104; if the anti-lock braking system is triggered, proceed from step S103 to step S105.

[0086] In this application, when the failure of the master cylinder pressure sensor is detected, the anti-lock braking controller first issues a flag based on whether the wheel deceleration and wheel slip ratio exceed the instability threshold, and then determines whether ABS control is triggered.

[0087] Step S104: Estimate the master cylinder pressure based on the vehicle deceleration to obtain the current master cylinder pressure estimate.

[0088] In this application, if the vehicle anti-lock braking system (ABS) is not triggered at this time, the master cylinder pressure is estimated using the vehicle deceleration. Figure 2 It is known that when the vehicle is under normal braking and anti-lock braking system (ABS) is not triggered, the booster valve is normally open, and the master cylinder pressure is the same as the wheel cylinder pressure. If the wheel cylinder pressure value can be obtained, the master cylinder pressure can be calculated. Because the vehicle deceleration and wheel cylinder pressure have a linear relationship, the vehicle deceleration is often used to estimate the wheel cylinder pressure in engineering. When ABS is not triggered, the wheel cylinder pressure is calculated using the vehicle deceleration. At this time, the wheel cylinder pressure is equal to the master cylinder pressure, thus allowing the estimation of the master cylinder pressure under non-ABS conditions.

[0089] Step S105: Determine whether the current state is the first anti-lock braking control cycle.

[0090] If the system is in the first anti-lock braking control cycle, proceed from step S103 to step S106; if the system is not in the first anti-lock braking control cycle, proceed from step S103 to step S107.

[0091] In this application, after the anti-lock braking system (ABS) controller determines that the wheel has triggered ABS, it then determines whether it is in the first ABS cycle. During emergency braking, the driver quickly depresses the brake pedal, causing both the master cylinder pressure and wheel cylinder pressure to rise simultaneously. After ABS is triggered, the wheel cylinder pressure decreases, while the master cylinder pressure continues to rise. At this point, the booster valve closes, and the master cylinder pressure and wheel cylinder pressure are no longer the same. Because the master cylinder pressure estimation strategy proposed in this application mainly utilizes a comparison with the wheel dynamic characteristics in the previous ABS cycle to correct the estimated master cylinder pressure, it is necessary to determine whether it is in the first control cycle of ABS and to estimate the master cylinder pressure in the first ABS cycle.

[0092] Step S106: Estimate the master cylinder pressure based on the maximum wheel deceleration of the current cycle to obtain the current master cylinder pressure estimate.

[0093] Specifically, based on the maximum wheel deceleration of the current cycle, and according to the preset mapping relationship between the maximum wheel deceleration and the master cylinder pressure, the estimated value of the current master cylinder pressure is obtained. The mapped estimated value of the current master cylinder pressure is not lower than the actual pressure value measured by a high-precision pressure sensor under standard test conditions.

[0094] In this application, during the first ABS cycle, the master cylinder pressure is estimated using the maximum wheel deceleration. Since a higher master cylinder pressure results in a higher maximum wheel deceleration, a curve between the maximum wheel deceleration and the master cylinder pressure is established through testing. During the first ABS cycle, the master cylinder pressure is estimated using the maximum wheel deceleration, and to prevent over-braking that could lead to wheel lockup, the master cylinder pressure is generally estimated to be higher.

[0095] Step S107: Determine the wheel braking state based on at least one wheel state parameter in the current cycle, and correct the master cylinder pressure estimate based on the determination result, and use the corrected master cylinder pressure estimate as the current master cylinder pressure estimate.

[0096] Specifically, the system determines whether an under-braking condition has occurred. If an under-braking condition is present, the estimated master cylinder pressure is adjusted downwards based on the degree of under-braking. Furthermore, after adjusting the estimated master cylinder pressure downwards based on the degree of under-braking, the detection threshold for over-braking is lowered. If an under-braking condition is not present, the system determines whether an over-braking condition has occurred. If an over-braking condition is present, the estimated master cylinder pressure is continuously adjusted upwards based on the degree of over-braking until an under-braking condition is detected.

[0097] In some embodiments, the determination of whether an under-braking state occurs specifically includes: determining whether the road surface adhesion coefficient has changed abruptly; if no abrupt change occurs, determining whether an under-braking condition is met based on the difference in locking pressure between the current anti-lock braking cycle and the previous anti-lock braking cycle and / or the difference in boost phase time; if the number of wheels meeting the under-braking condition exceeds a first preset threshold, then the vehicle is determined to be in an under-braking state. The under-braking condition includes: the difference in locking pressure between the current anti-lock braking cycle and the previous anti-lock braking cycle is greater than a first pressure threshold; and / or the difference in boost phase time between the current anti-lock braking cycle and the previous anti-lock braking cycle is greater than a first time threshold.

[0098] In other embodiments, the determination of whether an over-braking state has occurred specifically includes: determining whether the road surface adhesion coefficient has changed abruptly; if no abrupt change has occurred, determining whether the over-braking condition is met based on the difference in locking pressure, the difference in boosting time, and the difference in depressurization time between the current anti-lock braking cycle and the previous anti-lock braking cycle; if the number of wheels meeting the over-braking condition exceeds a second preset threshold, then the vehicle is determined to be in an over-braking state. The over-braking condition includes: the difference in locking pressure between the current and previous anti-lock braking cycles is less than a second pressure threshold, the difference in boosting time between the current and previous anti-lock braking cycles is less than a second time threshold, and the difference in depressurization time between the current and previous anti-lock braking cycles is greater than a third time threshold.

[0099] In this application, after ABS is triggered, and if this is not the first ABS cycle, the estimated pressure of the master cylinder needs to be corrected based on the ABS control results to prevent insufficient or excessive wheel cylinder pressure. First, it is determined whether the wheel is under-pressurized. This application proposes using the lock-up pressure and pressurization time of the current cycle to determine if the wheel is under-braking. After determining that the wheel is under-braking, the estimated pressure of the master cylinder is corrected downwards according to the degree of under-braking, increasing the pressurization valve opening time and increasing the change in wheel cylinder pressure. To prevent excessive drop in the estimated pressure of the master cylinder, leading to over-braking, after detecting under-braking and correcting the estimated pressure of the master cylinder downwards, the wheel over-braking detection threshold is lowered to make it easier to trigger, thereby preventing wheel lock-up and potential danger. If under-braking is not detected, the next step is to determine whether the wheel is over-pressurized. Similar to the under-braking detection method, over-braking detection also uses the ABS control results to correct the estimated pressure of the master cylinder. Over-braking detection utilizes the lock-up pressure, pressurization time, and depressurization time of the current cycle. When over-braking is detected, the estimated pressure in the master cylinder is adjusted upwards based on the degree of over-braking, reducing the opening time of the boost valve and decreasing the increase in wheel cylinder pressure. Because over-braking can easily lead to wheel lock-up, which is highly dangerous, the estimated pressure in the master cylinder is continuously adjusted upwards after over-braking is detected until insufficient braking is detected.

[0100] Proceed from steps S102, S104, S106, and S107 to step S108.

[0101] Step S108: Output the current master cylinder pressure estimate for braking control.

[0102] In this application, after processing the estimated pressure of the master cylinder according to different working conditions, the estimated pressure value of the master cylinder is output and participated in the ABS control. Based on the wheel state caused by the pressure increase of the ABS, the estimated pressure of the master cylinder is corrected again.

[0103] In some specific implementation processes, the wheel under-braking detection procedure is as follows: Figure 12 As shown, it includes the following steps:

[0104] Step S201: Input the locking pressure and boosting time of the previous cycle, and determine whether the road surface adhesion coefficient jumps.

[0105] If yes, proceed from step S201 to step S202; if no, proceed from step S201 to step S203.

[0106] In this implementation, after the program starts running, the first step is to determine whether the road surface adhesion coefficient has changed abruptly. The master cylinder pressure correction strategy proposed in this application is based on the observation of the boost time, depressurization time, and lock-up pressure during the ABS control process. When the road surface adhesion coefficient changes abruptly, the wheel state will also be different. Therefore, when determining whether the wheel is in an under-braking state, the first step is to determine whether the road surface coefficient has changed abruptly.

[0107] Step S202: No insufficient braking was detected.

[0108] In this implementation process, if a step change in the road surface adhesion coefficient is detected, it is considered that the wheel does not show insufficient braking. In this cycle, the estimated pressure of the master cylinder will not be corrected, and the wheel condition will not be judged.

[0109] Step S203: Determine whether both the seizure pressure and the pressurization time have increased in this cycle.

[0110] If not, proceed from step S203 to step S204; if yes, proceed from step S203 to step S205.

[0111] In this implementation, after no step change in the road adhesion coefficient is detected, the system begins to determine whether the wheel is under-braking based on the lock-up pressure and boosting time. If the estimated master cylinder pressure is greater than the actual master cylinder pressure, the pressure difference across the boosting valve is too large, and the boosting valve flow rate calculated using the valve flow formula is also too large. When the target wheel cylinder pressure is determined, the volume of brake fluid flowing into the wheel cylinder through the boosting valve can also be determined by referring to the wheel cylinder PV curve table. At this time, the boosting valve flow rate calculated based on the estimated master cylinder pressure is too large, resulting in a shorter boosting valve opening time. This leads to a slower wheel cylinder pressure rise, a longer boosting phase, and a larger calculated wheel cylinder lock-up pressure. Therefore, if the lock-up pressure in the current anti-lock braking cycle minus the lock-up pressure in the previous anti-lock braking cycle is greater than the pressure threshold, and the boosting phase time in the current anti-lock braking cycle minus the boosting phase time in the previous anti-lock braking cycle is greater than the time threshold, both of these conditions are met. The wheel is considered to be under-braking, and the estimated master cylinder pressure is too high.

[0112] Step S204: No insufficient braking was detected.

[0113] In this implementation process, if no under-braking is detected in the wheels, the vehicle is considered not to be in a state of insufficient braking.

[0114] Step S205: Determine whether the number of wheels under-braking exceeds two.

[0115] If not, proceed from step S205 to step S206; if yes, proceed from step S205 to step S207.

[0116] In this implementation, after detecting that a wheel is under-braking, it is necessary to determine how many wheels are under-braking. Because the master cylinder pressure of all four wheels is the same, if the estimated master cylinder pressure is too high, multiple wheels will be under-braking simultaneously. To avoid false triggering of wheel under-braking, it is necessary to determine the status of multiple wheels.

[0117] Step S206: No insufficient braking was detected.

[0118] In this implementation, if the number of wheels in an under-braking state is less than two, the vehicle is considered not to be in an under-braking state, and no correction is made to the master cylinder estimated pressure.

[0119] Step S207: Insufficient braking was detected.

[0120] In this implementation, when the number of wheels in an under-braking state is greater than three, the vehicle is considered to be in an under-braking state, the master cylinder estimated pressure is too high, and the master cylinder estimated pressure needs to be corrected downward.

[0121] Proceed from steps S202, S204, S206, and S207 to step S208.

[0122] Step S208: Determine whether under-braking is detected.

[0123] If not, proceed from step S208 to step S209; if yes, proceed from step S208 to step S210.

[0124] In this implementation process, it is determined whether the vehicle is in an under-braking state and the correction amount of the estimated pressure of the master cylinder is calculated.

[0125] Step S209: The estimated pressure of the master cylinder is not corrected.

[0126] In this implementation, when no under-braking signal is detected, the master cylinder estimated pressure is not corrected, and the correction amount for the master cylinder estimated pressure is zero.

[0127] Step S210: Calculate the under-braking correction amount for the master cylinder pressure.

[0128] In this implementation, if the vehicle is under-braking, the correction amount for the master cylinder estimated pressure is calculated based on the difference between the lock-up pressure of the current cycle and the previous cycle, and the difference between the boost phase time of the current cycle and the previous cycle. The larger the difference, the more obvious the under-braking, and the larger the correction amount for the master cylinder estimated pressure.

[0129] Proceed from steps S209 and S210 to step S211.

[0130] Step S211: Output the estimated pressure correction amount for the master cylinder.

[0131] In this implementation process, the process ends and the correction amount for the estimated pressure of the main cylinder is output.

[0132] In other specific implementation processes, the wheel over-braking detection procedure is as follows: Figure 13 As shown, it includes the following steps:

[0133] Step S301: Input the locking pressure, pressurization time, and depressurization time of the previous cycle, and determine whether the road surface adhesion coefficient jumps.

[0134] If yes, proceed from step S301 to step S302; if no, proceed from step S301 to step S303.

[0135] In this implementation process, similar to underbraking detection, after the program starts running, it first determines whether the road surface adhesion coefficient jumps.

[0136] Step S302: No over-braking occurred.

[0137] In this implementation process, if a step change in the road surface adhesion coefficient is detected, it is considered that the wheel has not shown excessive braking, and the wheel status will not be judged in this cycle.

[0138] Step S303: Determine whether the locking pressure and pressurization time both decrease in this cycle, and whether the depressurization time increases in this cycle.

[0139] If not, proceed from step S303 to step S304; if yes, proceed from step S303 to step S305.

[0140] In this implementation, after no step change in the road adhesion coefficient is detected, the determination of whether the wheel is in an over-braking state is based on the locking pressure, the time of the boosting phase, and the time of the depressurization phase. If the estimated master cylinder pressure is less than the actual master cylinder pressure, the pressure difference across the boosting valve will be smaller, and consequently, the boosting valve flow rate calculated by the valve flow formula will also be smaller. When the target pressure of the wheel cylinder is determined, the volume of brake fluid that needs to flow into the wheel cylinder through the boosting valve can also be determined by referring to the table based on the wheel cylinder PV curve. At this time, the boosting valve flow rate calculated based on the estimated master cylinder pressure will be smaller, resulting in a larger boosting valve opening time. This leads to a faster rise in wheel cylinder pressure, causing overshoot in the actual wheel cylinder pressure, a shorter boosting phase time, and a smaller calculated wheel cylinder locking pressure. In the latter case, the actual wheel cylinder pressure will be larger, therefore, a longer depressurization time is required, resulting in a longer depressurization phase. In summary, the conditions for determining wheel over-braking are as follows:

[0141] If the difference between the locking pressure in the current anti-lock braking cycle and the locking pressure in the previous anti-lock braking cycle is less than the pressure threshold, and the difference between the time of the boost phase in the current anti-lock braking cycle and the time of the boost phase in the previous anti-lock braking cycle is less than the time threshold 1, and the difference between the time of the decompression phase in the current cycle and the time of the decompression phase in the previous anti-lock braking cycle is greater than the time threshold 2, then all three conditions are met, and the wheel is considered to be in an over-braking state.

[0142] Step S304: No over-braking occurred.

[0143] In this implementation process, if no wheel is detected to be in an over-braking state, it is considered that the vehicle has not experienced over-braking.

[0144] Step S305: Determine whether the number of wheels that have been braked exceeds two.

[0145] If not, proceed from step S305 to step S306; if yes, proceed from step S305 to step S307.

[0146] In this implementation, after detecting that a wheel is in an over-braking state, it is also necessary to determine how many wheels are in an over-braking state. To avoid false triggering of wheel over-braking, it is necessary to determine the state of multiple wheels.

[0147] Step S306: No over-braking occurred.

[0148] In this implementation, if the number of wheels in the over-braking state is less than two, it is considered that the vehicle is not in an under-braking state, and no correction is made to the estimated pressure of the master cylinder.

[0149] Step S307: Over-braking was detected.

[0150] In this implementation, when the number of wheels in the over-braking state is greater than three, the vehicle is considered to be in an over-braking state, the master cylinder estimated pressure is too low, and the master cylinder estimated pressure needs to be corrected upward.

[0151] Proceed from steps S302, S304, S306, and S307 to step S308.

[0152] Step S308: Determine whether over-braking has been detected.

[0153] If yes, proceed from step S308 to step S309; ​​if no, proceed from step S308 to step S310.

[0154] In this implementation process, it is determined whether the vehicle is in an over-braking state and the correction amount of the estimated pressure of the master cylinder is calculated.

[0155] Step S309: Calculate the over-braking correction amount for the master cylinder pressure.

[0156] In this implementation, when a vehicle over-braking signal is detected, the correction amount of the master cylinder estimated pressure is calculated based on the difference between the locking pressure of the current cycle and the previous cycle, the difference between the boosting phase time of the current cycle and the previous cycle, and the difference between the depressurization phase time of the current cycle and the previous cycle.

[0157] Step S310: Determine whether under-braking is detected.

[0158] If not, proceed from step S310 to step S311; if yes, proceed from step S310 to step S312.

[0159] In this implementation, if over-braking is not detected at this time, it is necessary to check again whether under-braking has been triggered. Because over-braking of the wheel can easily cause wheel lock-up, this application proposes that after detecting that the wheel is in over-braking and the master cylinder estimated pressure is too low, the master cylinder estimated pressure will be continuously corrected upward until the wheel triggers the under-braking condition. Therefore, it is necessary to determine whether the wheel has triggered under-braking at this point.

[0160] Step S311: Maintain the master cylinder pressure correction amount from the previous cycle.

[0161] In this implementation process, if the wheel does not trigger under-braking, the estimated pressure of the master cylinder still needs to be corrected upward until the wheel triggers under-braking.

[0162] In step S312, the estimated pressure of the master cylinder is not corrected.

[0163] In this implementation, if under-braking is detected in the wheel, the correction amount of the master cylinder estimated pressure is zero, and the master cylinder estimated pressure will no longer be corrected upward.

[0164] Proceed from steps S309, S311, and S312 to step S313.

[0165] Step S313: Output the estimated pressure correction amount for the master cylinder.

[0166] In this implementation process, the process ends and the correction amount for the estimated pressure of the main cylinder is output.

[0167] This application utilizes the characteristics of anti-lock braking system (ABS), pointing out that on a uniform road surface, the lock-up pressure in each ABS control cycle should be approximately the same. Furthermore, based on the control method of the booster / depressurization valve, the boosting and depressurization phase times in each ABS cycle should also be approximately the same. Therefore, this application proposes using wheel lock-up pressure, boosting phase time, and depressurization phase time to determine wheel status. If multiple wheels are under-braked, the master cylinder estimated pressure is considered too high, requiring a downward correction by increasing the booster valve opening time. Conversely, if multiple wheels are over-braked, the master cylinder estimated pressure is considered too low, requiring an upward correction by decreasing the booster valve opening time.

[0168] This application corrects the estimated master cylinder pressure based on the different wheel dynamic characteristics caused by the estimated master cylinder pressure, thus preventing the wheels from being in an under-braking state for a long time, which would lead to insufficient braking; and also preventing the wheels from being in an over-braking state, which would cause wheel lock-up. The master cylinder pressure estimation method proposed in this application can meet the anti-lock braking control requirements after the ESC system master cylinder pressure sensor fails.

[0169] Corresponding to the above method embodiments, another embodiment of this application provides a master cylinder pressure estimation system based on wheel state, including: a processor and a memory, the processor being coupled to the memory, the memory being used to store a computer program, and when the computer program is executed by the processor, the above-mentioned master cylinder pressure estimation method based on wheel state is implemented.

[0170] The above system embodiments correspond to the method embodiments and have the same technical effects. For detailed descriptions, please refer to the method embodiments. The system embodiments are derived from the method embodiments; detailed descriptions can be found in the method embodiments section, and will not be repeated here. Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for estimating master cylinder pressure based on wheel condition, characterized in that, The master cylinder pressure estimation method, applied to the Electronic Stability Control (ESC) system, includes: Detect the validity of the master cylinder pressure sensor signal; If the master cylinder pressure sensor signal is valid, the collected value of the master cylinder pressure sensor is used as the current estimated value of the master cylinder pressure. If the master cylinder pressure sensor signal fails, determine whether to trigger anti-lock braking control; If anti-lock braking system is not triggered, the master cylinder pressure is estimated based on the vehicle deceleration to obtain the current master cylinder pressure estimate. If anti-lock braking control has been triggered, determine whether the current state is the first anti-lock braking control cycle; If it is in the first anti-lock braking control cycle, the master cylinder pressure is estimated based on the maximum wheel deceleration of the current cycle to obtain the current master cylinder pressure estimate; specifically, it includes: based on the maximum wheel deceleration of the current cycle, and according to the preset mapping relationship between the maximum wheel deceleration and the master cylinder pressure, the current master cylinder pressure estimate is not lower than the actual pressure value measured by a high-precision pressure sensor under standard test conditions; If it is not in the first anti-lock braking control cycle, the wheel braking state is determined based on at least one wheel state parameter of the current cycle, and the master cylinder pressure estimate is corrected according to the judgment result. The corrected master cylinder pressure estimate is used as the current master cylinder pressure estimate. Output the current master cylinder pressure estimate for braking control.

2. The master cylinder pressure estimation method based on wheel state according to claim 1, characterized in that, The process of determining the wheel braking state based on at least one wheel state parameter in the current cycle, and correcting the master cylinder pressure estimate based on the determination result, specifically includes: Determine if under-braking occurs; If the system is under-braking, the estimated master cylinder pressure will be corrected downwards based on the degree of under-braking.

3. The master cylinder pressure estimation method based on wheel state according to claim 2, characterized in that, After correcting the master cylinder pressure estimate downward based on the degree of underbraking, the method further includes lowering the detection threshold for overbraking conditions.

4. The master cylinder pressure estimation method based on wheel state according to claim 2, characterized in that, The determination of whether an under-braking state has occurred specifically includes: Determine whether the road surface adhesion coefficient experiences a step change; If no step occurs, the under-braking condition is determined based on the difference in locking pressure between the current anti-lock braking cycle and the previous anti-lock braking cycle and / or the difference in the boost phase time. If the number of wheels that meet the under-braking conditions exceeds the first preset threshold, the vehicle is determined to be in an under-braking state.

5. The master cylinder pressure estimation method based on wheel state according to claim 4, characterized in that, The underbraking conditions include: The difference between the locking pressure of this anti-lock braking cycle and the locking pressure of the previous anti-lock braking cycle is greater than the first pressure threshold; and / or The difference between the boost phase time of this anti-lock braking cycle and the boost phase time of the previous anti-lock braking cycle is greater than the first time threshold.

6. The master cylinder pressure estimation method based on wheel state according to claim 2, characterized in that, The process of determining the wheel braking state based on at least one wheel state parameter in the current cycle, and correcting the master cylinder pressure estimate based on the determination result, specifically includes: If it is not in an under-braking state, then determine whether an over-braking state has occurred; If the vehicle is in an over-braking state, the master cylinder pressure estimate will be continuously corrected upwards based on the degree of over-braking until an under-braking state is detected.

7. The master cylinder pressure estimation method based on wheel state according to claim 6, characterized in that, The determination of whether a braking state has occurred specifically includes: Determine whether the road surface adhesion coefficient experiences a step change; If no step occurs, the over-braking condition is determined based on the difference in locking pressure, the time difference in the boost phase, and the time difference in the depressurization phase between the current anti-lock braking cycle and the previous anti-lock braking cycle. If the number of wheels that meet the over-braking conditions exceeds the second preset threshold, the vehicle is determined to be in an over-braking state.

8. The master cylinder pressure estimation method based on wheel state according to claim 7, characterized in that, The over-braking conditions include: The difference between the locking pressure of this anti-lock braking cycle and the locking pressure of the previous anti-lock braking cycle is less than the second pressure threshold, and the difference between the pressurization phase time of this anti-lock braking cycle and the pressurization phase time of the previous anti-lock braking cycle is less than the second time threshold. At the same time, the difference between the decompression phase time of this anti-lock braking cycle and the decompression phase time of the previous anti-lock braking cycle is greater than the third time threshold.

9. A master cylinder pressure estimation system based on wheel state, characterized in that, include: A processor and a memory, the processor being coupled to the memory, the memory being used to store a computer program that, when executed by the processor, implements the master cylinder pressure estimation method based on wheel state as described in any one of claims 1–8.

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