A pressure control method and system for a hydraulic braking system of a four-wheel vehicle

Abstract

The present application belongs to the technical field of hydraulic brake control, and particularly discloses a pressure control method and system for a hydraulic brake system of a four-wheel vehicle. The method comprises the following steps: obtaining initial target braking torques of four wheels, and calculating corresponding initial target pressures of the four wheels; calculating first theoretical target pressures of hydraulic cylinders of the four wheels, and obtaining first loss pressures and braking forces lost by the four wheels, and calculating first compensation pressures of the same side; obtaining second theoretical target pressures of the hydraulic cylinders of the four wheels without exceeding working capacity, and obtaining a sum of braking forces lost by the left two wheels and a sum of braking forces lost by the right two wheels; calculating residual compensation capabilities of braking forces of the four wheels based on the second theoretical target pressures and with the maximum pressure allowed by the hydraulic cylinders as a constraint; performing cross-side compensation of pressures of the four wheels, obtaining cross-side compensation pressures of the four wheels, and calculating execution target pressures of the hydraulic cylinders of the four wheels. The present application maximizes the braking force demand of the whole vehicle, shortens the braking distance, and improves the braking safety of the vehicle.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydraulic brake control, and more particularly to a pressure control method and system for a hydraulic brake system of a four-wheel vehicle. BACKGROUND

[0002] The brake system is an important part of the vehicle structure. The brake system has various structural forms. With the progress of brake system technology, a brake system with each wheel independently configured with a brake pump and a brake hydraulic cylinder appears. The brake force of each wheel can be independently controlled in real time, which can improve the stability of the vehicle. However, the control strategy of the brake system with this structure is more complex. Due to the different output capacities of the brake hydraulic cylinders, the brake hydraulic cylinders are prone to damage or have a low service life, and the output capacity of the brake system cannot be maximized, resulting in a longer braking distance. SUMMARY

[0003] In view of the above defects or improvement needs of the prior art, the present application provides a pressure control method and system for a hydraulic brake system of a four-wheel vehicle to solve the problems of the brake system with each wheel independently configured with a brake pump and a brake hydraulic cylinder due to the different output capacities of the brake hydraulic cylinders, the brake hydraulic cylinders are prone to damage or have a low service life, and the output capacity of the brake system cannot be maximized, resulting in a longer braking distance.

[0004] To achieve the above-mentioned purpose, according to one aspect of the present application, a pressure control method for a hydraulic brake system of a four-wheel vehicle is provided, comprising the following steps:

[0005] S1 obtaining the initial target braking torque of the four wheels and calculating the corresponding initial target pressure of the four wheels;

[0006] S2 calculating the first theoretical target pressure of the four-wheel brake hydraulic cylinders based on the working capacity of the four-wheel brake hydraulic cylinders, obtaining the first loss pressure and the lost braking force of the four wheels, and calculating the first compensation pressure of the same side according to the lost braking force;

[0007] S3 obtaining the second theoretical target pressure of the four-wheel hydraulic cylinders without exceeding the working capacity, calculating the second loss pressure according to the second theoretical target pressure and the first compensation pressure, and obtaining the sum of the lost braking force of the left two wheels and the sum of the lost braking force of the right two wheels;

[0008] S4 calculating the remaining compensation capacity of the braking force of the four wheels based on the second theoretical target pressure and the maximum pressure allowed by the hydraulic cylinder as a constraint;

[0009] S5 compensating the pressure of the four wheels on the opposite side to obtain the opposite side compensation pressure of the four wheels, and calculating the execution target pressure of the four-wheel hydraulic cylinders according to the opposite side compensation pressure of the four wheels and the second theoretical target pressure.

[0010] As a further preferred, in step S1, the four-wheel initial target braking torque obtained according to the driver's intention and the vehicle state, the initial target braking torque includes the product of the brake cylinder initial target pressure, the contact area of the brake caliper and the brake disc and the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel.

[0011] As a further preferred, in step S2, the first theoretical target pressure of the four-wheel brake cylinder is calculated based on the working capacity of the four-wheel brake cylinder:

[0012]

[0013] Wherein, P flmax is the maximum pressure allowed to work of the left front wheel brake cylinder, P rlmax is the maximum pressure allowed to work of the left rear wheel brake cylinder, P frmax is the maximum pressure allowed to work of the right front wheel brake cylinder, P rrmax is the maximum pressure allowed to work of the right rear wheel brake cylinder, P1 fl is the first theoretical target pressure of the left front wheel brake cylinder, P1 rl is the first theoretical target pressure of the left rear wheel brake cylinder, P1 fr is the first theoretical target pressure of the right front wheel brake cylinder, P1 rr is the first theoretical target pressure of the right rear wheel brake cylinder, P fl is the initial target pressure of the left front wheel brake cylinder, P rl is the initial target pressure of the left rear wheel brake cylinder, P fr is the initial target pressure of the right front wheel brake cylinder, P rl is the initial target pressure of the right rear wheel brake cylinder.

[0014] As a further preferred, in step S3, the second theoretical target pressure is the smaller one of the first theoretical target pressure and the corresponding same side first compensation pressure added to the maximum pressure allowed to work of the hydraulic cylinder.

[0015] As a further preferred, in step S3, the total sum of the braking force lost by the left two wheels and the total sum of the braking force lost by the right two wheels based on the second loss pressure includes:

[0016]

[0017] Wherein: ΔT l is the total sum of the braking force lost by the left two wheels, ΔT r is the total sum of the braking force lost by the right two wheels, ΔP3 flΔP3 is the second loss pressure of the left front wheel brake hydraulic cylinder based on the second theoretical target pressure rl ΔP3 is the second loss pressure of the left rear wheel brake hydraulic cylinder based on the second theoretical target pressure fr ΔP3 is the second loss pressure of the right front wheel brake hydraulic cylinder based on the second theoretical target pressure rr ΔP3 is the second loss pressure of the right rear wheel brake hydraulic cylinder based on the second theoretical target pressure fl S is the contact area of the left front wheel brake caliper and the brake disc rl S is the contact area of the left rear wheel brake caliper and the brake disc fr S is the contact area of the right front wheel brake caliper and the brake disc rr S is the contact area of the right rear wheel brake caliper and the brake disc fl r is the radius from the center of the contact area of the left front wheel brake caliper and the brake disc to the center of the wheel rl r is the radius from the center of the contact area of the left rear wheel brake caliper and the brake disc to the center of the wheel fr r is the radius from the center of the contact area of the right front wheel brake caliper and the brake disc to the center of the wheel rr r is the radius from the center of the contact area of the right rear wheel brake caliper and the brake disc to the center of the wheel μ is the friction coefficient between the brake caliper and the brake disc.

[0018] As a further preferred, in step S4, the pressure remaining compensation capability of the four wheels is equal to the maximum pressure allowed for the hydraulic cylinder to work minus the second theoretical target pressure multiplied by the contact area of the brake caliper and the brake disc and the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel.

[0019] As a further preferred, in step S5, the total brake force lost by the left two wheels is compensated by the remaining compensation capability of the right front wheel and the right rear wheel brake force, and the right front wheel and the right rear wheel opposite side compensation pressure is obtained, specifically:

[0020] (1) When the total brake force lost by the left two wheels is less than or equal to the remaining compensation capability of the right front wheel brake force, the right front wheel opposite side compensation pressure is equal to the total brake force lost by the left two wheels divided by the contact area of the brake caliper and the brake disc of the right front wheel, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

[0021] (2) When the total brake force lost by the left two wheels is greater than the remaining compensation capability of the right front wheel brake force, the right front wheel opposite side compensation pressure is equal to the remaining compensation capability of the right front wheel brake force, and the right rear wheel opposite side compensation pressure is equal to the total brake force lost by the left two wheels minus the right front wheel opposite side compensation pressure divided by the contact area of the brake caliper and the brake disc of the right rear wheel, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

[0022] (2) When the total lost braking force of the left two wheels is greater than the remaining compensation capability of the right front wheel and the total lost braking force of the left two wheels is less than the sum of the remaining compensation capability of the right front wheel and the remaining compensation capability of the right rear wheel, the right front wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the right front wheel divided by the contact area of the right front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the total lost braking force of the left two wheels minus the remaining compensation capability of the right front wheel divided by the product of the contact area of the right rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc;

[0023] (3) When the total lost braking force of the left two wheels is greater than or equal to the sum of the remaining compensation capability of the right front wheel and the remaining compensation capability of the right rear wheel, the right front wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the right front wheel divided by the contact area of the right front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the right rear wheel divided by the contact area of the right rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

[0024] As a further preferred, in step S5, the total lost braking force of the right two wheels is compensated by the remaining compensation capability of the left front wheel and the left rear wheel, and the left front wheel and the left rear wheel opposite side compensation pressure is obtained, in particular:

[0025] (1) When the total lost braking force of the right two wheels is less than or equal to the remaining compensation capability of the left front wheel, the left front wheel opposite side compensation pressure is equal to the total lost braking force of the right two wheels divided by the product of the contact area of the left front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to 0;

[0026] (2) When the total lost braking force of the right two wheels is greater than the remaining compensation capability of the left front wheel braking force and the total lost braking force of the right two wheels is less than the sum of the remaining compensation capability of the left front wheel braking force and the remaining compensation capability of the left rear wheel braking force, the left front wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the left front wheel braking force, the contact area of the left front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to the product of the total lost braking force of the right two wheels minus the remaining compensation capability of the left front wheel braking force, the contact area of the left rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc;

[0027] (3) When the total lost braking force of the right two wheels is greater than or equal to the sum of the remaining compensation capability of the left front wheel braking force and the remaining compensation capability of the left rear wheel braking force, the left front wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the left front wheel braking force, the contact area of the left front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the left rear wheel braking force, the contact area of the left rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

[0028] As a further preferred, in step S5, the execution target pressure of the four-wheel hydraulic cylinders is calculated according to the opposite side compensation pressure of the four wheels and the second theoretical target pressure, and the execution target pressure of the four-wheel brake hydraulic cylinders is equal to the second theoretical target pressure plus the corresponding opposite side compensation pressure. That is:

[0029]

[0030] Wherein: P3 fl is the target pressure executed by the left front wheel brake hydraulic cylinder, P3 rl is the target pressure executed by the left rear wheel brake hydraulic cylinder, P3 fr is the target pressure executed by the right front wheel brake hydraulic cylinder, P3 rr is the target pressure executed by the right rear wheel brake hydraulic cylinder.

[0031] According to another aspect of the present application, there is also provided a pressure control system of a four-wheel vehicle hydraulic braking system, comprising:

[0032] a first master control module, configured to obtain the initial target braking torque of the four wheels and calculate the corresponding initial target pressure of the four wheels;

[0033] The second master module is used for calculating a first theoretical target pressure of the four-wheel brake hydraulic cylinder based on the working capacity of the four-wheel brake hydraulic cylinder, obtaining a first loss pressure and a four-wheel loss brake force, and calculating a first compensation pressure of the same side according to the loss brake force;

[0034] The third master module is used for obtaining a second theoretical target pressure of the four-wheel hydraulic cylinder not exceeding the working capacity, calculating a second loss pressure according to the second theoretical target pressure and the first compensation pressure, and obtaining a sum of left two-wheel loss brake forces and a sum of right two-wheel loss brake forces;

[0035] The fourth master module is used for calculating a four-wheel brake force remaining compensation capacity based on the second theoretical target pressure and a maximum pressure allowed by the hydraulic cylinder.

[0036] The fifth master module is used for performing a cross-side compensation of the four-wheel pressure, obtaining a cross-side compensation pressure of the four-wheel, and calculating an execution target pressure of the four-wheel hydraulic cylinder according to the cross-side compensation pressure of the four-wheel and the second theoretical target pressure.

[0037] Overall, compared with the prior art, the above technical scheme of the present application mainly has the following technical advantages:

[0038] 1. The present application obtains the initial target pressure of each hydraulic cylinder of the hydraulic brake system based on the driver's intention and the vehicle state, limits the pressure of each hydraulic cylinder of the brake system again in combination with the pressure output capacity of the hydraulic brake system, then maximizes the use of the pressure output capacity of each hydraulic cylinder of the brake system, first compensates the loss brake force through the same side pressure, if the same side compensation cannot meet the brake force demand of the vehicle, then compensates the loss brake force again through the cross side. That is, the present application protects each hydraulic cylinder of the brake system from being damaged due to over-capacity work, improves the service life of the brake system, maximizes the realization of the brake force demand of the vehicle through the same side compensation and then the cross side compensation, shortens the braking distance, and improves the braking safety of the vehicle. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a flow chart of a pressure control method of a four-wheel vehicle hydraulic brake system. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0041] As shown in the figure, the pressure control method of the hydraulic braking system of the four-wheel vehicle provided by the embodiment of the present application specifically comprises the following steps: Figure 1

[0042] Step 1: Calculate the initial target pressure of the four wheels according to the initial target braking torque of the four wheels obtained according to the driver's intention and the vehicle state.

[0043]

[0044] Wherein: T fl —left front wheel initial target braking torque; T rl —left rear wheel initial target braking torque; T fr —right front wheel initial target braking torque; T rr —right rear wheel initial target braking torque; P fl —left front wheel brake hydraulic cylinder initial target pressure; P rl —left rear wheel brake hydraulic cylinder initial target pressure; P fr —right front wheel brake hydraulic cylinder initial target pressure; P rl —right rear wheel brake hydraulic cylinder initial target pressure; S fl —contact area of left front wheel brake caliper and brake disc; S rl —contact area of left rear wheel brake caliper and brake disc; S fr —contact area of right front wheel brake caliper and brake disc; S rr —contact area of right rear wheel brake caliper and brake disc; r fl —radius from contact area center of left front wheel brake caliper and brake disc to wheel center; r rl —radius from contact area center of left rear wheel brake caliper and brake disc to wheel center; r fr —radius from contact area center of right front wheel brake caliper and brake disc to wheel center; r rr —radius from contact area center of right rear wheel brake caliper and brake disc to wheel center; μ—friction coefficient between brake caliper and brake disc.

[0045] Further, wherein: T fl , T rl , T fr , T rr ​The size of the driver's intention represented by the brake pedal opening degree and the additional yaw stability torque required by the vehicle yaw stability control are superimposed to obtain the overall vehicle state calculation.

[0046] Further, it is known that P fl , P rl , P fr , P rr :

[0047]

[0048] Step 2: The brake hydraulic system of the four-wheel hydraulic cylinder has limited working capacity, and if it exceeds the working capacity, there is a risk of unrecoverable damage. The first theoretical target pressure of the four-wheel brake hydraulic cylinder is calculated based on the working capacity of the four-wheel brake hydraulic cylinder.

[0049]

[0050] Wherein: P flmax is the maximum pressure allowed for the left front wheel brake hydraulic cylinder to work; P rlmax is the maximum pressure allowed for the left rear wheel brake hydraulic cylinder to work; P frmax is the maximum pressure allowed for the right front wheel brake hydraulic cylinder to work; P rrmax is the maximum pressure allowed for the right rear wheel brake hydraulic cylinder to work; P1 fl is the first theoretical target pressure of the left front wheel brake hydraulic cylinder; P1 rl is the first theoretical target pressure of the left rear wheel brake hydraulic cylinder; P1 fr is the first theoretical target pressure of the right front wheel brake hydraulic cylinder; P1 rr is the first theoretical target pressure of the right rear wheel brake hydraulic cylinder.

[0051] Further, it is known that P1 fl , P1 rl , P1 fr , P1 rr is always less than or equal to the corresponding P fl , P rl , P fr , P rr :

[0052]

[0053] Step 3: Since P1 fl , P1 rl , P1 fr , P1 rr is always less than or equal to the corresponding P fl , P rl , P fr , P rr, then the pressure of the first theoretical target pressure loss relative to the initial target pressure is calculated, and the calculation method is the initial target pressure minus the first theoretical target pressure. The loss pressure (i.e., the first loss pressure) is:

[0054]

[0055] wherein: ΔP1 fl loss pressure of the left front wheel brake hydraulic cylinder based on the first theoretical target pressure; ΔP1 rl loss pressure of the left rear wheel brake hydraulic cylinder based on the first theoretical target pressure; ΔP1 fr loss pressure of the right front wheel brake hydraulic cylinder based on the first theoretical target pressure; ΔP1 rr loss pressure of the right rear wheel brake hydraulic cylinder based on the first theoretical target pressure;

[0056] Further, it is known that:

[0057]

[0058] Step 4: Calculate the four-wheel loss braking force based on the loss pressure of the first theoretical target pressure (i.e., the first loss pressure). The four-wheel loss braking force is equal to the loss pressure multiplied by the contact area of the corresponding brake caliper and brake disc, i.e.:

[0059]

[0060] Further, it is known that:

[0061]

[0062] wherein: ΔT1 fl first braking force lost by the left front wheel; ΔT1 rl first braking force lost by the left rear wheel; ΔT1 fr first braking force lost by the right front wheel; ΔT1 rr first braking force lost by the right rear wheel.

[0063] Step 5: To avoid changing the additional yaw moment of the vehicle, calculate the same side compensation pressure based on the four-wheel loss first braking force.

[0064] Further, the same side compensation pressure of the left front wheel and the left rear wheel is calculated as:

[0065] (1) When the left front wheel and the left rear wheel pressure do not need to be compensated, i.e., ΔT1 fl = 0 and ΔT1r l = 0, the same side compensation pressure of the left front wheel and the left rear wheel is equal to 0, i.e.:

[0066]

[0067] wherein: ΔP2 fl — the left front wheel same side compensation pressure based on the lost first braking force; ΔP2 rl — the left rear wheel same side compensation pressure based on the lost first braking force;

[0068] (2) when the left front wheel and the left rear wheel pressure both need to be compensated, i.e. ΔT1 fl > 0 and ΔT1 rl > 0, the left front wheel and the left rear wheel same side compensation pressure is equal to the lost first braking force divided by the product of the contact area of the brake caliper and the brake disc, the radius from the contact area center of the brake caliper and the brake disc to the wheel center, and the friction coefficient between the brake caliper and the brake disc, i.e.:

[0069]

[0070] (3) when the left front wheel pressure needs to be compensated and the left rear wheel pressure does not need to be compensated, i.e. ΔT1 fl > 0 and ΔT1 rl = 0, the left front wheel same side compensation pressure is equal to 0, and the left rear wheel same side compensation pressure is equal to the lost first braking force of the left front wheel divided by the product of the contact area of the brake caliper and the brake disc, the radius from the contact area center of the brake caliper and the brake disc to the wheel center, and the friction coefficient between the brake caliper and the brake disc, i.e.:

[0071]

[0072] (4) when the left front wheel pressure does not need to be compensated and the left rear wheel pressure needs to be compensated, i.e. ΔT1 fl = 0 and ΔT1 rl > 0, the left front wheel same side compensation pressure is equal to the lost first braking force of the left rear wheel divided by the product of the contact area of the brake caliper and the brake disc, the radius from the contact area center of the brake caliper and the brake disc to the wheel center, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel same side compensation pressure is equal to 0, i.e.:

[0073]

[0074] Further, the right front wheel and the right rear wheel same side pressure compensation is calculated as:

[0075] (1) when the right front wheel and the right rear wheel pressure both do not need to be compensated, i.e. ΔT1 fr = 0 and ΔT1 rr = 0, the right front wheel and the right rear wheel same side compensation pressure is equal to 0, i.e.:

[0076]

[0077] wherein: ΔP2fl - the right front wheel same side compensation pressure based on the lost first braking force; ΔP2 rl - the right rear wheel same side compensation pressure based on the lost first braking force;

[0078] (2) when both the right front wheel and the right rear wheel pressure need to be compensated, i.e. ΔT1 fr > 0 and ΔT1 rr > 0, the right front wheel and the right rear wheel same side compensation pressure is equal to the lost first braking force divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, i.e.

[0079]

[0080] (3) when the right front wheel pressure needs to be compensated and the right rear wheel pressure does not need to be compensated, i.e. ΔT1 fr > 0 and ΔT1 rr = 0, the right front wheel same side compensation pressure is equal to 0, and the right rear wheel same side compensation pressure is equal to the lost first braking force of the right front wheel divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, i.e.

[0081]

[0082] (4) when the right front wheel pressure does not need to be compensated and the right rear wheel pressure needs to be compensated, i.e. ΔT1 fr = 0 and ΔT1 rr > 0, the right front wheel same side compensation pressure is equal to the lost first braking force of the right rear wheel divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel same side compensation pressure is equal to 0, i.e.

[0083]

[0084] Step 6: combine the first theoretical target pressure and the same side compensation pressure and protect the four-wheel hydraulic cylinders from exceeding the working capacity to calculate the second theoretical target pressure of the four-wheel brake hydraulic cylinders. The second theoretical target pressure of the four-wheel brake hydraulic cylinders is equal to the sum of the first theoretical target pressure and the corresponding same side compensation pressure, and the maximum pressure allowed by the hydraulic cylinder, i.e.

[0085]

[0086] wherein: P2 fl - the left front wheel brake hydraulic cylinder second theoretical target pressure; P2 rlP2 ——the second theoretical target pressure of the left rear wheel brake hydraulic cylinder; fr P2 ——the second theoretical target pressure of the right front wheel brake hydraulic cylinder; rr P2 ——the second theoretical target pressure of the right rear wheel brake hydraulic cylinder;

[0087] Further, it is known that:

[0088]

[0089] Step 7: Calculate the loss pressure (i.e., the second loss pressure) based on the sum of the second theoretical target pressure of the four-wheel brake hydraulic cylinder and the first theoretical target pressure plus the corresponding same-side compensation pressure.

[0090]

[0091] ΔP3 ——the loss pressure of the left front wheel brake hydraulic cylinder based on the second theoretical target pressure; fl ΔP3 ——the loss pressure of the left front wheel brake hydraulic cylinder based on the second theoretical target pressure; rl ΔP3 ——the loss pressure of the left rear wheel brake hydraulic cylinder based on the second theoretical target pressure; fr ΔP3 ——the loss pressure of the right front wheel brake hydraulic cylinder based on the second theoretical target pressure; rr ΔP3 ——the loss pressure of the right rear wheel brake hydraulic cylinder based on the second theoretical target pressure.

[0092] Step 8: Calculate the total sum of the lost braking force of the left two wheels and the total sum of the lost braking force of the right two wheels based on the loss pressure of the four-wheel brake hydraulic cylinder of the second theoretical target pressure, i.e.,

[0093]

[0094] ΔT ——the total sum of the lost braking force of the left two wheels; l ΔT ——the total sum of the lost braking force of the left two wheels; r ΔT ——the total sum of the lost braking force of the right two wheels.

[0095] Step 9: Calculate the remaining compensation capability of the braking force of the four wheels based on the second theoretical target pressure, with the maximum pressure allowed for the hydraulic cylinder to work as the constraint. The pressure remaining compensation capability of the four wheels is equal to the maximum pressure allowed for the hydraulic cylinder to work minus the second theoretical target pressure, multiplied by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, i.e.,

[0096]

[0097] ΔT2 ——the remaining compensation capability of the braking force of the left front wheel; fl ΔT2 ——the remaining compensation capability of the braking force of the left front wheel; rl ΔT2 ——the remaining compensation capability of the braking force of the left rear wheel;fr — right front wheel braking force residual compensation capability; ΔT2 rr — right rear wheel braking force residual compensation capability.

[0098] Step 10: According to the braking force residual compensation capability of the four wheels, the total of the braking force lost by the left two wheels and the total of the braking force lost by the right two wheels, the pressure of the opposite side compensation is obtained.

[0099] Further, the total of the braking force lost by the left two wheels is compensated by the right front wheel and the right rear wheel braking force residual compensation capability, and the right front wheel and the right rear wheel opposite side compensation pressure is obtained:

[0100] (1) When the total of the braking force lost by the left two wheels is less than or equal to the right front wheel braking force residual compensation capability, that is, ΔT l ≤ ΔT2 fr , then the right front wheel opposite side compensation pressure is equal to the total of the braking force lost by the left two wheels divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to 0. That is:

[0101]

[0102] Wherein: ΔP4 fr — right front wheel opposite side compensation pressure; ΔP4 rr — right rear wheel opposite side compensation pressure;

[0103] (2) When the total of the braking force lost by the left two wheels is greater than the right front wheel braking force residual compensation capability and the total of the braking force lost by the left two wheels is less than the sum of the right front wheel braking force residual compensation capability and the right rear wheel braking force residual compensation capability, that is, ΔT fr < ΔT l < ΔT2 fr + ΔT2 rr , then the right front wheel opposite side compensation pressure is equal to the right front wheel braking force residual compensation capability divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the total of the braking force lost by the left two wheels minus the right front wheel braking force residual compensation capability divided by the product of the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc. That is:

[0104]

[0105] (3) When the total loss of braking force of the left two wheels is greater than or equal to the sum of the remaining compensation capability of the right front wheel braking force and the remaining compensation capability of the right rear wheel braking force, i.e. ΔT2 l ≥ ΔT2 fl + ΔT2 rr , then the right front wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the right front wheel braking force divided by the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the product of the remaining compensation capability of the right rear wheel braking force divided by the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc. That is:

[0106]

[0107] Further, the total loss of braking force of the right two wheels is compensated by the remaining compensation capability of the left front wheel and the left rear wheel braking force, and the left front wheel and the left rear wheel opposite side compensation pressure is obtained:

[0108] (1) When the total loss of braking force of the right two wheels is less than or equal to the remaining compensation capability of the left front wheel braking force, i.e. ΔT2 r ≤ ΔT2 fl , then the left front wheel opposite side compensation pressure is equal to the product of the total loss of braking force of the right two wheels divided by the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to 0. That is:

[0109]

[0110] Wherein: ΔP4 fl — The left front wheel opposite side compensation pressure; ΔP4 rl — The left rear wheel opposite side compensation pressure;

[0111] (2) When the total loss of braking force of the right two wheels is greater than the remaining compensation capability of the left front wheel braking force and less than the sum of the remaining compensation capability of the left front wheel braking force and the remaining compensation capability of the left rear wheel braking force, i.e. ΔT2 fl < ΔTr < ΔT2 fl + ΔT2 rlWhen the left front wheel's opposite-side compensating pressure is equal to the left front wheel's remaining braking force compensation capacity divided by the product of the contact area between the brake caliper and the brake disc, the radius from the center of the contact area between the brake caliper and the brake disc to the wheel center, and the coefficient of friction between the brake caliper and the brake disc, the left rear wheel's opposite-side compensating pressure is equal to the sum of the braking force lost by the two right wheels minus the left front wheel's remaining braking force compensation capacity, divided by the product of the contact area between the brake caliper and the brake disc, the radius from the center of the contact area between the brake caliper and the brake disc to the wheel center, and the coefficient of friction between the brake caliper and the brake disc. That is:

[0112]

[0113] (3) When the total braking force lost by the two right wheels is greater than or equal to the sum of the remaining compensating capacity of the left front wheel and the left rear wheel, i.e., ΔT r ≥ΔT2 fl +ΔT2 rl When the left front wheel's opposite-side compensating pressure is equal to the remaining compensating capacity of the left front wheel's braking force divided by the product of the contact area between the brake caliper and the brake disc, the radius from the center of the contact area between the brake caliper and the brake disc to the center of the wheel, and the coefficient of friction between the brake caliper and the brake disc, the left rear wheel's opposite-side compensating pressure is equal to the remaining compensating capacity of the left rear wheel's braking force divided by the product of the contact area between the brake caliper and the brake disc, the radius from the center of the contact area between the brake caliper and the brake disc to the center of the wheel, and the coefficient of friction between the brake caliper and the brake disc. That is:

[0114]

[0115] Step 11: Calculate the target pressure for the four-wheel hydraulic cylinders based on the offset compensation pressure of the four wheels and the second theoretical target pressure. The target pressure for the four-wheel brake hydraulic cylinders is equal to their second theoretical target pressure plus the corresponding offset compensation pressure. That is:

[0116]

[0117] Among them: P3 fl —The target pressure applied by the left front wheel brake hydraulic cylinder; P3 rl —The target pressure applied by the left rear wheel brake hydraulic cylinder; P3 fr —The target pressure applied by the right front wheel brake hydraulic cylinder; P3 rr —The target pressure applied by the right rear wheel brake hydraulic cylinder.

[0118] According to another aspect of the present invention, a system for implementing the methods of any of the above embodiments is also provided, comprising:

[0119] The first main control module is used to obtain the initial target braking torque of the four wheels and calculate the initial target pressure of the four wheels.

[0120] The second main control module is used for calculating a first theoretical target pressure of the four-wheel brake hydraulic cylinders based on the working capacity of the four-wheel brake hydraulic cylinders, obtaining a first loss pressure and a loss braking force of the four-wheel, and calculating a first compensation pressure of the same side according to the loss braking force;

[0121] The third main control module is used for obtaining a second theoretical target pressure of the four-wheel hydraulic cylinders not exceeding the working capacity, calculating a second loss pressure according to the second theoretical target pressure and the first compensation pressure, and obtaining a sum of the loss braking force of the left two wheels and a sum of the loss braking force of the right two wheels;

[0122] The fourth main control module is used for calculating a residual compensation capacity of the braking force of the four-wheel based on the second theoretical target pressure and the maximum pressure allowed by the hydraulic cylinders as a constraint;

[0123] The fifth main control module is used for performing pressure opposite side compensation of the four-wheel, obtaining an opposite side compensation pressure of the four-wheel, and calculating an execution target pressure of the four-wheel hydraulic cylinders according to the opposite side compensation pressure of the four-wheel and the second theoretical target pressure.

[0124] In summary, the present application obtains the initial target pressure of the hydraulic cylinders of the hydraulic brake system based on the driver's intention and the state of the vehicle, limits the pressure of the hydraulic cylinders of the brake system again in combination with the pressure output capacity of the hydraulic brake system, then maximizes the use of the pressure output capacity of the hydraulic cylinders of the brake system, first compensates the loss braking force through the same side pressure, if the same side compensation cannot meet the braking force demand of the vehicle, then compensates the loss braking force again through the opposite side. That is, the present application protects the hydraulic cylinders of the brake system from being damaged due to over-capacity work, improves the working life of the brake system, maximizes the realization of the braking force demand of the vehicle through the same side compensation and then the opposite side compensation, shortens the braking distance, and improves the braking safety of the vehicle.

[0125] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A pressure control method for a hydraulic brake system of a four-wheel vehicle, characterized by, The method comprises the following steps: S1: obtaining initial target braking torques of four wheels and calculating initial target pressures corresponding to the four wheels; S2: calculating first theoretical target pressures of four-wheel brake hydraulic cylinders based on working capabilities of the four-wheel brake hydraulic cylinders, obtaining first loss pressures and braking forces lost by the four wheels, calculating first compensation pressures on the same side according to the lost braking forces, and the first loss pressure being a pressure lost by the first theoretical target pressure relative to the initial target pressure; calculating first theoretical target pressures of four-wheel brake hydraulic cylinders based on working capabilities of the four-wheel brake hydraulic cylinders: P1 fl is the maximum pressure allowed for the left front wheel brake hydraulic cylinder to work, P rl is the maximum pressure allowed for the left rear wheel brake hydraulic cylinder to work, P fr is the maximum pressure allowed for the right front wheel brake hydraulic cylinder to work, P rr is the maximum pressure allowed for the right rear wheel brake hydraulic cylinder to work, P1 fl is the first theoretical target pressure of the left front wheel brake hydraulic cylinder, P1 rl is the first theoretical target pressure of the left rear wheel brake hydraulic cylinder, P1 fr is the first theoretical target pressure of the right front wheel brake hydraulic cylinder, P1 rl is the first theoretical target pressure of the right rear wheel brake hydraulic cylinder, P1 fl is the initial target pressure of the left front wheel brake hydraulic cylinder, P1 rl is the initial target pressure of the left rear wheel brake hydraulic cylinder, P1 fr is the initial target pressure of the right front wheel brake hydraulic cylinder, P1 rr is the initial target pressure of the right rear wheel brake hydraulic cylinder. S3: obtaining second theoretical target pressures of the four-wheel hydraulic cylinders that do not exceed the working capabilities, calculating second loss pressures according to the second theoretical target pressures and the first compensation pressures, and obtaining sums of braking forces lost by left two wheels and sums of braking forces lost by right two wheels; the second theoretical target pressure being a smaller one of a sum of corresponding first compensation pressures on the same side and a maximum pressure allowed by the hydraulic cylinder to work; the second loss pressure being: ΔP3 fl is the loss pressure of the left front wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 rl is the loss pressure of the left rear wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 fr is the loss pressure of the right front wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 rr is the loss pressure of the right rear wheel brake hydraulic cylinder based on the second theoretical target pressure, ΔP2 fl is the same side compensation pressure of the left front wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the left rear wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the right front wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the right rear wheel based on the lost first braking force, P2 fl is the second theoretical target pressure of the left front wheel brake hydraulic cylinder; P2 rl is the second theoretical target pressure of the left rear wheel brake hydraulic cylinder; P2 fr is the second theoretical target pressure of the right front wheel brake hydraulic cylinder; P2 rr is the second theoretical target pressure of the right rear wheel brake hydraulic cylinder; S4: calculating remaining compensation capabilities of braking forces of the four wheels based on the second theoretical target pressures and taking the maximum pressure allowed by the hydraulic cylinder to work as a constraint; S5: performing cross-side compensation of pressures of the four wheels, obtaining cross-side compensation pressures of the four wheels, and calculating execution target pressures of the four-wheel hydraulic cylinders according to the cross-side compensation pressures of the four wheels and the second theoretical target pressures.

2. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 1, characterized by, In step S1, the initial target braking torques of the four wheels are obtained according to a driver's intention and a state of the whole vehicle, and the initial target braking torque comprises a product of a brake hydraulic cylinder initial target pressure, a contact area of a brake caliper and a brake disc, and a radius from a center of the contact area of the brake caliper and the brake disc to a center of the wheel.

3. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 1, characterized by, In step S3, calculating the sums of the braking forces lost by the left two wheels and the sums of the braking forces lost by the right two wheels based on the second loss pressures comprises: ΔT = ΔP1 + ΔP2 l ΔT = ΔP1 + ΔP2 r ΔT = ΔP1 + ΔP2 fl ΔT = ΔP1 + ΔP2 rl ΔT = ΔP1 + ΔP2 fr ΔT = ΔP1 + ΔP2 rr ΔT = ΔP1 + ΔP2 fl S = S1 + S2 rl S = S1 + S2 fr S = S1 + S2 rr S = S1 + S2 fl r = r1 + r2 rl r = r1 + r2 fr r = r1 + r2 rr r = r1 + r2 μ = coefficient of friction between brake caliper and brake disc.

4. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 1, characterized by, In step S4, the remaining compensation capability of the pressure of the four wheels is equal to the maximum pressure allowed by the hydraulic cylinder to work minus the second theoretical target pressure multiplied by the contact area of the brake caliper and the brake disc and the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel.

5. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 1, wherein In step S5, the sums of the braking forces lost by the left two wheels are compensated by using the remaining compensation capabilities of braking forces of the right front wheel and the right rear wheel to obtain cross-side compensation pressures of the right front wheel and the right rear wheel, and specifically: (1) when the sums of the braking forces lost by the left two wheels are less than or equal to the remaining compensation capability of the braking force of the right front wheel, the cross-side compensation pressure of the right front wheel is equal to the sums of the braking forces lost by the left two wheels divided by a product of the contact area of the right front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and a friction coefficient between the brake caliper and the brake disc, and the cross-side compensation pressure of the right rear wheel is equal to 0; (2) When the total loss of braking force of the left two wheels is greater than the remaining compensation capability of the right front wheel and the total loss of braking force of the left two wheels is less than the sum of the remaining compensation capability of the right front wheel and the remaining compensation capability of the right rear wheel, the right front wheel opposite side compensation pressure is equal to the remaining compensation capability of the right front wheel divided by the product of the contact area of the right front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the total loss of braking force of the left two wheels minus the remaining compensation capability of the right front wheel divided by the product of the contact area of the right rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc; (3) When the total loss of braking force of the left two wheels is greater than or equal to the sum of the remaining compensation capability of the right front wheel and the remaining compensation capability of the right rear wheel, the right front wheel opposite side compensation pressure is equal to the remaining compensation capability of the right front wheel divided by the product of the contact area of the right front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the right rear wheel opposite side compensation pressure is equal to the remaining compensation capability of the right rear wheel divided by the product of the contact area of the right rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

6. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 5, wherein In step S5, the total loss of braking force of the right two wheels is compensated by the remaining compensation capability of the left front wheel and the left rear wheel, and the left front wheel and the left rear wheel opposite side compensation pressure is obtained, specifically: (1) When the total loss of braking force of the right two wheels is less than or equal to the remaining compensation capability of the left front wheel, the left front wheel opposite side compensation pressure is equal to the total loss of braking force of the right two wheels divided by the product of the contact area of the left front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to 0; (2) When the total loss of braking force of the right two wheels is greater than the remaining compensation capability of the left front wheel and the total loss of braking force of the right two wheels is less than the sum of the remaining compensation capability of the left front wheel and the remaining compensation capability of the left rear wheel, the left front wheel opposite side compensation pressure is equal to the remaining compensation capability of the left front wheel divided by the product of the contact area of the left front brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to the total loss of braking force of the right two wheels minus the remaining compensation capability of the left front wheel divided by the product of the contact area of the left rear brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc. (3) When the total of the lost braking force of the right two wheels is greater than or equal to the sum of the left front wheel braking force remaining compensation capability and the left rear wheel braking force remaining compensation capability, the left front wheel opposite side compensation pressure is equal to the product of the left front wheel braking force remaining compensation capability, the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc, and the left rear wheel opposite side compensation pressure is equal to the product of the left rear wheel braking force remaining compensation capability, the contact area of the brake caliper and the brake disc, the radius from the center of the contact area of the brake caliper and the brake disc to the center of the wheel, and the friction coefficient between the brake caliper and the brake disc.

7. The pressure control method of a hydraulic brake system of a four-wheel vehicle according to claim 1, wherein In step S5, the execution target pressure of the four-wheel hydraulic cylinders is calculated according to the opposite side compensation pressure of the four wheels and the second theoretical target pressure, and the execution target pressure of the four-wheel brake hydraulic cylinders is equal to the second theoretical target pressure plus the corresponding opposite side compensation pressure, that is: P3 fl P3 rl P3 fr P3 rr P3 8. A pressure control system for a hydraulic braking system of a four-wheel vehicle, characterized by Comprise: The first main control module is used for acquiring the initial target braking torque of the four wheels and calculating the corresponding initial target pressure of the four wheels; The second main control module is used for calculating the first theoretical target pressure of the four-wheel brake hydraulic cylinders based on the working capability of the four-wheel brake hydraulic cylinders, acquiring the first lost pressure and the lost braking force of the four wheels, and calculating the same side first compensation pressure according to the lost braking force; the first lost pressure is the pressure lost by the first theoretical target pressure relative to the initial target pressure; The first theoretical target pressure of the four-wheel brake hydraulic cylinders is calculated based on the working capability of the four-wheel brake hydraulic cylinders: P1 flmax is the maximum pressure allowed for the left front wheel brake hydraulic cylinder to work, P rlmax is the maximum pressure allowed for the left rear wheel brake hydraulic cylinder to work, P frmax is the maximum pressure allowed for the right front wheel brake hydraulic cylinder to work, P rrmax is the maximum pressure allowed for the right rear wheel brake hydraulic cylinder to work, P1 fl is the first theoretical target pressure of the left front wheel brake hydraulic cylinder, P1 rl is the first theoretical target pressure of the left rear wheel brake hydraulic cylinder, P1 fr is the first theoretical target pressure of the right front wheel brake hydraulic cylinder, P1 rr is the first theoretical target pressure of the right rear wheel brake hydraulic cylinder, P fl is the initial target pressure of the left front wheel brake hydraulic cylinder, P rl is the initial target pressure of the left rear wheel brake hydraulic cylinder, P fr is the initial target pressure of the right front wheel brake hydraulic cylinder, P rl is the initial target pressure of the right rear wheel brake hydraulic cylinder; The third main control module is used for acquiring the second theoretical target pressure of the four-wheel hydraulic cylinders that does not exceed the working capability, calculating the second lost pressure according to the second theoretical target pressure and the first compensation pressure, and acquiring the total of the lost braking force of the left two wheels and the total of the lost braking force of the right two wheels; The second theoretical target pressure is the smaller one of the sum of the first compensation pressure corresponding to the first theoretical target pressure and the maximum pressure allowed by the hydraulic cylinder to work; The second lost pressure is: wherein ΔP3 fl is the loss pressure of the left front wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 rl is the loss pressure of the left rear wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 fr is the loss pressure of the right front wheel brake hydraulic cylinder based on the second theoretical target pressure; ΔP3 rr is the loss pressure of the right rear wheel brake hydraulic cylinder based on the second theoretical target pressure, ΔP2 fl is the same side compensation pressure of the left front wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the left rear wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the right front wheel based on the lost first braking force, ΔP2 fl is the same side compensation pressure of the right rear wheel based on the lost first braking force, P2 fl is the second theoretical target pressure of the left front wheel brake hydraulic cylinder; P2 rl is the second theoretical target pressure of the left rear wheel brake hydraulic cylinder; P2 fr is the second theoretical target pressure of the right front wheel brake hydraulic cylinder; P2 rr is the second theoretical target pressure of the right rear wheel brake hydraulic cylinder; The fourth main control module is used for calculating the braking force remaining compensation capability of the four wheels based on the second theoretical target pressure and the maximum pressure allowed by the hydraulic cylinder to work as a constraint; The fifth main control module is used for opposite side compensation of the pressure of the four wheels, acquiring the opposite side compensation pressure of the four wheels, and calculating the execution target pressure of the four-wheel hydraulic cylinders according to the opposite side compensation pressure of the four wheels and the second theoretical target pressure.

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