Passenger Car Braking System Matching Design Method

Abstract

The present invention relates to a matching design method for a passenger car braking system, belonging to the technical field of automotive braking. The method includes the following steps: S1: Determine the design specifications of the front axle brake of the vehicle when fully loaded according to the calculation of vehicle parameters; S2: Select the distribution ratio β of the front and rear brakes according to the design specifications and capabilities of the front axle brake; S3: Calculate and obtain the design specifications of the rear brake; S4: Calculate the utilization adhesion coefficients of the front and rear brakes according to the specifications of the front and rear brakes and vehicle parameters and draw curves until meeting the regulatory requirements; S5: Calculate and draw the utilization rate of the road adhesion coefficient; S6: Select the diameter of the master cylinder bore and determine the maximum stroke size of the piston according to the design specifications of the front and rear brakes; at the same time, calculate and determine the specifications of the vacuum booster and determine the liquid volume of the oil pot; S7: Determine the size of the brake pedal leverage ratio, calculate and draw the brake pedal feel curve, and judge whether the pedal feel requirements are met; at the same time, judge whether the requirements of the braking system are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive braking, and relates to a matching design method for a passenger car braking system. Background Art

[0002] The matching of a passenger car braking system mainly refers to the matching of the components and performance of the braking system to ensure the safety, reliability, and good braking performance of the braking system.

[0003] First of all, the components of the braking system need to be matched, including brake discs, brake pads, brake fluid, brake pumps, brakes, etc. The selection of these components needs to consider factors such as the vehicle model, mass, power, etc. to ensure that the quality and performance of the components meet the requirements of the vehicle.

[0004] Secondly, the performance of the braking system also needs to be matched, including braking force, braking sensitivity, braking efficiency, etc. The matching of these performances needs to be adjusted according to factors such as the vehicle's use environment, vehicle speed, load, etc. to achieve the best braking performance.

[0005] Finally, in order to ensure the safety and reliability of the braking system, debugging and testing of the braking system also need to be carried out to ensure that all indicators of the braking system meet the standard requirements, as well as the braking performance and stability under different road conditions and driving states.

[0006] In addition, the following factors also need to be considered in the matching of a passenger car braking system:

[0007] Adaptability of the braking system: Different vehicle models and uses require different braking systems. For example, vehicles traveling on highways need stronger braking force and better braking sensitivity, while vehicles traveling on urban roads need smoother braking performance.

[0008] Stability of the braking system: The stability of the braking system is directly related to the safety and ride comfort of the vehicle. The stability of the braking system is affected by various factors such as brake pads, brake discs, brake fluid, etc., and strict testing and debugging are required to ensure the stability of the braking system.

[0009] Maintenance and repair of the braking system: The braking system needs to be regularly inspected and maintained to ensure its normal operation. In the design of the braking system, the convenience and feasibility of maintenance and repair need to be considered to reduce maintenance costs and maintenance time.

[0010] The matching of a passenger car braking system has an important impact on both the safety and performance of the vehicle, and strict design and testing are required to ensure the safety, reliability, and good braking performance of the braking system.

[0011] The design method for the matching of a passenger car braking system includes the following aspects:

[0012] Usage environment of the vehicle: The design of the braking system needs to determine parameters such as braking force and braking sensitivity according to the usage environment of the vehicle. For example, vehicles traveling on highways require stronger braking force and better braking sensitivity, while vehicles traveling on urban roads require smoother braking performance.

[0013] Matching of brake disc and brake pad: Brake discs and brake pads are the core components of the braking system and need to be selected according to factors such as the mass, power, and usage environment of the vehicle. The diameter and thickness of the brake disc determine the magnitude of the braking force, while the material and friction coefficient of the brake pad affect the braking sensitivity and braking efficiency.

[0014] Matching of brake fluid and brake pump: Brake fluid is the transmission medium of the braking system and needs to be selected according to factors such as the braking force and working temperature of the vehicle. The working pressure and flow rate of the brake pump need to match the performance of the brake fluid to ensure the stability and reliability of the braking system.

[0015] Matching of brake: The brake is the component that transmits the braking force to the wheels and needs to be selected according to factors such as the mass and usage environment of the vehicle. The number, size, and position of the brakes need to be adjusted according to different vehicle models and usage environments to ensure the performance, safety, and reliability of the braking system.

[0016] Testing and debugging of the braking system: After the design of the braking system is completed, strict testing and debugging are required to ensure that all indicators of the braking system meet the standard requirements. Different road conditions and driving states need to be considered during the testing process to ensure the performance and stability of the braking system.

[0017] The design method for the matching of the passenger car braking system needs to take into account factors such as the usage environment, mass, power, and usage habits of the vehicle, and be adjusted according to different vehicle models and usage environments to ensure the safety, reliability, and good braking performance of the braking system. Summary of the Invention

[0018] In view of this, the purpose of the present invention is to provide a design method for the matching of a passenger car braking system to ensure the safety, reliability, and good braking performance of the braking system.

[0019] To achieve the above purpose, the present invention provides the following technical solutions:

[0020] A design method for the matching of a passenger car braking system includes the following steps:

[0021] S1: According to the calculation of the vehicle parameters, when ensuring that the front axle brake meets the design goal, determine the design specifications of the front axle brake of the vehicle when fully loaded.

[0022] S2: Select the distribution ratio β of the front and rear brakes according to the design specifications and capabilities of the front axle brake, so as to obtain reasonable synchronization adhesion coefficients and synchronization hydraulics under the full-load and no-load conditions of the vehicle.

[0023] S3: Calculate and obtain the design specifications of the rear brake according to the distribution ratio β of the front and rear brakes.

[0024] S4: Calculate the utilization adhesion coefficients of the front and rear brakes based on the specifications of the front and rear brakes and the vehicle parameters, and determine whether they comply with the regulations. If they comply, proceed to the next step; if not, adjust the distribution ratio β of the front and rear brakes until the regulatory requirements are met.

[0025] S5: Calculate and plot the utilization rate of the road adhesion coefficient.

[0026] S6: Calculate the braking hydraulic pressure and liquid volume required for the vehicle to reach the maximum braking target according to the design specifications of the front and rear brakes, select the diameter of the master cylinder bore and determine the maximum stroke size of the piston; calculate and determine the specifications of the vacuum booster (diaphragm diameter, boost ratio, maximum boost point output force), and determine the liquid volume of the oil pot.

[0027] S7: Determine the size of the brake pedal leverage ratio, calculate and plot the brake pedal feel curve, and determine whether the pedal feel requirements are met; at the same time, determine whether the requirements of the braking system are met.

[0028] Optionally, the calculation method of the design specifications in step S1 includes the following steps:

[0029] S11: Input the vehicle parameters, and according to the current road conditions and the tread pattern of the tires, the grip Φ max Take 1.2; the maximum braking torque M of the front brake FB should not be less than M FMax ;

[0030] The vehicle parameters include:

[0031] F F : Ground braking force, unit is N

[0032] M F : Ground braking torque, unit is N·m

[0033] W F : Static front axle load of the vehicle, unit is N

[0034] W: Total weight of the vehicle, unit is N

[0035] h: Height of the vehicle's center of mass, unit is mm

[0036] L: Wheelbase of the vehicle, unit is mm

[0037] r: Rolling radius of the wheel, unit is m

[0038] Φ: Road adhesion coefficient;

[0039] S12: Front braking force and front brake design specification calculation:

[0040]

[0041] M FB = A F × P × BEF F × R ef

[0042] Where: A F : Sum of the cross-sectional areas of the front wheel cylinder pistons, unit: mm 2

[0043] BEF F : Front brake efficiency factor, take 2 times the friction coefficient for floating caliper disc brakes; take the friction coefficient for fixed caliper disc brakes.

[0044] R ef : Effective braking radius of the front brake, unit: mm.

[0045] P: Braking hydraulic pressure, unit: MPa.

[0046] Optionally, the braking hydraulic pressure P depends on the ability of the master cylinder booster. When Φ max takes 1.0, the value of P should not be greater than 9.5 MPa; when Φ max takes 1.2, the value of P should not be greater than 12 MPa; Φ max is the maximum adhesion coefficient between the tire and the ground at a slip ratio s = 15% - 20%. When s = 100%, the tire and the ground are in pure sliding, and at this time the adhesion coefficient is the sliding friction coefficient, and the sliding friction coefficient can only reach about 80% of Φ max ; This is how the vehicle adjusts the hydraulic pressure under the action of ABS or ESP to reach the optimal slip ratio, prevent the wheels from locking, obtain the maximum adhesion coefficient and braking efficiency, and get the minimum braking distance.

[0047] Optionally, the front and rear braking distribution ratio β in steps S2 and S3, that is, the front braking force divided by the sum of the front braking force and the rear braking force:

[0048]

[0049] A R : Sum of the cross-sectional areas of the rear wheel cylinder pistons, unit: mm 2

[0050] BEF R: Rear brake efficiency factor. For floating caliper disc brakes, take 2 times the friction coefficient; for fixed caliper disc brakes, take the friction coefficient.

[0051] R er : Effective braking radius of the rear brake, unit is mm.

[0052] Optionally, in step S3, according to the front-rear brake distribution ratio β, calculate and determine the synchronous adhesion coefficient: The braking synchronous adhesion coefficient refers to the road adhesion coefficient when the front and rear wheels lock simultaneously during vehicle braking:

[0053]

[0054] L R : Horizontal distance from the vehicle's center of mass to the rear axle, unit is mm.

[0055] Optionally, in step S4, according to the front-rear brake distribution ratio β and vehicle parameters, calculate and determine the utilization adhesion coefficient, and judge whether it meets the regulatory requirements; The utilization adhesion coefficient refers to the ratio of the front axle brake force to the front axle load, which is called the front utilization adhesion coefficient Φ F , and the ratio of the rear axle brake force to the rear axle load is called the rear utilization adhesion coefficient Φ R

[0056]

[0057] z: Braking intensity z = a / g;

[0058] a is the braking deceleration, unit is m / s 2 ;

[0059] g is the gravitational acceleration, with a value of 9.8 m / s 2 ;

[0060] W R : Static rear axle load of the vehicle, unit is N.

[0061] Optionally, calculate the Φ values when Z = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 respectively; F 、Φ R value;

[0062] According to the requirements of GB21670 regulations:

[0063] Under all load conditions of the vehicle, when the braking intensity is between 0.15 and 0.80, the rear axle adhesion coefficient utilization curve must be below the straight line z = 0.9k;

[0064] When the k value is between 0.2 and 0.8, z ≥ 0.1 + 0.7(k - 0.2).

[0065] Optionally, in step S5, the utilization rate of the road adhesion coefficient is calculated. The utilization rate of the adhesion coefficient refers to the ratio of the braking intensity z when the front axle or rear axle brake reaches lock-up during the braking process of the vehicle to the road adhesion coefficient Φ on a road surface with an adhesion coefficient of Φ;

[0066]

[0067] Utilization rate of the front axle adhesion coefficient:

[0068] Utilization rate of the rear axle adhesion coefficient:

[0069] Substitute the road adhesion coefficients Φ = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 into the above formula. The higher the utilization rate of the adhesion coefficient, the closer the braking intensity is to the road adhesion coefficient.

[0070] Optionally, in step S6, according to the design specifications of the front and rear brakes, calculate the braking hydraulic pressure and fluid volume required for the vehicle to reach the maximum braking target, select the diameter of the master cylinder bore, and determine the maximum stroke size of the piston; at the same time, calculate and determine the specification size of the vacuum booster and determine the fluid volume of the oil pot;

[0071] Consider the hydraulic pressure required to achieve 1g deceleration:

[0072]

[0073] Then at this time, under the action of Temp max , P max the required fluid volume V max of the braking system;

[0074] The maximum displacement V mc

[0075] V mc = A mc ×(S1 + S2) - V spring

[0076] A mc : cross-sectional area of the master cylinder bore, unit is mm 2

[0077] V spring : volume of the master cylinder piston return spring, unit is mm 3

[0078] V mc ≥1.3V max ;

[0079] Calculate the required hydraulic pressure value for the braking system to reach the maximum braking target, and based on this hydraulic pressure value, determine the boosting ratio of the booster, the input and output forces at the maximum boosting point, and calculate the relationship between the input force and the output hydraulic pressure;

[0080] When the input force F in <F action , F out =0

[0081] When the input force F action ≤F in ≤F knee , F out =F jump +(F in -F action )×K

[0082] When the input force F in >F knee , F out =F jump +(F knee -F action )×K+F in -F knee .

[0083] Optionally, step S7 for calculating the brake pedal feel specifically includes:

[0084] Calculate the pedal travel T Pedal :

[0085]

[0086] V F : The required fluid volume for the front brake, unit: ml

[0087] V R : The required fluid volume for the rear brake, unit: ml

[0088] V FH +V RH : The required fluid volume for the front and rear hoses, unit: ml

[0089] T MC +T booster : The pressure build-up travel of the master cylinder and the booster, unit: mm

[0090] i: Pedal leverage ratio;

[0091] Obtain the relationship between the pedal input force F pedal and the output hydraulic pressure P out of the master cylinder:

[0092] When the pedal input force P out =0

[0093] When the pedal input force

[0094] When the pedal input force

[0095]

[0096] The beneficial effects of the present invention are as follows:

[0097] The advantages of the matching design for the passenger car braking system are as follows:

[0098] (1) Improve the braking system performance: Through the matching design, the coordinated action between the various components of the braking system can be achieved, thereby improving the performance of the entire braking system, such as braking force, braking distance, etc.

[0099] (2) Reduce the cost of the braking system: The matching design can avoid the incompatibility between the various components of the braking system, thereby reducing the design and manufacturing costs of the braking system.

[0100] (3) Improve vehicle safety: Through the matching design, it can be ensured that the performance and reliability of the various components of the braking system are fully exerted, thereby improving vehicle safety.

[0101] (4) Reduce the failure rate of the braking system: The matching design can avoid failures and malfunctions caused by the incompatibility between the various components of the braking system, thereby reducing the maintenance and replacement costs of the braking system.

[0102] (5) Improve the user experience: The matching design can make the operation of the braking system more stable and comfortable, improving the user's driving experience.

[0103] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, wherein:

[0105] Figure 1 Schematic diagram of vehicle parameters Figure 1 ;

[0106] Figure 2 Schematic diagram of vehicle parameters Figure 2 ;

[0107] Figure 3 For the adhesion coefficient curve;

[0108] Figure 4 is the adhesion coefficient utilization curve;

[0109] Figure 5 is the schematic diagram for checking the capacity of the main hydraulic cylinder;

[0110] Figure 6 is the relationship between the input force and the output hydraulic pressure Figure 1 ;

[0111] Figure 7 is the relationship between the input force and the output hydraulic pressure Figure 2 ;

[0112] Figure 8 is the relationship between the braking deceleration and the pedal force Figure 1 ;

[0113] Figure 9 is the relationship between the braking deceleration and the pedal force Figure 2 ;

[0114] Figure 10 is the flow chart of the present invention. Detailed implementation manners

[0115] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0116] Among them, the drawings are only used for illustrative purposes, showing only schematic diagrams, rather than physical diagrams, and cannot be understood as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0117] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the accompanying drawings are only for illustrative purposes and cannot be construed as a limitation of the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0118] The present invention discloses a matching design method for a passenger car braking system, as Figure 10 shown, which includes the following steps:

[0119] S1: According to the calculation of the vehicle parameters, when ensuring that the front axle brake meets the design objectives, determine the design specifications of the vehicle's fully-loaded front axle brake;

[0120] S2: According to the design specifications and capabilities of the front axle brake, select the distribution ratio β of the front and rear brakes so that reasonable synchronous adhesion coefficients and synchronous hydraulics can be obtained under the fully-loaded and unloaded states of the vehicle;

[0121] S3: Calculate and obtain the design specifications of the rear brake according to the distribution ratio β of the front and rear brakes;

[0122] S4: Calculate and draw the utilization adhesion coefficients of the front and rear brakes according to the specifications of the front and rear brakes and the vehicle parameters, and judge whether it complies with the regulations. If it complies, proceed to the next step; if not, adjust the distribution ratio β of the front and rear brakes until it meets the regulatory requirements;

[0123] S5: Calculate and draw the utilization rate of the road adhesion coefficient;

[0124] S6: According to the design specifications of the front and rear brakes, calculate the braking hydraulic pressure and liquid volume required for the vehicle to reach the maximum braking target, select the diameter of the master cylinder bore and determine the maximum stroke size of the piston; at the same time, calculate and determine the specifications of the vacuum booster (diaphragm diameter, boost ratio, maximum boost point output force), and determine the liquid volume of the oil pot;

[0125] S7: Determine the size of the brake pedal lever ratio, calculate and draw the brake pedal feel curve, and judge whether it meets the pedal feel requirements; at the same time, judge whether it meets the requirements of the braking system.

[0126] The calculation method of the design specifications of the front brake described in step S1 is as follows:

[0127] S11: Input the vehicle's overall vehicle parameters, and the specific parameter limitations can be referred to Figure 1 、 Figure 2。

[0128] Wherein:

[0129] F F : Ground braking force, unit is N

[0130] M F : Ground braking torque, unit is N·m

[0131] W F : Static front axle load of the vehicle, unit is N

[0132] W: Total weight of the vehicle, unit is N

[0133] h: Height of the vehicle's center of mass, unit is mm

[0134] L: Wheelbase of the vehicle, unit is mm

[0135] r: Rolling radius of the wheel, unit is m

[0136] Φ: Road adhesion coefficient

[0137] According to the current road conditions and the tread pattern (grip) of the tire, Φ max Take 1.2. The maximum braking torque M of the front brake FB Should not be less than M FMax

[0138] S12: Calculation of front braking force and front brake design specifications:

[0139]

[0140] M FB = A F × P × BEF F × R ef

[0141] A F : Sum of the cross-sectional areas of the front wheel cylinder pistons, unit is mm 2

[0142] BEF F : Front brake efficiency factor, take 2 times the friction coefficient for floating caliper disc brakes; take the friction coefficient for fixed caliper disc brakes.

[0143] R ef : Effective braking radius of the front brake, unit is mm.

[0144] P: Braking hydraulic pressure MPa. This hydraulic pressure depends on the capacity of the master cylinder booster. When Φ max Take 1.0, the value of P should not be greater than 9.5 MPa; when Φ max Take 1.2, the value of P should not be greater than 12 MPa. Φ maxis the maximum adhesion coefficient between the tire and the ground at a slip ratio s = 15% - 20%. When s = 100%, the tire and the ground are in pure sliding, and at this time, the adhesion coefficient is the sliding friction coefficient, and the sliding friction coefficient can only reach about 80% of Φ max ; this is why when the vehicle is under the action of ABS or ESP, the hydraulic pressure is adjusted to reach the optimal slip ratio, prevent the wheels from locking, and at the same time obtain the maximum adhesion coefficient and braking efficiency, and get the minimum braking distance.

[0145] Calculation and determination of the front and rear braking distribution ratio β described in step S2:

[0146] The braking distribution ratio β is the ratio of the front braking force to the sum of the front and rear braking forces:

[0147]

[0148] A R : Sum of the cross-sectional areas of the rear wheel cylinder pistons, in mm 2

[0149] BEF R : Braking efficiency factor of the rear brake. For floating caliper disc brakes, take 2 times the friction coefficient; for fixed caliper disc brakes, take the friction coefficient

[0150] R er : Effective braking radius of the rear brake, in mm.

[0151] In step S3, according to the front and rear braking distribution ratio β, calculate and determine the design specifications of the rear brake.

[0152] In step S3, according to the front and rear braking distribution ratio β, calculate and determine the synchronous adhesion coefficient:

[0153] The braking synchronous adhesion coefficient refers to the road adhesion coefficient when the front and rear wheels lock simultaneously during vehicle braking

[0154]

[0155] L R : Horizontal distance from the vehicle's center of mass to the rear axle, in mm

[0156] In step S4, according to the front and rear braking distribution ratio β and vehicle parameters, calculate and determine the utilization adhesion coefficient, and draw a curve to judge whether it meets the regulatory requirements

[0157] Definition of the utilization adhesion coefficient: The ratio of the front axle brake braking force to the front axle load is called the front utilization adhesion coefficient Φ F , and the ratio of the rear axle brake braking force to the rear axle load is called the rear utilization adhesion coefficient Φ F

[0158]

[0159] z: Braking intensity, z = a / g;

[0160] a is the braking deceleration, with the unit of m / s 2 ;

[0161] g is the gravitational acceleration, with a value of 9.8 m / s 2 ;

[0162] W R : Static rear axle load of the vehicle, with the unit of N.

[0163] Calculate Φ values when z = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 respectively. Plot them into F Φ R value. Draw a Figure 3 curve.

[0164] According to the requirements of GB21670 regulations:

[0165] 1. Under all load conditions of the vehicle, when the braking intensity is between 0.15 and 0.80, the rear axle adhesion coefficient utilization curve must be below the straight line z = 0.9k

[0166] 2. When the k value is between 0.2 and 0.8, Z ≥ 0.1 + 0.7(k - 0.2)

[0167] In step S5, calculate and plot the road adhesion coefficient utilization rate.

[0168] Definition of adhesion coefficient utilization rate: On a road surface with an adhesion coefficient of Φ, the ratio of the braking intensity z to the road adhesion coefficient Φ when the front axle or rear axle brake reaches lockup during the vehicle braking process;

[0169]

[0170] Front axle adhesion coefficient utilization rate:

[0171] Rear axle adhesion coefficient utilization rate:

[0172] Substitute the road adhesion coefficients Φ = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 into the above formula; obtain the corresponding ξ values. Plot them into the following Figure 4 curve; the higher the adhesion coefficient utilization rate, the closer the braking intensity is to the road adhesion coefficient.

[0173] Step S6 calculates the braking hydraulic pressure and liquid volume required for the vehicle to reach the maximum braking target according to the design specifications of the front and rear brakes, selects the master cylinder bore diameter, and determines the maximum stroke size of the piston; at the same time, calculates and determines the specifications of the vacuum booster (diaphragm diameter, boost ratio, output force at the maximum boost point), and determines the liquid volume of the oil pot.

[0174] The working stroke of the piston in a single chamber of the master cylinder should ensure that the braking system has a certain margin under extreme working conditions. For example, during the AMS test, the friction coefficient decays from μ nom to μ min , and the temperature of the friction plate rises to the maximum value Temp max ; at this time, it is necessary to consider the hydraulic pressure required to achieve 1g deceleration:

[0175]

[0176] Then at this time, under Temp max , P max , the required liquid volume V max (including the sum of the required liquid volumes of the brake, hose, and master cylinder booster)

[0177] The maximum displacement V mc of the master cylinder V mc = A mc × (S1 + S2) - V spring

[0178] A mc : cross-sectional area of the master cylinder bore, unit is mm 2

[0179] V spring : volume of the master cylinder piston return spring, unit is mm 3

[0180] V mc ≥ 1.3V max

[0181] The schematic diagram for checking the capacity of the master hydraulic cylinder is as shown in Figure 5 . In the figure, S1 and S2 are the working strokes of the piston.

[0182] Determination of the booster design:

[0183] According to the above steps, the required hydraulic pressure value for the braking system to reach the maximum braking target can be calculated. Based on this hydraulic pressure value, determine the boost ratio of the booster, the input and output forces at the maximum boost point, and calculate the relationship between the input force and the output hydraulic pressure, as shown in Figures 6 - 7 .

[0184] When the input force F in < F action , F out= 0

[0185] When the input force F action ≤ F in ≤ F knee , F out = F jump +(F in - F action ) × K

[0186] When the input force F in > F knee , F out = F jump +(F knee - F action ) × K + F in - F knee

[0187] The output hydraulic pressure of the master cylinder is equal to the output of the booster divided by the cross-sectional area of the master cylinder piston.

[0188] Step S7 calculates the brake pedal feel:

[0189] When the vehicle brakes, due to certain clearances in the brake system components, such as between the piston and the friction block, the friction block and the brake disc; the pedal and the booster push rod; the master cylinder cup and the compensation hole, etc. When braking, the hydraulic pressure generated causes the system components to deform, such as the caliper deforming axially, the friction block compressing and deforming, the hose expanding, etc.; all of which require a certain amount of hydraulic fluid to be replenished in the brake system, and the brake pedal will also have a certain working stroke. When the pedal stroke is within a certain range, better comfort can be obtained. Otherwise, either the pedal stroke is too short, resulting in a sharp nod during braking; or the pedal stroke is too long, feeling that the pedal is lack of rigidity, soft, and the brake system lacks a sense of security. Therefore, it is necessary to control the required hydraulic fluid volume and the empty stroke of the brake system to obtain a better pedal stroke.

[0190] The stroke T of the brake pedal Pedal The calculation formula is as follows:

[0191]

[0192] V F : The required hydraulic fluid volume for the front brake, unit is ml

[0193] V R : The required hydraulic fluid volume for the rear brake, unit is ml

[0194] V FH + V RH : The required hydraulic fluid volume for the front and rear hoses, unit is ml

[0195] T MC + T booster : The pressure build-up stroke of the master cylinder and the booster, unit is mm.

[0196] i: Pedal leverage ratio.

[0197] The relationship between the braking deceleration and the pedal force is as Figures 8 - 9 shown.

[0198] According to the above formula, the pedal input force F pedal and the master cylinder output hydraulic pressure P out are related as follows:

[0199] When the pedal input force P out = 0

[0200] When the pedal input force

[0201] When the pedal input force

[0202]

[0203] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A matching design method for a passenger car braking system, characterized in that, It includes the following steps: S1: Based on the calculation of vehicle parameters, when ensuring that the front axle brake meets the design goal, determine the design specifications of the front axle brake of the fully-loaded vehicle; S2: According to the design specifications and capabilities of the front axle brake, select the distribution ratio β of the front and rear brakes so that reasonable synchronous adhesion coefficients and synchronous hydraulics are obtained in the fully-loaded and unloaded states of the vehicle; S3: Calculate and obtain the design specifications of the rear brake according to the distribution ratio β of the front and rear brakes; S4: Calculate the utilization adhesion coefficients of the front and rear brakes based on the specifications of the front and rear brakes and vehicle parameters, and determine whether they comply with the regulations. If they comply, proceed to the next step. If not, adjust the distribution ratio β of the front and rear brakes until the regulatory requirements are met; S5: Calculate and plot the utilization rate of the road adhesion coefficient; S6: According to the design specifications of the front and rear brakes, calculate the braking hydraulic pressure and liquid volume required for the vehicle to reach the maximum braking goal, select the bore diameter of the master cylinder and determine the maximum stroke size of the piston; Calculate and determine the specifications of the vacuum booster and then determine the liquid volume of the oil pot. The specification parameters specifically include the diaphragm diameter, boost ratio, and output force at the maximum boost point; S7: Determine the size of the brake pedal lever ratio, calculate and plot the brake pedal feel curve, and determine whether it meets the pedal feel requirements; At the same time, determine whether it meets the requirements of the braking system; Among them, the calculation method of the design specifications in step S1 includes the following steps: S11: Input the vehicle's overall parameters. According to the current road conditions and the tire tread pattern, the maximum adhesion coefficient Φ between the tire and the ground max is taken as 1.2; the maximum braking torque M of the front brake FB should not be less than M FMax ; Vehicle parameters include: F F : Braking force on the ground, unit: N; M F : The ground braking torque, unit: N·m; W F : Static front axle load of the vehicle, unit: N; W: Total vehicle weight load, unit is N; h: Vehicle center of mass height, unit is mm; L: Vehicle wheelbase, unit is mm; r: Wheel rolling radius, unit is m; Φ: Road adhesion coefficient; S12: Calculation of front braking force and front brake design specifications: M FB = A F × P × BEF F × R ef Where: A F : The sum of the cross-sectional areas of the front wheel cylinder pistons, in mm 2 ; BEF F : Front brake efficiency factor, take 2 times the friction coefficient for floating caliper disc brakes; take the friction coefficient for fixed caliper disc brakes; R ef : Effective braking radius of the front brake, unit: mm; P: Braking hydraulic pressure, unit is MPa.

2. The matching design method of the passenger car braking system according to claim 1, characterized in that The braking hydraulic pressure P depends on the capacity of the master cylinder booster. When Φ max takes 1.0, the value of P should not be greater than 9.5 MPa; when Φ max takes 1.2, the value of P should not be greater than 12 MPa; Φ max is the maximum adhesion coefficient between the tire and the ground at a slip ratio s = 15% - 20%. When s = 100%, the tire and the ground are in pure sliding, and at this time, the adhesion coefficient is the sliding friction coefficient, and the sliding friction coefficient can only reach about 80% of max φ.

3. The matching design method of the passenger car braking system according to claim 1, wherein: The front and rear brake distribution ratio β in steps S2 and S3, that is, the front braking force divided by the sum of the front braking force and the rear braking force: A R : The sum of the cross-sectional areas of the rear wheel cylinder pistons, in mm 2 ; BEF R : Rear brake efficiency factor, take 2 times the friction coefficient for floating caliper disc brakes; take the friction coefficient for fixed caliper disc brakes; R er : Effective braking radius of the rear brake, unit: mm.

4. The matching design method of the passenger car braking system according to claim 1, characterized in that: In step S3, according to the front and rear brake distribution ratio β, calculate and determine the braking synchronous adhesion coefficient Φ0: The braking synchronous adhesion coefficient refers to the road adhesion coefficient when the front and rear wheels lock simultaneously during vehicle braking: L R : The horizontal distance from the vehicle's center of mass to the rear axle, in mm; Lβ: Horizontal distance from the vehicle center of mass to the rear axle, unit is mm.

5. The matching design method of the passenger car braking system according to claim 1, characterized in that: In step S4, the utilization adhesion coefficient is calculated and determined based on the front and rear braking distribution ratio β and vehicle parameters, and it is judged whether it meets the regulatory requirements; the utilization adhesion coefficient refers to the ratio of the braking force of the front axle brake to the front axle load, which is called the front utilization adhesion coefficient Φ F , and the ratio of the braking force of the rear axle brake to the rear axle load is called the rear utilization adhesion coefficient Φ R z: Braking intensity z = a / g; a is the braking deceleration, with the unit of m / s 2 ; g is the acceleration due to gravity, with a value of 9.8 m / s 2 ; W R : Static rear axle load of the vehicle, unit: N.

6. The matching design method of the passenger car braking system according to claim 5, characterized in that: Calculate the values of Φ when z = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 respectively F and Φ R values; Under all load states of the vehicle, when the braking intensity is between 0.15 and 0.80, the rear axle adhesion coefficient utilization curve must be below the straight line z = 0.9k; When the k value is between 0.2 and 0.8, z ≥ 0.1 + 0.7(k - 0.2).

7. The matching design method of the passenger car braking system according to claim 5, characterized in that: Step S5 calculates the utilization rate of the road adhesion coefficient. The adhesion coefficient utilization rate refers to the ratio of the braking intensity z to the road adhesion coefficient Φ when the front or rear axle brake reaches lockup during the braking process of the vehicle on a road surface with an adhesion coefficient of Φ; Utilization rate of front axle adhesion coefficient: Rear axle adhesion coefficient utilization rate: Substitute the road adhesion coefficients Φ = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 into the above formula. The higher the adhesion coefficient utilization rate, the closer the braking intensity is to the road adhesion coefficient.

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