Method for calculating braking distance of passenger car in power failure state

Abstract

The application discloses a kind of passenger car brake distance calculation method in boost failure state, belong to vehicle safety technical field, including the following steps, given initial parameter;MFDD (average deceleration of full discharge) is calculated;Brake distance of brake coordination phase is calculated;Brake distance of brake establishment phase is calculated;Brake distance of brake keeping phase is calculated;Total brake distance is calculated.The method is combined with the experience value of different booster and brake manufacturer, and the calculation result is more close to the actual vehicle measurement result, provides data basis for early design development stage, shortens verification period, and can confirm whether passenger car this performance meets national standard requirement or vehicle development target in vehicle development stage.

Description

Technical Field

[0001] This invention belongs to the field of vehicle safety technology, specifically a method for calculating the braking distance of a passenger vehicle in a state of power assist failure. Background Technology

[0002] With the rapid development of automobiles, vehicle safety has become a particularly prominent issue. The vehicle's braking system plays a crucial role in safe driving, and the "braking distance under power assist failure" is a very important indicator for evaluating the safety performance of a vehicle.

[0003] Braking distance under power assist failure conditions is a crucial indicator of vehicle braking performance and a test item required by GB21670. Braking distance under power assist failure conditions represents a braking system performance target. During vehicle development, this performance target needs to be broken down into the performance parameters of relevant components. Only when each component meets its corresponding performance parameters can the overall vehicle's braking distance target under power assist failure conditions be achieved. Therefore, its calculation method is of paramount importance.

[0004] The braking distance of a vehicle in a power assist failure state is not only related to the braking system efficiency, but also closely related to the system free travel, the reaction time of the brake and the booster.

[0005] Currently, the calculation of braking distance under power assist failure conditions mostly relies on empirical data from brakes and power boosters. Before conducting full vehicle testing, it's impossible to accurately predict the braking distance under power assist failure conditions, thus hindering forward development. Therefore, a calculation method is needed in the early development stage for verification, thereby clarifying the development plans for each braking system component.

[0006] Therefore, there is an urgent need for a method to calculate the braking distance under power assist failure conditions. Summary of the Invention

[0007] To address the above problems, this invention provides a method for calculating the braking distance of passenger vehicles under power assist failure conditions. The method involves: providing initial parameters; calculating MFDD (mean deceleration at full exertion); calculating the braking distance during the braking coordination phase; calculating the braking distance during the braking build-up phase; calculating the braking distance during the braking hold phase; and calculating the total braking distance. This method, by incorporating empirical values ​​from different power assist and brake manufacturers, yields calculation results that more closely match actual vehicle measurements. This provides data support for the early design and development phases, shortens the verification cycle, and enables confirmation during vehicle development whether this performance meets national standards or vehicle development goals.

[0008] The technical solution of this invention is as follows: a method for calculating the braking distance of a passenger vehicle in a power assist failure state, comprising the following steps:

[0009] S1. Set the performance parameters of the braking system components according to the vehicle development requirements;

[0010] S2. The entire braking process is divided into three stages according to the vehicle speed;

[0011] S3. Calculate the MFDD and braking distance S throughout the entire braking phase.

[0012] Furthermore, vehicle development requirements include: unloaded mass, design mass, axle load ratio, center of gravity height, fully loaded mass, and wheel rolling radius.

[0013] Furthermore, the three phases include: phase T1, phase T2, and phase T3;

[0014] Furthermore, the entire braking phase T is from the initial moment of braking to the moment when the vehicle speed is 0, the time elapsed is t, the braking distance is S, and the initial braking speed of the vehicle is V0.

[0015] Furthermore, stage T1 is from the initial moment of braking to the moment when the vehicle begins to decelerate, the time elapsed is t1, and the braking distance is S1; stage T2 is from the moment when the vehicle begins to decelerate to the moment when the vehicle decelerates to the threshold, the time elapsed is t2, and the braking distance is S2; stage T3 is from the moment when the vehicle decelerates to the threshold to the moment when the vehicle speed is 0, the time elapsed is t3, the deceleration in this stage is d3, and the braking distance is S3.

[0016] Furthermore, the threshold is the value that the vehicle deceleration can reach when the brake pedal operating force is 500N.

[0017] Furthermore, MFDD = d3, and braking distance S = S1 + S2 + S3.

[0018] Furthermore, the formula for calculating the braking distance S1 in stage T1 is as follows:

[0019]

[0020] In the formula, V0 is the initial braking velocity of the vehicle, t1 = 0.15s, and the formula for calculating the braking distance S2 in stage T2 is as follows:

[0021]

[0022] The formula for calculating the braking distance S3 in stage T3 is as follows:

[0023]

[0024] Furthermore, the deceleration d3 during the T3 braking phase is a constant value, as shown by the formula:

[0025]

[0026] Calculate, where K p For the brake pedal lever ratio, η p For brake pedal efficiency, F b To assist system resistance

[0027] D mc For the diameter of the brake master cylinder piston, η mc For the hydraulic efficiency of the brake master cylinder, D fc For the diameter of the front brake piston, R f The effective braking radius of the front brake, K fc For the front brake friction coefficient, η fc For front brake efficiency, D rc For the rear brake piston diameter, R r The effective braking radius of the rear brake, K rc The coefficient of friction of the rear brake, η rc For rear brake efficiency, R w Where G is the tire rolling radius, and D is the vehicle's full load mass. s To reduce the speed of the vehicle while it is coasting.

[0028] The beneficial effects of this invention are as follows:

[0029] This method combines the experience values ​​of different booster and brake manufacturers, and the calculation results are closer to the actual vehicle measurement results. It provides data basis for the early design and development stage, shortens the verification cycle, and can confirm whether the performance of passenger vehicles meets the national standard requirements or the vehicle development goals during the vehicle development stage. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of each stage in the braking distance test process of the present invention. Detailed Implementation

[0031] It should be noted that in the description of this invention, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation.

[0032] In this invention, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; a connection can be a mechanical connection or an electrical connection; a link can be a direct connection or an indirect connection through an intermediate medium, and can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0033] MFDD: Mean Fully Developed Deceleration is an automotive term referring to the average deceleration of a vehicle during a braking performance test, measured as it decelerates from 80% of its initial braking speed to 10% of its initial braking speed. It is an important braking performance parameter.

[0034] A method for calculating the braking distance of a passenger vehicle in a power assist failure state includes the following steps:

[0035] S1. Pre-set the performance parameters of the braking system components according to the vehicle development requirements (full load mass, wheel rolling radius);

[0036] S2. The entire braking phase T is divided into three phases according to the vehicle speed: phase T1, phase T2, and phase T3. See [link / reference] Figure 1 ;

[0037] S3. Calculate the MFDD (fully exerted average deceleration) and braking distance for the entire phase;

[0038] Furthermore, the braking system component parameters included in step S1 are as follows:

[0039]

[0040]

[0041] Further, step S2 includes:

[0042] S21. The entire braking phase T is from the initial moment of braking to the moment when the vehicle speed is 0, the time elapsed is t, the braking distance is S, and the vehicle speed at this time is the initial braking speed V0;

[0043] The S22.T1 stage is from the initial moment of braking to the moment when the vehicle has deceleration, generally called the braking coordination stage, and the time elapsed is t1. The braking distance in this stage is S1.

[0044] The S23.T2 stage, from the moment the vehicle begins to decelerate to the moment the vehicle's deceleration reaches the threshold, is generally called the braking establishment stage. The time elapsed is t2, and the braking distance during this stage is S2.

[0045] The S24.T3 stage is from the moment the vehicle deceleration reaches the threshold to the moment the vehicle speed reaches 0. It is generally called the braking holding stage, and the time elapsed is t3. The deceleration during this stage is d3, and the braking distance during this stage is S3.

[0046] The threshold is the vehicle deceleration value that can be achieved when the brake pedal operating force is 500N. Different vehicles will have different values, but the pedal operating force can be quantified and has a maximum value.

[0047] Further, step S3 includes:

[0048] S31. During the entire braking phase, the formula for calculating MFDD (fully exerted average deceleration) is as follows:

[0049] MFDD = d3

[0050] S32. The formula for calculating the braking distance S during the entire braking phase is as follows:

[0051] S = S1 + S2 + S3

[0052] Furthermore, in step S31, the deceleration d3 during the braking phase T3 is a constant value, and its calculation formula is as follows:

[0053]

[0054] Furthermore, in step S32,

[0055] The formula for calculating the braking distance S1 during the S321.T1 braking phase is as follows:

[0056]

[0057] In the formula, V0 is the initial braking speed of the vehicle, and the unit is km / h;

[0058] t1 = 0.15s, this value is an empirical value summarized from a large amount of experimental data.

[0059] The formula for calculating the braking distance S2 during the S322.T2 braking phase is as follows:

[0060]

[0061] In the formula, V0 is the initial braking speed of the vehicle, and the unit is km / h;

[0062] The formula for calculating the braking distance S3 during the S323.T3 braking phase is as follows:

[0063]

[0064] In the formula, V0 is the initial braking speed of the vehicle, and the unit is km / h.

[0065] Example 1

[0066] This embodiment takes the B70III model as an example to provide a method for calculating the braking distance of a passenger vehicle in a power assist failure state, specifically including the following steps:

[0067] Step 1: Given initial parameters

[0068] serial number Parameter name numerical values unit 1 Brake pedal lever ratio 3 2 Brake pedal efficiency 100％ 3 Assist system resistance 340 N 4 Brake master cylinder piston diameter 22.22 mm 5 brake master cylinder hydraulic efficiency 100％ 6 Front brake piston diameter 57.15 mm 7 Effective braking radius of front brake 130 mm 8 Front brake friction coefficient 0.78 9 Front brake efficiency 100％ 10 Rear brake piston diameter 34.93 mm 11 Effective braking radius of the rear brake 125 mm 12 rear brake friction coefficient 0.72 13 Rear brake efficiency 100％ 14 Tire rolling radius 333 mm 15 Vehicle full load weight 1955 kg 16 Vehicle coasting deceleration 0.5 <![CDATA[m / s 2 ]]> 17 Initial braking velocity 100 km / h

[0069] Step 2: Calculate MFDD;

[0070]

[0071] Step 3: Calculate the braking distance S1 during braking phase T1;

[0072]

[0073] Step 4: Calculate the braking distance S2 during braking phase T2;

[0074]

[0075] Step 5: Calculate the braking distance S3 during the T3 braking phase;

[0076]

[0077] Step 6: Calculate the braking distance S for the entire braking phase;

[0078] S = 4.2 + 62.6 + 90.7 = 157.5m.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

[0080] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

Claims

1. A method for calculating the braking distance of a passenger vehicle under power assist failure conditions, characterized in that, include: S1. Set the performance parameters of the braking system components according to the vehicle development requirements; S2. The entire braking process is divided into three stages according to the vehicle speed; S3. Calculate the MFDD and braking distance S throughout the entire braking phase; In step S2, the three stages include: stage T1, stage T2, and stage T3; The entire braking phase is from the initial moment of braking to the moment the vehicle speed reaches 0, with a time of t and a braking distance of S. The initial braking speed of the vehicle is V0. Phase T1 is from the initial moment of braking to the moment the vehicle begins to decelerate, with a time of t1 and a braking distance of S1. Phase T2 is from the moment the vehicle begins to decelerate to the moment the vehicle decelerates to the threshold value, with a time of t2 and a braking distance of S2. Phase T3 is from the moment the vehicle decelerates to the moment the vehicle speed reaches 0, with a time of t3, a deceleration of d3, and a braking distance of S3. The threshold is the value that the vehicle deceleration can reach when the brake pedal operating force is 500N; In step S3, MFDD = d3, and the braking distance S = S1 + S2 + S3; The formula for calculating the braking distance S1 in stage T1 is as follows: In the formula, V0 is the initial braking velocity of the vehicle, and t1 = 0.15s; The formula for calculating the braking distance S2 in stage T2 is as follows: The formula for calculating the braking distance S3 in stage T3 is as follows: During the braking phase T3, the deceleration d3 is a constant value, as shown by the formula: Calculate, where K p For the brake pedal lever ratio, η p For brake pedal efficiency, F b To assist system resistance D mc For the diameter of the brake master cylinder piston, η mc For the hydraulic efficiency of the brake master cylinder, D fc For the diameter of the front brake piston, R f The effective braking radius of the front brake, K fc For the front brake friction coefficient, η fc For front brake efficiency, D rc For the rear brake piston diameter, R r The effective braking radius of the rear brake, K rc The coefficient of friction of the rear brake, η rc For rear brake efficiency, R w Where G is the tire rolling radius, and D is the vehicle's full load mass. s To reduce the speed of the vehicle while it is coasting.

2. The method for calculating the braking distance of a passenger vehicle under power assist failure state as described in claim 1, characterized in that, In step S1, the vehicle development requirements include: unloaded mass, design mass, axle load ratio, center of gravity height, fully loaded mass, and wheel rolling radius.

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