Drum brake braking force distribution method and system

Abstract

The invention discloses a drum brake braking force distribution method and system, a drum brake braking force prediction model is established based on a drum brake temperature model, a drum brake braking force observer and a whole vehicle longitudinal dynamics simulation model are established according to the drum brake braking force prediction model, the drum brake braking force observer is used to obtain the real braking force of each brake shaft, and the braking force distribution coefficient boundary conditions are set and the braking force distribution coefficient is optimized, so that the reasonable distribution of braking force is achieved under the premise of meeting the braking intensity, and the braking performance stability of the brake is fully exerted, and the problem of rapid reduction of the braking efficiency of the whole vehicle caused by overheating and failure of some brakes can be effectively prevented, thereby ensuring the stability of the braking efficiency of the whole vehicle of the drum brake vehicle, and under the premise of ensuring braking safety and handling stability, the probability of thermal decay of the brake drum is reduced, and the braking performance of the brake is fully exerted.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy truck braking control, and relates to a method for improving the stability of vehicle braking performance by secondary distribution of braking force based on brake temperature, and specifically to a drum brake braking force distribution method and system. Background Art

[0002] Drum brakes have poor heat dissipation performance. Frequent braking on long downhill sections can easily cause thermal decay, which can cause the brake device to fail. Related test studies have shown that brake assembly errors or uneven structural wear can cause a rapid increase in the temperature of a brake or a certain axle brake, which reduces the stability of the vehicle's braking performance. Therefore, suppressing the rapid increase in local brake temperature to ensure the stability of the vehicle's braking performance and improve the safety of the vehicle's braking is an effective way.

[0003] At present, in order to improve the braking safety performance of the whole vehicle, the main technologies are to rely on the optimization design of the brake structure, the application of high temperature resistant brake materials, and the installation of brake temperature monitoring and early warning systems. Although some methods are used to optimize the braking control strategy of the whole vehicle, and the braking force distribution of heavy trucks is adjusted based on the axle load by the load sensing proportional valve, the failure evolution mechanism of the thermal decay of the whole vehicle brake is ignored, and the braking performance of the braking system cannot be effectively exerted. Summary of the invention

[0004] The purpose of the present invention is to provide a drum brake braking force distribution method and system to overcome the shortcomings of the prior art. The present invention can improve the reliability of drum brakes, give full play to the braking performance of the braking system, and improve the stability of the braking efficiency of heavy-duty trucks on long downhill sections.

[0005] A drum brake braking force distribution method comprises the following steps:

[0006] S1, establishing a braking force observation model of a drum brake based on a drum brake temperature model;

[0007] S2, a braking force observation model of the drum brake is established according to the drum brake temperature model, the actual braking force of each axle of the brake is obtained by using the drum brake braking force observation model and the vehicle longitudinal dynamics model, and the braking force is distributed according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient.

[0008] Furthermore, a temperature model of the drum brake is constructed based on mathematical methods to simulate and observe the change of the drum brake temperature over time during the braking process.

[0009] Furthermore, the expression of the temperature change of the friction working surface during the braking process of the drum brake over time is:

[0010]

[0011] T * is the friction working surface temperature, λ i is the thermal conductivity; b i is the effective thickness of the friction pair components involved in heat absorption during braking, in m; τ N is the friction power ratio, τ N =2(1-τ),τ W is the ratio of friction work to braking work, τ W =2τ-τ 2 , τ N is the time ratio, F oi is the Fourier number at point i on the drum brake; φ vi is the heat influence coefficient; S ai is the actual friction area during braking, in m 2 ;t T is the continuous braking time, in seconds; a Tni is the thermal field distribution coefficient, a Tn1 +a Tn2 =1;W τn is the braking work, the unit is J.

[0012] Furthermore, the relationship between the friction work done by the brake and the change of speed over time is obtained:

[0013]

[0014] Furthermore, according to the brake friction work and the brake temperature change, the brake force observation model is obtained as follows:

[0015]

[0016] Furthermore, the braking force observation model of the drum brake is used to obtain the braking force of each axle of the brake, so as to obtain the real braking force distribution coefficient. In order to ensure the braking safety of the vehicle, the real braking force distribution coefficient β satisfies the following conditions:

[0017] β≤h g φ / L+[bφ / (0.85φ-0.07)L];

[0018] The utilization curve of the front axle adhesion coefficient is above the rear axle utilization curve: φ0 = (Lβ-b) / h g ≥0.3.

[0019] Furthermore, the braking force distribution coefficient β∈[0.45,0.9].

[0020] Furthermore, β is set to 0.9.

[0021] A drum brake braking force distribution system comprises a real braking force observation module and a power distribution module;

[0022] The braking force observation module establishes a braking force observation model of the drum brake based on the drum brake temperature model;

[0023] The power distribution module is used to establish a braking force observation model for drum brakes according to the drum brake temperature model, obtain the actual braking force of each axle of the brake using the drum brake braking force observation model and the vehicle longitudinal dynamics model, and distribute the braking force according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient.

[0024] Furthermore, the braking force distribution coefficient β∈[0.45,0.9].

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The present invention discloses a drum brake braking force distribution method. A drum brake braking force prediction model is established based on a drum brake temperature model. A drum brake braking force observer and a whole vehicle longitudinal dynamics simulation model are established according to the drum brake braking force prediction model. The drum brake braking force observer is used to obtain the real braking force of each axle of the brake. By setting the boundary conditions of the braking force distribution coefficient and optimizing the braking force distribution coefficient, reasonable distribution of braking force is achieved under the premise of meeting the braking intensity, and the braking performance stability of the brake is fully utilized. The problem of rapid reduction of the braking efficiency of the whole vehicle caused by overheating and failure of some brakes can be effectively prevented, thereby ensuring the stability of the braking efficiency of the whole vehicle of the drum brake vehicle.

[0027] Furthermore, a temperature model of the drum brake is constructed based on mathematical methods, and a temperature and braking force model is established. Under the premise of ensuring braking safety and handling stability, the probability of thermal decay of the brake drum is reduced, and the braking performance of the brake is fully utilized.

[0028] The invention discloses a drum brake braking force distribution system, which has a simple structure and can adjust and distribute the braking force of a vehicle brake, thereby improving the stability of the braking efficiency of a heavy-duty truck on a long downhill section. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the power distribution method in an embodiment of the present invention.

[0030] Figure 2 3 is a diagram of the brake friction surface temperature actually measured in an embodiment of the present invention.

[0031] Figure 3 It is a simulation comparison diagram of the two-axis and three-axis braking forces in an embodiment of the present invention where the distribution coefficient is not adjusted.

[0032] Figure 4 1 is a diagram for solving the braking force distribution coefficient in an embodiment of the present invention.

[0033] Figure 5 It is a braking force variation diagram of the braking strategy simulation in the embodiment of the present invention.

[0034] Figure 6 It is a two-axis and three-axis temperature comparison diagram without adjusting the distribution coefficient in the embodiment of the present invention.

[0035] Figure 7 It is a temperature variation diagram of the braking strategy simulation in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0037] like Figure 1 As shown, a drum brake braking force distribution method comprises the following steps:

[0038] S1, establishing a braking force observation model of a drum brake based on a drum brake temperature model;

[0039] S2, a braking force observation model of the drum brake is established according to the drum brake temperature model, the actual braking force of each axle of the brake is obtained by using the drum brake braking force observation model and the vehicle longitudinal dynamics model, and the braking force is distributed according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient.

[0040] The temperature model of drum brakes is constructed based on mathematical methods, and the change of drum brake temperature over time during braking is simulated and observed. The relationship between the braking force friction work and temperature during the braking process of drum brakes is established, and the relationship between braking force and speed and temperature is derived using mathematical relationships to obtain the braking force prediction model of drum brakes.

[0041] Determine the material properties of the drum brake:

[0042] Material properties include thermal diffusivity (i.e. thermal conductivity) α i , thermal conductivity λ i , density ρ i , specific heat capacity c i and part thickness.

[0043] Model the drum brake temperature:

[0044] The expression of the temperature change of the friction working surface with time during the braking process of the drum brake is specifically expressed as:

[0045]

[0046] T * is the friction working surface temperature, λ i is the thermal conductivity; b i is the effective thickness of the friction pair components involved in heat absorption during braking, in m; τ N is the friction power ratio, τ N =2(1-τ),τ W is the ratio of friction work to braking work, τ W =2τ-τ 2 , τ N is the time ratio, F oi is the Fourier number at point i on the drum brake; φ vi is the heat influence coefficient; S ai is the actual friction area during braking, in m 2 ;t T is the continuous braking time, in seconds; a Tni is the thermal field distribution coefficient, a Tn1 +a Tn2 =1;W τn is the braking work, the unit is J. Assuming the initial temperature of the friction working surface is T, the actual temperature change during the braking process is:

[0047] T Z =T+T * (2)

[0048] Drum brake braking force F b The relationship between speed and temperature during braking is:

[0049]

[0050] v is the data of the heavy-loaded vehicle's speed changing with time during braking.

[0051] The temperature of the drum brake during braking is T i The relationship between the braking time t and the number of times is related to the heat emitted by the friction pair material to the surrounding environment medium. The simple temperature field model established is:

[0052]

[0053]

[0054] r is the brake drum radius, T i is the drum brake during braking, t is the braking time, α i is the thermal diffusion coefficient, i=1 represents the brake drum, and i=2 represents the brake shoe.

[0055] In the temperature field model of drum brake friction, the temperature of any point in the radial direction of the friction element is proportional to its volume temperature as time changes.

[0056] The formula for calculating the temperature T at point i of the drum brake is:

[0057]

[0058]

[0059] ε i is the radial coordinate value of the drum brake temperature field model and b i ratio; b i is the effective thickness of the friction pair component participating in heat absorption during braking, i=1 is the brake drum, i=2 is the brake shoe, the unit is m, and its calculation formula can be:

[0060]

[0061] ρ i is the density of the brake material; c i is the specific heat capacity of the brake material. T is the continuous braking time, in seconds.

[0062] F oi is the Fourier number at point i on the drum brake, i=1 is the brake drum, i=2 is the brake shoe, and the calculation formula is:

[0063]

[0064] ε i is the radial coordinate value of the drum brake temperature field model and b i The ratio of φ vi is the thermal influence factor, which can be calculated numerically using the following formula:

[0065]

[0066] In the above formula, d2 is the friction diameter, b is iφ It is the actual thickness of the friction pair component.

[0067] During the braking process of a heavy truck, the brakes generate a large amount of heat that is released to the external low-temperature medium. In a short period of time, if the heat dissipation problem of the drum brake is not considered, the heat generated during braking is absorbed by the brake drum and brake shoe. The ratio of the heat absorbed by the brake drum (or brake shoe) to the total heat generated during braking is called the heat distribution coefficient, and the heat distribution coefficient can be calculated by the following formula:

[0068]

[0069]

[0070]

[0071] a TnZ +a Tn1 =1

[0072] When measuring temperature in road tests, the temperature sensor can only measure the temperature of the friction surface of the drum brake, so the parameter ε in the formula i The value of is 0.

[0073] F o1 、F o2 They are the Fourier numbers on the brake drum and brake shoe.

[0074] So at this time, we can get the expression of the temperature change of the friction working surface with time during the braking process of the drum brake, which is specifically expressed as:

[0075]

[0076] In the actual braking process, the braking force is a constantly changing process. Using calculus, the braking work W τn It can be expressed by the following formula:

[0077] W τn =F b *S=∫F b ds (15)

[0078] S is the braking distance;

[0079] Convert the braking work into an integral over time:

[0080]

[0081] v is the data of the speed of the heavy-loaded vehicle changing with time during braking;

[0082] The relationship between braking work and speed over time is obtained:

[0083]

[0084] Combining the above formula, the relationship between the braking force and the speed and temperature during braking is obtained, which is expressed by the following formula:

[0085]

[0086] A drum brake braking force observation model and a vehicle longitudinal dynamics simulation model are established. The drum brake braking force observation model is used to obtain the real braking force of the second and third axes of the brake, the braking force of the second and third axes of the brake during the braking process is obtained, and the true value of the braking force distribution coefficient is calculated.

[0087] The ratio of the braking force of each axle of the car is called the brake force distribution coefficient, which is represented by the symbol β:

[0088]

[0089] F μ2 is the braking force of the second-axle brake, F μ3 is the braking force of the three-axis brake.

[0090] According to automobile theory, the front wheel braking efficiency when the front wheel is locked first can be calculated using the following formula:

[0091] E f =Z / φ f =b / (Lβ-φ f h g ) (20)

[0092] Where: Z is the braking strength, φ f is the front axle adhesion coefficient, b is the distance from the center of mass to the rear axle, L is the wheelbase, h is g is the height of the centroid;

[0093] The maximum braking intensity when locking is about to occur is expressed as:

[0094] J=bφ f / (Lβ-φ f h g ) (twenty one)

[0095] β is the utilization adhesion coefficient. When β∈[0.2,0.8] is within the range, for heavy-loaded vehicles, the braking strength should meet the following requirements:

[0096] Z≥0.1+0.85(φ-0.2) (22)

[0097] The conditions that β satisfies when the front wheel is locked are:

[0098] β≤h g φ / L+[bφ / (0.85φ-0.07)L](23)

[0099] The utilization curve of the front axle adhesion coefficient when the car is in various load states should be above the rear axle utilization curve. Therefore, it can be seen that φ≥0.3 can meet the requirements, that is:

[0100] φ=(Lβ-b) / h g ≥0.3 (24)

[0101] In order to meet the requirements of vehicle braking strength and stability, the vehicle must satisfy equations (23) and (24) at the same time when it is unloaded or fully loaded.

[0102] Take the intersection of the above full-load calculation values ​​to obtain the braking force distribution coefficient β∈[0.45,0.9] that meets the safety regulations when fully loaded. In order to fully exert the braking efficiency of the brakes of each axis, the temperature rise process of the brakes of each axis should be similar. Under the premise of meeting the safety requirements, adjust the braking pressure to make the braking force of each axis as similar as possible, that is, the braking force distribution coefficient is as close to 1 as possible. Therefore, β is taken as 0.9.

[0103] The material properties of drum brakes affect the temperature rise characteristics of the shaft. Using this characteristic, a suitable temperature field model and braking force prediction model are established based on the basic knowledge of heat transfer and automotive tribology. By optimizing the braking force distribution coefficient, the braking force of each shaft is reasonably distributed to avoid the occurrence of thermal decay and other phenomena.

[0104] The braking force distribution is simulated according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient to obtain the temperature change, and the collected temperature and the simulated temperature change before adjustment are compared and analyzed.

[0105] Example:

[0106] The test section is: K25-K174 section of Ya'an-Xichang section of Beijing-Kunming Expressway, of which the right line: K25-K174 (Yingjing Service Area-Pushenggang Service Area); left line: K174-K25 (Pushenggang Service Area-Yingjing Service Area); the total length is 149km.

[0107] The vehicle parameters are:

[0108]

[0109] The brake friction surface temperature of the above vehicle during actual braking was carefully measured, and the results are as follows: Figure 2 As shown, from Figure 2 The data shows that when the braking force distribution coefficient is not adjusted, the braking force difference between the second and third axes is large. The braking force distribution result at this time is solved as follows: Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that there is a large difference in the temperature rise between the second and third axles at this time. The drum brake temperature of the third axle rises quickly, while the brake temperature of the second axle rises slowly. The corresponding result is that during continuous braking, the third axle brake is more prone to thermal decay than the second axle brake, thereby causing thermal decay failure of the vehicle's braking force.

[0110] Figure 4is the braking force distribution coefficient after braking strategy simulation. It can be seen that after adjusting the braking force distribution coefficient, the result is as follows Figure 5 , Figure 6 As shown, the braking forces of the three-axis and two-axis are closer. Figure 7 The braking strategy simulation shows that the temperature difference between the second and third axes is reduced, and the temperature rises evenly. Under the premise of ensuring braking safety and handling stability, the probability of thermal decay of the brake drum is reduced, and the braking performance of the brake is fully utilized.

Claims

1. A drum brake braking force distribution method, characterized in that: The following steps are involved: S1, establishing a drum brake braking force prediction model based on a drum brake temperature model; S2, using the drum brake braking force prediction model and the vehicle longitudinal dynamics model to obtain the actual braking force of each axle, and distribute the braking force according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient; The temperature model of drum brake is constructed based on mathematical methods, and the change of drum brake temperature over time during braking is simulated and observed; The expression of the temperature change of the friction working surface during the braking process of the drum brake is: T * is the friction working surface temperature, λ i is the thermal conductivity; b i is the effective thickness of the friction pair components involved in heat absorption during braking, in m; τ N is the friction power ratio, τ N =2(1-τ),τ W is the ratio of friction work to braking work, τ W =2τ-τ 2 ; F oi is the Fourier number at point i on the drum brake; φ vi is the heat influence coefficient; S ai is the actual friction area during braking, in m 2 ; t T is the continuous braking time, in seconds; a Tni is the thermal field distribution coefficient, a Tn1 +a Tn2 =1, i=1,2; W τn is the friction work done by the brake, with the unit of J; the relationship between the friction work done by the brake and the change of speed over time is obtained: According to the brake friction work and brake temperature changes, the brake force prediction model is expressed as: The drum brake braking force prediction model is used to obtain the braking force of each axle of the brake, so as to obtain the real braking force distribution coefficient. In order to ensure the braking safety of the vehicle, the real braking force distribution coefficient β satisfies the following conditions: β≤h g φ / L+[bφ / (0.85φ-0.07)L]; The utilization curve of the front axle adhesion coefficient is above the rear axle utilization curve: φ0 = (Lβ-b) / h g ≥0.

3.

2. A drum brake braking force distribution method according to claim 1, characterized in that: Braking force distribution coefficient β∈[0.45,0.9].

3. The drum brake force distribution method according to claim 1, characterized in that: β is taken as 0.

9.

4. A drum brake braking force distribution system based on the distribution method according to claim 1, characterized in that: Including real braking force prediction module and power distribution module; The braking force prediction module establishes a braking force prediction model of the drum brake based on the drum brake temperature model; The power distribution module is used to obtain the actual braking force of each axle of the brake using the drum brake braking force prediction model and the vehicle longitudinal dynamics model, and to distribute the braking force according to the braking force distribution coefficient boundary conditions and the braking force distribution coefficient.

5. A drum brake force distribution system according to claim 4, characterized in that: Braking force distribution coefficient β∈[0.45,0.9].

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