阅读说明：本技术 一种车辆气压制动压力变化率测量方法及装置 (Method and device for measuring change rate of vehicle air pressure brake pressure ) 是由 李刚炎 赵燃 杨凡 胡剑 包汉伟 杨锐 于 2020-05-07 设计创作，主要内容包括：本发明公开了一种车辆气压制动压力变化率测量方法及装置,属于汽车制动技术领域,旨在实现制动压力变化率的实时精确测量,为基于制动压力变化率的车辆态势控制提供参考信息,可提升车辆态势控制精度,提高车辆行驶稳定性、平顺性和乘客舒适性。应用层流阻尼管、等温容器、压差传感器和压力传感器进行制动压力变化率的测量；当待测气容压力p<Sub>s</Sub>改变时,等温容器内气体压力p<Sub>c</Sub>受层流阻尼管影响,其压力变化滞后于待测气容,等温容器与待测气容间形成压差p<Sub>j</Sub>,通过压差传感器测得等温容器和待测容器间的压差p<Sub>j</Sub>,压力传感器测得等温容器内的压力p<Sub>c</Sub>,并通过温度补偿算法,可实时精确获取待测容器内压力变化率dp<Sub>s</Sub>/dt。(The invention discloses a method and a device for measuring the change rate of vehicle air pressure brake pressure, belongs to the technical field of automobile braking, and aims to realize real-time accurate measurement of the change rate of the brake pressure, provide reference information for vehicle situation control based on the change rate of the brake pressure, improve the vehicle situation control accuracy and improve the vehicle driving stability, smoothness and passenger comfort. Measuring the change rate of the braking pressure by using a laminar flow damping tube, an isothermal container, a differential pressure sensor and a pressure sensor; when the gas capacity pressure p to be measured s While changing, the gas pressure p in the isothermal vessel c Influenced by the laminar flow damping tube, the pressure change lags behind the gas volume to be measured, and a pressure difference p is formed between the isothermal container and the gas volume to be measured j Measuring the pressure difference p between the isothermal container and the container to be measured by the pressure difference sensor j The pressure sensor measures the pressure p in the isothermal container c And can accurately obtain in real time through a temperature compensation algorithmTaking the pressure change rate dp in the container to be measured s /dt。)

1. A method of measuring a rate of change of a vehicle pneumatic brake pressure, comprising:

when the pressure in the brake chamber to be measured changes, the pressure is influenced by the laminar flow damping tube, the change of the gas pressure in the isothermal container lags behind the pressure in the brake chamber to be measured, and the pressure difference between the isothermal container and the brake chamber is measured by using a pressure difference sensor;

and measuring the pressure in the isothermal container by using a pressure sensor, and then obtaining the pressure change rate in the brake air chamber to be measured according to the pressure in the isothermal container and the pressure difference between the isothermal container and the brake air chamber.

2. The method according to claim 1, wherein the laminar flow damper pipe is located between the brake air chamber and the isothermal container, the laminar flow damper pipe is formed by inserting n capillary tubes with inner radius r and length L into an air pipe with inner diameter D in parallel, and the flow resistance coefficient in the laminar flow damper pipe is as follows:the mass flow G of air flowing through the laminar flow damping tube is as follows: wherein p is_aAt atmospheric pressure, p_aIn terms of atmospheric density,. mu.is the aerodynamic viscosity, p_cDenotes the pressure in the isothermal vessel, p_sRepresenting the brake chamber pressure to be measured.

3. The method of claim 2, wherein the method is performed byDetermining the change in gas pressure in said isothermal vessel by Determining the temperature change in the isothermal container, wherein R is the gas state constant in the isothermal container, V is the volume of the isothermal container, W is the mass of the gas in the isothermal container, theta is the temperature in the isothermal container, and C_vSpecific heat of constant volume, C_pThe specific heat at a constant pressure is used,θ_ais the ambient temperature, h_uIs the heat exchange coefficient, S, of the isothermal vessel_hIs the heat exchange area of the isothermal vessel.

4. The method of claim 3, wherein p is selected from the group consisting of_j＝p_s-p_cDetermining a pressure difference p between the isothermal container and the brake chamber_jNeglecting the effect of temperature variations in the isothermal vesselDetermining a measure of the rate of change of brake pressure, and determining a measure of the rate of change of brake pressure Andanalyzing to obtain a brake pressure change rate measured value dp neglecting the influence of temperature change_c ^*And the temperature theta in the warm container is obtained through fitting a relation between the temperature theta and the dt and compensating the temperature influence.

5. A method according to claim 4, characterized by neglecting the brake pressure change rate measurement dp as a function of temperature_c ^*The temperature theta in the corresponding isothermal container is obtained by the temperature/dt, and then a gas state change equation in the isothermal container and a mass flow equation in the laminar flow resistance pipe are considered when the temperature changes, so that the measured value of the change rate of the braking pressure when the temperature change influence is considered is as follows:

6. a vehicle air brake pressure rate of change measuring device, comprising: the device comprises a laminar flow damping tube, an isothermal container, a differential pressure sensor, a pressure sensor and an AD conversion module;

the first end of the laminar flow damping tube and the first end of the differential pressure sensor are respectively connected with a brake chamber to be measured, the second end of the laminar flow damping tube and the second end of the differential pressure sensor are both connected with the isothermal container, the other end of the isothermal container is connected with one end of the pressure sensor, and the other end of the pressure sensor and the other end of the differential pressure sensor are both connected with the AD conversion module;

when the pressure in the brake chamber to be measured changes, the pressure change in the isothermal container is influenced by the laminar flow damping tube and lags behind the pressure in the brake chamber to be measured, and the pressure difference between the isothermal container and the brake chamber is measured by using the pressure difference sensor;

and measuring the pressure in the isothermal container by using the pressure sensor, and then obtaining the pressure change rate in the brake air chamber to be measured by the AD conversion module according to the pressure in the isothermal container and the pressure difference between the isothermal container and the brake air chamber.

7. The device of claim 6, wherein the laminar flow damper pipe is located between the brake air chamber and the isothermal container, the laminar flow damper pipe is formed by inserting n capillary tubes with inner radius r and length L into an air pipe with inner diameter D in parallel, and the flow resistance coefficient in the laminar flow damper pipe is as follows:the mass flow G of air flowing through the laminar flow damping tube is as follows: wherein p is_aAt atmospheric pressure, p_aIn terms of atmospheric density,. mu.is the aerodynamic viscosity, p_cDenotes the pressure in the isothermal vessel, p_sRepresenting the brake chamber pressure to be measured.

8. The device of claim 7, wherein the device is made ofDetermining the change in gas pressure in said isothermal vessel by Determining the temperature change in the isothermal container, wherein R is the gas state constant in the isothermal container, V is the volume of the isothermal container, W is the mass of the gas in the isothermal container, theta is the temperature in the isothermal container, and C_vSpecific heat of constant volume, C_pSpecific heat at constant pressure, [ theta ]_aIs the ambient temperature, h_uIs the heat exchange coefficient, S, of the isothermal vessel_hIs the heat exchange area of the isothermal vessel.

9. The apparatus of claim 8, wherein p is p_j＝p_s-p_cDetermining a pressure difference p between the isothermal container and the brake chamber_jNeglecting the effect of temperature variations in the isothermal vesselDetermining a measure of the rate of change of brake pressure, and determining a measure of the rate of change of brake pressure Andanalyzing to obtain a brake pressure change rate measured value dp neglecting the influence of temperature change_c ^*And fitting a relation between the temperature and the temperature in the isothermal container to compensate the temperature influence.

10. An arrangement according to claim 9, characterised by a brake pressure change rate measurement dp by ignoring the effect of temperature changes_c ^*The temperature theta in the corresponding isothermal container is obtained by the temperature/dt, and then a gas state change equation in the isothermal container and a mass flow equation in the laminar flow resistance pipe are considered when the temperature changes, so that the measured value of the change rate of the braking pressure when the temperature change influence is considered is as follows:

Technical Field

The invention belongs to the field of automobile braking, and particularly relates to a method and a device for measuring the change rate of vehicle air brake pressure in real time.

Background

With the development of advanced intelligent safety technologies such as automobile active safety, auxiliary driving and automatic driving, the brake system is used as a core for guaranteeing the safety of the automobile, and the intelligent safety puts forward new requirements on the control precision of the brake system. The air pressure brake is one of a plurality of braking modes, is widely applied to vehicle braking systems of passenger cars, trucks and the like, and has the advantages of simple structure, high reliability, capability of maintaining braking capability even when a power source fails instantaneously and the like, so that the air pressure braking system occupies an irreplaceable position in the field of vehicle braking. However, when the pneumatic brake system works, due to the problems of compressibility of gas, transmission delay, easy leakage, under-pressure and the like, a pressure deviation or a time deviation exists between the actual brake pressure response and the expected brake pressure response.

The brake pressure-time response during pneumatic braking is shown in fig. 1. On the vertical axis, at a predetermined time (shown), the actual brake pressure is either greater than (Δ p)₁) Or less than (Δ p)₂) Anticipating a brake pressure, the deviation being a brake pressure deviation; on the horizontal axis, the braking time or advance (Δ t) required to reach the desired braking pressure₁) Or hysteresis (Δ t)₁) At the expected time, the deviation is the braking time deviation.

For an auxiliary driving or automatic driving vehicle, the autonomous intervention capability of a brake system is enhanced, the manual intervention capability is weakened, and any brake pressure deviation or brake time deviation can cause brake failure, so that the brake pressure and brake time can meet the brake expectation. Therefore, the change of the braking pressure in unit time, namely the change rate of the braking pressure, is taken as a new evaluation index and a new control index of the electric control air pressure braking system by comprehensively considering the pressure and the time response, and the change rate of the braking pressure can be expressed as:

wherein p is_cIs brake chamber pressure, kPa; t is time, s.

The pressure change rate of the brake system is mainly obtained by measuring pressure, differentiating the pressure and then indirectly calculating, and due to the influence of the resolution of a pressure sensor and a noise signal, pressure differential data has large fluctuation and low calculation precision. Therefore, if the accurate measurement of the brake pressure change rate can be realized, the technical support is provided for the accurate brake control of the brake system, and the method has important significance for improving the smoothness of the vehicle and the comfort of passengers.

Disclosure of Invention

In view of the above defects or improvement requirements of the prior art, the present invention provides a method and an apparatus for measuring a change rate of a pneumatic brake pressure of a vehicle, so as to solve the technical problem of how to accurately measure the change rate of the brake pressure and reduce measurement errors through temperature compensation.

To achieve the above object, according to one aspect of the present invention, there is provided a vehicle air brake pressure change rate measuring method including:

when the pressure in the brake chamber to be measured changes, the pressure is influenced by the laminar flow damping tube, the change of the gas pressure in the isothermal container lags behind the pressure in the brake chamber to be measured, and the pressure difference between the isothermal container and the brake chamber is measured by using a pressure difference sensor;

and measuring the pressure in the isothermal container by using a pressure sensor, and then obtaining the pressure change rate in the brake air chamber to be measured according to the pressure in the isothermal container and the pressure difference between the isothermal container and the brake air chamber.

Preferably, the laminar flow damper pipe is located between the brake air chamber and the isothermal container, the laminar flow damper pipe is formed by inserting n capillary tubes with an inner radius r and a length L into an air pipe with an inner diameter D in parallel, and the flow resistance coefficient in the laminar flow damper pipe is as follows:the mass flow G of air flowing through the laminar flow damping tube is as follows:wherein p is_aAt atmospheric pressure, p_aIn terms of atmospheric density,. mu.is the aerodynamic viscosity, p_cDenotes the pressure in the isothermal vessel, p_sRepresenting the brake chamber pressure to be measured.

Preferably, is prepared fromDetermining the change in gas pressure in said isothermal vessel byDetermining the temperature change in the isothermal container, wherein R is the gas state constant in the isothermal container, V is the volume of the isothermal container, W is the mass of the gas in the isothermal container, theta is the temperature in the isothermal container, and C_vSpecific heat of constant volume, C_pSpecific heat at constant pressure, [ theta ]_aIs the ambient temperature, h_uIs the heat exchange coefficient, S, of the isothermal vessel_hIs the heat exchange area of the isothermal vessel.

Preferably, from p_j＝p_s-p_cDetermining a pressure difference p between the isothermal container and the brake chamber_jNeglecting the effect of temperature variations in the isothermal vesselDetermining a measure of the rate of change of brake pressure, and determining a measure of the rate of change of brake pressureAndanalyzing to obtain a brake pressure change rate measured value dp neglecting the influence of temperature change_c ^*The temperature in the isothermal container is theta, and a relation between the temperature in the isothermal container and the temperature in the isothermal container is fittedThe temperature effect is compensated.

Preferably by ignoring the effect of temperature changes on the brake pressure rate of change measurement dp_c ^*The temperature theta in the corresponding isothermal container is obtained by the temperature/dt, and then a gas state change equation in the isothermal container and a mass flow equation in the laminar flow resistance pipe are considered when the temperature changes, so that the measured value of the change rate of the braking pressure when the temperature change influence is considered is as follows:

according to another aspect of the present invention, there is provided a vehicle air brake pressure change rate measuring apparatus, comprising: the device comprises a laminar flow damping tube, an isothermal container, a differential pressure sensor, a pressure sensor and an AD conversion module;

the first end of the laminar flow damping tube and the first end of the differential pressure sensor are respectively connected with a brake chamber to be measured, the second end of the laminar flow damping tube and the second end of the differential pressure sensor are both connected with the isothermal container, the other end of the isothermal container is connected with one end of the pressure sensor, and the other end of the pressure sensor and the other end of the differential pressure sensor are both connected with the AD conversion module;

when the pressure in the brake chamber to be measured changes, the pressure change in the isothermal container is influenced by the laminar flow damping tube and lags behind the pressure in the brake chamber to be measured, and the pressure difference between the isothermal container and the brake chamber is measured by using the pressure difference sensor;

and measuring the pressure in the isothermal container by using the pressure sensor, and then obtaining the pressure change rate in the brake air chamber to be measured by the AD conversion module according to the pressure in the isothermal container and the pressure difference between the isothermal container and the brake air chamber.

Preferably, the laminar flow damper pipe is located between the brake air chamber and the isothermal container, the laminar flow damper pipe is formed by inserting n capillary tubes with inner radius r and length L into an air pipe with inner diameter D in parallel, and a flow resistance system in the laminar flow damper pipeThe number is as follows:the mass flow G of air flowing through the laminar flow damping tube is as follows:wherein p is_aAt atmospheric pressure, p_aIn terms of atmospheric density,. mu.is the aerodynamic viscosity, p_cDenotes the pressure in the isothermal vessel, p_sRepresenting the brake chamber pressure to be measured.

Preferably, is prepared fromDetermining the change in gas pressure in said isothermal vessel byDetermining the temperature change in the isothermal container, wherein R is the gas state constant in the isothermal container, V is the volume of the isothermal container, W is the mass of the gas in the isothermal container, theta is the temperature in the isothermal container, and C_vSpecific heat of constant volume, C_pSpecific heat at constant pressure, [ theta ]_aIs the ambient temperature, h_uIs the heat exchange coefficient, S, of the isothermal vessel_hIs the heat exchange area of the isothermal vessel.

Preferably, from p_j＝p_s-p_cDetermining a pressure difference p between the isothermal container and the brake chamber_jNeglecting the effect of temperature variations in the isothermal vesselDetermining a measure of the rate of change of brake pressure, and determining a measure of the rate of change of brake pressureAndanalyzing to obtain the change rate of the brake pressure when the influence of the temperature change is ignoredMeasured value dp_c ^*And fitting a relation between the temperature and the temperature in the isothermal container to compensate the temperature influence.

Preferably by ignoring the effect of temperature changes on the brake pressure rate of change measurement dp_c ^*The temperature theta in the corresponding isothermal container is obtained by the temperature/dt, and then a gas state change equation in the isothermal container and a mass flow equation in the laminar flow resistance pipe are considered when the temperature changes, so that the measured value of the change rate of the braking pressure when the temperature change influence is considered is as follows:

in general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

the invention applies the laminar flow damping tube, the isothermal container, the differential pressure sensor and the pressure sensor to measure the brake pressure change rate, aims to realize the real-time accurate measurement of the brake pressure change rate, provides reference information for the vehicle situation control based on the brake pressure change rate, can improve the vehicle situation control precision, and improves the vehicle running stability, the smoothness and the passenger comfort.

Drawings

FIG. 1 is a graph of brake pressure versus time response during a pneumatic brake application provided by an embodiment of the present invention;

FIG. 2 is a schematic flow chart of a method for measuring a change rate of a pneumatic brake pressure of a vehicle according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a brake pressure change rate testing device according to an embodiment of the present invention;

FIG. 4 is an exemplary graph of a brake pressure change rate during inflation test curve provided in accordance with an embodiment of the present invention;

FIG. 5 is an exemplary exhaust event brake pressure change rate test curve provided in accordance with an embodiment of the present invention;

wherein, 1 is a brake air chamber, 2 is a laminar flow damping tube, 3 is an isothermal container, 4 is a differential pressure sensor, and 5 is a pressure sensor.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

In the present embodiment, the terms "first", "second", and the like are used for distinguishing different objects, and are not necessarily used for describing a specific order or sequence.

Fig. 2 is a schematic flow chart of a method for measuring a change rate of a pneumatic brake pressure of a vehicle according to an embodiment of the present invention, where the method shown in fig. 2 includes the following steps:

s1: pressure p in the brake chamber to be measured_sWhen changed, is influenced by the laminar flow damping tube, and the gas pressure p in the isothermal container_cThe change lags behind p_sMeasuring the pressure difference p between the isothermal container and the brake chamber by using a pressure difference sensor_j；

S2: measurement of the pressure p in an isothermal vessel by means of a pressure sensor_cThen according to the pressure p in the isothermal vessel_cAnd the pressure difference p between the isothermal vessel and the brake chamber_jObtaining the pressure change rate dp in the brake chamber to be measured_sMeasured value dp of/dt_c/dt。

Specific implementations of the steps are described in detail below.

FIG. 3 is a schematic structural diagram of a brake pressure change rate testing device provided by an embodiment of the present invention, when the pressure p in the brake chamber 1 to be measured_sWhen changing, the gas flows into the isothermal container 3 after flowing through the laminar flow damping tube 2_cChanges later, when the pressure difference sensor 4 measures the pressure difference p between the isothermal container 3 and the brake chamber 1_jThe pressure sensor 5 measures the pressure p in the isothermal vessel 3_cAnd takes into account the temperature variations within the isothermal vessel 3 to reduce measurement errors. Thus, inWithin the error allowable range, the pressure change rate dp in the brake chamber can be obtained in real time_sMeasured value dp of/dt_cAnd/dt. After the pressure difference signal and the pressure signal are collected and converted by the AD conversion module, the current brake pressure change rate value is displayed in the LED display in real time, and the collected data can be sent to a computer for storage and processing through serial port communication.

As a preferred embodiment, the laminar flow damping tube 2 is formed by inserting a plurality of (for example, 54) capillary tubes with an inner diameter of 0.6mm, an outer diameter of 1mm and a length of 100mm into an air tube with an inner diameter of 9mm, an outer diameter of 12mm and a length of 100mm in parallel, and the flow resistance coefficient in the laminar flow damping tube 2 is as follows:

the mass flow G of air flowing through the laminar flow damping tube 2 is as follows:

wherein p is_a、ρ_aRespectively, atmospheric pressure (Pa) and density (kg/m)³) (ii) a μ is aerodynamic viscosity (Pa · s). L represents the capillary length, n represents the number of capillaries, and r represents the inner radius of the capillaries.

In a preferred embodiment, the isothermal container is a metal container with a volume V filled with a certain density of copper wires. When the pressure change in the container is less than 200kPa/s, the temperature change in the container is less than 3K, and the measurement error does not exceed 1 percent when the temperature change is ignored. However, when an isothermal vessel is used for brake pressure rate of change measurement, the pressure change in the vessel is much more than 200kPa/s, which causes a large temperature change, and therefore, in order to reduce the measurement error, the influence of the temperature change must be considered.

At volume V4 × 10^-5m³Has a filling wire diameter of 50 μm and a filling rate of 300kg/m³The fine copper wires of (2) constitute an isothermal vessel. When the brake pressure change rate is measured, the internal temperature change of the brake pressure is over-increased due to the overlarge change of the internal pressureWhen the isothermal characteristic threshold value is reached, the pressure change caused by the temperature change needs to be compensated, and the gas state change in the isothermal container is as follows:

wherein R is a gas state constant; v is the volume (m) of the isothermal vessel³) (ii) a W and theta are respectively the mass (kg) and the temperature (K) of the gas in the isothermal container; c_vIs constant specific heat (J/kg/K); c_pIs the specific heat at constant pressure (J/kg/K); theta_aIs ambient temperature (K); h is_u、S_hRespectively the heat exchange coefficient (W/m) of the isothermal vessel²K) and heat transfer area (m)²)。

The output of the pressure sensor is p_cThe output of the differential pressure sensor is:

p_j＝p_s-p_c

neglecting the effect of temperature changes in the isothermal vessel, the measured value of the rate of change of the brake pressure is:

since the actual temperature inside the isothermal vessel is difficult to measure accurately in real time, the temperature is determined by the formula:

and the formula:

analyzing to obtain a brake pressure change rate measured value dp neglecting the influence of temperature change_c ^*Two rows of values of temperature theta in the isothermal container corresponding to the values of/dt and applying polynomial fittingObtaining the relation between the two. In the process of measuring the actual brake pressure change rate, firstly, the brake pressure change rate measured value dp is obtained by neglecting the temperature change_c ^*And dt, and then obtaining the temperature theta in the isothermal container through a fitted relation. And then, by combining the gas state equation in the isothermal container and the mass flow equation in the laminar flow resistance pipe when the temperature changes, the measured value of the change rate of the braking pressure when the temperature change is considered is as follows:

FIG. 4 is a diagram illustrating an example of a brake pressure change rate test curve during an inflation process implemented in accordance with the present invention; fig. 5 is a diagram showing an example of a test curve of the exhaust process brake pressure change rate implemented by the method of the present invention.

It should be noted that, according to the implementation requirement, each step/component described in the present application can be divided into more steps/components, and two or more steps/components or partial operations of the steps/components can be combined into new steps/components to achieve the purpose of the present invention.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.