Method and control for determining brake cylinder pressure in a commercial vehicle pneumatic brake system

Abstract

A method and apparatus for reliably determining brake chamber pressure without the use of a pressure sensor. A method for determining brake cylinder pressure in a pneumatic brake system of a commercial vehicle, comprising: BrkCyl In the method, where the brake cylinder pressure p is estimated using a mathematical model, BrkCyl is the brake cylinder pressure p BrkCyl The air mass flow rate m is adjusted by the opening or closing of electronically controllable solenoid valves 10, 11 arranged immediately before the brake cylinder 6 in the air supply line outside the control device 2 for the brake cylinder 6. · and the physical properties of the air in the chambers of the brake cylinders, taking into account the currently set open or closed state of the solenoid valves 10, 11.

Description

[Technical Field]

[0001] The present invention relates to a method for determining brake cylinder pressure in a pneumatic braking system of a commercial vehicle, in which the brake cylinder pressure is estimated using a mathematical model, and to a control device for carrying out the method. [Background technology]

[0002] Patent Document 1 discloses a method and apparatus for estimating brake pressure in a brake cylinder based on a simplified mathematical model. The mathematical model is limited to the operating conditions of the brake cylinder, and higher-order terms and certain terms dependent on the fluid are omitted. The brake pressure in the brake cylinder is estimated as a function of the displacement of the cylinder piston, while the piston is in contact with the rotor of a disc brake that holds the brake shoes.

[0003] A vehicle braking system for supplying compressed air to brake chambers is known from US Pat. No. 5,623,999. To obtain a desired braking response, the vehicle braking system includes a pneumatically controlled relay valve for supplying compressed air to the brake chambers. A solenoid receives a variable signal that depends on a control input pressure and supplies the control input pressure to the relay valve as a function of the state of the solenoid. A control device controls the solenoid according to a control model to supply compressed air to the brake chambers and obtain a desired braking behavior.

[0004] Patent document 3 describes a method for operating an automated parking brake, in which the pressure level is determined and / or set (adjusted) using an algorithm for pressure estimation.

[0005] A method for estimating brake chamber pressure in a vehicle is known from DE 10 200 04 133 A1. The chamber pressure is estimated using a statistical model which estimates the inertial coupling pressure with a time constant which is variable with time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 6,508,522 [Patent Document 2] US Patent Application Publication No. 2005 / 0137773 [Patent Document 3] German Patent Application Publication No. 102016213645 [Patent Document 4] Chinese Patent Application Publication No. 113688584 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for reliably determining brake chamber pressure without using a pressure sensor. [Means for solving the problem]

[0008] This problem is solved by a method according to claim 1, for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, in which the brake cylinder pressure is estimated by means of a mathematical model, and the brake cylinder pressure is determined continuously depending on the air mass flow, which is regulated by the open or closed state of an electronically controllable solenoid valve arranged in the air supply line immediately before the brake cylinder, outside the brake cylinder pressure control device, and on the physical properties of the air in the brake cylinder chamber, taking into account the currently set open or closed state of the solenoid valve.

[0009] The above problem is also solved by a control device for determining the brake cylinder pressure in a pneumatic braking system of a commercial vehicle, which regulates the air flowing into the brake cylinder via an air supply line, wherein an electronically controllable solenoid valve is arranged in the air supply line to the brake cylinder and is connected to a computing unit, which determines the brake cylinder pressure depending on at least one of the features of the method proposed in the present application.

[0010] In the following, the air mass flow rate is understood to be the time derivative of the air mass flowing through the solenoid valve. Because the use of a separate solenoid valve in the air supply line prevents direct pressure measurement by the control device for controlling the brake pressure, a real-time estimator based on simplified equations of fluid dynamics and thermodynamics is used for the actual brake cylinder pressure to reduce calculation time. The behavior of the solenoid valve and the brake cylinder is empirically derived. In particular, the dead time between the energization of the solenoid valve and its pneumatic opening and closing is taken into account, thereby improving the accuracy of the real-time estimation. The dead time is also derived using measurement techniques.

[0011] Such real-time estimation is particularly suitable for driving dynamics control functions that use solenoid valves and intervene in the brake control process. Such driving dynamics control is, for example, an ABS system, which includes an ABS valve to prevent the wheels from locking up during full braking. Information about the pressure level in the brake cylinders is particularly important during function transitions (e.g., from normal brake control to ABS system intervention). However, this information can also be used for function optimization.

[0012] In a preferred embodiment, brake cylinder pressure is calculated based on the "upstream" temperature and "upstream and downstream" pressure of three air mass flow fractions, with a first fraction considered to flow from the control device to the brake cylinder, a second fraction considered to flow from the brake cylinder back to the control device, and a third fraction considered to flow from the brake cylinder to the surroundings of the brake system. Consideration of the characteristics of the fractions of air mass flowing in various directions allows for improved accuracy of the brake cylinder pressure to be determined in real time.

[0013] In another preferred embodiment, the partial air mass flow is determined depending on the pressures upstream and downstream of the solenoid valve and the air temperature upstream of the solenoid valve, and the brake cylinder pressure is determined based on the partial air mass flow at the time of opening or closing the brake cylinder, which is set based on the physical properties of the air in the brake cylinder chamber. The determination of the pressure and air temperature can be achieved using simple means in terms of measurement technology, which simplifies the measurement effort required for the estimation.

[0014] In another embodiment, the temperature and volume of the air are calculated as physical properties of the air in the chamber. This can be achieved by a simple thermodynamic equation. The volume of air in the brake cylinder chamber can be particularly conveniently determined depending on the displacement stroke of the brake cylinder piston in the brake cylinder chamber, which characterizes the brake cylinder pressure. For this purpose, only the travel distance of the brake cylinder piston needs to be determined by the existing displacement sensor.

[0015] In another preferred embodiment, the temperature of the air in the brake cylinder chamber is determined as a function of the enthalpy flow and / or the heat flow between the air in the brake cylinder chamber and the surroundings and / or the work of volume change. Furthermore, when the solenoid valve is open, a set cross-sectional area through which the air mass flows is assumed in the air supply line, while when the solenoid valve is closed, the cross-sectional area is set to zero. The two set cross-sectional areas in the air supply reduce the measurement effort on the one hand and the calculation effort on the other hand, since only two set quantities representing the open and closed states of the solenoid valve have to be calculated.

[0016] In another preferred embodiment, an electronically controllable solenoid valve is arranged in the air supply line to the brake cylinder, and the solenoid valve is connected to a computing unit, which is a component of a control device for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, and the control device includes a pressure sensor for detecting a primary pressure at the solenoid valve, which is taken into account to determine a first partial flow of the air mass flow from the control device to the brake cylinder.

[0017] In another preferred embodiment, the electrically controllable solenoid valves are configured as wheel-mounted ABS valves controlled by an ABS control device. The control device is configured to control the brake cylinder pressure on both sides of one axle of the vehicle, thereby reducing the hardware effort. Such a control device is also called an axle modulator. The axle modulator has two independent pneumatic pressure control passages, each with a vent valve and a bleed valve, a pressure sensor, and a control electronic component commonly used as a computing unit.

[0018] The aspects described herein for methods also apply to the disclosed apparatus. The disclosed methods can be executed, for example, by a computing unit with appropriate write and read access to a memory allocated to the vehicle. The methods can be implemented in hardware or software, or a combination of hardware and software, particularly within a motor vehicle. Hardware includes, among others, digital signal processors, application-specific integrated circuits, field programmable gate arrays, and other suitable circuit and computing components.

[0019] Further features, advantages and characteristics of the present invention will be explained based on the description of preferred embodiments of the invention with reference to the drawings. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a principle of an embodiment of the device according to the invention for a pneumatic braking system on the front axle of a vehicle; [Figure 2] 2 shows a schematic representation of the partial air mass flows in a pressure control situation of the device according to FIG. 1; [Figure 3] 1 shows a schematic diagram of an embodiment of the method according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0021] 1 shows a schematic diagram of an embodiment of the device according to the invention for a pneumatic braking system of the front axle of a vehicle. The device 1 is configured as an axle modulator 2 that functions as a control device for brake cylinder pressure in brake cylinders 6, 7 of a pneumatic brake system. In such a pneumatic brake system, pistons 3 of the brake cylinders 6, 7 are pressed against service brakes arranged on the respective wheels by compressed air, thereby assisting the vehicle's braking process, which is carried out by service brakes (foot brakes) 14, which may be configured as disc brakes.

[0022] The axle modulator 2 is connected to the right and left brake cylinders 6, 7 via air supply lines 4, 5. To assist the braking process at the wheels of the vehicle's front axle, the axle modulator 2 introduces air to both brake cylinders 6, 7 via the brake cylinders. Each air supply line 4, 5 forms a separate pressure control train with the brake cylinders 6, 7. The axle modulator 2 includes control electronics 8, which determines the air supply set for each brake cylinder 6, 7, and a pressure sensor 9, which determines the pressure in the air supply lines 4, 5. Immediately before each brake cylinder 6, 7, an ABS valve 10, 11 is installed in each air supply line 4, 5, and the ABS valve's open or closed state is controlled by an ABS control device 12. The ABS control device 12 prevents the vehicle's wheels from locking during full braking, which could cause the driver to lose control of the vehicle. This is achieved by repeatedly increasing and decreasing the brake pressure via the electronically controlled ABS valves 10, 11. The wheels are braked in a controlled manner by varying the opening state of the ABS valves.

[0023] An axle modulator 2, such as one integrated into the front axle, has only one pressure sensor 9 and is therefore capable of adjusting only one pressure. This pressure occurs at both wheels of the front axle, so that both wheels are subjected to the same pressure. Because each front wheel has its own ABS valve 10, 11, the wheel pressure can be adjusted individually and repeatedly without the pressure sensor being able to measure the pressure adjusted by the ABS valve 10, 11. Since operation of the ABS valve 10, 11 means that the pressure measured at the axle modulator 2 no longer corresponds to the wheel pressure, if the ABS valve 10, 11 is installed between the axle modulator 2 and the wheel, the real-time estimator described below can be used at all times.

[0024] During operation of the ABS valves 10, 11, the brake cylinder pressure p BrkCyl cannot be determined by the pressure sensor 9 of the axle modulator 2, the brake cylinder pressure is determined by the air mass flow m · (The dots on the alphabet (time derivatives) are used.) As can be seen from Figure 2, the air mass flow rate m · is divided into three parts m · 1,m · 2,m · 3. The first partial flow m · 1 flows from the axle modulator 2 through the ABS valve 10 to the brake cylinder 6, while the second partial flow m · 2 flows from the brake cylinder 6 through the ABS valve 10 and back to the axle modulator 2. The third partial flow m · flows out of the chamber 13 of the brake cylinder 6 through the ABS valve 10 to the surroundings.

[0025] Air mass flow rate m · The estimation of is based on a mathematical model as shown for the pressure control situation in Figure 3. The ABS valve 10 is shown as an inlet valve in the first situation, which receives the pressure p measured by the pressure sensor 9 as the primary pressure (system pressure) in the axle modulator 2. AxM and the ambient temperature T Env and mass flow rate m · In the second state, the ABS valve 10 is closed. In one of the two states, the cross-sectional area A of the air supply line is then zero. In the second open state of the ABS valve 10, this cross-sectional area is assumed to be 100%. Furthermore, in this case, the incoming air mass flow rate m · Inl and its enthalpy flow h · Inl The pressure p occurring in the brake cylinder 6 is taken into account. BrkCyland the resulting temperature T, the heat flow Q that must be taken into account · Another enthalpy flow, h · outl air mass flow rate m · outl is regarded as the output quantity of the ABS valve 10. Env and ambient temperature T Env is considered as another input quantity.

[0026] Brake chamber pressure p BrkCyl can be estimated in real time based on the model and on the basis of Equation (1).

[0027]

number

[0028] where: p BrkCyl is the brake cylinder pressure, m · is the air mass flow rate, R is the specific gas constant, T is the air temperature in the brake cylinder, V is the volume of air in the chamber of the brake cylinder.

[0029] The individual components m of [Equation 1] · ,T,V can be calculated as follows:

[0030] The volume V is calculated by the following equation:

[0031]

number

[0032] where: A BrkCyl is the base area of ​​the brake chamber, x(p BrkCyl ) is the displacement of the piston in the brake cylinder, V tot is the dead volume of the brake cylinder.

[0033] Here, the displacement of the piston 3 of the brake cylinder 6 is determined using a displacement sensor 16 .

[0034] Air mass flow rate m · is calculated based on the following formula:

[0035]

number

[0036] where: A is the cross-sectional area of ​​the air guide pipe, C q is the flow coefficient (a factor that compensates for the effective area of ​​the air mass flow), C m is a flow parameter, p up is the "upstream" pressure, T up is the "upstream" temperature.

[0037] The temperature T is calculated as follows:

[0038]

number

[0039] where: h · is the enthalpy flow, Q · is the heat flow between the air and the surroundings in the brake chamber volume (space), V · is the volume change, m is the mass of air in the volume (space).

[0040] Alternatively, the pressure gradient can be derived empirically or experimentally.

[0041] The above solution is not limited to application to wheels on the front axle, but can also be used on the rear axle if the vehicle configuration requires the use of ABS valves on the wheels on the rear axle. [Explanation of symbols]

[0042] 1 device 2 Axle Modulator 3 Brake cylinder piston 4 Air supply line 5 Air supply line 6 Brake cylinder 7 Brake cylinder 8 Control electronic components 9. Pressure Sensor 10 ABS valve 11 ABS valve 12 ABS control equipment 13 Brake cylinder chamber 14 Service brake 15 Surroundings 16 Displacement Sensor

Claims

1. 1. A method for determining brake cylinder pressure in a pneumatic brake system of a commercial vehicle, comprising: ＢｒｋＣｙｌ ) is estimated using a mathematical model, The brake cylinder pressure (p ＢｒｋＣｙｌ ) is the brake cylinder pressure (p ＢｒｋＣｙｌ The air mass flow rate (m) is adjusted by the opening or closing state of electronically controllable solenoid valves (10, 11) arranged immediately before the brake cylinders (6, 7) in the air supply lines (4, 5) outside the control device (2) for the brake cylinders (6, 7). ・ ) and the physical properties of the air in the chambers (13) of the brake cylinders (6, 7), taking into account the currently set open or closed state of the solenoid valves (10, 11).

2. 2. The method according to claim 1, wherein the behavior of the electronically controlled solenoid valves (10, 11) and / or the brake cylinders (6, 7) is determined by measurement technology.

3. 3. The method according to claim 1, wherein the dead time between the energization of the electrically controllable solenoid valve (10, 11) and its pneumatic opening or closing is determined by measurement technology.

4. The brake cylinder pressure (p ＢｒｋＣｙｌ ) are the three air mass flow fractions (m ・ 1,m ・ 2,m ・ 3) is calculated based on the "upstream" temperature (T) and "upstream and downstream" pressure of the first partial flow (m ・ 1) is considered to flow from the control device (2) to the brake cylinders (6, 7), and a second partial flow (m ・ 2) is considered to flow from the brake cylinders (6, 7) back to the control device (2), and a third partial flow (m ・ 4. The method according to claim 1, wherein the brake fluid is considered to flow from the brake cylinders (6, 7) to the surroundings of the braking system.

5. The partial flow of the air mass flow (m ・ 1,m ・ 2,m ・ 3) is determined depending on the pressure (p) upstream and downstream of the solenoid valve (10, 11) and the air temperature (T) upstream of the solenoid valve (10, 11), and the brake cylinder pressure (p ＢｒｋＣｙｌ 5. The method according to claim 1, wherein the air mass flow rate is determined based on a partial flow of the air mass flow together with physical properties of the air in the chamber (13) of the brake cylinder (6, 7) at the time of the set opening or closing state.

6. 6. The method according to claim 1, wherein the temperature (T) and the volume (V) of the air in the chamber (13) of the brake cylinder (6, 7) are calculated as physical properties of the air.

7. The volume (V) of air in the chamber (13) of the brake cylinder (6, 7) is ＢｒｋＣｙｌ 7. The method according to claim 1, wherein the brake cylinder pressure is determined as a function of the displacement stroke of the piston (3) in the chamber (13) of the brake cylinder (6, 7), characterizing the displacement stroke of the piston (3) in the chamber (13).

8. The temperature (T) of the air in the chamber (13) of the brake cylinder (6, 7) is proportional to the enthalpy flow (h ・ ) and / or the flow of heat between the air in the chamber (13) of the brake cylinder and the surroundings (Q ・ 8. The method according to claim 1, wherein the volume change is determined depending on the volumetric capacity and / or the volumetric work.

9. When the solenoid valves (10, 11) are open, the air mass flow rate (m ・ 9. The method according to claim 1, wherein a cross-sectional area (A) through which the air flows is assumed in the air supply lines (4, 5), while in the closed state of the solenoid valves (10, 11), the cross-sectional area (A) is set to zero.

10. 10. The method according to claim 1, wherein the electronically controllable solenoid valve is an ABS valve (10, 11).

11. 1. A control device for determining brake cylinder pressure in a pneumatic brake system of a commercial vehicle, the control device adjusting air flow to the brake cylinders (6, 7) via air supply lines (4, 5), comprising: The calculation unit (8) calculates the brake cylinder pressure (p) in accordance with any one of claims 1 to 10, provided that electronically controllable solenoid valves (10, 11) are arranged in the air supply lines (4, 5) to the brake cylinders (6, 7). ＢｒｋＣｙｌ ) 。

12. 12. The control device according to claim 11, further comprising a pressure sensor (9) for detecting a primary pressure in the solenoid valve (10, 11).

13. 13. The control device according to claim 11 or 12, characterized in that the computing unit (8) is a component of the control device (2).

14. 13. The device according to claim 11 or 12, characterized in that the electrically controllable solenoid valves are configured as wheel-mounted ABS valves (10, 11) controlled by an ABS control device (12).

15. Brake cylinder pressure (p ＢｒｋＣｙｌ 15. The control device according to claim 11, wherein the control device is configured to control a

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