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

Abstract

The invention relates to a method for determining a brake cylinder pressure in a pneumatic brake system of a utility vehicle, in which method the brake cylinder pressure (pBrkCyl) is estimated by means of a mathematical model. The invention relates to a method for reliably determining the pressure of a brake chamber without using a pressure sensor, according to the invention, the air mass flow () and the physical properties of the air in the chamber (13) of the brake cylinder (6, 7) are adjusted by means of the open or closed state of an electronically controllable solenoid valve (10, 11) arranged directly in front of the brake cylinder (6, 7) in the air supply line (4, 5) outside the control device (2) for the brake cylinder pressure (pBrkCyl). The brake cylinder pressure (pBrkCyl) is continuously determined taking into account a currently predetermined open or closed state of the solenoid valve (10, 11).

Description

Technical Field

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

[0002] US Pat. No. 6,508,522 B1 discloses a method and apparatus for estimating brake pressure in a brake cylinder using a simplified mathematical model. This mathematical model is limited to the operating conditions of the brake cylinder and omits higher-order terms and certain fluid-related terms. The brake pressure in the brake cylinder is estimated based on the displacement of the cylinder piston while the piston is in contact with the rotor of a disc brake to hold the brake pad.

[0003] US 2005 / 0137773 A1 discloses a vehicle brake system for supplying compressed air to a brake chamber. To achieve a desired braking response, the vehicle brake system includes a compressed air-controlled relay valve for supplying compressed air to the brake chamber. A solenoid receives a variable signal related to a control input pressure and supplies this control input pressure to the relay valve depending on the state of the solenoid. A controller controls the solenoid according to a control model to supply compressed air to the brake chamber and achieve the desired braking behavior.

[0004] DE 10 2016 213 645 A1 describes a method for operating an automated parking brake, in which the pressure level is determined and / or adjusted with the aid of an algorithm for estimating the pressure.

[0005] A method for estimating the brake chamber pressure in a vehicle is known from CN 113688584 A. The brake chamber pressure is estimated using a statistical model in which the inertia element pressure is estimated over the operating time with a variable time constant. Summary of the Invention

[0006] The object of the present invention is to specify a method and a device with which the brake chamber pressure can be reliably determined without the use of a pressure sensor.

[0007] This object is achieved by a method according to claim 1. According to this method, for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, the brake cylinder pressure is estimated using a mathematical model. The brake cylinder pressure is determined continuously, taking into account the currently predetermined open or closed state of the solenoid valve, as a function of the air mass flow set by the open or closed state of an electronically controllable solenoid valve arranged directly upstream of the brake cylinder in the air supply system, and the physical properties of the air in the chamber of the brake cylinder, as a function of the current air mass flow set by the open or closed state of the solenoid valve, which is arranged outside the control device for the brake cylinder pressure.

[0008] The object is also achieved by a regulating device for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, the regulating device controlling the air flowing into the brake cylinder via an air supply, wherein an electronically controllable solenoid valve is arranged in the air supply to the brake cylinder and is connected to a computing unit, which determines the brake cylinder pressure on the basis of at least one feature of the method proposed in the patent application.

[0009] Furthermore, air mass flow should be understood as the time-dependent 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 that regulates the brake pressure, a real-time estimator based on simplified fluid dynamics and thermodynamic formulas is used for the actual brake cylinder pressure to save computation time. The behavior of the solenoid valve and brake cylinder is derived experimentally. In particular, the dead time between energizing the solenoid valve and pneumatically opening and closing is taken into account, which increases the accuracy of the real-time estimation. This dead time is also derived using measurement technology.

[0010] This real-time estimation is particularly useful for driving dynamics control functions that use solenoid valves and intervene in the brake control process. An example of such a driving dynamics control system is an ABS system, which includes ABS valves to prevent wheel locking during full braking. Information about the pressure level in the brake cylinder is particularly important during function switching (e.g., switching from normal brake control to ABS intervention). However, this information can also be used for function optimization.

[0011] In a preferred embodiment, the brake cylinder pressure is calculated based on the "upstream" temperature and "upstream and downstream" pressures of three air mass flow sub-flows. This includes a first sub-flow from the control device to the brake cylinder, a second sub-flow from the brake cylinder back to the control device, and a third sub-flow from the brake cylinder into the surroundings of the brake system. This consideration of the properties of the air mass flow sub-flows flowing in different directions allows for increased accuracy in the brake cylinder pressure to be determined in real time.

[0012] In another preferred embodiment, these air mass flows are determined as a function of the pressures prevailing upstream and downstream of the solenoid valve and the air temperature prevailing upstream of the solenoid valve. Based on these variables and the physical properties of the air in the brake cylinder chamber, the brake cylinder pressure is determined at the time of the predetermined open or closed state. The pressure and air temperature can be determined using simple measurement technology components, which simplifies the measurement effort required for the estimation.

[0013] In another embodiment, the air temperature and volume are calculated as physical properties of the air in the brake cylinder chamber. This can be achieved using simple thermodynamic formulas. The volume of the air in the brake cylinder chamber can be determined particularly conveniently based on the displacement travel of the brake cylinder piston in the brake cylinder chamber, which represents the brake cylinder pressure. To this end, it is only necessary to determine the travel traveled by the brake cylinder piston using the existing travel sensor.

[0014] 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 and / or the volume change work between the air in the brake cylinder chamber and the surrounding environment. Furthermore, in the open state of the solenoid valve, a predetermined cross-sectional area through which the air mass flow flows is assumed in the air supply line, while in the closed state of the solenoid valve, a zero cross-sectional area is provided. By providing these two cross-sectional areas in the air supply, both the measurement effort and the computation effort are reduced, since only two fixed variables representing the open or closed state of the solenoid valve need to be calculated.

[0015] In another preferred embodiment, an electronically controllable solenoid valve is arranged in the air supply line to the brake cylinder. The solenoid valve is connected to a computing unit that is part of a control device for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle. The control device includes a pressure sensor for detecting the inlet pressure at the solenoid valve. This inlet pressure is used to determine a first partial air mass flow from the control device to the brake cylinder.

[0016] In another preferred embodiment, the electrically controllable solenoid valve is configured as an ABS valve mounted at the wheel, which is controlled by an ABS controller. Here, the regulating device is configured to regulate the brake cylinder pressure on both sides of the vehicle's axle, thereby reducing hardware expenditure. This regulating device is also known as an axle modulator. The axle modulator has two pneumatically independent pressure regulating channels, each with a charging valve and a deflation valve, each with a pressure sensor, and shared regulating electronics serving as a computing unit.

[0017] The aspects described herein with reference to the method also apply to the disclosed apparatus. The disclosed method can be implemented, for example, by a computing unit. This can be accomplished by providing appropriate read and write access to a memory associated with the vehicle. The method is implemented, in particular, within a motor vehicle using hardware or software, or a combination of hardware and software. The hardware includes, in particular, digital signal processors, application-specific integrated circuits, field-programmable gate arrays, and other suitable switching and computing components. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further features, advantages and properties of the present invention are explained with the aid of the description of preferred embodiments of the present invention with reference to the accompanying drawings, in which:

[0019] Figure 1 A schematic diagram showing an exemplary embodiment of the device according to the invention for a pneumatic braking system at the front axle of a vehicle;

[0020] Figure 2 Shown in accordance with Figure 1 Schematic diagram of the air mass flow distribution under the pressure regulation state of the equipment;

[0021] Figure 3 A schematic diagram showing an embodiment of the method according to the invention is shown. DETAILED DESCRIPTION

[0022] exist Figure 1 shows a schematic diagram of an embodiment of a device according to the present invention for a pneumatic brake system on the front axle of a vehicle. Device 1 is designed as an axle modulator 2, which functions as a device for regulating the brake cylinder pressure in brake cylinders 6, 7 of the pneumatic brake system. In this pneumatic brake system, the braking process of the vehicle, which is performed by service brakes 14, which can be designed as disc brakes, is assisted by the introduction of compressed air to press pistons 3 of brake cylinders 6, 7 against the service brakes arranged at each wheel.

[0023] Axle modulator 2 is connected to the right and left brake cylinders 6 and 7 via air supply lines 4 and 5. Axle modulator 2 supplies air to both brake cylinders 6 and 7 via the air supply lines to support braking operations at the wheels on the vehicle's front axle. Each air supply line 4 and 5 forms a separate pressure control branch for each brake cylinder 6 and 7. Axle modulator 2 includes control electronics 8 for determining the air supply provided to the respective brake cylinder 6 and 7, and pressure sensors 9 for determining the pressure in the air supply lines 4 and 5. ABS valves 10 and 11 are installed directly upstream of the respective brake cylinders 6 and 7 in the air supply lines 4 and 5. Their open and closed states are controlled by an ABS controller 12. The ABS controller 12 prevents the vehicle's wheels from locking under full braking, potentially causing the driver to lose control of the vehicle. This is achieved by repeatedly reducing and increasing the brake pressure using the electronically controlled ABS valves 10 and 11. The wheels are braked in a metered manner by varying the opening state of the ABS valves.

[0024] Axle modulator 2, such as that installed on the front axle, has only one pressure sensor 9 and can therefore only adjust one control pressure. This pressure is applied to both wheels at the front axle, so both wheels are subjected to the same pressure. Because each front wheel has its own ABS valve 10, 11, the wheel pressure is modulated again by the ABS valve on a wheel-by-wheel basis, and the pressure sensors cannot measure the pressure modulated by the ABS valves 10, 11. If ABS valves 10, 11 are positioned between axle modulator 2 and the wheels, the real-time estimator described below can always be used, because actuating the ABS valves 10, 11 will cause the pressure measured at axle modulator 2 to no longer be consistent with the wheel pressure.

[0025] Since the brake cylinder pressure p in the brake cylinders 6 , 7 cannot be determined by the pressure sensor 9 of the axle modulator 2 during the actuation of the ABS valves 10 , 11 BrkCyl , so the brake cylinder pressure depends on the air mass flow through the ABS valves 10, 11 To make an estimate. Figure 2 It can be seen that the air mass flow in the pressure regulating circuit is By three diversions 、 and First diversion From the axle modulator 2 through the ABS valve 10 to the brake cylinder 6, the second branch From the brake cylinder 6, it flows back to the axle modulator 2 through the ABS valve 10. The fluid flows out of the chamber of the brake cylinder 6 via the ABS valve 10 into the surroundings.

[0026] Air mass flow The estimation is done with the help of a mathematical model, which is as follows Figure 3 The ABS valve 10 is shown in the first situation as an inlet valve with the pressure p measured in the axle modulator 2 by the pressure sensor 9 as the inlet pressure. AxM and ambient temperature T Env Air mass flow Flows into the inlet valve. Furthermore, the ABS valve is considered an outlet valve in the second state. In one state, the ABS valve 10 is closed. In this case, the cross-sectional area A of the air supply line is zero. In the second open state of the ABS valve 10, this cross-sectional area is assumed to be 100%. Furthermore, the accompanying air mass flow is taken into account in this calculation. and its enthalpy flow Due to the pressure p occurring in the brake cylinder 6 BrkCyl and the resulting temperature T, which results in a heat flux to be taken into account and dissipated to the outside . will have another enthalpy flow Air mass flow is considered as the output variable of the ABS valve 10. The ambient air pressure p Env and ambient temperature T Env is taken into account as an additional input variable.

[0027] This model can be used to estimate the brake chamber pressure p in real time based on formula 1: BrkCyl :

[0028] Formula 1,

[0029] in:

[0030] p BrkCyl Brake cylinder pressure,

[0031] Air mass flow,

[0032] R is the specific gas constant of air,

[0033] TThe air temperature in the brake cylinder,

[0034] V is the volume of air in the brake cylinder's chamber.

[0035] The components of Formula 1 , T and V can be calculated as follows.

[0036] Depend on

[0037] Formula 2,

[0038] Determine the volume V,

[0039] in:

[0040] A BrkCyl The effective cross-sectional area of ​​the brake chamber,

[0041] x(p BrkCyl ) displacement of the piston in the brake cylinder,

[0042] V tot Dead volume of the brake cylinder.

[0043] In this case, the displacement of the piston 3 of the brake cylinder 6 is determined with the aid of the travel sensor 16 .

[0044] The air mass flow is calculated by the following formula :

[0045] Formula 3,

[0046] in:

[0047] A is the cross-sectional area of ​​the air delivery line,

[0048] C q Flow coefficient (factor used to compensate for the effective area of ​​air mass flow),

[0049] C m Flow parameters,

[0050] p up "Upstream" pressure,

[0051] T up “Upstream” pressure.

[0052] The temperature T is obtained as follows:

[0053] Formula 4,

[0054] in:

[0055] Enthalpy flow

[0056] heat flow between the air in the brake chamber volume and the surroundings,

[0057] Volume change rate

[0058] The mass of air in volume m

[0059] Alternatively, the pressure gradient may also be derived empirically or experimentally.

[0060] The described solution is not limited to application to the wheels of the front axle, but can also be used on the rear axle if the vehicle configuration requires the use of ABS valves at the wheels of the rear axle.

[0061] Reference Signs List

[0062] 1 device

[0063] 2 axle modulator

[0064] 3. Brake cylinder piston

[0065] 4 Air delivery lines

[0066] 5 Air delivery lines

[0067] 6 brake cylinders

[0068] 7 brake cylinders

[0069] 8. Adjustment electronics

[0070] 9. Pressure sensor

[0071] 10ABS valve

[0072] 11ABS valve

[0073] 12ABS controller

[0074] 13 Brake cylinder chamber

[0075] 14 Service brakes

[0076] 15 Surrounding environment

[0077] 16 stroke sensor

Claims

1. A method for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, wherein the brake cylinder pressure (p BrkCyl ), characterized in that, Depends on the brake cylinder pressure (p BrkCyl The air mass flow ( ) and the physical properties of the air in the chamber (13) of the brake cylinder (6, 7), continuously determining the brake cylinder pressure (p BrkCyl ).

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

3. The method according to claim 1 or 2, characterized in that The dead time between energizing an electrically controllable solenoid valve (10, 11) and pneumatically opening or closing the solenoid valve (10, 11) is determined by measurement technology.

4. The method according to claim 1, 2 or 3, characterized in that Based on three air quality splits ( 、 、 )'s "upstream" temperature (T) and "upstream and downstream" pressures to calculate the brake cylinder pressure (p BrkCyl ), wherein a first branch flow ( ), a second branch flow ( ) returning from the brake cylinder (6, 7) to the regulating device (2) ) and a third partial flow ( ).

5. The method according to at least one of the preceding claims, characterized in that Air quality diversion ( 、 、 ) is determined based on the pressure (p) prevailing upstream and downstream of the solenoid valve (10, 11) and the air temperature (T) prevailing upstream of the solenoid valve (10, 11), and based on these variables and the physical properties of the air in the chamber (13) of the brake cylinder (6, 7), the brake cylinder pressure (p) is determined at a predetermined time point in the open state or closed state. BrkCyl ).

6. The method according to at least one of the preceding claims, characterized in that As physical properties of the air in the chamber (13) of the brake cylinder (6, 7), the temperature (T) of the air and the volume (V) of the air are calculated.

7. The method according to at least one of the preceding claims, characterized in that The volume (V) of the air in the chamber (13) of the brake cylinder (6, 7) depends on the pressure of the piston (3) in the chamber (13) of the brake cylinder (6, 7), which represents the brake cylinder pressure (p BrkCyl )’s displacement stroke.

8. The method according to at least one of the preceding claims, characterized in that The temperature (T) of the air in the chamber (13) of the brake cylinder (6, 7) depends on the enthalpy flow (ḣ) and / or the heat flow ( ) and / or volume change work.

9. The method according to at least one of the preceding claims, characterized in that In the open state of the magnetic valve (10, 11), it is assumed that there is an air mass flow ( ) flows through a cross-sectional area (A), while in the closed state of the solenoid valve (10, 11), a cross-sectional area (A) of zero is specified.

10. The method according to at least one of the preceding claims, characterized in that The ABS valves (10, 11) are used as electronically controllable solenoid valves.

11. A regulating device for determining the brake cylinder pressure in a pneumatic brake system of a commercial vehicle, the regulating device controlling the air flowing into the brake cylinder (6, 7) via an air supply line (4, 5), characterized in that The calculation unit (8) is designed to determine the brake cylinder pressure (p) by means of the method according to any one of the preceding 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. The adjustment device according to claim 11, characterized in that A pressure sensor (9) is provided for detecting the inlet pressure at the solenoid valve (10, 11).

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

14. The adjustment device according to claim 11 or 12, characterized in that The electrically controllable solenoid valve is configured as an ABS valve (10, 11) mounted on a wheel and controlled by an ABS controller (12).

15. The regulating device according to claim 11 , wherein the regulating device is configured to adjust the brake cylinder pressure (p BrkCyl ) to make adjustments.

Images