Method for determining a power-assisted cylinder pressure

Abstract

The invention relates to a method for determining a corrected potential power-assisted cylinder pressure (pF) of a power-assisted brake system (1). The method comprises the steps of determining (A) at least one motor value (MM) of a power-assisted cylinder motor (20), determining (B) a potential power-assisted cylinder pressure (pF) from the motor value (MM) on the basis of a correlation model (pF(MM)) between the motor value (MM) and potential power-assisted cylinder pressure (pF), and determining (C) a power-assisted cylinder pressure (pESP) by means of an ESP pressure sensor (36) in the ESP brake system (8). Furthermore, the method comprises the steps of comparing (D) the potential power-assisted cylinder pressure (pF) with the power-assisted cylinder pressure (pESP) of the ESP pressure sensor (36) with the inclusion of a time delay (tv) between the potential power-assisted cylinder pressure (pF) and measured power-assisted cylinder pressure (pESP) of the ESP pressure sensor (36), and correcting (E) the correlation model (pF(MM)) in accordance with a determined deviation (Δp).

Description

[0001] Description

[0002] Title:

[0003] Procedure for determining a

[0004] The present invention relates to a method for determining an external power cylinder pressure of an external power brake system.

[0005] State of the art

[0006] Today's power braking systems are characterized by the fact that they are mechanically and / or hydraulically coupled to the driver. This is achieved via a brake pedal connected to an input rod. This input rod detects the driver's braking input in the full system, and pedal feel is realized in the form of a force-displacement characteristic curve. Pressure is then built up via a power piston that is hydraulically decoupled from the driver's foot. To regulate this pressure buildup, the brake pressure generated by the power piston is measured by a pressure sensor. In the fallback mode, the driver's foot is then coupled to the wheel brake cylinders via a muscle-operated brake cylinder, allowing the driver to apply braking pressure with their foot. This means that the vehicle can still be braked in the event of a fault.

[0007] DE 10 2018 222 488 A1 discloses an electrohydraulic powered vehicle braking system for an autonomously driving land vehicle. Such an electrohydraulic powered vehicle braking system is equipped with two redundant powered brake pressure generators, so that when driving autonomously and if one powered brake pressure generator fails, the other powered brake pressure generator can brake the motor vehicle without driver intervention. An electrohydraulic powered vehicle braking system is also known from DE 10 2019 201 536 A1. In this electrohydraulic powered vehicle braking system, a powered brake pressure generator is designed as a piston-cylinder unit, which is connected to a pressureless brake fluid reservoir via a pressure relief valve and a controllable valve. The pressure of the external brake pressure generator is measured by a pressure sensor arranged on the piston-cylinder unit.The pressure relief valve prevents pressure peaks in the vehicle brake system when inlet valves of the hydraulic wheel brakes of the vehicle brake system are closed during pressure build-up with the external brake pressure generator.

[0008] The object underlying the invention is to provide a method for determining the power cylinder pressure, which allows the power cylinder pressure to be determined more economically. Furthermore, a device for carrying out such a method is to be provided.

[0009] This object is achieved by a method for determining an external power cylinder pressure having the features of claim 1. Additionally, a device for implementing the method is provided. The respective dependent claims represent advantageous developments of the invention.

[0010] Disclosure of the invention

[0011] The invention specifies a method for determining a power cylinder pressure of a power brake system. The method comprises the steps of determining at least one engine value of a power cylinder motor, determining a potential power cylinder pressure from the engine value using a correlation model between the engine value and the potential power cylinder pressure, and determining a power cylinder pressure using an ESP pressure sensor in the ESP braking system. The method further comprises the steps of comparing the potential power cylinder pressure with the power cylinder pressure of the ESP pressure sensor, taking into account a time delay between the potential power cylinder pressure and the measured power cylinder pressure of the ESP pressure sensor, and correcting the correlation model according to a determined deviation.

[0012] External power cylinder pressure is understood to be a pressure generated by an external power cylinder to produce a braking force. In the previously mentioned prior art, this pressure is generally determined using a pressure sensor arranged directly downstream of the external power cylinder. The potential external power cylinder pressure is a pressure that is not measured but calculated. This potential pressure is assumed to correspond to a measured pressure. However, due to uncertainties in the calculation, a minimal difference may exist. An engine value within the meaning of the invention is understood to be any measured value that depends on the operating state of the engine and varies over time. Advantageously, the engine value is calculated using already known values, so that no additional measuring sensors need to be used.

[0013] The correlation model is a model that can be designed, for example, as a mathematical function, through which an external power cylinder pressure can be determined for each engine value. This correlation model includes all factors that influence the external power cylinder pressure. Since environmental conditions such as temperature or wear on the external power brake system are difficult to take into account, a high degree of accuracy in the determined external power cylinder pressure can be achieved by constantly correcting the correlation model. The time delay is a time value by which the external power cylinder pressure determined by the ESP pressure sensor is delayed compared to the actual pressure or the potential external power cylinder pressure determined using the correlation model.

[0014] The method makes it possible to determine the external power cylinder pressure precisely without using a pressure sensor. This saves the cost of a pressure sensor, allowing the external power cylinder pressure to be determined economically. In a preferred embodiment of the invention, the transit time of the measured external power cylinder pressure from the ESP pressure sensor is measured, and the time delay between the potential external power cylinder pressure and the measured external power cylinder pressure from the ESP pressure sensor is adjusted based on the transit time. By determining the transit time, the time delay can be determined, allowing the pressure difference and thus the correlation model to be calculated more accurately. The potential external power cylinder pressure can thus be determined more precisely, improving the control of the external power cylinder. The transit time is advantageously measured regularly in order to achieve a high level of accuracy over the long term.

[0015] In a further preferred embodiment of the invention, the propagation time of test signals is determined to measure the time delay. Such a test signal can include a transmission time. By comparing the reception time with the transmission time, the propagation time can be easily determined. This allows the propagation time to be easily measured independently of a braking maneuver, thereby increasing the accuracy of the determined potential power cylinder pressure.

[0016] Preferably, torque is used as the engine value to determine the potential power cylinder pressure. The torque can be measured. It is also possible to calculate this value in the control unit. This makes determining the torque easy.

[0017] In an advantageous further development, the motor current is used as the motor value to determine the potential external power cylinder pressure. Since the motor current is known through regulation via the control unit, this value does not need to be determined. This allows a motor value to be determined easily.

[0018] The object underlying the invention is additionally achieved by a device for carrying out the method. The device comprises an external power cylinder, via which an external power cylinder pressure can be generated using an external power cylinder motor, an ESP pressure sensor, via which a time-delayed pressure of the external power cylinder pressure can be measured, and a control unit in which a potential external power cylinder pressure can be determined based on a correlation model between a motor value and the potential external power cylinder pressure. By determining the external power cylinder pressure in this way, a pressure sensor-free external power cylinder pressure measurement can be provided. Accordingly, the advantages mentioned for the method are achieved with such a device.

[0019] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows:

[0020] Figure 1 shows an embodiment of a power brake system in which the power cylinder pressure is to be determined according to the method according to the invention,

[0021] Figure 2 Embodiment of a method for determining a

[0022] Power cylinder pressure of a power brake system, and

[0023] Figure 3 Embodiment of a method for determining the

[0024] Time delay.

[0025] Figure 1 shows an embodiment of a power brake system 1, in which the power cylinder pressure is to be determined according to the method according to the invention. The power brake system 1 comprises two units 4, 8. A first unit 4 shows an essentially known power system. A detailed description is therefore omitted and only components relevant to the invention are discussed. The first unit 4 comprises an external power brake pressure generator 12 with an external power cylinder 16, via which the external power cylinder pressure can be generated via an external power cylinder motor 20 by moving an external power piston 24. The external power cylinder motor 20 is connected to a control unit 28, via which this motor 20 is controlled. The external power cylinder pressure is applied at a point X.In the prior art, a power cylinder pressure sensor is typically located at this point X to determine the power cylinder pressure. However, in the power brake system 1, the power cylinder pressure is determined without using a power cylinder pressure sensor.

[0026] In the present embodiment, the second unit 8 is an ESP braking system, via which braking pressure can be applied to wheel brakes 32. An ESP pressure sensor 36 is arranged to measure the braking pressure in the ESP braking system 8 and is also connected to the control unit 28 for transmitting the pressure to the latter. The rest of the ESP braking system 8 is designed in a known manner, so a detailed description thereof is omitted.

[0027] Figure 2 shows an exemplary embodiment of a method for determining an external power cylinder pressure of the external power brake system 1 described in Figure 1. In a first step A, a motor value of the external power cylinder motor 20 is determined. In this exemplary embodiment, the torque MM is determined. Since this value is determined as standard, no additional sensors are necessary. Alternatively, the motor current of the external power cylinder motor 20 can also be determined. Based on the torque MM, the potential external power cylinder pressure PF is determined in a second step B. For this purpose, a correlation PF(MM) between the potential external power cylinder pressure PF and torque MM is used. The correlation PF(MM) can include values ​​such as the transmission properties of the external power cylinder motor 20, the elasticity of the braking system, and a piston area.

[0028] The potential external power cylinder pressure PF determined in this way is used for external power cylinder control R, so that a separate pressure sensor is not required. In a third step C, the pressure of the ESP pressure sensor 36 is determined. This is then transmitted to the control unit 28. In the control unit 28, in a fourth step D, the determined external power cylinder pressure PF is compared with an external power cylinder pressure PESP of the ESP pressure sensor 36. Due to the delayed transmission of the external power cylinder pressure PESP of the ESP sensor 36 to the control unit 28 and the signal processing, the external power cylinder pressure PESP of the ESP sensor 36 has a time delay tv compared to the determined potential external power cylinder pressure PF. When comparing the two values, this time delay tv is taken into account for the external power cylinder pressure PESP.

[0029] In a fifth step E, if a deviation Ap between the two values ​​is detected during the comparison, the correlation PF(MM) is adjusted according to the deviation Ap and re-entered for the calculation of the potential power cylinder pressure PF. This can increase the accuracy of the determined potential power cylinder pressure PF.

[0030] Figure 3 illustrates an embodiment of a method for determining the time delay t. For this purpose, in a first determination step M, a test signal is applied between the control unit and the ESP pressure sensor. In a second determination step N, the propagation time of the test signal is measured. Based on the propagation time, the time delay tv is determined. This value can then be updated in the method according to Figure 2. The corrected value of the time delay tv increases the accuracy when comparing both values, so that a more precise correlation (P^MM) can be determined.

Claims

Claims 1. A method for determining a power cylinder pressure (PF) of a power brake system (1), comprising the steps: Determining (A) at least one engine value (MM) of a power cylinder engine (20), Determining (B) a potential power cylinder pressure (pr) from the engine value (MM), using a correlation model (PF(MM)) between engine value (MM) and potential power cylinder pressure (PF), Determining (C) an external power cylinder pressure (PESP) by means of an ESP pressure sensor (36) in the ESP brake system (8), Comparison (D) of the potential power cylinder pressure (PF) with the power cylinder pressure (PESP) of the ESP pressure sensor (36) including a time delay (tv) between the potential power cylinder pressure (PF) and the measured power cylinder pressure (PESP) of the ESP pressure sensor (36), and Correction (E) of the correlation model (PF(MM)) according to a determined deviation (Ap).

2. Method according to claim 1, characterized in that the running time of the measured external power cylinder pressure (PESP) of the ESP pressure sensor (36) is measured, and based on the running time, the time delay (tv) between potential external power cylinder pressure (PF) and measured external power cylinder pressure (PESP) of the ESP pressure sensor (36) is adjusted.

3. Method according to claim 2, characterized in that the propagation time of test signals is determined to measure the time delay (tv).

4. Method according to one of the preceding claims, characterized in that the torque is used as the engine value (MM) to determine the potential external power cylinder pressure (PF).

5. Method according to one of claims 1 to 3, characterized in that the motor current is used as the motor value to determine the potential external power cylinder pressure (PF).

6. Device for carrying out the method according to one of the preceding Claims, comprising an external power cylinder (16), via which an external power cylinder pressure can be generated with an external power cylinder motor (20), an ESP pressure sensor (36), via which a time-delayed pressure of the external power cylinder pressure (PESP) can be measured, and a control unit (28) in which a potential external power cylinder pressure (PF) can be determined on the basis of a correlation model (PF(MM)) between a motor value (MM) and the potential external power cylinder pressure (PF).

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