Method for determining a control current for axle-individual blending of a brake system and hydraulic brake system

Abstract

The present invention relates to a method for determining a control current for a first isolating valve (24) of a hydraulic brake system (2) of a vehicle, in which the first isolating valve (24) is arranged between a brake pressure generator (4) and a first brake circuit (20) assigned to the wheel brakes (32, 34) of a first vehicle axle, and a second isolating valve (26) is arranged between the brake pressure generator (4) and a second brake circuit (22) assigned to the wheel brakes (40, 42) of a second vehicle axle, wherein the first and second isolating valves (24, 26) are designed as current-controllable differential pressure valves, with the method steps of opening the first and second isolating valves (24, 26), increasing the pressure in the first and second brake circuits (20, 22) by the brake pressure generator (4) up to a predetermined first pressure, closing the first isolating valve (24) by a control current,Reducing the pressure generated by the brake pressure generator (4) while reducing the pressure in the second brake circuit (22) to a second pressure and achieving a pressure difference between the first pressure in the first brake circuit (20) and the second pressure in the second brake circuit (22), reducing the control current at the first isolating valve (24), detecting a control current value when an opening of the first isolating valve (24) is detected, and determining and storing a correction current value (k) for the pressure difference as the difference between the detected control current value and a predetermined control current value.

Description

State of the art

[0001] The present invention relates to a method for determining a control current for axle-individual blending of a brake system and a hydraulic brake system.

[0002] It is known from the state of the art to pre-control regenerative braking torques depending on driving condition variables. In vehicles with two generators, i.e. one generator per axle, the level of recuperation is controlled individually. Current braking systems offer blending (alternating / mixed operation of hydraulic and regenerative braking force), sometimes with limitations. This is evident, for example, in scalar blending, in which a fixed hydraulic brake force distribution occurs across all braked wheels, or sequential blending, in which a fixed hydraulic brake force distribution occurs with the restriction that no outlet valves are used for pressure adjustment. With so-called axle-individual blending, the brake force distribution is freely adjustable. This makes it possible to achieve a compromise between driving stability and maximum regenerative deceleration even in driving dynamics-limited situations.With free partitioning, attention must be paid to the actuation properties in terms of pressure setting accuracy, dynamics, etc. The quality of the free partitioning of the hydraulic braking torques is limited by mechanical and electrical tolerances via the axle or individual wheel pressure setting. With axle-specific orifices, there is a pressure sensor for the pressure setting, but this sensor measures on the second vehicle axle, while the first vehicle axle is controlled via an ESP pump in so-called delta pressure mode. This pressure is set via a so-called "pressure compensator" in relation to the pressure on the second vehicle axle. This delta pressure control is limited by mechanical and electrical tolerances. These can lead to pressure setting errors on the first vehicle axle.

[0003] DE 10 2019 207 056 A1 describes a previously known example of a hydraulic brake system with a first brake circuit for the front axle and a second brake circuit for the rear axle of a vehicle. Disclosure of the invention

[0004] With the present invention, the pressure setting error in axle-individual diaphragms can be advantageously reduced in order to avoid an insufficient braking force on the respective vehicle axle, which is perceived by the person driving the vehicle as a lack of deceleration, or an excessive braking force, which is perceived as an impairment of controllability or driving comfort.

[0005] According to the invention, a method for determining a control current for a first isolating valve of a hydraulic brake system of a vehicle having the features of patent claim 1 and a hydraulic brake system having the features of patent claim 9 are therefore provided.

[0006] Accordingly, a method is provided for determining a control current for a first isolating valve of a hydraulic brake system of a vehicle, in which the first isolating valve is arranged between a brake pressure generator and a first brake circuit assigned to the wheel brakes of a first vehicle axle and a second isolating valve is arranged between the brake pressure generator and a second brake circuit assigned to the wheel brakes of a second vehicle axle, wherein the first and second isolating valves are designed as current-controllable differential pressure valves.The method comprises the steps of opening the first and second isolating valves, increasing the pressure in the first and second brake circuits by means of the brake pressure generator up to a predetermined first pressure, closing the first isolating valve by means of a control current, and reducing the pressure generated by the brake pressure generator while reducing the pressure in the second brake circuit to a second pressure and achieving a pressure difference between the first pressure in the first brake circuit and the second pressure in the second brake circuit. Following this, the control current at the first isolating valve is reduced, preferably linearly and / or continuously, in order to detect a control current value at which an opening of the first isolating valve is determined.From this, a correction current value is determined for the pressure difference as the difference between the recorded control current value and the specified control current value, which is also stored in order to take this into account for future axis-specific orifices.

[0007] Furthermore, a hydraulic brake system for a vehicle is provided, which has a first isolating valve between a brake pressure generator and a first brake circuit assigned to the wheel brakes of a first vehicle axle and a second isolating valve between the brake pressure generator and a second brake circuit assigned to the wheel brakes of a second vehicle axle, wherein the first and second isolating valves are designed as current-controllable differential pressure valves and the brake system is designed to carry out the above-mentioned method.

[0008] One idea of ​​the invention is to minimize the pressure setting error when operating in delta pressure mode in the respective vehicle axle, especially when using axle-specific apertures.

[0009] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures.

[0010] According to a preferred embodiment of the method according to the invention, the correction current value is determined at least twice for the same pressure difference, wherein the stored correction current value is formed from an average value of the determined correction current values ​​in order to achieve a particularly reliable minimization of the pressure setting error.

[0011] According to a further preferred embodiment of the method according to the invention, the opening of the first isolation valve is determined in a particularly simple manner, namely based on a reduction in the actuation volume of the brake pressure generator. In this case, it is preferred if a linear actuator and / or a piston-cylinder unit is used as the brake pressure generator.

[0012] According to a further preferred embodiment of the method according to the invention, the method is repeated at least once, preferably while the vehicle is stationary and / or automatically. It is particularly advantageous if the method is repeated regularly during the vehicle's operating life. For example, the method can initially be performed as an end-of-line routine. During the vehicle's service life, the method can also be performed during charging processes of the vehicle—preferably an electric vehicle—after the vehicle has been parked, and / or as a service routine.

[0013] According to a further preferred embodiment of the method according to the invention, the correction current value is determined and stored for at least two different pressure differences, preferably for a plurality of different pressure differences, in order to reliably reduce a pressure setting error for a wide variety of braking situations.

[0014] According to a further preferred embodiment of the method according to the invention, at least one correction current value is determined and stored for the first and second isolation valves. In other words, the method is carried out for both the first and second isolation valves.

[0015] According to a further preferred embodiment of the method according to the invention, axle-specific blending is carried out by the brake system, wherein the respective first and / or second isolating valve is controlled taking into account the correction current value determined for the first and / or second isolating valve for the respective pressure difference in order to increase driving comfort and improve the controllability of the vehicle.

[0016] The invention will be explained in more detail below using exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 shows the circuit diagram of a hydraulic brake system for carrying out an embodiment of the method, Fig. 2 a flow chart illustrating an embodiment of the method and Fig. 3 a) - i) Diagrams illustrating the determination of the correction current value.

[0017] The accompanying figures are intended to provide a further understanding of embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the noted advantages will become apparent upon review of the drawings. Elements of the drawings are not necessarily shown to scale relative to one another.

[0018] In the figures of the drawing, identical, functionally identical and acting elements, features and components are provided with the same reference symbols, unless otherwise stated.

[0019] Fig. 1 shows the circuit diagram of a hydraulic brake system 2 for carrying out an embodiment of the method.

[0020] The hydraulic brake system 2 has a brake pressure generator 4. The brake pressure generator 4 is driven by an electric motor 6 and is designed as a piston-cylinder unit, which can also be referred to as a so-called plunger unit. The brake pressure generator 4 has a cylinder 8 with an internal first piston 10 and a floating second piston 12, wherein the first piston 10 is directly driven by the electric motor 6. The brake pressure generator 4, with the electric motor 6, cylinder 8, and pistons 10 and 12, is designed as a linear actuator. Within the cylinder 8, a first pressure chamber 14 is formed between the first and second pistons 10, 12, and a second pressure chamber 16. Both pressure chambers 14, 16 are in fluid communication with a brake fluid reservoir 18, depending on the position of the respective piston 10, 12.

[0021] The braking system 2 of the vehicle, which is preferably designed as an electric vehicle, has a first brake circuit 20 assigned to the front axle of the vehicle and a second brake circuit 22 assigned to the rear axle of the vehicle. The braking system 2 is designed such that it can perform axle-specific blending during braking. The first pressure chamber 14 of the brake pressure generator 4 is in flow connection with the first brake circuit 20 via a first isolating valve 24, while the second pressure chamber 16 of the brake pressure generator 4 is in flow connection with the second brake circuit 22 via a second isolating valve 26. On the side facing away from the brake pressure generator 4, the first isolating valve 24 is in flow connection with wheel brakes 32, 34 for braking the wheels of the front axle via an inlet valve 28, 30 of the first brake circuit 20.In a corresponding manner, the side of the second separating valve 26 facing away from the brake pressure generator 4 is in flow connection via inlet valves 36, 38 with wheel brakes 40, 42 for braking the wheels of the rear axle.

[0022] In addition, each of the wheel brakes 32, 34 of the first brake circuit 20 and the wheel brakes 40, 42 of the second brake circuit 22 are assigned an outlet valve 44, 46 and 48, 50 in order to be able to individually control or regulate the braking force of the wheel brakes 32, 34 and 40, 42 of the same vehicle axle. On the output side, the outlet valves 44, 46, 48, 50 are in flow connection in a known manner via a check valve with a pump 52 of the first brake circuit 20 or a pump 54 of the second brake circuit 22, which here interact with the inlet valves 28, 30; 36, 38 and the outlet valves 44, 46; 48, 50 of the respective wheel brake 32, 34; 40, 42 enables targeted control and regulation of the respective wheel braking force, for example as part of an electronic stability program.

[0023] The motor drive 56 of the pumps 52 and 54 is also in Fig.1, as well as a suction valve 58 or 60 which is regularly used in such systems and which, on the one hand, is fluidly connected to the first or second pressure chamber 14 or 16 and, on the other hand, opens into the brake circuit 20 or 22 between the said check valve and the pump 52 or 54.

[0024] The first and second isolating valves 24, 26 are each designed as pressure difference valves, so that a differential pressure between the inlet side and the outlet side of the respective isolating valve 24, 26 can be set via the isolating valves 24, 26 by appropriately applying a control current.

[0025] Fig. Figure 2 shows a flow chart illustrating an embodiment of the method, while the Fig. 3 a) to i) show diagrams illustrating the determination of the correction current value within the framework of the method.

[0026] In a first method step 62 for determining an advantageous control current for the first isolating valve 24 of the hydraulic brake system 2, the first isolating valve 24 and the second isolating valve 26 are opened. Subsequently, the pressure in the first brake circuit 20 and in the second brake circuit 22 is increased by the brake pressure generator 4 up to a predetermined first pressure in method step 64. The Fig. The pressure increase shown in Figure 3a takes place between times t0 and t1. Fig. 3c shows that the volume V displaced by the linear actuator in the form of the brake pressure generator 4 increases accordingly, while the first and second separating valves 24, 26 remain de-energized and thus open ( Fig. 3b).

[0027] If the predetermined first pressure, here 10 bar as an example, is reached, then - as in Fig.3b - the first isolating valve 24 is closed by a maximum control current at time t2, while the second isolating valve 26 remains in its open position, wherein the closing of the first isolating valve 24 at time t2 is caused by the maximum control current in Fig. 2 is indicated by method step 66.

[0028] Subsequently, the pressure generated by the brake pressure generator 4 is reduced by reducing the pressure in the second brake circuit 22 to a second pressure, here 5 bar, for example, which is reached at time t3, so that a pressure difference is achieved between the first pressure in the first brake circuit 20 and the second pressure in the second brake circuit 22, wherein the pressure difference here is 5 bar due to the first pressure enclosed in the first brake circuit 20 and the second pressure reduced in the second brake circuit 22 (method step 68). As can be seen from Fig.3c, the second pressure in the second brake circuit 22 is reached at time t3, which is accompanied by a reduction in the volume displaced by the brake pressure generator 4. In method step 70, the control current applied to the first isolating valve 24 is now continuously or linearly reduced. In this case, it is continuously monitored whether the first isolating valve 24 opens during the reduction of the control current, as indicated by method step 72. If the first isolating valve 24 remains closed, the control current is further reduced. If, on the other hand, an opening of the first isolating valve 24 is detected orregistered, the current control current value - here at time t4 - is determined in method step 74, wherein in method step 76 a correction current value for the selected pressure difference - here 5 bar - is determined as the difference between the recorded control current value and a predetermined control current value and is then stored, wherein the correction current value k in . Fig. 3b is indicated. As is particularly evident from Fig. 3c, the above-mentioned opening of the first isolating valve 24 is determined or registered on the basis of a reduction in the actuation volume of the brake pressure generator 4, wherein the abrupt or sudden drop in the actuation volume can be seen at time t4 in the embodiment shown.

[0029] The with reference to the Fig.The method illustrated in Figures 3a to 3c can advantageously be carried out at least twice for the same pressure difference, here the pressure difference of 5 bar, in order to determine possibly differing correction current values ​​k, wherein the ultimately stored correction current value k is then preferably formed from an average value of the determined correction current values ​​k.

[0030] If the correction current value for the first isolation valve 24 at a pressure difference of 5 bar has been determined and stored on this basis, the procedure according to Fig. 2 again for the first separating valve 24, but based on a different pressure difference, as shown by way of example in the Fig.3d to 3f, in which the correction current value for a pressure difference of 20 bar is determined by the predetermined first pressure being 40 bar, while the second pressure is 20 bar. In this way, a plurality of correction current values ​​for the first isolation valve 24 can be determined for a wide variety of pressure differences, as can be further seen from the Fig. 3g to 3i, in which the first pressure is, for example, y + x bar, while the set second pressure should be y bar. A corresponding tabular result of the correction current values ​​thus determined for the first isolation valve 24 at different pressure differences could look as shown below. pressure difference 5 bar 20 bar x bar Correction current value (mA) k1 k2 kx

[0031] Although not shown in detail again, the method described above can also be repeated in order to determine and store corresponding correction current values ​​for the second isolating valve 26 as well, so that corresponding correction current values ​​are available for both the first and the second isolating valve 24, 26.

[0032] If axle-specific diaphragm control is carried out by the hydraulic brake system 2, the respective first and / or second isolating valve 24 or 26 is controlled taking into account the correction current values ​​k for the respective pressure difference determined in this way, thus the control current is corrected or adjusted with the aid of the correction current value for the respective desired pressure difference between the brake circuits 20, 22 of the two vehicle axles in order to reduce the pressure setting error that sometimes occurs during axle-specific diaphragm control and thus to increase driving comfort and controllability.

[0033] It has also proven advantageous to perform the described method for determining the correction current values ​​for the different pressure differences multiple times during the lifetime of a vehicle. In other words, the method should be repeated at least once, and it is advantageous to perform the method while the vehicle is stationary and / or automatically. For example, performing the method as a so-called end-of-line routine is suitable. Performing the method during the charging process of the electric vehicle, after the vehicle has been parked, and / or as a service routine is also advantageous.

[0034] In the present invention, several features have been designated "first" and "second." These designations serve only to clearly distinguish the individual features. In particular, they are not intended to imply any spatial or functional arrangement or prioritization.

[0035] When a list of alternatives in this application is marked with the designation “or / and”, this should be understood to mean both the listed alternatives taken individually and, where appropriate, a combination of several or all of the listed alternatives. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 207 056 A1

[0003]

Claims

[1] Method for determining a control current for a first isolating valve (24) of a hydraulic brake system (2) of a vehicle, in which the first isolating valve (24) is arranged between a brake pressure generator (4) and a first brake circuit (20) assigned to the wheel brakes (32, 34) of a first vehicle axle, and a second isolating valve (26) is arranged between the brake pressure generator (4) and a second brake circuit (22) assigned to the wheel brakes (40, 42) of a second vehicle axle, wherein the first and second isolating valves (24, 26) are designed as current-controllable differential pressure valves, with the method steps Opening the first and second isolating valves (24, 26), Increasing the pressure in the first and second brake circuits (20, 22) by the brake pressure generator (4) up to a predetermined first pressure, Closing the first isolating valve (24) by a control current, Reducing the pressure generated by the brake pressure generator (4) while reducing the pressure in the second brake circuit (22) to a second pressure and achieving a pressure difference between the first pressure in the first brake circuit (20) and the second pressure in the second brake circuit (22), Reducing the control current at the first isolating valve (24), Detecting a control current value when an opening of the first isolation valve (24) is detected, and Determination and storage of a correction current value (k) for the pressure difference as the difference between the recorded control current value and a specified control current value. [2] Method according to claim 1, wherein the correction current value (k) is determined at least twice for the same pressure difference, wherein the stored correction current value (k) is formed from an average value of the determined correction current values ​​(k). [3] Method according to one of claims 1 or 2, in which an opening of the first isolating valve (24) is determined on the basis of a reduction in the control volume (V) of the brake pressure generator (4). [4] Method according to claim 3, wherein a linear actuator and / or a piston-cylinder unit is used as the brake pressure generator (4). [5] Method according to one of the preceding claims, in which the method is repeated at least once, preferably with the vehicle stationary and / or automated. [6] Method according to one of the preceding claims, in which the correction current value (k) is determined and stored for at least two different pressure differences. [7] Method according to one of the preceding claims, in which at least one correction current value (k) for the first and second isolating valve (24, 26) is determined and stored. [8] Method according to one of the preceding claims, in which the brake system (2) carries out an axle-individual blending, wherein the control of the respective first and / or second isolating valve (24; 26) takes place taking into account the correction current value (k) for the respective pressure difference. [9] Hydraulic brake system (2) for a vehicle, comprising a first isolating valve (24) between a brake pressure generator (4) and a first brake circuit (20) assigned to the wheel brakes (32, 34) of a first vehicle axle, and a second isolating valve (26) between the brake pressure generator (4) and a second brake circuit (22) assigned to the wheel brakes (40, 42) of a second vehicle axle, wherein the first and second isolating valves (24, 26) are designed as current-controllable differential pressure valves, wherein the brake system (2) is designed to carry out the method according to one of claims 1 to 8. [10] Hydraulic brake system (2) according to claim 9, in which the brake pressure generator (4) is a linear actuator and / or a piston-cylinder unit and / or in the first and second brake circuits (20, 22) an inlet valve (28; 36) assigned to a wheel brake (32; 40) is provided.

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