Control device and method for operating a regenerative brake system of a vehicle

Abstract

The invention relates to a control device (16) for a regenerative brake system of a vehicle and to a method for operating a regenerative brake system of a vehicle if a requested vehicle deceleration can be caused only in part by means of at least one electric motor, if so, a differential pressure adjustment is carried out in wheel cylinders (10, 12) of the brake system by means of the following sub-steps: determining a target differential pressure for a first wheel cylinder (10) of the brake system and a second wheel cylinder (12) of the brake system; actuating at least one wheel inlet valve (22) of the brake system, which is arranged upstream of the second wheel brake cylinder (12), by means of a current signal (52) output to the at least one wheel inlet valve (22) taking into account the determined target pressure difference; and determining a target current intensity of the current signal (52) taking into account the determined target voltage difference by selecting the target current intensity of the current signal (52) or an initial value of the target current intensity from a set of values having at least three current intensity values taking into account the determined target voltage difference.

Description

Technical Field

[0001] The invention relates to a control device for a regenerative braking system of a vehicle and to a regenerative braking system for a vehicle. The invention also relates to a method for operating a regenerative braking system of a vehicle. Background Art

[0002] Figure 1a and Figure 1b A coordinate system is shown for explaining a conventional procedure for operating a regenerative braking system of a vehicle, which is known to the applicant as internal prior art. Figure 1a and Figure 1b The horizontal axis of the coordinate system is the time axis t.

[0003] With the help of Figure 1a In the first braking process described by the coordinate system of , the driver of the vehicle requires a vehicle deceleration a not equal to zero by means of his actuation of the brake actuating element of the brake system from time t0. Therefore, in the conventional approach, the energy of the brake system in its regenerative mode Φ is r The operating state Φ of the electric motor operating in the process is switched from its inactive mode Φ0 to its regenerative mode Φ r Between time t0 and t1, by virtue of being able to be in its regenerative mode Φ r The electric motor operated in the vehicle causes a vehicle deceleration a requested by the driver which is not equal to zero. A first target brake pressure p to be set in a first wheel brake cylinder of the brake system assigned to a first axle of the vehicle 1target and a second target brake pressure p to be set in a second wheel brake cylinder of the brake system assigned to a second axle of the vehicle. 2target To this end, between times t0 and t1, the second wheel outlet valve is switched to its open state between times t0 and t1. However, between times t0 and t1, the second wheel outlet valve is switched to its open state between times t0 and t1. Figure 1a This is not graphically depicted in the coordinate system of . However, according to Figure 1a The coordinate system of φ makes it possible to recognize that, while opening the first wheel inlet valve arranged upstream of the first wheel brake cylinder, the second wheel inlet valve arranged upstream of the second wheel brake cylinder is also switched to its open state between times t0 and t1. For this purpose, the current intensity I of the current signal output to the second wheel inlet valve opened without current is plotted on φ Figure 1a Between times t0 and t1 , first actual brake pressure p1 present in the first wheel brake cylinder and second actual brake pressure p2 present in the second wheel brake cylinder are therefore (almost) equal to zero.

[0004] From time t1 onwards, the vehicle deceleration a requested by the driver is no longer solely controlled by the vehicle in its regeneration mode Φ r However, the required vehicle deceleration a can be achieved between times t1 and t2 by operating the electric motor in its regenerative mode Φ r The electric motor is operated in the vehicle and is caused by means of a first wheel brake cylinder assigned to a first axle of the vehicle. For this purpose, a first target brake pressure p which is not equal to zero and is to be set in the first wheel brake cylinder is determined between times t1 and t2. 1target , and the second target brake pressure p to be set in the second wheel brake cylinder 2target Between times t1 and t2, it remains equal to zero. Furthermore, the first wheel outlet valve arranged downstream of the first wheel brake cylinder remains closed from time t1, while the second wheel outlet valve arranged downstream of the second wheel brake cylinder is controlled to its open state between times t1 and t2. By means of a pressure difference control performed by the second wheel inlet valve of the second wheel brake cylinder during time interval T0, an attempt is made to adjust the pressure according to the determined first target brake pressure p 1target The first actual brake pressure p1 present in the first wheel brake cylinder is adjusted. According to conventional procedures, a pressure difference control is carried out during time interval T0 by means of a switch between an overcurrent of the second wheel inlet valve and an undercurrent of the second wheel inlet valve. In addition, brake fluid can also be pumped into the brake system from at least one low-pressure reservoir arranged downstream of the first wheel outlet valve and the second wheel outlet valve by means of a pump speed n not equal to zero of at least one pump of the brake system. However, as indicated by arrow 2, a "wave-like" pressure increase often occurs in the first wheel brake cylinder between times t1 and t2.

[0005] From time t2, in its regeneration mode Φ r The electric motor operating in the vehicle and the first wheel brake cylinder assigned to the first axle of the vehicle are no longer sufficient to bring about the required vehicle deceleration a which is not equal to zero. Therefore, starting from time t2, a second target brake pressure p which is not equal to zero and is to be set in the second wheel brake cylinder is also determined. 2target The second wheel outlet valve, which is arranged downstream of the second wheel brake cylinder (like the first wheel outlet valve, which is arranged downstream of the first wheel brake cylinder), remains closed from time t2. By means of the pressure difference control implemented by the second wheel inlet valve, an attempt is also made to adjust the brake pressure according to the determined first target brake pressure p 1target The first actual brake pressure p1 present in the first wheel brake cylinder is adjusted, and the second target brake pressure p 2targetThe second actual brake pressure p2 present in the second wheel brake cylinder is adjusted. According to conventional procedures, this is also achieved by switching between an overcurrent of the second wheel inlet valve and an undercurrent of the second wheel inlet valve. Arrow 4 indicates that the pressure buildup in the second wheel brake cylinder caused in this way can trigger a strong pressure drop in the first wheel brake cylinder in an undesirable manner.

[0006] With the help of Figure 1b In the second braking process described in the coordinate system of FIG. 1 , the driver also requires a vehicle deceleration a not equal to zero from time t0 by means of his operation of the brake operating element, but the vehicle deceleration can also be reduced between times t0 and t1 by means of the regeneration mode Φ r However, in the second braking process, the driver requests a significantly faster braking of his vehicle than in the first braking process explained above. In the second braking process, the vehicle deceleration a requested by the driver, which is not equal to zero, can also only be achieved between times t0 and t1 by means of the regeneration mode Φ r and by means of the first wheel brake cylinder of the first axle, and from time t2 only by means of the electric motor in its regenerative mode Φ r The first target brake pressure p to be set in the first wheel brake cylinder is determined accordingly. 1target and the second target brake pressure p to be set in the second wheel brake cylinder 2target In order to adjust the first actual brake pressure p1 present in the first wheel brake cylinder and the second actual brake pressure p2 present in the second wheel brake cylinder, a pressure difference regulation is again carried out during time interval T0 by means of a second wheel outlet valve arranged upstream of the second wheel brake cylinder by switching between an overcurrent of the second wheel inlet valve and an undercurrent of the second wheel inlet valve in accordance with the conventional procedure. Arrow 6 indicates that, due to the required faster braking of the vehicle, the first target brake pressure p1 to be set in the first wheel brake cylinder is increased. 1target A significant difference may occur from first brake pressure p1 actually built up in the first wheel brake cylinder, which may appear unpleasant to the driver as a “soft” brake actuation element. Summary of the invention

[0007] The invention provides a control device for a regenerative braking system of a vehicle having the features of claim 1 , a regenerative braking system for a vehicle having the features of claim 6 , and a method for operating a regenerative braking system of a vehicle having the features of claim 7 .

[0008] Advantages of the present invention.

[0009] The invention makes it possible to operate a regenerative braking system of a vehicle in such a way that the driver of the vehicle does not (substantially) feel the mixing process that is carried out during his actuation of a brake actuating element of the braking system. Switching between braking the vehicle solely by means of at least one electric motor operating in its regenerative mode and braking the vehicle by means of at least one electric motor and a first wheel brake cylinder of a brake system assigned to a first axle of the vehicle, for example, does not / hardly results in an undesired "wave-like" pressure increase in the first wheel brake cylinder. Switching between braking the vehicle by means of at least one electric motor, by means of the first wheel brake cylinder, and by means of a second wheel brake cylinder of a brake system assigned to a second axle of the vehicle (usually) also does not result in a pressure drop in the first wheel brake cylinder or in a significant deviation of the first actual brake pressure present in the first wheel brake cylinder from the first target brake pressure desired for the first wheel brake cylinder. Thus, the possibility for operating a regenerative brake system of a vehicle realized by means of the present invention achieves improved driving comfort and braking comfort for the driver of the vehicle. The present invention thus helps to motivate the driver to purchase a vehicle equipped with a regenerative brake system, the driving of which is associated with lower energy consumption and possibly also with reduced emissions of pollutants.

[0010] In an advantageous embodiment of the control device, the electronics present in its differential pressure control mode are designed and / or programmed to determine a target current intensity or an initial value of the target current intensity of the current signal as a function of the determined target differential pressure according to a predetermined continuous function having a value set with at least three current intensity values. This enables a "smooth" actuation of at least one (second) wheel inlet valve arranged upstream of the second wheel brake cylinder by means of the embodiment of the control device described here.

[0011] The electronic device is preferably also additionally designed and / or programmed after the start of its differential pressure control mode to determine an offset value for the target current intensity of the current signal taking into account a respective deviation of a first actual brake pressure measured or estimated in at least one of the first wheel brake cylinders during a predetermined comparison time interval from a first target brake pressure to be set in each case in the first wheel brake cylinder at the same time, and to determine the target current intensity of the current signal as the sum of an initial value of the target current intensity and the offset value. By means of the offset value determined in this way or the target current intensity resulting therefrom, component tolerances and / or aging effects at the respective regenerative braking system can advantageously be compensated.

[0012] As an advantageous development, the electronic device can be additionally designed and / or programmed after its differential pressure control mode has been started to determine a time period during which at least one measured or estimated first actual brake pressure in the first wheel brake cylinder deviates from a first target brake pressure to be set in the first wheel brake cylinder at the same time by at least one predetermined minimum pressure deviation, and if the determined time period exceeds a predetermined time threshold, to determine a target current intensity of the current signal within a predetermined or determined closing time in such a way that at least one wheel inlet valve switches to its closed state within the predetermined or determined closing time by means of the current signal output thereto. In this way, in particular by means of the embodiment of the control device described here, a "soft" brake actuating element / brake pedal, as often occurs in the prior art, can be avoided.

[0013] As a further advantageous development, the electronic device can also be designed and / or programmed at the start of its differential pressure control mode to determine the target differential pressure as the difference between a predetermined or determined first target brake pressure to be set in the first wheel brake cylinder and a predetermined or determined second target brake pressure to be set in the second wheel brake cylinder, but if the measured or estimated first actual brake pressure in the first wheel brake cylinder is less than the first target brake pressure to be set in the first wheel brake cylinder by at least one predetermined limit deviation, the electronic device is designed and / or programmed within a predetermined or determined transition time to determine the target differential pressure as the difference between the measured or estimated first actual brake pressure in the first wheel brake cylinder and the second target brake pressure to be set in the second wheel brake cylinder. The development of the control device described here can therefore advantageously react to significant deviations of the first actual brake pressure from the first target brake pressure, thereby preventing an identical / corresponding deviation of the second actual brake pressure in the second wheel brake cylinder from the second target brake pressure to be set in the second wheel brake cylinder.

[0014] The advantages described above are also ensured in a regenerative braking system for a vehicle having such a control device, a first wheel brake cylinder associated with a first axle of the vehicle, a second wheel brake cylinder associated with a second axle of the vehicle, and at least one wheel inlet valve arranged upstream of the second wheel brake cylinder.

[0015] Furthermore, the implementation of a corresponding method for operating a regenerative braking system of a vehicle also achieves the advantages explained above. It should be explicitly pointed out that the method for operating a regenerative braking system of a vehicle can also be improved according to the specific embodiment of the control device explained above. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Next, further features and advantages of the present invention are explained based on the accompanying drawings. It is shown:

[0017] Figure 1a and Figure 1b A coordinate system is shown for illustrating a conventional approach for operating a regenerative braking system of a vehicle;

[0018] Figure 2 A schematic diagram of a regenerative braking system of a vehicle is shown in order to explain the functional mode of an embodiment of a control device that interacts therewith; and

[0019] Figure 3a and 3b The figure shows a coordinate system for explaining one specific embodiment of a method for operating a regenerative braking system of a vehicle. DETAILED DESCRIPTION

[0020] Figure 2 A schematic diagram of a regenerative braking system of a vehicle is shown in order to explain the mode of functioning of an embodiment of a control device that interacts therewith.

[0021] Figure 2 The regenerative braking system schematically depicted in has a first wheel brake cylinder 10 and a second wheel brake cylinder 12, wherein first wheel brake cylinder 10 is assigned to a first axle of a vehicle equipped with the brake system and second wheel brake cylinder 12 is assigned to a second axle of the vehicle. This can be understood to mean that first wheel brake cylinder 10 is mounted on the first axle of the vehicle and second wheel brake cylinder 12 is mounted on the second axle. Figure 2 In the brake system of , an X-brake circuit distribution is realized only by way of example, wherein each first wheel brake cylinder 10 and each second wheel brake cylinder 12 is connected to one of two brake circuits 14a and 14b. The first axle can be, for example, the front axle and the second axle the rear axle. Alternatively, however, the first axle can also be the rear axle and the second axle can be the front axle.

[0022] The brake system cooperating with control device 16 also includes at least one first wheel inlet valve 18 arranged upstream of first wheel brake cylinder 10, at least one first wheel outlet valve 20 arranged downstream of first wheel brake cylinder 10, at least one second wheel inlet valve 22 arranged upstream of second wheel brake cylinder 12, and at least one second wheel outlet valve 24 arranged downstream of second wheel brake cylinder 12. For example, first wheel inlet valve 18 and first wheel outlet valve 20 are connected to first wheel brake cylinder 10, and second wheel inlet valve and second wheel outlet valve are connected to second wheel brake cylinder 12. Brake circuits 14a and 14b are preferably connected to a master brake cylinder 26, upstream of which a brake actuating element 28, such as, for example, a brake pedal 28, can be arranged. A brake booster 30 and / or a brake fluid reservoir 32 can also be optionally connected hydraulically to master brake cylinder 26.

[0023] Alternatively, a storage chamber 34, such as in particular a low-pressure storage chamber 34, can be arranged downstream of at least one first wheel outlet valve 20 and / or second wheel outlet valve 24 of each brake circuit 14a and 14b. It can also be advantageous if brake circuits 14a and 14b have at least one pump 36, which can preferably be operated by means of a common pump motor 38 of the brake system. Figure 2 The brake circuits 14 a and 14 b of the brake system of EMBODIMENT 1 each further have a switching valve 40 and a high-pressure switching valve 42 as further optional components.

[0024] However, it should be pointed out that the braking system should only be explained as an example. Figure 2 In other words, any regenerative braking system can be used with the control device 16 described below, the hydraulic system of which has at least components 10, 12 and 18 to 24. Furthermore, the usability of the control device 16 or a regenerative braking system cooperating therewith is not limited to a specific vehicle type / motor vehicle type of vehicle / motor vehicle equipped with the braking system.

[0025] The control device 16 has an electronic device 16a which is designed and / or programmed to query or determine whether the required vehicle deceleration can be brought about only partially by means of at least one (not shown) electric motor of the brake system or of the vehicle which is operated in its regeneration mode. The at least one electric motor can be, for example, an electric drive motor of the vehicle. The required vehicle deceleration can be understood, for example, as the vehicle deceleration required by the driver of the vehicle by means of his actuation of the brake actuating element 28. In particular, at least one brake actuating element sensor 44, such as, for example, a lever travel sensor and / or a differential displacement sensor, can be installed on the brake system, which outputs a sensor signal 46 corresponding to the actuation of the brake actuating element 28. Alternatively or additionally, the required vehicle deceleration can also be required by a speed control automatic device (not shown) of the vehicle by means of a corresponding brake request signal.

[0026] If the sensor signal 46 of the brake actuating element sensor 44 and / or the brake request signal of the automatic speed control are supplied to the electronic device 16a, the electronic device 16a can be designed / programmed to actuate / activate the regeneration mode of the at least one electric motor. In this case, the electronic device 16a detects when (automatically) actuating the at least one electric motor whether the required vehicle deceleration can be brought about only by means of the at least one electric motor operating in its regeneration mode. However, the actuation of the at least one electric motor can alternatively also be carried out by the motor control device, which then actuates / activates the regeneration mode of the at least one electric motor taking into account the at least one sensor signal 46 of the at least one brake actuating element sensor 44 and / or the brake request signal of the automatic speed control. In this case, the electronic device 16a detects by querying / reading the information signal output by the motor control device to the electronic device 16a that the required vehicle deceleration can be brought about not only by means of the at least one electric motor operating in its regeneration mode.

[0027] If necessary, that is to say if the required vehicle deceleration can only be partially caused by means of at least one electric motor operating in its regeneration mode, the electronic device 16a is present in its differential pressure control mode. The electronic device 16a present in its differential pressure mode is designed and / or programmed for determining a target differential pressure of the first wheel brake cylinder 10 and the second wheel brake cylinder 12. The target differential pressure that can be determined by means of the electronic device 16a present in its differential pressure control mode is defined as the difference between a first target brake pressure or actual brake pressure and a second target brake pressure. The first target brake pressure can be understood as a pressure to be set in the first wheel brake cylinder 10, which can be predetermined to the electronic device 16a or determined by the electronic device 16a. As an alternative to the first target brake pressure, a first actual brake pressure can be considered for determining the target differential pressure, which first actual brake pressure is a measured or estimated first actual brake pressure in the first wheel brake cylinder 10. The pressure sensor 48 connected to one of the brake circuits 14a and 14b can, for example, output a pressure sensor signal 50 corresponding to the first actual brake pressure to the electronic device 16a. The second target brake pressure is the pressure to be set in second wheel brake cylinder 12, which can likewise be predetermined for electronic device 16a or determined by electronic device 16a. The information signal output by the engine control unit to electronic device 16a can, for example, include the first target brake pressure and / or the second target brake pressure. Advantageous possibilities for determining the first target brake pressure and / or the second target brake pressure by electronic device 16a are also discussed below.

[0028] The electronic device 16a present in its differential pressure control mode is furthermore designed and / or programmed to output a current signal 52 to at least one second wheel inlet valve 22 taking into account a determined target pressure difference, so that at least one second wheel inlet valve 22 is actuated / actuable with the aid of the output current signal 52. The electronic device 16a present in its differential pressure control mode is furthermore designed and / or programmed to determine a target current intensity of the current signal 52 taking into account a determined target pressure difference. For this purpose, a target current intensity or an initial value of the target current intensity of the current signal 52 is / can be selected from a value set of at least three current intensity values ​​taking into account a determined target pressure difference by means of the electronic device 16a present in its differential pressure control mode. The electronic device 16a present in its differential pressure control mode then outputs a current signal 52 having an (actual) current intensity corresponding to the determined target current intensity to at least one second wheel inlet valve 22.

[0029] Based on the advantageous design / programming of the electronic device 16a described in the previous paragraphs, the control device 16 or the regenerative braking system cooperating therewith brings about the advantages explained with reference to the following figures. The electronic device 16a of the control device 16 can be designed / programmed in particular for carrying out the process / method steps explained below. For further advantageous properties of the control device 16 or the regenerative braking system cooperating therewith, reference is therefore made to the following explanation.

[0030] Figure 3a and Figure 3b A coordinate system is shown for explaining one specific embodiment of a method for operating a regenerative braking system of a vehicle. Figure 3a and Figure 3b The horizontal axis of the coordinate system is the time axis t.

[0031] The method described below is implemented only by way of example with the aid of the regenerative braking system explained above. However, it should be pointed out that the feasibility of the method is not limited to this type of brake system. In other words, the method can be implemented with (almost) any type of brake system, which has at least a first wheel brake cylinder 10 assigned to a first axle of the vehicle, a second wheel brake cylinder 12 assigned to a second axle of the vehicle, at least one first wheel inlet valve 18 arranged upstream of the first wheel brake cylinder 10, at least one first wheel outlet valve 20 arranged downstream of the first wheel brake cylinder 10, at least one second wheel inlet valve 22 arranged upstream of the second wheel brake cylinder 12, and at least one second wheel outlet valve 24 arranged downstream of the second wheel brake cylinder 12. The feasibility of the method is also not limited to a specific vehicle type / motor vehicle type of vehicle / motor vehicle equipped with a corresponding brake system.

[0032] With the help of Figure 3a In the schematically described first braking process, starting from time t0, a vehicle deceleration a not equal to zero is requested of a vehicle equipped with the above-described regenerative braking system. A vehicle deceleration a not equal to zero can be requested, for example, by the driver of the vehicle by means of his actuation of the brake actuating element 28 of the braking system or by an automatic speed control of the vehicle. Once a vehicle deceleration a not equal to zero is requested, it is determined in the method described here whether the requested vehicle deceleration a can be achieved only partially by means of at least one of the braking system / vehicle in its regenerative mode Φ. r Additionally, starting from time t0, the operating state Φ of at least one electric motor is switched from its inactive mode Φ0 to its regenerative mode Φ r .

[0033] In the first braking process explained here, the required vehicle deceleration a is so small between times t0 and t1 that it can be decelerated only by means of at least one regenerative braking operation in its regenerative mode Φ. r In order to achieve the highest possible regeneration efficiency during the first braking process, a first target brake pressure p is set in first wheel brake cylinder 10 between times t0 and t1. 1target and a second target brake pressure p to be set in second wheel brake cylinder 12 2target (almost) equal to zero or less than or equal to the response pressure of the respective wheel brake cylinder 10 or 12. Furthermore, between times t0 and t1, at least one first wheel inlet valve 18 arranged upstream of first wheel brake cylinder 10, at least one first wheel outlet valve 20 arranged downstream of first wheel brake cylinder 10, at least one second wheel inlet valve 22 arranged upstream of second wheel brake cylinder 12, and at least one second wheel outlet valve 24 arranged downstream of second wheel brake cylinder 12 are actuated in such a way that a brake pressure buildup in first wheel brake cylinder 10 and in second wheel brake cylinder 12 is (substantially) prevented, and that a first brake pressure p1 (possibly) present in first wheel brake cylinder 10 and a second brake pressure p2 (possibly present in second wheel brake cylinder 12 are therefore less than or equal to the response pressure of the respective wheel brake cylinder 10 or 12. To this end, at least one first wheel outlet valve 20 arranged downstream of first wheel brake cylinder 10 and at least one second wheel outlet valve 24 arranged downstream of second wheel brake cylinder 12 are switched to their open state between times t0 and t1, but at Figure 3a This is not illustrated in the coordinate system of FIG. At least one first wheel inlet valve 18 arranged upstream of first wheel brake cylinder 10 can also be switched into its open state between times t0 and t1. Figure 3a As can be identified from the coordinate system of , at least one second wheel inlet valve 22 arranged upstream of the second wheel brake cylinder 12 is controlled into its open state between times t0 and t1 by means of a current signal 52, wherein, since at least one second wheel inlet valve 22 is (usually) designed as a valve that opens without current, the current intensity I of the current signal 52 is equal to zero between times t0 and t1.

[0034] With the help of Figure 3a In the first braking process described, the required vehicle deceleration a is so great from time t1 that the vehicle deceleration a can only be partially achieved by at least one braking device in its regeneration mode Φ r Therefore, in the subsequent time interval T Δp During this time, a differential pressure control (Δp control) described below is carried out in first wheel brake cylinder 10 and second wheel brake cylinder 12 of the brake system.

[0035] At time interval T Δp In a first partial step of the differential pressure regulation performed during the above process, a target differential pressure Δp between first wheel brake cylinder 10 and second wheel brake cylinder 12 is determined. target In order to determine the target pressure difference Δp target , the first target brake pressure p to be set in first wheel brake cylinder 10 can be determined continuously in this way 1target and a second target brake pressure p to be set in second wheel brake cylinder 12 2target , so that the target brake pressure p in the wheel brake cylinders 10 and 12 of the brake system is reliably maintained. 1target and p 2target In the case of r The electric motor, which is operated in the vehicle, brings about the required vehicle deceleration a by means of a first brake pressure p1 present in first wheel brake cylinder 10 and by means of a second brake pressure p2 present in second wheel brake cylinder 12 .

[0036] Preferably, if during the pressure difference control a first target brake pressure p 1 is achievable in first wheel brake cylinder 10 (via a corresponding first brake pressure p 1 present in first wheel brake cylinder 10 ), then the first target brake pressure p 2 is achievable in first wheel brake cylinder 10 . 1target , at the first target brake pressure by means of at least one regenerative mode Φ r If the electric motor operating in the vehicle applies a motor braking torque to the vehicle and causes / can cause a vehicle deceleration a by means of first wheel brake cylinder 10, a second target brake pressure p equal to zero to be set in second wheel brake cylinder 12 is determined. 2target If the required vehicle deceleration a can be achieved only with the aid of at least one r The electric motor running in the regenerative mode and by means of first wheel brake cylinder 10 (with a high probability) can cancel the braking of the second axle of the vehicle by means of second wheel brake cylinder 12. Otherwise, that is, if at least one of the axles in its regenerative mode Φ r When the motor braking torque caused by the electric motor operating in the vehicle and the first wheel brake cylinder 10 are no longer sufficient to cause the required vehicle deceleration a, it is possible to determine not only the first target brake pressure p 1target Furthermore, a second target brake pressure p which is not equal to zero is also determined. 2target , where the second target brake pressure p 2target It is usually predetermined to be less than or equal to the first target brake pressure p 1target In this case, in particular, the required vehicle deceleration a, the motor braking torque of the at least one electric motor and the first target brake pressure p 1target The second target brake pressure p is determined in the case of2target .

[0037] Then, the first target brake pressure p is determined 1target Or the first actual brake pressure p1 and the second target brake pressure p 2target The difference between them is taken as the target pressure difference Δp target . Target pressure difference Δp target Therefore, according to equation (Gl.1) or equation (Gl.2), where:

[0038] (Gl.1) Δp target =p 1target –p 2target

[0039] (Gl.1) Δp target =p1–p 2target

[0040] First actual brake pressure p 1 may be understood to be a measured or estimated pressure value which is present (with a high probability) in first wheel brake cylinder 10 .

[0041] In a further substep, a target current intensity of current signal 52 output to at least one second wheel inlet valve 22 is determined. target To this end, taking into account the determined target pressure difference Δp target In the case of , a target current intensity or an initial value of the target current intensity of the current signal 52 is selected from a value set having at least three current intensity values. It is also possible to use the determined target pressure difference Δp target In the case of , this is interpreted as a “smooth Δp regulation” achieved by means of a continuous control of the target current intensity of the current signal 52 .

[0042] In a further substep, at least one second wheel inlet valve 22 is actuated by means of a current signal 52 output to the at least one second wheel inlet valve 22, wherein the (actual) current intensity I of the output current signal 52 (substantially) corresponds to the determined target current intensity. The actuation of the at least one second wheel inlet valve 22 thus takes place at a time interval T Δp During this period, taking into account the determined target pressure difference Δp target In the case of the pressure difference regulation described here. Figure 3a As indicated by the arrow 60 in the coordinate system of , a “smooth” control / switching of the at least one second wheel inlet valve 22 is achieved in this way. Figure 3aIn the case of a “continuous” pressure buildup in first wheel brake cylinder 10 , which is indicated by arrow 62 in the coordinate system of , no “wave-like” pressure increase occurs, as in the above-described prior art. Figure 3a Arrow 64 in the coordinate system of 1 also indicates that only a first actual brake pressure p1 in first wheel brake cylinder 10 and a first target brake pressure p2 to be set in first wheel brake cylinder 10 occur. 1target relatively small deviation.

[0043] Preferably, the target pressure difference Δp is determined according to target , a target current intensity or an initial value of the target current intensity of the current signal 52 is determined according to a predetermined continuous function having a value set with at least three current intensity values. This can be easily implemented. The continuous function preferably has a value set with at least four current intensity values. The value set of the continuous function can in particular include more than four current intensity values. The value set of the continuous function is dependent on the determined target pressure difference Δp target The obtained value can also be compared with the target pressure difference Δp target Alternatively, it is possible to determine the target pressure difference Δp target The target current intensity or the initial value of the target current intensity of current signal 52 is determined according to a predetermined step function having at least three steps, preferably at least four steps, in particular having more than four steps.

[0044] The initial value of the target current intensity can be understood to be a value, taking into account which the target current intensity is subsequently determined. Δp In the pressure difference control performed during this period, for example, at least one further variable can also be determined, which is additionally taken into account when determining the target current intensity while taking into account the initial value. In particular, a comparison between at least one measured or estimated first actual brake pressure p1 in first wheel brake cylinder 10 and a first target brake pressure p2 to be set in first wheel brake cylinder 10 at the same time can be determined during a predetermined comparison time interval. 1target The deviation of the target current intensity of the current signal 52 can then be determined taking into account the determined deviation. The target current intensity of the current signal 52 can be determined in this case as the sum of the initial value of the target current intensity and the offset value. By means of the determination of the target current intensity described here, component tolerances and / or aging effects at the brake system can be advantageously compensated.

[0045] As an optional improvement, it is possible to ΔpDuring the pressure difference control implemented in the embodiment, the time period during which at least one measured or estimated first actual brake pressure p1 in first wheel brake cylinder 10 is inversely proportional to the first target brake pressure p2 to be set in first wheel brake cylinder 10 is determined (continuously). 1target If the determined time period exceeds a predetermined time threshold, the target current intensity of current signal 52 can be determined preferably within a predetermined or determined closing time in such a way that at least one second wheel inlet valve 22 is switched to its closed state by means of current signal 52 output thereto within the predetermined or determined closing time. In this way, a first actual brake pressure p1 in first wheel brake cylinder 10 that is inconsistent with a first target brake pressure p2 to be set in first wheel brake cylinder 10 can be prevented. 1target A large deviation during a time period that exceeds the time threshold.

[0046] In a preferred manner, at the time interval T Δp At the beginning of the pressure difference regulation implemented during the period, the target pressure difference Δp is determined according to equation (Gl.1) target , that is to say a first target brake pressure p which is predetermined or determined and is to be set in first wheel brake cylinder 10 1target The second target brake pressure p 2target The difference between .

[0047] With the help of Figure 3a In the first braking process schematically described, between times t1 and t2, at least one braking device in its regenerative mode Φ r The electric motor running in the vehicle and with the aid of first wheel brake cylinder 10 assigned to the first axle of the vehicle can bring about the required vehicle deceleration a. Therefore, first wheel outlet valve 20 arranged downstream of first wheel brake cylinder 10 remains closed from time t1, while second wheel outlet valve 24 arranged downstream of second wheel brake cylinder 12 is controlled to its open state between time t1 and t2. Then, the pressure difference control is carried out between time t1 and t2 as explained above.

[0048] From time t2 onwards, it is possible to use only at least one r, by means of first wheel brake cylinder 10 and by means of second wheel brake cylinder 12 assigned to a second axle of the vehicle. To this end, second wheel outlet valve 24, which is arranged downstream of second wheel brake cylinder 12 (similar to first wheel outlet valve 20, which is arranged downstream of first wheel brake cylinder 10), remains closed from time t2. In addition, brake fluid can also be pumped into the brake system from at least one storage chamber 34, which is arranged downstream of first wheel outlet valve 20 and second wheel outlet valve 24, by means of a pump speed n not equal to zero of at least one pump 36 of the brake system. However, in contrast to the prior art explained above, the pressure buildup in second wheel brake cylinder 12, which occurs from time t2, does not (almost) trigger a pressure drop in first wheel brake cylinder 10.

[0049] With the help of Figure 3b In the second braking process described in the coordinate system of FIG. 1 , starting from time t0, a vehicle deceleration a not equal to zero is also required, but the vehicle deceleration can also be reduced between time t0 and t1 by means of at least one regeneration mode Φ r However, compared with the first braking process, a significantly faster braking of the vehicle is required. In the second braking process, the required vehicle deceleration a, which is not equal to zero, is also only achieved between times t0 and t1 by means of at least one regenerative braking system in its regenerative mode Φ. r The electric motor is operated in the regenerative mode Φ and is realized by means of the first wheel brake cylinder 10 of the first axle and from time t2 only by means of at least one r The first target brake pressure p to be set in first wheel brake cylinder 10 is determined accordingly. 1target and a second target brake pressure p to be set in second wheel brake cylinder 12 2target .

[0050] However, if during the pressure difference control the measured or estimated first actual brake pressure p1 detected in first wheel brake cylinder 10 is greater than the first target brake pressure p2 to be set in first wheel brake cylinder 10 at the same time, 1target If the pressure difference Δp is less than at least one predetermined limit deviation, the target pressure difference Δp is preferably determined according to equation (G1.2) within a predetermined or determined transition time. target , that is to say as a function of the measured or estimated first actual brake pressure p1 in first wheel brake cylinder 10 and the second target brake pressure p to be set in second wheel brake cylinder 12 2targetTherefore, it is possible to reliably prevent the second actual brake pressure p2 in second wheel brake cylinder 12 from being equal to the second target brake pressure p2 to be set in second wheel brake cylinder 12. 2target The deviation exceeds the limit deviation.

[0051] In order to set a first actual brake pressure p1 present in first wheel brake cylinder 10 and a second actual brake pressure p2 present in second wheel brake cylinder 12 , again at time interval T Δp During this process, the target pressure difference Δp is set / regulated by means of the pressure difference regulation explained above. target For this reason, Figure 3b During the second braking process, the target pressure difference Δp is determined taking into account target In the case of , a target current intensity or an initial value for the target current intensity of the current signal 52 is selected from a value set having at least three current intensity values. Figure 3b Arrow 64 in the coordinate system of φ again indicates that only a first actual brake pressure p1 in first wheel brake cylinder 10 and a first target brake pressure p2 to be set in first wheel brake cylinder 10 occur. 1target Therefore, unlike the prior art explained above, in the time interval T Δp During the differential pressure control carried out in the meantime, no “soft” brake actuating element 28 occurs.

[0052] It should be pointed out that the differential pressure control performed in both braking processes eliminates the switchover between an overcurrent of at least one second wheel inlet valve 22 and an undercurrent of at least one second wheel inlet valve 22. This is due to the fact that, taking into account the determined target differential pressure Δp target In the case of , a target current intensity or an initial value of the target current intensity of current signal 52 is determined from a value set having at least three current intensity values ​​without the need.

Claims

1. A control device (16) for a regenerative braking system of a vehicle, the control device comprising: An electronic device (16a) designed and / or programmed to query or determine whether the required vehicle deceleration (a) can be achieved only partially by means of the braking system or at least one of the vehicle's braking systems in its regenerative mode (φ r ) causes, and if necessary is in its differential pressure control mode, in which: A target pressure difference for a first wheel brake cylinder (10) of the brake system assigned to a first axle of the vehicle and for a second wheel brake cylinder (12) of the brake system assigned to a second axle of the vehicle can be determined as a a predetermined or determined first target brake pressure (p 1target ) or a measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) and a second target brake pressure (p 2 ) which is predetermined or determined and is to be set in the second wheel brake cylinder (12); 2target ) The difference between The invention relates to a method for controlling the braking system of a wheel inlet valve (22) of the brake system. The method comprises: outputting a current signal (52) to at least one wheel inlet valve (22) of the brake system arranged upstream of the second wheel brake cylinder (12) under consideration of the determined target pressure difference, so that the at least one wheel inlet valve (22) can be actuated by means of the output current signal (52); It is characterized in that The electronic device (16a) present in its differential pressure control mode is additionally designed and / or programmed to determine a target current intensity of the current signal (52) taking into account a determined target differential pressure in the following manner: the target current intensity of the current signal (52) or an initial value of the target current intensity can be selected from a value set of at least three current intensity values ​​by means of the electronic device (16a) taking into account the determined target differential pressure.

2. The control device (16) according to claim 1, wherein: The electronic device (16a) present in its differential pressure control mode is designed and / or programmed to determine a target current intensity or an initial value of the target current intensity of the current signal (52) as a function of the determined target differential pressure according to a predetermined continuous function having a value set with at least three current intensity values.

3. The control device (16) according to claim 1 or 2, wherein: The electronic device (16a) is additionally designed and / or programmed to compare, after the start of its differential pressure control mode, a first actual brake pressure (p1) measured or estimated in at least one of the first wheel brake cylinders (10) during a predetermined comparison time interval with a first target brake pressure (p2) to be set in each case simultaneously in the first wheel brake cylinders (10). 1target ), an offset value of a target current intensity of the current signal (52) is determined in the case of a corresponding deviation thereof and the target current intensity of the current signal (52) is determined as the sum of an initial value of the target current intensity and the offset value.

4. A control device (16) according to any one of the preceding claims, wherein: The electronic device (16a) is additionally designed and / or programmed to determine, after the start of its differential pressure control mode, a time period during which a first actual brake pressure (p1) measured or estimated in at least one of the first wheel brake cylinders (10) is determined to be inversely proportional to a first target brake pressure (p2) to be set in each case simultaneously in the first wheel brake cylinders (10). 1target ) deviates from at least one predetermined minimum pressure deviation, and if the determined time period exceeds a predetermined time threshold, a target current intensity of the current signal (52) within a predetermined or determined closing time is determined in such a way that the at least one wheel inlet valve (22) is switched to its closed state within a predetermined or determined closing time by means of the current signal (52) output thereto.

5. The control device (16) according to any one of the preceding claims, wherein: The electronic device (16a) is designed and / or programmed to determine the target pressure difference as a predetermined or determined first target brake pressure (p) to be set in the first wheel brake cylinder (10) at the beginning of its differential pressure control mode. 1target ) and a predetermined or determined second target brake pressure (p) to be set in the second wheel brake cylinder (12). 2target ), however, if the measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) is greater than the first target brake pressure (p2) to be set simultaneously in the first wheel brake cylinder (10), 1target ) is smaller than at least a predetermined limit deviation, the electronic device (16a) is designed and / or programmed to determine the target pressure difference as a difference between a measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) and a second target brake pressure (p2) to be set in the second wheel brake cylinder (12) within a predetermined or determined transition time. 2target ) 6. A regenerative braking system for a vehicle, the regenerative braking system comprising: A control device (16) according to any one of the preceding claims; The first wheel brake cylinder (10) assigned to a first axle of the vehicle; the second wheel brake cylinder (12) assigned to a second axle of the vehicle; and At least one wheel inlet valve (22) is arranged upstream of the second wheel brake cylinder (12).

7. A method for operating a regenerative braking system of a vehicle, the method comprising the steps of: Determine whether the vehicle deceleration (a) requested by the driver of the vehicle and / or the automatic speed control device of the vehicle can be achieved only partially by means of the braking system or at least one of the vehicle in its regenerative mode (φ r ) caused by an electric motor operating in If the vehicle deceleration (a) can be brought about only partially by means of the at least one electric motor, a pressure difference control is carried out in the wheel brake cylinders (10, 12) of the brake system using the sub-steps: A target pressure difference is determined for a first wheel brake cylinder (10) of the brake system assigned to a first axle of the vehicle and a second wheel brake cylinder (12) of the brake system assigned to a second axle of the vehicle, wherein: Determine the target pressure difference as a predetermined or determined first target brake pressure (p 1target ) or a measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) and a second target brake pressure (p 2 ) which is predetermined or determined and is to be set in the second wheel brake cylinder (12); 2target ) The difference between and actuating at least one wheel inlet valve (22) of the brake system, which is arranged upstream of the second wheel brake cylinder (12), by means of a current signal (52) output to the at least one wheel inlet valve (22) taking into account the determined target pressure difference; It is characterized by the sub-steps: A target current intensity of the current signal (52) is determined taking into account the determined target differential pressure by selecting the target current intensity of the current signal (52) or an initial value of the target current intensity from a value set having at least three current intensity values ​​taking into account the determined target differential pressure.

8. The method according to claim 7, wherein: A target current intensity of the current signal (52) or an initial value of the target current intensity is determined as a function of the determined target differential pressure according to a predetermined continuous function having a value set with at least three current intensity values.

9. The method according to claim 7 or 8, wherein: During the pressure difference regulation, taking into account a first actual brake pressure (p1) measured or estimated in at least one of the first wheel brake cylinders (10) during a predetermined comparison time interval and a first target brake pressure (p2) to be set in each case simultaneously in the first wheel brake cylinder (10), the first actual brake pressure (p3) being determined is calculated. 1target ), determine an offset value for a target current intensity of the current signal (52) in response to a corresponding deviation thereof, and determine the target current intensity of the current signal (52) as the sum of an initial value of the target current intensity and the offset value.

10. The method according to any one of claims 7 to 9, wherein: During the pressure difference regulation, a time period is determined during which at least one measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) is inversely proportional to a first target brake pressure (p2) to be set in each case simultaneously in the first wheel brake cylinder (10). 1target ) deviates from at least one predetermined minimum pressure deviation, and if the determined time period exceeds a predetermined time threshold, a target current intensity of the current signal (52) can be determined within a predetermined or determined closing time in such a way that the at least one wheel inlet valve (22) is switched to its closed state within a predetermined or determined closing time by means of the current signal (52) output thereto.

11. The method according to any one of claims 7 to 10, wherein: At the start of the differential pressure regulation, the target differential pressure is determined as a predetermined or determined first target brake pressure (p 1target ) and a predetermined or determined second target brake pressure (p) to be set in the second wheel brake cylinder (12). 2target ), however, if the measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) is greater than the first target brake pressure (p2) to be set in the first wheel brake cylinder (10) at the same time 1target ) is smaller than at least a predetermined limit deviation, then within a predetermined or determined transition time, the target pressure difference is determined as a difference between a measured or estimated first actual brake pressure (p1) in the first wheel brake cylinder (10) and a second target brake pressure (p2) to be set in the second wheel brake cylinder (12). 2target ) 12. The method according to any one of claims 7 to 11, wherein: If a first target brake pressure (p 1target ), at the first target brake pressure, by means of at least one regenerative mode (Φ r ) applies a motor braking torque to the vehicle and causes a deceleration (a) of the vehicle by means of the first wheel brake cylinder (10), then a second target brake pressure (p) equal to zero to be set in the second wheel brake cylinder (12) is determined. 2target ), and otherwise, taking into account the vehicle deceleration (a), the motor braking torque and the first target brake pressure (p 1target ) is used to determine the second target brake pressure (p 2target ).

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