Method for controlling a braking device and braking device for a vehicle

Abstract

The present invention relates to a method for controlling a braking device of a vehicle with a plurality of frictionally engaged wheel brakes (14, 16, 18, 20) when the vehicle is stationary and at least one wheel brake (18, 20) is locked, comprising the method steps: selecting an individual locked wheel brake (18), generating, increasing or maintaining an application force between the friction partners (22, 24) of at least one further wheel brake (14; 16; 20) or all further wheel brakes (14, 16, 20), releasing the selected wheel brake (18) and re-locking the selected wheel brake (18). Alternatively or additionally with the method steps: increasing the clamping force between the friction partners (22, 24) of the at least one locked wheel brake (18, 20) and finally releasing the at least one locked wheel brake (18, 20) before the vehicle starts moving.Furthermore, the present invention relates to a braking device for carrying out the method according to the invention.

Description

State of the art

[0001] The present invention relates to a method for controlling a braking device and a braking device for a vehicle.

[0002] Braking devices for vehicles are known from the prior art, which have multiple frictionally engaged wheel brakes, such as drum brakes. When the vehicle is stationary or parked, the wheel brakes can be locked and thus function as a parking brake to prevent the vehicle from rolling away. Particularly when the vehicle is stationary for an extended period, the friction partners of the frictionally engaged wheel brakes can adhere to one another due to chemical reactions in the friction surfaces or in cold temperatures, so that the friction partners of the affected wheel brake remain stuck together despite the previously locked wheel brake being released.If the vehicle is put back into motion with a stuck wheel brake, the drive torque of the vehicle's power unit is usually able to release the stuck friction partners. However, at the moment of release, a sudden torque jump occurs at the corresponding wheel, which is not only noticeable and audible, but also perceived as uncomfortable by the driver. This is also referred to as the release shock. Disclosure of the invention

[0003] With the present invention, the probability of a release impact in a braking device of a vehicle can be reduced in a simple and safe manner long before the vehicle continues to drive and / or immediately before it starts moving when the vehicle is stationary.

[0004] According to the invention, a method for controlling a braking device with the features of patent claim 1 and a braking device with the features of patent claim 10 are therefore provided.

[0005] Accordingly, a method is provided for controlling a braking device of a vehicle with several frictionally engaged wheel brakes when the vehicle is stationary and at least one wheel brake is applied. The method involves carrying out the steps described below. First, a single applied wheel brake is selected. In this context, a applied wheel brake is understood to mean a wheel brake that is activated as a holding or parking brake. Furthermore, an application force between the friction partners of at least one further wheel brake or all further wheel brakes apart from the selected wheel brake is generated, increased or maintained. If one of the further wheel brakes is also a applied wheel brake, for example, its application force could be maintained or increased if necessary.If the additional wheel brake is, for example, a pure service brake, it could be activated as a service brake by generating an application force between the friction partners of this service brake. After this method step, the selected and previously applied wheel brake is released and then applied again in order to eliminate any adhesion between the friction partners of the selected wheel brake. The step of releasing and re-applying the selected wheel brake is preferably repeated one or more times in order to be able to reliably eliminate any adhesion between the friction partners. In this case, it is also preferred if the application force between the friction partners of the selected wheel brake is increased before release, particularly preferably up to a maximum achievable application force. This supports the release of the adhesion between the friction partners of the selected wheel brake.By selecting an individual detected wheel brake in each case, releasing it and then re-engaging it while at least one of the other wheel brakes prevents the stationary vehicle from rolling away, the method ensures, on the one hand, that the probability of a release impact is reduced, while, on the other hand, ensuring that the stationary vehicle will not roll away despite the selected wheel brake being released. The aforementioned method steps can also be repeated, preferably by selecting another individual detected wheel brake, particularly preferably by selecting all other individual detected wheel brakes, in order to reduce the probability of a release impact for all of the vehicle's detected wheel brakes.Thus, in this preferred embodiment, the selected wheel brakes can be successively released and re-applied without two or more applied wheel brakes being released at the same time, thus providing increased safety against the stationary vehicle rolling away.

[0006] Furthermore, a method for controlling a braking device of a vehicle with multiple frictionally engaged wheel brakes when the vehicle is stationary and at least one wheel brake is applied is provided, which method comprises the following method steps as an alternative or in addition to the method steps described above. Thus, the application force between the friction partners of the at least one applied wheel brake, preferably all applied wheel brakes, is initially increased, particularly preferably to a maximum application force, in order to finally release the at least one applied wheel brake before the vehicle starts moving, whereby any possible adhesion of the friction partners of the previously applied wheel brakes to one another can be particularly reliably eliminated.If the procedural steps mentioned here are carried out in combination with the procedural steps described previously, a release impact when the vehicle starts moving can be prevented particularly effectively, although the two procedural variants alone also provide increased security against the occurrence of a release impact.

[0007] Furthermore, a braking device for a vehicle is provided, which has a plurality of frictionally engaged wheel brakes, preferably at least one drum brake, and a control device, wherein the control device is designed to carry out the above-mentioned method according to the invention.

[0008] Advantageous embodiments and further developments emerge from the subclaims and from the description with reference to the figures.

[0009] In a preferred embodiment of the method according to the invention, before the at least one detected wheel brake is applied or the selected wheel brake is applied again, an application force is generated between the friction partners of the at least one detected wheel brake or selected wheel brake in such a way that the application force increases in a first phase up to a predetermined application force value and changes at least once in a second phase before the at least one detected wheel brake or the selected wheel brake is applied with an application force equal to the predetermined application force value. This variation of the application force in the second phase before the at least one detected wheel brake is applied or the selected wheel brake is applied again can reduce the friction partners sticking to one another during the subsequent idle time.The clamping force curve in the second phase is preferably wave-like and / or sinusoidal in order to support this effect.

[0010] In a further preferred embodiment of the method according to the invention, in which two or more detected wheel brakes are provided, the application forces of these wheel brakes are changed before the detected wheel brakes are detected in the aforementioned second phase such that the sum of the application forces in the second phase divided by the number of wheel brakes to be detected essentially corresponds to the predetermined application force value. In this way, it is ensured that, despite the variation in the application forces on the two or more detected or to be detected wheel brakes, a total braking force is exerted on the vehicle that essentially corresponds to the braking force acting on the vehicle after the aforementioned wheel brakes have been applied.This means that increased safety against the stationary vehicle rolling away is provided at an earlier point in time, while the probability of the friction partners sticking to each other later and thus of a subsequent release impact when driving off is reduced.

[0011] In a further preferred embodiment of the method according to the invention, the method steps, optionally the repeated method steps, are carried out preventively after a predetermined downtime of the vehicle and / or at time intervals after the vehicle has been parked. This fundamentally eliminates the need to determine whether the friction partners at the detected or selected wheel brakes are actually or likely to be adhering to one another.

[0012] Notwithstanding the foregoing, in a further preferred embodiment of the method according to the invention, at least one state or operating variable of the wheel brakes, the braking device, and / or the vehicle is recorded, and based on the recorded state or operating variable, a probability is determined with which the friction partners of one or more detected wheel brakes adhere to one another. Subsequently, the individual detected wheel brake is only selected and released accordingly and re-applied if the probability thus determined is greater than a predetermined probability threshold. Alternatively, if the determined probability is sufficiently high, the aforementioned predetermined idle time can be reduced, or the aforementioned time intervals can be shortened.This embodiment is advantageous in that the individual wheel brakes that have been applied are only released and re-applied with a corresponding expenditure of energy when sticking is likely, so that energy savings can be achieved.

[0013] As already explained above, in one embodiment variant of the method according to the invention, only the application force between the friction partners of at least one further wheel brake in addition to the selected wheel brake needs to be generated, increased, or maintained. In order to be able to determine how many further wheel brakes should be actuated accordingly in order to reliably prevent the stationary vehicle from rolling away when the selected wheel brake is released, in a further preferred embodiment of the method according to the invention, at least one environmental variable characterizing the parking situation of the vehicle, for example a gradient of the parking area and / or an ambient temperature, is recorded, wherein the application force between the friction partners of at least two further wheel brakes, preferably all further wheel brakes, is generated, increased, or maintained if the determined parking situation corresponds to a predetermined critical parking situation.For example, a steep incline of the parking area on which the vehicle is parked and / or an ambient temperature that suggests an icy parking area can lead to the detection of a parking situation that is classified as critical, so that a corresponding number or all of the other wheel brakes are applied, increasing the braking force of the vehicle, before the selected wheel brake is released.

[0014] The invention will be explained in more detail below using exemplary embodiments with reference to the accompanying drawings. Fig. 1 a schematic representation of a vehicle with an embodiment of the braking device according to the invention, Fig. 2 Method steps of an embodiment of the method according to the invention for controlling the braking device according to Fig. 1 Fig. 3 Clamping force curves before and after applying two locked wheel brakes from Fig. 1, Fig. 4 Clamping force curves of two selected wheel brakes from Fig. 1 and Fig. 5 Clamping force curves during the final release of the locked wheel brakes Fig. 1.

[0015] 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 be apparent upon consideration of the drawings. Elements of the drawings are not necessarily shown to scale relative to one another.

[0016] 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.

[0017] Fig. 1 shows a schematic representation of a vehicle with an embodiment of the braking device according to the invention.

[0018] The vehicle has a front axle 2 and a rear axle 4, with two wheels 6, 8 arranged on the front axle 2 and two wheels 10, 12 on the rear axle 4. Each of the wheels 6, 8, 10, 12 is assigned a frictionally engaged wheel brake 14, 16, 18, 20. Regardless of the specific design of the wheel brakes 14, 16, 18, 20, they each have at least one first friction partner 22 fixed to the vehicle and at least one second friction partner 24 rotating with the associated wheel 6, 8, 10, 12, which can be brought into frictional engagement with one another by applying an application force. The wheel brakes 14, 16, 18, 20 can be disc brakes and / or drum brakes. Furthermore, the wheel brakes 14, 16, 18, 20 can be actuated electromechanically and / or hydraulically.Furthermore, the aforementioned wheel brakes 14, 16, 18, 20 can generally be designed as a service brake, a parking brake or a parking brake and / or as a combination of a service brake with a parking brake or a parking brake.

[0019] In the illustrated embodiment, the front wheel brakes 14, 16 are designed, for example, as drum brakes, preferably electromechanically actuated drum brakes, with the wheel brakes 14, 16 intended to function exclusively as service brakes. The electromechanical actuator device of the two wheel brakes 14, 16 (not shown in detail) is preferably not self-locking. The two rear wheel brakes 18, 20 are also designed, for example, as drum brakes, to which an electromechanical actuator device is preferably assigned, which is particularly preferably not self-locking. The rear wheel brakes 18, 20 can be activated both as a service brake and as a parking brake.For this purpose, a locking mechanism designed separately from the electromechanical actuator device can be provided, but in the embodiment shown, a locking device is used as an example, by means of which the electromechanical actuator device of the two rear wheel brakes 18, 20 can be locked in order to use the wheel brakes 18, 20 as a parking brake in the locked or arrested state.

[0020] In addition, the braking device comprises a control device 26, by means of which the wheel brakes 14, 16, 18, 20 can be controlled, in particular their application force can be controlled and / or regulated. Furthermore, the control device 26 interacts with a sensor system 28, which has a plurality of sensors and with which at least one state or operating variable and / or an environmental variable characterizing the parking situation of the vehicle can be detected, as will be described below with reference to Fig. 2 is explained in more detail.

[0021] Fig. 2 shows method steps of an embodiment of the method according to the invention for controlling the braking device according to Fig. 1.

[0022] In a first method step 30, the vehicle is brought to a standstill by actuating at least one of the wheel brakes 14, 16, 18, 20, preferably all of the wheel brakes 14, 16, 18, 20, wherein the wheel brakes 14, 16, 18, 20 are activated as service brakes. As soon as the vehicle is brought to a standstill, the rear wheel brakes 18, 20, which can be actuated as parking brakes, are applied, which results in Fig. 2 is shown using method step 32. For this purpose, a clamping force is generated between the friction partners 22, 24 of the two wheel brakes 18, 20 by the associated electromechanical actuator device. This occurs in Fig. 3 shown manner, where Fig. 3 shows the application force curve 34 of the wheel brake 18 and the application force curve 36 of the wheel brake 20 before and after the two wheel brakes 18, 20 are applied.

[0023] Thus, the application force of both wheel brakes 18, 20 is increased in a first phase from t0 to t1 to a predetermined application force value F v increased. In a subsequent second phase from t1 to t2, the application force of the wheel brakes 18, 20 is increased at least once compared to the predetermined application force value F v changed before the two wheel brakes 18, 20 are applied with an application force equal to the predetermined application force value F v at time t2. As can be seen from Fig. 3, the clamping force curves 34, 36 deviate from each other in the second phase between t1 and t2, whereby the predetermined clamping force value F vis exceeded at least once and undershot once in the second phase. Specifically, the two application force curves 34, 36 are wave-like and / or sinusoidal in the second phase. It can also be seen that the application force curves 34, 36 are in phase opposition in the second phase. The application force curves 34, 36 are changed relative to one another in the second phase in such a way that the sum of the application forces of the wheel brake 18 and the wheel brake 20 in the second phase divided by the number of wheel brakes 18 and 20 that are applied or to be applied essentially corresponds to the predetermined application force value F vIn other words, at any time between times t1 and t2, i.e., in the second phase, an increased application force of the wheel brake 18 is compensated by a correspondingly lower application force of the wheel brake 20, and vice versa. Thus, at time t1, a total braking force is applied to the vehicle that corresponds to the braking force at time t2, when the two wheel brakes 18, 20 are applied. Furthermore, the changes in the application force curves 34, 36 in the second phase reduce the probability of the friction partners 22, 24 subsequently sticking to one another.

[0024] After a certain period of inactivity and / or if certain criteria are met, in method step 38 an individual wheel brake 18 or 20 detected in the manner described above is selected, which in the present example is wheel brake 18. Furthermore, in method step 40 an application force between the friction partners 22, 24 of at least one further wheel brake 14, 16 or 20 or all further wheel brakes 14, 16, 20 is generated, increased or maintained. For example, the application force already present in the detected wheel brake 20 could be maintained or increased. Alternatively or additionally, at least one of the wheel brakes 14, 16 designed as pure service brakes could be actuated by generating a corresponding application force between the friction partners 22, 24. The purpose of method step 40 is to ensure that the vehicle does not roll away when the selected wheel brake 18 is subsequently released.

[0025] In the subsequent method step 42, the selected wheel brake 18 is first released and then re-applied in order to counteract any subsequent or existing adhesion of the friction partners 22, 24 of the wheel brake 18, wherein the selected wheel brake 18 is preferably released and re-applied twice or more times. The corresponding application force curve 44 of the wheel brake 18 is shown in Fig. 4. Thus, the wheel brake 18 is released at time t1 and re-applied at a subsequent time t2, with the predetermined clamping force value F vAfter that, you can return to process step 38, this time selecting the other detected wheel brake 20 before performing process steps 40 and 42. Since in this procedure only one of the detected wheel brakes 18, 20 is selected, the application force curve 44 of the wheel brake 18 and the further Fig. 4 are offset in time from one another in such a way that only one of the two detected wheel brakes 18, 20 is always released, namely the wheel brake 18 in the period t1 to t2 and the wheel brake 20 in the period t2 to t3.

[0026] Although in Fig. 4, it is preferred if the clamping force between the friction partners of the respectively selected wheel brake 18 or 20 is increased before release at time t1 or t2, preferably up to a maximum clamping force F max , to which reference is made to Fig. 5. Furthermore, before the respective selected wheel brake 18 or 20 is re-engaged, the clamping force between the friction partners 22, 24 of the selected wheel brake 18 or 20 can be generated in such a way that the clamping force increases in a first phase up to the predetermined clamping force value F v increased, as is the Fig. 4, while in addition the corresponding clamping force is changed at least once in a second phase, as already described with reference to Fig. 3, before the respectively selected wheel brake 18 or 20 is again applied with an application force equal to the predetermined application force value F v is observed, although this intermediate phase in Fig. 4 itself is not indicated.

[0027] If the vehicle is to be put into motion again after a long period of inactivity, the clamping force between the friction partners 22, 24 of the two wheel brakes 18 and 20 is suddenly increased to a maximum clamping force F max increased in order to finally release the two locked wheel brakes 18, 20 abruptly before the vehicle starts moving. The corresponding application force curves 50 and 52 of the wheel brakes 18 and 20 are shown in Fig. 5. First, the application forces of both wheel brakes 18, 20 are calculated starting from the predetermined application force value F v increased at time t1 in order to achieve the maximum possible clamping force F at time t2 max to achieve, whereby after reaching the maximum clamping force F maxAt time t2, the final release of the two locked wheel brakes 18, 20 takes place. This also counteracts the adhesion of the two friction partners 22, 24 of the two wheel brakes 18, 20 after the release of the lock, in order to avoid a subsequent release shock when starting off.

[0028] In principle, the previously described method steps 38, 40, 42 and their repetition can be carried out preventively after a predetermined downtime of the vehicle after it has been parked or / and at time intervals after the vehicle has been parked.

[0029] Alternatively or additionally, the previously described sensor system 28 can detect at least one state or operating variable of the wheel brakes 18, 20, the braking device as a whole and / or the vehicle, and, based on the detected state or operating variable, determine a probability with which the friction partners 22, 24 of the detected wheel brakes 18, 20 adhere to one another when the detected wheel brakes 18, 20 are released. If the probability calculated on this basis is greater than a predetermined probability threshold, the individual detected wheel brake 18 or 20 is selected in method step 38, and the method is carried out in the manner described above with method steps 40, 42 and repeated if necessary.Alternatively or additionally, the aforementioned predetermined downtime can be reduced or the time intervals shortened if the predetermined probability threshold is exceeded. In a preferred embodiment of the method, a probability above the probability threshold is determined if, during a vehicle start attempt, no rotation of a wheel is detected whose previously detected wheel brake 18 or 20 has been released.

[0030] As already mentioned above, the sensor system 28 can also detect at least one environmental variable characterizing the parking situation of the vehicle. This includes, for example, the gradient of the vehicle's parking area and / or an ambient temperature. If, for example, a parking situation is determined based on the at least one environmental variable that corresponds to a predetermined critical parking situation, the number of wheel brakes other than the selected wheel brake whose application force is generated, increased, or maintained can be varied in method step 40.For example, if a parking situation is detected in which, on the one hand, the gradient of the parking area exceeds a predetermined gradient limit and / or, on the other hand, the detected environmental variable in the form of the ambient temperature indicates icy ground, a critical parking situation can be detected and the clamping force between the friction partners 22, 24 of at least two additional wheel brakes or even all additional wheel brakes can be generated, increased, or maintained. If, on the other hand, no critical parking situation has been detected, only the clamping force between the friction partners 22, 24 of at least one additional detected wheel brake 20 or 18 could be maintained. In this way, the method is specifically adapted to the parking situation of the vehicle and, if necessary, energy can be saved.

[0031] In the present application, “substantially corresponding” is to be understood as meaning that two values are either identical or differ only so slightly from each other that no functional difference results.

Claims

[1] Method for controlling a braking device of a vehicle with several frictionally engaged wheel brakes (14, 16, 18, 20) when the vehicle is stationary and at least one wheel brake (18, 20) is engaged with the procedural steps Selecting a single locked wheel brake (18), Generating, increasing or maintaining a clamping force between the friction partners (22, 24) of at least one further wheel brake (14; 16; 20) or all further wheel brakes (14, 16, 20), Releasing the selected wheel brake (18) and re-engaging the selected wheel brake (18) and / or with the procedural steps Increasing the clamping force between the friction partners (22, 24) of the at least one locked wheel brake (18, 20) and finally releasing the at least one locked wheel brake (18, 20) before the vehicle starts moving. [2] Method according to claim 1, wherein, before the at least one detected wheel brake (18, 20) or the re-detecting of the selected wheel brake (18), an application force is generated between the friction partners (22, 24) of the at least one detected wheel brake (18, 20) or selected wheel brake (18) in such a way that the application force increases in a first phase up to a predetermined application force value (F v ) and is changed at least once in a second phase before the at least one detected wheel brake (18, 20) or the selected wheel brake (18) is applied with an application force equal to the predetermined application force value (F v ) is detected. [3] Method according to claim 2, wherein the clamping force in the second phase exceeds the predetermined clamping force value (F v) at least once and falls below it once and / or a clamping force curve (34; 36) in the second phase is wave-like and / or sinusoidal. [4] Method according to one of claims 2 or 3, wherein the application forces of two or more detected wheel brakes (18, 20) are changed before the two or more detected wheel brakes (18, 20) are detected in the second phase such that the sum of the application forces in the second phase divided by the number of two or more detected wheel brakes (18, 20) substantially corresponds to the predetermined application force value (F v ) corresponds. [5] Method according to one of the preceding claims, wherein the application force between the friction partners (22, 24) of the selected wheel brake (18) is increased before release, preferably up to a maximum application force (F max ). [6] Method according to one of the preceding claims, wherein the method steps are carried out repeatedly and / or preventively after a predetermined stationary time of the vehicle and / or at time intervals after the vehicle has been parked, selecting another individual detected wheel brake (20), preferably all other detected wheel brakes (20). [7] Method according to one of the preceding claims, in which at least one state or operating variable of the wheel brakes (18, 20), the braking device and / or the vehicle is detected and, on the basis of the detected state or operating variable, a probability is determined with which the friction partners (22, 24) of one or more detected wheel brakes (18, 20) adhere to one another, wherein the individual detected wheel brake (18; 20) is selected, the predetermined downtime is reduced or the time intervals are shortened if the probability is greater than a predetermined probability limit value. [8] Method according to claim 7, in which a probability above the probability limit is determined if, during an attempt to start the vehicle, no rotation of a wheel (10; 12) is detected, the previously determined wheel brake (18; 20) of which is released. [9] Method according to one of the preceding claims, in which at least one environmental variable characterising the parking situation of the vehicle, preferably a gradient of the parking surface and / or an ambient temperature, is detected, wherein the application force between the friction partners (22, 24) of at least two further wheel brakes (14, 16, 20), preferably all further wheel brakes (14, 16, 20), is generated, increased or maintained and / or all further wheel brakes (14, 16) operable as service brakes or exclusively as service brakes, is generated when the determined parking situation corresponds to a predetermined critical parking situation. [10] Braking device for a vehicle with a plurality of frictionally engaged wheel brakes (14, 16, 18, 20) and a control device (26) designed to carry out the method according to one of the preceding claims.

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