Method for stopping a two-track motor vehicle

Abstract

Method for holding a two-track motor vehicle, wherein the motor vehicle comprises at least one electric drive motor and wherein each of the four wheels of the motor vehicle is held by a service brake, - wherein the motor vehicle is in an initial position at rest by the application of an engine torque (M Antrieb ) the electric drive motor is held on at least two wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the motor vehicle, - where the engine torque (M Antrieb ), which holds at least two wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the motor vehicle, is removed from one wheel (wheel_1, wheel_2, wheel_3, wheel_4) or from two wheels, - whereby after the reduction of the engine torque (M Antrieb ) on one wheel or on the two wheels, the service brake is activated on that wheel or on those two wheels, - whereby, after activation of the service brake on one wheel or on both wheels, the engine torque (M Antrieb ) is removed from another wheel of the vehicle, - whereupon the reduction of the engine torque (M Antrieb ) on the other wheel of the vehicle, the service brake is activated on this other wheel.

Description

[0001] The invention relates to a method for holding a two-track motor vehicle, in particular on an inclined surface, according to claim 1. For the prior art, reference is made, by way of example, to DE 10 2017 113 016 A1, DE 10 2012 223 867 A1, DE 10 2012 223 866 A1, DE 10 2012 015 617 A1, DE 10 2014 003 992 A1, US 2013 / 0 054 062 A1, DE 10 2008 032 824 A1 and US 2018 / 0 290 655 A1.

[0002] Known holding functions (such as a so-called "Autohold" function, "Hill Assist", or the so-called B-hold function) of motor vehicles, especially those with internal combustion engines, hold the vehicle, particularly on an inclined surface, by means of the service brake.

[0003] In a motor vehicle with an electric drive system, the electric drive motor can impart a motor torque to the drivetrain. To prevent the vehicle from rolling backwards after braking by the electric drive motor, particularly when stopping on an inclined surface, the service brake must conventionally be applied depending on the incline. Such a braking and holding concept is known, for example, from DE 10 2017 113 016 A1.

[0004] Current electric vehicle concepts feature a pronounced deceleration when the accelerator pedal is released, extending to a complete stop. This is achieved by adjusting the recuperation torque of the electric drive motor accordingly, allowing the driver to both accelerate by pressing the accelerator pedal and initiate deceleration when releasing it. This results in a so-called "one-pedal feeling," meaning the vehicle can be controlled using only the accelerator pedal. This "one-pedal feeling" significantly reduces the need for the brake pedal.

[0005] In this concept, unlike typical automatic vehicles, the electric vehicle does not exhibit creep; that is, on a level surface without incline, the vehicle will not move forward when a drive mode corresponding to the vehicle's forward direction is engaged (typically designated as D-Drive); the same applies to reverse. Creep is difficult to reconcile with a "one-pedal driving" experience, as this would require, for example, frequent use of the brake pedal to prevent the vehicle from creeping.

[0006] From DE 10 2012 223 867 A1 and DE 10 2012 223 866 A1, it is further known that vehicles with electric drive systems utilize motor torque from the electric drive system to hold the vehicle, which is already stationary, particularly on an inclined surface. Depending on the gradient of the road and the length of time the vehicle remains stationary, the power output of the electric drive motor decreases sooner or later. The motor torque of the electric drive motor is then reduced (for example, after a certain time), and an alternative holding system, in particular the service brake, takes over and holds the vehicle stationary.

[0007] A disadvantage of the aforementioned state of the art, however, is that during the transition from holding the vehicle by the electric drive motor to holding it by the service brake, particularly during the reduction of the electric drive motor's torque while the service brake is engaged or activated, undesirable and uncomfortable noises and vibrations occur for vehicle occupants. This is because, in order to keep the vehicle safely stationary, the transition from drive-side holding to holding by the service brake must occur simultaneously. In particular, vehicle occupants experience such vibrations as a creaking noise.

[0008] The object of the invention is therefore to improve a method for keeping a two-track motor vehicle stationary with regard to the comfort of a vehicle occupant.

[0009] The solution to the problem is achieved by a method for holding a two-track motor vehicle with the features of claim 1. Advantageous developments and refinements are the subject of the dependent claims.

[0010] For the purposes of the application, the term "motor vehicle with an electric drive motor" preferably includes both an electric vehicle that can be charged via an external electrical power supply with an optional combustion engine range extender and a hybrid vehicle with a combustion engine and one (or more) electric drive motor.

[0011] In a first exemplary embodiment, the motor vehicle comprises two electric drive motors, one for driving the wheels on the front axle and one for driving the wheels on the rear axle.

[0012] In another exemplary embodiment, the motor vehicle comprises four wheel-specific electric drive motors, which are particularly known as so-called wheel hub motors. In such a case with wheel-specific electric drive motors, each wheel can be driven individually by its assigned electric drive motor.

[0013] As mentioned at the beginning, the two-track motor vehicle comprises at least one (preferably at least two) electric drive motor. If, for example, the motor vehicle comprises only a single electric drive motor, it is preferably provided that this motor drives only the wheels of one axle, i.e., either the wheels of the front axle or those of the rear axle.

[0014] Furthermore, the two-track motor vehicle comprises at least four wheels, each of which can be held or secured against rotation by a service brake. The service brake can be, for example, an electrically, electro-hydraulically, electro-mechanically, or hydraulically actuated braking device. Particularly preferred is the aforementioned concept of an electric vehicle with a "one-pedal feeling".

[0015] In a starting position of the motor vehicle (hereinafter referred to as "vehicle"), the vehicle is at a standstill, being held by the application of a motor torque from at least one electric drive motor.

[0016] In the case of only a single electric drive motor, it is preferably provided that the wheels of one axle are held by a motor torque of the single electric drive motor, while the wheels of the other axle can be held by a conventional service brake.

[0017] It is also possible that the vehicle is held at a standstill by the application of a service brake and simultaneously by the application of motor torque through the electric drive motor.

[0018] In the case of the aforementioned design with two electric drive motors (for example, one for driving the wheels of the front axle and one for driving the wheels of the rear axle), it is preferably provided that all wheels of the vehicle are held in the starting position by means of a motor torque of the electric drive motors (and possibly additionally by means of a respective service brake) or are secured against twisting or rolling.

[0019] Likewise, in the case of the aforementioned embodiment with (four) wheel-individual electric drive motors, it is preferably provided that in the starting position all four wheels are held by a motor torque of the respective electric drive motor or secured against rolling or twisting.

[0020] The motor vehicle is particularly preferably located in its starting position on an inclined surface or on a roadway that has a gradient, for example on a slope.

[0021] In a next step, it is planned that the motor torque for holding the vehicle in the starting position, in particular depending on the situation and / or gradient and / or time, will be reduced at a single wheel or at a maximum of two wheels of the motor vehicle.

[0022] In the case of a single electric drive motor generating the torque to hold two of the vehicle's wheels, it is preferably provided that the torque is dissipated at both wheels. At the same time, however, it is provided that the other two wheels are held by a service brake.

[0023] In particular, in the case of two or more electric drive motors, it is preferably provided that the motor torque of the electric drive motor(s) is initially reduced at only one wheel, while no such reduction takes place at the other wheels which are held by the motor torque of the electric drive motor(s).

[0024] This ensures that, during the reduction of the engine torque at only one wheel (or at most two wheels), the vehicle continues to be held in place by, preferably, an applied engine torque at the other wheels, thus preventing unwanted movement of the vehicle.

[0025] The reduction of the torque of the electric drive motor at the aforementioned one wheel (or at a maximum of two wheels) preferably takes place completely, i.e., until no motor torque is applied to this wheel, so essentially a reduction to 0 Nm takes place.

[0026] During the period in which the motor torque of the electric drive motor(s) is reduced at the respective wheel(s), it is preferably provided that no service braking torque of the service brake of the respective wheel is applied to that wheel(s). In other words, it is provided that the service brake on the respective wheel is not activated or open during the reduction of the motor torque of the electric drive motor(s).

[0027] After (preferably complete) reduction of the engine torque at one wheel or a maximum of two wheels of the motor vehicle, it is intended that the service brake takes over holding that respective wheel.

[0028] For example, if the motor torque at a single wheel is completely dissipated, the service brake at that wheel remains open (i.e., not yet active) until the motor torque is completely dissipated. The vehicle is then prevented from rolling away by an anti-rotation device on the other wheels, specifically by the application of motor torque from the electric drive motor(s). Once the motor torque is completely dissipated in this example, the service brake at that wheel is activated, so that this wheel also contributes to stopping the vehicle.

[0029] Because the service brake is not activated during the (preferably complete) reduction of engine torque, but only becomes active after the torque has been reduced, the aforementioned adverse creaking noise does not occur. The time gap during which the wheel where the reduction is taking place is no longer secured against rolling, until the service brake actually becomes active, is compensated for by holding the other wheels, thus preventing the vehicle from rolling away.

[0030] As previously mentioned, it is preferably intended that the reduction of the motor torque of the electric drive motor(s) at the respective wheel is dependent on the situation, time, and / or gradient. For example, such a reduction can occur depending on a predictable stationary duration of the vehicle, such as a known traffic light cycle time or a predictable duration of a traffic jam, or similar factors. Alternatively or additionally, it is possible that the aforementioned reduction of motor torque at the respective wheel is also dependent on the gradient of the road surface on which the stationary vehicle is located.If the vehicle is on a flat road, for example, which can be determined by various sensors or data, the aforementioned reduction of motor torque might occur very late or not at all, since the electric drive motor is energetically capable of holding the vehicle in its starting position for a long period of time by applying motor torque to the respective wheels.

[0031] Conversely, if the vehicle is found to be stationary on a road with a steeper incline, where the electric drive motor can only maintain the vehicle's position for a certain period of time due to energy constraints, it could be provided that the motor torque is reduced at the respective wheel after a shorter period of time.

[0032] Alternatively or additionally, it is also possible for the reduction of the motor torque to be time-dependent. For example, if a predetermined dwell time of the vehicle in the starting position (the vehicle's holding position via the motor torque of the electric drive motor) is registered, the reduction of the motor torque can occur at the respective wheel.

[0033] Alternatively or additionally, it is possible that the aforementioned reduction takes place depending on a recorded performance level of the electric drive motor.

[0034] After a change or transition has taken place at one wheel (or at most two wheels) of the vehicle from a drive-related holding due to the motor torque of the drive motor to a brake-related holding due to the service brake, it is intended that these process steps are now repeated at the other wheels, which are held by a motor torque of the electric drive motor(s).

[0035] It is therefore intended that (again preferably depending on the situation, time, and / or gradient) after the service brake is activated at the aforementioned one wheel (or at a maximum of two wheels), the motor torque of the electric drive motor(s) is reduced at another wheel of the vehicle. This reduction also preferably occurs completely, i.e., until the applied torque has reached essentially 0 Nm. Following the aforementioned reduction of torque at this other wheel, the service brake is activated at this other wheel.

[0036] These two process steps ("reduction of the motor torque" and subsequent "activation of the service brake" at the respective wheel), preferably dependent on the situation, time or gradient, are thus carried out one after the other or sequentially at each wheel, which is held in the starting position of the vehicle by a motor torque of the electric drive motor.

[0037] During the execution of these two process steps at each wheel, the other wheels take over holding the vehicle, either via an already activated service brake or via an existing motor torque of the electric drive motor(s).

[0038] During the reduction of the motor torque at one wheel, the service brake is preferably not active at any wheel of the vehicle. This effectively avoids the aforementioned creaking noise during the transition from holding the vehicle by the electric drive motor to holding it by the service brake. This ensures comfortable and quieter holding of the vehicle.

[0039] In a preferred embodiment of the invention, the claimed method is carried out depending on the situation or gradient. Thus, if a certain gradient of the road surface is reached while the vehicle is in the aforementioned starting position (stopping position), the method is carried out. Alternatively or additionally, the method can be carried out if, besides the aforementioned gradient, it is detected that the power output of the electric drive motor is no longer sufficient to hold the vehicle in the stopping position for a certain duration on its own, or if it is detected that, due to a foreseeable or already reached stopping duration, it is no longer energetically efficient to hold the vehicle using the motor torque of the electric drive motor.

[0040] In addition to the aforementioned method, a motor vehicle is also proposed that enables the implementation of this method. As already mentioned, the motor vehicle comprises at least one electric drive motor and at least four wheels. Each of the four wheels is secured by a service brake or by a mechanism to prevent rotation.

[0041] These and other features are evident not only from the claims and the description but also from the drawings, whereby the individual features may be realized individually or in combination in one embodiment of the invention and may represent advantageous and, in themselves, protectable embodiments for which protection is claimed here.

[0042] The invention will now be explained in more detail using an exemplary embodiment. All features described in more detail may be essential to the invention.

[0043] The diagram shown schematically illustrates an example of a torque curve (holding or braking torque curve) of a four-wheeled motor vehicle (wheel_1; wheel_2; wheel_3, wheel_4) over time. Each wheel (wheel_1; wheel_2; wheel_3, wheel_4) has a service brake, which generates a braking torque or service braking torque M. Brems (dashed line) can be applied to the respective wheel. Furthermore, a motor torque M can be applied individually to each wheel. Antrieb (solid line) of the electric drive motor. In particular, each wheel has its own electric drive motor, for example in the form of a wheel hub motor.

[0044] In a starting position, the vehicle is in a stationary position, particularly on a slope. The vehicle is moved until time t1 by the application of a motor torque M. Antrieb The electric drive motor, which is applied to all four wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the vehicle, holds the vehicle. Additionally, but not limited to, the vehicle is held in this specific case by the application of the service brake to all four wheels (wheel_1, wheel_2, wheel_3, wheel_4). However, it is also conceivable that the vehicle could be held solely by the application of a motor torque M. Antrieb The vehicle is held stationary at each wheel. Through a vehicle concept featuring the "one-pedal feeling" described earlier, the vehicle is propelled by a motor torque M applied to each wheel. Antrieb held at a standstill by the respective wheel-individual electric drive motor.

[0045] For example, the vehicle might be stopped at a red light and on a road with an incline.

[0046] The braking process until the vehicle comes to a standstill is preferably also carried out by the respective electric drive motor (see above, "One-Pedal Feeling" concept). As already mentioned, it is also possible that the service brake is applied simultaneously with the electric drive motor to hold the vehicle by applying a service braking torque M. Brems is activated on the wheels.

[0047] If, at time t1, low performance or an energy-inefficient setting of the electric drive motors is detected, for example via sensors, navigation data, online data, vehicle data or the like, due to an excessive gradient of the road or due to a foreseeable or already existing excessively long dwell time of the vehicle in the stationary position, it is intended that the service brake is applied by applying a corresponding braking torque M Brems ensures and takes over the holding position of the vehicle at the respective wheel.

[0048] In contrast to the state of the art, the service brake is then not simultaneously and comprehensively applied with a still-present engine torque M. Antrieb not activated at each wheel, but built up sequentially at each wheel one after the other, while the motor torque at the respective wheel has already been completely reduced.

[0049] If the service brake is already activated while the vehicle is stationary, it will be fully released at the first wheel (Rad_1) before time t1, so that no service brake torque M is present. Brems at time t1, there is no longer any contact with the first wheel Rad_1.

[0050] At time t1, the engine torque M is then Antrieb The torque of the first wheel (wheel_1) of the vehicle is reduced to 0 Nm. Only at time t2, when the motor torque M Antrieb Once the electric drive motor of the first wheel is completely disengaged, the service brake on this first wheel is activated by a building-up braking torque M. Brems The service brake is activated. The braking deficit, which occurs between the point at which the reduction of the engine torque M begins, Antrieb at the first wheel and the complete build-up of the service brake torque M BremsThe braking torque M, which arises at the first wheel, can be caused by the braking torque M still acting on the other three wheels (wheel_2, wheel_3, wheel_4). Brems or M Antrieb can be compensated or bridged. Thus, the holding torque M Brems or M Antrieb The other three wheels (wheel_2, wheel_3, wheel_4) are raised high enough to hold the vehicle in the stationary position. This is achieved by completely dissipating the engine torque M. Antrieb On the first wheel Rad_1, during which the service brake of the first wheel Rad_1 is open or not active, an uncomfortable noise development can be advantageously avoided.

[0051] In a next step, at time t3, when the service braking torque M Brems Once the first wheel (Rad_1) is fully assembled and has completely taken over holding the first wheel, the motor torque M is applied to the second wheel (Rad_2). AntriebThe electric drive motor of the second wheel, wheel_2, is reduced to 0 Nm. It must again be ensured that at time t3 of the reduction of the motor torque M Antrieb At the second wheel (Rad_2), the service brake at the second wheel is no longer activated (i.e., open). After the complete reduction of the motor torque M Antrieb The electric drive motor of the second wheel Rad_2, at time t4, engages the service brake on the second wheel Rad_2 by building up a service braking torque M. Brems The service brake is activated. The service brake of the second wheel (Rad_2) then takes over holding the second wheel.

[0052] Subsequently, as shown in the figure, the same procedure steps are carried out with the other two wheels, wheel_3 and wheel_4. After the service braking torque M has fully built up... BremsOn the second wheel Rad_2 and ensuring that the service brake of the third wheel Rad_3 is deactivated, at time t5, the motor braking torque M is applied. Antrieb The torque of the third wheel (Rad_3) is reduced to 0 Nm. Then, once the motor torque M has completely dissipated... Antrieb At time t6, the service brake of the third wheel Rad_3 is activated.

[0053] After the service brake on the third wheel (Rad_3) is fully activated and ensuring that the service brake on the fourth wheel (Rad_4) is not activated (i.e., open), the applied motor torque M An- trieb The torque on the fourth wheel (wheel_4) is reduced to 0 Nm (time t7). Only after this torque M has completely dissipated (dissipation begins at time t7). Antrieb When the fourth wheel Rad_4 is activated, the service brake of the fourth wheel Rad_4 is activated (time t8).

[0054] During each reduction of the engine torque M Antrieb and a subsequent build-up of an operating braking torque M Brems The action on the respective wheel secures the holding torques M acting on the other wheels. Brems or M Antrieb the vehicle is stationary and prevents it from rolling away.

[0055] This is because the service brake on the respective wheels is applied during the reduction of the engine torque M Antrieb If the respective wheels are not activated, i.e., open, no creaking noise is produced.

Claims

[1] Method for holding a two-track motor vehicle, wherein the motor vehicle comprises at least one electric drive motor and wherein each of the four wheels of the motor vehicle is held by a service brake, - wherein the motor vehicle is in an initial position at rest by the application of an engine torque (M Antrieb ) the electric drive motor is held on at least two wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the motor vehicle, - where the engine torque (M Antrieb ), which holds at least two wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the motor vehicle, is removed from one wheel (wheel_1, wheel_2, wheel_3, wheel_4) or from two wheels, - whereby after the reduction of the engine torque (M Antrieb ) on one wheel or on the two wheels, the service brake is activated on that wheel or on those two wheels, - whereby, after activation of the service brake on one wheel or on both wheels, the engine torque (M Antrieb ) is removed from another wheel of the vehicle, - whereupon the reduction of the engine torque (M Antrieb ) on the other wheel of the vehicle, the service brake is activated on this other wheel. [2] Method according to claim 1, wherein the motor vehicle comprises two electric motor drive machines and wherein in the initial situation two wheels of the motor vehicle are each driven by a motor torque (M Antrieb ) are each held by an electric motor drive unit of the motor vehicle. [3] Method according to claim 1, wherein the motor vehicle comprises four electric motor drive machines and wherein in the initial situation four wheels (wheel_1, wheel_2, wheel_3, wheel_4) of the motor vehicle are driven by a motor torque (M Antrieb) is held by one of the four drive machines. [4] Method according to one of the preceding claims, wherein, depending on the situation and / or gradient and / or time, the method according to one of claims 1 to 3 is carried out successively on all electrically held wheels of the motor vehicle. [5] Method according to any of the preceding claims, wherein the reduction of the motor torque (M Antrieb ) on each wheel depending on the situation, gradient, and / or time. [6] Method according to claim 5, wherein the reduction of the motor torque (M Antrieb ) at each wheel from a foreseeable and / or achieved dwell time of the vehicle in the held position and / or from the detection of a limit performance capability of the electric drive motor. [7] Method according to any of the preceding claims, wherein the reduction of the motor torque (MAntrieb ) is reduced at each wheel from the point at which a limit gradient of the vehicle roadway is reached. [8] Method according to one of the preceding claims, wherein the method is carried out from the point at which a limit gradient of the vehicle roadway is reached. [9] Method according to one of the preceding claims, wherein during the reduction of the motor torque (M Antrieb ) on a particular wheel, the service brake on that particular wheel is deactivated. [10] Motor vehicle for carrying out the method according to any one of claims 1 to 9, comprising at least one electric drive motor, wherein each of the four wheels of the motor vehicle comprises a service brake for holding the respective wheel.

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