Method for preventing a vehicle from rolling backward when starting from a standstill on a slope

Abstract

Method for preventing a vehicle from rolling backwards when starting from a standstill on a slope, - wherein in an initial situation the vehicle is held by an automatic holding brake torque (M Halt ) generating and activated hold function is held at a standstill - and where in the initial situation a creep moment (M Kriech ) of the vehicle drive is at least approximately 0 Nm - and where in the initial situation a brake pedal (B Fahrer ) is activated, - wherein the vehicle is initially located on an inclined road surface and is subject to a measured downhill force (K Hang is exposed, - where, upon detection of a start-up request, the creep torque (M Kriech ) of the vehicle drive is automatically established, independently of any driving and / or clutch pedal operation, characterized by the fact that - the holding braking torque (M Halt) upon reaching a threshold creep moment (M Schwell ) of the vehicle drive is automatically degraded, independently of any driving and / or clutch pedal operation, at a balanced degradation rate, - where the starting time and the starting speed of the vehicle are controlled solely by means of a brake pedal actuation (B Fahrer ) is adjustable without using the accelerator and / or clutch pedal, - where the vehicle occupant's desire to start moving results in a decrease in brake pedal actuation (B Fahrer ) is and - whereby the reduction of the holding braking torque (M Halt ) during the still ongoing and decreasing brake pedal application (B Fahrer ).

Description

[0001] The invention relates to a method for preventing a vehicle from rolling backward when starting from a standstill on a slope, according to the preamble of claim 1. For the prior art, reference is made, by way of example, to DE 10 2016 208 077 A1 and DE 101 51 846 A1 as well as DE 10 2015 226 130 A1, DE 10 2015 226 134 A1 and DE 102 21 835 A1.

[0002] Various brake holding functions are known in vehicles from the state of the art. For example, the brake holding function is used in so-called hill start assist systems. These systems automatically support vehicles when starting on inclines to prevent the vehicle from rolling backwards unintentionally.

[0003] With known hill start assist systems, the brake holding function is only activated above a certain gradient or road incline or gradient, because vehicles with internal combustion engines in particular have a constant creep torque when stationary, which makes the use of a brake holding function obsolete before this limit.

[0004] To then accelerate smoothly from a standstill with the brake hold function activated, the brake hold function is released while the brake pedal is released and the accelerator pedal is depressed. The rate at which the brake hold function is released is represented by a balancing mechanism, whereby the holding brake torque is typically reduced in relation to the available drive torque.

[0005] An exemplary brake holding system is shown in DE 10 2016 208 077 A1. This proposes a method for determining a brake torque reduction parameter for brake torque reduction in a motor vehicle with a brake holding assistant.

[0006] A disadvantage of the current state of the art, however, is that the constantly available creep torque during standstill is energetically inefficient. Furthermore, it is inconvenient for a driver to constantly switch between the brake and accelerator pedals or the clutch pedal when starting from a standstill, especially into a near-standstill speed range, in order to control or modulate the vehicle's speed on an incline.

[0007] The object of the invention is therefore to demonstrate a method for preventing a vehicle from rolling backward when starting from a standstill on a slope, which is as energy-efficient as possible and also ensures greater comfort for a vehicle driver.

[0008] The solution to the problem is achieved by a method for preventing a vehicle from rolling backward when starting from a standstill on a slope, comprising the features of claim 1. Advantageous embodiments and further developments are the subject of the dependent claims.

[0009] In the initial situation, the vehicle is stationary on a slope.

[0010] A holding function that generates a holding braking torque is activated. This holding function is preferably activated automatically when certain boundary conditions, such as a specific road gradient, are present. Furthermore, this holding function is preferably implemented by automatically actuating or controlling a service brake on at least one wheel of the vehicle.

[0011] The holding brake function can, for example, be designed as a so-called hill hold assist or “hill holder”, which is known from the state of the art.

[0012] The vehicle is held stationary by the aforementioned holding function. This effectively prevents the vehicle from rolling backward or downhill while stationary.

[0013] In the aforementioned initial situation, a brake pedal or a similar actuating device for manually operating a service brake is in an actuated position. For example, this actuated position of a brake pedal is achieved by the driver pressing it down with their foot. Preferably, the driver has at least one foot on the brake pedal and actuates it.

[0014] As already mentioned, it is further stipulated that the vehicle is located on a slope or that the road surface on which the vehicle is located has an incline. Because the vehicle is on a road surface with an incline, it is subject to a downward force of gravity, which is counteracted by pressing the brake pedal or by activating the automatic hold function, thus holding the vehicle stationary on the slope. The downward force of gravity is therefore the force that would cause the vehicle to roll down the slope and move from a standstill without the brakes being applied or the hold function being activated.

[0015] It is further stipulated that in the initial situation, the creep torque of the vehicle drive is at least approximately 0 Nm, or that no creep torque is actively applied when the vehicle is stationary.

[0016] This has the particular advantage that, while the vehicle is stationary, no energy is required to generate and maintain a creep torque that is not needed at that moment. Energy can thus be advantageously saved. This is especially beneficial for electric or hybrid vehicles, as the reduced creep torque of 0 Nm while the vehicle is stationary increases or prevents it from decreasing the vehicle's maximum range. For internal combustion engines, this results in lower fuel consumption.

[0017] The first step of the process detects a request to start moving. This request is initiated, in particular, by a vehicle occupant through a gradual release of the brake pedal. For example, if the driver slowly releases the brake pedal, it is assumed that a request to start moving exists.

[0018] However, the desired approach can also be captured by other boundary conditions.

[0019] The data is collected using suitable recording devices, calculations, or sensors.

[0020] Once the driver's request to start moving is detected, a creeping torque is automatically built up, regardless of whether or not the driver operates the accelerator or clutch pedal.

[0021] The creep moment is preferably initiated by a control unit.

[0022] The rate at which the creep moment builds up can be set or calculated, for example, depending on the road gradient. It is also possible to set the rate based on predefined characteristic curves.

[0023] Preferably, the build-up speed is chosen to be relatively high so that a maximum creep moment or a target creep moment is built up as quickly as possible, especially within 300-500 ms (which corresponds to a creep moment of approximately 3000 Nm / s), in order to be able to hold the vehicle at a standstill as far as possible, even with the holding function deactivated and the service brake not applied, or even to cause the vehicle to move.

[0024] The triggering event for the start of the reduction of the holding brake torque, or for the start of a balancing of the holding brake torque as a function of the creep torque or the drive torque, is considered to be the reaching of a threshold creep torque.

[0025] In the context of this invention, a balancing mechanism is a calculation of the rate at which the holding brake torque decreases as a function of various boundary conditions, for example, as a function of the accumulating creep torque or drive torque of the vehicle's drive system. It is preferably provided that the balancing is performed such that the rate at which the holding brake torque decreases is calculated such that, at the point in time when the accumulating creep torque has overcome the aforementioned downhill force, the holding brake torque has decreased to at least approximately 0 Nm.

[0026] This threshold creep torque represents a specific minimum creep torque at which the aforementioned "balancing" begins. Reaching this threshold creep torque is intended to ensure that a starting signal is desired. The creep torque is established after the driver reduces the braking torque. The balancing process begins when this threshold creep torque is reached.

[0027] For robustness reasons, the creep moment is preferably set or determined differently depending on the road slope.

[0028] The aforementioned creep moment is preferably a comparatively low creep moment, which is usually reached within approximately 300 - 500 ms after the creep moment build-up begins.

[0029] The automatic reduction of the holding brake torque, or the commencement of the aforementioned balancing mechanism, is initiated independently of any accelerator and / or clutch pedal actuation. This means that the balancing mechanism, or the reduction of the holding brake torque, begins as soon as the threshold creep torque is reached, without the driver having actuated an accelerator or clutch pedal.

[0030] Furthermore, it is provided that the reduction of the holding braking torque by the holding function occurs during the continued, decreasing deceleration of the brake pedal. Preferably, the start of the reduction of the holding torque is therefore not dependent on a released brake pedal, but only on reaching the aforementioned threshold creep torque.

[0031] Furthermore, it is provided that the starting time and the starting speed of the vehicle can be adjusted solely by means of the force applied to the brake pedal, in particular by a vehicle driver, without the need to operate a driving and / or clutch pedal.

[0032] A driving torque initiated by the driver, particularly by actuating the accelerator and / or clutch pedal, is preferably not required to move the vehicle up to a road gradient of approximately 12% to 20%, as this movement can be achieved solely through creep torque. In other words, the maximum creep torque that can be generated is preferably selected such that the vehicle is able to start moving even on a road gradient between 12% and 20% without a driving torque initiated by the driver.

[0033] This allows the driver to control the starting speed and the point of departure by simply using the brake pedal when approaching an incline. Therefore, to move the vehicle from a standstill on a slope, the driver no longer needs to operate any other pedals, such as the accelerator or clutch. The vehicle's starting speed on an incline can thus be controlled solely by applying the brake pedal. This is particularly convenient when low starting speeds are desired, such as when parking or maneuvering on an incline, as it eliminates the need for the driver to constantly switch between the accelerator or clutch pedal and the brake pedal. Instead, this method enables starting from a standstill with speed control achieved solely through the application of the brake pedal.This means significantly increased comfort.

[0034] The dosing range or dosing period in which the driver can control the starting speed and the starting period preferably begins from the point in time when the holding brake torque falls to the driver's braking torque while the vehicle is moving forward and preferably ends when the driver has completely released the brake pedal.

[0035] At the same time, the claimed method enables an energy-saving hill start capability, which is particularly beneficial for electric vehicles with increased range and for vehicles with an internal combustion engine with fuel savings.

[0036] These and other features are evident not only from the claims and the description but also from the drawings, wherein 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.

[0037] 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.

[0038] The single figure shows a diagram in which a driver's braking request B is displayed over time t. Fahrer through an actuation characteristic of a brake pedal, a holding braking torque M Halt through an automatic holding function and a creep torque M KriechThe vehicle drive system is shown. The temporal relationship between the recorded characteristic curves according to an embodiment of the invention will be explained in more detail.

[0039] In the initial situation, from time 0 to time t1, the vehicle is stationary on a slope or on a road with a gradient, where the vehicle is subject to a certain downhill force K. Hang is exposed.

[0040] Furthermore, in the initial situation (time 0 to time t1) a holding braking torque M is present. Halt by an activated holding function on the service brake of at least one vehicle wheel, in particular of 4 vehicle wheels.

[0041] Furthermore, in the initial situation (time 0 to time t1) there is a constant driver braking request, in that the driver presses the brake pedal B. Fahrer presses down and activates Constancy.

[0042] In the initial situation (time 0 to time t1), the creep moment M is also Kriech at least approximately 0 Nm, or no additional creep torque M is generated. Kriech , which is constantly placed in a stationary position.

[0043] At time t1, the vehicle detects that the driver has initiated a move-away request from a standstill. This move-away request is triggered by the driver releasing the brake pedal B. Fahrer initiated by the vehicle driver at time t1.

[0044] As soon as the start-up request is detected, a creeping torque M is generated. Kriech built into the vehicle's drive system.

[0045] The holding function remains fully intact at time t1 due to the full holding braking torque M. Halt active.

[0046] Only at time t2, when the creep moment MKriech becomes a slope-dependent throttling creep moment M schwellOnce the holding brake torque MHalt is reached, it is reduced. The reduction of the holding brake torque M Halt The holding function is performed with a calculated or balanced degradation rate, in particular depending on the build-up of the creep moment M. Kriech This balancing is carried out in such a way as to determine the rate at which the holding braking torque M decreases. Halt is calculated in such a way that the creep moment M at time t3, at which the accumulating creep moment occurs, is Kriech the downslope force K Hang has reached or overcome the holding braking torque M Halt is completely dissipated or will be dissipated at time t3, i.e., when the creep moment M Kriech is so high that this vehicle, which is subject to the downward force K Hang is exposed without being able to hold an additional brake lever; the holding braking torque M Halt Completely reduced to 0 Nm.

[0047] The rate at which the creeping moment builds up M Kriech As can be seen in the figure, the initial phase is very gradual until the start of the balancing process at time t2. From the start of the balancing process, i.e., at time t2, until the moment is reached that overcomes the downslope force K, the force increases significantly. Hang , i.e., up to time t3, the magnitude of the creep moment M increases Kriech The braking torque M decreases relatively steeply in a short time. Accordingly, the holding torque also drops steeply and rapidly. Halt away.

[0048] Since the creep moment is so high (at time t3) that it exceeds the downslope force K Hang Once the obstacle has been overcome and the vehicle can therefore hold itself stationary on the slope, the curve of the accumulating creep moment M flattens out. Kriech It decreases again slightly. It is designed so that the vehicle, at a maximum road gradient of approximately 20%, still only experiences creeping torque M. KriechIt can be started from a standstill without using a foot pedal.

[0049] At time t 2.1 The decreasing holding braking torque reaches a gradient-dependent or creep torque-dependent torque threshold M Halt'-Schwell .

[0050] For a vehicle driver, it is possible to achieve a certain outcome simply by applying the brake pedal B. Fahrer , to control the vehicle's acceleration speed and the point at which it starts moving from a standstill. This period, in which the driver can only control the vehicle by applying the brake pedal B Fahrer The amount of time the vehicle accelerates is metered is referred to as the metering range D. The metering range D, or the metering period in which the driver can meter the acceleration speed and acceleration time, preferably begins at time t. 2.1 , from which the holding braking torque M Halt on the driver's braking torque B FahrerIt falls while the vehicle is moving forward and preferably ends when the driver has completely released the brake pedal (time t5).

[0051] This dosage allows the driver to do so comfortably, simply by pressing B. Faher to control the braking pedal, the starting speed and the starting time of the vehicle.

[0052] In this specific case, the driver selects the dosage D such that the vehicle already begins to move or accelerate at time t3 at a (for example, constant) speed v. From time +t4, the dosage D by the driver ends, who ends the brake pedal operation at time t5.

Claims

[1] Method for preventing a vehicle from rolling backwards when starting from a standstill on a slope, - wherein in an initial situation the vehicle is held by an automatic holding brake torque (M Halt ) generating and activated hold function is held at a standstill - and where in the initial situation a creep moment (M Kriech ) of the vehicle drive is at least approximately 0 Nm - and where in the initial situation a brake pedal (B Fahrer ) is activated, - wherein the vehicle is initially located on an inclined road surface and is subject to a measured downhill force (K Hang is exposed - where, upon detection of a start-up request, the creep torque (M Kriech ) of the vehicle drive is built up automatically, independently of any driving and / or clutch pedal operation characterized by , that - the holding braking torque (M Halt) upon reaching a threshold creep moment (M Schwell ) of the vehicle drive is automatically degraded, independently of any driving and / or clutch pedal operation, at a balanced degradation rate, - where the starting time and the starting speed of the vehicle are controlled solely by means of a brake pedal actuation (B Fahrer ) is adjustable without using the accelerator and / or clutch pedal, - where the vehicle occupant's desire to start moving results in a decrease in brake pedal actuation (B Fahrer ) is and - whereby the reduction of the holding braking torque (M Halt ) during the still ongoing and decreasing brake pedal application (B Fahrer ). [2] Method according to claim 1, wherein the rate of reduction of the holding braking torque (M Halt ) is calculated such that at time (t3) in which the accumulating creep moment (M Kriech ) the downslope force (K Hang) has overcome the holding braking torque (M Halt ) has been reduced to at least approximately 0 Nm. [3] Method according to claim 1 or 2, wherein the maximum applicable creep moment (M Kriech ) of the vehicle drive is selected in such a way that it enables vehicle movement without the use of the accelerator pedal on inclines of up to 12% - 20%. [4] Method according to one of the preceding claims, wherein the swell creep moment (M Schwell ) is determined depending on the gradient of the roadway. [5] Method according to any of the preceding claims, wherein the rate of increase of the creep moment (M Kriech ) depending on the road gradient and / or by stored characteristic curves. [6] Method according to one of the preceding claims, wherein the setting of the starting time and the starting speed of the vehicle is carried out by means of a brake pedal actuation (B Fahrer) by a vehicle driver within a metering range (D), wherein the metering range (D) begins when the driver's braking torque (B) Fahrer ) the holding braking torque (M Halt ) is reached and the dosing range (D) is terminated when the driver has fully released the brake pedal.

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