Method for stopping a vehicle comprising a drive unit and a braking device and vehicle for carrying out such a method

Abstract

Method for autonomously braking a vehicle comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), in which a device is provided for determining the instantaneous speed v(t) of the vehicle, wherein for braking the vehicle below a predeterminable limit speed v threshold the braking torque T Brake (t) is increased by means of a control unit, characterized in that - the braking torque T Brake (t) is increased linearly with a gradient (dT Brake (t) / dt)1 = k1, as soon as a current speed v(t) of the vehicle is detected which exceeds the specified limit speed v threshold where k1 is a constant, and the braking torque T Brake (t) additionally by an amount (dT Brake(t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k 1 + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle.

Description

[0001] The invention relates to a method for autonomous braking of a vehicle comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), in which a device is provided for determining the instantaneous speed v(t) of the vehicle, wherein for braking the vehicle below a predeterminable limit speed v threshold the braking torque T Brake (t) is increased by means of a control unit.

[0002] Such a process is described, for example, in German patent application DE 10 2017 204 639 A1. Similar processes are also known from the publications DE 10 2007 000 195 A1, DE 10 2015 119 773 A1, DE 10 2019 112 455 A1, and DE 100 47 048 A1.

[0003] Furthermore, the invention relates to a vehicle for carrying out such a method.

[0004] A drive unit of the type mentioned can, in principle, be any torque source for driving a vehicle, in particular an internal combustion engine. Within the scope of the present invention, the term "internal combustion engine" encompasses gasoline engines and diesel engines, but also hybrid internal combustion engines that utilize a hybrid combustion process, as well as hybrid drives that, in addition to the internal combustion engine, comprise at least one further torque source for driving a motor vehicle, for example, an electric motor that can be connected to or is connected to the internal combustion engine and that delivers power instead of or in addition to the internal combustion engine.

[0005] Modern vehicles have braking systems, i.e. braking devices, that operate autonomously or semi-autonomously to slow the vehicle down and regulate its speed. Autonomously operated braking systems are used in autonomously driving vehicles where the driver has no or at most very limited influence on the driving maneuvers performed by the vehicle. Semi-autonomously operated braking systems can initiate a braking maneuver in certain driving situations without the driver having to take active action, even if they are behind the wheel. Examples of this are adaptive cruise control, which uses targeted braking interventions to ensure that a certain distance from the vehicle in front is not undercut. In collision protection systems, braking is initiated automatically if an impact with an object, in particular a vehicle, is expected.Further applications of semi-autonomous braking systems include traffic jam assistants, where the driver does not need to accelerate or decelerate the vehicle below a certain speed, especially in traffic jams. Furthermore, braking systems are operated autonomously in parking assistants, which independently maneuver the vehicle into a parking space or garage. Another example of autonomous or semi-autonomous stopping of a vehicle is the precise positioning of the vehicle as a preparatory measure for parking, in order to facilitate or enable the subsequent parking maneuver for the driver.

[0006] In individual cases, the autonomous and semi-autonomous stopping and braking of the vehicle are uniformly referred to as autonomous stopping and braking of the vehicle within the scope of the present invention.

[0007] For comfort reasons, braking noise, which the driver regularly perceives as a groan, should be minimized or eliminated as much as possible. For this reason, the goal is to keep the braking process as short as possible, although, for comfort reasons, a smooth deceleration is preferred by the driver. A compromise is necessary.

[0008] State-of-the-art braking systems found in modern vehicles are often hydraulically or pneumatically operated. Such braking systems have a relatively low pressure resolution of the pressure medium, meaning they can only be operated with a minimum braking torque that deviates more or less significantly from 0 Nm. Depending on the braking system, the minimum braking torque is between 30 Nm and 50 Nm. If a braking torque below this braking torque is requested, the braking system will not respond. This results in a situation where a vehicle traveling at low speed can only be braked relatively abruptly, as at least the minimum braking torque must be used, even if a lower braking torque would be sufficient.In addition, it may happen that the vehicle rolls for a certain period of time even though braking has been initiated, which is problematic from a safety perspective.

[0009] In addition to the loss of comfort, this also involves other disadvantages. As already mentioned, the vehicle's current speed plays a very important role in braking and the braking torque provided. The vehicle's speed can be determined, for example, using incremental encoders. These produce signals that are passed on to a control unit, which in turn controls the braking system based on the determined vehicle speed. The control unit of the vehicle in question often uses a so-called PI controller (proportional-integral controller), which consists of a proportional element and an integrating element.PI controllers are part of a linear control concept, whereby the above-described property of hydraulically or pneumatically operated braking systems, namely that they only react above a certain brake pressure, represents a discontinuity that is difficult to control with PI controllers despite the integrating element. Since the PI controller is a continuous controller, at low speeds it can happen that the incremental encoder does not produce a speed signal for a certain period of time, even though the vehicle is moving, and the PI controller no longer has a reference variable and does not know whether the vehicle is moving or not. If, for example, an autonomously moving vehicle is to be driven into a garage or parking space, this can lead to the situation where the vehicle comes to a stop before reaching the intended position (target position), even though it still needs to be moved at a low speed to reach the target position.In this case, the control unit releases the brakes and the vehicle accelerates, only to then be braked again with the minimum braking torque already mentioned above. This results in an undesirable sequence of acceleration and braking processes. This sequence of acceleration and braking processes can be intensified if the vehicle is accelerated due to external influences such as a gust of wind or the slope of the parking space. Another point is that when the vehicle transitions from higher to lower speeds, which will be referred to below as crawling speed, the friction, particularly between the vehicle's wheels and the ground, changes from dynamic to static, which changes the vehicle dynamics and makes controlling the braking processes even more difficult.

[0010] A method for resolving the problem described above is described in German patent application DE 10 2017 204 639 A1. When the vehicle's speed falls below a threshold, a control unit is used to decelerate the vehicle moving at low speed by increasing the drive torque transmitted to the drive train and increasing the braking torque acting on the vehicle's wheels.

[0011] Against the background of the above, it is an object of the present invention to provide a method according to the preamble of claim 1, with which the autonomous braking of a vehicle moving at low speed is improved.

[0012] A further sub-object of the present invention is to provide a vehicle for carrying out such a method.

[0013] The first sub-task is solved by a method for autonomously braking a vehicle comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), in which a device is provided for determining the instantaneous speed v(t) of the vehicle, wherein for braking the vehicle below a predeterminable limit speed v threshold the braking torque T Brake (t) is increased by means of a control unit, and which is characterized in that the braking torque T Brake (t) is increased linearly with a gradient dT Brake (t) / dt = k1, as soon as a current speed v(t) of the vehicle is detected, which exceeds the specified limit speed v thresholdfalls below, where k1 is a constant, and the braking torque TBrake(t) is additionally increased by an amount (dTBrake(t) / dt)3 with (dTBrake(t) / dt)3 = k3*a(t), so that: dTBrake(t) / dt =k1 + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle. .

[0014] The braking method according to the invention decelerates the vehicle if the vehicle speed v(t) exceeds a predetermined limit speed v threshold falls below.

[0015] The braking torque T Brake (t) is continuously increased by a control unit with a constant gradient dT Brake (t) / dt = k1.

[0016] The braking procedure according to the invention ensures smooth yet rapid deceleration. The control system is comparatively simple, i.e., straightforward, since current operating parameters of the vehicle, such as speed, acceleration, or, when using an internal combustion engine as the drive unit, the currently engaged transmission gear, are not taken into account.

[0017] The method according to the invention improves the autonomous braking of a vehicle moving at low speed. The method according to the invention thus solves the first sub-problem underlying the invention.

[0018] Further advantageous embodiments of the method according to the invention are discussed in connection with the subclaims.

[0019] Embodiments of the method in which the vehicle is stopped by braking are advantageous.

[0020] This process variant is used, for example, as a preparatory measure when parking, especially for precisely positioning the vehicle before parking. This makes the subsequent parking maneuver easier for the driver or prepares for or initiates autonomous parking of the vehicle.

[0021] Another application is stop-and-go traffic, such as traffic jams on highways and country roads. In inner-city traffic, stop-and-go traffic is no longer the exception, but rather the rule, due to existing and uncoordinated traffic lights and increased traffic volumes. Other application areas include level crossings with barriers and similar systems.

[0022] Embodiments of the method are advantageous in which, when initiating a braking process, a balance of forces between the braking force, the driving force and the inertial force acting on the vehicle is initially assumed.

[0023] If this requirement is met, the method according to the invention works particularly accurately, ie with the smallest deviation or the smallest error.

[0024] However, if the speed v(t) of the vehicle was higher than originally assumed when the braking process was initiated, or if the vehicle accelerates with a(t) > 0 during the braking process, it is advantageous to increase the braking torque in addition to the linear increase by further amounts that take these special circumstances into account.

[0025] Therefore, embodiments of the method are advantageous in which the braking torque T Brake (t) additionally by an amount (dT Brake(t) / dt)2 is increased with (dT Brake (t) / dt)2 = k2*v(t), so that: dT Brake (t) / dt = k1 + k2*v(t), where k2 is a constant.

[0026] In this context, embodiments of the method are advantageous in which the braking torque T Brake (t) only if additionally by an amount (dT Brake (t) / dt)2 is increased if the speed v(t) of the vehicle was higher than originally detected when initiating a braking process.

[0027] In this context, embodiments of the method are also advantageous in which the braking torque T Brake (t) only if additionally by an amount (dT Brake (t) / dt)2 is increased if the speed v(t) of the vehicle when initiating a braking process was higher than the specified limit speed v threshold .

[0028] Furthermore, embodiments of the method are advantageous in which the braking torque T Brake(t) additionally by an amount (dT Brake (1) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k1 + k2*v(t) + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle.

[0029] In this context, embodiments of the method are advantageous in which the braking torque T Brake (t) only if additionally by an amount (dT Brake (t) / dt)3 is increased if the vehicle is accelerated during braking with a(t) > 0.

[0030] Embodiments of the method are advantageous in which the speed v(t) of the vehicle is above the predetermined limit speed v threshold controlled by closed-loop control.

[0031] The second sub-task, namely to provide a vehicle for carrying out a method of the above type, is achieved by a vehicle comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), with a device for determining the instantaneous speed v(t) of the vehicle and a control unit for autonomously braking the vehicle below a predeterminable limit speed v threshold , and which is characterized in that the control unit is arranged in such a way that the braking torque T Brake (t) is increased linearly with a gradient (dT Brake (t) / dt)1 = k1, as soon as a current speed v(t) of the vehicle is detected which exceeds the specified limit speed v thresholdfalls below, where k1 is a constant, and the braking torque TBrake(t) is additionally increased by an amount (dTBrake(t) / dt)3 with (dTBrake(t) / dt)3 = k3*a(t), so that: dTBrake(t) / dt =k1 + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle.

[0032] What has already been said for the method according to the invention also applies to the vehicle according to the invention, which is why reference is generally made here to the statements made with regard to the method variants.

[0033] Embodiments of the vehicle are advantageous in which the control unit is designed in such a way that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)2 is increased with (dT Brake (t) / dt)2 = k2*v(t), so that: dT Brake (t) / dt = k1 + k2*v(t), where k2 is a constant.

[0034] In this context, embodiments of the vehicle are advantageous in which the control unit is set up in such a way that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k1 + k2*v(t) + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle.

[0035] Embodiments of the vehicle in which the control unit is part of an engine control system are advantageous.

[0036] In the following, the invention is explained with reference to two diagrams according to the Fig. 1 and Fig. 2 is explained in more detail. Here: Fig. 1 the vehicle speed v(t) over time t, and Fig. 2 the braking torque T Brake (t) over time t.

[0037] Fig. Figure 1 shows the vehicle speed v(t) versus time t, with time t on the abscissa and the vehicle speed v(t) on the ordinate.

[0038] Both the actual speed curve (curve A) and the target speed curve (curve B) are plotted.

[0039] Fig. 2 shows the braking torque T Brake (t) over time t, where time t is on the abscissa and the braking torque T Brake (t) are plotted on the ordinate axis.

[0040] If the current vehicle speed v(t) reaches a specified limit speed v threshold To brake the vehicle, the braking torque T Brake (t) is increased by means of a control unit.

[0041] In this case, the braking torque T Brake (t) is not only increased linearly, but also by additional amounts. Reference symbol a(t) acceleration of the vehicle k1 constant, first constant k2 constant, second constant k3 constant, third constant T Brake (t) Braking torque, braking torque as a function of time (dT Brake (t) / dt)1 first gradient (dT Brake (t) / dt)2 second gradient, additional amount (dT Brake (t) / dt)2 third gradient, additional amount t time v(t) speed of the vehicle v threshold predeterminable speed limit

Claims

[1] Method for autonomously braking a vehicle comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), in which a device is provided for determining the instantaneous speed v(t) of the vehicle, wherein for braking the vehicle below a predeterminable limit speed v threshold the braking torque T Brake (t) is increased by means of a control unit, characterized by , that - the braking torque T Brake (t) is increased linearly with a gradient (dT Brake (t) / dt)1 = k1, as soon as a current speed v(t) of the vehicle is detected which exceeds the specified limit speed v threshold where k1 is a constant, and the braking torque T Brake (t) additionally by an amount (dT Brake(t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k 1 + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle. [2] Method according to claim 1, characterized by that the vehicle is stopped by braking. [3] Method according to claim 1 or 2, characterized by that when initiating a braking process, an equilibrium of forces is initially assumed between the braking force, the driving force and the inertial force acting on the vehicle. [4] Method according to one of the preceding claims, characterized by that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)2 is increased with (dT Brake (t) / dt)2 = k2*v(t), so that: dT Brake (t) / dt = k1 + k2*v(t), where k2 is a constant. [5] Method according to claim 4, characterized by that the braking torque T Brake(t) only if additionally by an amount (dT Brake (t) / dt)2 is increased if the speed v(t) of the vehicle was higher than originally detected when initiating a braking process. [6] Method according to claim 4, characterized by that the braking torque T Brake (t) only if additionally by an amount (dT Brake (t) / dt)2 is increased if the speed v(t) of the vehicle when initiating a braking process was higher than the specified limit speed v threshold . [7] Method according to one of claims 4 to 6, characterized by that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k1 + k2*v(t) + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle. [8] Method according to claim 1 or 7, characterized by that the braking torque T Brake(t) only if additionally by an amount (dT Bake (t) / dt)3 is increased if the vehicle is accelerated during braking with a(t) > 0. [9] Method according to one of the preceding claims, characterized by that the speed v(t) of the vehicle is above the specified limit speed v threshold controlled by closed-loop control. [10] Vehicle for carrying out a method according to one of the preceding claims, comprising a drive unit with which a torque can be introduced into a drive train of the vehicle, and a braking device with which the vehicle can be braked by providing a generated braking torque T Brake (t), with a device for determining the instantaneous speed v(t) of the vehicle and a control unit for autonomously braking the vehicle below a predeterminable limit speed v threshold , characterized by , that - the control unit is set up in such a way that the braking torque T Brake (t) is increased linearly with a gradient (dT Brake (t) / dt)1 = k1, as soon as a current speed v(t) of the vehicle is detected which exceeds the specified limit speed v threshold where k1 is a constant, and - the control unit is set up in such a way that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k 1 + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle. [11] Vehicle according to claim 10, characterized by that the control unit is set up in such a way that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)2 is increased with (dT Brake (t) / dt)2 = k2*v(t), so that: dT Brake (t) / dt = k 1 +k2*v(t), where k2 is a constant. [12] Vehicle according to claim 11, characterized by that the control unit is set up in such a way that the braking torque T Brake (t) additionally by an amount (dT Brake (t) / dt)3 is increased with (dT Brake (t) / dt)3 = k3*a(t), so that: dT Brake (t) / dt = k1 + k2*v(t) + k3*a(t), where k3 is a constant and a(t) is the instantaneous acceleration a(t) of the vehicle. [13] Vehicle according to one of claims 10 to 13, characterized by that the control unit belongs to an engine control unit.

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