Method for starting up a vehicle, brake system and vehicle

Abstract

In a method for limiting a maximum brake pressure when starting up a vehicle, if a driver brake pressure is detected in a parking phase (P1) of the vehicle in order to start the vehicle, the maximum brake pressure is electronically limited to an initial pressure (p1) which is lower than a maximum brake pressure when the vehicle (p3) is moving. The invention additionally relates to a brake system having a control unit which is designed to carry out such a method, and to a vehicle having such a brake system.

Description

[0001] ZF Active Safety GmbH

[0002] Our reference: 304456-WO-PCT

[0003] Procedure for putting a vehicle, braking system and vehicle into operation

[0004] The invention relates to a method for starting up a vehicle, in particular one with an automatic transmission. The invention further relates to a braking system for a vehicle, in particular one with an automatic transmission, comprising a control unit configured to perform such a method. The invention further relates to a vehicle, in particular one with an automatic transmission, comprising such a braking system.

[0005] To start a vehicle with an automatic transmission, it is usually necessary to press the brake pedal so that the ignition can be triggered and the vehicle or its engine can start.

[0006] Driven by an irrational need for safety, drivers often apply the brakes unnecessarily hard to ensure the vehicle remains stationary. This subjects the braking system to unnecessarily high stress, which can lead to increased wear.

[0007] The object of the invention is to provide a method for starting a vehicle that reduces wear on the braking system. A further object of the invention is to provide a braking system and a vehicle with such a braking system in which the wear on the braking system is reduced when starting the engine.

[0008] The problem is solved by a method for limiting the maximum brake pressure during the start-up of a vehicle, especially one with an automatic transmission, by the step:

[0009] a) If a driver brake pressure is detected during a parking phase of the vehicle in order to start the vehicle, the maximum brake pressure will be electronically limited to an initial pressure that is lower than a maximum brake pressure when the vehicle is moving.

[0010] For the purposes of the invention, maximum brake pressure is understood to be the maximum pressure applied to the vehicle's brakes at a given time, regardless of the driver's brake pressure or braking request, which is detected, for example, by actuating the brake pedal. During the parking phase, the vehicle is stationary and the vehicle's parking brake is engaged.

[0011] It was discovered according to the invention that high brake pressures are not required to hold the vehicle stationary during the parking phase. By limiting the maximum brake pressure to a correspondingly low initial pressure during commissioning, regardless of whether the driver's braking request would actually correspond to a higher brake pressure, the loads to which the braking system is subjected are also effectively limited. In this way, the braking system is only subjected to a maximum load that prevents unnecessarily high wear of the braking system, regardless of the level of driver braking pressure, i.e., regardless of how hard the driver presses the brake pedal.

[0012] According to one embodiment, the initial pressure to which the maximum braking pressure is limited is at least 25% lower than the maximum braking pressure when the vehicle is in motion, in order to effectively reduce the load and thus the wear of the braking system.

[0013] According to a further embodiment, after being limited to the initial pressure, the brake pressure is increased to an intermediate pressure after a defined period, in particular measured from the detection of an initial driver braking request. This intermediate pressure is lower than the maximum brake pressure when the vehicle is moving, in particular by at least 20%. Thus, even in the phase after the vehicle has been started but is still stationary, the load on the brake system is limited and its wear is reduced accordingly.

[0014] The period can range from 1 to 3 seconds. This corresponds to the length of time a driver typically maintains excessive pressure on the brake pedal after ignition before regaining the confidence that the vehicle can be held stationary with less brake pressure. Additionally or alternatively, the initial pressure can be gradually and continuously increased to the intermediate pressure, particularly linearly. This ensures that the maximum brake pressure also increases gradually and continuously, thus preventing sudden pressure surges that could cause excessive wear.

[0015] In one embodiment, an activated parking brake of the vehicle is only released when the maximum brake pressure is limited to the intermediate pressure. This ensures that the brake pressure is sufficiently high to reliably hold the vehicle stationary even when the parking brake is deactivated.

[0016] Furthermore, it may be provided that the maximum brake pressure is increased to the maximum brake pressure when the vehicle starts moving and / or as soon as an acceleration request from the driver is detected. This ensures that full brake pressure is available as soon as the vehicle starts moving.

[0017] In another embodiment, the intermediate pressure is determined based on the vehicle's inclination. The inclination corresponds to the gradient of the road surface or the standing surface on which the vehicle is parked. In this way, the brake pressure is sufficiently high to reliably hold the vehicle stationary on an inclined plane with the parking brake deactivated.

[0018] Furthermore, the intermediate pressure can remain constant until the vehicle starts moving and / or until an acceleration request from the driver is detected.

[0019] According to one embodiment, the initial pressure is determined depending on the inclination of the vehicle in order to adapt the maximum braking power to the current vehicle position at this point in time.

[0020] The procedure can be performed with a brake-by-wire braking system.

[0021] According to the invention, to solve the above-mentioned problem, a braking system for a vehicle, in particular with an automatic transmission, is also provided with a control unit which is designed to carry out the inventive method with the aforementioned advantages, in particular with a brake-by-wire braking system.

[0022] Furthermore, according to the invention, a vehicle, in particular with automatic transmission, is also provided to solve the above-mentioned problem, with a braking system according to the invention with the above-mentioned advantages, in particular a brake-by-wire braking system.

[0023] Further advantages and features will become apparent from the following description and the accompanying drawings. These show:

[0024] - Figure 1 shows a schematic representation of a vehicle according to the invention with a braking system according to the invention, and

[0025] - Figure 2 shows a diagram of the method according to the invention.

[0026] The detailed description below, in conjunction with the accompanying drawings, in which identical numbers refer to identical elements, is intended to describe various embodiments of the disclosed subject matter and is not meant to represent the only embodiments. Each embodiment described in this disclosure serves only as an example or illustration and should not be construed as preferable or advantageous over other embodiments.

[0027] All features disclosed below with reference to the exemplary embodiments and / or the accompanying figures can be combined alone or in any subcombination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0028] Figure 1 shows a vehicle 10 with a braking system 20, which is standing on a roadway 22.

[0029] The roadway 22 is inclined at an angle α. Accordingly, the vehicle 10 also has an inclination α to the horizontal. The vehicle 10 has a parking brake 24, for example in the form of an electronic parking brake, which is designed to hold the vehicle 10 stationary during a parking phase.

[0030] Furthermore, vehicle number 10 has an automatic transmission.

[0031] The braking system 20 has a brake pedal 26, with which a driver can communicate his braking request to the braking system 20 and accordingly apply brake pressure to the brakes (not shown) of the braking system 20.

[0032] In this context, vehicle 10 also has an accelerator pedal (not shown) with which a driver can communicate his acceleration request to vehicle 10 and accelerate vehicle 10 accordingly.

[0033] In the present embodiment, the braking system 20 is designed as a brake-by-wire braking system.

[0034] In principle, however, the braking system 20 can be any braking system.

[0035] In all embodiments, the braking system 20 has a control unit 28 which is configured to execute a method for limiting a maximum brake pressure when the vehicle 10 is put into operation, which is explained below with reference to Figure 2.

[0036] The control unit 28 can be part of an on-board computer of the vehicle 10.

[0037] The graph shown in Figure 2 depicts the course of several parameters over time t.

[0038] Up to time b, vehicle 10 is in parking phase P1, in which vehicle 10 is stationary and the parking brake 24 is activated.

[0039] The state of the parking brake 24 is illustrated here by curve 40, where the upper level represents the activated state and the lower level the deactivated state of the parking brake 24. At time ti, the parking brake 24 changes from the activated state to the deactivated state.

[0040] Between time ti and h, the vehicle 10 is in the standstill phase P2, in which the vehicle 10 remains stationary, but the parking brake 24 is released.

[0041] From time t2 onwards, vehicle 10 is in driving phase P3, in which the speed of vehicle 10 is greater than zero.

[0042] The speed of vehicle 10 is illustrated here by curve 50 and shows an acceleration of vehicle 10 in driving phase P3, which occurs, for example, due to an acceleration request from the driver and / or a rolling start of vehicle 10 due to the incline a.

[0043] In this context, curve 60 illustrates the state of the automatic transmission, with the upper level representing (parking) gear "P" and the lower level representing (driving) gear "D". In the illustrated embodiment, gear "P" changes to gear "D" during the parking phase P1.

[0044] Curve 70 illustrates the course of the maximum brake pressure. The maximum brake pressure is an electronically preset value from control unit 28, limiting the maximum pressure that can be applied to the brakes, regardless of the driver's actual braking request.

[0045] An exemplary, very typical progression of the driver's braking request or the force with which the brake pedal 26 is actuated is illustrated in curve 80, while the progression of the actual brake pressure applied to the brakes during a start and driving off is shown according to an example in curve 90.

[0046] The exact way in which the maximum brake pressure is limited when the vehicle 10 is put into operation will now be explained.

[0047] At time to, the vehicle 10, or rather its on-board electronics, is already activated and detects an initial driver braking request at time to, which signals to the vehicle 10 that the driver wants to start the vehicle 10 and then drive off. In other words, the driver presses the brake pedal 26 in order to then engage gear "D".

[0048] At this point, the maximum brake pressure is increased from a base value Po to an initial pressure pi.

[0049] The base value po can be, for example, 0 bar.

[0050] The initial pressure pi is 40 bar.

[0051] In principle, the initial pressure pi can be arbitrarily large, as long as it is lower than the maximum brake pressure p3 when the vehicle is moving, and in particular by at least 25%. The pressure exerted by the driver on the brake pedal, as can be seen in curve 80, is extremely high and would correspond to a significantly higher brake pressure than either pi or p2.

[0052] In this context, the maximum brake pressure p3 for a moving vehicle is 100 bar.

[0053] Furthermore, the initial pressure pi can be defined depending on the inclination a. For example, the initial pressure pi is 40 bar for an inclination a up to 14° and 50 bar for an inclination a over 14°.

[0054] Over a period At of 2 seconds, the maximum brake pressure is now increased linearly from the initial pressure pi to an intermediate pressure pz, for example.

[0055] In an alternative embodiment, the initial pressure pi can be increased to the intermediate pressure p3 in any way, in particular steadily and continuously.

[0056] Furthermore, the period At can be of any length, however a value between 1 and 3 seconds is preferred.

[0057] The intermediate pressure p3 is 60 bar and remains constant until time t3.

[0058] In principle, the intermediate pressure pz can be arbitrarily large, as long as it is higher than the initial pressure pi and lower than the maximum brake pressure p3 when the vehicle is in motion, in particular by at least 20%. Furthermore, the intermediate pressure p2 can be set depending on the inclination a. For example, the intermediate pressure p2 is 60 bar for an inclination a up to 14° and 70 bar for an inclination a over 14°.

[0059] In this context, the control unit 28 is configured to block the deactivation of the parking brake 24 as long as the maximum brake pressure is below the intermediate pressure p2.

[0060] At time t2, when the vehicle 10 starts moving, the maximum brake pressure is increased from the intermediate pressure p2 to the maximum brake pressure when the vehicle is moving p2.

[0061] In the illustrated embodiment, curve 90, which represents the actual brake pressure applied to the brakes, initially follows the curve of the maximum brake pressure, illustrated by curve 70, even though the driver's braking request here forms a pressure request peak 100 that is far above the maximum brake pressure. This means that the maximum brake pressure applied to the brakes is limited to the maximum brake pressure in this range.

[0062] After some time following t0, when the actual driver braking request has fallen below the maximum brake pressure, curve 80 is identical to curve 90. In other words, in this range, the actual brake pressure applied to the brakes corresponds to the actual driver braking request.

[0063] If the driver continued to apply very strong pressure to the brake pedal, the actual brake pressure (curve 90) could increase along curve 70 and then remain constant until the driver finally reduces the pressure on the brake pedal, causing the pressure to fall below curve 70.

[0064] In this way, a method, a vehicle 10, and a braking system 20 are provided that ensure that the actual load on the braking system 20 does not exceed the value specified by the maximum brake pressure, thereby significantly reducing the wear of the braking system compared to corresponding conventional methods, vehicles, and braking systems. In particular, pressure request peaks 100 during pressurization are capped, which, especially when starting up the vehicle 10, would correspond to the driver's braking request but are unnecessarily high to keep the vehicle 10 stationary.

[0065] Thus, the maximum braking pressure applied to the brakes and therefore the maximum load on the braking system 20 is effectively limited via the maximum braking pressure.

Claims

Patent claims 1. Method for limiting a maximum brake pressure during the start-up of a vehicle (10), in particular with an automatic transmission, comprising the step: a) when a driver brake pressure is detected in a parking phase (P1) of the vehicle (10) to start the vehicle (10), the maximum brake pressure is electronically limited to an initial pressure (p1) which is lower than a maximum brake pressure when the vehicle is moving (p3).

2. Method according to claim 1, characterized in that the initial pressure (p1) to which the maximum brake pressure is limited is at least 25% lower than the maximum brake pressure when the vehicle is moving (pa).

3. Method according to claim 1 or 2, characterized in that the brake pressure, after being limited to the initial pressure (p1), is increased to an intermediate pressure (p2) from a defined period of time (At), in particular measured from the detection of an initial driver braking request, wherein the intermediate pressure (p2) is lower than the maximum brake pressure when the vehicle is moving (p3), in particular by at least 20%.

4. Method according to claim 3, characterized in that the time period (At) is between 1 and 3 seconds.

5. Method according to claim 3 or 4, characterized in that the initial pressure (p1) is increased steadily and continuously to the intermediate pressure (p2), in particular linearly.

6. Method according to one of claims 3 to 5, characterized in that an activated parking brake (24) of the vehicle (10) is only released when the maximum brake pressure is limited to the intermediate pressure (p2).

7. Method according to one of claims 3 to 6, characterized in that the maximum brake pressure is increased to the maximum brake pressure when the vehicle (10) starts moving and / or as soon as an acceleration request from the driver is detected.

8. Method according to one of claims 3 to 7, characterized in that the intermediate pressure (p2) is determined as a function of the inclination (a) of the vehicle (10).

9. Method according to one of claims 3 to 8, characterized in that the intermediate pressure (p2) remains constant until the vehicle (10) starts moving and / or until an acceleration request from the driver is detected.

10. Method according to one of the preceding claims, characterized in that the initial pressure (p1) is determined as a function of the inclination (a) of the vehicle (10).

11. Method according to one of the preceding claims, characterized in that the method is carried out in a brake-by-wire braking system.

12. Braking system (20) for a vehicle (10), in particular with automatic transmission, comprising a control unit (28) configured to perform the method according to one of the preceding claims, in particular with a brake-by-wire braking system.

13. Vehicle (10), in particular with automatic transmission, with a braking system (20) according to claim 12, in particular a brake-by-wire braking system.

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