GB2461150A

GB2461150A - Vehicle trailer braking system

Info

Publication number: GB2461150A
Application number: GB0908823A
Authority: GB
Inventors: Hardy Haas; Manfred Gerdes; Frank Niewels; Urs Bauer; Armin Verhagen; Volker Mehl; Daniel Fellke; Peter Ziegler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-06-23
Filing date: 2009-05-21
Publication date: 2009-12-30
Anticipated expiration: 2029-05-21
Also published as: DE102008002584A1; GB0908823D0; FR2932754A1; GB2461150B

Abstract

A method for setting a braking system in a vehicle trailer 3, the state of movement of the vehicle trailer 3 is determined, preferably by sensor 13, and in the event of it being at a standstill the vehicle trailer 3 is automatically braked, by braking device 9, 10. The method may be carried out by a closed-loop or open loop control circuit 8. The braking force may be set as a function of slope inclination.

Description

Method for setting a braking system in a vehicle trailer The invention relates to a method for setting a braking system in a vehicle trailer.

Prior art

DE 199 50 034 Al describes a so-called hill-holder function which is used to assist starting, in particular on uphill slopes, in order to prevent undesired rolling back of the vehicle when starting. With the hill-holder function, an additional braking force is produced until a characteristic holding force is reached, which ensures that the vehicle is at a standstill even when there is too little brake pedal actuation by the driver. When the driver releases the brake pedal, the braking force is still maintained for a defined period of time via the hill-holder function, so that the starting is carried out with continuing braking pressure and rolling back of the vehicle is prevented.

However, DE 199 50 034 Al relates only to the starting of a single vehicle. By contrast, in the case of combination vehicles, there is the additional problem that, in particular given a heavy loading state, the trailer on an uphill slope exerts a considerable force on the tractive vehicle, with the result that the starting is made more difficult.

Disclosure of the invention

Proceeding from this prior art, the object on which the invention is based is to facilitate the starting of combination vehicles by simple measures.

This object is achieved according to the invention by the features of the independent claims. The subclaims provide expedient developments.

The method according to the invention relates to the setting of a braking system in a vehicle trailer, in which the state of movement of the vehicle trailer is determined and automatic braking is carried out if the vehicle trailer is at a standstill. This automatic braking procedure on the one hand increases the security, in particular if the trailer is on an inclined road, against undesired rolling away. On the other hand, the starting procedure of the vehicle combination, consisting of tractive vehicle and trailer, is facilitated since the driver of the tractive vehicle is not forced to hold the vehicle combination using the brake. In particular with heavy trailers, when starting on an uphill slope the entire vehicle combination is pulled backwards opposite the starting direction by a component of the weight vector, which in the prior art has to be compensated for on the one hand via the brake pedal actuation by the driver and on the other hand by a correspondingly increased accelerator pedal actuation. With manual gearboxes, however, there is a risk here of increased clutch wear.

By contrast, in the case of the method according to the invention, the downhill force of the trailer is compensated for by the trailer wheel brake, so that the driver of the vehicle combination is not forced to actuate the brake pedal and manually produce a braking force. On the one hand, this increases the security, in particular against undesired rolling back of the entire vehicle combination, on the other hand components in the drive train are stressed considerably less, for example the coupling device between tractive vehicle and trailer, and in the case of a manual gearbox the clutch and in automatic gearboxes the torque-transmitting parts.

The automatic braking procedure in the vehicle trailer can be carried out until a characteristic braking force is reached, which is determined either as a fixed quantity or situation-dependently from the current driving state or the ambient conditions. Thus, it may be expedient to determine the characteristic braking force or the characteristic braking pressure as a function of the slope inclination, in order to ensure that the vehicle trailer stands securely on any current inclination and on the other hand no unnecessarily high braking force has to be expended. The characteristic braking force is automatically set, with optionally a brake pedal actuation which is produced by the driver but does not reach the characteristic braking force and which has an effect on the wheel brake in the trailer being automatically supplemented until the characteristic braking force is reached.

To reduce the braking force or the braking pressure in the vehicle trailer, various criteria can be employed alternatively or cumulatively. One possibility is, for example, the transmission of the driver's desire to set the vehicle combination in motion via a communication device to a closed-loop or open-loop control unit in the vehicle trailer, which unit thereupon produces actuating signals via which the braking pressure in the vehicle trailer is reduced. It is, however, also possible to detect the starting procedure automatically, for example by detecting a starting jerk either in the tractive vehicle and/or in the vehicle trailer, whereupon a reduction of the braking pressure in the vehicle trailer is ensured in analogous fashion to that for the detection of a corresponding driver's desire. The starting jerk is detected either from a rotational movement of at least one wheel in the tractive vehicle and/or in the vehicle trailer, for which corresponding wheel speed sensors are provided. Furthermore, it is also possible to detect a starting jerk via an acceleration sensor in the tractive vehicle or in the vehicle trailer.

The reduction of the braking pressure in the vehicle trailer preferably does not take place abruptly, but according to a decreasing function, in order to ensure a holding braking force in the vehicle trailer at the beginning of the starting procedure as well. In this case, the braking force is reduced gradually over a defined period of time until the value zero is reached. Nevertheless, it is also possible to reduce the braking force immediately, i.e. abruptly, as soon as a corresponding request comes from the driver or the driver's desire to start is detected.

A further aspect of the invention relates to a moving vehicle combination in which it is provided according to the invention that the braking system in the vehicle trailer is automatically actuated in a manner that a speed profile preset by the driver is adhered to. By this means, it is possible, for example, to realise a speed control function on downhill driving, where a speed preset by the driver is automatically adhered to, for which on the one hand the engine power in the tractive vehicle is correspondingly adapted and on the other hand the braking system in the vehicle trailer is actuated in such a way that the vehicle trailer automatically maintains the same speed as the tractive vehicle, and the coupling device between tractive vehicle and vehicle trailer is stressed with little force as far as possible. Optionally, an automatic braking force also acts in the tractive vehicle.

The method according to the invention is carried out in a closed-loop or open-loop control unit which is a constituent of the braking system in the vehicle trailer. As input variables, the closed-loop or open-loop control unit in the vehicle trailer is either supplied with sensor signals which come from sensors in the vehicle trailer and/or in the tractive vehicle, or has the driver's requests directly transmitted to it via a communication device between tractive vehicle and vehicle trailer. As output variables, the closed-loop or open-loop control unit delivers actuating signals which are applied to the braking system, that is to say the wheel brakes in the vehicle trailer.

To carry out the method, the trailer braking system is equipped with the closed-loop or open-loop control unit, furthermore with the braking device and also with at least one sensor for detecting the current state of movement of the vehicle trailer.

The sensor is preferably an at least one wheel rotational-speed sensor, preferably an active rotational-speed sensor, which is capable of sensing both positive and negative wheel speeds. The sensor system as a constituent of the trailer braking system may comprise, alternatively or additionally to the wheel rotational-speed sensor, also acceleration sensors, in particular longitudinal-acceleration sensors, transverse-acceleration sensors and/or vertical-acceleration sensors, via which both the current slope inclination is to be detected and a starting jerk, the latter optionally also being detectable via the wheel rotational-speed sensors.

In the wider sense, the sensor system in the vehicle trailer also comprises the communication device via which the closed-loop or open-loop control unit in the vehicle trailer communicates with a corresponding closed-loop or open-loop control unit in the tractive vehicle, both data acquired by sensory means from the tractive vehicle and a desire specified directly by the driver being transmittable via the communication device.

Further advantages and expedient embodiments can be found in the further claims, the description of the figures, and the drawings, in which: Fig. 1 shows a schematic illustration of a vehicle combination, consisting of tractive vehicle and vehicle trailer, a trailer braking system for automatically braking the trailer being installed in the vehicle trailer, Fig. 2 shows a flow chart with the method steps for setting the trailer braking system for automatically braking the trailer.

The vehicle combination 1 illustrated in Fig. 1 consists of a tractive vehicle 2 and a vehicle trailer 3, which is connected to the tractive vehicle via a drawbar 4 and a trailer coupling 5. In the tractive vehicle 2 there is located a closed-loop or open-loop control unit 6, which is supplied with information from sensors in the tractive vehicle as input variables and which applies manipulated variables to the actuator system in the tractive vehicle, for example the wheel brakes in the tractive vehicle.

The vehicle trailer 3 is equipped with a trailer braking system 7, by which the vehicle trailer 3 can be braked, to be precise both automatically, that is without direct exertion of influence by the driver, and in dependence on the brake pedal actuation by the driver in the tractive vehicle 2. The trailer braking system 7 comprises, as the actuator system, wheel brakes 9 and 10 on the wheels 11 and 12 of the vehicle trailer 3, and furthermore a closed-loop or open-loop control unit 8 and a sensor device 13.

The wheel brakes 9 and 10 which constitute the braking device are set via actuating signals of the closed-loop or open-loop control unit 8 in the vehicle trailer 3. The sensor device 13 in the vehicle trailer 3 supplies the closed-loop or open-loop control unit 8 with sensor signals which contain information about the current state of movement of the vehicle trailer.

The sensor device 13 is constituted, for example, by wheel speed sensors, it being the case that either only one wheel speed sensor is provided on a wheel 9 or 10 or-each wheel is equipped with respectively one wheel rotational-speed sensor or wheel speed sensor. The wheel speed sensor(s) allow, in particular, both the detection of a positive and a negative wheel speed.

Additionally or alternatively, the sensor device 13 can also include acceleration sensors, in particular a longitudinal-acceleration sensor and a vertical-acceleration sensor, which detect the longitudinal acceleration and vertical acceleration in a coordinate system fixed to the trailer.

The closed-loop or open-loop control unit 8 in the vehicle trailer 3 communicates with the closed-loop or open-loop control unit 6 in the tractive vehicle 2, the two closed-loop or open-loop control units constituting a communication device via which information is exchanged in both directions. It is thus possible to transmit sensor information or the driver's desire from the tractive vehicle to the vehicle trailer, and conversely sensor or computer information can be transmitted from the vehicle trailer to the tractive vehicle.

Fig. 2 illustrates an exemplary flow chart for carrying out the method for automatically setting a braking force in the vehicle trailer and releasing the braking force. In the first method step Vi, it is firstly ascertained whether the vehicle trailer is at a standstill. This takes place via an inquiry as to whether the vehicle trailer speed v is equal to zero or less than or equal to a small threshold value Vk, which is 0.01 rn/s for example. For this purpose, it is possible to use information from the wheel rotational-speed sensors in the vehicle trailer, which is evaluated in the closed-loop or open-loop control unit in the vehicle trailer. If the inquiry according to method step Vi is not fulfilled, the vehicle trailer is not at a standstill and the method is not initiated; in this case, the no branch is followed back to the beginning of the method step Vl again and a new inquiry is carried out at cyclical intervals.

In contrast, if the inquiry according to method step Vi shows that the vehicle trailer is at a standstill, the method proceeds to the next method step V2, in which it is checked whether the vehicle trailer is on an inclined road. The road angle a can be determined from the information from acceleration sensors which are part of the sensor device of the vehicle trailer. If the vehicle trailer is on an inclined road, the value for the longitudinal acceleration is aX,A > 0 owing to a weight component. From the measured longitudinal acceleration aX,A and the measured vertical acceleration the angle of inclination a of the road can be determined from a known trigonometric relationship.

In the next method step V3, the braking pressure Psr,A for the wheel brakes in the vehicle trailer as a function of the angle of inclination a is determined and set in the wheel brakes. This has the advantage that a varyingly high, characteristic holding or braking force can be set depending on the angle of inclination a, with the result that a secure standstill of the vehicle trailer can be ensured on the one hand, and no unnecessarily high braking force has to be produced on the other hand.

In the method steps V4 and V5, an inquiry takes place as to whether the vehicle trailer is rolling back. Rolling back of the trailer can take place, for example, owing to an impulse excitation on the trailer in that the latter experiences a jolt opposite the forward direction of the vehicle, whereupon negative wheel speeds occur on the vehicle trailer. To detect the rolling back, according to method step V4 the inquiry is carried out as to whether the vehicle trailer speed Vx,A is less than 0; if this is the case, rolling back is present and the yes branch is followed to proceed to the next method step V5, according to which the existing braking pressure P,A in the vehicle trailer is increased by a factor k, which is preferably greater than one. The increase of the braking pressure PBr,A serves as an additional safeguard and is intended to prevent further rolling back of the vehicle trailer.

In contrast, if the inquiry in the method step V4 shows that no rolling back is present, the no branch is followed and the method block V5 with the increase of the braking force is skipped, so that the hitherto existing braking pressure PBr,A 1.5 retained.

The following method steps V6 and V7 relate to the ending of the automatic braking function in the vehicle trailer. According to method step V6, an inquiry takes place as to whether the vehicle speed v,z of the tractive vehicle is greater than zero. This can be ascertained either via a sensor system in the tractive vehicle, for example wheel rotational-speed sensors in the tractive vehicle. It is, however, also possible to interpret the inquiry according to method step V6 as a driver's desire, according to which the driver wishes to set the vehicle combination in motion; in this case, for example, the actuation of the accelerator pedal by the driver is considered as a driver's desire, the actuation of the accelerator pedal being transmitted via the communication device from the tractive vehicle to the closed-loop or open-loop control unit in the vehicle trailer.

If the inquiry according to method step V6 shows that the vehicle combination has been set in motion or is to be set in motion, the yes branch is followed to proceed to the next method step V8 and the braking pressure PBr,A is either abruptly or gradually reduced to the value zero.

In contrast, if the inquiry in the method step V6 shows that either there is no driver's desire to start or, via the speed inquiry, no starting could be ascertained, the no branch is followed to branch off to the method step V7, in which a further inquiry is carried out, from which starting can be inferred.

According to method step V7, the longitudinal acceleration aX,A in the vehicle trailer is checked. If the longitudinal acceleration aX,A is > 0, this is attributed to a starting jerk which suggests starting of the entire vehicle combination. In this case, the yes branch is followed likewise to proceed to the method step V8 and the braking pressure PBr,A in the braking device of the vehicle trailer is reduced to zero. In contrast, S if the inquiry according to method step V7 shows that there is no starting jerk, the no branch is followed back to the beginning of the method step V6 again and a new check according to method step V6 and, if necessary, according to method step V7 is carried out at cyclical intervals.

Alternatively or additionally to checking the vehicle speed of the tractive vehicle, the inquiry as to whether the vehicle combination is starting to move may also be based on the speed vX,A of the vehicle trailer. In order to be able to detect a starting jerk, it may additionally be expedient to carry out a differentiation of the longitudinal speed value or the longitudinal acceleration and, if necessary, a single or double differentiation of the speed or acceleration either of the tractive vehicle or of the trailer.

After the braking pressure PBr,A of the vehicle trailer has been reduced to zero in the method step V8, there follows a return to the beginning of the method again and the latter is rerun at cyclical intervals.