Method and System for Preventing Unwanted Rolling Away of a Vehicle

The present invention relates to a method and system for preventing unwanted rolling away of a vehicle, and more particularly, to a method in which rolling away is prevented by maintaining a brake pressure in wheel brake cylinders, and the brake pressure maintained being dependent on the actuation of the brake pedal, the speed of the vehicle being determined.

DE 29 11 372 discloses a brake system which has a rotational-speed detection system which is linked to the direction of rotation and actuates the brakes if the vehicle starts to roll in the opposite direction to the direction of the gear selected, i.e. rolling backwards when a forward gear has been selected and vice versa. When the brake system is deactivated, the pressure dissipation takes place as a function, inter alia, of the engine speed. Owing to the system configuration, triggering the brake actuation requires an engaged gear. No brake actuation takes place at idle. Moreover, the driver has no influence on the triggering of brake actuation.

DE 031 13 362 discloses that the ignition and the brakes can be coupled to ensure that the brakes are automatically actuated when the vehicle is parked.

An object on which the invention is based is to provide a system which prevents a stationary vehicle from unintended movement and which can be activated at will by the driver.

According to the present invention, this object has been achieved by providing that a variable which represents the actuating force applied by the driver is detected, a first value of the variable being determined in a first time interval following the onset of the stationary condition of the vehicle and, when the current value of the variable exceeds a second value of the variable, which is higher by a predetermined amount than the first value, at least the brake pressure which corresponds to an actuation of the brake pedal with the first value of the variable is maintained irrespective of a subsequent release of the brake pedal.

The system of the present invention has the advantage that, when the vehicle is stationary, brakes are actuated only if the brake pedal has been actuated. The brake system is triggered by the driver by an additional actuation of the brake pedal. This has the advantage, as compared with the conventional approach, that the system can be controlled at will by the driver.

A further advantage of the present invention is that components of the existing ABS can be used. The system furthermore remains activated when the idling speed has been selected to facilitate, among other things, parking.

According to another embodiment of the invention, a signal from the ignition is detected and, if the engine stalls but the ignition is still switched on, braking force is maintained to ensure that the vehicle does not roll away. Moreover, the brake pressure does not necessarily have to be dissipated when the ignition is off because, otherwise, the vehicle would roll away when the driver restarted the vehicle.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

FIG. 1 is a schematic view of a hydraulic brake system using the principles of the present invention;

FIG. 2 is a flow diagram of a method according to the invention;

FIG. 3 is a flow diagram of an alternative embodiment of the method; and

FIG. 4 is a flow diagram of another embodiment of the method according to the invention, with the position of the ignition switch being taken into account.

FIG. 1 illustrates a hydraulic brake system having a brake pedal 1 which is connected to the master cylinder 3 by way of a vacuum brake booster 2. The brake fluid reservoir 4 is connected to the master cylinder 3 by two fluid connections. The brake system is divided into two circuits, only one axle being braked in each circuit 5, 6. A respective shut-off valve 7, 8 for maintaining the brake pressure is arranged in each circuit.

The first circuit 5 for the front axle is divided, with each branch leading to one brake disc 9, 10. A brake-power regulator 11 is arranged in the second circuit, downstream of the shut-off valve 8. The second circuit also divides into two following the brake-power regulator 11, with each branch leading to a drum brake 12, 13.

The brake system described operates in a conventional manner i.e. an actuating force F1 is applied to the pedal. This force F1 is intensified by means of a lever action (F2) and then further intensified by the brake booster (F3). Together with the cross-sectional area of the tappet of the brake master cylinder, this force F3 determines the brake pressure.

The shut-off valves 7, 8 serve to maintain the brake pressure when the actuating force is no longer being applied to the brake pedal. The shut-off valves 7, 8 are driven by a control unit 14, the action of which will be described in greater detail below. In the unactuated state of the shut-off valves 7, 8, the wheel brake cylinders are fluidically connected to the brake master cylinder 3.

FIG. 2 shows a flow diagram which illustrates the individual steps of a method according to the invention for preventing a vehicle from rolling away.

Step 201, the wheel speed n.sub.v is detected by wheel-speed sensors 15, 16, 17, 18. If the wheel speed n.sub.v is not equal to zero, i.e. the vehicle is not stationary, the method is not started and the brakes are controlled exclusively by the driver. If the wheel speed is equal to zero and the vehicle is thus stationary, then, in Step 202, a first time interval t1, for example t1=0.2 s, is begun, over which time interval the current brake pressure P.sub.b is determined in Step 203. In Step 204, the system using, for example, conventional data processing technology determines whether or not the time interval t1 has expired. If the interval t1 has not expired, the current brake pressure P.sub.b continues to be determined. The brake pressure P.sub.b corresponds to the brake pressure required to hold the vehicle stationary (the holding pressure P.sub.h). Once the time t1 has expired, the maximum value determined for the brake pressure P.sub.b, i.e. P.sub.h, is stored in a logic unit of a microprocessor or the like in accordance with Step 205. The status in Step 205 represents the starting position for the method according to the invention.

Step 206, the current brake pressure P.sub.b continues to be detected. In order to begin the prevention of rolling away, the driver must actuate the brake pedal with a greater force. In Step 207, the current brake pressure P.sub.b is compared with the holding pressure P.sub.h. If the current brake pressure does not exceed the holding pressure by a predetermined amount, for example 10 bar, the current brake pressure continues to be detected and compared with the holding pressure P.sub.h in Step 206. If the current braking value P.sub.b exceeds the holding pressure P.sub.h by a predetermined amount, then, in accordance with Step 208, the shut-off valves are closed, and the holding pressure P.sub.h or the current pressure are thus maintained.

FIG. 3 represents an alternative sequence of the method to that in Steps 207 and 208 of FIG. 2.

In Step 307, a second time interval t2 is begun, where t2=0.1 s for example. In Step 308, the current brake pressure is determined over the time interval t2. Once the time interval t2 has expired in Step 309, the brake pressure is raised, in Step 310, either to the maximum value P.sub.bmax of the current brake pressure during the time interval t2 or to the average value P.sub.bmit of the current brake pressure, and the vehicle is thereby held.

FIG. 4 shows a preferred configuration of the method, wherein the position of the ignition switch is determined and the maintenance of the brake pressure is dependent on this position.

The following steps are inserted in the method of FIG. 4 after Step 205 of FIG. 2.

In Step 401, the engine speed N.sub.m is determined. If the engine speed is not equal to zero and the vehicle is stationary, the method is continued with step 206. If the engine speed is equal to zero, the system determines whether or not the ignition is switched on. If the ignition is switched on and the engine speed is equal to zero, the driver has stalled the engine. In Step 402, the previously stored holding pressure P.sub.h is applied in order to prevent the vehicle from rolling away. The method then returns to Step 206 to ensure that the driver can increase the current brake pressure if this is required. If the ignition is switched off and the engine speed is equal to zero, the vehicle is parked. Here, the holding pressure P.sub.h could be applied in the already conventional manner.

According to another embodiment of the present invention, the position of the parking brake is continuously determined after Step 205. If the parking brake is operated or released, the holding pressure P.sub.h is dissipated, allowing the system to be relieved. If the holding pressure is dissipated, for example after operation of the parking brake or the accelerator pedal, this takes place progressively as a function of the position of the clutch pedal and/or the engine torque.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.