BRAKING METHOD IN THE CASE OF EMERGENCY OR FULL BRAKING

Abstract

A vehicle's electronic brake system is controlled to prevent rear-to-front body sway. A clamping force is applied to the rear and front axle brakes such that the clamping force is built up in the brakes of the rear axle before the clamping force is built up in the brakes of the front axle such that the distance of a rear part of the vehicle body relative to the roadway is substantially constant at the beginning of braking.

Claims

1. A method for controlling a vehicle's electronic brake system in which a rapidly responding brake on the rear axle of the vehicle is combined with a slowly responding brake on the front axle and in which during a brake actuation a clamping force is built up independently on the rear axle and the front axle, the method comprising: providing a clamping force to the rear and front axle brakes such that the clamping force is built up in the brakes of the rear axle before the clamping force is built up in the brakes of the front axle such that the distance of a rear part of the vehicle body relative to the roadway is substantially constant at the beginning of braking.

2. The method of claim 1, wherein an electromechanical brake on the rear axle is combined with a hydraulic brake on the front axle.

3. The method of claim 1, wherein a wheel-selective brake control is applied wherein a locking sequence is determined with a brake slip control system.

4. The method as of claim 1, wherein the distance of the rear part of the vehicle body relative to the roadway is delayed using a shock absorber.

5. The method of claim 4, wherein a soft damping mode is provided by shock absorbers for the rear axle and in the event of action of the brake of the front axle, the shock absorbers of the rear axle are set in a fixed mode.

7. The method of claim 1, wherein the distance of the rear part of the vehicle body relative the roadway is additionally prevented from increasing using a weight force increase on the rear axle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0022] In the figures:

[0023] FIG. 1 shows a motor vehicle having a weight distribution which occurs in the event of braking of the front axle according to the prior art,

[0024] FIG. 2 shows a schematic illustration of a motor vehicle during braking with sinking of the vehicle center of gravity,

[0025] FIG. 3 shows the vehicle corresponding to FIG. 1 with a weight distribution which occurs in the event of braking of the rear axle, and

[0026] FIG. 4 shows a force-time diagram, in which the clamping force Z of the rear and front axles is plotted over the time T.

DETAILED DESCRIPTION

[0027] FIG. 1 illustrates the prior art. The figure shows the displacement of the vehicle center of gravity 7 in the travel direction during braking. The vehicle weight is distributed in this case, for example, with 70% on the front axle 4 and 30% on the rear axle 3. This occurs in that in case of braking, the brake of the front axle 4 acts before the brake of the rear axle 3 with respect to time.

[0028] FIG. 2 shows the sinking of the vehicle center of gravity 7 during braking, in the case of which the brake system starts first on the rear axle 3. Due to the prior action of the brake of the rear axle 3, the rear vehicle part 5 dives and the vehicle center of gravity is displaced perpendicularly in relation to the roadway 6. This is assisted by soft rear axle damping or a chronologically restricted mass increase on the rear axle.

[0029] In the further procedure, as shown in FIG. 3, the more uniform weight distribution on front and rear axles according to the invention takes place. During braking, in which the brake system 2 on the front axle 4 builds up brake pressure after the rear axle 3 with respect to time, the vehicle center of gravity 7 is displaced less intensely in the travel direction than shown in FIG. 1. This is because the vehicle center of gravity 7 has already sunk perpendicularly in relation to the roadway 6.

[0030] The braking distance is thus significantly shortened in relation to the prior art by means of the displacement of the vehicle center of gravity 7. A higher weight on the rear axle thus results, or the contact pressure is increased, whereby the existing brake force can be utilized better and therefore the tire adhesion on the roadway 6 is also increased.

[0031] In the force-time diagram shown in FIG. 4, the clamping force Z is plotted over the time axis t. In this case, the different curves of the clamping force Z of the respective axle are shown with Z.sub.HA for the rear axle and with Z.sub.VA for the front axle. The time T.sub.1 shows a time in the first time curve of the clamping forces in the case of emergency or full braking according to the method according to the invention. In this case, at time T.sub.1, the clamping force of the rear axle Z.sub.HA is greater than the clamping force of the front axle Z.sub.VA. At time T.sub.2, the slip control system of the electronic brake system starts and controls the locking behavior of the wheels. In the further time curve of the emergency or full braking at T.sub.3, the clamping force of the front axle Z.sub.VA is then greater than the clamping force of the rear axle Z.sub.HA to ensure the driving stability.