Fluid-pressure and analogous brake systems – Speed-controlled – Odd condition or device detection
Reexamination Certificate
1999-09-30
2004-11-09
Butler, Douglas C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Odd condition or device detection
C303S009620, C303S186000, C188SDIG002
Reexamination Certificate
active
06814414
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and method for preventing rollback of a vehicle on an incline. In order to prevent a vehicle from rolling back, the braking pressure is increased on at least the rear wheels, independently from the driver, if certain conditions are met.
BACKGROUND INFORMATION
Methods and devices for influencing the braking pressure in order to prevent vehicle movement that is not intended by the driver are known from the conventional methods and devices.
For example, a vehicle with automatic transmission can be held at a standstill by the driver, as known, using the brakes, since with the transmission engaged, the vehicle tends to move slowly forward (“creeping”) due to the converter. The required driver effort can be reduced if the required braking pressure is held constant once it is applied. This can be accomplished, for example, by “locking” the braking pressure initiated by the driver on the wheel by a valve located between the main brake cylinder and the wheel brake cylinder as long as the vehicle is stopped. A vehicle speed sensor detects the standstill state for this purpose. The driver can then remove his foot from the brake pedal, while the wheels remain blocked by the brake. The braking pressure in the wheels is reduced as soon as the driver actuates the accelerator and thus signals his intent to start the vehicle moving. Such conventional system for creep inhibition is described in, for example, German Patent Other “hill holder” systems are also known. These conventional systems concern the following situation: Driving off a vehicle having a manual transmission system is a complex procedure requiring the combined use of accelerator and clutch pedals in conjunction with actuating the hand brake. It is difficult to apply the correct amount of braking action, i.e., braking torque when the vehicle starts moving so that the vehicle does not roll in the wrong direction until the driving torque transmitted by the transmission is sufficient for actual motion start. There are many proposals on how to facilitate the driver's task in this situation. In vehicles with hydraulic brake systems, for example, the wheel braking pressure can be isolated from the main brake cylinder by using a control valve. The pressure, once applied by the driver, remains even if the driver is no longer actuating the brake. This procedure is activated using a special switch. The driver can now initiate the procedure of moving the vehicle without concerning himself with the brakes. The control valve is opened as soon as vehicle motion is detected via a change in the rotary position of the drive shaft. German Patent Application No. 38 32 025 describes such a conventional hill holder starting aid.
German Patent Application No. 196 25 919 describes a system for controlling the braking action in a motor vehicle having means for setting the braking action independently of the driver's action. Upon detecting a predefinable operating mode, in which at least the longitudinal velocity of the vehicle 0 is determined, a certain braking action is applied. Such an operating mode may be present, for example, when the driver wishes to have the aforementioned creep inhibition or the aforementioned starting aid. For this purpose, when a predefinable longitudinal vehicle speed is detected during this operating mode, the braking action is increased independently of the driver. By observing the longitudinal vehicle speed, a forward motion of the vehicle that is not desired by the driver is reliably inhibited during the operating mode (creep inhibition mode or hill holder mode). This conventional system is based on the fact that all wheel brake cylinders have the same braking pressure at the beginning of the driver-independent braking action. The situation where the braking pressure in the front and rear wheels is different is not considered.
Furthermore, methods and devices for controlling the brake system of a vehicle are known where at least the braking pressure in the wheel brakes of one rear wheel is influenced in order to distribute the braking action between at least one front wheel and one rear wheel. This influencing scheme is accomplished by setting a differential between the braking pressures of the front wheel and the rear wheel. German Patent Application No. 196 53 230 provides that the differential set between the braking pressure of the front wheel and the rear wheel is reduced when a predefinable situation is present. The predefinable situation is present when a measured quantity, representing the longitudinal vehicle speed, drops below a predefinable threshold value. As the longitudinal vehicle speed diminishes, the differential set between the braking pressure of the front wheel and the rear wheel is continuously reduced.
An object of the present invention is to improve existing devices and methods for vehicles equipped with a braking system with which, in order to distribute the braking action between at least one front wheel and one rear wheel, at least the braking pressure on the wheel brakes of a rear wheel is influenced, so that when braking action is performed on an incline, in which a suitable differential is set between the braking pressure of the front wheel and the rear wheel, the vehicle is prevented from rolling back.
SUMMARY OF THE INVENTION
The device according to the present invention prevents a vehicle from rolling back on an incline. In vehicles having a heavy rear load (caused, for example, by the vehicle cargo), which are equipped with a brake system with which, in order to distribute the braking action between at least one front wheel and one rear wheel by actuating actuators assigned to the rear wheel so that a differential is set between the brake pressure in the front wheel and the rear wheel, it may occur in the case of such braking (hereinafter referred to as EBD—electronic braking force distribution) on steep inclines that the braking pressure in the rear axle is insufficient for holding the vehicle on the incline after braking to a complete stop. The vehicle with a heavy rear load may then slip downward on the incline with blocked front wheels. The front axle, bearing little load, can barely transmit any braking force.
EBD braking is defined as follows: a differential is set between the braking pressure on the front wheels and the rear wheels and thus the braking action is distributed at least by actuating actuators assigned to the rear wheels of the vehicle. This distribution of the braking pressure and thus of the braking action ensures that the rear axle is not locked before the front axle. In EBD distribution the braking action is “locked” in the rear wheels by appropriately activating the actuators assigned to the rear wheels, i.e., the pressure remains unchanged during EBD braking and cannot be increased by the driver. On the other hand, the braking pressure of the front wheels can be increased by the driver at any time. This can be disadvantageous under certain circumstances in the case of braking a vehicle having a heavy load on an incline, namely when the braking pressure on the rear wheels is insufficient, as described above, to hold the vehicle at standstill on the incline.
The device according to the present invention has a first arrangement which determines whether the vehicle is at a standstill due to braking, in which an appropriate differential is set between the front wheel and the rear wheel, i.e., in EBD braking. Furthermore, the device according to the present invention has a second arrangement which determines whether the vehicle is rolling back from standstill. If the second arrangement detects a rollback of the vehicle, the braking pressure is increased on one rear wheel of the vehicle in order to inhibit rollback.
As long as no vehicle rollback is detected, the braking pressure that has been set is advantageously maintained at least for the rear wheels. On the other hand, the braking pressure on the front wheels can be increased by the driver.
In order to inhibit vehicle rollback, the braking pr
Koch Matthäus
Schmitt Johannes
Butler Douglas C.
Kenyon & Kenyon
King Bradley
Robert & Bosch GmbH
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