Vehicle brake system having two brake circuits

Details Vehicle brake system having two brake circuits Vehicle brake system having two brake circuits

2001-05-18

2003-01-14

Schwartz, Christopher P. (Department: 3613)

Fluid-pressure and analogous brake systems

Speed-controlled

With failure responsive means

C303S127000, C303S140000, C303S146000

Reexamination Certificate

active

06505893

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a vehicle brake system having two brake circuits, which each comprise at least one wheel brake, a fluid control module for fluid pressure control at the at least one wheel brake, and at least one brake line for connecting the fluid control module to the at least one wheel brake, such that only one brake line is connected to each wheel brake.
Vehicle brake systems are generally split into two brake circuits so that, in the event of failure of one brake circuit, the vehicle provided with the brake system may still be decelerated by means of the second intact brake circuit and at least an adequate emergency braking action is ensured.
DIN 74000 defines five conventional ways of splitting a vehicle brake system into two brake circuits:
1) the II split according to
FIG. 1
, in which the wheel brakes VL and VR of a front axle V and the wheel brakes HL and HR of a rear axle H are associated in each case with one of two brake circuits
1
and
2
,
2) the X split according to
FIG. 2
, in which each brake circuit
1
or
2
comprises the diagonally opposite wheel brakes VL and HR or VR and HL,
3) the HI split according to
FIG. 3
, in which the wheel brakes VL and VR of the front axle V are associated with both brake circuits
1
and
2
and the wheel brakes HL and HR of the rear axle H are both associated with one brake circuit
1
,
4) the LL split according to
FIG. 4
, in which each brake circuit
1
and
2
controls the wheel brakes VL and VR of the front axle V and one of the brake wheels HL or HR of the rear axle H, and
5) the HH split according to
FIG. 5
, in which each brake circuit
1
and
2
acts upon all of the wheel brakes VL, VR, HL and HR.
Of said possibilities, according to“Kraftfahrtechnisches Taschenbuch” [Automotive Engineering Handbook], Bosch, 22nd edition, 1995, page 622, the II and the X split have gained acceptance. Given a minimum outlay for lines, hoses, detachable connections and static and/or dynamic seals, in terms of the risk of failure as a result of leakages they are comparable with a single-circuit brake system.
In order to comply with the statutory regulations regarding the emergency braking action in passenger cars, front-wheel drive cars are equipped with the X split. The II split is preferably used for rear-wheel drive passenger cars as well as medium- and heavy-duty utility vehicles.
In light utility vehicles, on the other hand, the HI, LL and HH splits are used. This is necessary because light utility vehicles, as designed, have a less advantageous chassis layout, e.g. with regard to axle load distribution, wheelbase and roll radius, with the result that braking with only one brake circuits generates in the vehicle a not inconsiderable torque about its vertical axis, the so-called yawing moment G illustrated in FIG.
1
. Said high yawing moment may lead to potentially hazardous driving situations. In the case of the HI, LL and HH splits, both wheel brakes of the front axle are connected to each brake circuit so that, even in the event of failure of one brake circuit, the front axle is always uniformly braked and a high yawing moment of the light utility vehicle either does not occur at all or is compensated relatively well.
The HI, LL and HH splits do however present problems because, in the event of failure of both wheel brakes of an axle, e.g. as a result of thermal overstressing, total failure of the brake system may occur. Furthermore, with the HI, LL and HH split the outlay in terms of the number of brake lines and the connection of two brake lines to the wheel brakes is higher than with the II and X split. The higher number of brake lines and connections also increases the risk of leakages.
For passenger cars with II and X brake circuit splits, control units of an antiblocking system (ABS), of traction control (ASR) or of an electronic stability program (ESP) are being developed and produced in large numbers. A special feature of a brake system with an HI, LL or HH split is that one wheel brake is controlled by two brake circuits. It is therefore impossible to use standard ABS, ASR or ESP control units and necessary to develop separate control units. For said reason, adding ABS, ASR or ESP to a brake system with an HI, LL or HH split is possible only with a high outlay.
OBJECT OF THE INVENTION
The object of the invention is to increase the safety of a vehicle brake system during braking with only one intact brake circuit and, in particular, to enable the use of a vehicle brake system with an II or X split also in light utility vehicles.
SOLUTION ACCORDING TO THE INVENTION
The object is achieved according to the invention by a vehicle brake system of the type described initially, in which a sensor arrangement for determining failure of a brake circuit is provided, and the fluid control modules in the event of failure of a brake circuit are capable of controlling the fluid pressure at the at least one wheel brake of the intact brake circuit in such a way that the gradient of a developing yawing moment of a vehicle provided with the vehicle brake system does not exceed a predetermined maximum value.
The object is moreover achieved by a method, whereby a sensor arrangement for determining failure of a brake circuit is provided, failure of a brake circuit is determined and the fluid pressure at the at least one wheel brake of the intact brake circuit is controlled so that the gradient of a developing yawing moment of a vehicle provided with the vehicle brake system does not exceed a predetermined maximum value.
According to the invention, the increase of the yawing moment of the vehicle which occurs during braking with only one intact brake circuit is slowed down by suitable fluid pressure modulation at the wheel brake(s) of the intact brake circuit and/or said increase of the yawing moment is prevented from exceeding a value which would lead to a potentially hazardous driving situation. For example, a pressure rise, which is flatter compared to a normal braking operation, is generated at the wheel brake of a front wheel so that the maximum brake pressure there is reached slightly later. The yawing moment is substantially proportional to said brake pressure and therefore has, in accordance with the invention, a lower gradient. The vehicle therefore starts to yaw only slowly. Said yawing behaviour may be brought under control by a driver more easily than a sudden“swerving” of the vehicle as a result of a rapidly increasing yawing moment.
The fluid pressure modulation differs from that of an ABS, ASR or ESP modulation with an intact vehicle brake system in that the braking deceleration at individual wheel brakes is reduced, in particular at the wheel brake of the front wheel, and/or increased, in particular at the wheel brake of the rear wheel.
In said case, a “standard” reduction or increase for each emergency braking situation may be effected, which is constant or dependent only upon parameters such as the speed or loaded state of the vehicle. Alternatively, the yawing behaviour of the vehicle may be determined, e.g. by means of a sensor for the rate of turning and/or yawing of the vehicle about the vehicle vertical axis, and used as a basis for determining a reduction and/or increase of the braking decelerations at the wheel brake(s) which is “individually” adapted to the yawing behaviour of the individual braking situation. The braking decelerations are at the same time controlled so as to comply with the statutory regulations regarding the residual deceleration to be achieved in the event of a fault (ECE13 regulation).
In an advantageous form of application of the invention, four wheel brakes are disposed in pairs at a front and a rear axle of a vehicle provided with the vehicle brake system and the, in each case, diagonally opposite wheel brakes are associated with a brake circuit. Thus, an X split of the brake circuits as described initially is provided, with which the invention may be used in a particularly advantageous manner because, with said X split, in the event of failur

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