Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-10-27
2001-02-27
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S009620, C303S155000, C303S113500
Reexamination Certificate
active
06193328
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic motor vehicle brake system with electronic anti-lock control, with a pedal actuated brake pressure transducer, with electrically actuated pressure medium inlet valves and outlet valves inserted into the pressure medium paths, by which the inflow of pressure medium into the wheel brakes of the individual wheels and the pressure medium drainage into a pressure equalization reservoir of the brake system are individually controlled, with wheel sensors to determine the rotational relationship of the wheels, as well as with an electronic control circuit to evaluate the sensor signals, to determine the driving conditions and to generate the brake pressure control signals.
A circuit arrangement for a brake system with electronic anti-lock control is also a constituent of the invention.
anti-lock braking systems (ABS) are available in many different types. Hydraulic systems in which the wheel brakes of the individual wheels are connected to a multi-circuit brake pressure transducer or master cylinder by means of electrically actuated hydraulic valves have proven themselves to be of particular value. An inlet valve is located in the pressure medium path from the master cylinder to the wheel brake, switched to through-flow when in its normal position, while it switches to the blocking position when in the constant pressure phase or in the pressure reduction phase. An outlet valve blocked when in the resting position is located in the return flow line which leads from the wheel brake to the low pressure reservoir or—in open systems—to the pressure equalization reservoir of the brake system. To return the pressure medium drained off during the pressure reduction phase, depending on the system, a return flow pump (in closed systems) or a hydraulic pump that advances fluid from the pressure equalization reservoir into the brake circuit (in open systems) is used.
The reduction of manufacturing expenses for such anti-lock braking systems (ABS) resulting from the simplification of the system and its components, from skillful construction of the hydraulic brake circuit, from the elimination of components and from the transfer of functions to the allocated electronics has been the object of intensive investigation for some considerable time. These efforts are fundamentally constrained by the fact that a brake system is also expected to perform with the highest reliability even under unfavorable, seldom arising circumstances. An “exhaustion” of the pressure medium volume required for effective braking—as a consequence of frequent, long lasting pressure reductions on a smooth road or under rapidly changing road conditions must naturally be avoided in order to maintain proper brake operation.
An important cost factor for such anti-lock systems is represented by the hydraulic pump and the associated electro-motor drive. It is therefore now recommended that a pump-less ABS be developed. An example of this is the brake system known from DE 31 09 372 A1, which provides that pressure medium drained off by means of outlet valves in order to regulate the anti-lock protection be collected in a low pressure reservoir, from where, after releasing the brakes, it can then flow back into the brake circuit. This known system contains two brake circuits with a diagonal brake circuit subdivision, whereby each brake circuit is equipped with a common inlet/outlet valve arrangement and additionally with a further, electrically switchable inlet valve which is inserted in the pressure medium path leading to the rear wheel brake. This inlet valve can, on the one hand, be switched into a blocking position interdependent with the anti-lock control, and on the other hand interdependent with the load. Completely independent control of all wheels, however, is not provided.
Furthermore, a two circuit hydraulic brake system with anti-lock control is known from DE 43 34 838 A1, by which the pressure medium that is led away from the wheel brakes in the brake pressure reduction phase reaches the low pressure reservoirs, which have two separated inlets for the connection of a rear wheel and a front wheel. Upon achieving a predetermined degree of filling of the reservoir the pressure medium inflow from the front wheel brake, and thereby a further pressure reduction on the front brake, is blocked. Up to this point in time there are hardly any limits on the ABS operation, although the volume through-flow is drastically reduced with the help of specific control algorithms. When a locking of the front wheel is sensed, a switch-over of the control algorithm for the rear wheel is carried out, and a locking of the rear axle is avoided (safety control mode). Maintenance of the brake function is assured by the limited volume uptake of the low pressure reservoir.
The present invention now has the basic object of developing a pump-less ABS of this type, that functions without the use of a low pressure reservoir and that, even under unfavorable circumstances, still features the desired high reliability of operation.
SUMMARY OF THE INVENTION
It has been shown that this object can be achieved with a motor vehicle brake system, the particular nature of which resides in the fact that one or more path sensors are provided for directly or indirectly determining the path and/or the position of the pedal and/or of the piston of the brake pressure transducer, that the anti-lock control can be switched from a standard control mode into a safety control mode interdependent with the current driving or road conditions, the brake conditions and the advancement or the position of the pedal or of the piston. and that in the safety control mode a further reduction in brake pressure in the front wheel brakes, and a further brake pressure increase in the rear wheel brakes is limited, delayed or even blocked during an anti-lock control procedure by means of the switching of the control.
According to the invention a pump-less ABS based on an open system is developed that includes one or more pedal path sensors and that, as a result of switching into a safety control mode when certain conditions are at hand, makes a full -ranging “complete” ABS control possible and at the same time assures that the braking function is also maintained, even under very unfavorable conditions. According to a particularly advantageous exemplified embodiment of the invention a limiting value for the pedal advancement is determined interdependent with the current driving (road) conditions, the brake conditions and the pedal path, whereby when this limiting value is exceeded the switch- over of the standard control mode into the safety control mode takes place.
The limit value is expediently predetermined as a function of the current vehicle deceleration, taking into consideration the volume uptake characteristic of the respective wheel brake. However, it is also possible, and in many cases advantageous, to predetermine the limit value (S
pGrenz
) of the pedal advancement interdependent with the pedal position upon initiating the anti-lock control, and interdependent with the pedal path available for the control according to the relationship
S
pGrenz
=S
pStart
+S
pReg
.
Furthermore, a circuit arrangement for a brake system of this type is indicated, which can basically be employed advantageously for pump-less ABS with a low pressure reservoir. This circuit arrangement could also increase the operating reliability of an ABS that is equipped with a hydraulic pump, for example by assuring brake functioning in extremely unfavorable circumstances for which the auxiliary pressure supply or the hydraulic pump was either not designed or for which it is insufficient.
Other characteristics, advantages and possible applications of the invention become evident from the following specification of further details, based on the attached illustrations.
REFERENCES:
patent: 4576419 (1986-03-01), Leiber
patent: 4790607 (1988-12-01), Atkins
patent: 5201573 (1993-04-01), Leiber et al.
patent: 5333942 (1994-08-01), Peczkowski et al
Bayer Ronald
Feigel Hans-Jorg
Jungbecker Johann
Butler Douglas C.
Continental Teves AG & Co. oHG
Rader & Fishman & Grauer, PLLC
Siconolfi Robert A.
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