Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present inven-tion is concerned with a method and a device
for controlling the braXe force distribution to the front axle
and to the rear axle of an automotive vehicle in response to the
static and dynamic axle load distribution and/or other measured
variables derived from the braking behaviour, wherein electric
signals corresponding to the wheel behaviour at the front axle
and at the rear axle and to the translational deceleration of
the vehicle are generated, electronically combined and processed.
The brake slip on the front and rear wheels and the measured
values proportional to the brake slip, respectively, are deter-
mined from the signals generated therefrom, and the brake slip
of the rear wheels is limited with the aid of a control to the
value of the brake slip on the front wheels or to a va~ue
slightly therebelow. This invention is a development of that
disclosed in our copending Canadian Application 445,780.
Sensors are provided for measuring the rotational behavlour of
the wheels and the translational deceleration/ the output
signals of which sensors are combined with Eirmly wired or pro-
gramme-controllecl electronic circuits, e.g. a microprocessor,
and processed. The brake pressure is controlled with the aid of
modulators, e.g. electromagnetically operated control valves.
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A brake force distributor is already known in the art in ~hich
the static axle load distribution with the vehicle at standstill
i5 measured by sensors and the measured data fed into a micro-
computer which under consideration of the said measured values
and of the measured pressure controls the brake force distrlbution
pursuant to a memorlzed mathematical expression in the front and
rear axle circuit (European patent application EP~Al 062Z46).
It iB a oisadvantage of such a brake force distributor that the
value of adherence between road and wheel at the rear and front
axles actually prevailing at the time of the braking operation
and depending on numerous parametPrs, cannot exert an influence
on the brake force distribution. For this reason, it i5 imperative
for the brake, in order to safely avoid the dangerous overbraklng
of the rear axle, to oe so designed that in the ma~ority of cases,
the rear axle wlll cuntribute little to the braking operation.
Moreover, lt has proved to bP disadvantageous that the actual
values in practice considerably differ from the numerically
calculated should-be values. The brake characteristics assumed
to be constant in the layout of ~he braking force distribution
and the memorized mathematical expressian, in practice, are
subject to substantial changes, e.g. as a result of manufacturing
tolerances in the coefficient of friction, aging, contamination,
changes in the spring constant in operation, defective adjustment,
heavy temperature changes etc~ ~11 this might result in that
the actual characteristic of the brake force distribution
considerably differes from the precalculated values.
ThP brake force distributors commonly used nowadays are limited
to an invariaoly adjusted pressure-responsive contrnl. Load-
responsive or decelearation~responsive brake force regulators
are likewise known in a great number of variants. For the
afore-going reasons, even when maklng great assembly and adjustment
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efforts, a satisfactory adaptation can be attained with these
prior art devices, at best, in one of the two extreme "unloaded/
loaded" conditions so that, in a multiplicity of operating con-
ditions, the exploitation of the adherence value at the front
and rear axles, that is theoretically possible, will not be
attained.
It is, therefore, an object of the invention to overcome the
afore-mentioned disadvantages involved with the prior art
systems and to improve the brake force distribution in auto-
motive vehicles such that both in the extreme "unloaded/loaded"conditions and in every braking operation of the vehicle, the
brake force distribution will be adapted in close approximation
to the actual static and dynamic axle load distribution thereby
attaining an optimum brake function, i.e. road stability, short
stopping distance and a uniform load on the two axles. More-
over, high importance has been attached to meeting the require
ments of comparatively low effort in the manufacture and assem-
bly of the brake system.
The invention provides a pumpless hydraulic fluid pressure
distributor control for automotive vehicles having a hydraulic
brake system with two front brake assemblies and two rear brake
assemblies hydraulically connected to a tandem master cylinder
pressure source, said control comprising: sensors for gener-
ating electric signals proportional to wheel rotation character-
istics at a front axle and at a rear axle of the vehicle; an
electronic circuit for combining, processing and evaluating the
sensor signals for generating control signals therefrom; at
least one control valve slip modulator connected between said
pressure source and said rear brake assemblies for controlling
the brake pressure at the rear axle in response to said control
signals; and, at least one control valve lock modulator oper-
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atively coupled between said pressure source and said rear
bra]ce assemblies to decrease the pressure at the rear axle in
response to electric signals indicative of a tendency to lock
said rear brake assemblies; whereby said slip modulator is
normally closed and opens in response to said control signals
thereby ensuring that said rear axle is braked at a rate not
greater than said front axle by braking said rear axle following
in time braking of said front axle, and said lock modulator
ensures that said rear axle is not locked.
The invention is based on the consideration that by measuring
the wheel and vehicle velocities and the time-responsive changes
in the said measured variables, respectively, by processing the
said measured values to form a control signal in an electronic
circuit, e.g. in a microprocessor, and by using simple control
valves as pressure modulators, a brake force distributor can be
realized which, under consideration of the conditions actually
prevailing at the
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time of the brake operation, inclusive of the road conditions,
condition of the brake system, static and dynamic axle load
distribution etc., in almost ideal manner distributes the brake
force onto the front and rear wheels thereby, above all, attaining
a short stopping distance, a low locking risk and, hence, a high
road stability and a uniform load of the braking system. Owing to
the fact that only in exceptional cases, the pressure on the rear
axle is required to be decreased, also the relatively rare driving
situations caused e.g. by rapidly changing road conditions, will
be taken into account. FOI~ in such situations, after attaining
an initially proper wheel cylinder pressure and a constantly
maintained braking pressure, a wheel blocking on the rear axle
could subsequently occur. As opposed to brake slip control systems,
in the brake force distrihutor sf the present invention, no
renewed brake pressure build-up will occur withln a braking
operation; and in contrast to brake slip control systems,no
external eneryy supply, for rehuilding the brake pressure, as a
rule, is required. In the light of the required manufacturing
efforts for the brake system and the operational safety thereof,
this will be of a special importance.
Further advantages and applicabilities of the invention will
oecome obvious from the following description nf details and
of embodiments of this invention.
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In the drawings:
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Fig. 1 is a schematically~simplified block diagram of an embodiment
of the brake force distributar according to the invention
for a double-circuit brake system having a diagnnal oraking
force split-op;
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Flg. Z is the diagram of the time-responsive curve of pressure
when using the brake force distributor Df the invention;
F~g. 3 is, alike the illustration of Fig. 1, a form of embodiment
of a double-circuit brake system with respectively one
brake circuit for the front axle and ~or the rear axle.
In the douole~circuit brake system according to Fig. 1, the brake
circuitsare diagonally split. In a standard construction-type
tandem master cylinder 1 as symbolically shown, nn which as
symbolized oy the arrow - trake force F is exerted vla a pedal,
the lefthand front wheel VRl End the righthand rear wheel HRr
are connected to a brake circuit Z. The second brake circuit 3
will act upon the t~o other wheels VRr and HRl.
In the illustrated form of embodiment of the invention, the
pressure modulatQrs are quick-acting, two-way, two-position valves
4,5,6. ~hile the two front wheels are directly connected to the
associated braking circuit 2 and 3, respectively, of the tandem
master cylinDer 1; a pressure build-up on the rear wheels will be
possiblE only after the two control valves 4,5 being energizeo.
Activation of these valves is effected via an electronic control 7,
to which measured variables generated with the aid of sensors 8,9
and ~0 are fed via signal lines ~', 9~, 10~ in the form of elecbric
signals and which, by a logic combination, will compute the
required cuntrol signal and will control the brake pressure
modulators. Control 7 may contain e~g. a microprocessor for
processing the sensor signals and for generating the control
signals.
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In the form of embodiment as described here,- by sensor ~, an
average value cv~R of the wheel speed at the front axle i9
determined; by sensor 10, an average value ~vHR of the wheel
speeds at the rear axle is determined; and by sensor 9, the
transla$ory deceleration -b of the vehicle during the braking
operation, or measured values proportional to the wheel speeds
and the deceleration, respectively, are determined. If the vehicle
ls already equipped with an electronic sensor for the speedometer
the same may, at the sa~e time, be used for generating the
measured variable ~VR
The pressure curve PHA on the rear axle generated with the aid
Df the modulators and control valves 4757 respectively7 and the
brake pressure cur~e P~Q on the front axle on which PHA i9
dependent, i9 illustrated by FigO 2. In that example of embodiment,
control 7 will generate - laterally delayed over the rise in the
front axle pressure PVA - activation pulses for control valves 4,5,
with the pressure rise PHA required for an ideal pressure
distribution, being adjusted at the rear wheel3 by pulsating or clock
controlled reswitching of valves 4,5 from the (shown) clnsing
position into the through-flow position.
Moreover, in accordance with the invention, another two-way, two
position valve 6 i9 provided for decreasing the rear wheel pressure.
6y hydraulically connecting the two rear wheel circuits via a line
having two series connected and oppositeIy directed non-return
valves 11,12, a single two-way, two-position valve 6 will be
sufficient for the pressure decrease in the two rear wheel
circuits. The illustration of Fig. 1 conveys that via the electrical
connection o~ the electronic control 7 leading to the operating
magnet of valve 6, the normally closed two-way, two-position valve 6
for the pressure decrease can be reswitched into the through-flow
position whereupon both rear wheel circuits via the non-return
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valves 11,1Z are connected to the pressure cDmpensating unit 13
being part of the brake system.
As sho~n in Fig. Z, the pressure, as soon as a locking tendency is
indicated, is stepwise reduced to a lower value at which the brake
slip at the rear axle corresponds to the brake slip at the front
axle or lags beh1nd the same. The pressure decrease starts at a time t
after control 7 having detected a locking tendency at the rear
wheels at the time to by comparing the wheel deceleration at the rear
axle with the vehicle deceleration.
Non-return valves 14,15 provided in parallel to the pressure build-up
valves 4,5 ~ill accelerate the decrease in the brake pressure ~hen
releasing the brake.
In a double-circuit hrake split-up in which one circuit acts upon the
front axle, while the other circuit acts upon the rear axle, the
brake force distributor according to the invention ~ill require a
still smaller numoer of components. As sho~n in Fig. 3, respectively
nne electromagnetically operated two-way, two-position valve 16 and
17, will be sufficient for the build-up Df the braking pressure
at the rear axle and for the pressure reduction released as soon as
control 7'~has concluded a locking tendency of the rear wheels from
the sensor signals fed to it via signal lines 8',9',10'. The non-
return valves 11,12 disposed in the embodiment according to Fig. 1
in the feedline to the pressure reducing valve 6, are eliminated in
the embodiment according to Fig. 3.
Fig. 1, moreover, sho~s a difference pressure switch 18 signalizing
failure of a brake circuit and a pressure difference caused thereby
between the twn brake circuits Z,3, to control 7 via line 19. This
will cause a permanent energization of valves 4,5 and a permanent
locking of valve 6 in order that upon failure of a brake circuit,
at least in the second brake circuit, the full brake pressure can be
built up on the front and rear axles~ The track or directional stability
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of the vehicle, in that case, will al50 be maintained with a
locking of the wheels of the intact diagonal circoit by the
non-braked wheels of the failing oraking circuit.
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