Brake system antilocking mechanism

In an antilock system for vehicle brake control, the wheel having the worst road contact is disregarded and the remaining wheel brake pressures are regulated in accordance with the "select-low" principle. In a brake system which is divided into two circuits each controlling diagonally opposite wheels, the circuit containing the minimum contact wheel is regulated according to "select-low". In this way, the assignment of the wheel to the group regulated at select-high will be optimized.

SPECIFICATION 
This invention relates to a antilocking apparatus for a vehicle brake 
system in which braking pressure is controlled in accordance with the 
retardation of certain wheels of the vehicle. 
BACKGROUND OF THE INVENTION 
It has been known, for the antilocking regulation of the wheels of a 
vehicle, not to regulate all wheels individually, but, according to the 
discretion of the designer, to equip certain groups of wheels with a 
single regulating arrangement wherein, in such a case, the regulation 
takes place in response to the selection of one of the sensor signals of 
the jointly regulated wheels. 
This selection can be accomplished, for example, in accordance with the 
"select-low" principle, which means that the signal from the sensor 
associated with the wheel braked or retarded most strongly is chosen for 
regulation. The reason for this is that the more weakly retarded wheels 
have greater frictional values relative to the road surface and, if one of 
these wheels were selected, the control would cause the wheel retarded 
most strongly to lock. In this case, therefore, several wheels are 
regulated at an equal braking pressure which is valid for the wheel having 
the least contact with the road surface, so that the non-utilization of 
the greater braking action of the other wheel or other wheels is tolerated 
in order to prevent locking of the wheel having the least contact with the 
road. 
The antilocking mechanisms hitherto known have, however, the disadvantage 
that the assignment of wheels to a certain group which is then regulated 
as a whole according to the "select-low" principle, is fixed, which 
arrangement is unfavorable for covering all possibilities of the different 
loads on the wheels during braking actions. Thus, there will always be 
situations for which the selected division is not optimal. 
BRIEF DESCRIPTION OF THE INVENTION 
Accordingly, it is an object of the present invention, while maintaining 
the advantage of the saving of material in the arrangement where groups of 
wheels are formed for regulation on the "select-low" principle, of 
providing an additional possibility for the optimization of the brake 
system pressure medium distribution to the regulated wheels. 
Briefly described, the invention includes a vehicle brake system 
antilocking mechanism of the type having at least one modulator regulating 
the braking fluid pressure in dependence on wheel retardation and having 
wheel sensors, wherein there are fewer modulators than wheels or sensors, 
and wherein the braking pressure to at least one group of wheels is 
regulated according to the "select-low" principle, comprising the 
combination of means for identifying the wheel which has been retarded 
most strongly; control means for selecting the wheel or wheels in 
accordance with the "select-low" principle as a function of the position 
of the wheel retarded most strongly and for regulating braking pressure in 
accordance with that selection.

In each of FIGS. 1 and 2, a vehicle is shown schematically, and the parts 
which are essential to the invention will be described in the following 
discussion. Referring first to FIG. 1, the apparatus includes a main brake 
cylinder 1 in which the brake fluid is put under pressure by means of 
activating the brake pedal 20 in the direction of the arrow 21, and the 
brake fluid is then fed through a line 23 to an antilocking modulator 
(ALM) 2. The modulator has four outlets, or one outlet with a quadruple 
distributor, and is connected with the brake mechanisms of wheels 3, 4, 5 
and 6 through fluid lines 12, 13, 14 and 15, respectively, which wheels 
are braked by means of conventional brake mechanisms operated by the fluid 
and not illustrated. 
The wheels are provided with sensors 7, 8, 9 and 10, each sensor being 
capable of producing a signal representative of the rate of braking or 
deceleration of its associated wheel, permitting measurement of that 
factor. From sensors 7-10, signal lines 16-19 are connected to a 
recognizing or detection arrangement 11 in which one of the four sensor 
signals is selected and is converted into a control signal. The control 
signal thus formed is fed through a line 22 to the antilocking modulator 
2. In FIG. 2, the above components are also present, except that the 
control signal is delivered on lines 22 and 22' to antilocking modulators 
2 and 2', respectively. 
The manner in which the apparatus illustrated in FIG. 1 operates will now 
be described. In the case of a vehicle which, when standing at rest, has 
substantially equal axle loads on the front and rear axles, it will be 
recognized that the distribution of the load shifts when the vehicle is 
moving and is subjected to braking force so that the load on the front 
axle is significantly greater than that on the rear axle. The following 
discussion will proceed from this usual circumstance, although it will be 
recognized that unequal loads can occur and that the system will function 
in such situations. It will also be assumed, in the following discussion, 
that a change of direction of the vehicle, for example to the left, takes 
place simultaneously with the braking. 
It has been known that when the vehicle is driving around a curve the 
outside wheels are put under greater stress than the inside wheels, so 
that, therefore, in the event of braking during a left-hand curve, the 
right, front, outside wheel 3 is placed under the highest stress, the 
adjacent wheels 4 and 6 are put under medium stress, and the rear inside 
wheel 5 is subjected to the least stress. 
The wheel put under the least stress transmits the smallest braking force 
onto the road and, in the event of excessive braking action (and an 
antilocking arrangement is provided only for such circumstances) will have 
a negligible effect on the velocity reduction of the vehicle. As a 
consequence of that, it will be recognized that even if this wheel 5 which 
is under the least stress, does lock, that will have no negative effects 
on the braking behavior of the vehicle, on the stability of travel, or on 
the steerability of the vehicle. 
For this purpose, recognition arrangement 11 is arranged to identify and 
recognize the wheel subjected to smallest stress and to exclude that wheel 
from any influence on the regulation of the braking system. Of the three 
remaining wheels 3, 4, and 6, one is under strong stress and the other two 
under a less great stress and in a good or at least fair frictional 
contact with the road surface. 
These three wheels are now regulated according to the "select-low" 
principle, that is to say, the wheel being braked or retarded most 
strongly, or being under the least stress, or having the worst frictional 
contact of the three with the road is taken to be a measure for the 
pressure decrease in the brake cylinders of all three wheels. This 
selected wheel, in the case of braking occurring during a left-hand turn, 
is either wheel 4 or wheel 6, depending upon whether the load distribution 
on the axles is changed more strongly or less strongly by the braking than 
by the shifting of the load from the inside to the outside wheels as a 
result of going around the curve. The four wheels regulated jointly, 
therefore, all have the same braking pressure which is selected such that 
the wheel endangered most strongly by locking is locked and the wheel 
which is second most in danger of locking is not locked. 
As will be recognized, in the case of the vehicle making a right-hand 
curve, what was described above is valid with a corresponding interchange 
of left and right. 
In the case of straight ahead travel, or in the case of a very slight 
curve, it will necessary, especially with vehicles having a relatively 
great load on their front axles, for some safety device to be inserted 
which additionally influences the braking force regulation. 
In this situation both rear wheels would be under a very weak load in the 
event of strong braking, so that the wheel which, perchance, would be the 
weaker one would be eliminated and the other one which is still under too 
small a load in order to be used for antilocking regulation, would in this 
case cause too small a braking force of the remaining three wheels. In 
this case, for example, the braking installation on the rear wheels can be 
additionally equipped with a braking pressure limiter which, depending on 
the type of vehicle, limits the braking pressure to a fixed value or to a 
maximum value which is regulated as a function of the axle load. 
In the event of excessive braking actions (which occur rarely) in the event 
of reverse travel, what was described previously will be valid with a 
suitable interchange of front and rear wheels. Furthermore, this principle 
is not only applicable in the case of traveling around curves but also in 
the case of other variable conditions of friction of the wheels with the 
road surface which might occur. 
In FIG. 2 is shown a braking installation with a diagonal distribution of 
two braking circuits, and the components, for the most part, use the same 
reference numbers as those employed in connection with FIG. 1, the 
components being essentially the same. 
Two antilocking modulators 2 and 2' are connected with the main cylinder 1 
by way of lines 23, 23'. Each of these modulators has two outlets, the two 
outlets of each modulator being connected with the brake cylinders of two 
diagonally opposite wheels. 
The operation of the apparatus of FIG. 2 will now be described. It will 
again be assumed that we are considering a vehicle which is braking during 
a left-hand curve, in which case wheel 3 is placed under the highest 
stress and wheel 5 under the smallest stress. The braking circuit is 
selected by means of the recognition mechanism 11 which recognizes the 
wheel 5 to be under the weakest load and therefore produces a control 
signal selecting the braking circuit operated by modulator 2', and this 
modulator is switched to "select high", that is to say, the right-hand 
front wheel 3 is braked optimally and the left-hand rear wheel 5 will be 
braked at the same time with a correspondingly strong brake pressure which 
may lead to locking. But, however, this locking is insignificant since we 
are dealing with the wheel which is under the least stress. The other 
braking circuit operated by modulator 2 and the wheels 4 and 6 is switched 
to "select-low", as result of which the modulator regulates in such a way 
that the wheel most inclined to lock would just be the one which does not 
lock. 
In the case of the system of FIG. 2, the additional safety feature for 
straight ahead travel is not necessary since both front wheels are braked 
sufficiently strongly and no essential part of the braking capability of 
the braking installation is lost. On the other hand, in the case of this 
system, and depending upon the design of the steering geometry of the 
vehicle, it may be necessary to insert a limiting arrangement which keeps 
the difference between the braking pressures in the two braking circuits 
below a predetermined or predeterminable threshold value, depending upon 
the type of vehicle. With that, the result is that the difference between 
the braking forces of the two front wheels will never be so great for the 
vehicle in which the system is installed that the travel stability will no 
longer be guaranteed. 
In either of these types of installations under consideration, therefore, 
it is uncertain from the outset for which wheels a "select-low" principle 
will be used, but by recognition of the wheel which is least important for 
good braking action and permitting locking among the remaining wheels, the 
group of "select-low" regulated wheels will be determined depending only 
upon the position of the wheel which is not to be considered further. 
While certain advantageous embodiments have been chosen to illustrate the 
invention it will be understood by those skilled in the art that various 
changes and modifications can be made therein without departing from the 
scope of the invention as defined in the appended claims.