Device and method for termination an automatic braking process in motor vehicles

A device and method for terminating an automatic braking process in a motor vehicle ensures that the automatic braking process is reliably switched off. The relative movement between the pressure rod of the brake system and a component which can be moved with respect thereto within a defined movement play is detected by two control switches, namely a make contact and a break contact which are actuated via a common switching cam. A switching process of the control switches takes place whenever the brake pedal is moved in the direction of its rest position. If a switching process which corresponds to this relative movement takes place during an automatic braking process, the braking process is terminated.

CROSS-REFERENCE TO RELATED APPLICATION 
This application is related to application Ser. No. 08/377,426 filed on 
Nov. 8, 1994 in the name of Manfred Franz BRUGGER et al. for MONITORING 
METHOD AND DEVICE IN AUTOMATIC BRAKING PROCESS; to application Ser. No. 
08/337,429 filed on Nov. 8, 1994, in the name of Siegfried RUMP et al. for 
METHOD FOR CONTROLLING THE TRIGGERING SENSITIVITY OF A VEHICLE AUTOMATIC 
BRAKING PROCESS TO MATCH DRIVER BEHAVIOR; to application Ser. No. 
08/337,427 filed on Nov. 8, 1994 in the name of Siegfried RUMP et al. for 
METHOD FOR AUTOMATIC BRAKING OF MOTOR VEHICLES WITH AN ANTI-LOCK BRAKE 
SYSTEM; to application Ser. No. 08/337,425 filed on Nov. 8, 1994 in the 
name of Manfred STEINER et al. for METHOD FOR TERMINATING A MOTOR VEHICLE 
AUTOMATIC BRAKING PROCESS; and to application Ser. No. 08/337,432 filed on 
Nov. 8, 1994 in the name of Manfred STEINER for METHOD OF CONTROLLING 
SENSITIVITY OF VEHICLE AUTOMATIC BRAKING PROCESS. 
BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a device and method for terminating an 
automatic braking process in a motor vehicle and, more particularly, to a 
device for terminating in a motor vehicle, an automatic braking process 
which has been triggered by a control unit as a function of brake pedal 
actuation and which is terminated when a breaking-off criterion is 
fulfilled, the vehicle having a brake system in which a brake pedal force 
is transmitted via a pressure rod to a brake booster. 
DE 40 28 290 C1 describes an automatic braking process which is triggered 
when a specific actuation speed of the brake pedal is exceeded and is 
terminated at least when the driver no longer acts on the brake pedal. 
Further criteria for initiating and terminating such an automatic braking 
process are illustrated in non-prepublished Patent Application DE-P. 43 25 
940.5 where it is also proposed to detect the pedal force applied to the 
brake pedal by the driver and to terminate the automatic braking process 
as a function of this pedal force. 
The detection of the pedal force in the brake pedal requires additional 
sensor and evaluation logic, which, particularly with a component which is 
safety critical, requires an additional design and development outlay. 
An object of the present invention is to provide a device and method which 
ensures reliable switching off of the automatic braking process but only 
with a low additional outlay. 
The foregoing object has been achieved in accordance with the present 
invention by detecting the relative movement between the pressure rod of 
the brake system and a component which can be moved with respect thereto 
within a defined movement play. The detection of the relative movement of 
the component with respect to the pressure rod takes place by two control 
switches, i.e. a make contact and a break contact, which are actuated via 
a common switching cam. A switching process of the control switches takes 
place whenever the brake pedal is moved in the direction of its rest 
position. If a switching process which corresponds to this relative 
movement takes place during an automatic braking process the braking 
process is terminated.

DETAILED DESCRIPTION OF THE DRAWINGS 
A brake booster designated generally by numeral 10 is shown in its rest 
position in FIG. 1. A switching cam 15 of switching element 14 arranged on 
a bolt 16 is also in the rest position. If the brake pedal (not shown) is 
actuated, first the valve piston 12 is moved by the pressure rod 11 in the 
direction of the main brake cylinder 19. Then, after the switching path of 
the valve piston 12 in the control housing 13 is overcome, both the valve 
piston 12 and the control housing 13 are moved in the main brake cylinder 
direction. During this movement, the switching cam 15 is also not 
actuated, because the bolt 16 is moved away during this movement from the 
front stop 18 which serves as an actuation element. The valve piston 12 
does not move in the control housing 13 sufficiently far to the rear for 
the bolt 16 to reach the front stop 18 until the brake pedal is released 
and quickly moved in the direction of its rest position. Then, the 
switching cam 15 is actuated by the front stop 18. With the switching 
element 14 functioning normally, a switching process takes place. In cases 
in which an automatic braking process is carried out, the breaking-off 
criterion of the automatic braking process is then fulfilled and it is 
terminated. 
However, since the switching process also takes place in the case of 
actuation of the brake pedal in which an automatic braking process is not 
triggered, the function of the switching-off criterion can be continuously 
monitored. As soon as the braking process is terminated and a pressure 
compensation has taken place between the chambers of the brake booster 10, 
the valve piston 12 moves in the control housing 13 into its rest position 
again. The bolt 16 then no longer lies against the front stop 18, the 
switching cam 15 is no longer acted on and the switching element 15 is, 
also in the rest position, provided normal functioning is taking place. 
FIG. 2 shows the signal timing characteristic at binary inputs of a control 
unit which is fed the signals of two control switches and of a brake light 
switch. A signal "1" corresponds to a closed circuit and a signal "0" 
corresponds to a broken circuit. The pedal travel sP realized by the brake 
pedal has been superimposed on the graph with synchronous timing. The 
pedal travel curve sP is shown by a dotted line. The signal characteristic 
of the brake light switch Bls is represented as solid line. The signal 
characteristic T1of the control switch which is realized as a break 
contact represented by a heavier broken line. The signal characteristic T2 
of the control switch which is a maker contact is represented by a 
dot-dash line. 
At the time t0, the brake pedal is moved out of its rest position to the 
extent that the brake light switch is actuated. Before this time, both 
control switches must be in a rest position. Since the brake light switch 
is usually realized as a break contact, the signal Bls of the brake light 
switch switches from "1" to "0" at the time t0. 
At the time t1, when the brake pedal is retracted by the driver, the 
control switch used as a break contact switches. At the time t2, the 
switching process of the other control switch which is used as a break 
contact is terminated. As a result, provided an automatic braking process 
is taking place, the breaking-off criterion is fulfilled and the braking 
process is terminated. A time interval between the times t2 and t1 which 
is greater than a threshold value St1 which has the value of a low number 
of working cycles of the control device permits it to be concluded that 
there is a fault in the switching device. Here, one working cycle of the 
control device last approximately 10 ms, a low number of working cycles is 
for example a maximum up to five working cycles of 10 ms each (preferably, 
however, only two working cycles). 
If a fault is detected, the triggering of an automatic braking processing 
is prevented. The failure of the automatic braking process is indicated 
via a display or a monitoring lamp and the driver is requested to go to a 
garage. If the fault occurs at the end of the automatic braking process, 
that process is preferably not terminated until the breaking-off criterion 
is detected. The failure is not indicated until the automatic braking 
process is terminated or even not until after the brake light switch 
indicates the termination of the braking process. 
During the further chronological sequence, the brake pedal is depressed 
again more strongly by the driver, and the peal travel increases again. 
Providing the system is operating correctly, the control switches switch 
between the times t3 and t4 and assume the rest position. When the brake 
is released again, a further switching process takes place between the 
times t5 and t6 since the control switches are actuated again. At the time 
t7, the brake light switch closes since the pedal travel has become so 
small that it is no longer actuated. However, the switching back of the 
switching element only takes place between the times t8 and t9. Even in 
the case of these switching processes of the switching element, the time 
intervals between the switching of one control switch and the switching of 
the other control switch must not exceed the prescribed limit. In 
addition, the time interval prescribed by the switching times t7 
(switching process of the brake light switch Bls from "0" to "1") and t9 
(termination of the switching process of the last control switch to 
switch) must also not exceed a prescribed limit value St2 which lies in 
the region of a low number of the control device working cycles, for 
example up to 15. The limit value St2 here should lie above the time 
period during which the valve piston is moved in the control housing out 
of the rest position and into the switched position in which a pressure 
compensation takes place between the chambers of the pressure vacuum brake 
booster with simultaneous evacuation for example via the manifold. 
According to one embodiment of the present invention, analog signals, or 
digital signals produced from analog signals by analog-to-digital 
conversion, are fed to the control unit. This feed not only permits a 
fault to be discovered but also permits the type of fault to be 
determined. For this purpose, a test circuit can be used, for example for 
each control switch. The test circuit consists of a resistor which is 
connected in series with the control switch. A resistor is connected in 
parallel to the series circuit consisting of the resistor and control 
switch. A further resistor is connected in series with this parallel 
circuit. This resistor is connected to a voltage source. The parallel 
circuit is connected to ground. The voltage to the resistor which is in 
series with the parallel circuit is detected as a signal. Preferably, all 
the resistors have the same impedance R. If the voltage source supplies 
the voltage U, the voltage signal has the value U/2 when the control 
switch is opened and the value U/3 when the switch is closed. A voltage 
signal "1" indicates a break in the cable downstream of the measuring 
point and a voltage signal "0" indicates a break in the cable upstream of 
the measuring point. Conclusions as to the operation of the control switch 
are made by reference to the occurrence or non-occurrence of switching 
processes. 
The operational monitoring of the switching device described in FIG. 1 is 
shown in FIG. 3 and takes place in parallel with the control of the 
automatic braking process and has two interfaces thereto. According to the 
first interface in the steps 114 and 120, the automatic braking process is 
terminated since, during the operational monitoring, it is detected that 
the breaking-off criterion of the automatic braking process has been 
fulfilled. The termination of the automatic braking process can be 
performed by the control of the automatic braking process after an 
approximate signal has been transmitted from the operational monitoring 
system of the deactivator to the control of the automatic braking process. 
After the automatic braking process is terminated, a signal is then 
transmitted to the operational monitoring to cause the operational 
monitoring to carry on to the next step. 
The second interface is made of the steps 105, 115 and 121 which are 
reached when the operational monitoring system detects an operational 
fault in deactivation. Then, triggering of the automatic braking process 
must be terminated. For this purpose also, an appropriate signal to the 
control of the automatic braking process can take place, and the control 
itself then prevents triggering of the automatic braking process. For the 
sake of safety, the deactivation of the automatic braking process can take 
place such that it lasts until the appropriate signal has been reset in a 
visit to a garage. 
For example, a signal representing measured pedal travel can be supplied to 
the control unit. The control unit concludes an absence of a fault in 
deactivating the automatic braking process if the control switches do not 
switch when the pedal travel is smaller than, say 50 mm and also the pedal 
speed is smaller than a pedal speed threshold value of, say between 100 
mm/s and 200 mm/s. 
In step 100, it is tested whether the brake light switch Bls which is 
constructed as a break contact is closed, that is to say the signal "1" is 
produced. If this is the case, in step 101 a variable t which represents 
the time is reset to the value 0. In the steps 102 and 103 it is tested 
whether the control switches T1 and T2 are in their position of rest, that 
is to say whether the signals T1="1" and T2="0" are transmitted to the 
control unit. If this is the case, no operational fault of the 
deactivation can be detected and the system jumps back to the start of the 
program. If it is detected in one of the two steps 102 or 103 that the 
signal corresponding to the position of rest of the control switch is not 
transmitted to the control device, .t is tested whether or not the time 
threshold value St2 has passed since the resetting of the variable t. If 
the time threshold value St2 has not been exceeded, the system jumps back 
to step 102. If, on the other hand, the time threshold value St2 has been 
exceeded, a fault is deemed present in the deactivation. Accordingly, in 
step 105, the triggering of the automatic braking process is then 
prevented and a corresponding item of information is made available to the 
driver. 
If, on the other hand, it is detected in step 100 that the brake light 
switch is actuated, and therefore the signal Bls="0" is transmitted to the 
control, it is initially tested in step 106 whether the control switch T1 
which is realized as a break contact is actuated and thus the signal 
TI="0" is transmitted to the control unit. If this is not the case, it is 
tested in step 107 whether the control switch T2 which is used as a maker 
contact is actuated and thus the signal T2="1" is transmitted to the 
control unit. If this is also not the case, the system jumps back to step 
100. 
If it is detected in one of the two steps 106 or 107 that the corresponding 
control switch T1 or T2 is actuated, the variable t is reset to 0 in the 
step 108 or 116. In the step 109 or in the step 117, it is then tested 
whether the other control switch T2 or T1 is also actuated. If this is the 
case, it is tested in step 110 whether an automatic braking process is 
taking place or not. If an automatic braking process is occurring, 
according to step 111, it is transmitted to the control of the automatic 
braking process that the breaking-off criterion is fulfilled and the 
automatic braking process is then terminated. Subsequently, the 
operational monitoring jumps back to step 100 which is also done if it has 
been detected in step 110 that an automatic braking process is not taking 
place. 
If it has been detected in step 109 or 117 that the second control switch 
T2 or T1 is not actuated, it is then tested in steps 112 or 118 whether or 
not the time threshold St1 is exceeded by the time variable t. If the time 
threshold St1 is not exceeded, a jump back to step 109 or 117 takes place. 
If, however, it is detected in step 112 or 118 that the time threshold St1 
has been exceeded, in step 113 or step 119 it is tested whether an 
automatic braking process is taking place or not. If an automatic braking 
process is occurring, according to step 114 or 120, the fulfillment of the 
breaking-off criteria is transmitted to the control of the automatic 
braking process. The automatic braking process is then terminated, and 
subsequently the step 115 or 121 is carried out. The system jumps directly 
to step 115 or 121 if it is detected in step 113 or 119 that an automatic 
braking process is not taking place. In step 115 or 121, the triggering of 
the automatic braking process is prevented and a corresponding item of 
information is made available to the driver. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.