Monitoring method and device in automatic braking process

A device monitors an automatic braking process by using a fault-detecting, operational testing method which takes place via an automatic braking process lasting only briefly, typically about 50 ms. The method is initiated by a test control device and can take place during different vehicle states. If, for example, current through a solenoid valve does not lie within specific acceptable limit values or pedal travel which results from the actuation is not determined at the brake pedal, the device concludes that an operational fault has occurred

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to a method for monitoring the operation of a 
device for carrying out an automatic braking process and to the device for 
carrying out an automatic braking process comprising a solenoid valve 
actuator carrying out an automatic braking process, a switch for 
terminating the automatic braking process under specific switching 
conditions, a displacement sensor for detecting travel of a brake pedal, a 
control device for controlling the automatic braking process and a test 
control device. 
DE 42 08 496 C1 shows a partial-vacuum brake booster which has a solenoid 
valve for venting the pedal-side chamber in order to produce a higher 
brake pressure than results from the position of the brake pedal. Arranged 
on the brake pedal is, on one hand, a displacement sensor which detects 
the position of the brake pedal and, on the other hand, a switch which is 
actuated at least when the brake is released by the driver. 
In this known device, the presence of operational faults of the device for 
carrying out an automatic braking process is not monitored. As a result, 
faults may occur which prevent automatic braking processes from being 
carried out in an operationally reliable way. 
An object of the present invention is to provide a monitoring method for an 
automatic braking device to detect faults which could prevent an automatic 
braking process from being reliably carried out. 
This object has been achieved according to the present invention by 
providing a method in which monitoring takes place by way of a test 
control device with a brief actuating of the solenoid valve by the test 
control device taking place under prescribed vehicle states, determining 
at least whether switching current of the solenoid actuator valve lies 
within prescribed limit values and via the displacement sensor, whether a 
pedal travel has occurred which corresponds to the pedal travel caused by 
the automatic braking process as criteria as to whether or not an 
operational fault of the automatic braking process has occurred, and if 
the determined criteria are not fulfilled the presence of an operational 
fault in the device for carrying out an automatic braking process is 
detected and appropriate intervention in the automatic braking process 
occurs. 
The operational testing takes place by an automatic braking process which 
only lasts briefly and is not triggered by the control device of the 
automatic braking process but rather by a test control device. "Brief 
actuation" is used here in the sense of an actuation about a few tenths of 
a second, preferably only in the order of magnitude of approximately 50 
ms. The actuation can take place during different travel states which are 
specified in the test control device. If it is detected here that the 
current through the solenoid valve is not within prescribed limit values 
or that a pedal travel which results from the actuation is not determined 
at the brake pedal, the presence of an operational fault of the device is 
concluded. 
The actuation of the solenoid valve by the test control device can be 
carried out when the ignition of the vehicle is switched on, after the 
engine starts up and when the brake pedal is not being actuated for the 
first time after starting up. In addition, in the case of an operational 
fault the execution of an automatic braking process is prevented and the 
driver is informed of this via a display. Furthermore, other criteria are 
also presented which are used to test the operation of the device for 
carrying out an automatic braking process.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows the test control device 10 and a device for carrying out an 
automatic braking process which comprises a control device 1 separate from 
the test control device 10 which, like the test control device, is 
supplied from the voltage source 6, usually the voltage of the vehicle 
electrical system. The test control device 10 is connected to the control 
device 1 via the data lines 15. The control device 1 has an input for a 
data line 9 which for example permits the control device 1 to be connected 
to a databus in the vehicle or to a diagnostic device. 
A displacement sensor designated generally by the numeral 2 of the brake 
pedal has a switch 3 of double configuration (double throw/double pole) in 
this embodiment and a solenoid valve 4 which are also connected to the 
control device 1. The lines leading from these components to the control 
device 1 each have a branch leading to the test control device 10. 
Furthermore, the brake light switch 5 is connected to the test control 
device 10. The brake light switch 5 is a single switch (single 
throw/single pole) because its operation can be monitored via the signals 
of the displacement sensor 2. It is, therefore, not necessary to make the 
brake light switch 5 of a double configuration, in contrast with switch 3, 
even when using other control devices in the vehicle which are critical 
for safety and dependent on the switched position of the switch 5. In 
addition, the display 11, e.g. as lamp, is also connected to the test 
control device 10 to indicate to the driver the occurrence of an 
operational fault which is detected by the test control device 10. 
FIG. 1a shows another embodiment in which the test control device 10 and 
the control device 1 form a single unit 19 connected with a conventional 
anti-lock brake control system 20. 
FIG. 2 is a flow diagram which illustrates testing of the device for 
carrying out an automatic braking process. It is assumed here that the 
switch 3 which causes the automatic braking process to be switched off is 
moved out of a rest position into its switched position during the 
actuation of the brake pedal and remains in this position until the brake 
pedal is moved in the direction of its position of rest. According to 
other embodiments of the switch 3 which are within the contemplation of 
the present invention, the switching process which causes the automatic 
braking process to be broken off may also be dependant on the pedal force 
which the driver applies. Therefore, the switch 3 can be other than a pure 
displacement sensor, such as the brake light switch 5, because the switch 
3 also switches back into the rest position when the brake pedal is not 
moved back completely into its rest position. 
Step 100 represents the operational logic of the automatic braking process, 
where the fulfillment of triggering and breaking-off criteria is tested 
and the execution of the automatic braking process is controlled. In step 
101, the system is interrogated as to whether an automatic braking process 
is carried out. If the process has not been carried out, the system jumps 
back immediately to step 100, and testing of the operation of the elements 
therefore does not take place. As a result, the automatic braking process 
is prevented from being broken off prematurely when the present automatic 
braking process is being carried out and an operational fault occurs 
during that process. 
In step 102 it is investigated whether the brake light switch 5 is 
actuated. If the switch 5 is activated and if in step 103 it is detected 
that the signal of the displacement sensor represents a pedal travel X 
which exceeds the pedal travel threshold value X1, it is tested in step 
104 whether the switch 3 is actuated or not. Here, the switch 3 can be of 
the aforementioned double configuration and actuation of the switch is 
only concluded if both switching elements of the switch are actuated. 
Correct operation is concluded when the switch 3 is actuated. The jump 
back to step 100 then takes place. If it has been detected in step 104 
that the switch is not actuated, the presence of a defective switch 3 is 
then concluded in step 105. The fault is then stored in the fault memory 
according to step 114. 
The state of the fault memory is tested in step 115. If, because of its 
state, a fault which impairs the reliability of the automatic braking 
process is detected, the automatic braking process is switched off. 
Otherwise, the system jumps back to step 100. Testing of the fault memory 
according to step 115 takes place here after each new entry in step 114. 
If, however, it has been detected in step 103 that the pedal travel X does 
not exceed the pedal travel threshold value X1 whose value lies at a pedal 
travel of a few millimeters, in particular at approximately 5 mm, the 
switched state of the switch 3 is tested in step 106. If the switch 3 is 
actuated, according to step 107 the presence of a fault of the 
displacement sensor 2 is concluded. If the switch 3 is not actuated, then 
in step 108 the presence of a defect of the brake light switch 5 is 
concluded. In both cases, in step 114 an appropriate entry is made in the 
fault memory. 
If, on the other hand, in step 102 an actuation of the brake light switch 5 
has not been detected, in step 109 the pedal travel X is compared with a 
pedal travel threshold value X2. This pedal travel threshold value X2 can 
have here the same value as the pedal travel threshold value X1. If it is 
detected in step 109 that the pedal travel threshold value X2 has been 
exceeded, it is tested in step 110 whether the switch 3 is actuated or 
not. If the switch 3 has been actuated, the system jumps back to step 108. 
Otherwise, in step 111 the presence of a defective displacement sensor 2 
is concluded, and the system jumps then to step 114. 
If it has not been detected in step 109 that the pedal travel threshold 
value X2 has been exceeded, then in step 112 the switch 3 is tested. If 
the switch 3 is actuated, according to step 113 the presence of a 
defective switch 3 is concluded and the system jumps to step 114. 
Otherwise, all the tested elements are operative and the system jumps back 
to step 100. 
As above described, operational fault is detected based upon the 
determination of certain criteria which includes testing as to whether the 
pedal travel determined by the displacement sensor lies within an interval 
formed by a lower pedal travel limit value X1 and an upper pedal travel 
limit value X2. Alternatively, the system can test whether a pedal speed 
value which is fed to the test control device 10 exceeds a threshold 
value, or in lieu of determining the switching current, the voltage at the 
terminals of the solenoid valve actuation 4 can be measured. 
In addition, the supply voltage U of the control device 10 can be 
monitored. The system deems an operational fault to occur when the supply 
voltage U is outside a prescribed operating voltage interval and to be 
terminated what the supply voltage U is within a switch-on interval which 
is narrower than the operating voltage interval. 
The flow diagram described here represents testing of the operation 
elements, during the "normal" braking operations in which automatic 
braking is not taking place. Since these normal braking operations are the 
overwhelming majority of braking operations which take place continuously, 
continuous testing of the operational elements of the automatic braking 
process is ensured. 
FIG. 3 shows the flow diagram of a method for monitoring the operation of 
the device at the start of a journey. In step 200, it is tested whether 
the ignition switch has been switched on, whether the starter has been 
actuated or whether the brake is initially unactuated after starting up. 
If one of these criteria is fulfilled, the system jumps to step 201, 
otherwise the interrogation is renewed. 
In step 201, the solenoid valve 4 is briefly actuated, that is to say for 
up to 500 ms, preferably, however, only for 50 ms to 200 ms, by the test 
control device 10. The switching current of the solenoid valve is measured 
according to step 202. If it is within the acceptable limit values, which 
are for example stored in the control test device 10 or in the control 
device 1, in step 203 it is measured whether the pedal travel X exceeds a 
pedal travel threshold value X3. The acceptable limit values are 
determined by the operating range of the switching currents of the 
solenoid valve 4. If this is also the case, correct operation of the 
device for carrying out the automatic braking process is concluded and 
according to step 204 the brake pressure is reduced. Then, for example if 
all the three criteria of step 200 have not yet been fulfilled, a jump 
back to step 200 may occur or else a jump to step 100 (FIG. 1) as 
illustrated in FIG. 3. 
If one of the two criteria of steps 202 and 203 has not been fulfilled, a 
jump to step 205 takes place. It is indicated to the driver that an 
operational fault of the automatic braking process has occurred. Execution 
of the automatic braking process can be prevented. An automatic braking 
process which may be present is either carried out completely or broken 
off. In the event that the automatic braking process is broken off, the 
additional brake pressure which has been built up is thus reduced again as 
would be the case when the normal breaking-off criteria is fulfilled. 
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.