DE3417144C2 - - Google Patents

Description

The invention relates to an anti-lock braking system for a vehicle brake system according to the preamble of Claim 1. Such a system is from DE-AS 22 53 867 known.

This document describes a multi-channel Anti-lock brake control system that is multiple autonomous Control channels and has a faulty Control channel immediately after an error occurs already decelerates during braking. The Other control channels remain unaffected by this. H. the system remains essentially what however, in the long run to undesirable reactions of the Can lead vehicle when braking.

Practice has shown that it is cheaper that shut down entire control system when a critical Error is detected. One such is that the Wheel speed of a wheel to be braked no longer recognized can be. Accordingly, the magazine "Bosch Technical Reports ", 1980, Issue 2, pages 80 to 88, an anti-lock brake control system that occurs when it occurs a critical error is completely switched off.

The applicant has found that when it is switched off an anti-lock brake control system during a straight brake control process in progress undesirable reactions of the vehicle can occur, and in particular if such a failure to the steered wheels of a vehicle occurs. It could then lock on one of the wheels. It  is therefore favorable in such a case To complete the braking process before the Brake control system is switched off. In the above DE-AS 22 53 867 describes this that faulty control channel only after braking has ended is switched to uncontrolled operation. Indeed remain, as mentioned, with that brake control system other control channels unaffected.

The invention is based on the object To specify the anti-lock braking system of the type mentioned at the outset, the one in the event of a speed sensor failure Backup function performs without being surprising Effects on the driving behavior of the vehicle if such a failure occurs during a braking should occur.

This task is characterized by the characteristics of claim 1 solved. An advantageous embodiment the invention is the subject of the dependent claim.

In the anti-lock braking system according to the present invention as in the above-mentioned magazine described object in the event of failure of a Speed sensor the entire brake control system except Put into operation, d. H. the braking system is on switched to uncontrolled operation. This is done in Depending on the location of the wheel on the vehicle either immediately with regard to the entire brake control system or gradually.

Thus, the properties of the brake control system as long as possible in an advantageous manner are made and unexpected reactions of the Vehicles are largely avoided.

In the following, the invention is based on exemplary embodiments explained in more detail with reference to the drawing. It shows

Fig. 1 is a schematic step or block diagram of a preferred embodiment of an anti-lock brake control system according to the present invention;

Fig. 2 is a perspective representation of the hydraulic circuits of an antilock brake control system in which the present invention is applied;

Figure 3 shows a circuit arrangement of the hydraulic circuits performing the anti-skid control according to the present invention.

Fig. 4 is a step or block diagram of a preferred embodiment of a controller unit in the anti-lock brake control system according to the present invention;

Fig. 5 is a flowchart of a fail-safe program which is executed by the front control units of Fig. 4;

Fig. 6 is a flowchart showing a failure-safety program, which is executed by the controller unit of the rear wheels;

Fig. 7 is a flowchart of a wheel speed sensor check program in the fail safe program of Figs. 5 and 6;

. Fig. 8 is a flowchart of a main program of the controller unit of Figure 4 for carrying out the antiskid control;

Fig. 9 is a flowchart of an interrupt routine which is executed by the controller unit;

FIG. 10 is a schematic block diagram of another embodiment of an anti-lock brake control system according to the present invention;

FIG. 11 is a schematic block diagram of still another embodiment of an anti-lock brake control system according to the present invention;

Fig. 12 is a block diagram of a controller unit in the anti-lock brake control system of Fig. 11;

FIG. 13 is a flowchart of a failure protection program to be executed by the controller unit in the anti-lock brake control system of FIG. 12; and

Fig. 14 is a block diagram of a still further embodiment of the antilock brake control system according to the present invention.

It should now be made to 3, which show a preferred embodiment of an anti-lock brake control system according to the present invention to the drawings, particularly FIGS. 1. This system comprises three controller units 202, 204 and 206 , each of which comprises a microprocessor. The controller unit 202, 204 and 206 are accommodated in a common housing and form a controller module 200 of the anti-lock control system. Referring to FIG. 1, a hydraulic actuator unit 300 includes three independently working braking systems 302, 304 and 306. Since the embodiment is illustrated in connection with a front-engine, rear-wheel drive vehicle, brake system 302 may apply braking force to a front left wheel (FL) , braking system 304 may apply braking force to a front right wheel (FR), and braking system 306 may apply braking force Feed the rear wheels (R) . Accordingly, the driven rear wheels are controlled together, while the non-driven front wheels are controlled individually.

It should be noted that although the embodiment shown an anti-lock brake control system in connection with a vehicle with front engine and rear-wheel drive illustrated is the present invention on such vehicles is not limited and also applicable to vehicles can get any other drive design have, such as  Front engine and with front wheel drive or Four wheel drive.

The controller unit 202 is assigned to the brake system 302 (FL) in order to regulate the braking force which is supplied to the left front wheel brake cylinder (not shown: see 30 a in FIG. 2). The regulator unit 204 is assigned to the brake system 304 (FR) in order to regulate the braking force which is supplied to the right front wheel brake cylinder (not shown: see 34 a in FIG. 2). The controller unit 206 is assigned to the brake system 306 (R) in order to regulate the braking force which is supplied to the rear wheel brake cylinders (not shown: see 38 a in FIG. 2), so that an anti-lock control of both rear wheels is carried out.

The controller unit 202 is connected to a wheel speed sensor 10 to obtain sensor signal pulses separated by intervals corresponding to the speed of the left front wheel. The controller unit 202 is further connected to an electromagnetic actuation device 16 , which controls the operation of an electromagnetic valve 16 a , which is arranged in the brake system 302 . The controller unit 202 , the brake system 302 and the wheel speed sensor 10 form an anti-lock brake control system 402 for the left front wheel. In the same way, the controller unit 204 is connected to a wheel speed sensor 12 to receive sensor signal pulses which represent the speed of the right front wheel, and is further connected to an electromagnetic actuator 18 of an electromagnetic valve 18 a , which in the braking system 304 is arranged. The controller unit 206 is also connected to a wheel speed sensor 14 to receive sensor signal pulses which represent the average speed of the rear wheels. An electromagnetic actuation device 20 controls the pressure of the working medium in the rear wheel brake cylinders. With the help of the brake pressure and through the wheel brake cylinders 30 a , 34 a and 38 a , corresponding brake disks 28, 32 and 36 , which are mounted on the wheel axles and rotate with the corresponding vehicle wheels, are braked by brake shoe assemblies 30, 34 and 38 .

Although the brake system shown includes disc brakes, can the anti-lock brake control system according to the present Invention equally well applicable to drum brake systems bring.

The controller units 202, 204, and 206 are associated with the actuator drive circuits 214, 216, and 218 , respectively , to control the operations of the respective actuators 16, 18, and 20 . Each of the controller units 202, 204 and 206 is connected to a corresponding wheel speed sensor 10, 12 and 14 via signal shaping circuits 208, 210 and 212 which are contained in the controller module 200 . Each of the wheel speed sensors 10, 12 and 14 can generate an AC sensor signal in a suitable manner, which is converted with the aid of an associated signal-shaping circuit 208, 210 or 212 into a rectangular pulse signal, which will be referred to below as the "sensor pulse signal" .

The controller units 202, 204 and 206 work independently and continuously process the sensor pulse signal, thereby controlling control signals for controlling the brake medium pressure in each of the wheel brake cylinders 30 a , 34 a and 38 a in such a way that the slip R at each of the vehicle wheels optimal is and the distance required to stop the vehicle is shortened, which distance will be referred to as "braking distance" in the following.

Each controller unit 202, 204 and 206 monitors the reception of the corresponding sensor pulses. On the basis of the pulse interval determined, the controller units 202, 204 and 206 calculate the current wheel speed or wheel speed V _w and also the current wheel acceleration or wheel deceleration a _w . A target wheel speed V _{i is} derived from these measured and derived values, which forms an assumed value which is derived from the wheel speed at which slip is assumed to be zero or almost zero. The target wheel speed V _i changes with a constant deceleration which is derived from changes in the wheel speed. The target wheel speed thus corresponds to an assumed vehicle speed based on the changes in the wheel speed. Based on the difference between the current wheel speed V _w and the target wheel speed V _i , a slip quantity R is derived. The controller units 202, 204 and 206 determine the appropriate operating mode for increasing, decreasing or maintaining the hydraulic brake pressure, which is supplied to the wheel brake cylinders 30 a , 34 a and 38 a . The control mode in which the brake pressure is increased will be referred to as "body mode" in the following. The control mode in which the brake pressure is reduced will be referred to as "degradation mode" hereinafter. The operating mode in which the brake pressure is kept essentially constant will be referred to below as the "holding mode".

The anti-lock control mode consists of a sequence of build mode, hold mode, break mode and Hold mode. This sequence is cycled through repeats the anti-lock brake control operation. Man therefore generally speaks of a brake control cycle.

Fig. 2 shows portions of the hydraulic brake system of a motor vehicle, in which the preferred embodiment of the anti-lock control system passes to the application. The wheel speed sensors 10 and 12 are provided near and rotate with the brake disc rotor 28 and 32 , respectively, to generate sensor signals whose frequencies are proportional to the wheel speed. The wheel speed sensor 14 is arranged near a propeller shaft in the vicinity of the differential gear 40 or the drive axle shaft 116 and rotates therewith. Since the speeds of the left and right rear wheels can change with each other depending on the driving conditions due to the action of the differential gear 40 , the rear wheel speed detected by the rear wheel speed sensor 14 is the average of the speeds of the left and right rear wheels In the description, the term "rear wheel speed" is intended to mean that it is the average speed of the left and right rear wheels.

Referring to FIG. 2, the operation unit 300 is provided with a brake master cylinder 24 via primary and secondary outlet ports 41 and 43 and via pressure lines 44 and 42 are connected. The master brake cylinder 24 is in turn assigned to a brake pedal 22 via a brake booster stage 26 , which in a suitable manner amplifies the braking force that is applied via the brake pedal 22 before it reaches the master brake cylinder. The actuation unit 300 is also connected to the wheel cylinders 30 a , 34 a and 38 a via brake pressure lines 46, 48 and 50 .

The circuit structure of the hydraulic brake control system will now be described in detail with reference to FIG. 3, which shows only one example of a hydraulic brake system in which the preferred embodiment of the anti-lock brake control system according to the present invention can be used therefore it should be noted that the hydraulic system is not limited to the embodiment shown. In Fig. 3, the secondary outlet port 43 is provided with inlet openings 16 b and 18 16 b of the electromagnetic flow control valves a and 18 a connected to the respective exhaust ports 16 c and 18 c with respective left and right wheel brake cylinders 30 a and 34 a via the secondary pressure line 42 are connected.

The primary outlet opening 41 is connected to an inlet opening 20 b of the electromagnetic valve 20 a , the outlet opening 20 c of which is connected to the brake cylinders 38 a of the rear wheels, specifically via the primary pressure line 44 .

The electromagnetic valves 16 a , 18 a and 20 a are also equipped with discharge openings 16 d , 18 d and 20 d . The drain openings 16 d and 18 d are connected via drain channels 80, 82 and 78 to the inlet opening 72 a of a fluid pump 90 . The fluid pump 90 is assigned to an electric motor 88 which drives it, this motor in turn being connected to a motor relay 92 , the operating cycle of which is controlled by the control module 200 with the aid of a control signal. When the motor relay 92 is energized to turn on, the motor 88 comes into operation and drives the fluid pump 90 . A drain port 20d of the electromagnetic flow control valve 20 a is connected to the inlet port 58 a of the fluid pump 90 via a drain channel 64th

The outlet openings 72 b and 58 b are each connected to the pressure lines 42 and 44 via return conduits 72 c and 58 c . The outlet ports 16 c, 18 c and 20 c 16 of respective electromagnetic flow control valves a, 18 a and 20 a are connected to the braking pressure lines 46, 48 and 50th Bypass channels 96 and 98 are also provided to connect brake pressure lines 46, 48 and 50 to pressure lines 42 and 44 , respectively, bypassing the electromagnetic flow control valves.

Check valves 52 and 66 are installed in the pressure lines 42 and 44 , which prevent the working fluid which has been pressurized by the fluid pump 90 from transmitting pressure pulses to the master brake cylinder 24 . Since the fluid pump 90 is designed to quickly reduce the brake pressure in the brake pressure lines 46, 48 and 50 and thus reduce the brake pressure in the wheel brake cylinders 30 a , 34 a and 38 a , the pump is driven after the brake pedal is released. This would result in pressure waves in the working fluid that migrate from the fluid pump 90 to the master cylinder 24 if the check valves 66 and 52 were not provided. The check valves 66 and 52 serve as one-way valves, which allow the flow of fluid from the master cylinder 24 to the inlet openings 16 b , 18 b and 20 b of the electromagnetic valves 16 a , 18 a and 20 a .

Pressure accumulators 70 and 56 are installed in the pressure lines 42 and 44 , these pressure accumulators serving to store the fluid pressure which is generated at the outlet openings 72 b and 58 b of the fluid pump 90 when the inlet openings 16 b , 18 b and 20 b are closed. For this purpose, the pressure accumulators 70 and 56 are connected to the outlet openings 72 b and 58 b of the fluid pump 90 via the return flow channels 72 c and 58 c . The exhaust valves 68 and 54 consist of one-way check valves that allow one-way fluid communication from the fluid pump to the pressure accumulators. These exhaust valves 68 and 54 prevent the pressure accumulated in the pressure accumulators 70 and 56 from going to the fluid pump in the form of pressure waves when the pump is shut down. In addition, the exhaust valves 68 and 54 also prevent the pressurized fluid flowing through the pressure lines 42 and 44 from flowing into the fluid pump 90 via the return channels 72 c and 58 c .

The inlet valves 74 and 60 are inserted into the drain channels 78 and 64 to prevent a shock wave of the pressurized fluid into the fluid 90 to the electromagnetic flow control valves 16 a , 18 a and 20 a after the brake pressure in the wheel brake cylinders released or dismantled. The fluid flowing through drain channels 78 and 64 is temporarily retained in fluid reservoirs 76 and 62 connected to the first.

Furthermore, bypass check valves 85, 86 and 84 are inserted into the bypass channels 98 and 96 to prevent the fluid in the pressure lines 42 and 44 from flowing to the brake pressure lines 46, 48 and 50 without first passing through the electromagnetic flow control valves 16 a , 18 a and 20 a to have happened. On the other hand, the bypass valves 85, 86 and 84 allow the fluid to flow from the brake pressure lines 46, 48 and 50 to the pressure lines 42 and 44 when the master cylinder 24 is released, and thereby the line pressure in the pressure lines 42 and 44 becomes lower than the pressure in the brake pressure lines 46, 48 and 50 .

The actuators 16, 18 and 20 of the electromagnetic flow control valves 16 a , 18 a and 20 a are controlled by the control signals from the control module 200 . The actuators 16, 18 and 20 are all connected to the control module 200 via an actuation relay 94 which thus controls the energization and de-energization of all devices. The mode of operation of the electromagnetic valves, which serve to protect against blocking, in an error-free brake control cycle is of a known type and therefore need not be explained here.

In order to carry out the failure protection in the event of a speed sensor failure, each of the controller units 202, 204 and 206 is composed of the components which are illustrated in FIG. 4. Since the circuitry and components used in units 204 and 206 are substantially the same as those of controller unit 202 , the following explanation applies only to controller unit 202 . Differences in the functions of the controller units 202 and 206 will be explained in detail.

According to FIG. 4, the controller unit 202 includes an input interface 230, a CPU 232, an output interface 234, a RAM 236 and a ROM 238th The input interface 230 is connected to the wheel speed sensor 16 via a waveform shaping circuit 208 to convert the AC sensor signal into digital sensor signal pulses so that the signal is adapted to the digital processor which forms the main part of the controller unit 202 . The input interface 230 includes an interrupt command generator 229 which produces an interrupt command in response to each sensor pulse and which contains a microprocessor to execute an interrupt routine, in which the input timing of sensor signal pulses are detected. The input interface also includes an intermediate register to temporarily store the input timing data of the sensor signal pulses. RAM 236 similarly has a storage section 240 for storing input timing data of the sensor signal pulses. The contents of the RAM memory section 240 can be shifted whenever calculations of the pulse interval, wheel speed, wheel acceleration and wheel deceleration, target wheel speed, slip amount, etc. are completed.

An interrupt identifier 256 is provided in the controller unit 202 in order to signal interrupt requests to the CPU. The interrupt flag 256 is set depending on the interrupt command from the interrupt command generator 229 . A time overrun interrupt flag stage 258 may suitably set an overflow flag if the measured interval between a pair of the monitored sensor pulses exceeds the capacity of a clock counter.

In order to control the arrival of the sensor pulses in time, a clock generator is connected to the controller unit 202 in order to supply time signals which indicate the elapsed real time. The timer signal value is disabled whenever a sensor pulse is received and stored in one or both of the intermediate registers 231 in the input interface 230 and the memory section 240 of the RAM 236 .

The controller unit 202 is also equipped with a registration register 257 , which must be set while the anti-lock brake control is being carried out. Furthermore, a further characteristic register 258 is set in the control unit 202 if a failure of the wheel speed sensor is determined. In the description, the flag register 257 is to be referred to as an "operation flag (FL _AS ) register" and the flag register 258 is to be referred to as an "error flag (FL _EFL ) register". The error flags in the controller units 204 and 206 are to be referred to as "error flags (FL _EFR or FL _ER )" in the following description. The controller unit 202 also includes a failure flag (FL _DIS ) register 255 , which must be set when the anti-lock control is deactivated due to a failure of one of the wheel speed sensors, so that the braking mode is then in the control mode the unregulated operating mode is switched over, and further comprises a clock counter 259 for counting the clock pulses of the clock generator 11 . The controller unit 202 also includes a timer 253 which can appropriately count the clock pulses of the clock generator 11 and which is reset depending on each successive sensor signal pulse. The timer 253 can therefore measure the pulse interval.

It should be noted that the operation of the anti-lock brake control system is determined by predetermined operating parameters, such as the amount of wheel deceleration. In practice, the operating state of the controller unit after a given time period of z. B. 2 sec after the termination of the degradation mode. To determine the end of the degradation mode, the high value of an input signal EV is monitored, as will be explained later. In addition, a circuit break detector 10 a is connected to the magnetic winding 126 of the wheel speed sensor 10 . The circuit break detector 10 a sends a weak detector current to the coil 126 . Since the voltage on the coil 126 rises when the circuit is interrupted, the detector 10 a emits a detector signal when the voltage on the winding is higher than a given voltage.

In operation, the failsafe program of Fig. 5 is executed repeatedly. Immediately after starting the failover program, the failure flag FL _{DIS of} the corresponding controller unit is checked in step 1001 . Under normal conditions, the failure flag is reset (FL _DIS = 0) and control then passes through step 1002 , in which the wheel speed sensor check program of FIG. 7 is executed. In this case, the input variable of the detector 10 a is first checked to determine the interruption of the circuit in a step 1002-1 . If the detector signal from the detector 10 a is missing, the value t _{FL of} the timer 253 is read out in the controller unit 202 in a step 1002-2 . Then a value t _{FL of} the corresponding timer is read out in the controller unit 204 in a step 1002-3 . The absolute value t _FL - t _FR | the difference between the timer values t _FL and t _FR is determined in a step 1002-4 . This difference is then compared to a reference value t _ref in step 1002-5 . A short circuit in the circuit can be determined by comparing the difference with the reference value. When the circuit is broken, when the check is performed at step 1002-1 , or when the absolute value | t _FL - t _FR | is greater than the reference value t _ref , the error flag FL _{EFL is} set in a step 1002-6 . If the absolute value of the determined difference is less than the reference value t _ref or after step 1002-6 , control returns to the fail-safe program at step 1004 .

At step 1004 , the error flag (FL _EFL ) is checked. If the error flag FL _{EFL is} not set, the anti-lock brake control is carried out in step 1006 . During the execution of this step 1006 , the main program of FIG. 8 is executed with the usual brake pressure control routine.

After a cycle of the anti-lock brake control in step 1006 , the error flag FL _{EFR is checked} in the control unit 204 for the anti-lock control of the right front wheel in step 1008 . If this is not set, the error flag FL _{ER of} the controller unit 206 for the rear wheels is checked in step 1010 . If both error flags FL _EFR and FL _{ER are} not set, the execution of the failover program is ended.

If the error flag FL _{EFR is} set when the check is performed at step 1008 , the operation flag FL _{AS is} checked in the flag register 257 at step 1012 . If the FL _AS indicator is set, the program ends. On the other hand, if the operation flag FL _{AS is} not set, the operating mode is switched to uncontrolled operation, so that the anti-lock brake control is deactivated and the brake pressure is set uncontrolled solely by brake pedal pressure in step 1014 . Thereafter, the failure flag FL _{DIS is set} in the flag register 255 at a step 1016 . After step 1016 , the program ends.

On the other hand, if the error flag FL _{ER is} set when the test is performed at step 1010 , control again goes to step 1014 to switch the operation to the unregulated operation.

When the failure flag FL _SID in step 1001 is set, or the error flag FL _EFL is set at the step 1004, the mode is switched at a step 1018 in the unregulated operating mode and it will be the default flag FL _DIS the controller 202 at step 1020 . The failure flags FL _DIS are then checked in a step 1022 in the corresponding flag registers of the controller units 204 and 206 . After both failure flags FL _{DIS are} set, a failure alarm monitor 17 is switched on to indicate that the anti-lock control is deactivated in step 1024 . After that, the execution of the failover program ends.

It should be pointed out that the controller unit 204 executes a fail-safe program in an analogous manner, which, however, is not identical to the previously explained program.

FIG. 6 shows a flow diagram of the fail-safe program for the rear wheels, which is analogous to that of FIG. 5. In addition to the necessary reorganization of the designation of the license plates, the only difference between FIGS. 6 and 7 is the arrangement of steps 1010 and 1012 . Specifically, in FIG. 7, one of the FL _EFR or FL _EFL flags is set when a check is performed at steps 1008 and 1010 , control goes to step 1012 . This means that as long as the speed sensor 14 for the rear wheels continues to function normally, the rear controller unit 206 continues to operate to complete the current anti-lock control process.

If one compares FIGS. 6 and 7 with one another, it becomes apparent that, in the sense of the present invention, if the speed sensor 14 for the rear wheels does not work properly, all three control units 202, 204 and 206 are switched off immediately, but then if one or both of the speed sensors 10 and 12 of the front wheels are working poorly or incorrectly, only the front controllers 202 and 204 are switched off immediately and the rear controller unit 206 is only deactivated after the current anti-lock control process has been completed. As a result, safety is achieved by the fail-safe system without running the risk that the driver of the vehicle trusts the anti-lock control system too shortly before it fails.

In the process explained above, the switching takes place Operating mode from the anti-lock control mode to the uncontrolled Operating mode in that the electromagnetic  Valves in the position corresponding to the body mode being held. To do this, the control signal kept at its low value.

Figure 8 illustrates the main program for the anti-lock control system. In practice, this program is generally carried out as a background task, ie it has a lower priority than all other programs under the control of the same processor. In the first step 1006-1 , it is waited until at least one sampling period and the coverage of a single sensor pulse or a group thereof, as will be explained in more detail, is completed, as is indicated when a sampling flag FL unites has a non-zero value. At subsequent step 1006-2 , the sampling flag FL is checked for a value greater than one, which then indicates that the sampling period is too short. If this is the case, control runs to the sampling control program, which is identified as " 2000 ". If FL = 1, then the control process has to be planned and the control goes to the usual main routine. Finally, after the completion of the main routine, a time overflow flag OFL is reset to signal successful completion of another sampling processing cycle at step 1006-3 , whereupon the main program ends.

Fig. 9 shows the interrupt program stored in the memory section 246 of the ROM 238 which is executed in response to the interrupt command generated by the interrupt command generator 229 whenever a sensor pulse is received. It should be noted that a counter value NC of an auxiliary counter 233 is initially set to 1, a register N which represents the frequency division ratio is set to 1 and a counter value M of an auxiliary counter 235 is set to -1. After the start of the execution of the interrupt program, the counter value NC of the auxiliary counter 233 is decremented by 1, specifically in a step 3002 . The auxiliary counter value NC is then checked in a step 3004 whether this value is greater than zero. For the first sensor pulse, since the counter value NC was decremented by 1 in step 3002 (1-1 = 0) and is therefore zero, the answer of step 3004 is NO. In this case, the clock counter value t is blocked in an intermediate register 231 in the input coupling electronics 230 in a step 3006 . The counter value NC of the auxiliary counter 233 is thereafter assigned the value N in a register 235, the register value N is representative of the frequency dividing ratio, which is determined during execution of the main routine, which is done at step 3008th The value M of an auxiliary counter 235 is then incremented by 1. The counter value M of the auxiliary counter 235 identifies each of a series of sampling periods which cover an increasing number of sensor pulses. Thereafter, the sampling flag FL is incremented by 1 at step 3012 . After step 3012 , the interrupt program ends, control is returned to the main program or back to step 3002 , which is dependent on the first occurrence.

On the other hand, if the counter value NC deviates from zero when a check is made in step 3004 , this indicates that not all pulses of this sampling period have been received, so that the interrupt program then ends immediately.

This interrupt routine is thus used to monitor the input timing t of each pulse sampling period, ie the time t required to receive the NC pulses, and signals the completion of each sampling period (for example M = 0 to M = 10) for the information of the main program .

Fig. 10 shows a further embodiment of an antilock brake control system according to the present invention, which performs a fail-safe function, similar to that of the embodiment described first. In this embodiment, each of the left front, right front and rear anti-lock control systems 502, 504 and 506 is equipped with a control unit 508, 510 and 512 . The controller units 508, 510 and 512 are connected to the corresponding wheel speed sensors 10, 12 and 14 via waveform shaping circuits 514, 516 and 518 . Controller units 508, 510 and 512 all have the same circuitry. The controller unit 514 is illustrated in more detail in FIG. 10 and will be described later.

The controller units 514, 516 and 518 are connected to electromagnetic actuators 16, 18 and 20 of the corresponding pressure control valves 16 a , 18 a and 20 a in order to bring the valve in question into one of its assembly, disassembly and holding positions. In order to control the positions of the pressure control valve, each controller unit 514, 516 and 518 sends an inlet signal EV and an outlet signal AV to the corresponding actuators 16, 18 and 20 . The actuator 16, 18 and 20 actuates the pressure control valve 16 a , 18 a and 20 a depending on the combinations of the inlet signal EV and the outlet signal AV , which combinations are the following:

Each anti-lock control system 502, 504 and 506 is also equipped with an error detector 520, 522 and 524 which suitably compares the error signal pulse intervals of the corresponding sensor with those of the others to detect discrepancies in the pulse interval. If it is determined that the sensor signal pulse interval is much longer than that of the other sensors, short circuits can be detected. Each error detector 520, 522 and 524 generates a detector signal when a pulse interval deviation is greater than a given value.

In addition, each wheel speed sensor 10, 12 and 14 is provided with a circuit interruption detector 10 a , 12 a and 14 a , which applies a search detector current to the winding 126 of the wheel speed sensor, further monitors the voltage on the winding or coil and generates a detector signal when the detected voltage becomes higher than a given value. Each circuit interruption detector 10 a , 12 a and 14 a is connected to the respective error detector 520, 522 and 524 . Each of the error detectors 520, 522 and 524 also responds to the detector signal of the corresponding circuit interruption detector 10 a , 12 a and 14 a to generate the detector signal.

Each fault detector 520, 522 and 524 is also connected to a corresponding reserve circuit 526, 528 and 530 . The reserve circuit 526, 528 and 530 is responsive to the detector signal of the error detector and sends a reserve signal to the corresponding controller unit 508, 510 and 512 . The controller unit 508, 510 and 512 is responsive to the reserve or additional protection signal from the reserve circuit to both inlet and Auslaßsignalwerte to lock to HIGH, to thereby set the corresponding pressure control valve 16 a, 18 a to keep us 20 a in the configuration mode. Since the build-up operating mode of the pressure control valve is held by the entire reserve or additional operation depending on the failure of the wheel speed sensor, the brake pressure can be set in an unregulated manner by pressing a brake pedal.

The detector signal from each of the error detectors 520 and 522 is fed to an input terminal of a corresponding AND gate 532 and 534 , the output terminal of which is connected to a corresponding error signal generator 538 and 540 . The other input terminal of the AND gate 532 and 534 is connected to the corresponding controller unit 508 and 510 to receive a signal indicating that the controller unit 508 and 510 is disabling or terminating the anti-lock control operation. Specifically, while the controller unit is operating and performing an anti-lock brake control operation, the input level on the AND gate remains at a low voltage value and when the controller unit is not working, the input variable from the controller unit increases to a high voltage value. On the other hand, the error detector's detector signal is at a high voltage value when a malfunction of the wheel speed sensor is detected by checking when the pulse intervals of the various sensors do not match. Therefore, only when the controller unit is not working and the fault detector detects a malfunction or a fault in the wheel speed sensor, the AND gate is opened in order to supply a gate control signal to the fault signal generator. The error signal generator is responsive to the gate control signal and transmits the error signal to a corresponding switch circuit 544 and 546 . In the normal position, the switch circuit 544 connects the error signal generator 538 of the left front anti-lock control system 502 to the reserve circuit 528 of the front right anti-lock control system 504 . Depending on the error signal from the error signal generator 538 of the front left anti-lock control system, the reserve or additional circuit 528 is activated to keep the intake and exhaust signals EV and AV at a high voltage value in order to enable an uncontrolled braking operation.

At the same time, the error signal generated by the error signal generator 538 is supplied via the switching circuit 544 to an input terminal of the AND gate 534 , which in turn is connected to the error signal generator 540 . The other input terminal of the AND gate 534 is connected to the controller unit 504 to receive a high level signal when the controller unit is not operational. Therefore, similar to the error signal generator 538 in the front left anti-lock control system 502, the error signal generator 540 always generates an error signal when the error signal is sent by the error signal generator 538 or when the error detector 522 detects a malfunction of the wheel speed sensor 18 and thus a detector signal with a high voltage level emits while the controller unit 510 is inoperable.

The error signal generator 540 is connected to the reserve circuit 530 of the rear anti-lock control system 506 via the circuit 546 . The rear anti-lock control system performs essentially the same functions as previously explained to disable the anti-lock brake control and to switch the mode to uncontrolled operation and to activate the error signal generator 542 to emit an error signal. The error signal generated by the error signal generator 542 is transmitted to the reserve circuit 526 of the front left anti-lock control system 502 and is simultaneously transmitted to the error signal generator 538 via the AND gate 532 . The error signal of the error signal generator 542 is also transmitted to a switching signal generator 550 in order to actuate the latter and to supply a switching signal to the switching circuit 544 . Depending on the switch signal of the switch signal generator 550 , the switch circuit 544 switches the electrical connection in order to connect the error signal generator 538 to an input terminal of an OR gate 552 . The OR gate 552 is also connected to the switch circuit 546 and the error signal generator 542 in the front right and rear anti-lock control systems 504 and 506 , which is responsive to a switching signal of the switching signal generator 554 . Similar to the switching signal generator 550 , the switching signal generator 554 also responds to the error signal of the error signal generator 538 in order to supply a switching signal to the corresponding switching circuit 546 .

The OR gate 552 is responsive to a high voltage signal from one of the switch circuits 544 and 546 and the error signal generator 542 to activate an alarm monitoring stage 558 to generate an alarm.

In the rear anti-lock control system 506 , the switch circuit, the AND gate and the switch signal generator, which are present in the control systems 502 and 504 explained above , are not required. In addition, the error signal generator 542 is only connected to the controller unit 512 . Therefore, the error signal generator 542 only generates an error signal when the controller is stopped due to an error in one of the wheel speed sensors 10, 12 and 14 . In order to make the error signal generator active only when the controller unit 512 is stopped due to a malfunction of a wheel speed sensor, the controller unit sends a signal indicating the failure of the system directly to the error signal generator.

If a malfunction of the wheel speed sensor 14 is determined, the operating mode is switched to the uncontrolled operating mode. As soon as the operating mode is switched to the unregulated operating mode, the error signal generator 542 is activated, depending on the high level signal from the control unit 512 , in order to send the error signal to the auxiliary circuit 526 of the front left anti-lock control system 502 . As a result, the front left and front right anti-lock control systems are disabled and the mode is switched to uncontrolled.

This consequence of the reserve or additional protection operation can be certain switch the operating mode to uncontrolled operation, while simultaneously skidding or blocking the rear wheels is prevented.  

FIGS. 11 and 12 show a further embodiment of the antilock brake control system according to the present invention. According to this embodiment according to FIGS. 11 and 12, the wheel speed sensor 10 for detecting the speed of the front left wheel is connected to the controller unit 202 via a switching circuit 201 . Switch circuit 201 is also connected to wheel speed sensor 12 , which detects the wheel speed of the right front wheel. The switch circuit 201 normally connects the wheel speed sensor 10 to the controller unit 202 , but switches depending on a failure or failure of the wheel speed sensor to connect the controller unit 202 to the wheel speed sensor 12 . The controller unit 202 then receives the sensor signal pulses from the wheel speed sensor 12 and performs an anti-lock control operation based on the wheel speed parameters of the right front wheel.

Similarly, controller unit 204 in front right anti-lock control system 404 is connected to wheel speed sensor 12 via switch circuit 203 . Switch circuit 203 is also connected to wheel speed sensor 10 . Switch circuit 203 normally connects wheel speed sensor 12 to controller unit 204 . However, if a failure or error of the wheel speed sensor 12 is determined, the switching circuit 203 changes its switching position in order to connect the controller unit to the wheel speed sensor 10 .

The circuit structure of each controller unit 202, 204 and 206 is essentially the same as that illustrated in FIG. 4. In order to avoid repetitions in the description, a detailed description of the controller units 202, 204 and 206 is therefore omitted. Similarly, the circuit interruption detectors 10 a , 12 a and 14 a and the associated connections from FIG. 11 are omitted for the sake of clarity.

Fig. 13 is a flowchart showing a failsafe program is executed by which the controller units 202 and 204. Fig. 13 shows specifically the program for the controller unit 202; the program for controller 204 has the same control flow and acts on analog tags and devices. The corresponding program for the rear controller 206 is not shown, since the differences between this program and FIG. 13 correspond to the differences between FIGS. 5 and 6.

At the initial step 6001 , the failure flag FL _{DIS is} checked. If this is not set, then at step 6002 the wheel speed check routine as illustrated in FIG. 7 is executed. In a step 6004 , the error flag FL _EFL is then checked. If the error flag FL _{EFL is} not set, an anti-lock control is carried out in a normal manner in step 6006 . The error flag FL _{EFR is then} checked again in a step 6008 . If it is not set, the error flag FL _{ER is} checked in step 6010 . If both indicators are not set, the program ends. On the other hand, if the error flag FL _{EFR is} set, the operation flag FL _{AS is} checked in step 1012 . If the FL _AS operation indicator is set, the execution of the program runs to the end. Otherwise, the mode is switched from the control mode to the unregulated mode by holding the position of the pressure control valve in the body mode at step 6014 . Thereafter, the shutdown flag FL _{DIS is set} in the flag register 255 at step 6016 .

On the other hand, if the error flag FL _{ER is set} in the rear anti-lock control system when the test is made in step 6010 , the mode is immediately switched to unregulated mode in step 6014 .

If a malfunction or error of the wheel speed sensor 10 is determined, in the test at step 6002 , the switching circuit 201 is activated and connects the controller unit 202 to the wheel speed sensor 12 for the right front wheel at step 6018 . The operation identifier FL _{AS is then} checked in step 6020 . If the operation flag FL _{AS is} set, control proceeds to step 6006 and otherwise the anti-lock control system is deactivated by switching from the control mode to the unregulated mode at step 6022 . Thereafter, the failure flags FL _{DIS of} the other controller units 204 and 206 are checked in step 6024 , and after both these failure flags are set, an alarm is generated in step 6028 .

Fig. 14 is a block diagram of a still further embodiment of the antilock brake control system according to the present invention. This embodiment follows a procedure similar to that illustrated in FIG. 13.

In FIG. 14, the wheel speed sensors 10 and 12 for the left front wheel and the right front wheel are connected to signal-forming circuits 614 and 616 of the front left and front right anti-lock control systems via switch circuits 618 and 620 , respectively. The signal shaping circuits 614 and 616 are connected to the controller units 608 and 610 , respectively, in order to supply them with sensor signal pulses. The wheel speed sensor 14 of the rear wheels is connected to the signal-shaping circuit 622 of a rear anti-lock control system with a controller unit 612 . Each of the wheel speed sensors 10, 12 and 14 is also connected to the output of a fault detector circuit 624 .

In this embodiment, each wheel speed sensor 10, 12 and 14 is supplied with a constant voltage that defines a minimum sensor signal value. Error detector circuit 624 checks the output level of each wheel speed sensor and generates an error signal indicating a failure or error of a given wheel speed sensor when the corresponding output level drops below the minimum level. If a failure or error of one of the wheel speed sensors is detected, the error detector circuit 624 sends the corresponding error signal to a reserve or additional circuit 626 . Auxiliary circuit 626 performs a reserve or auxiliary protection operation according to the following schedule.

1. If the wheel speed sensor 10 fails:

• 1) activate switch circuit 618 to connect controller unit 608 to wheel speed sensor 12 ;
• 2) perform anti-lock control for the left front wheel using the sensor signals of the wheel speed sensor 12 ;
• 3) set the anti-lock control for the right front wheel and the rear wheels as under normal conditions away;
• 4) generate an alarm after the anti-lock operations of all anti-lock control systems 602, 604 and 606 end; and
• 5) simultaneously with 4) switch the operating modes of all Anti-lock control systems to unregulated operating mode.

2. If the wheel speed sensor 12 fails:

• 1) activate switch circuit 620 to connect controller unit 610 to wheel speed sensor 10 ;
• 2) perform anti-lock control for the left front wheel using the sensor signals of the wheel speed sensor 10 ;
• 3) set the anti-lock control for the left front wheel and the rear wheels as under normal conditions away;  
• 4) generate an alarm after the anti-lock operation of all anti-lock control systems 602, 604 and 606 ends; and
• 5) simultaneously with 4) switch the operating modes of all Anti-lock control systems to unregulated operating mode.

3. If the wheel speed sensor 14 fails:

• 1) switch the operating modes of all anti-lock control systems 602, 604 and 606 to uncontrolled operating mode;
• 2) generate an alarm at the same time.

In order to carry out the procedure explained above, the reserve or additional circuit 626 is connected to the switch circuits 618 and 620 in order to supply the switching commands. The reserve circuit 626 is also connected to the controller units 602, 604 and 606 in order to supply the signals indicating an error and to receive from them a signal which indicates the absence or the end of an anti-lock control. The backup circuit 626 is also connected to an alarm generator circuit 628 , which includes a switching transistor 630 , as well as a switching relay 632 and an alarm indicator lamp 634 .

Claims (2)

1.Anti-lock braking system for a vehicle brake system, containing at least three independent control channels for the individual wheels of the vehicle with independent wheel control on the front axle, each with a speed sensor for determining the wheel rotation speed, an evaluation circuit that evaluates the speed signals and independently of them control signals Blockage protection valves passes on, and with a failure circuit which, in the event of faulty behavior or failure of the speed sensor, switches off its associated control channel and thereby permits uncontrolled brake pressure on the wheel, characterized in that

• a) if one of the speed sensors ( 10 or 12 ) on the steered wheels fails, the associated control channels ( 202 and 204 ) are switched off immediately, the other control channel ( 206 ), on the other hand, only after the current control process has ended,
• b) in the event of failure of another speed sensor ( 14 ), however, the entire brake system is immediately switched to uncontrolled operation.

2. Anti-lock braking system according to claim 1, characterized in that it contains a failure alarm stage ( 558 ) which emits an alarm when the entire system is switched to uncontrolled operation.