GB1596938A

GB1596938A - Anti-lock brake control devices for motor vehicles

Info

Publication number: GB1596938A
Application number: GB288078A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-01-24
Filing date: 1978-01-24
Publication date: 1981-09-03
Also published as: JPS6228024B2; DE2702800A1; DE2702800C2; JPS5393280A

Description

(54) IMPROVEMENTS RELATING TO ANTI-LOCK BRAKE CONTROL DEVICES FOR MOTOR VEHICLES (71) We, WABCO FAHRZEUG BREMSEN GMBH, formerly Wabco Westinghouse GMBH, a Company organised according to the laws of the Federal Republic of Germany, of 3000 Hannover 91, Postfach 91 12 80, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to anti-lock brake control devices for motor vehicles especially road vehicles, of the kind having a signal generating device or sensor associated with at least one wheel and responsive to its rate of rotation at least during a braking operation, an electronic recognition circuit for the generation of deceleration, acceleration and slip signals in response to the signals from the generating device, a logic circuit connected to the electronic recognition circuit by way of which one or more solenoid inlet valves and outlet vaLves are operated for controlling the wheel brake pressure and means for monitoring the operated periods of the solenoid inlet valves and outlet valves and for disabling the anti-lock control device if necessary.

Such anti-lock brake control devices operate in such a manner that, on the occurrence of the tendency of a wheel to lock, a deceleration signal - b is transmitted from the electronic recognition circuit via the logic circuit to the solenoid valves (inlet and outlet valves) arranged upstream of a wheel brake cylinder so that these valves are energised.

The solenoid inlet valve closes and prevents the further supply of a pressure medium to the wheel brake cylinder. At the same time, the solenoid outlet valve opens so that the brake pressure in the wheel brake cylinder is reduced.

When a certain slip value is reached a slip signal is generated which overlaps the --b signal and maintains the energisation of the solenoid inlet valve and the solenoid outlet valve even after the reduction of the -b signal. When the rotational deceleration of the wheel has fallen below the critical value again (i.e. its locking tendency is avoided by the brake pressure reduction) the electronic recognition circuit emits an acceleration signal + 6 which blocks the slip signal, so that the solenoid outlet valve is no longer energised and closes, but the recognition circuit maintains the solenoid inlet valve closed for a short period longer in order to permit a more rapid re-starting of the wheel.

If a fault occurs in the anti-lock device which results in an excessively long presence of the deceleration signal - 6 the corresponding wheel brake cylinder is subjected to brake pressure reduction for too long and the wheel is no longer adequately braked. If there is too long an acceleration signal + 6 the pressure in the wheel brake cylinder is maintained constant for too long, i.e. no further pressure can be supplied which likewise results in insufficient braking of the wheel. A faulty slip signal, similarly to a faulty deceleration signal - 6, leads to the wheel brake cylinder losing too much pressure.

In order to avoid these disadvantages it has been proposed to provide the anti-lock control device with a monitoring circuit by means of which the operated period of the solenoid valves is monitored, and if the maximum permissible time period for the solenoid valves to be energized is exceeded, the anti-lock control device is disabled so that conventional brake pressure control by sensitive operation of the brake pedal is rendered possible.

The monitoring circuits proposed hitherto, however, have the disadvantage that the monitoring time is too long which results in delayed reaction to a faulty condition and too great a reduction of the brake pressure in the wheel brake cylinder. The result is an insufficient braking of the vehicle.

It is an object of the invention to provide a security or reliability circuit for an anti-lock brake control device which circuit recognises faults in the anti-lock control device sufficiently early for the effect of the faults on the behaviour of the vehicle during a braking operation to be substantially reduced.

According to the present invention there is provided an anti-lock brake control device for a vehicle having signal generating means for monitoring the rotational behaviour of at least one wheel of the vehicle, a recognition circuit responsive to the signal generating means for deriving deceleration, acceleration and slip control signals, a logic circuit by means of which one or more brake pressure medium inlet valves and outlet valves for controlling the wheel brake pressure are operated and also means for monitoring the operation periods of the inlet valves and outlet valves, wherein there is provided a device for monitoring the deceleration, acceleration and slip control signals which is connected to means for monitoring the operation periods of the inlet valves and outlet valves and to the logic circuit in such a manner that, in the case of a faulty deceleration, acceleration or slip control signal, the faulty control signal branch can be disconnected and the remaining faultfree control signal branches continue to be used for control.

Among the advantages achieved by the invention compared to known reliability circuits are that the source of failure in the anti-lock control device is localised, so that it is possible to disconnect the faulty control signal branches individually, and that it is possible to reduce the monitoring time compared with that of previously proposed devices by approximately 50% as a result of the early recognition of the fault.

In order that the invention may be fully understood and readily carried into effect it will now be explained in more detail below with reference to the accompanying drawings.

To make the drawings clearer components, circuit elements and lines not forming part of the invention are shown either only in block form or are omitted altogether. In the drawings: Figure la shows a logic circuit which couples the signals emitted from an electronic recognition circujt to solenoid inlet valves and/or outlet valves; Figure lb shows an embodiment of a reliability circuit according to the invention by means of which the signal branches for acceleration, deceleration and slip control signals, and also the signals delayed at the solenoid inlet valves and/or outlet valves are monitored and on the occurrence of a fault, are disabled; Figure 2a shows a circuit similar to the one shown in Figure la;; Figure 2b shows a circuit substantially identical to the reliability circuit shown in Figure Ib except that there is no circuit portion for monitoring the period during which the deceleration, acceleration and slip control signals are present; Figure 3 shows a reliability circuit where a single digital counting device establishes the duration of the presence of the decelera tion, acceleration and slip control signals and also of the signals at the solenoid inlet valves and outlet valves;; Figures 4a to 4g show the wave forms of deceleration, slip and acceleration control signals during a control operation in the case of a correctly functioning anti-lock brake control system and also the reset signals, which occur at the beginning of each of these signals, of the device monitoring the duration of the presence of the control signals and the signals present at the solenoid inlet valves and outlet valves during a control operation; Figures Sa to 5h show the typical wave forms of the signals in the case of a faulty deceleration signal - 6; Figures 61 a to i show the typical wave forms of the signals in the case of a faulty acceleration signal +bl;; Figures 6L1 a to f show the wave forms of the signals in the case of a faulty - 6 signal when the wheel is not braked; Figure 7 shows a reliability circuit in which the operated periods of the solenoid inlet valves and outlet valves are monitored separately; Figure 8 shows a reliability circuit wherein separate counting devices are arranged to monitor the delay, acceleration and slip con trol signals and also to monitor the solenoid operation periods; and Figure 9 shows a block diagram of an anti lock brake control device having a reliability circuit wherein the anti-lock device is connected by means of a single signalling line per signal branch to the reliability circuit.

Figure la shows a conventional logic circuit and the solenoid valves of the automatic control system of an anti-lock brake control device for a vehicle.

On the occurrence of a tendency of brakes to lock a wheel signalling device 2 of an electronic recognition circuit 1 generates a deceleration signal --b and supplies this via an AND gate 3, an OR gate 4, an OR gate 5, an AND gate 6 and a terminal amplifier 7 to a.

solenoid inlet valve 8. Simultaneously, the -6 signal passes via an AND gate 9, one input of which is connected to the output of the OR gate 4 and the other input of which is connected to the output of the AND gate 3, and via an OR gate 10, an AND gate 11 and a ter minal amplifier 12 to a solenoid outlet valve 13. The two solenoid valves 8 and 13 are energised by the - 6 signal so that the solenoid inlet valve 8 closes and the solenoid outlet valve 13 opens. Further supply of pressure medium to a wheel brake cylinder (not shown) is therefore prevented by the - 6 signal, and the brake pressure in the wheel brake cylinder is reduced by the opening of the solenoid outlet valve 13.

On reaching a certain slip value, a slip signal X is generated by a signalling device 21 of the circuit 1, which signal passes via a first input of an AND gate 22, a first input of an AND gate 24, the second input of the OR gate 4 and the OR gate 5 to the solenoid inlet valve 8 and also from the output of the OR gate 4 via an input of the AND gate 9, the OR gate 10 and the AND gate 11 to the solenoid outlet valve 13 and maintains the energisation of the solenoid inlet valve 8 and the solenoid outlet valve 13 even after the end of the deceleration signal -6. When the rotational deceleration of the wheel has fallen below the critical value again (i.e. the locking tendency is past) there is emitted by a signalling device 14 of the circuit 1 an acceleration signal +bl which blocks the slip signal X so that the solenoid outlet valve 13 is no longer energised and closes. The acceleration signal +bl passes from the signalling device 14 via a first input of an AND gate 15, a first input of an AND gate 16 and also the OR gate 5 to the solenoid inlet valve 8 and maintains the energisation of this valve - closed - for a while longer in order to prevent an increase in.the brake pressure and permit a more rapid re-starting or acceleration of the wheel.An AV signal is always applied via an OR gate 17, a reduction delay time element 18 and an inverter 19 to the inverting input of the AND gate 15, if at least one of the solenoid outlet valves is energized. This means that the acceleration signal +bl can become effective only if a solenoid outlet valve has been actuated beforehand.

The circuit illustrated makes it possible to effect a brake pressure adjustment, as early as the starting phase of the wheel, by means of another acceleration signal +b2 generated by a signalling device 20 of the circuit 1.

Figure 1b shows a reliability circuit for monitoring, and optionally switching off, the signals -b, +bl and X and also the signals applied to the solenoid valves in the circuit of Figure 1.

The reliability circuit has two OR gates 25 and 26, the OR gate 25 receiving via terminals I and II the signals applied to the solenoid inlet valve 8 and to the solenoid outlet valve 13 and the OR gate 26 receiving the -b and the +bl signals via the terminals III and VI. Terminal III is connected between the signalling device 2 and the AND gate 3, and terminal VI between the signalling device 14 and the AND gate 15. The output of the OR gate 25 is connected to the reset input R of a counting device 27, the task of which is, during the period that a signal is present at the solenoid inlet valve 8 and/or the solenoid outlet valve 13, to count the pulses transmitted from a pulse generator 28 to the second input of the counting device 27 and, in this manner, to determine the time of operation of the solenoid valve or valves.

Since, for safety reasons, the solenoid outlet valve must never be actuated if the solenoid inlet valve is not also actuated, the maximum time of operation of both solenoid valves 8, 13 can be determined by the same counting device. As soon as the limit time set by a decoding unit included in the counting devices 27 is exceeded an output signal appears at the output Qn of the counting device.

The output of the OR gate 26 is connected to a reset input R of a second counting device 29. The pulses emitted from the pulse generator 28 are applied to the second input of the counting device 29 and are counted for the duration of the presence of a -b or a + b1 signal. The signal at the output Qn of the counting device 29 corresponds to the duration of the -b signal and/or the +b signal.

Both the output of the counting device 27 determining the operation times of the valves and the output of the counting device 29 measuring the period during which the -b and +b signals are present are connected, to the inputs of an AND gate 30 and, to the inputs of an AND gate 31. An inverter 34 is connected in the input of the AND gate 31 to which the output of the device 29 is applied.

The inputs of a third AND gate 32 are connected to the terminals I and II, the input associated with the terminal II being inverted, and to the output of the AND gate 30. The output of the AND gate 30 is also connected to an input of an AND gate 33. The two terminals I and II are also connected to the AND gate 33. Digital stores 35, 36 and 37 are connected to the outputs of the AND gate 33, the AND gate 32 and the AND gate 31 respectively. The task of the stores 35, 36 and 37 is to store the fault signals coming from the associated AND gates 33, 32 and 31.

If a signal being monitored is present for an inadmissibly long period the associated store 35, 36 or 37 is set, which is used in the blocking of the signal branch generating the faulty signal as described below. A signal can be emitted by the AND gate 30 only if there are signals from both the counting device 27 and the counting device 29. An output from the device 27 alone causes the AND gate 31 to produce an output.

The individual signal branches in Figure la are blocked by means of the outputs IV, VII, and V from the stores 35, 36 and 37 which are connected to the terminals having the same reference numerals, IV, VII and V in Figure la. Terminals IV in Figure la leads to the inverted input of the AND gate 3 and blocks the deceleration signal - b if the digital store 35 stores a fault signal. By way of terminal VII, the emission of a fault signal by the digital store 36, controls the.

AND gate 16 and thus the acceleration signal +bl is blocked. By way of the terminal V the slip signal X is blocked by the AND gate 22 when there is a fault signal at the digital store 37.

An OR gate 38, which has four inputs, is connected to the outputs of the stores 35, 36 and 37 and also directly to the output of the counting device 27. If a signal is present which is emitted either from one of the stores 35, 36, 37 or from the counting device 27 the OR gate 38 produces an output signal which is supplied to a counting device 39, which counts the pulses generated by the pulse generator 28 for the period during which this signal is present at the output of the gate 38 and thus measures the duration of the presence of a -b, +b, or Signal or the operation time of the solenoid valves 8 and 13.If a first limit value is exceeded by the count in the device 39 a warning lamp 40 is switched on by a first output signal of the counting device 39 and if it exceeds a second limit value the entire anti-lock control device is switched off by a second output signal by means of a switch 41.

The function of the reliability circuit is explained again briefly below.

The signals -b and +bl emitted by the signalling devices 2 and 14 pass by way of the terminals III and VI into the logic circuit and into the reliability circuit. At the same time the signals applied to the solenoid valves are supplied by way of the terminals I and II to the counting device 27 of the reliability circuit which device establishes the operation times of the solenoid valves. Since, in the case of each control operation, the -b signal always occurs before the + b1 signal the counting device 29 is reset at the end of the -b signal and begins a new count when the +bl signal occurs. The digital stores 35 and 36 receive output signals from the counting devices 27 and 29 by way of the AND gates 30, 32, and 33.If one of the signals -b, +bl or one of the solenoid operating signals exceeds a limit value the corresponding store is set and both the faulty signal branch is blocked and the counting device 39 is reset.

After a limit value is exceeded the warning lamp 40 is switched on and, if a second limit value is exceeded, the entire anti-lock control device is switched off by way of the relay 41.

In order to establish which of the signals has caused the inadmissibly long operation time of the solenoid valves, the outputs of the counting devices 27 and 29 are connected on the one hand to an AND gate 30, the output of which leads to a first input of the AND gate 33, which is connected by means of its second and third input to the terminals I and II, and on the other hand, via the AND gate 30, to the AND gate 32 which is likewise connected to the terminals I and II. If a signal remains for too long a period energizing the solenoid inlet valve or the solenoid outlet valve the counting device 27 transmits an output signal, when the limit value is exceeded in this device, to one of the inputs of the AND gate 30.However, the AND gate 30 can let this fault signal through only if an output signal indicating a faulty -b or +b signal is generated by the counting devices 29 and applied to the other input of the AND gate 30. If this is the case, the output signal of the AND gate 30 passes to the AND gate 33, connected downstream, and to the AND 32 connected in parallel with this. If the solenoid inlet valve 8 and the solenoid outlet valve 13 are energized it may be deduced that the -b signal is faulty since only the -b signal can energise both valves and the -b signal branch is therefore disconnected via the terminal IV by blocking the AND gate 3. If the solenoid inlet valve 8 only is energised for too long the +b signal branch is disconnected via the terminal VII by blocking the AND gate 16.

If no output signal is generated by the counting device 29 the AND gate 30 cannot let through the signal emitted by the counting devices 27 indicating that the admissible operation time of the solenoid valves has been exceeded. In this case the deduction is that the b signals are not faulty. The output signal of the counting device 27 passes via the AND gate 31 to the store 37 which transmits an output signal by way of the terminal V and to AND gate 22 and thus blocks the signal branch for the slip signal which is assumed to be the cause of the faulty operation.

Immediately after disconnecting one of the three signal branches the solenoid valves must be dead. If this is not the case, the cause of the fault cannot be in the signal generation and recognition portion of the anti-lock control device but in the logic circuit to which the signals are applied or in the amplifiers.

It is then impossible to switch off the solenoid valves early by eliminating the faulty signal during the control operation. After a predetermined period the counting device 39 monitoring the operation periods of the solenoid valves emits a signal which firstly switches on a warning lamp and then after a further period switches off the entire anti-lock control device.

Figure 2a shows a logic circuit and also, in block form the signal generating unit and the solenoid inlet valves and outlet valves.

Since the circuit arrangement shown in Figure 2a is identical to the circuit arrangement according to Figure la the same reference numerals are used to mark the components except that they have a prime. It is therefore not proposed to give a description of this circuit arrangement.

The reliability circuit shown in Figure 2b is substantially identical to the reliability circuit according to Figure lb so that, in this case too, the same reference numeral are used except that they have a prime.

This reliability circuit is a simplified embodiment of the circuit shown in Figure ib. A single counting device is provided to monitor the operation periods of the solenoid valves and the duration of the presence of the deceleration, acceleration and slip signals.

The signals applied by the logic circuit to operate the solenoid valves 8', 13' (Figure 2a) also pass via the terminals I', II' and an OR gate 25' to the reset input R of a counting device 27' (Figure 2G) which measures the operation periods of the solenoid valves.

If a pre-determined operation period of a solenoid valve, (or of both solenoid valves) is exceeded a fault signal is transmitted from the output Qn of the counting device 27' to the first input of an AND gate 30'. The AND gate 30' can transmit the fault signal to the setting input of a store 35' for -b signals or of a store 36' for +b signals only if at the same time the electronic recognition circuit 1' (Figure 2a) transmits via an OR gate 26' a -b or +b signal to the second input of the AND gate 30'. The fault signal passes from the output of the AND gate 30' to AND gates 33' and 32'.

One input of the AND gates 33' and one input of the AND gate 32' are each connected to the input of the solenoid inlet valve 8' via the terminal I' and a further input of the AND gate 33' and a further input of the AND gate 32' are connected to the input of the solenoid outlet valve 13' via the terminal II'.

The input of the AND gate 32' connected to the input of the solenoid outlet valve 13' is inverted. The result achieved by this measure is that a fault signal arising from the +b signal and causing the solenoid inlet valve 8' to be energised for too long can set the store 36 only. Thus, a faulty -b signal cannot, in spite of the common monitoring of the - b and +b signals in one counting device, result in the +b signal branch being disconnected. On the other hand a faulty -b signal will result in the setting of the store 35'. In this manner it is possible to establish whether it is the -b signal branch or the +b signal branch which is operating defectively.

If a fault signal is emitted from the counting device 27' without a -b or a +b signal appearing simultaneously at the output of the OR gate 26', the AND gate 30' cannot let the fault signal through. In this case the fault signal passes via the first input of an AND gate 31', which is closed by an output from the gate 26' to the store 37' for signals and sets this. As a result the signal branch for the generation of signals is disconnected.

Figure 3 shows a circuit in which the fault signal is switched off immediately after the maximum permitted period of occurrence of a control signal -b, +b, instead of only after the maximum possible solenoid operation period.

From the terminals I" and II", which are identical to the terminals I, II and I', II' shown in Figures la and 2a, the solenoid valve operating signals pass via an OR gate 43 to the first input of a counting device 44. The second input of the counting device 44 is connected to a pulse generator 45. The task of the counting device 44 is to count the pulses emitted by the pulse generator 45 during the period of the presence of solenoid valve operating signals. Deceleration signals -b, acceleration signals +bl and slip signals X are emitted from a recognition circuit which is not shown. The rise of the -b signal passes via a delayed response element 46 and the inverted input of an AND gate 47 to an input of an OR gate 48.The fall of the -b signal is transmitted via an inverter 49, a delayed response element 50 and the inverted input of an AND gate 51 to a further input of the OR gate 48. In the same manner, the rise of the + b1 signal passes via a delayed response element 52 and the inverted input of an AND gate 53 to the OR gate 48, and the fall of the +bl signal passes via an inverter 54, a delayed response element 55 and the inverted input of an AND gate 56 to the OR gate 48.The rise of the slip signal is likewise transmitted via a delayed response element 57, and the inverted input of an AND gate 58 to the OR gate 48, and the fall of the slip signal via an inverter 59, a delayed response element 60 and the inverted input of an AND gate 61 to the OR gate 48.

The output of the OR gate 48 is connected to a reset input R of the counting device 44. A signal emitted by the OR gate 48 always causes the counting device 44 to be reset to zero after a rise or fall of a signal. The output Q1 of the counting device 44 is connected via an AND gate 62 and an AND gate 63 to the setting input S of a store 64, via an AND gate 65 and an AND gate 66 to the setting input S of a store 67 and via an AND gate 68 and an AND gate 69 to the setting input S of a store 70. The reset inputs of the stores 64, 67 and 70 are connected via an inverter 71 and a capacitor resistance filter 72 to a voltage supply. A signal appearaing at the output of the OR gate 43, in addition to be applied to the counting device 44, is applied directly to the AND gates 63 and 69. In order to be able to determine whether too long a solenoid valve operating signal is caused by a faulty -b, +bl, or X signal, these latter signals are transmitted to the second inputs of the AND gates 62, 65 and 68, respectively, the first inputs of which receive the output signals of the counting device 44, as described above. The AND gates 62, 65 and 68 cannot let a single through to one of the associated stores 64, 67 or 70 unless the corresponding -b, +bl or X signal is present at the same time as the output signal of the counting device 44.It is possible to dis tinguish between the +bl signal and the -b signal in the case of a fault, because the second input of the AND gate 66 is connected directly to the terminal I" of the solenoid inlet valve since a +b signal can energise only the solenoid inlet valve.The output signals of the three stores 64J 67 and 70 are applied via an OR gate 73 to a counting device 74 the task of which is to determine the operation times of the solenoid valves by counting the pulses transmitted to it by a pulse generator 75 for the period during which the signal emitted by any of the stores 64, 67 and 70 is present and, when a limit value is exceeded, to switch on a warning lamp 76 and then, via a terminal amplifier 77 and a valve relay 78, to switch off the voltage at the sblenoid inlet and outlet valves.Output lines from the stores 64, 67 and 70 lead directly to the terminals IV, V, VII of the individual signal branches so that, as soon as a faulty -b, +bl, or X signal occurs, the corresponding signal branch can be disconnected without first having to wait for the counting device 74 to check the signal.

The operation of the circuit described above is explained below with reference to the graphs shown in Figure 4.

In the course of a brake control cycle the signals -b, and +bl occur consecutively. The maximum solenoid valve operation time is composed of an overlapping sequence of these control signals.

The solenoid valve operating signal transmitted via the OR gate 43 to the counting device 44 starts the counting of the pulses generated by the pulse generator 45 and thus begins with the determination of the operation time of the solenoid valves.

Since the solenoid inlet valve and the solenoid outlet valve are normall energised on the occurrence of a - b signal, the - b signal, too, is present at the counting device 44. The slip signal A appears even before the fall of the - b signal. A trigger signal is derived from the rise and fall of each control signal and this trigger signal is transmitted to the reset input of the counting device 44 and brings about the resetting of the counting device 44 to zero. and the commencement of a new count.If the electronic recognition circuit is functioning correctly the acceleration signal +bl will occur between the rise and fall of the X signal, which acceleration signal energises the solenoid inlet valve to keep it closed for a further period to allow more rapid re-starting of the wheel. The deceleration signal -b must fall before the rise of the +b signal.

The graphs shown in Figure 4 represent the progress of a signal of a recognition circuit operating correctly during one control cycle.

The curve drawn in Figure 4a corresponds to the progress of the wheel speed during one control cycle. The lines having the references V, AV1 and AV2 represent the reference speed approximating to the vehicle speed and the switching thresholds for the speed difference signals (slip) X1 and A2.

If the wheel deceleration exceeds a certain value during a braking operation, the electronic recognition circuit emits a deceleration signal - b - Figure 4b - which energises the solenoid inlet valve EV and the solenoid outlet valve AV - Figure 4f and 4g. The solenoid inlet valve closes and, as a result, the supply of a pressure medium to the wheel brake cylinder is interrupted and the solenoid outlet valve opens and brings about a reduction in the pressure in the wheel brake cylinder.

When a certain slip value is reached, the electronic recognition circuit generates a slip signal A overlapping the - b signal -- Figure 4c - which maintains the energisation of the solenoid inlet valve EV and the solenoid outlet valve AV even after the reduction of the -b signal.The solenoid outlet valve AV is energised and closes only after the fall of the slip signal A. However, before the slip signal falls the electronic recognition circuit generates an acceleration signal +bl -- Figure 4d which leads to the fall of the slip signal x and maintains the energisation of the solenoid inlet valve EV, so that the valve is closed a while longer in order to permit a more rapid restarting of the wheel. The counting device monitoring the duration of the signals is reset by a reset signal during the period of the occurrence of the rises and falls of the signals -- Figure 4a. It can be seen from the typical course of the control of a braked wheel that it is not necessary to use all the rises and falls to reset the counting device.The rises of the X signal, -b signal and + b signal are sufficient. These three rises are the signals for the alteration of the control criterion, i.e. they either introduce new energisation conditions for the solenoid valves or they continue previously accepted conditions.

No output signals are generated by the counting device 44 as long as certain limit values, which correspond to the maximum permitted durations for the signals concerned are not exceeded.

With the reliability circuit shown in Figure 7 it is possible to monitor the operation periods of the solenoid inlet and outlet valves separately and thus to recognise a faulty signal more rapidly and disconnect the faulty signal branch as early as possible.

In Figure 7, the operating signal for the solenoid inlet valve passes from terminal I which is identical to the terminals I and I' shown in Figures la and 2a, to the first input Ce of a counting device 79. The second input of the counting device 79 is connected to the output of a pulse generator at a terminal 80.

The counting device 79 has the task of counting the pulses emitted by the pulse generator during the period of the presence of the operating signal for the solenoid inlet valve. The operating signal for the solenoid outlet valve passes from terminal II, which is identical to the terminals II and II' shown in Figures la and 2a, to the first input Ce of a counting device 81. The second input of the counting device 81 is likewise connected to the output of the pulse generator at the terminal 80. It is the task of this counting device 81 to count the pulses emitted by the pulse generator during the presence of a signal energising the solenoid outlet valve.

Deceleration signals - b, acceleration signals +b and slip signals A are emitted from a recognition circuit which is not shown. The rise of the -b signal passes via a delayed response element 82 and the inverted input of an AND gate 83 to an OR gate 84 connected downstream and also to an OR gate 85 connected in parallel with the OR gate 84.

The fall of the -b signal is transmitted via an inverter 86, a delayed response element 87 and the inverted input of an AND gate 88 to another input of the OR gate 84 and also another input of the OR gate 85. In the same manner, rise of the +bl signal passes via a delayed response element 89 and the inverted input of an AND gate 90 to the OR gate 84 and the fall of the + b1 signal passes via an inverter 91, a delayed response element 92 and the inverted input and AND gate 93 to the OR gate 84.The rise of the slip signal X is likewise transmitted via a delayed response element 94 and the inverted input of an AND gate 95 to the OR gates 84 and 85 and the fall of the slip signal is transmitted via an inverter 96, a delayed response element 97 and the inverted input of an AND gate 98 to the OR gates 84 and 85. The output of the OR gate 84 is connected to a reset input R of the counting device 79, and the output of the OR gate 85 is connected to the reset input R of the counting device 81. The signal emitted from the OR gate 84 always brings about the resetting of the counting device 79 to zero after a rise or fall of a -b, +bl or A signal.The counting device 81 is set to zero when the OR gate 85 transmits a signal to the reset input R of the counting device 81 after a rise or fall of a -b or A signal. The output Q1 of the counting device 79 is connec ted via an AND gate 99 and an AND gate 100 to the setting input S of a store 101, via an AND gate 102 and an AND gate 103 to the setting input S of a store 104 and via an OR gate 105 to the setting input S of a store 106.

There is a connection from the output Qm of the counting device 81 to the second inputs of the AND gate 99 and the AND gate 102.

By means of this arrangement it is possible to monitor separately the signal branches for the deceleration, slip and acceleration signals.

The reset inputs of the stores 101, 104 and 106 are connected to a voltage supply at a terminal R.

From the electronic recognition circuit, which is not shown, the -b signal is also applied to the AND gate 100, the X signal to the AND gate 103 and the +bl signal to the -OR gate 105. The output signals of the three stores 101, 104 and 106 are applied via an OR gate 107 to a counting device 108, the task of which is, when a limit value of the duration of the presence of these signals is exceeded, to switch on a warning lamp 109 first of all and then to switch off, via a terminal amplifier 110 and a valve relay 111, the voltage supply at the solenoid inlet valves and solenoid outlet valves so that the brakes are returned to normal operation, the antilocking device being disabled.Output lines from the stores 101, 104 and 106 lead directly to the terminals IV, VII and V of the individual signal branches for -b, +bl and A signals so that the corresponding signal branch can be disconnected as described above with reference to Figures la and 2a as soon as a faulty -b, +bl or A signal occurs without having to wait for the counting device 108 to check all the signals. The outputs of the count ing device 79 and 81 are also connected via an OR gate 113 and the OR gate 107 directly to the counting device 108.

Figure 8 shows a circuit arrangement with which the solenoid valve operation times, the b signals and the X signals are monitored separately. From the terminals I and II of the logic portion (not shown) of the anti-lock brake control device (see Figures la and 2a), lines EV - coming from the solenoid inlet valve - and AV - coming from the solenoid outlet valve - ledd to the inputs of an OR gate 134.The output of the OR gate 134 is connected to the reset input R of a digital counting device 135, the task of which is to monitor the operation periods of the solenoid valves by counting the pulses emitted by a pulse generator 136 to the input CL of the digital counting device 135 during the period a signal is present at the solenoid inlet valve and/ or solenoid outlet valve. The deceleration signals -b and the acceleration signals +b1 generated by an electronic recognition circuit (not shown) pass via the inputs of an OR gate 137, the output of which is connected to the reset input R of a digital counting device 138, which likewise receives its counting pulses from the pulse generator 136 via its input CL.

The number of pulses occurring during the presence of a -b or a +bl signal is the measure for the duration of the -b and +bl signals. In the same manner the slip signal A is monitored by another digital counting device 140, the output CL of which is connected to the pulse generator 136 and the reset input R of which is connected via an inverter 139 to the signal line for the A signals of the electronic recognition circuit.The output Qn of the digital counting device 135 is connected via an OR gate 141 to the reset input R of a digital counting device 142, the task of which is to switch on a warning lamp 143 via a first output Qn when a predetermined time (i.e. number of clock pulses) is exceeded and, after a predetermined waiting period, to switch off the entire anti-lock brake control device via a second output Qn + m, an amplifier 144 and a relay 145. The digital counting device 138 has two outputs Q-b and Q+bl which are connected respectively via AND gates 146 and 148 to the setting inputs of two stores 147 and 149. The second inputs of the AND gates 146 and 148 are connected respectively to the signal lines for the -b and +bl signals.The result of this arrangement is that, e.g. in the case of a faulty -b signal, the output signal of the digital count ing device 138 opens the AND gate 146 so that the -b signal transmitted from the -b signal line to the second input of the AND gate 146 is passed to the setting input S of the store 147. The procedure is similar if the bl signal is faulty. In such a case the signal coming from the +b3 signal line and the signal emitted from the output Q+bl of the digital counting device 138 pass to the AND gate 148. The faulty +bl signal sets the store 149. It is, of course, also possible to monitor the -b and +b signals in separate counting devices.The counting device 140 monitoring the duration of the slip signal A is connected via its output QA directly to the setting inputs S of a store 150. If the X signal exceeds a predetermined time the store 150 is set. The reset inputs of the stores 147, 149 and 150 are connected via an inverter 151 and a capacitor resistance filter to a voltage supply so that after the occurrence of a faulty signal, which has led to the setting of a store and the switching off of the entire anti-lock brake control device, the store can be cleared when the anti-lock brake control device is set in operation again.Lines lead from the outputs of the stores 147, 149 and 150 to the terminals IV, VII and V of the logic portion of the anti-lock brake control device (as in Figures la and 2a) by means. of which, on the occurrence of fault in a signal branch, this fault is blocked by the signal emitted from the corresponding store. The output signals of the stores 147, 149 and 150 are also applied via the OR gate 141 to the reset input R of the digital counting device 142. The result of this is that after a signal branch has been disconnected on the occurrence of a fault in it and the control cycle of the brake control process, in which the fault has occurred, has been terminated using the intact signal branches, the entire anti-lock brake device is switched off.The warning lamp 143 connected to the output Qn of the digital counting device 142 is switched on when the faulty signal branch is disabled.

The operation of this circuit arrangement is explained in more detail with reference to the graphs shown in Figures 5a - h and 6 I a 1.

Similarly to Figure 4a, Figures 5a and 6 I a show the progress of the wheel speed during one control cycle, the reference speed Ref: V and also the two different speeds aV1 and AV2 corresponding to different slip thresholds.

It is assumed that, during a braking operation, a vehicle wheel shows a tendency to lock so that the electronic recognition circuit generates a deceleration signal -b bringing about a reduction in the brake pressure Figure 5b. The solenoid valves - solenoid inlet (EV) and outlet (AV) valves - are energised -- Figure 5e, f - i.e. the solenoid inlet valve closes and the solenoid outlet valve opens so that the brake pressure in the wheel brake cylinder is reduced. Apart from being applied to the logic portion of the anti-lock control device the -b signal is also applied to the counting device 138 of the reliability circuit, which device measures the duration of the presence of the -b signal.

The measurement of the duration of the -b signal begins after the reduction of the .previous signal which is the +b signal when the control operation is proceeding normally; for, in the case of at least each rise of a control signal, the counting device is reset by a reset signal -- Figure Sg.

At the same time the solenoid valve operating signals are monitored in the counting device 135. If a fault occurs in the electronic recognition circuit which results in the -b signal continuing even after a predetermined wheel deceleration value is no longer exceeded the counting device 138 continues to a predetermined limit value and then transmits an output signal to the -b store 147. The - b store 147 now transmits a blocking signal to the -b signal branch of the logic portion of the anti-lock control device so that the solenoid valves can ne longer be actuated by the faulty -b signal.

The brake pressure control is not, however, interrupted abruptly but is continued with the intact remaining signals following the -b signal, i.e. the slip signal and the + b1 signal - Figure Sc, d -- until a control cycle has been completed. Simultaneously with the disconnection of the faulty -b signal branch the counting device 142 was released by the signal emitted by the set -b store 147. When the counting device 142 has counted up to a predetermined limit value the warning lamp 143 is switched on. When a second limit value is reached which is above the first limit value the entire anti-lock control device is switched off via the valve relay 145.As can be seen from the graph in Figure 5g, in the case of a reliability circuit according to the invention, the monitoring time and the disconnection time, from the beginning of the occurrence of a signal to the determination of a fault and the elimination of the cause of the fault, amounts to approximately half the solenoid operation time, i.e. approximately half the monitoring time hitherto achieved - Figure 5h.

If in a control operation the acceleration signal +bl is faulty and not the -b signal, Figure 6 I d, the counting device 138 monitoring the +bl signal will set the +bl store and thus bring about the blocking of the +bl signal branch. In a case such as this, also, the brake pressure control is continued with the aid of the intact signal branches for the deceleration and slip signals -- Figure 6b, c - until the counting device 142 reset by the signal emitted by the set +bl store 149 has counted up to a limit value and, after switching on the warning lamp, has switched off the entire anti-lock control device by way of the relay 145.The monitoring time Figure 6 I h - is reduced likewise by about 50% compared to the monitoring time hither to achieved.

Figure 6 II shows the progress of a signal in the case of a faulty -b signal when the wheel is not braked.

As is generally known, even in the case of normal travel i.e. when the vehicle is not braked, the sensors arranged on the wheels emit voltages corresponding to the wheel speeds and supply them to the electronic recognition circuit. If the electronic recognition circuit operates free of faults it does not generate control signals since, in the case of wheels that are not braked, the voltages corresponding to the wheel speeds do not reach the threshold value indicating the tendency to lock. If, however, the electronic recognition circuit is defective, a deceleration signal -b, for ex ample, can be generated -- Figure 6 II b which energises the solenoid inlet valve EV and the solenoid outlet valve AV - Figure 6 c, d.

The results are that a pressure medium can not be directed into the wheel brake cylinder and the wheels can thus no longer be braked.

As a result of the fact that, in addition to the solenoid valve operation period being monitored, each control signal is also checked continuously for the duration of its presence the faulty signal branch, and, in this assumed case, thus the faulty -b signal, can be dis connected even before the monitoring period of the solenoid valves is complete. As a result the monitoring time of the solenoid valves and also the time from the faulty operation of the solenoid valves to the recognition of the fault and release of the solenoid valves is reduced compared to known monitoring devices by approximately 50% - Figure 6 II e, f.

A circular arrangement is shown in Figure 9 with which it is possible, on the occurrence of a fault in the electronic recognition circuit or in the logic portion, to switch off the erroneous signal via the same line as that with which it is recognised.

Control signals corresponding to the rotating behaviour of a wheel are generated in a switching circuit 114, which may be an integrated circuit, to influence the brake pressure and thus to influence the rotating behaviour of the wheel during a braking operation. These control signals -b - brake pressure reduction; X - brake pressure reduction; and +b - maintenance of brake pressure -- pass, on the one hand, via signal lines 115, 116, an amplifier 117 and control lines 118, 120 to solenoid inlet and outlet valves 119, 121 and, on the other hand, via signal lines 122, 123, 124 and transistors 125, 126, 127, connected in these, and conductors 131, 132 and 133 to the inputs of a monitoring circuit 128.

Conductors 129, 130 lead from the control lines 118, 120 to two other inputs of the monitoring circuit 128. The monitoring circuit may be the same as any one of the monitoring circuits described above. If a fault occurs in one of the signal branches which leads to the excessively long presence of a control signal a blocking signal is generated by the monitoring circuit. If the faulty signal is a -b signal the blocking signal is applied to the base of the transistor 125 to switch on and thus the signal branch for the -b signals is short-circuited by means of the transistor 125. The -b signal can therefore no longer pass to the solenoid valves 119,. 121.If the +.b signal branch is faulty a signal is emitted from the second output of the monitoring circuit 128 to the base of the transistor 126 arranged in the signal line 123, which signal short-circuits the +b signal branch te earth. In the case of a faulty A signal a blocking signal is applied to the base of the transistor 127 arranged in the signal line 124 and blocks the faulty A signal branch by short circuiting it.

An improvement can be made to the examples of the invention described above by linking the device for monitoring the deceleration, acceleration and slip control signals to a device for determining the value of the coefficient of friction between the wheels and the road so that the maximum permissible durations for the control signals and dependent on the value of the coefficient of friction.

WHAT WE CLAIM IS: 1. An anti-lock brake control device for a vehicle having signal generating means for monitoring the rotating behaviour of at least one wheel of the vehicle, a recognition circuit responsive to the signal generating means for deriving deceleration, acceleration and slip control signals, a logic circuit by means of which one or more brake pressure medium inlet valves and outlet valves for controlling

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

reliability circuit according to the invention, the monitoring time and the disconnection time, from the beginning of the occurrence of a signal to the determination of a fault and the elimination of the cause of the fault, amounts to approximately half the solenoid operation time, i.e. approximately half the monitoring time hitherto achieved - Figure 5h.

If in a control operation the acceleration signal +bl is faulty and not the -b signal, Figure 6 I d, the counting device 138 monitoring the +bl signal will set the +bl store and thus bring about the blocking of the +bl signal branch. In a case such as this, also, the brake pressure control is continued with the aid of the intact signal branches for the deceleration and slip signals -- Figure 6b, c - until the counting device 142 reset by the signal emitted by the set +bl store 149 has counted up to a limit value and, after switching on the warning lamp, has switched off the entire anti-lock control device by way of the relay 145.The monitoring time Figure 6 I h - is reduced likewise by about 50% compared to the monitoring time hither to achieved.

Figure 6 II shows the progress of a signal in the case of a faulty -b signal when the wheel is not braked.

As is generally known, even in the case of normal travel i.e. when the vehicle is not braked, the sensors arranged on the wheels emit voltages corresponding to the wheel speeds and supply them to the electronic recognition circuit. If the electronic recognition circuit operates free of faults it does not generate control signals since, in the case of wheels that are not braked, the voltages corresponding to the wheel speeds do not reach the threshold value indicating the tendency to lock. If, however, the electronic recognition circuit is defective, a deceleration signal -b, for ex ample, can be generated -- Figure 6 II b which energises the solenoid inlet valve EV and the solenoid outlet valve AV - Figure 6 c, d.

The results are that a pressure medium can not be directed into the wheel brake cylinder and the wheels can thus no longer be braked.

As a result of the fact that, in addition to the solenoid valve operation period being monitored, each control signal is also checked continuously for the duration of its presence the faulty signal branch, and, in this assumed case, thus the faulty -b signal, can be dis connected even before the monitoring period of the solenoid valves is complete. As a result the monitoring time of the solenoid valves and also the time from the faulty operation of the solenoid valves to the recognition of the fault and release of the solenoid valves is reduced compared to known monitoring devices by approximately 50% - Figure

6 II e, f.

A circular arrangement is shown in Figure 9 with which it is possible, on the occurrence of a fault in the electronic recognition circuit or in the logic portion, to switch off the erroneous signal via the same line as that with which it is recognised.

Control signals corresponding to the rotating behaviour of a wheel are generated in a switching circuit 114, which may be an integrated circuit, to influence the brake pressure and thus to influence the rotating behaviour of the wheel during a braking operation. These control signals -b - brake pressure reduction; X - brake pressure reduction; and +b - maintenance of brake pressure -- pass, on the one hand, via signal lines 115, 116, an amplifier 117 and control lines 118, 120 to solenoid inlet and outlet valves 119, 121 and, on the other hand, via signal lines 122, 123, 124 and transistors 125, 126, 127, connected in these, and conductors 131, 132 and 133 to the inputs of a monitoring circuit 128.

Conductors 129, 130 lead from the control lines 118, 120 to two other inputs of the monitoring circuit 128. The monitoring circuit may be the same as any one of the monitoring circuits described above. If a fault occurs in one of the signal branches which leads to the excessively long presence of a control signal a blocking signal is generated by the monitoring circuit. If the faulty signal is a -b signal the blocking signal is applied to the base of the transistor 125 to switch on and thus the signal branch for the -b signals is short-circuited by means of the transistor 125. The -b signal can therefore no longer pass to the solenoid valves 119,. 121.If the +.b signal branch is faulty a signal is emitted from the second output of the monitoring circuit 128 to the base of the transistor 126 arranged in the signal line 123, which signal short-circuits the +b signal branch te earth. In the case of a faulty A signal a blocking signal is applied to the base of the transistor 127 arranged in the signal line 124 and blocks the faulty A signal branch by short circuiting it.

An improvement can be made to the examples of the invention described above by linking the device for monitoring the deceleration, acceleration and slip control signals to a device for determining the value of the coefficient of friction between the wheels and the road so that the maximum permissible durations for the control signals and dependent on the value of the coefficient of friction.

WHAT WE CLAIM IS: 1. An anti-lock brake control device for a vehicle having signal generating means for monitoring the rotating behaviour of at least one wheel of the vehicle, a recognition circuit responsive to the signal generating means for deriving deceleration, acceleration and slip control signals, a logic circuit by means of which one or more brake pressure medium inlet valves and outlet valves for controlling

the wheel brake pressure are operated and also means for monitoring the operation periods of the inlet valves and outlet valves, wherein there is provided a device for monitoring the deceleration, acceleration and slip control signals which is connected to the means for monitoring the operation periods of the inlet valves and outlet valves and to the logic circuit in such a manner that, in the case of a faulty deceleration, acceleration or slip control signal, the faulty control signal branch can be disconnected and the remaining faultfree control signal branches continue to be used for control.
2. A device according to claim 1, wherein the device for monitoring the deceleration, acceleration and slip control signals includes a counting device arranged to count pulses for the duration of at least one of the signals and three stores corresponding respectively to the deceleration, acceleration and slip control signals, the counting device being connected to the stores via a logical arrangement responsive to an output from the means for monitoring the operation times of the inlet and outlet valves which are solenoid valves.
3. A device according to claim 2 wherein the output of each store is connected to a means in the logic circuit for disabling the signal branch for the corresponding control signal.
4. A device according to claim 3, wherein each disabling means consists of an AND gate having an inverted input which is connected to the output of the corresponding store.
5. A device according to claim 3 wherein each disabling means is arranged to short circuit to a reference voltage level the signal branch for the corresponding control signal.
6. A device according to claim 5 wherein each disabling means is a transistor to the base of which the output of the corresponding store is applied so as to cause the transistor to conduct and thereby short circuit the signal branch.
7. A device according to claim 5 or 6 wherein the device for monitoring the deceleration, acceleration and slip control signals is connected to the logic circuit by only a single conductor for each of the control signals and the corresponding disabling means is connected to short circuit the single conductor to the reference voltage level.
8. A device according to any of claims 2 to 7, wherein the device for monitoring the deceleration signals, acceleration signals and slip control signals consists of a digital counting device which is connected to respond to the control signals so as to start a new time count at each change of a control signal.
9. A device according to claim 8, wherein the digital counting device is arranged to be reset by the rises and the falls of the control signals.
10. A device according to any of claims 2 to 9 including a further counting device arranged to count pulses under the control of both the outputs of the stores and also the output of the means for monitoring the operation times of the solenoid inlet and oulet valves.
11. A device according to claim 10 wherein the further counting device is arranged to produce an output signal when the count exceeds a predetermined value which output signal is connected to operate a warning means.
12. A device according to claim 11 wherein the further counting device is also arranged to produce a second output signal when the count exceeds a second predetermined value higher than the first-mentioned predetermined value and means is provided responsive to the second output signal to disable the entire antilock brake control device.
13. A device according to claim 1 wherein the device for monitoring the deceleration, acceleration and slip control signals includes a counting device for measuring the duration of a respective one of the control signals and being arranged to produce an output signal when the duration exceeds a maximum permissible value, the output signals of the counting devices being connected to operate disabling devices for disconnecting the respective control signals.
14. A device according to claim 1, wherein the device for monitoring the deceleration, acceleration and slip control signals is linked to a device for evaluating a value for , in such a manner that the maximum permissible duration of the control signal are made dependent on the ,a value present.
15. An anti-lock brake control device substantially as described herein with reference to Figures la and ib, 2a and 2b, Figure 3, 7, 8 or 9 of the accompanying drawings, or modified as described herein.