GB1600060A

GB1600060A - Anti-lock regulating system for vehicle braking systems

Info

Publication number: GB1600060A
Application number: GB11336/78A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-03-23
Filing date: 1978-03-22
Publication date: 1981-10-14
Also published as: DE2712693C2; IT7821489A0; DE2712693A1; JPS53117187A; IT1093887B; SE426222B; FR2384659B1; SE7803325L; JPS6344102B2; FR2384659A1

Description

(54) IMPROVEMENTS IN OR RELATING TO ANTI-LOCK REGULATING SYSTEM FOR VEHICLE BRAKING SYSTEMS (71) We, ROBERT BOSCH GMBH, a German company of Postfach 50, 7 Stuttgart 1, 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 present invention relates to anti-lock regulating systems for vehicle braking systems.

German Offenlegungsschrift 2,232,034, Figure 2, with associated description, discloses an anti-lock regulating system of the type in which signals, derived from the wheels of one axle by means of sensors, are fed to an evaluating circuit which, in dependence upon the measured movement characteristic of these wheels, produces trigger signals for brake pressure control members associated with these wheels, in order, normally, to regulate the brake pressure at these wheels separately, and additional switching means are provided which respond under predetermined exceptional conditions and then effect parallel switching of the pressure control members for control by the trigger signals present in one regulating channel.

In the known system, the response time of the pressure control valves is monitored by means of a safety circuit. There are cases in which the regulator is switched off after a predetermined response time has expired.

However, when a slip signal, that is a signal produced by the pressure drop as a result of too great a wheel slip, is present on one of the two regulating channels after the expiry of this predetermined response time, the pressure at the two wheel brakes is regulated in the same manner by means of this slip signal by connecting the channels in parallel for a predetermined period of time.

This phase of the parallel switching is regarded as a waiting phase, and a fault in the regulating system is assumed, and the regulator is switched off, only when a change in the wheel behaviour does not ensue during this waiting phase.

In contrast to this, the present invention is based on the problem that in the event of a fault in one of the sensors associated with the wheels (and this also includes the amplifiers and transducers directly connected to them, if desired), this sensor initiates high yawing moments since one wheel is locked or one wheel brake is non-pressurized while braking is effected by the other brake with regulated pressure.

Accordmg to the present invention an anti-lock regulating system for vehicle braking systems comprises sensors for providing signals representative of the speeds of two wheels of one axle of a vehicle, an evaluating circuit including two regulating channels for producing in dependence on the movement characteristics of said two wheels trigger signals for pressure control members associated with these wheels in order normally to regulate the brake pressures at these wheels separately, said trigger signals comprising signals for reducing brake pressure and signals for holding brake pressure constant thereafter, test means for monitoring the functioning of the sensors and in the event of a fault in a sensor being detected producing an interference signal associated with the faulty sensor, blocking means for rendering ineffective the trigger signals of the regulating channel associated with the faulty sensor when an interference signal is produced, parallel switching means for responding to an interference signal and effecting the parallel switching of the two pressure control members such that the trigger signals of the regulating channel associated with the sensor which is not faulty are fed to both pressure control members in parallel, and timing circuits for, after the parallel switching of the pressure control members, prolonging the periods of pressure reducing signals and of hold pressure constant signals for the two wheel brakes beyond the ends of the corresponding signals from the evaluating circuit.

A sensor which is not functioning, or which is not functioning correctly, can be detected by, for example, the means described in German Offenlegungsschrift 2,546,481 which relates to a circuit for monitoring, during travel, the operating ability of at least two sensors which are associated with different vehicle wheels and which each detect the rotational speed and produce a corresponding electrical signal, these sensors producing pulse-shaped sign- als whose pulse frequency is proportional to the speed.

Monitoring is performed for example by providing at least one comparison circuit to which the signals of two sensors are fed and which produce an output signal when no change in one sensor occurs between two successive output pulses of the other sensor, and by providing a switching device which responds upon the appearance of an output signal and triggers a switching operation.

In German Offenlegungsschift 2,546,481 one sensor is in each case used to monitor another sensor. Thus, it is possible for two sensors to monitor one another by means of two comparison circuits. n comparison circuits are required in the case of n sensors, the sensors being connected to these comparison circuits such that each sensor is monitored by comparison with the signals of another sensor. Preferably, the combinations A and B, B and C, C and D, D and A are compared in the case of, for example, 4 sensors A, B, C, D.

In one preferred form of monitoring device each comparison circuit comprises two bistable circuits each having a dynamic input and a static input, the signal of the first sensor being present at the static input of one circuit, and the inverse signal thereto being present at the other input, and the signal of the second sensor being fed in each case to the dynamic input, and the outputs of the bistable circuits, producing an output signal after the bistable circuit has been switched to its second state, are connected to the static input of a third bistable circuit whose dynamic input is fed with the signals of the second sensor, and the output of this bistable circuit is connected to the switching device.

It is of importance to the present invention that not only is switching effected in parallel, but the pressure reducing and hold constant periods are also slightly prolonged beyond the ends of the corresponding signal from the evaluating circuit (for example 25 msec for a pressure reducing signal and 50 msec for a hold pressure constant signal) under the condition of a faulty sensor, so that a wheel cannot lock. The prolongation periods can be made dependent upon the vehicle velocity, the prolongation being reduced as the velocity decreases and, for example, becoming 0 below, for example, 40km1li.

Preferably parallel switching is initiated in the following manners: Upon the appearance of an interference signal only the parallel switching of the control members for pressure reducing (outlet valve function) is effected and thereby a timing circuit for effecting a prolongation of brake pressure reducing signal becomes effective. This signal triggering both pressure-control members additionally sets switching means which then trigger the two pressure control members for holding the pressure constant (inlet valve function) for a period of time which is slightly prolonged relative to the period of the signal from the evaluating circuit.In this arrangement too the signals coming from the incorrectly operating sensor are blocked when the interference signal appears, but parallel triggering of the pressure control members for holding pressure constant is initiated only with the following pressure reduction.

If a fault occurs in a sensor before brake pressure regulation commences, "parallel regulation" is effected during the entire regulation. On the other hand, in the event that a fault in a sensor only occurs during brake pressure regulation, it is advantageous, in the case of the type of regulation described in the last paragraph, not only to block the regulating signals of the channel having the faulty sensor but also to maintain a constant pressure at the brake associated with the faulty sensor until with the next following pressure reducing signal the parallel switching is effective. Additional switching means are provided for this purpose and respond to the appearance of an interference signal and then produce a hold pressure constant signal for the period of time at least up to the appearance of a pressure reducing signal.

The invention will be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a block circuit diagram of an embodiment constructed in accordance with the invention, having inlet valves and outlet valves acting as pressure-control members, Fig. 2 shows a detailed block circuit diagram of one form of the parallel switching circuit, and Fig. 3 shows the pressure characteristic achieved by the embodiment of Fig. 2.

Referring to Fig. 1, two rotational speed sensors associated with the wheels of one axle are designated 1 and 2, and their input amplifiers are designated 3. An evaluating circuit, which produces trigger signals for inlet valves 5 and 7 and outlet valves 6 and 8 associated with individual wheel brakes, is designated 4, the said trigger signals being fed to the said valves by way of output amplifiers 9. A parallel switching circuit 10 is controlled by a monitoring device 11 which monitors the signals of the two sensors 1 and 2 and their amplifiers with respect to the occurrence of faults and produces an inter ference signal on output leads 12 or 13 when a fault is detected in one or other sensor.AND gates 14 which are incorporated in these leads and which are also acted upon by a signal produced by the evaluating circuit 4 at a predetermined vehicle velocity of, for example, 30 km/h, only allow the signals of the monitoring circuit 11 to become effective at a higher velocity.

The parallel switching circuit 10 can block the signals coming from the evaluating circuit by means of AND gates 15 to 18 and in turn can feed control signals into the channels by way of OR gates 19 to 22, so that it is possible to control the inlet and outlet valves in parallel.

It is also indicated by broken lines (11') in Fig. 1 how the monitoring circuit 11 can be connected in a different manner for the sensor 2. Alternatively, it can, for example, only check whether a short-circuit or a break in a lead has occured at a sensor.

Referring to Fig. 2, the blocking members (AND gates 15 to 18) the coupling-in members (OR gates 19 to 22), the amplifiers 9, and the valves 5 to 8 are provided with the same reference numerals as in Fig. 1. The parallel switching circuit 10 is additionally shown in detail in Fig. 2.

For the purpose of explaining the circuit, it will be assumed that a signal appears on lead 13 which indicates a fault in the sensor 2. Furthermore, it will be assumed that the fault occurs during brake regulation.

By virtue of normal regulation of the brake pressure (that is, regulating the pressure at a brake in dependence upon the associated sensor), the curves illustrated in Fig. 3 should occur in the period of time 0 to tl. The characteristic of the velocity v, of the vehicle braked from the time 0 onwards, the characteristics of the speeds of the two vehicle wheels VR and vL, and the characteristics of the brake pressure at the two wheel brakes PR and PL are plotted against time in Fig. 3. It will be assumed that the sensor 2, which ascertains the characteristic of the speed v, of the right-hand wheel, develops a fault at the instant ti, so that an interference signal appears on lead 13 from this instant onwards.This signal on the one hand blocks the AND gates 17 and 18 and, on the other hand, sets bistable circuits 102 and 103 by way of AND gate 101. The output signal of the bistable circuit 102 thus produced is fed to the inlet valve 7 by way of OR gate 21 so that the pressure at the right-hand wheel is in the first instance maintained constant, namely up to the instant t2. A pressurereducing signal appears at the outlet valve 6 at this instant.Owing to the existence of the interference signal, the pressure reducing signal is applied to the two OR gates 20 and 22 by way of AND gate 104 and a timing circuit 105, and owing to the timing circuit 105, acts upon the outlet valves 6 and 8 for a period of time prolonged for a predetermined period of time (for example 20 msec) (t to t4) beyond the end of the pressure reducing signal coming from the evaluating circuit (t2 to t4). The output signal of the AND gate 104 also resets the bistable circuit 102. However, the AND gate 101 is blocked by the bistable circuit 103 which has been set in the manner described previously. This insures that the bistable circuit 102 can only become effective upon the appearance of the interference signal.The third input of the AND gate 101 is connected to the outlet valve 6 by way of the timing circuit 106; the time constant of this timing circuit is relatively large, so that; after the outlet valve 6 has once responded, the timing circuit produces an output signal during an entire brake regulation. Thus, it is ensured that the described initial hold pressure constant period (tl to t2) is only triggered after a pressure reducing signal has already been received (during the period 0 to tl). The bistable circuit 103 can be reset when, for example, the vehicle velocity drops below a predetermined velocity, such as when the signal, which renders the AND gates 14 of Fig. 1 conductive, and which is coupled in by way of terminal 107, disappears.

However, the output signal of the AND gate 104 also sets a bistable circuit 108 which is not reset until the disappearance at instant t5 of a hold pressure constant signal which is effective at the output of the AND gate 15 at the end of the pressure reducing signal at t4. This means that the pressure in the two channels is held constant by the set bistable circuit 108 for a period of time (t4 to t6) which comprises the period of time (t4 to ts) from the end of the pressure reducing signal to the disappearance of the hold pressure constant signal at the output of the AND gate 15, and the time constant (for example 100 msec) (t5 to t6) of a timing circuit 109. Pressure is then built up again in parallel, and the operation is repeated.

The circuits 101 to 109 described above are again provided in case the other sensor should develop a fault, corresponding circuits being provided with the same numerals but with an addition The fact that a fault in one of the sensors has been detected can be indicated by means of a warning lamp 111 by way of an OR ate 160.

AT WE CLAIM IS: 1. An anti-lock regulating system for vehicle braking systems, comprising sensors for providing signals representative of the speeds of two wheels of one axle of a vehicle, an evaluating circuit including two regulating channels for producing in dependence on the movement characteristics of

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ference signal on output leads 12 or 13 when a fault is detected in one or other sensor. AND gates 14 which are incorporated in these leads and which are also acted upon by a signal produced by the evaluating circuit 4 at a predetermined vehicle velocity of, for example, 30 km/h, only allow the signals of the monitoring circuit 11 to become effective at a higher velocity. The parallel switching circuit 10 can block the signals coming from the evaluating circuit by means of AND gates 15 to 18 and in turn can feed control signals into the channels by way of OR gates 19 to 22, so that it is possible to control the inlet and outlet valves in parallel. It is also indicated by broken lines (11') in Fig. 1 how the monitoring circuit 11 can be connected in a different manner for the sensor 2. Alternatively, it can, for example, only check whether a short-circuit or a break in a lead has occured at a sensor. Referring to Fig. 2, the blocking members (AND gates 15 to 18) the coupling-in members (OR gates 19 to 22), the amplifiers 9, and the valves 5 to 8 are provided with the same reference numerals as in Fig. 1. The parallel switching circuit 10 is additionally shown in detail in Fig. 2. For the purpose of explaining the circuit, it will be assumed that a signal appears on lead 13 which indicates a fault in the sensor 2. Furthermore, it will be assumed that the fault occurs during brake regulation. By virtue of normal regulation of the brake pressure (that is, regulating the pressure at a brake in dependence upon the associated sensor), the curves illustrated in Fig. 3 should occur in the period of time 0 to tl. The characteristic of the velocity v, of the vehicle braked from the time 0 onwards, the characteristics of the speeds of the two vehicle wheels VR and vL, and the characteristics of the brake pressure at the two wheel brakes PR and PL are plotted against time in Fig. 3. It will be assumed that the sensor 2, which ascertains the characteristic of the speed v, of the right-hand wheel, develops a fault at the instant ti, so that an interference signal appears on lead 13 from this instant onwards.This signal on the one hand blocks the AND gates 17 and 18 and, on the other hand, sets bistable circuits 102 and 103 by way of AND gate 101. The output signal of the bistable circuit 102 thus produced is fed to the inlet valve 7 by way of OR gate 21 so that the pressure at the right-hand wheel is in the first instance maintained constant, namely up to the instant t2. A pressurereducing signal appears at the outlet valve 6 at this instant.Owing to the existence of the interference signal, the pressure reducing signal is applied to the two OR gates 20 and 22 by way of AND gate 104 and a timing circuit 105, and owing to the timing circuit 105, acts upon the outlet valves 6 and 8 for a period of time prolonged for a predetermined period of time (for example 20 msec) (t to t4) beyond the end of the pressure reducing signal coming from the evaluating circuit (t2 to t4). The output signal of the AND gate 104 also resets the bistable circuit 102. However, the AND gate 101 is blocked by the bistable circuit 103 which has been set in the manner described previously. This insures that the bistable circuit 102 can only become effective upon the appearance of the interference signal.The third input of the AND gate 101 is connected to the outlet valve 6 by way of the timing circuit 106; the time constant of this timing circuit is relatively large, so that; after the outlet valve 6 has once responded, the timing circuit produces an output signal during an entire brake regulation. Thus, it is ensured that the described initial hold pressure constant period (tl to t2) is only triggered after a pressure reducing signal has already been received (during the period 0 to tl). The bistable circuit 103 can be reset when, for example, the vehicle velocity drops below a predetermined velocity, such as when the signal, which renders the AND gates 14 of Fig. 1 conductive, and which is coupled in by way of terminal 107, disappears. However, the output signal of the AND gate 104 also sets a bistable circuit 108 which is not reset until the disappearance at instant t5 of a hold pressure constant signal which is effective at the output of the AND gate 15 at the end of the pressure reducing signal at t4. This means that the pressure in the two channels is held constant by the set bistable circuit 108 for a period of time (t4 to t6) which comprises the period of time (t4 to ts) from the end of the pressure reducing signal to the disappearance of the hold pressure constant signal at the output of the AND gate 15, and the time constant (for example 100 msec) (t5 to t6) of a timing circuit 109. Pressure is then built up again in parallel, and the operation is repeated. The circuits 101 to 109 described above are again provided in case the other sensor should develop a fault, corresponding circuits being provided with the same numerals but with an addition The fact that a fault in one of the sensors has been detected can be indicated by means of a warning lamp 111 by way of an OR ate 160. AT WE CLAIM IS:

1. An anti-lock regulating system for vehicle braking systems, comprising sensors for providing signals representative of the speeds of two wheels of one axle of a vehicle, an evaluating circuit including two regulating channels for producing in dependence on the movement characteristics of

said two wheels trigger signals for pressure control members associated with these wheels in order normally to regulate the brake pressures at these wheels separately, said trigger signals comprising signals for reducing brake pressure and signals for holding brake pressure constant thereafter, test means for monitoring the functioning of the sensors and in the event of a fault in a sensor being detected producing an interference signal associated with the faulty sensor, blocking means for rendering ineffective the trigger signals of the regulating channel associated with the faulty sensor when an interference signal is produced, parallel switching means for responding to an interference signal and effecting the parallel switching of the two pressure control members such that the trigger signals of the regulating channel associated with the sensor which is not faulty are fed to both pressure control members in parallel, and timing circuits for after the parallel switching of the pressure control members, prolonging the periods of pressure reducing signals and of hold pressure constant signals for the two wheel brakes beyond the ends of the corresponding signals from the evaluating circuit.

2. An anti-lock regulating system as claimed in claim 1, in which when an interference signal is produced, the parallel switching means initiate the triggering of the pressure control members for reducing brake pressure by means of a parallel control signal through a timing circuit which prolongs the period of the control signal relative to the period of a pressure reducing signal from the evaluating circuit, and the parallel control signal sets switching means for triggering the two pressure inlet control members to hold the brake pressures constant for a period prolonged relative to the period of a hold pressure constant signal from the evaluating circuit.

3. An anti-lock regulating system as claimed in claim 2, in which further switching means are provided which respond to an interference signal and which produce a hold pressure constant signal for the control member normally associated with the faulty sensor for a period at least until a pressure reducing signal appears from the evaluating circuit.

4. An anti-lock regulating system as claimed in claim 1, 2 or 3, in which switching means are provided for switching on a warning device when an interference signal is produced.

5. An anti-lock regulating system as claimed in claim 1, 2, 3 or 4, in which the prolongation times are dependent on vehicle velocity and become shorter as the velocity decreases.

6. An anti-lock regulating system as claimed in claim 5, in which the prolongation times becomes zero below a predetermined velocity.

7. An anti-lock regulating system as claimed in claim 6, in which said predetermined velocity is 4 km/h.

8. An anti-lock regulating system for braking systems for vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in the accompanying drawings.