GB1603459A

GB1603459A - Process and apparatus for detecting spurious control signals in an anti-skid brake control system

Info

Publication number: GB1603459A
Application number: GB22840/78A
Authority: GB
Original assignee: Wabco Fahrzeugbremsen GmbH
Current assignee: Wabco Fahrzeugbremsen GmbH
Priority date: 1977-06-14
Filing date: 1978-05-25
Publication date: 1981-11-25
Also published as: SU786935A3; DE2726738C2; DE2726738A1; FR2394430B1; JPS6228023B2; SE438292B; JPS547085A; SE7806755L; IT1159711B; IT7868284A0; FR2394430A1; YU139978A

Description

(54) PROCESS AND APPARATUS FOR DETECTING SPURIOUS CONTROL SIGNALS IN AN ANTI SKID BRAKE CONTROL SYSTEM (71) We, WABCO FAHRZEUG B REMSEN G. m. b. H. formerly Wabco Westinghouse G. m. b. H., 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 a process and apparatus for detecting spurious control signals in an anti-skid brake control system.

In normal travel jolting and shaking movements and vertical oscillations in the vehicle body caused by uneven roads can result in changes in the rolling radius of the vehicle tyres. These changes in the rolling radius are detected by sensors responsive to the rotating speed of the vehicle wheel. If the rate of change is so great that it exceeds the values of a deceleration threshold a brake control operation is triggered in a brake control unit for preventing skidding.

If such changes in the rolling radius occur in rapid succession a control operation is triggered correspondingly often. The operating values obtained may soon reach the limit service life values of components of the anti-skid control system and these then break down.

An object of the present invention is to alleviate the above problem by detecting when spurious control signals are produced and inhibiting the response of the anti-skid control system to such signals.

According to one aspect of the present invention there is provided a process for detecting and blocking spurious signals due to variations in rotational speed of a vehicle wheel running on an uneven surface, which signals may initiate undesirable brake control operations in an anti-skid brake control system of the vehicle, the system including means for deriving signals representing the angular velocity of at least two of the vehicle wheels, means responsive to the angular velocity signals for deriving acceleration, deceleration and slip control signals for the at least two wheels respectively when specific threshold values are exceeded, and means responsive to the control signals for energising one or more solenoid operated valves for controlling the flow of brake pressure medium, wherein for each of the at least two wheels a test is made for a frequency component in one or more of the control signals above a threshold frequency, or the presence or absence of one or more of the control signals in relation to another control signal in accordance with a particular combination or sequence of control signals, the occurrence of which frequency component, combination or sequence indicates whether or not a normal controlled braking process is taking place, and the other control signal or a signal derived from the other control signal is blocked if the result of the test indicates that a normal controlled braking process is not taking place, thereby blocking an undesirable brake control operation.

According to a second aspect of the present invention there is provided apparatus for carrying out a process according to the above paragraph having at least two sensors respectively responsive to the rotational behaviour of at least two of the vehicle wheels, and for each of the at least two wheels acceleration, deceleration and slip threshold value stages respectively for the generation of the acceleration, deceleration and slip control signals, and means responsive to the control signals for energising the one or more solenoid operated valves, the apparatus further including logic means responsive to the one or more of the control signals to block the other control signal or the signal derived therefrom.

As a result of the use of the invention the consequences of changes in the angular velocity caused, for example, by the changes in the rolling radius during travel, are eliminated ; it is, of course, impossible to eliminate the causes of the changes in the rolling radius.

During unbraked travel, changes in the rolling radius may occur at a frequency of approximately 10 Hz. In the case of control operations for preventing wheel locking, control frequencies can be limited to 6 Hz or below without deterioration in the quality of the brake control. To prevent interference with the brake response in unbraked travel, according to one example development of the invention the actual frequency of the one control signal or several control signals is compared with a predetermined frequency threshold and if this threshold is exceeded a switching signal is produced which blocks the initiation of a brake control operation by another control signal or signals. The blocking may take the form of raising a threshold for the other signal which would give rise to the spurious control operation or of a signal derived from it used to initiate a control operation.

Alternatively the other signal may be inhibited altogether.

During controlled braking a certain sequence of control signals is to be expected. In general, the control operation is triggered by the occurrence of a deceleration signal and normally a slip control signal would follow after an interval.

This slip control signal, however, presupposes a certain magnitude of deceleration. In the case of changes in the rolling radius during unbraked travel the slip threshold would not be exceeded but the deceleration threshold probably would be, and this triggers a pulse generator or other means which energises brake pressure medium solenoid valves in a certain manner after the deceleration signal has ended. If the sequence of the various control signals to be expected in a normal control operation is not observed this must be regarded as spurious, and in order to avoid resulting undesirable control operations the triggering signals of the pulse generator may be blocked, or one of the signals (e. g. an acceleration control signal) used to generate the tnggering signals may be blocked. Alternatively, the deceleration threshold may be raised if a deceleration signal is not followed by a slip signal, the threshold being reset on the occurrence of a slip signal.

The pulse generator may be blocked by a signal that is generated by a flip-flop, which would be set by a signal initiating a control operation, and reset by a slip control signal.

Use may be made of the fact that, in the case of controlled braking, wheel speed variations greater than 8 km/h usually occur and these variations do not occur as a result of changes in the rolling radius.

It is to be expected in unbraked travel that the wheel speed which varies as a result of the unevenness in the road etc. always reverts to the original value, i. e. to the vehicle speed. This criterion can be used to eliminate the spurious control signals. To achieve this, the degree of wheel deceleration may be compared with the degree of wheel acceleration and if they are equal the control disabled by blocking or increasing the threshold of response or altering the characteristic of response of a control signal. If the difference is zero and a control signal occurs (during unbraked travel) this must be regarded as a spurious control signal and should be inhibited.

As a result of external influences, for example as a result of uneven roads, wheel decelerations occur during normal travel which, as a rule, are less than 3 g. This criterion may be used to eliminate the triggering of spurious control operations during unbraked travel, but overriden during braking. In order that no deceleration signals should cause a response at these wheel deceleration values the threshold value is set at a value that is greater than e. g. 3 g. In order that during controlled braking a smaller threshold value favorable therefor (e. g. 1. 5 g) can be used, the signal that indicates a braking operation (e. g. a signal which is produced by the brake light switch or as a result of the energisation of a brake pressure solenoid valve) may be used to connect this lower threshold for the duration of the control operation.

Various circuit arrangements can be employed to implement the methods described above.

In order that the invention may be fully understood and readily carried into effect, it will now be described in more detail with reference to the attached drawings, of which : Figure I shows a block diagram of a circuit arrangement according to an example of the invention utilising blocking of a control signal triggering a control operation (e. g deceleration or-b control signal) in unbraked travel if the frequency of another control signal (e. g. acceleration or +b control signal) should exceed a predetermined threshold ; Figure 2 shows a block diagram of another circuit arrangement according to the invention for blocking a control signal (e. g. the-b signal) triggering a control operation by increasing the threshold of response in unbraked travel if the frequency of another control signal (e. g. the +b signal) should exceed a predetermined threshold; Figure 3 shows a block diagram of another circuit arrangement according to the invention for blocking a pulse generator energised by a-b signal (in unbraked travel) should the control amplitude fall below a predetermined threshold value ; Figure 4 shows a block diagram of another circuit arrangement according to the invention similar to Figure 3, except that it is ensured, in addition, that the +b signal remains blocked ; Figure 5 shows a block diagram of another variation of the circuit arrangement according to Figure 3 in which a +b signal remains blocked only until the occurrence of a slip control signal; Figure 6 shows a block diagram of another variation of the circuit arrangement according to Figure 3 in which the-b signal, and not the pulse generator, remains blocked until the occurrence of a slip signal (A signal) ; Figure 7 shows a block diagram of another circuit arrangement according to the invention for blocking the pulse generator in the case of-b signals following one another at short intervals ; and Figure 8 shows a block diagram of a further circuit arrangement according to the invention for blocking-b signals in the case of low wheel deceleration values by increasing the threshold of response.

Changes in the angular velocity of the vehicle wheel, occurring during unbraked travel as a result of changes in the rolling radius, and the associated acceleration and deceleration signals have a higher frequency (e. g. 10 Hz) than the control signal frequency acceptable in controlled braking (approximately 6 Hz). In Figures I and 2 circuits are shown with which, in unbraked travel over the frequency range of acceleration signals, the occurrence of control signals, brought about by such changes in the angular velocity, is prevented.

Reference will now be made to Figure 1.

The rotating behaviour of one or more vehicle wheels is monitored with one or more sensors which produce wheel speed signals, one of the sensors 2 being shown in Figure 1. Acceleration and deceleration signals (+h and-h signals) are produced from the wheel speed signals from the sensor 2 by differentiating stages 4 and 6 and slip signals (A signals) are produced by a circuit 8 which typically compares the speeds of different wheels and if the speeds differ by more than the amount resulting from the vehicle turning normally the circuit 8 causes a slip signal to be generated.

The +b signal-is applied to a threshold circuit 10 having a low amplitude threshold and the frequency of the +b signals passed by the threshold circuit 10 is compared with a threshold value, for example 6 Hz, in a frequency comparison stage 12. If the frequency threshold is exceeded the stage 12 produces a high signal which is converted by an inverter 14 to a] ow signal which is applied to an input of an AND gate 16 and blocks it. The-b signal is compared in a comparator 18 with a fixed amplitude threshold, which applies a high signal to the other input of the AND gate 16 if the threshold is exceeded. Since the gate 16 is blocked the-b signal, which normally triggers a brake control operation, cannot become effective and the energisation of a brake solenoid valve 20 via an OR gate 22 and an amplifier 24 does not take place.

When the brakes are subject to anti-skid control the-b signal energises the solenoid valve 20 via the OR gate 22 and at the same time blocks pulse generator 28 via an OR gate 26 and energises a delayed release timing element 30. After the end of the-b signal the timing element continues to provide a high output signal which is applied via an inverter and the OR gate 26 as a low signal to the reset input of the pulse generator 28 so that during the operation of the timing element the pulse generator emits pulses and energises the solenoid valve 20. After the output of the timing element has terminated, its output goes to low and the pulse generator is blocked again.

The deceleration signal (-b) and the slip signal (i) result in operation of the solenoid valve 20 in normal brake control operation and a slow build up of the brake pressure after a reduction due to operation of the valve 20 is provided by the pulse generator 28.

The circuit shown in Figure 2 corresponds in many respects to that of Figure I so that for the sake of simplicity the same reference symbols are used for the same components except that a prime is provided in Figure 2. Figure 2 differs from Figure I in that it does not include an ANDgate to block the-b signal when the frequency threshold is exceeded by the +b signals, but the amplitude threshold for the -b signal is increased via a terminal 34 in the comparator 18'for the-b signal.

Otherwise the functioning of Figure 2 is the same as Figure I In the case ofcontroNed hrak < ng a certain sequence of control signals is to be expected. The control operation is generally triggered by the occurrence of a deceleration signal and a slip control signal would normally follow after an interval.

This slip control signal, however, presupposes a certain magnitude of deceleration will have occurred earlier. In the case of changes in the rolling radius during unbraked travel the slip threshold is not exceeded but the deceleration threshold probably is, so that it would energise a pulse generator driving the solenoid valves after the end of the deceleration signal unless steps were taken to prevent it doing so. If the sequence of the various control signals to be expected in a normal brake control operation is not detected then the initiation of a brake control operation must be regarded as spurious. Examples of circuits for preventing the spurious initiation of a control operation under such circumstances are shown in Figures 3,4,5 and 6.

Reference will now be made to Figure 3.

From the signals obtained from a sensor 40,-b signals are generated by a differentiator 42, and A signals are generated by a circuit 44. The-b signal is compared with a fixed threshold in a comparator 46. If the threshold is exceeded the comparator 46 produces a signal which energises a solenoid valve 52 (outlet valve) via an OR gate 48 and an amplifier 50, which blocks a pulse generator 54 via an OR gate 56, and which energises a delayed release timing element 58 the output of which is connected via an inverter 60 and the OR gate 56 to the blocking input R of the pulse generator 54. The pulse generator 54 is connected via an input of an AND gate 62 to the OR gate 48 and thence to the solenoid valve 52. Applied to the other input of the AND gate 62 is the output of an RS flip-flop 64, the setting input of which is connected to the output of the circuit 44 for the generation of slip signals and the reset input of which is connected via an inverter 66 to the output of a delayed response timing element 68 which is energised by a signal that is produced as a result of the energisation of the solenoid valves and indicates the commencement of a brake control operation. If there is a spurious condition as described above the-6 signal firstly energises the solenoid valve 52 and blocks the pulse generator 54. Both timing elements 58 and 68 are energised and operate to produce signals after the end of the-b signal. The element 58 causes the pulse generator 54 to emit pulses for a short period as described above with respect to Figure 1. The element 68 after operation resets the flip-flop 64, causing it to produce a low output signal which blocks the AND gate 62 so that energisation of the solenoid valve 52 by pulses from the pulse generator 54 is prevented after the operation of the timing element 58. If this were a normal brake control operation the A signal would follow after an interval and set the flip-flop so that the AND gate 62 is opened again.

The circuit arrangement according to Figure 4 has some additional circuit elements compared to the circuit arrangement according to Figure 3. The circuit of Figure is however essentially different from the circuit according to Figure 3 in that an additional delayedresponse, delayed-release timing element is provided to block the +b signals as long as the outlet solenoid valves are not energised.

By means of differentiating stages 72 and 74 and circuit 76, +b,-b and A signals are again produced from the signals of a sensor 70. Comparators 78 and 80 having fixed thresholds are connected downstream of the differentiating stages 72 and 74 respectively.

The output of the comparator 78 is connected via an AND gate 82 and an OR gate 84 to a solenoid valve (inlet valve) 86.

The output of the comparator 80 is connected on the one hand via the OR gate 84 to the valve 86 and via an OR gate 88 to another solenoid valve 90 (outlet valve) and on the other hand via an OR gate 92 to the blocking input of a pulse generator 94 and to the input of a delayed-release element 96, the output of which is applied, via an inverter 98 and the OR gate 92, to the blocking input of the pulse generator 94.

The blocking input of the pulse generator 94 is also connected to receive via the gate 92 the output of the AND gate 82. The input to the valve 90 is also applied to a delayedresponse and delayed-release timing element 100, the output of which is connected via an inverter 102 to the reset input of a flip-flop 104 and is also applied to a second input of the AND gate 82.

The outputs of the pulse generator 94 and of the flip-flop 104 are connected to the inputs of an AND gate 106, the output of which is connected via the OR gate 84 to the inlet valve 86. The setting input of the flip-flop 104 is connected to the output of the slip signal generation circuit 76 as in the case of the circuit according to Figure 3.

The output of the circuit 76 is also connected to inputs of the OR gates 84 and 88.

Acceleration (+b) signals exceeding the threshold of the comparator 78 are blocked by the gate 82 for as long as the timing element 100 is not operating, i. e. its output is zero. At this time the flip-flop 104 is also reset. Deceleration (-b) signals that exceed the threshold of the comparator 80 first of all block the pulse generator 94 and bring about the energisation of the timing element 100 by energising the valve 90. If the-b signal and thus the energising signal disappear the timing elements 96 and 100 operate with the result that the pulse generator 94 is unblocked and the AND gate 82 is opened.

After the operation of the timing element 100 the flip-flop 104 is reset, so that the AND gate 106 is blocked and the energisation of the valve 86 by the pulses from the pulse generator 94 is prevented, and also the AND gate 82 is blocked again.

The flip-flop 104 is set again, and therefore the AND gate 106 opened, only as a result of the occurrence of a A-signal.

The circuit according to Figure 5 differs from the circuit according to Figure 4 only in that the AND gate 106 is blocked by the output of the flip-flop 104 as long as the latter is reset instead of by the output of the timing element 100', which is now only a delayed-release timing element. Therefore, for the sake of simplicity, the same reference numerals are used as in the circuit according to Figure 4 except that a prime is added and otherwise the operation can be deduced from the above description of Figure 4.

The circuit of Figure 6 corresponds in principe to that of Figure 3 so that, in this case too, for the sake of simplicity, the same reference numerals are used as in Figure 3 except that they are provided with a prime to distinguish them from those of Figure 3.

However, in the circuit of Figure 6 the pulse generator 54'is not blocked by an AND gate controlled by the output of the flip-flop 64'. In the circuit of Figure 6 the AND gate 62'is connected downstream of the comparator 46'and blocks the-b signals as long as the flip-flop 64'is reset. Otherwise the operation of Figure can be inferred from the description relating to Figure 3.

On the occurrence of a rapid succession of-b signals the circuit arrangement of Figure 7 can be used to prevent the energisation of the solenoid valves by the pulse generator.

The +b and-b signals generated by differentiating circuits 110 and 112 for the output of a sensor are compared in comparators 114 and 116 respectively with fixed threshold values. Slip signals are generated in a circuit 118 from the sensor output.

If a-b signal of suitable magnitude occurs the solenoid valves 120 and 122 are energised. At the same time a delayedresponse and delayed-release timing element 124 is energised the delays of which are so long that the rapid succession of-b signals results in continuous operation of the element. The result of this is that an AND gate 126 blocks the output of a pulse generator 128 for sufficiently long to make it impossible for the pulses generated after a -b signal has disappeared to energise the solenoid valve 120 and thus a dangerously high frequency of energisation of the valve which might lead to damage or excessive wear is avoided.

As a result of external influences, for example uneven roads, wheel decelerations occur during normal travel that, as a rule, are less than 3 g. A circuit is shown in Figure 8 which eliminates-b signals representing such decelerations by increasing correspondingly an initially lower predetermined threshold value.

A sensor 130 scans the wheel behaviour.

The-b signals are generated in a differentiating circuit 132 and A signals are generated in a circuit 134 from the sensor output. During unbraked travel a normal, lower threshold of response is normally disabled in a comparator circuit 136 to which the-b signals are applied, because if there is no brake control operation in progress the-b signal is compared with an increased threshold of response (e. g. > 3 g) and thus blocked since, in the case of unbraked travel, as already mentioned above, decelerations ; 3 g do not occur as a rule so that, as a result,"spurious control signals"are prevented.

In the case of controlled braking where the deceleration 3 g is usually exceeded, an appropriate signal, which can be derived from the energisation of a brake light switch or the energisation of a solenoid valve 138, for example, brings about the energisation of a delayed-release timing element 140 which-as long as it is in operation-switches in the normal lower threshold of response (for example 1. 5 g) for the-b signals for the remainder of the brake control operation. The functioning of the other components of the circuit, i. e. the pulse generator 142, the timing element 144, the inverter 146 and the OR gate 148 can be inferred from the above descriptions of Figures I to 7.

Claims

WHAT WE CLAIM IS : 1. A process for detecting and blocking spurious signals due to variations in rotational speed of a vehicle wheel running on an uneven surface, which signals may initiate undesirable brake control operations in an anti-skid brake control system of the vehicle, the system including means for deriving signals representing the angular velocity of at least two of the vehicle wheels, means responsive to the angular velocity signals for deriving acceleration, deceleration and slip control signals for the at least two wheels respectively when specific threshold values are exceeded, and means responsive to the control signals for energising one or more solenoid operated valves for controlling the flow of brake pressure medium, wherein for each of the at least two wheels a test is made for a frequency component in one or more of the control signals above a threshold frequency or the presence or absence of one or more of the control signals in relation to another control signal in accordance with a particular combination or sequence of control signals, the occurrence of which frequency component, combination or sequence indicates whether or not a normal controlled braking process is taking place, and the other control signal or a signal derived from the other control signal is blocked if the result of the test indicates that a normal controlled braking process is not taking place, thereby blocking an undesirable brake control operation.
2. A process according to claim 1, wherein the actual frequency of the acceleration control signal is compared with a predetermined frequency threshold, and when this threshold is exceeded, a switching signal is generated that blocks the initiation of a brake control operation by the deceleration control signal or signals.
3. A process according to claim 1 or 2 wherein the other control signal or the signal derived from the other control signal is blocked by raising the threshold value for the generation of the other control signal.
4. A process according to claim I or 2 wherein the other control signal or the signal derived from the other control signal is blocked by gating means responsive to the one or more of the control signals.
5. A process according to any of claims I to 4 in which the system inclues a pulse generator connected to energise a solenoid valve so as to produce a slow build-up of brake pressure following a reduction thereof, wherein a control signal for starting the pulse generator and/or the signals from the pulse generator are blocked.
6. A process according to claim 5 wherein the signals from the pulse generator can be blocked by a bistable, which bistable can be reset by the end of a signal initiating a brake control process and set by a slip control signal.
7. A process according to claim I wherein the threshold value for the derivation of the deceleration control signal is increased if a slip control signal does not occur within the duration of a deceleration control signal.
8. A process according to claim 7 wherein the threshold value is increased by a specific amount.
9. A process according to claim 7 or 8 wherein the threshold value for the derivation of the deceleration control signal is reduced after having been increased on the first occurrence of a slip control signal within the duration of a deceleration control signal.
10. A process according to claim 9 wherein the threshold value for the derivation of the deceleration control signal is reduced to an initial value on the second occurrence of a slip control signal within the duration of a deceleration control signal.
11. A process according to claim 5 in which the acceleration control signal is applied to block the operation of the pulse generator and both the acceleration control signal and the output of the pulse generator are blocked if a rapid succession of deceleration control signals occurs.
12. A process according to claim 6 wherein the signal initiating a brake control process is derived from the deceleration control signal and/or the slip control signal.
13. A process according to claim 12 wherein the signal initiating a brake control process is used to unblock the acceleration control signal which can then be applied to operate a solenoid valve and block the operation of the pulse generator.
14. A process for detecting and blocking spurious signals due to variations in rotational speed of a vehicle wheel running on an uneven surface, which signals may initiate undesirable brake control operations in an anti-skid brake control system of the vehicle, the process being substantially as described herein with reference to any of Figures) to 8 of the accompanying drawings.
15. Apparatus for carrying out a process according to any of claims I to ! 4 having at least two sensors respectively responsive to the rotational behaviour of at least two of the vehicle wheels, and for each of the at least two wheels acceleration, deceleration and slip threshold value stages respectively for the generation of the acceleration, deceleration and slip control signals, and means responsive to the control signals for energising the one or more solenoid operated valves, the apparatus further including logic means responsive to the one or more of the control signals to block the other control signal or the signal derived therefrom.
16. Apparatus according to claim 15 having a pulse generator connected to energise one of the solenoid valves and including a circuit for causing the pulse generator to generate pulses for a predetermined period of time following the end of the deceleration control signal and for blocking the operation of the pulse generator at the end of the period of time.
17. Apparatus according to claim 16 including an AND-gate through which the pulses from the pulse'generator are applied to energise the one solenoid valve, a bistable having an output connected to control the AND-gate, a first input for a setting signal connected to receive the slip control signal and a second input for a resetting signal connected to receive a delayed signal following the end of an ORlogical combination of the deceleration control signal and the slip control signal.
18. Apparatus according to claim 17, wherein the acceleration control signal is also connected to block the operation of the pulse generator.
19. Apparatus according to claim 18 including an AND-gate connected in the path of the acceleration control signal, which gate is controlled either by the output of the bistable or by an inverted form of the signal applied to the second input of the bistable.
20. Apparatus according to claim 15 wherein the deceleration threshold value stage for the generation of the deceleration control signals has a high threshold value and is reduced in response to a signal from the logic means indicating that a normal controlled braking process is taking place.
21. Apparatus according to claim 15 wherein the logic means inclues a bistable circuit connected to block the deceleration control signal until the occurence of a slip control signal.
22. Apparatus according to claim 15 including a pulse generator connected to energise one of the solenoid valves so as to produce a s!owbui)d-up of brake pressure following a reduction thereof, wherein the logic means is connected to block the output of the pulse generator on the occurrence of a rapid succession of deceleration control signals.
23. Apparatus according to claim 15 wherein the logic means includes a circuit responsive to the frequency of the acceleration control signal being above a threshold frequency the output signal of which is connected to block completely or raise the threshold value for the generation of the deceleration control signal.
24. Apparatus for detecting and blocking spurious signals due to variations in speed of a vehicle wheel running on an uneven surface, which signals may initiate undesirable brake control operations in an anti-skid brake control system of the vehicle, the apparatus being substantially as herein described with reference to any of Figures I to 8 of the accompanying drawings.