GB1599086A

GB1599086A - Anti-lock regulating systems for braking systems of motor vehicles

Info

Publication number: GB1599086A
Application number: GB1816778A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-12-24
Filing date: 1978-05-08
Publication date: 1981-09-30
Also published as: FR2412444A1; JPS5490720A; JPS6344101B2; FR2412444B1; DE2757911A1

Description

(54) IMPROVEMENTS IN OR RELATING TO ANTI-LOCK REGULATING SYSTEMS FOR BRAKING SYSTEMS OF MOTOR VEHICLES (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 braking systems of motor vehicles.

The object of one known anti-lock regulating system for braking systems of motor vehicles having a regulating logic circuit which adapts the brake pressure in accordance with the rotational behaviour of a wheel is to obtain a braking distance which is as short as possible. However, the travelling stability is insufficient for all conditions of vehicle and of travelling.

The large number of types of commercial vehicles requires, to some extent, regulating circuit arrangements which are specific for each vehicle. However, only those arrangements are permissible in which the vehicle remains stable and controllable by the driver with the shortest possible braking distance even under extreme conditions of road and of travelling.

In "select low" regulation of brake pressure applied at an individual wheel or at a group of wheels, the rotational behaviour of at least two individual wheels or groups of wheels are compared with one another during braking, and the individual wheel or group of wheels which has or have an instantaneous rotational speed lower than any other individual wheels or groups of wheels is determined indicative of the individual wheel or group of wheels at which the coefficient of friction with the roadway is lower than elsewhere, and the brake pressure at an individual wheel of group of wheels is regulated in response to the rotational speed of the wheel or wheels with the lower coefficient of friction in order to reduce the risk of a wheel or wheels locking.

Critical travelling situations frequently occur only in the case of a particular condition of vehicle and travelling. Thus, a regulating circuit system matched thereto is also only optimum for that one condition.

By way of example, an empty commercial vehicle having a short wheel base is critical with respect to travelling stability.

Thus, a regulating circuit system in which a common brake pressure control for rear axle wheel brakes is regulated to the lowest coefficient of friction of a wheel with the roadway; that is to say "select low" regulation would be optimum for the empty condition of the vehicle. On the other hand, in the case of a laden vehicle, that is to say when the rear axle carries a higher axle load, "select low" regulation would result in an unacceptably long braking distance, In this condition individual wheel regulation with individual brake pressure control of the rear axle wheel brakes would constitute the optimum regulating circuit system.

According to the present invention there is provided an anti-lock regulating system foi braking systems of motor vehicles in which means for regulating the brake pressure at each of at least two wheels of a vehicle during braking are responsive through a regulating logic circuit to signals derived from the rotational behaviour of each of said at least two wheels, and the regulating logic circuit which in one mode operates to regulate the brake pressure at each of said at least two wheels individually in accordance with the rotational behaviour of that wheel, can be changed over in response to a control signal to operate in another mode to establish a common brake pressure at said at least two wheels and to regulate that common brake pressure with "select low" regulation, and vice versa.

An anti-lock regulating system embodying the present invention can have the advantage that optimum regulator performance can be obtained under all vehicle and travelling conditions. Compared with known solutions, a vehicle can be braked more efficiently.

The invention will be further described by way of example with reference to the accompanying drawings in which.

Fig. 1 in a block circuit diagram of a changeover regulating logic circuit for an anti-lock system according to one embodiment of the present invention, Fig. 2 is a table of the logic states of the regulating logic circuit of Fig. 1, Fig. 3 is a block circuit diagram of a modification of the change-over logic circuit of Fig. 1 Fig. 4 is a graph to illustrate the effects of the change-over logic circuit of Figs. 1 and 3, Fig. 5 is a side elevation of a position switch for providing a control signal for the regulating logic circuit dependent on vehicle and travelling conditions, Fig. 6 is a side elevation of a vehicle with a lifting axle from which a control signal can be derived dependent on vehicle and travelling conditions, Fig. 7 is a diagrammatic representation of plug and socket connection between a tractor vehicle and a trailer vehicle from which a control signal can be derived dependent on vehicle conditions, Fig. 8 is a diagrammatic illustration of a tractor vehicle and a trailer vehicle showing how a control signal for regulating logic circuit can be derived and applied thereto, Fig. 9 is a plan view, partly in section, of a coupling between a tractor vehicle and a trailer vehicle and from which a control signal for the regulating logic circuit can be derived dependent on travelling conditions, Fig. 10 is a side elevation of part of a steering mechanism from which a control signal for the regulation logic circuit can be derived dependent on travelling conditions, and Fig. 11 is a graph illustrating the effect of the change-over logic circuit with a control signal dependent on slip-threshold and a time delay.

Referring to Fig. 1 which illustrates a changeover logic system, a vehicle wheel 1 has a sensor 1', and a vehicle wheel 2 has a sensor 2'. Each wheel 1, 2 has an input amplifier 3', 4' respectively and an individual wheel regulating channel 3, 4 respectively, and both wheels have a common comparator 5.

The individual wheel regulating channels 3, 4 supply solenoid control signals 6, 7 respectively to output stages 8, 9 for controlling solenoid valves 10, 11. Two AND gates 12 and 13 are arranged on the input sides of the output stages 8 and 9, and two AND gates 14 and 15 are connected to the output of the comparator 5. Further AND gates 16 and 17 are associated with the AND gates 14, 15 and the AND gates 12, 13, and two OR gates 18 and 19 are connected to the outputs of the AND gates 12 and 13 and to the outputs of the AND gates 16 and 17. A control signal terminal is designated 20.

The logic system of Fig. 1 operates as follows: Signals proportional to the speeds of rotation of the wheels 1, 2 are supplied by the sensors 1' and 2', and signals by which the changeover of regulation is to be effected are derived therefrom in the input amplifiers 3' and 4' respectively and, on the input side of the respective associated individual wheel regulating channels 3 and 4, are fed to a comparator 5 which effectively compares the wheel rotational speeds and selects the lower, thus rendering "select low" detection possible in a simple manner. The logic 1 or logic 0 output signal of the comparator 5 is associated with the respective low channel in a freely selectible manner.By way of example, in the present embodiment, when the rotational speed of wheel 1 is the lower the output signal is logic 1, thus indicating that wheel 1 is the low channel, and when the rotational speed of wheel 2 is the lower the output signal is logic 0 thus indicating that wheel 2 is the low channel.

In conformity with the table of Fig. 2: I) With a logic 0 control signal at terminal 20, the solenoid control signals 6, 7, commencing from the individual wheel regulating channels 3, 4, are to be switched separately to the associated output stages 8, 9 for the purpose of controlling the solenoid valves 10, 11. In this case, the desired individual wheel regulation with individual brake pressure control is effective.

The logic 0 signal at the terminal 20 enables AND gates 12 and 13 so that control signals 6, 7 pass through the AND gates 12, 13 and at the same time blocks the action of the comparator 5 by disabling the AND gates 14, 15.

II) On the other hand with a logic 1 control signal at terminal 20 the separate actions of the solenoid control signals 6, 7 are blocked since the AND gates 12, 13 are disabled. When low detection logic 1 exists at the output of the comparator 5, AND gate 14 is enabled so that both the output stages 8, 9 respond to solenoid control signal 6 by way of the AND gate 16 and the two OR gates 18, 19.

III) On the other hand with a logic 1 control signal at terminal 20, when a low detection logic 0 exists at the output of the comparator 5, the AND gate 15 is enabled so that both the output stages 8, 9 respond to the solenoid control signal 7 by way of the AND gate 17 and the two OR gates 18, 19.

For the sake of clarity, only one solenoid valve 10 or 11 is shown in each case in the logic circuit of Fig. 1. However, two solenoid valves and an inlet and an outlet valve respectively are usually associated with each brake pressure regulating circuit.

A combination logic circuit identical to that of Fig. 1 is required for the solenoid inlet anal outlet valve in the case of control with two solenoid valves. The mode of operation is also identical.

Fig. 3 shows a development of the system of Fig. 1. In this instance, a control signal at a terminal 20' is transmitted to a timing circuit 21 and a pulse generator 22. An input 23 for low detection, as well as the output of the pulse generator 22, is connected to the inputs of the solenoid valves 10' and 11' by way of two AND gates 24 and 25 and two OR gates 26 and 27, the two solenoid valves 10' and 11' only being solenoid inlet valves for wheels 1 and 2 respectively.

This embodiment takes into account the fact that, upon a change-over from "select low" regulation to individual wheel regulation, particularly on asymmetrical roadways, an abrupt pressure rise of the notlow channel effects an equally abrupt increase in the yawing moment which has to be compensated for by rapid steering adjustment. However, this frequently overtaxes the driver and critical travelling situations also arise.

Thus, in this case, that is, upon changeover from "select low" to individual wheel regulation, only a reduced rate of pressure rise is permitted for the first build-up of pressure in the not-low channel immediately after the change-over operation.

The trailing edge of the control signal at terminal 20' when changing from logic 1 to logic 0, which effects the change-over operation, at the same time sets the timing circuit which for a predetermined period of time enables the pulse generator 22 which permits only a pulsed, and thereby gradual, build up of pressure to the pressure level of the not-low channel. The pulse generator 22 thereby only acts upon the solenoid inlet valve 10' or 11'.

Fig. 4 in the form of a graph of brake pressure against time shows the efficacy of this arrangement. The brake pressure is plotted on the ordinate, and the time t is plotted on the abscissa. Curve a shows the brake pressure characteristic which, up to the instant tu of the changeover, is valid as a common brake pressure control with "select low" regulation for the relevant wheels.

On the other hand, after the instant tu, the build up of brake pressure to the transmissible brake pressure level c of the notlow channel is delayed in accordance with curve b. If the arrangement described were not effective, the pressure rise after the changeover operation would be effected in a non-delayed manner corresponding to curve d.

Fig. 5 shows a position switch 30, acting as a sensor circuit, on an actuating linkage 31 of an automatically load-dependent braking device 32.

As shown in the embodiment described initially, in order to obtain adequate travelling stability, an empty vehicle in which, for example the load on the rear axle is smaller, preferably has "select low" regulation. On the other hand, a high load on the rear axle of a laden vehicle renders individual regulation essential for the purpose of obtaining a short braking distance.

By coupling the sensor circuit (position switch 30) to a load-detecting brake device 32 for producing a control signal, the optimum regulating circuit arrangement can be associated with empty and laden travelling conditions by change-over.

As is illustrated, in the case of steelsprung axles the sensor circuit can comprise a simple position switch 30 which detects the prevailing condition of the vehicle by the deflection of the spring suspension.

In the case of axles with air suspension, the sensor circuit can comprise a pressure switch which detects the prevailing load condition by means of bellows pressure.

Change-over of the regulating circuit arrangement in dependence upon load is also desirable in vehicles having trailer axles which are in the form of lifting axles which are raised when the vehicle is empty and which are lowered when the vehicle is laden. A vehicle 33 of this type having a lifting axle 34 is shown in Fig. 6.

When the lifting axle 34 is raised, and thus the vehicle 33 is empty, "select low" regulation for the rear axle wheel brake is imperative, since, when the vehicle is combined with a trailer, any other regulation such as indivdual wheel regulation, cannot result in adequate lateral guidance forces owing to the large amount of overhang S between trailer coupling and operative rear axle. The required lateral guidance force for the vehicle in this travelling condition can only be ensured by "select low" regulation of the rear axle wheel brakes. On the other hand, the lowered lifting axle applies an additional lateral guidance force when the vehicle is laden, so that, when the vehicle is in this travelling condition, the rear axle wheel brakes can be regulated in accordance with individual wheel criteria for the purpose of obtaining a short braking distance.

In the vehicle 33, the necessary control signal can be derived directly from an actuating switch for lifting the axle 34 or from an additionally mounted limit switch.

Exhaustive road tests have shown that, as a result of the short wheel base and the low load on the rear axle on asymmetric roadways, a semi-trailer vehicle travelling solo, that is to say travelling without a trailer, can only be controlled by the driver when the rear axle wheel brakes have "select low" regulation. However, with the same controller action and on the same roadway, the braking distance would be inadmissibly long when a trailer is coupled to the tractor vehicle and the tractor vehicle and trailer combination is laden. In this condition, only individual wheel regulation is satisfactory. The necessary control signal can then be produced by means of a sensor circuit of Fig. 5, or alternatively produced by an electrical plug-in unit of a cable connection between the trailer and the tractor vehicle.

Referring to Fig. 7, a tractor vehicle plug connection is designated 35, and a trailer plug connection is designated 36. A switching contact 37, a switching tongue 38, and a control signal line 39 are shown. When the trailer plug connection 36 is not connected, that is to say when the tractor vehicle is travelling solo, the switching contact 37 on the electrical plug-in unit is closed and a logic 1 signal is established on the control signal line 39. On the other hand, when the trailer is coupled, the switching contact 37 is open and then a logic 0 is established.

Referring to Fig. 8, the combination of a tractor vehicle 40 and a trailer 41 is provided with brake anti-lock brake regulation (ABS) device 42, 43 respectively on each individual vehicle 40, 41. In this construction, for the purpose of change-over, a warning signal 44 from the trailer 41 is fed to the ABS device 42 of the tractor vehicle in addition to being fed to a warning device 45 of the tractor vehicle. The ABS devices 42 and 43 are equipped with electronic switching elements.

When a trailer 41 without ABS is coupled, or when the ABS device in the trailer is faulty, increasing thill or draw bar forces which are, to some extent, considerable, are established as a result of the physical conditions of a regulated and a non-regulated wheel during braking operations and, when cornering, have to be reinforced partially, for example, by way of a lateral guidance force of the rear axle of the tractor vehicle 40.

In order to compensate for the differing retardations of the individual vehicles, that is to say of the tractor vehicle and of the trailer, as a cause of the draw bar forces, it is, in this case, desirable to reduce the braking action of the tractor vehicle 40 by "select low" regulation of the rear axle wheel brakes. In the case of a tractor vehicle travelling solo or, alternatively, in the case of a tractor vehicle and trailer combination with the trailer ABS intact and functioning, the rear axle wheel brakes of the tractor vehicle must have individual wheel regulation in order to obtain a short braking distance.

When a trailer without ABS is coupled, the control signal required for detecting the prevailing condition of the vehicle can be effected in the manner shown in Fig. 7. On the other hand, in the case of a trailer having an ABS device 43 installed, as in the trailer 41 illustrated in Fig. 8, the warning signal 44 for the warning device 45, which indicates to the driver that the trailer ABS is malfunctioning, is tapped as a control signal.

It will be appreciated that the control signal, which is to effect change-over to "select low" regulation, can, alternatively, be triggered directly in dependence upon the draw bar force.

Fig. 9 shows a switching contact 46 on the tractor vehicle coupling device or trailer coupling device 47. This switching contact 46 detects increasing draw bar forces by way of a spring arrangement 48 and, upon attaining a set threshold value, effects the change-over of the regulation.

Quite different reasons render it necessary to change-over the front axle to "select low" regulation during the phase in which braking commences. As already mentioned in the description relating to Fig. 3 and Fig. 4, considerable demands on the ability of the driver to react are made by a yawing moment which becomes effective abruptly.

The driver is frequently overtaxed particularly when he applies the brakes in panic on asymmetrical roadways and constitutes a risk for oncoming traffic as a result of deviations in the course of his vehicle.

"Select low" regulation of the front axle wheel brakes which is effective upon the commencement of braking, and which, in the manner described with reference to Fig.

3 and Fig. 4 changes over to individual wheel regulation after the first regulating cycle or after a time delay, gives the driver the time required to apply any steering lock necessary to compensate for yawing moment and to correct the course of the vehicle.

A similar situation can arise in the case of a large steering angle. A large steering angle is necessary when a large yawing moment has to be compensated for, or when sharp cornering or evading manoeuvres are performed. The large steering angle is at the same time an indication that high lateral guidance forces have to be applied. In many cases, these lateral guidance forces can only be made available by "select low" regulation.

In order to prevent the change-over from having a build-up effect on the steering behaviour, a throttled or pulsed pressure drop in the not-low channel is advantageous during change-over from individual wheel regulation to "select low" regulation, in addition to the throttled pressure increase upon change-over from "select low" regulation to individual wheel regulation in the manner described with reference to Fig. 3 and Fig. 4.

The logic circuit required for this purpose is of similar construction to that of Fig. 3, although the pulse generator is triggered by the leading edge of the control signal and acts upon a solenoid outlet valve.

The control signal itself can, as is shown in Fig. 10, be derived from a simple switching contact 50 on a steering mechanism 51.

A cam 52 is located opposite the switching contact 50.

The lateral guidance force is also greatly impaired when a wheel has a large amount of wheel slip over a predetermined period of time. It may then be necessary for at least the other wheel of the relevant axle or, alternatively, of the vehicle side, to produce an optimum side guidance force. However. this can only be ensured by regulating this wheel in a stable range of slip, or returning it thereto, by "select low" regulation. In this case, the control signal for change-over is a slip threshold which is monitored by a timing circuit for the purpose of filtering-out large slip values which exist for only a short period of time.

Fig. 11 shows a curve of wheel rotational speed against time in which the control signal is effective only after a specific time t, despite the fact that the slip threshold has been attained. The wheel rotational speed V is plotted on the ordinate, and the time t is plotted on the abscissa. A curve 55 illustrates the vehicle velocity, curve 56 shows the rotational speed of the wheel 1 with "select low" regulation, and curve 57 shows the rotational speed of the other wheel 2.

The slip threshold is shown by a broken line designated 58. Finally, the control signal s is also plotted on the abscissa.

WHAT WE CLAIM IS: 1. An anti-lock regulating system for braking systems of motor vehicles, in which means for regulating the brake pressure at each of at least two wheels of a vehicle during braking are responsive through a regulating logic circuit to signals derived from the rotational behaviour of each of said at least two wheels, and the regulating logic circuit which in one mode operates to regulate the brake pressure at each of said at least two wheels individually in accordance with the rotational behaviour of that wheel, can be changed over in response to a control signal to operate in another mode to establish a common brake pressure at said at least two wheels and to regulate that common brake pressure with "select low" regulation, and vice versa.

2. An anti-lock regulating system as claimed in claim 1, in which the control signal is controlled by a sensor circuit during critical vehicle and travelling conditions.

3. An anti-lock regulating system as claimed in claim 1 or 2, in which the control signal is responsive to the load condition of the vehicle.

4. An anti-lock regulating system as claimed in claim 1 or 2, for a vehicle having a lifting axle, in which the control signal is responsive to load condition of the vehicle or to the position of the lifting axle, such that the mode of operation of the regulating logic circuit with "select low" regulation is established when the vehicle is empty or when the lifting axle is raised.

5. An anti-lock regulating system as claimed in claim 1 or 2, for a tractor vehicle having a trailer, in which the control signal is responsive to the vehicle rear axle load condition when a trailer without, or with a defective, anti-lock regulating system is coupled to the tractor vehicle for establishing "select low" regulation.

6. An anti-lock regulating system as claimed in claim 1 or 2, for a semi-trailer vehicle, in which when the vehicle is travelling without a trailer the control signal is derived from the load condition of at least a rear axle of the vehicle for establishing "select low" regulation.

7. An anti-lock regulating system as claimed in claim 1 or 2, for a tractor vehicle and trailer combination, in whidh the control signal is derived from a high draw bar force occurring as a result of the trailer overrunning the tractor vehicle for establishing "select low" regulation at least at the wheels of one axle of the tractor vehicle.

8. An anti-lock regulating system as claimed in claim 1 or 2, in which the control signal is derived from part of the vehicle steering mechanism whereby in the event of a steering angle greater than a predetermined value "select low" regulation is established at the wheels of the steering axle.

9. An anti-lock regulating system as claimed in claim 1 or 2, in which the control signal is responsive to the existence of a predetermined amount of wheel slip continuing for a predetermined period of time.

10. An anti-lock regulating system as claimed in claim 1 or 2, in which a pulse generating circuit permits only step-wise increase in pressure for a first build up of brake pressure after a change of the regulating logic circuit to said one mode immediately after a "select low" regulation mode.

11. An anti-lock regulating system as claimed in any of claims 1 to 11, in which the regulating logic circuit regulates the first build-up in brake pressure associated with

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. regulation to "select low" regulation, in addition to the throttled pressure increase upon change-over from "select low" regulation to individual wheel regulation in the manner described with reference to Fig. 3 and Fig. 4. The logic circuit required for this purpose is of similar construction to that of Fig. 3, although the pulse generator is triggered by the leading edge of the control signal and acts upon a solenoid outlet valve. The control signal itself can, as is shown in Fig. 10, be derived from a simple switching contact 50 on a steering mechanism 51. A cam 52 is located opposite the switching contact 50. The lateral guidance force is also greatly impaired when a wheel has a large amount of wheel slip over a predetermined period of time. It may then be necessary for at least the other wheel of the relevant axle or, alternatively, of the vehicle side, to produce an optimum side guidance force. However. this can only be ensured by regulating this wheel in a stable range of slip, or returning it thereto, by "select low" regulation. In this case, the control signal for change-over is a slip threshold which is monitored by a timing circuit for the purpose of filtering-out large slip values which exist for only a short period of time. Fig. 11 shows a curve of wheel rotational speed against time in which the control signal is effective only after a specific time t, despite the fact that the slip threshold has been attained. The wheel rotational speed V is plotted on the ordinate, and the time t is plotted on the abscissa. A curve 55 illustrates the vehicle velocity, curve 56 shows the rotational speed of the wheel 1 with "select low" regulation, and curve 57 shows the rotational speed of the other wheel 2. The slip threshold is shown by a broken line designated 58. Finally, the control signal s is also plotted on the abscissa. WHAT WE CLAIM IS:

1. An anti-lock regulating system for braking systems of motor vehicles, in which means for regulating the brake pressure at each of at least two wheels of a vehicle during braking are responsive through a regulating logic circuit to signals derived from the rotational behaviour of each of said at least two wheels, and the regulating logic circuit which in one mode operates to regulate the brake pressure at each of said at least two wheels individually in accordance with the rotational behaviour of that wheel, can be changed over in response to a control signal to operate in another mode to establish a common brake pressure at said at least two wheels and to regulate that common brake pressure with "select low" regulation, and vice versa.

other wheels so as to be throttled or pulsed immediately after a change of mode establishing "select low" regulation at said at least two wheels.

12. An anti-lock regulating system for braking systems of motor vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to Figs.

I and 2 of the accompanying drawings.

13. An anti-lock regulating system for braking systems of motor vehicles, constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 1 as modified by Figs.

3 and 4 of the accompanying drawings.

14. An anti-lock regulating system for braking systems of motor vehicles as claimed in claim 12 or 13, including control means responsive to vehicle and/or travelling conditions constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 5, or Fig. 6, or Fig. 7, or Fig. 8, or Fig. 9, or Figs. 10 and 11 of the accompanying drawings.