GB2109882A

GB2109882A - Combined anti-wheel spin and anti-wheel lock control system for a motor vehicle

Info

Publication number: GB2109882A
Application number: GB08219599A
Authority: GB
Inventors: Manfred Burckhardt; Franz Brugger; Richard Zimmer
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1981-07-10
Filing date: 1982-07-07
Publication date: 1983-06-08
Also published as: DE3127301C2; FR2509243A1; DE3127301A1; JPS5816947A; IT1148986B; IT8248732A0

Abstract

A design of a propulsion control i.e. anti wheel-spin and propulsion torque reduction system for vehicles equipped with a four-channel anti- wheel lock system is given, permitting a combined system on the vehicle, at an additional cost which is only small in comparison with that of an anti-lock system alone, this propulsion control system utilising an auxiliary pressure source 41 and including the safety system which is required for monitoring its operation. The basic design of a propulsion control system is integrated with the anti-lock system. Wheel speed-sensors (17, 18, 19 and 21), brake-pressure regulating valves (26 and 27) of the driven vehicle wheels (14 and 16), the pump (33) associated therewith which returns dumped brake fluid upstream of the values (26 and 27), provided as components of the anti-lock system, as well as that signal input stage (53) of this system which receives the signals from the wheel speed-sensors, are utilised at the same time, as appropriate, as components of the propulsion control system (10). The respective safety circuits (37 and 52) of the anti-lock system (11) and of the propulsion control system (10) are designed in a manner such that, in the event of an operating fault in the anti- lock system (11), the propulsion control system (10) is switched off, at the same time, while only this latter system is switched off in the event of its operation becoming faulty. A warning indicator (39) is provided. <IMAGE>

Description

SPECIFICATION Propulsion control system for a motor vehicle having an anti-blocking system The invention relates to a propulsion control system for a vehicle, which is also equipped with an anti-blocking system (ABS).

This concept corresponds to the state of technical development which the Applicant has achieved, in-house, on experimental vehicles, this development being aimed at equipping vehicles with a propulsion control system (PCS), in addition te an anti-block system (ABS) which is known per se, in order by doing so, to gain added safety in critical driving situations, and to achieve optimum utilisation of the power of the drive unit of a vehicle. In this context, assuming that one axle on the vehicle is driven, the propulsion control system operates according to the principle whereby braking is applied, by means of the wheel-brake, to that drive wheel which is tending to spin, and whereby a reduction in the output torque of the drive unit is additionally triggered when both the driven wheels are tending to spin and both the wheel-brakes are consequently activated.

Embodiments of propulsion control systems of this type are described in our co-pending Patent Application No. 82 19600, which is being concurrently filed under the title "System for controlling the propulsion of motor vehicles", to the contents of which reference is also directed in the present document.

Since, for safety reasons, the propulsion control and the anti-block control must not influence each other, it is obvious that the relevant control systems, (ABS and PCS) should be designed as separate systems, both functionally and constructionally, so that the possibility of mutual interaction is effectively excluded, even in the event of faulty operation of either of the two systems. Since the technical effort required to produce a propulsion control system is comparable to that required for an antiblock system, an, as it were, additive design solution of this type would be very expensive.

The object of the invention is accordingly to indicate a design of a propulsion control system, of the type initially mentioned, which includes the safety system required for monitoring its operation, and which allows, on a vehicle, a combined practical embodiment of effective propulsion control and anti-block control, at an additional expense which is low in comparison with the cost of an anti-block system.

According to the invention, there is provided a propulsion control system for a vehicle which is also equipped with an anti-block system (ABS), this control system comprising the following components: a) for each wheel, a speed sensor, generating an electrical output signal which is proportional to the rotational speed of the wheel or to its peripheral velocity, b) for each wheel, a brake-pressure regulating valve, which can be controlled electrically to a flow position, a closed position, and a reverseflow position, c) an electronic control unit which generates output logic-signals from wheel slip signals and wheel acceleration and deceleration signals which are being received by the speed-sensors, and from the comparison of these signals with preset threshold values and which generates, from a combination operation on these logic-signals, the pressure build-up pressure-holding and pressurerelease signals required for appropriately controlling the brake-pressure regulating valves, d) a safety circuit which monitors the operational readiness of the anti-block system and which switches off this system in the event of faulty operation, thereby resetting the brake-pressure regulating valves to their normal position, which is appropriate for building-up the pressure, the propulsion control system furthermore activating the wheel-brake of any drive wheel which is tending to spin and, if both the driven wheels are tending to spin, additionally switching a torque-reducing command through to the drive unit, wherein A) the electronic control unit of the anti-block system includes a signal input stage, which generates velocity output signals and acceleration output signals which characterise the state of motion of the vehicle wheels, these signals being processed in a comparison/combination-stage to produce the control signals for the brake-pressure regulating valves, this comparison/combinationstage being series-connected after the input stage, B) an evaluation/switching-stage is provided, within scope of the propulsion control system, series-connected after the signal input stage of the ABS, this evaluation/switching stage processing the velocity signals and acceleration or deceleration signals which have been received, for the slip of the driven vehicle wheels, and generating, from the results, characteristic slipvalve signals, and generating, from the comparison of these signals, as well as of the velocity signals and acceleration or deceleration signals which continue to be received, with threshold values, output logic-signals which characterise the state of motion of the driven vehicle-wheels, and of the vehicle as a whole, and generating, from a combination operation on these output signals, the control signals which are required for controlling the brake-pressure regulating valves or the actuator for the torquereduction, in a manner appropriate to the driving situation.

C) an auxiliary pressure-source is provided, which effects the supply of pressure to the particular wheel-brake, or brakes, which is, or are, activated during the active phases of the propulsion control system.

D) a safety circuit is provided, which monitors the operation of the propulsion control system and, in the event of its operation becoming faulty, switches off its auxiliary pressure-source and its evaluation/switching-stage, and triggers a warning signal, and/or an indicator signal.

The propulsion control system according to the invention, practically embodied in this manner, provides at the minimum, the technical advantages described in the text which follows: As a result of the dual utilisation of the wheel speed-sensors, of the hydraulic unit, and of the signal input stage of the evaluation-circuit of the anti-block system, both for this system and for the propulsion control system, the additional expense required for the latter system decreasss to a friction, which is only comparatively small, of the expenditure required for an anti-block system or a propulsion control system considered in isolation, so that the additional costs for the propulsion control system which is combined, according to the invention, with an anti-block system, only amount to approximately 10 to 1 5% of the costs which must be attributed to an anti-block system on its own. Despite their extensive integration, the independent operation of the propulsion control system and of the anti-block system is ensured, the latter system remaining ready to operate even when a fault occurs in the propulsion control system and this system is switched off.

By means of a dividing piston, acting as a pressure intensifier, it becomes possible to utilise a pressure-source, which is available on the vehicle, as an auxiliary pressure-source for the propulsion control system, this pressure-source being available, for example, within the scope of a level regulating system or a servo system, this multiple utilisation further reducing the constructional expenditure for the propulsion control system.

In addition, when the hydraulic circuit of the propulsion control system is designed in this manner, the return pump which is provided within the scope of the anti-block system for reducing the braking pressure, can also be utilised concurrently for the propulsion control system, for an analogous purpose.

The propulsion control system is hydraulicaily decoupled from the anti-block system, so that, for example, a fault in the pressure supply to the propulsion control system cannot effect the functional readiness of the anti-block system, this decoupling being achieved, in a simple manner, by means of the pressure intensifier, the dividing piston of this intensifier being mounted to that it can float and, in the event of the auxiliary pressure-source being turned off, it automatically switches into its normal position, under the influence of the pressure prevailing in the brake line.

The switching-off of the propulsion control system in the event of faulty operation in the antiblock system, results immediately in effective monitoring of those components which are utilised both for the anti-block control and for the propulsion control, this monitoring being effected by the safety circuit of the anti-block system.

It is accordingly possible in designing the safety circuit which is additionally required for the propulsion control system to limit this circuit to monitoring those components which are specific solely to the propulsion control, namely to monitoring the evaluation/switching stage and the auxiliary pressure-source associated with the propulsion control system.

A test device, which is suitable for the purpose of functionally testing the evaluation circuit of the propulsion control system, can be provided, based on a function generator and a comparator, this test device being capable of activation, for example, by switching nn the ignition, and automatically effecting the above mentioned check procedure within a limited test timeinterval.

This test device is a functional part of a safety circuit, which checks the functional serviceability of the propulsion control system not only as the vehicle is started up, but also monitors the functional reliability of this system while the vehicle is being driven. Electronic circuit-units are additionally provided for this purpose, within the scope of the safety device.

A sub-unit of the safety circuit is characterised, by its function, it being possible to construct this sub-unit, in a simple manner, this sub-unit switching off the propulsion control system in the event of the simultaneous occurrence of a signal indicating an operating phase of the propulsion control system which is inconsistent with an operating state of the vehicle (e.g. idling) which has been brought about the driver, in which case the propulsion control system is operating in a faulty manner.

It is arranged, by means of a further sub-unit of the safety circuit, that a reduction in the output torque of the drive unit of the vehicle can be triggered only if, during an active phase of the propulsion control system, at least one of the brakes of the driven vehicle-wheels is activated.

A third sub-unit of the PCS safety circuit can be incorporated in the system, this sub-unit generating a faulty-operation signal, which causes the auxiliary pressure-source to be shut off, if the brake pressure rises at one or more of the wheel brakes of the driven vehicle-wheels, although the brake mechanism is neither being operated, nor has the propulsion control system been activated. An operating fault of this type can occur, for example, as the result of leaks in the hydraulic system of the propulsion control system. It is accordingly advantageous if the possibiiity for controlling the brake-pressure regulating valves, in the direction of a pressurereduction, is incorporated within the scope of the safety device.

By time-monitoring of the control signals output by the propulsion control system, and of signals which characterise a critical state of motion, especially of the driven vehicle-wheels, switching-off of the propulsion control system is triggered if these signals are present for longer than a comparison time-interval t which is compatible with the secondary physical conditions, as a result of which additional safety is achieved, this time-monitoring being implemented, in a simple manner.

The propulsion control system may be designed in such a way that a tuning of the switching-off of the propulsion control system is obtained, which is advantageous for safety reasons, for the case of faulty operation of the propulsion control system and/or of activation of the anti-block system, while ensuring that the propulsion control system cannot become effective in an impermissible manner.

Finally, a design for the actuator may be adopted, which effects the reduction of the output torque of the drive unit and prevents this control action, applied to the drive unit, from causing an excessive decleration of the vehicle, which is incompatible with the driving situation at that particular moment.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a block circuit diagram of a propulsion control system which is combined, according to the invention with an anti-block system, this representation being considerably simplified, Figure 2 shows details of the construction of the electronic control units provided for generating the signals for controlling the brakepressure regulating valves of the anti-block device, and of the propulsion control device, and Figure 3 shows details of a function-monitoring and safety circuit which is provided within the scope of the propulsion control device according to Figures 1 and 2.

Readers are explicitly advised to refer to the details of Figure 1, which shows, with reference to the application-example of a motor vehicle with rear-wheel drive, a propulsion control system 10 which is both constructionally and functionally combined, according to the invention, with a fourchannel anti-block system provided on the vehicle, the components which are provided for the anti-block system, marked in its entirety, 11, being concurrently utilised to the greatest possible extent in the implementation of this propulsion control system, in order to achieve as simple a construction of the overall installation as possible.

In this design, the propulsion control system 10 is matched to the anti-block system 1 which can be assumed to be a known system, in such a manner that it can be produced, so to say, as an accessory system.

The anti-block system 11 includes the wheel speed-sensors 1 7 and 18, which are assigned, in each case, to one of the undriven front wheels 1 2 and 1 3 of the vehicle, and the wheel speedsensors 19 and 21, which are assigned to the driven rear wheels 14 and 16, these sensors generating electrical output signals in the form of pulses, the frequency of which is proportional to the respective speeds of rotation of the front wheels 12 and 1 3, and of the rear wheels 14 and 1 6. An electronic control unit, provided for the anti-block system 11 and marked, in its entirety, 22, processes the output signals from the wheel speed-sensors 17, 18, 19 and 21 to produce electrical control output-signais, which enable brake-pressure regulating valves 23, 24, 26 and 27 to be directed, for the purpose of providing anti-block control, into a normal (flow) positipn, a shut-off position, or a reverse-flow position, corresponding to the pressure build-up phase, the pressure-holding phase, or the pressure-reduction phase in the wheel brakes 28,29, 31 and 32.

Furthermore, the electronic control unit 22 generates an output signal for activating the return pump 33 of the anti-block system 11, which conveys the brake fluid which flows out of the wheel brake-cylinders during the pressure reduction phases back into the brake lines 34 and 36 of the front-axle and rear-axle brake circuits.

An ABS safety circuit 37 is provided for monitoring the operation of the anti-block system 11, this safety circuit generating, in the event of faulty operation of the electronic control unit 22, and/or of other monitored components, a signal, at its output 38, which triggers the switching-off of the anti-block system 11 and activates a warning indicator,'39.

The propulsion control system 10, which is intended to bring about optimum transmission, to the road surface of the output torque which is delivered by the drive unit of the vehicle, and to provide additional driving safety, operates according to the following principle: As soon as one of the driven wheels, 14 or 16, tends to spin, its wheel brake, 31 or 32, is activated. If both the driven wheels 14 and 1 6 are tending to spin, a torque reducing control action is applied to the drive unit, in addition to activating the wheel brakes 31 and 32, for example, in the case of an engine employing a carburettor, by the electrically-controlled adjustment of the throttle valve ("E-Gas").Furthermore, it should be assumed that the propulsion control system 10 triggers the application, to the drive unit, of the torque-reducing control action, even when only one of the driven wheel, 14 or 16, is tending to spin, whenever defined threshold values for the vehicle velocity, and for the longitudinal and/or transverse accelerations affecting the vehicle, are exceeded.

In the propulsion control system 10, the brakepressure regulating valves 26 and 27 of the antiblock system 11 are utilised for appropriately regulating the brake pressure in the rear-wheel brakes 31 and 32.

The control signals required, for the purpose of the propulsion control, for controlling the brakepressure regulating valves 26 and 27 in a manner appropriate to the driving situation, are generated by a PCS electronic control unit, marked, in its entirety, 40, which likewise generates these control signals by suitably processing, in a manner to be explained in more detail with the aid of Figure 2, the output signals from the wheel speed-sensors 17,18, 19 and 21 which are proportional to the rotation speeds. During the active phases of the propulsion control system 10, the supply of brake pressure to the wheel brakes 31 and 32 is tapped from an auxiliary pressure-source which is marked in its entirety, 41.A pressure-source available on the vehicle, for example for a servo installation, is expediently utilised as an auxiliary pressure-source 41, it being possible to couple its output pressure, via a switching-valve arrangement 42, which can be triggered by the PCS electronic control unit, into a pressure intensifier 43, which is coupled, on the secondary side, onto the brake line 34 of the rearaxle brake circuit, this pressure intensifier being provided in order to match the pressure-level to the value required for the propulsion control.The pressure intensifier 43 possesses a floating piston 44, the piston-stage 46 of this piston, on the secondary side, forming the boundary of an inletpressure chamber 47, which is connected so that it communicates with that outlet-pressure space of the brake master cylinder which is assigned to the rear-axle brake circuit, this inlet-pressure space 47 also communicating with the outletpressure space 51 of the pressure intensifier 43, via a central valve 49, which is open in the normal position of the pressure-intensifier piston 44, as represented, but which is otherwise closed. As a result of this design of the pressure intensifier 43, the auxiliary pressure-source 41 is also hydraulically de-coupled from the brake master cylinder 48, this decoupling being necessary for the independent operation of the propulsion control system 10 and the anti-block system.

In the text which follows, the construction of the electronic control units 22 and 40 of the antiblock system 11, and of the propulsion control system 10, as well as of the safety circuits 37 and 52, which are provided for monitoring the operation of the overall installation 1 0, 11, will be discussed in detail, in association with Figures 2 and 3, the reader being expressly advised to refer to the details contained in these Figures, the above mentioned safety circuits causing the antiblock system 11 and/or the propulsion control system 10 to be switched off in the event of an operating fault.

The electronic control units 22 and 40, belonging to the anti-block system 11 and the propulsion control system 10, possess a common signal input and signal processing stage 53 to which the signals output by the speed-sensors are fed as input signals. From these signals, the signal input stage generates a total of eight output signals, which characterise, in each case, the peripheral velocity and the peripheral acceleration of one of the vehicle wheels 12,13, 14 and 16.

The system of reference-symbols, which follows, has been assumed in the indexing of these output signals, as indicated in the drawing, and in indexing the additional signals derived from these output signals: F=front, B=rear, L=left, R=right and V=vehicle.

The signals output by the signal processing stage 53 are fed into the combination, which can be seen in Figure 2, of, in each case, one evaluation stage 54 and 56 of the ABS electronic control unit 22 or, as the case may be, of the PCS electronic control unit 40, the reader being expressly referred to the relevant details in Figure 2. From these signals, the evaluation stage 54 of the ABS electronic control unit 22 generates A output signals which characterise the slip of the vehicle wheels 12,13, 14 and 16, these signals being compared, together with the acceleration signals, with threshold values (i 2 i3 +b and -b), in a comparator-stage 57, which is seriesconnected thereafter.The output logic-signals produced, as functions of the threshold values, by the ABS comparator-stage 57 are processed in a combining unit, series-connected after this comparator-stage, to produce control signals suitabis for controlling the brake-pressure regulating valves 23, 24, 26, and 27 in a manner appropriate to the anti-block control.

Within the scope of the electronic control unit 40 of the propulsion control system 1 0, the comparator-stage 59 is also connected after the evaluation stage 56, this comparator-stage generating, from a comparison of the received input signals with suitable threshold values, output logic-signals which characterise the instantaneous driving situation, the PCS logicstage 61, which is series-connected after the PCS comparator-stage 59, suitably combining these signals and using the results, thus obtained, to generate the signals which are required, for the purpose of the controlling function which has previously been explained, for controlling the brake-pressure regulating valve 26 and 27 of the driven rear wheels 14 and 16, for activating the auxiliary pressure-source 41, for activating the return pump 33, and for actuating the control element for reducing the output torque of the vehicle drive unit.

There follows a more detailed discussion, with reference to Figure 3, of the basic construction of the safety circuit 52, which is provided within the scope of the propulsion control system 10.

At a first input 62, this safety circuit receives those signals output by the PCS logic-stage 61, which are used to direct the brake-pressure regulating valve 26, which is assigned to the lefthand rear-wheel brake, into its pressure-holding position, or into its pressure- reduction position, while it receives, at its second input 63, the corresponding control signals for the brakepressure regulating valve 27. The output signal from an acceierator-pedai position-transmitter, which is a high-level signal when the accelerator pedal is in the idling position, is present at the third input 64. The control signal output by the PCS logic-state 61 is received at a fourth input 66, this signal triggering the torque-reducing control action which is applied to the drive unit.

At a fifth input 67, the safety circuit 52 receives a high-level input signal when the brake-light switch is closed, that is to say, when the driver operates his brake pedal. The slip-threshold signals output by the PCS comparator-stage 59 are fed to a sixth input 68, and the acceleration threshold signals output by this comparator-stage are fed to a seventh input 69.

An OR logic-element 72 is provided, within the scope of a first sub-unit 71 of the safety circuit 52, this logic-element receiving the control signals for the brake-pressure regulating valves which are received at the first input 62 and at the second input 63. The sub-unit 71 further includes a dual-input AND element 73, with a non-negated input 74, and a negated input 76. This negated input is connected to the third input 64 of the safety circuit 52, to which input the accelerator pedal position signal is fed. The sub-unit 71 monitors the fault-condition, according to which the propulsion control system must not operate when the accelerator pedal is in the idling position.

The accelerator pedal position-signal is fed, via a time-delay element 100, to the negated input 76 of the AND element 73, this time-delay element holding back the high-level signal output by the accelerator pedal position-sensor for a time-interval St, the length of this interval being chosen such that the propulsion control system is not switched off whenever the driver briefly lifts his foot from the accelerator pedal.

If a high-level output signal is provided at the output 77 of the AND element 73, a fault is present, and the propulsion control system is switched off.

A second sub-unit 78 of the safety circuit 52 contains a dual-input AND element 79, the output signal from the OR element 72 of the first subunit 71 being fed, after negation by means of an inverter 82, to the first input 81 of this element 79, which receives, at its second input 83, the input signal which was fed to the fourth input 66, this signal being capable of triggering the torquereducing control action which is applied to the drive unit.

This second sub-unit 78 monitors the condition, according to which a control action may be applied to the drive unit only when, at the same time, at least one of the wheel brakes, 31, or 32, is triggered. A third sub-unit 84 of the safety circuit 52 includes a triple-input AND element 85, which possesses two non-inverting inputs 86 and 87, and one inverting input 88. The inverted output signal from the OR logic-element 72 of the first sub-unit 71 is present at the first, non-inverting input 86 of this AND element 84.

The output signal from a dual-input OR element 89 is fed to the second, non-inverting, input 87, the inputs of this element 89 being connected to the inputs 68 and 69 of the safety circuit 52, to which the wheel-deceleration signals and the slipsignals are fed from the PCS comparator-stage 59. The brake-light signal is fed to the inverting input 88 of the AND element 84. This third subunit 84 monitors the condition according to which the propulsion control system 10 may not operate when the brake mechanism is activated. A highlevel output signal from the AND element 84 indicates that a fault relating to this condition is present, and triggers the switching-off of the propulsion control system 1 0.

A time-comparator element 98 is connected to the output 97 of the triple input AND element 85, this element 98 comparing the duration of the output signal from the AND element 85 with a comparison time-interval, st, of approximately one to two seconds. If the output signal from the AND element is present for longer than the comparison time-interval, the time-element 98 outputs a control signal which triggers the reduction of the braking pressure in the wheel brakes 31 and 32 of the driven vehicle wheels 14 and 1 6.

The signals for triggering the brake-pressure regulating valves 26 and 27, and the slip-signals and acceleration or deceleration signals, which characterise the state of motion of the driven vehicle wheels 14 and 16, arriving from the PCS comparator-stage 59 and received at the inputs 62, 63 and 68 and 69 of the safety circuit 52, is compared, in each case, by means of a timeelement 92, with a time-interval At of, for example, one second, which corresponds to a value, based on experience, for the maximum signal duration which occurs when the propulsion control system is operating correctly. If the signal duration is longer, a fault is present, and an output signal is generated which effects the switchingoff of the propulsion control system.

A monitoring relay 95 can be triggered by the fault-indication signals which are output via the common output 93 of the safety circuit 52, this relay possessing a break-contact 94, which is located in the exciting circuit of a valve-relay 96, which can, in its turn, be excited by an output signal from the PCS electronic control unit 40, which is present during the active phases of the propulsion control system. During the active phase of the propulsion control system, the battery voltage is applied as a control voltage, to the exciting windings of the switching-valve arrangement 42, via the operating contact 97 of this valve-relay, this contact being closed when the relay is in the excited state.

When a fault-signal is present at the output 93 of the safety circuit 52, the auxiliary pressuresource 41 is shut off with respect to the pressure intensifier 53.

Finally, care is taken to ensure, by means of an OR combination 97 of the fault signals output by the ABS safety circuit 37 and the PCS safety circuit 52 that both the anti-block system 11 and the propulsion control system 10 are switched off in the event of faulty operation of the anti-block system 11, while only the propulsion control system 10 is switched off in the event of its developing a fault.

Claims

1. Propulsion control system for a vehicle which is also equipped with an anti-block system (ABS), this control system comprising the following components: a) for each wheel, a speed sensor, generating an electrical output signal which is proportional to the rotational speed of the wheel or to its peripheral velocity, b) for each wheel, a brake-pressure regulating valve, which can be controlled electrically to a flow position, a closed position, and a reverseflow position, c) an electronic control unit which generates output logic-signals from wheel slip signals and wheel acceleration and deceleration signals which are being received by the speed-sensors, and from the comparison of these signals with preset threshold values and which generates, from a combination operation on these logicsignals, the pressure build-up pressure-holding and pressure-release signals required for appropriately controlling the brake-pressure regulating valves, d) a safety circuit which monitors the operational readiness of the anti-block system and which switches off this system in the event of faulty operation, thereby resetting the brakepressure regulating valves to their normal position, which is appropriate for building-up the pressure, the propulsion control system furthermore activating the wheel-brake of any drive-wheel which is tending to spin, additionally switching a torque-reducing command through to the drive unit, wherein A) the electronic control unit of the anti-block system includes a signal input stage, which generates velocity output signals and acceleration output signals which characterise the state of motion of the vehicle wheels, these signals being processed in a comparison/combination-stage to produce the control signals for the brake-pressure regulating valves, this comparison/combinationstage being series-connected after the input stage, B) an evaluation/switching-stage is provided, within the scope of the propulsion control system, series-connected after the signal input stage of the ABS, this evaluation/switching stage processing the velocity signals and acceleration or deceleration signals which have been received, for the slip of the driven vehicle wheels, and generating, from the results, characteristic slipvalue signals, and generating, from the comparison of these signals, as well as of the velocity signals and acceleration or deceleration signals which continue to be received, with threshold values, output logic-signals which characterise the state of motion of the driven vehicle-wheels, and of the vehicle as a whole, and generating, from a combination operation on these output signals, the control signals which are required for controlling the brake-pressure regulating valves or the actuator for the torquereduction, in a manner appropriate to the driving situation, C) an auxiliary pressure-source is provided, which effects the supply of pressure to the particular wheel-brake, or brakes, which is, or are, activated during the active phases of the propulsion control system, D) a safety circuit is provided, which monitors the operation of the propulsion control system and, in the event of its operation becoming faulty, switches off its auxiliary pressure-source and its evaluation/switching-stage, and triggers a warning signal, and/or an indicator signal.

2. A propulsion control system according to Claim 1, a brake line of the brake circuit of the driven vehicle-wheels is connected to the outletpressure chamber of a pressure intensifier which is fitted with a floating piston, it being possible to admit, under the control of a valve, the pressure of a pressure-source, which is available on the vehicle, to the primary-side piston-stage of this floating piston, while the secondaryside pistonstage of this floating piston forms the boundary of an inlet-pressure chamber, which communicates with that outlet pressure chamber of the master brake cylinder of the brake system which is assigned to the brake circuit of the driven vehicle wheels, this inlet-pressure chamber communicating with the outlet-pressure chamber of the pressure intensifier-via a central valve, which is open when the pressure-intensifier piston is in the normal position, but is otherwise closed.

3. A system according to Claim 1 or Claim 2, wherein a switching member for switching off the propulsion control system is activated by means of a faulty-operation indicator signal from the safety circuit of the anti-block system.

4. A system according to any one of the preceding Claims, wherein the safety circuit of the propulsion control system includes a test device, which contains a function-generator which can be activated, for example, by switching on the ignition, and which presents, within a defined test time-interval, a set of velocity input signals and acceleration or deceleration input signal to the evaluation circuit, in a defined chronological sequence, the processing of these signals enabling a series of pulses, corresponding to a prescribed signal pattern and representing the possible control system output signals, to be derived and in that a comparator is provided, which generates an operating-fault indicator signal in the event of this series of pulses deviating from the prescribed signal pattern.

5. A system according to any one of the preceding Claims, wherein a first sub-unit of the safety circuit of the propulsion control system generates an output signal, which effects the switching-off of the latter system, if a signal from the evaluation circuit or from the safety circuit, which is characteristic of an active phase of the propulsion control system, is present concurrently with a signal from an accelerator pedal positiontransmitter which indicates that the accelerator pedal is in the idling position.

6. A propulsion control system according to Claim 5, wherein the accelerator pedal positiontransmitter generates a high-level output signal when the accelerator pedal is in the idling position and, at all other time, generates a low-ievel output signal, and in that the sub-unit comprises an OR logic element, which receives, as input signals, the control signals for the brake-pressure regulating valves of the driven vehicle-wheels, and a dual-input AND element is provided, which has one negated input and one non-negated input, and which receives the output signal from the OR element at its non-negated input, and the output signal from the accelerator pedal positiontransmitter at its negated input.

7. A system according to any one of the preceding Claims, wherein a second sub-unit of the propulsion control system safety circuit is provided, this second sub-unit generating an output signal which brings about the switchingoff of the propulsion control system when a signal is present, on the one hand, which indicates that a reduction in the output torque of the drive unit should be triggered, and when, on the other hand, a signal is present, which indicates that neither of the two wheel-brakes of the driven vehiclewheels is activated.

8. A system according to Claim 7, when dependent on Claim 6, wherein the second subunit of the propulsion control system safety circuit possesses a dual-input AND logic element, which receives the inverted output signal from the OR element of the first sub-unit the safety circuit at its first input, and which receives, at its second input, the high-level signal which is characteristic for triggering the reduction in the torque of the drive unit.

9. A system according to any one of the preceding Claims, characterised in that a third sub-unit of the safety circuit is provided, this third sub-unit generating a faulty-operation output signal when characteristic slip-value signals or acceleration or deceleration signals are present for a peripheral deceleration of at least one of the driven vehicle-wheels outside a phase during which the propulsion control system is active and while the brake mechanism is not being operated.

10. A system according to Claim 9, when dependent on Claim 8, wherein the third sub-unit of the safety circuit possesses a triple-input AND element, which has two non-inverting inputs and one inverting input, and which receives the inverted output signal from the OR logic element of the first sub-unit of the safety circuit at its first, non-inverting-input, and the output signal from a dual-input OR element at its second non-inverting input, the wheel-deceleration signals being fed to one input of this dual-input OR element and the slip signals from the comparator-stage of the evaluation-circuit being fed to its other input.

11. A system according to Claim 10, wherein a time-comparison element is connected to the output of the triple-input AND element, this timecomparison element generating a signal which triggers the reduction of the pressure in the wheel brakes of the driven vehicle-wheels when the output signal from the triple-input AND element persists for longer than a defined comparison time-interval.

12. A system according to any one of the preceding Claims, wherein the slip-signals and the acceleration or deceleration signals from the comparator-stage of the evaluation-circuit, which characterise the state of motion of the driven vehicle-wheels, and, preferably, also the output signals from this evaluation-circuit, which direct the brake-pressure regulating valves into their shut-off (pressure-holding) position or into their return (pressure-reduction) position, as the case may be, are fed to time-comparison elements, which generate an output signal which effects the switching-off of the propulsion control system if the above mentioned signals persist for longer than a defined time-interval of, for example, one second.

13. A system according to any one of the preceding Claims, wherein the electrical triggering of a control valve assembly which brings about the coupling of the auxiliary pressure-source to the brake circuit of the driven vehicle-wheels, is effected by means of a valverelay, which is excited in an active phase of the propulsion control system, the exciting circuit of this valve relay running by means of a brake-contact of a monitoring relay which can be excited by faulty-operation output signals from the safety circuits of the propulsion control system and the anti-biocking system, as well as by a functional output signal from the anti-block system, and by a signal which is triggered in the event of the brake mechanism being activated, for example by means of a brake-light switch stop.

1 4. A system according to any one of the preceding Claims, wherein a control element which is provided, within the scope of the propulsion control system, for reducing the output torque of the drive unit, commands an incremental change in the output tbrque which, in each case, corresponds only to a predetermined fraction of the maximum operating travel of the accelerator pedal.

1 5. A propulsion control system for a vehicle substantiaily as hereinbefore described with reference to the accompanying drawings.