GB2262491A

GB2262491A - Regulating operation of a vehicle power-assisted steering system.

Info

Publication number: GB2262491A
Application number: GB9226440A
Authority: GB
Inventors: Walter Schlagmueller; Siegfried Schustek; Peter Ahner; Herbert Labitzke; Willi Steffens; Wolfgang Wagner; Eberhard Weiss; Peter Kleindieck
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-12-21
Filing date: 1992-12-18
Publication date: 1993-06-23
Also published as: GB9226440D0; DE4142580A1; JPH05238411A

Description

2262491 METHOD AND MEANS FOR REGULATING OPERATION OF A VEHICLE

POWER-ASSISTED STEERING SYSTEM The present invention relates to a method and means for regulating a vehicle power-assisted steering system.

A power-assisted steering system for a motor vehicle, in particular for the parking speed range, is described in DE-OS 39 33 5 771.

In this case, a step-down gear is provided between a servomotor and 'the steering column or the further drive components for tile T mechanical displacement of the wheel. in that case, at least one clutch cheek is so arranged that a driving connection from the servornotor drive to the steering gear side of the steering column is p oduced,,ihen an entraining member connected with the steering wheel side of the steering column produces, on manual introduction of torque alt- the steering wheel, the required clutch contact pressure through mechanical action on the clutch cheek. Gearwheels influenced by the clutch are hollow and are mounted on a clutch hub connected secure against relative rotation with the drive steering column region. A servomotor, which is electric and operates in merely one direction of rotation, drives two gearwheels rotating in opposite sense. The clutch then produces a driving connection from the servomotor to the steering col,,-inn or the drive output in dependence on the steering torque.

A further refinement of such a power-assisted steering is described in German patent application P 4-1 04 048.1.

There is scope for optimisation of power-assisted steering systems of the afore-described type in respect of power take-up, steering ease, operational reliability and/or noise production.

According to a first aspect of the present invention there is provided a method of regulating operation of a vehicle power-assisted steering system which comprises an electric servomotor, transmission means to transmit drive from the servomotor to steering means of the vehicle, clutch means to produce a drive coupling between the transmission means and the steering means, and actuating means connected to the steering means and responsive to torque manually applied to -the steering means to actuate the clutch means for production of said coupling, the method comprising the steps of selecting the rotational speed of the servomotor in dependence on at least one of vehicle travel speed, vehicle steering torque, engaged gear of the vehicle transmission, operating state of the vehicle engine and operating state of the power-assisted steering system.

In such a steering system, for prg!ference the transmission means comprises a gear between the servomotor and either the steering column or the drive output leading to the wheel displacement. At least one coupling cheek is provided, which produces a driving connection from the servomotor drive to the steering gear side of the vehicle steering column when an entraining member connected with the steering wheel side of the steering column on manual introduction of torque at the steering wheel produces the required clutch contact pressure through 25 mechanical action on the clutch cheek.

The 1 ower in g 0 '1 the rotational speed of the serv ornotor i n operating ranges in which only a reduced enhancement is needed, for example in the case of a vehicle rolling at low speed. relieves the onboard mains by way of reduced idling current take-up and reduces the wear, the fuel consumption and the noise production and also improves road contact at, higher travel speeds. For this purpose, it can be provided to lower or raise the roLational speed of the servomotor with increasing or reducing vehicle speed continuously according to a Predetermined characteristic curve. Such a continuous lowering does not impair the steering feel, but requires additional measures in the control arrangements.

An advantageous refinement of the method provides for lowering or raising of the rotational speed of the servomotor in steps with increasing or reducing vehicle speed in dependence on at least one threshold interrogation of the vehicle speed.

Moreover, it can be provided to lower or raise the rotational speed of the servomotor with reducing or increasing steering torque continuously according to a predetermined characteristic or to lower tational speed of the servomotor in steps,,iith reducing or raise the rol or increasing steering torque in dependence on at least one threshold interrogation of the steering torque. Whilst the continuous adaptation of the rotational speed to the steering torque may mean increased effort in the structuring of the control arrangement, switching- over by way of a relay (in addition to a main relay for the voltage supply) can be realised at more favourable costs. In the range of high steering torque, however, this switching-over can produce an unacceptable snatch in the steering train, which disturbs the road contact. If the speed change is undertaken in a steering torque range near the zero transition of the torque, steering feel is not impaired. It is thus to be taken into consideration, in those variants in which the rotational speed of the servomotor is raised or lowered in steps, that the changes are preferably undertaken in a steering torque range near the zero transition of the torque.

The change in the rotational speeds of the servomotor in dependence on vehicle speed thresholds requires travel speed recognition and corresponding signal processing. It is particularly suitable for vehicles with a higher steering force level, where enhancement is desired in the middle travel speed range. In the case of vehicles with an electronic speedometer or a brake anti-locking system (ABS), a vehicle speed sensor is normally present and can be used.

Preferably, the threshold values for the changes in the rotational speeds of the servomotor are selected in dependence on whether the travel speed and/or the steering torque increases or decreases (hysteresis-like change). Consequently, the number of changes is reduced.

In a further refinement, a lower rotational speed of the servomotor is changed over to when a selectable steering torque threshold value is fallen below after a selectable first travel speed threshold value is exceeded. A higher rotational speed of the servomotor can be changed over to when a selectable steering torque threshold value is fallen below after a selectable second travel speed threshold value has been fallen below.

According to a second aspect of the present invention there is provided regulating means comprising at least one power transistor arranged in a current feed for the servomotor and switching means arranged in a path parallel to the output path of the at least one transistor, the loss power of the switching means being less than that of the transistor or transistors.

For preference, the transmission means is provided between the servomotor and either the steering column or the drive output leading to the wheel displacement and the clutch means comprises at least one coupling cheek which produces a driving connection from the servomotor drive to the steering gear side of 'the steering column when an entraining member connected with the steering wheel side of the steering column produces, on manual introduction of -torque at the steering,.jhee 1, the required clutch contact pressure through mechanical action on the clutch cheek.

For preference, the regulating means comprises at least one power transistor arranged in a current feed for the servomotor and switching means arranged in a path parallel to the output path of the at least one transistor, the loss power of 'the Switching means being less than that of the transistor or transistors.

Examples of the method and embodiments of the regulating means of the present invention will now be more particularly described with reference to accompanying drawings, in which:

Fig. 1 is a circuit diagram of first regulating means embodying the invention; Fig. 2a Fig. 4 Fig. la is a circuit diagram regulating means of Fig.

Fig. 2 is a circuit diagram embodying the invention; is a circuit diagram of a modified part of the regulating means of Fig. 2; Fig. 3 is an end view of part of a power-assisted steering system regulable by the regulating means of Figs. 1, la, 2 or 2a; and is a sectional elevation of the part of the steering system shown in Fig. 3.

Referring now to the drawings, the principle of a power-assisted steering system, such as that disclosed in DE-OS 39 33 771, is that of actuating different coupling cheeks, according to direction of rotation, by an entraining member arranged at a vehicle steering column on the portion thereof affected by torque introduced by the vehicle driver. The coupling cheeks are mounted, secure against relative rotation, on that part of the steering column which can be regarded as drive output shaft and entrain the steering column leading on to the steering gear by frictional engagement. At the instant of torque introduction by the driver at the steering column, both directions of rotation are available for the steering column through oppositely running gearwheels of a gearwheel pair, which are driven in common by an electric servomotor, and it is determined by the entraining member which direction of rotation is chosen for the auxiliary force introduction. The entraining member can, for example, of a modified part of the of second regulating means be arranged at the end of a torsion rod or a f ixed part of a steering part-column fron the steering wheel. it serves for the selective pressing of the coupling cheeks according to the torque introduction from the driver.

In the steering system illustrated in Figs. 3 and 4, the steering column is denoted by 10. The arrow A indicates the direction to the steering wheel and the arrow A' the direction to the steering box or rack. The steering column forms a torsion rod 10a in an intermediate range, in particular through a thinning of the material of given strengths, so that a smaller diameter D' of the steering column by comparison with the normal diameter D results in -the region of the torsion rod 10a.

A sleeve 12 extends closely to a bearing flange 13, which is connected secure against relative rotation with the part of the steering column leading on to the steering box or rack and is mounted on this. The sleeve is fastened, preferably welded, to the column 10 in the region of the beginning of the torsion rod, thus at An entraining member 14 is mounted on 'the column to be rotatable through a predetermined angle. The member is disposed at the lefthand end of the sleeve 12 and fastened -1-hereto, for example by way of a welded connection shown at 15 The entraining member 14 can be in the form of a rod fastened in cantilever manner to the steering column or, as illustrated, in the form of a ring 14a, which surrounds the steering column 10 and from which an L-shaped web-like projection 14b extends. The projection 14b passes through an opening in the bearing flange 13 and penetrates into the flange. It will be recognised that the entraining member proejction 14b can therefore execute a slight rotation relative to the flange 13, this rotation being in the direction of the double arrow B in Fig. 3, due to a torque introduction from the steering wheel side.

The bearing flange 13 at its outer circumference carries two mutually independent, externally toothed hollow gearwheels Z3 and Z4, which are rotatable on the flange. In that case, the flange 13 at its outer circumf erence has passages 13a (Fig. 3), through which respective coupling cheeks 15a and 15b, which are axially offset relative to each other, can come to bear against the inner circumference of the gearwheels Z3 and Z4, respectively. The coupling cheeks 15a and 15b are mounted to be rotatable at, respectively, points 16a and 16b in suitable manner at the opposite wall regions of the flange 13 and each comprise a respective clutch shoe 16 and a respective lug-like prolongation 22. They bear by way of the clutch shoe against the inner circumference of the respectively associated gearwheel Z3 or Z4, whilst the prolongation 22 is operatively coupled to the entraining member 14, or more exactly to the projection 14b thereof, so that, according to the relative rotation of the projection 14b, either the clutch shoe 16 of the clutch cheek 15a of the shoes 16 of the cheek 15b is urged against the inner circumference of the 9 - associated gearwheel Z3 or Z4 on application of torque by the driver to the steering wheel. The gearwheels Z3 and Z4 are held in a suitable retaining device of the flange 13, yet arranged to be rotatable by this relative to each other.

The driving of the gearwheels is by way of a pinion '17 connected with the output shaft of an electrical servomotor (not shown). The motor can be operated, in the manner explained further below, so that a direction of rotation of the output shaft results in accordance with, for example, the arrow C. This direction of rotation applies for both directions of movement of the steering wheel and need not be ordered. the pinion '17 meshes with the first gearwheel Z1, which in turn meshes with the second, equal diameter, gearwheel Z2. The gearwheels Z1 and Z2 are mounted in suitable manner within an appropriate stationary housing which completely encloses the auxiliary steering unit as far as is possible, and are connected with further gearwheels Z1' and ZP, by way of -oIree,, iheels 19 of suitable construction, in prolongation of shafts 18 carrying them. A possible form of construction of such a freewheel is illustrated in the small drawing at the top right of Fig. 9. The freewheels can be arranged in usual manner and comprise a clamping body 191 (Fig. 4a), for example in the form of a ball, which is entrained into the clamping position by way of an incline on the larger 9 e arjjh e e 1 Z1 or Z2 be -1 n 9 dr v en, wh er e by the rotational entrainment of the small gearwheels Z1' and Z2' then takes place. These are arranged, axially displaced from the large gearwheels Z1 and Z2 and also at a given angle from each other (of Fig. 3), on the same shaft. In their turn, they mesh axially with the external toothing of the gearwheels Z11 and Z4.

Thus, when the servomotor is driven, all mentioned gearwheels rotate, driven from the pinion 17. The pinion rotates the gearwheels Z1 and Z2, the gearwheel Z1 being driven directly from the pinion and in turn driving the sister gearwheel Z2. The gearwheels Z1' and Z2' are then driven by way of the freewheels, which block on introduction of torque by the servomotor, and in their turn drive the gearwheels Z3 and Z4 in opposite sense. These gearwheels can be retained at the outer circumference of the flange 13 by way of retaining rings 19a or 19b, which are secured by screws to the flange 13, or in other suitable manner.

The following function then results. As soon as, due to deflection of the steering deflection, a corresponding twisting of the steering column occurs at the torsion rod 10a with simultaneously effected driving, which is explained further below, of the servomotor, is the coupling cheek appropriate to the direction of the steering wheel deflection is laid by its clutch shoe 16 by way of the entraining member projection 14b against the internal circumference either of the gearwheel Z3 or of the gearwheel Z4, so that, in addition to the introduced steering torque, a corresponding additional auxiliary servo-torque, which ultimately derives from the frictional engagement, results as steering assistance. This is enhanced by the corresponding gearwheel Z3 or Z4 being urged against the flange 13, namely against its outer periphery, by the reaction force on the application of the respective clutch cheek. It can be advantageous to structure the clutch cheeks so that they have a shape, as illustrated in Fig. 3, whereby a lever arm action results about the respective fulcrum 16a or 16b of the clamping cheek 15a or 15b. By virtue of the frictional inoi, nent brought about by the entraining member projection 14b, this leads to a self-amplification of tile bearing contact, as is recognisable from Fig. 3, similarly to the brake cheek self- amplification in the case of shoe brakes, since an entraining force is exerted in tangential direction on the shoe 16 through the frictional connection with the inner surface of the respective gearwheel Z3 or Z4. This entraining force can be resolved into a force acting directly or, the fulcrum 16a or 16b and a force which endeavours to urge the clutch shoe still more firmly against the inward wall of the respective gearwheel.

For resetting of the respective clutch cheek or to prevent the cheek, which is not acted on by the entraining member projection, from moving into frictional position relative to its associated gearwheel, is each clutch cheek can have a biassing leaf spring 20, which bears against a suitable inner projection 21 of the flange 13 and urges the shoe 16 away froni the associated gearwheel. It is desirable to aim at the greatest possible freedom from play of the movable parts for a satisfactory function. Thus, it can be worthy of recommendation for the entraining effect on the clutch cheeks to be adjustable by means of an eccentric pin (not illustrated), whereby the play in the system can be reduced to a necessary minimum amount. in that case, merely the behaviour of the torsion rod 10a is effective for the transmission of the steering torque.

An embodiment of regulating means for such a power-assisted steering system is illustrated in Fig. 1. In this embodiment, a method exemplifying the invention is realised predominantly in digital f orm. For this purpose, the output signals of a travel speed transmitter 113 (signal Vf), the signal G of a gear recognition unit 125, the current I Mot, tapped off by way of a resistor 119, of an electrical servomotor (M) 112, and the temperature T of the motor, are fed to the control device 111. The detection of the temperature of the electrical motor 112 can be effected by way of appropriate thermocouples. The signal Vf (vehicle speed), the signal G (gear recognition), the motor current signal I mot, which represents steering torque, and the signal T representing the motor temperature are processed in a control device 111 according to one or more variants of the method. For this purpose, the input signals are compared with characteristic curves or threshold values filed in the device 111 and the comparison results are interlinked logically. Signals, which by way of a pump stage 114 and a transistor 115 control the rotational speed of the motor 112, are present at the output of the device 111. This control of the motor can be effected by for example, pulse width modulation. In addition the servomotor 112 is to be switched off by way of a switch 118 through an actuation of a relay 116 by way of a pump stage 117 and by way of a transistor 124. Voltage supply is effected by way of a line, denoted by the reference symbol W5, connected with the ignition switch.

13 - In the embodiment illustrated in analog form in Fig. 2, the regulation oF the rotational speed of the servomotor 212 initially takes place in dependence on the steering torque. According to the presetting of the travel speed, the setting of the motor voltage Um is for example, between 10% and 60%. The motor current, which is proportional to the steering torque, is measured by way of a resistor 219. If the loading of the motor 212 rises, the voltage at a sum adder 220 is raised linearly by way of a matching amplifier 211 and by components 2219 and 230 described below, which means that the motor rotational speed r ema i n d s constant until reaching i t S natural char ac ter is ti c. Thus, the motor voltage Um can, for example, be raised through 40%, for example by a pulse-width-modulated driving by way of a pulse-width modulation stage (PMM) 213 and a transistor 215.

A signal representing the resistive voltage drop U1 in the motor 212 is present at the output side of the amplifier 211. The actual value of tthe induced voltage Un, which is fed to the component 230, is ascertained by the component 229 from the resistive voltage drop UI in the motor 212 and the motor terminal voltage Um. The actual value of the induced voltage Un is then compared with the associated target value Uns in the component 230, whereupon its deviation deltaUn is conducted to the adder 220. In that case:

Um = URi-notor) + Un, wherein Un = 2pinphi, phi is a constant, pi = 3.141... i s the circle number, Rmotor is the resistance, n is the rotational speed of the motor, and I is the motor current. Beside the afore-described difference deltaUn, a minimum voltage value bias Umin (base voltage) and the output signal Uv of an integrating and matching stage 224 described below are present at the input of the adder 220.

The regulation of the rotational speed of the servomotor 212 in dependence on the vehicle travel speed Vf occurs by the motor voltage Um being set by way of a monostable trigger stage 221, an integrating and matching stage 224, the adder 220 and the pulse-width modulation stage 213. Thus, the motor voltage Um can amount to 50% of the nominal voltage Umax, for example, for the travel speed Vf being equal to 0 kilometres per hour, whilst the motor voltage Um for the maximum travel speed can be set to 0% of the maximum motor voltage Um, which means that the maximum servopower is delivered in conjunction with the current regulation on standstill of the vehicle, whereas, however at most only 50% of the servopower is delivered at the maximum speed Vmax. Thus, the maximum torque, which as a direct effect on switch-on snatch, is also limited to 50% on activation of the steering system at a speed threshold Vmax.

When a certain speed threshold is exceeded, a threshold value switch 225 switches on a transistor 226 and thus a relay 216. The motor 212 is then switched off. The power-assisted steering system remains passive until the speed again falls below the threshold value.

The regulation in dependence on the motor temperature occurs in such a manner that the motor temperature T is measured by, for example, a thermocouple. A matching stage 227 supplies a voltage U T which is proportional to the motor temperature T. Above a critical motor temperature, a voltage is deducted by way of an adder 228 from a signal which is present at the output of the adder 220, so that only a reduced voltage is delivered to the motor by the pulse-width modulation stage 213. The motor current is thus limited. The motor 212 thus need not be switched off suddenly, but can run on with 10 reduced power.

The electronic system illustrated in the Fig. 2 can be constructed sirply and at favourable costs, since its failure leads 7 on,y to loss of comfort, but the function of the steering and thus the safety of the entire steering system is not influenced.

is The and gear noises and the power withdrawn from the on- board mains are reduced greatly by the regulation of the rotational s:, 3eed of the motor to, for example, one half to one tenth of the idling rotational speed.

An audible lowering in rotational speed, dependent on the loading, can be avoided in a wide range.

In particular, switch-on snatch can be reduced by the lowering of the voltage in dependence on speed.

The servopower can be reduced continuously through the temperature dependent lowering of the motor voltage, for example in the case of an erroneous operation, so that the steering system always remains available, even though with lower power Particularly advantageous refinements of the regulating means are illustrated in Figs. la and 2a. In these refinements, switching means R15, r15 are arranged in a conduction path parallel to the transistor or 215. As described above, the rotational speed of the motor is selected by way of the drive of the transistor 115 or 215. The drive of the transistor is effected, in particular, by pulse-width-modulated signals.

The switching means R15, r15 can be constructed in such a manner as to have a lower loss power than the transistor 115 or 215. The switching means can be a semiconductor component (transistor, thyristor) or an electrically drivable mechanical switch (relay).

If, for example, the switching state of the transistor 115 or 215 is changed by pulse-width-modulated signals, then the switching means R15, r15 can be switched into conductive setting when the transistor 115 or 215 is loaded in such a manner as to be switched to be conductive over a selectable time duration. In particular, it can be provided to switch the switching means R15, r15 into conductive setting when the transistor 115 or 215 driven in pulse-width-modulated manner operates for a certain time in continuous signal operation.

In a further refinement, the switching means can be switched into a conductive setting when the conductivity of the transistor exceeds a selectable conductivity threshold over a selectable duration of time.

This refinement is of advantage particularly when the conductivity of the transistor is varied continuously, thus not in pulse-width modulated manner.

The switching means R15, r15 can be switched, for example, into conductive setting when the vehicle, in which the steering system is installed, moves at a very low speed or is at rest. During these operational states, the current of the motor 112 or 212 exceeds about 15 amps, since high counteracting torque is generated by the road surface and correspondingly high steering assistance is needed.

The switching of the switching means R15, r15, illustrated as a relay in each of Figs. la and 2a, occurs through the actuation of the transistor Tr by the control device 111 in the principally digital circuit of Fig. 1 or Fig. la. Through such an actuation of the transistor Tr, the relay R15, r15 is preferably switched into conductive setting for current intensities above about 15 amps. In the circuit realised predominantly in analog form shown in Fig. 2 or 2a, the motor current is tapped off at, the input side of the amplifier 211. The transistor T2 is then switched by processing of the motor current by the threshold value switch 231 in such a manner that the relay is switched into conductive setting. As described above, this occurs for current intensities above about 15 amps. It is advantageous in the circuit arrangements shown in Figs. la 20 and 2a that the power transistor '115 or 215, and optionally present smoothing capacitors, can be designed for smaller currents. This means 1 ower ov er a 11 si ze and co St. Moreover, there will be appreciable reduction in heat delivery i'or the operational states of high servo-assi stance, due to the relieving of the power transistors, and the electromagnetic radiation of the overall system may be less due to the smaller switched current. In particular, power transistors with higher forward resistances can be used due to the circuit arrangements shown in Figs. la and 2a. Such power transistors are, in general, distinguished by being purchasable at favourable cost. Since the voltage drop across the power transistor 115 or 215 is greater than the voltage drop across the switching means R15, r15, the motor voltage is higher due to the bridging-over of the transistor (motor power is proportional to Um 2).

Apart from the embodiments illustrated in the figures, further advantageous refinements are possible as outlined below.

It is advantageous to switch over to a lower rotational speed of the servomotor when the steering torque falls below a selectable threshold value after a selectable time delay following leaving of a lower gear, preferably first gear and/or reverse gear, of the vehicle transmission. A higher rotational speed of the servomotor can be switched over to when a selectable steering torque value is fallen below after engagement of a lower gear, again preferably the first gear and/or reverse gear. The switching-over in dependence on gear recognition is suitable for such vehicles which require high steering torque during steering at standstill, but only moderate torque already at low travel speeds. In order that the steering assistance is not reduced during back-and-forth movement involving frequent changes between first and reverse gears, a suitabletime delay (such as about 3 seconds) is preferably provided for the switching-over to the lower rotational speed.

A further refinement consists in switching over to a lower rotational speed of the servomotor when ca selectable first steering torque threshold value is fallen below and to a higher rotational speed when a selectable second steering torque threshold value is exceeded. A hysteresis is provided between both the steering torque thresholds. This variant can be of use for those vehicles in which assistance can be dispensed with in the case -of extremely rapid steering movement.

The following refinements of the system can also be provided for 1 taking nto consideration the operational state of the power-assisted steering, in particular of the temperatures in and/or at the steering unit and/or in and/or at the control device of the steering:

A lower rotational speed of the servomotor is switched over to when the temperature in and/or cat the steering unit and/or in and/or at the control device of the steering system exceed a selectable limit value. Moreover, the servomotor can be s-iaitched off when the temperature in and/or at the steering unit and/or in and/or at the control device of the steering system exceed a selectable limit value. 20 A further possibility of taking -'the operational state of the power-assislted steering sy s tem, i n to consideration consists in switching over to a lower rotational speed of the servomotor when the temperature in and/or at the steering unit and/or in and/or at the control device of the steering system exceeds a first selectable limit value. It is additionally provided in this variant that the servomotor is switched off when the temperature exceeds a selectable second limit value.

The afore-mentioned measures serve for protection against thermal overloading of the steering system under extreme conditions and can be combined with other refinements of the system.

In the afore-described variants, the steering torque is ascertained starting from the current present directly or indirectly at the servomotor. This has the advantage that a steering torque sensor or motor rotational speed sensor can be dispensed with.

However, it can be provided that the steering torque or the motor rotational speed is detected by an appropriate sensor.

Different rotational speeds of the servomotor can be set by way of, for example, pulse-width modulation (PWM), switching-over of a two commutator electrical motor or three-brush electrical motor, or bypassing or switching in or out of a series resistor.

Two-commutator and three-brush electrical motors are known from the state of the art with two windings, by which different rotational speeds can be realised through driving both the windings by way of two commutators or three brushes.

Further variants of the method, which are particularly able to be combined with the afore-described variants, concern the behaviour of the servomotor on a new start or on switching-off of the engine of the vehicle. For this purpose, it can be provided that the servomotor and/or the control unit of the steering is switched on for a new start of the vehicle when the ignition of the engine is switched on and:

- when a current generator operationally connected with the engine delivers current (start after the engine has been started), c when the starter draw-in relay is actuated for starting of the engine (switching-on simultaneously with the starting of the engine), when a selectable number of ignition failure signals have been detected(engine runs for a certain time), when a signal, which represents the rotational speed of a current generator operationally connected with the engine exceeds a selectable threshold (start only when the generator supplies sufficient current), and/or when the vehicle speed exceeds a selectable threshold.

It can also be provided that the servomotor and/or the control device of the steering, after being switched on, remains switched on by way of a self-holding circuit as long as the ignition is switched on. A delayed switching-off, when the ignition is switched off, can be provided as advantageous refinement.

These variants shall serve the purpose that the regulating means is supplied with voltage only when the engine of the vehicle has come into operation or the vehicle is rolling, in order that the on-board mains loading is kept low and the battery is not discharged prematurely when the ignition is switched on, the combustion engine is still and the vehicle stationary (for example when a radio coupled with the ignition is in operation at standstill). The inclusion of the travel speed parameter produces a steering assistance when the vehicle is rolling (rolling into a parking gap, garage, etc). The steering system is activated when the engine is turning or the vehicle is rolling and remains activated until the driver intentionally switches the engine off. Thus, the steering system is also suitabl for vehicles with automatic utilisation of flywheel energy (hybrid vehicles). The afore-described variant, in which switching-off of the steering system takes place with time delay after switching-off of the ignition, serves for assistance in detenting of the steering wheel lock or when the vehicle is rolling out.

The afore-described variants for starting or switching-off of the steering system can be combined with each other.

Claims

I. A method of regulating operation of a vehicle power-assisted steering system which comprises an electric servomotor, transmission means to transmit drive from the servomotor to steering means of the vehicle, clutch means to produce a drive coupling between the transmission means and the steering means, and actuating means connected to the steering means and responsive to torque manually applied to the steering means to actuate the clutch means for production of said coupling, the method comprising the steps of selecting the rotational speed of the servomotor in dependence on at least one of vehicle travel speed, vehicle steering torque, engaged gear of the vehicle transmission, operating state of the vehicle engine and operating state of the power-assisted steering system.
2. A method as claimed in claim 1, wherein the rotational speed of the servomotor is lowered and raised continuously in accordance with a predeterniined characteristic curve, on respectively in the vehicle travel speed.
3. A method as claimed in claim 1, wherein the rotational speed of the servomotor is lowered and raised in steps, in dependence on at least one threshold value interrogation of the vehicle travel speed,or, increase and decrease, respectively, in that speed.

increase and decrease,
4. A method as claimed in claim 1, wherein the rotational speed of the servomotor is lowered and raised continuously, in accordance with a predetermined characteristic curve, on decrease and increase, respectively, in the steering torque.
5. A method as claimed in claim 1, wherein the rotational speed of the servomotor is lowered and raised continuously, in dependence on at least one threshold value interrogation of the steering torque, on decrease and increase, respectively, in that torque.
6. Method as claimed in any one of the preceding claims, comprising the steps of changing the rotational speed of the servomotor to a lower value when the steering torque falls below a selectable threshold value after the vehicle travel speed has exceeded a first threshold value and changing the rotational speed of the servomotor to a higher value when the steering torque falls below a selectable threshold value after the vehicle travel speed has fallen below a second threshold value.
7. A method as claimed in any one of claims 1 to 5, comprising the steps of changing the rotational speed of the servomotor to a lower value when the steering torque falls below a selectable threshold value and changing the rotational speed of the servomotor to a higher value when the steering torque exceeds a selectable threshold value.

z
8. A method as claimed in claim 6 or claim 7, wherein the steering torque threshold values are selectable in dependence on whether the torque increases or decreases.
9. A method as claimed in claim 6, wherein the travel speed threshold values are selected in dependence on whether the speed increases or decreases.
10. A method as claimed in any one of the preceding claims, comprising the step of changing the rotational speed of the servomotor to a lower value when the steering torque falls below a selectable threshold value after a selectable time delay following changing up of the vehicle transmission from a lower gear.
1-1. A method as claimed in any one of claims 1 to 4 and 10, comprising the step of changing the rotational speed of the servomotor to a higher value when the steering torque falls below a selectable threshold value after engagement of a lower gear of the vehicle transmission.
12. A method as claimed in claim 10 or claim 11, wherein thela,er gear is either or each of the 'Firstforward gear and the reverse gear.
13. A method as claimed in any one of the preceding claims, comprising the step of changing the rotational speed of the servomotor to a lower value when at least one of a temperature in and a temperature at a component of the steering means exceeds a selectable limit value.
14. A method as claimed in any one of claims 1 to 12, comprising the step of switching off the servomotor when at least one of a temperature in and a temperatureat a component of the steering means exceeds a selectable limit value.
15. A method as claimed in any one of claims 1 to 12, comprising the steps of changing the rotational speed of the servomotor to a lower value when at least one of a temperature in and a temperature at component means of or associated with the steering means exceeds a first selectable limit value and switching off the servomotor when at least one of a temperature in and a temperature at component means of or associated with the steering means exceeds a second selectable limit value.
16. A method as claimed in any one of claims 13 to 15, the component means being at least one of a steering unit and a control device for the steering.
17. A method as claimed in any one of the preceding claims, comprising the step of determining the steering torque from current present directly or indirectlyatthe servomotor.
18. A method as claimed in any one of the preceidng claims, comprising the step of determining the steering torque from torque measured by a sensor.

21
19 A method as claimed in any one of the preceding claims, comprising the step of determining the steering torque from engine speed measured by a sensor.
20. A method as claimed in any one of the preceding claims, comprising the step of effecting changes in the rotational speed of the servomotor in the proximity of zero transitions of said manually applied torque.
21. A method as claimed in any one of the preceding claims, comprising the step of effecting changes in the rotational speed of the servomotor by way of pulse width modulation in a current supply circuit of the servomotor.
22. A method as claimed in any one of claims 1 to 20, comprising the lecting changes in the rotational speed of the servomotor step of ef 1 by way of bypassing or switching in or out a series resistor in a current supply circuit of the servomotor.
23. A method as claimed in any one of claims 1 to 20, wherein the servomotor is a two commutator or three brush electric motor and the method comprises the step of effecting changes in the rotational speed of the servomotor by switching over the motor.
24. A method as claimed in any one of the preceding claims, comprising the step of switching off at least one of the servomotor and a control device for the steering when, on restarting of the vehicle engine, at least one of a plurality of predetermined parameters is present in conjunction with the engine ignition being switched on.
25. A method as claimed in claim 24, wherein said parameters are delivery of current by current generating means associated with the engine, actuation of a relay in a starter circuit of the engine, detection of a preselectable number of misfires, exceeding of a preselectable threshold value by the rotational speed of said current generating means, and exceeding of a preselectable threshold value by the vehicle travel speed.
26. A method as claimed in claim 24 or claim 25, comprising the step is of switching off at least one of the servomotor and said control device after elapse of a delay time following switching off of the ignition.
27. A method as claimed in claim 1 and substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.
28. A method as claimed in claim 27 and modified substantially as hereinbefore described with reference to Fig. la of the accompanying drawings.
29. A -method as claimed in claim 1 and substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.
A method as claimed in claim 29 and modified substantially as 'o Fig. 2a of the accompanying hereinbefore described with reference drawings.
Regulating means for regulating operation of a vehicle powerassisted steering system which comprises an electric servomotor, transmission means to transmit drive from the servomotor to steering means of the vehicle, clutch means to produce a drive coupling between the transmission means and the connected to the steering means applied t 0 tile steering means production of said coupling, the steering means, and actuating means and responsive to torque manually to actuate the clutch means for regulating means being operable to regulate 'the rotational speed of the servomotor in dependence on at 15]cast one of vehicle travel speed, vehicle steering torque, engaged gear of the vehicle transmission, operating state of the vehicle engine and operating state of the power-assisted steering system.
32. Regulating means as claimed in claim 31, theclutch means - means omprising at least one clutch cheek and the actuating comprising an entraining member connected to a steering column of the steering means and responsive to torque manually applied to a steering wheel at the column to cause, by mechanical action on the clutch cheek, the clutch cheek to produce the drive coupling.
33. Regulating means as claimed in claim 31 or claim 32, comprising at least one power transistor arranged in a current feed for the servomotor and switching means arranged in a path parallel to the output path of the at least one transistor, the loss power of the switching means being less than that of the transistor or transistors.
34. Regulating means substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.
35. Regulating means as claimed in claim 34 and mod if i ed substantially as hereinbefore described with reference to Fig. la of 10 the accompanying drawings.
36. Regulating means substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.
37. Regulating means as claimed in claim 36 and modified substantially as hereinbefore described with reference to Fig. 2a of 15 the accompanying drawings.
38. A motor vehicle provided with a power-assisted steering system and regulating means as claimed in any one of the preceding claims.
39. A motor vehicle as claimed in claim 38 and substantially as hereinbefore described with reference to Figs. 3 and 4 of the 20 accompanying drawings.

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