GB2260425A

GB2260425A - Feedforward position control system

Info

Publication number: GB2260425A
Application number: GB9221134A
Authority: GB
Inventors: Gunter Diessel
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1991-10-09
Filing date: 1992-10-08
Publication date: 1993-04-14
Also published as: ITMI922336A0; GB9221134D0; SE9202951L; IT1255682B; SE9202951D0; DE4133911A1; FR2682433A1; ITMI922336A1

Abstract

In a vehicle suspension feedforward control system, the difference between the actual and desired position of the vehicle is determined and stored as a number of divisions. A valve 1 is then actuated to supply pressurised fluid to the height adjusting system in pulses, one pulse being produced for each division. A pulse is immediately triggered when an externally induced position change eg from a bump, exceeds one division. Control can be modified by other vehicle parameters eg. weight, tilt, acceleration etc. The arrangement of inlet/exhaust valves 1, 2, 3, 5 is also disclosed. <IMAGE>

Description

m l 'IT!, ' 2 534-- 1 A POSITIONING DEVICE OPERATED BY A PRESSURE MEDIUM

AND A PROCESS FOR ITS OPERATION The invention relates to a positioning device operated by a pressure medium, and to a method of operating such a positioning device to incrementally change its position.

The use of Incremental position sensing systems in cylinders operated by a pressure medium has been disclosed in the article Nglectrohydraulics In Production Technology" ("Fluid". May 1984. pages 21 ff), wherein clockcontrolled operation by proportional valves, driven by stepping motors, is also disclosed. Here it is firstly known to use a digital system as a position sensing or detecting system for a hydraulic cylinder, where the position is either incrementally called up or Incrementally filed. The detected actual value is fed Into a digital controller which then actuates a proportional valve. operated by a stepping motor. via a stepping motor driver. This constitutes only quasi digitalisation of the overall control process.

Thus the described system consists of a 'controller', I.e. a feedback signal is always provided to control the control loop. In other words this means that the operation of an actuating element always leads to an Interrogation as to whether the theoretical position has been reached and Is possibly to be readjusted. Despite the pulse-controlled operation of the valves. such a control procedure requires a high outlay and is only slightly faster than constant analogue operation.

A positioning device operated by a pressure medium, in particular for regulating the level of a motor vehicle chassis. has been disclosed In DEOS 33 00 662, wherein valves are provided which enable positioning devices In the form of vibration dampers to be connected to a pressure medium source. Here the position of the positioning devices Is sensed by suitable position determining elements and fed to an electronics unit which drives and switches the valves In dependence upon these electric output values. Level 2 adjustments of this type are also provided, for example. for vehicles which must also carry out an adjustment of level during travel. However, in the operation of a motor vehicle, both due to external influences. such as road unevenness, and in the case of extreme steering locks and the like, situations can arise which make very heavy demands on the reliability and safety of such a level adjustment system. In the conventional level adjustment devices for motor vehicles, the actuating drive or vibration damper, the servo valves and the position determining elements form a closed control loop with the associated electronics unit and the load. If a fault occurs In such a closed control loop, for example in the region of the position determining elements or the electric leads. or simply contact faults, the positioning device conducts the load to the end stop. With the vehicle in motion, this can lead to sudden accelerations and to completely uncontrolled movements with sometimes catastrophic states of motion of the vehicle. As the conventional positioning devices and level adjustment devices are highly dynamic. Le. fast reacting systems, additionally provided safety or blocking valves are too slow.

Commencing from this prior art. the aim arises of providing a method for the operation of a positioning device operated by a pressure medium, and a positioning device operated by a pressure medium which, while ensuring a very high level of safety, reacts at high speed and possesses circuitry of simple construction.

In accordance with the present invention. in one aspect this aim Is fulfilled by a method for the operation of a positioning device, operated by a pressure medium, In particular a level regulating device for motor vehicles, wherein the position of a positioning device Is incrementally determined, fed to an electronic device and in dependence upon the respective determined position actual value of the positioning device a valve arrangement is operated in clock-controlled fashion in switching pulses, whereby the positioning device is changed in position in the direction of a desired theoretical value, and wherein each Incremental switching 1 q! r 1 TV 1 3 pulse results In a change in position by a corresponding amount of the positioning device and that as soon as an externally induced change in position corresponds in amount to one full position increment. an Incremental switching pulse is triggered accordingly to produce an oppositely directed change in position.

In accordance with a second aspect of the Invention the aim Is fulfilled by a positioning device, operated by a pressure medium, In particular a level regulating device for a motor vehicle chassis, with at least one positioning device which can be supplied with pressure medium via a valve arrangement, In particular a positionable vibration damper, which Is equipped with a position determining element, and an electronics unit for operating the valve arrangement In dependence upon the output values of the position determining element(s), wherein to enable the positioning device to be supplied with pressure medium, a first directional control valve Is connected at Its Input end to a pressure medium supply terminal and at its output end to a pressure amplifier so as to form a pressure medium circuit and that a self-resetting non-return valve Is connected In parallel to the Input end of the first directional control valve and the output end of the pressure amplifier, and that a second directional control valve, operating as a valve which can be driven In pressuredependent fashion, Is connected to the output of the pressure amplifier so as to form a pressure medium circuit. and at its output end leads Into the operating chamber of the positioning device and In parallel thereto Into a third directional control valve provided for venting, and that the directional control valves are designed to be electromagnetically operable In clock-controlled fashion. Further advantageous embodiments are described In the sub-claims.

As regards the process, the advantage is achieved that with digital storage of the determined position and with a corresponding clockcontrolled operation of the valve arrangement In short digital switching pulses. the positioning device can be adjusted very rapidly. This Is due to the fact that each changed position 4 increment is assigned an incremental switching pulse of the valve arrangement of the positioning device. Here an essential feature consists in that the positioning value is stored digitally at least in the electronic device. Depending upon the advantageously proposed design option, the position can either be determined digitally and also stored digitally in the electronic device, or the position can be determined in analogue fashion and, following analogue to digital conversion, stored digitally in the electronic device. That which is essential and advantageous in terms of the process consists in that the valve arrangement of the positioning device is operated accordingly in clock- controlled fashion in short digital switching pulses, where each changed position increment is assigned an incremental switching pulse. This means that.. for example, when the possible range of position is divided into incremental steps of 0.4 mm. each of these steps is assigned a respective switching pulse which produces a drive stroke of 0.4 mm on the positioning device. If the desired change of position amounts for example to 0.8 mm, accordingly two switching pulses are triggered and so on. The step size of the incremental steps and the drive stroke itself are freely selectable and can either amount to less or more than 0.4 mm. It should only be ensured that the dimensioning of the pressure medium, which governs the drive stroke, is adapted to the corresponding size of the drive stroke. A further advantage consists in that. in a process of this type corresponding to the invention, in a further development of the invention, other static or dynamic variables which arise during the motion of the vehicle can also be detected and used In the same way to operate the valves of the positioning device.

This appears to be particularly effective in the case of use In level regulating devices for motor vehicles. Static or dynamic variables can comprise, for example, the steering lock, transverse acceleration, rising or falling gradient angles, and angles of tilt or inclination of the vehicle. For use in motor vehicles which travel at very high speeds, for example racing cars, in this connection It would also appear effective to detect the aerodynamically occurring forces. This is due to the fact that aerodynamic forces which occur at high speeds can be substantially greater in magnitude than the weight forces and the inertia forces which occur in motion. Furthermore the use of the process proposed by the Invention is extremely advantageous in association with an anti-skid system. The effects of the anti-skid braking system can thus be supported In terms of safety technology in such manner that for example tilting moments. to which the vehicle Is subject as a result of braking. can be compensated by an appropriately operated level regulating device. This feature can be employed particularly effectively in the case of braking on bends. Overall, in the process proposed In accordance with the Invention, due to the short reaction time In every situation a very high level of safety is ensured.

One of the advantages of the positioning device operated by a pressure medium and proposed in accordance with the Invention resides In the fact that, due to the structural design of the positioning device, a control loop is provided which is open in the region of the position determining element and which. by dispensing with a control feedback line from the position determining element, can switch the positioning device at a correspondingly high speed. In an advantageous development of the Invention, In the case of the use of the positioning device for the level regulation of vehicles, It Is provided that further sensors are used to determine additional vehicle motion parameters. Although these sensors form a quasi closed control loop with the electronics unit as there Is permanent feedback from the sensor, In the region of the actuating drive and the valve arrangement this control loop section Is open In that, as mentioned In the aforegoing. feedback from the position determining element Is deliberately dispensed with. In this way it Is possible for the actuating drive to Immediately assume the desired theoretical position without the need for feedback from the position determining element Itself. Re-actuation of the valve arrangement for the adjustment of the positioning device does not occur until the change In position of the positioning device Is again greater than one 6 increment (in the above example 0.4 mm). In this way, as already mentioned in the aforegoing, no continuous feedback in terms of control technology is provided, which manifests extremely advantageously in correspondingly short actuating times. It is only important that the dimensioning should be appropriate to achieve a correspondingly accurate and repeatedly reproducible drive stroke. A further advantage which contributes substantially to safety arises from the fact that, even on the occurrence of an electrical fault, the last set position value of the positioning device is retained, preventing the extension or retraction of the positioning device Into an end position in the case of a fault. The positioning device is also connected in such manner that even in the case of a power failure and resultant failure of the electrical response of the directional control valves, no unmonitored extension or retraction of the positioning device occurs. but the last set position of the positioning device is retained in a 'self-locking' fashion.

Embodiments of the invention are illustrated in the accompanying drawings and will be explained in detail in the following.

In the drawings:

Figure 1 illustrates the connections of the pressure medium valves with the positioning device; Figure 2 illustrates the operation of a positioning device, operated by a pressure medium, in a level regulating device of a motor vehicle; and Figure 3 Is an overall view of the elements, operated electrically and by a pressure medium, of a level regulating device of a motor vehicle.

Figure 1 illustrates the pressure medium circuitry of the positioning device. The first valve 1 is connected at its input end to the pressure medium supply terminal Ps and to the venting line R. At Its output end the valve 1 leads Into the Input end of a pressure amplifier 4. The valve 1 is operated electromagnetically and Is provided with a readjusting spring la for resetting to the closed 7 position which prevails In the unoperated state. In the unoperated state the Input end of the pressure amplifier is Isolated from the pressure medium supply terminal Ps, but open to the venting line R. The venting line R also extends In parallel thereto. i.e. from the corresponding Input end of the valve 1, which bears the venting line. to the pressure amplifier 4, and this merely for the venting of the differential piston 4a, not however for the venting of the output end of the pressure amplifier. A second pressure medium supply channel from the pressure medium supply terminal Ps leads via the non-return valve 5 Into the pressure medium line at the output end of the pressure amplifier. With respect to the pressure medium the non-return valve 5 is arranged In such manner that it has a blocking action from the output end of the pressure amplifier in the direction of the pressure medium supply terminal Ps. This ensures that even in the event of the failure of the valve 1 or the pressure amplifier 4, the pressure medium line Itself is always full. This is achieved In that the non-return valve 5 is set to open against a spring at a differential pressure of approximately 2 bar. Thus if the pressure prevailing at the output end of the pressure amplifier falls below the supply pressure by an amount of 2 bar, the non-return valve 5 opens and fills this section of the pressure medium line and also returns the piston 4b of the pressure amplifier to its starting position. as in the unoperated state of the valve 1 the Input end of the pressure amplifier Is switched through to the venting line R. The pressure amplifier 4 and the non-return valve 5 are connected at their output end to the second valve 2 which switches In pressure-dependent fashion and which thus is operated simultaneously via the pressure of the pressure medium line.

Here the opening pressure Is selected to be such that It Is greater than the pressure prevailing In the pressure medium supply line Ps. This means that this valve 2 opens only when the pressure amplifier 4 Is operating correctly and generates an output pressure which Is higher than the supply pressure I.e. only when non-return valve 5 is closed. When the valve 2 has opened, the operating 8 chamber 6 of the positioning device 7, shown here as a working cylinder, is supplied with pressure medium at a pressure greater than the supply pressure in line Ps. Using the process provided by the invention, this supply of pressure medium takes place with pulse controlled operation of the valve 1.

In the circuit illustrated. an incremental extension of the positioning device 7 Is achieved by a short-term 'pulse' opening of the valve 1. This supplies fluid at supply pressure Ps to the pressure amplifier 4, moving the differential piston 4b to the right as shown in the Figure. This raises the pressure sensed by valve 2, opening it, and thus admitting fluid at a pressure higher than Ps to the positioning device 7, but only while valve 1 remains open. When the differential piston 4b reaches the end of its stroke, no further fluid can be transferred and thus the maximum incremental movement of the positioning device is limited to the movement commensurate with the transfer to its cylinder of a volume of fluid equal to the volume of the output side of the pressure amplifier 4, i.e. the smaller area of the differential piston 4b times its stroke. By adjusting the time Interval for which valve 1 is opened, and the bores and strokes of the pressure amplifier and positioning device, any desired movement increment can be achieved.

When the positioning device reaches its new position, valve 1 is returned to its closed position, connecting the input side of the pressure amplifier 4 to the vent. This relieves the pressure sensed at the output side of the pressure amplifier and as the pressure falls then valve 2 closes and shortly thereafter the ball valve 5 opens to admit fluid at supply pressure Ps. This returns the differential piston 4b to its leftmost position, ready for a further opening of valve 1.

If the positioning device is now to be moved back, i.e. in this case lowered, the third valve 3 is operated accordingly In pulse-controlled fashion, whereby the operating chamber 6 of the positioning device 7 is vented in a monitored and pulse controlled fashion. Also in the case of the lowering, it is provided that at z 9 the latest when the valve 3 opens to the venting device. the pressure- dependent valve 2 closes the connection to the pressure medium supply terminal. Also during venting. i.e. during the lowering process of the positioning device, the valve 3 Is operated in a pulse-controlled fashion. Le. the valve is opened for a predetermined time to provoke a corresponding incremental movement of the positioning device, and the lowering process takes place In a corresponding fashion. The position sensing element 8, which here has the form of an incremental sensor, detects the position of the positioning device In Incremental steps. However. the position determining element can also be of analogue design, in which case the position values are then digitalised within the electronic device. When the drive stroke has been executed, the value reached on the position determining element 8 is no longer fed-back. This is unnecessary because each position-assigned Increment which Is changed Is assigned a respective switching pulse which is dimensioned such that re-activation to reach the theoretical position is unnecessary. By applying an opening pulse to valve 1 which corresponds in duration to the desired linear movement of the positioning device from its actual position to Its theoretical position, the desired change is achieved at a single operation of valve 1.

1 Figure 2 Illustrates the mode of operation of the process proposed In accordance with the invention in the example of a simulated chassis. The curve 51 represents the opening movement i.e. the spool movement of the valve which Is connected to the output end of the pressure amplifier and switches in pressure-dependent fashion. Following an appropriate supply of pressure medium. the spool of this valve switches through the pressure medium channels, where It Is to be noted that this curve a Initially has a highly oscillatory characteristic which., however, Is damped after a time of approximately 10 ms. This oscillation Is produced by the steep switching flank, has a physical origin and does not exert a negative Influence on the operating process. The curve a as a whole characterises an executed switching pulse which In this case extends over approximately 20 ms. It can also be seen that at the start of the curve -a there is an idle time amounting to approximately 3 ms, which derives from the response time of the first switching valve in the form of an electromagnetic valve.

Resulting from this switching pulse (curve a-), curve -b represents the path of the effected drive stroke of the positioning device. Here the drive stroke is completed approximately at the end of the switching pulse, i.e. after 20 ms. The curve c represents the load pressure in the vibration damper, here a portion being shown in which a simulated oscillation which occurs during vehicle motion is dying out in damped fashion. It can be seen that the oscillation of the vibration damper in curve c is superimposed upon the movement path of the actuating drive in curve b. This indicates that the positioning device assumes its desired position virtually uninfluenced.

Curve d- illustrates the variation of the pressure at the output end of the pressure amplifier. Here a dependence between curves d and a can be noted, which however can be easily explained by the fact that the pressure-dependent switching valve is naturally dependent on the variation of the pressure at the output end of the pressure amplifier. Close to the time T=0 on the time axis it can be seen that after a specific pressure has been reached in curve d, the valve. which switches In pressure-dependent fashion. reacts and opens. By virtue of the switching pulse of approximately 20 ms shown here, a drive stroke of approximately 0.3 - 0.35 mm is thus achieved.

Figure 3 Illustrates the overall positioning device in the case of use in a level regulating device in a vehicle. Here It is provided that each vibration damper 9 Is driven by a separate valve arrangement. In this way each vibration damper. together with the supply of pressure medium, Is self-sufficient In relation to the others. The coordination of the individual valve arrangements and the individual vibration dampers one with another is carried out here by an electronic device or on-board computer 10. The individual valve arrangements can then be driven in coordinated fashion by this means.

', 1 1 j 11 The input variables to be input Into the on-board computer 10 can comprise not only the determined position of the positioning device, here the vibration damper. but also other variables occurring during travelling operation or in general in the vehicle. Thus. for example. the fuel weight G, vehicle speed V, braking retardation and acceleration al, vertical acceleration a2, inclination in the direction of travel and transverse thereto, as well as gradients, travel round bends and steering wheel position can be fed In. This results in a highly complex level regulating system which provides a high degree of safety. These additionally fed-in motion parameters are likewise incrementalised at the latest in the on-board computer. As electronic components, together with sensors and the like. can be Incorporated successfully in the vehicle construction, this does not present any great difficulty. Due to the relatively simple design of the pressure medium circuit in which simple switching valves are used. the arrangement proposed in accordance with the invention also allows a simple operation of the positioning device which Is relatively Insusceptible to faults. The circuitry ensures that even In the event of the failure of the electrical elements of the positioning device, a dangerous operating state does not occur, but the last set position of the positioning devices, or in this case of the vibration dampers. Is retained. Drastic temperature changes can lead to volumetric expansion and shrinkage which result in small changes In position. Such position changes can also be produced by small Internal leaks which undoubtedly are also time-dependent. In these cases, when a position Increment, e.g. 0.4 mm, is exceeded. such position changes are likewise corrected by the further triggering of a switching pulse.

Pressure changes In the supply pressure exert no influence on the positioning accuracy for such time as the maximum load does not exceed the product of the piston surface of the positioning device and the pressure. In the case of racing cars, the aerodynamic and vertical acceleration forces can exceed the weight by several orders of magnitude. Therefore the dimensioning of the actuating 12 drive must take Into account the sum of all the occurring loads and adapted thereto.

Overall, due to the simple design of the positioning device. operated by a pressure medium. and of the process according to the Invention for the operation thereof, applications also in other technical fields, for example for the level regulation of stretchers. construction machines etc. , are possible.

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Claims

1. A method for the operation of a positioning device, operated by a pressure medium, In particular a level regulating device for motor vehicles, wherein the position of a positioning device is Incrementally determinede fed to an electronic device and In dependence upon the respective determined position actual value of the positioning device a valve arrangement Is operated In clock-controlled fashion in switching pulses, whereby the positioning device is changed In position In the direction of a desired theoretical value. and wherein each incremental switching pulse results in a change In position by a corresponding amount of the positioning device and that as soon as an externally induced change In position corresponds in amount to one full position Increment, an incremental switching pulse is triggered accordingly to produce an oppositely directed change In position.

2. A method for the operation of a positioning device, operated by a pressure medium. as claimed in Claim 1. wherein the position Is determined incrementally and accordingly Is filed incrementally In the electronic device.

3. A method for the operation of a positioning device. operated by a pressure medium. as claimed in Claim 1, wherein the position Is determined In analoque fashion and is filed incrementally in the electronic device after analogue to digital conversion.

4. A method for the operation of a positioning device, operated by a pressure medium, as claimed In Claim 2 or 3, wherein In the case of use in level regulating devices for motor vehicles, in addition to the determined position of the positioning device, further static and dynamic variables which occur In travelling operation are detected and trigger a digital operation of the valve arrangement.

5. A method for the operation of a positioning device, operated by a pressure medium, as claimed in Claim 4, wherein the signals of an antiskid system which drive the vehicle brakes are fed into the electronics unit for the digital. clock-controlled operation of the valve arrangement of the positioning device.

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6. A positioning device, operated by a pressure medium, in particular a level regulating device for a motor vehicle chassis, with at least one positioning device which can be supplied with pressure medium via a valve arrangement. in particular a positionable vibration damper. which is equipped with a position determining element, and an electronics unit for operating the valve arrangement In dependence upon the output values of the position determining element(s). wherein to enable the positioning device to be supplied with pressure medium, a first directional control valve is connected at its Input end to a pressure medium supply terminal and at its output end to a pressure amplifier so as to form a pressure medium circuit and that a self-resetting non-return valve is connected in parallel to the input end of the first directional control valve and the output end of the pressure amplifier, and that a second directional control valve, operating as a valve which can be driven in pressuredependent fashion, is connected to the output of the pressure amplifier so as to form a pressure medium circuit, and at Its output end leads into the operating chamber of the positioning device and in parallel thereto Into a third directional control valve provided for venting, and that the directional control valves are designed to be electromagnetically operable in clock-controlled fashion.

7. A positioning device, operated by a pressure medium. as claimed In Claim 6, wherein the first directional control valve is an electromagnetically operated 312 directional control valve with spring resetting via which the Input end of the pressure amplifier can be vented in the unoperated state.

8. A positioning device. operated by a pressure medium, as claimed in Claims 6 and 7. wherein the pressure amplifier is connected in such manner that in the state in which it is supplied with pressure at its input end. a pressure higher than the supply pressure prevails at its output end.

1

9. A positioning device, operated by a pressure medium. as claimed In Claims 6 to 8, wherein the non-return valve is arranged so as to exert a blocking action In the direction of the pressure medium supply terminal and In the forward conveying direction can be opened against spring force in such manner that the opening pressure Is substantially lower than the supply pressure.

10. A positioning device. operated by a pressure medium. as claimed In Claims 6 to 9, wherein the operating pressure of the directional control valve. which Is operated In pressure-dependent fashion, is greater than the pressure prevailing at the pressure medium supply terminal.

11. A positioning device. operated by a pressure medium, as claimed In Claims 6 to 10, wherein the third directional control valve, which is provided for venting purposes, is electromagnetically operable, has a spring resetting facility, and Is connected In such manner that when the directional control valve Is In the unoperated state the pressure medium line Is Isolated from the venting line.

12. A positioning device, operated by a pressure medium, as claimed in Claims 6 to 11. wherein an incremental sensor is provided as position determining element.

13. A positioning device, operated by a pressure medium, as claimed In Claims 6 to 11, wherein an analogue potentiometer Is provided as position determining element and the electronics unit Is provided accordingly with an analogue to digital converter for the Incremental filing of the position values.

14. A positioning device. operated by a pressure medium, as claimed In one or more of the preceding claims, wherein when the positioning device is used for the level regulation of motor vehicles. a positionable vibration damper is provided for each chassis wheel, and that each vibration damper can be operated In terms of pressure medium via a separate valve arrangement, and the valve arrangements as a whole can be electrically operated via a central electronics unit In coordinated fashion.

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15. A positioning devicei operated by a pressure medium, as claimed in Claim 11, wherein the electronics unit is provided with an Integrated computer and the positionable vibration dampers, adapted to one another, can be operated In coordinated fashion via the input from a plurality of sensors which determine additional travel values.

16. A method for the operation of a positioning device, substantially as herein described.

17. A positioning device substantially as described herein with reference to Figure 1 or Figure 3 of the accompanying drawings.