GB2187346A

GB2187346A - Torque controlled motor for vibration damper

Info

Publication number: GB2187346A
Application number: GB08703775A
Authority: GB
Inventors: Bernd Albert; Udo Schneider; Wolfgang Fischer; Joachim Kuhnel
Original assignee: Sachs Systemtechnik GmbH
Current assignee: Sachs Systemtechnik GmbH
Priority date: 1986-02-27
Filing date: 1987-02-18
Publication date: 1987-09-03
Also published as: GB2187346B; DE3606306C2; DE3606306A1; FR2594756B1; GB8703775D0; FR2594756A1

Abstract

For a vibration damper with variable damping power, e.g. a vehicle shock absorber, an electric motor actuating apparatus is easily monitorable and guarantees low- wear operation over a long time. With the electric motor (1), in a current supply lead (8), there are associated a series resistor (9) and a switch (4, 10) which bridges over this series resistor (9). The function of this switch is such that the series resistor (9) is connected into circuit in dependence upon at least one pre- determined angle of rotation of the respective actuating element (5, 5') and before a stop (7, 7') is reached. <IMAGE>

Description

SPECIFICATION Actuating apparatus for a vibration damper with variable damping power The invention relates to an actuating apparatus for a vibration damper with variable damping power according to the opening statement of Claim 1.

Such an actuating apparatus for the variation of the damping power is proposed by Fed.

German Pat. Appln. No. P 34 46 133 (corresponding to British Patent Application No. 85.

30, 562 - Case 1018 - and French Patent Application No. 85. 19, 093 - Case 1018). In this case the fluid control elements are formed as rotary slide valves and are driven, against the force of a return spring, out of the zero position by means of electric motor displacement as far as a stop in each case, whereby a variation of damping power is effected as result of opening or closing of a- passage cross-section in a by-pass passage. For the whole displacement distance the electric motor is fed with the full motor voltage. Only after the elapse of a specific time, which is dimensioned so that the end position is reliably reached by the electric motor, does a switch-over to a holding voltage take place, usually by means of a time-switch member.

This holding voltage must be so great that the electric motor holds the fluid control element in each case securely in the end position against the force of the return spring. It is disadvantageous here that the full motor voltage is applied longer than necessary and thus an unnecessary heating of the electric motor takes place. Since moreover the actuating elements are driven with the full motor moment against the stop, considerable stop impacts occur which must be countered by correspondingly stout dimensioning of the parts and which after lengthy operation nevertheless cause considerable wear especially of the transmission parts.

It is the problem of the present invention to produce an actuating apparatus for an electric motor variation of damping power which is simple in assembly, has a small space requirement and guarantees reliable operation with low wear over a long time.

In accordance with the invention this problem is solved in that with the electric motor there are associated, in a current supply system, a series resistor and a switch bridging over this series resistor, which switch connects the series resistor into circuit in dependence upon at least one predetermined angle of the rotation of the fluid control element in each case and before the stop is reached.

Thus in a simple manner the motor is switched to holding voltage by the series resistor before the stop is reached. Accordingly the motor moment also reduces and thus so do the mechanical forces acting upon the stop, so that all mechanical parts are less loaded. The switch-over to the holding voltage, controlled by the angle of rotation, also prevents an unnecessary heating of the electric motor, and no high demands are made of the contact of the switch, despite inductive load of the motor, for the full motor current is connected with the contact closed, while in the opening of the contact the resistor prevents spark formation. Accordingly low-wear working of the movable parts is guaranteed over a long period.

An advantageous form of embodiment is obtained in accordance with the invention in that the switch is actuatable by an actuating apparatus dependent upon the angle of rotation, possibly in several positions in rotation.

The switching actions preferably take place in the region ofthe zero position and in the region of the end position in each case. Thus it is possible to start up the motor with the holding voltage and also to reach each end position with holding voltage, whereby reduced starting current and also reduced brush wear are achieved.

A very simple and operationally reliable formation of the switch is obtained in that the switch is formed with at least one slider and at least one sliding contact. The sliding contact, in a simple manner, is arranged on the drive-output side of the gear plate, while the slider is firmly connected with the drive-output shaft. Likewise other switches are conceivable, for example with contact lugs, which are secured to the gear and are actuated by a cam disc situated on the drive-output shaft.

According to a further feature of the invention the series resistor is arranged in the region of the electric motor in a cavity of the piston rod. In this case the series resistor is advantageously formed by a resistor which possesses an electric resistance decreasing with rising temperature. In this case the series resistor can possess such a temperature-dependence that the total resistance formed from the sum of the motor resistance, which increases greatly with rising temperature, and the series resistance forms a slightly rising characteristic curve with rising temperature.

Since vibration dampers must function satisfactorily over a wide temperature range for example from --40" to +20 C., the electric motor drive, advantageously arranged in the interior space of the piston rod, is also exposed to these temperatures. At high temperatures the resistance of the motor winding increases greatly, whereby the motor current and thus the available motor moment are reduced to the same degree. This reduction is compensated by a series resistor designed in this way. Moreover a total resistance which forms a weakly rising characteristic curve with rising temperatture provides the possibility of fixing the damper condition temperature-dependently from the total resistance. This is readily also possible by analogue evaluation of the current.

The invention will be explained in greater detail below by reference to the examples of embodiment represented in the drawing, wherein: Figure 1 shows a detail of a double-tube vibration damper in longitudinal section; Figure 2 shows an electric-motor-operated actuating apparatus in diagrammatic representation; Figure 3 shows the angular on rotation of an actuating element in diagrammatic representation; Figure 4 shows a form of embodiment for the switching of the electric motor by means of sliding contacts, and Figure 5 shows a diagram for the progress of the resistance over the temperature.

The electric-motor actuating apparatus will be explained by the example of a double-tube vibration damper. The detail of a double-tube vibration damper 11 as shown in Fig. 1 comprises a container 12 in which a cylinder 13 is coaxially arranged. A piston-rod unit 14, consisting of a piston rod forming cavity 15 and of an extension part carrying a damping valve device, is guided in a piston rod guide and sealed to the exterior by means of a piston rod seal. The damping valve device is formed by a first damping valve system 16 and a second damping valve system 17, is secured on the extension part of the piston rod unit and is formed as piston of the vibration damper 11.In a vehicle (not shown) by way of example the piston rod unit 14 is connected with the vehicle body and the container 12 with the vehicle axle, so that due to relative movement of the vehicle body in relation to the vehicle axle the piston rod unit 14 carries out an axial movement in the cylinder 13. In this case the damping valve device divides the damping-fluid-filled interior space of the cylinder 13 into an upper working chamber and a lower working chamber. In the extension part of the piston rod unit 14 a centrally arranged, axially extending by-pass passage 18 is provided with which the two damping valve systems 16 and 17 can be bridged over. An upper outer passage cross-section 19, a lower outer passage cross-section 20 and a central passage cross-section 21 open into this bypass passage 18.The upper outer passage cross-section 19 and the lower outer passage cross-section 20 are here controllable by means of fluid control elements 5 and 5' formed as rotary slide valves. These fluid control elements 5 and 5' are in connection with one another through a return spring 22 and are actuated according to choice by means of a cranked actuating shaft 23; a lower crank of this actuating shaft 23 co-operates with an abutment face 6 of the fluid control element 5, while the upper crank of the actuating shaft 23 acts upon an abutment face, which is not visible in this view, of the fluid control element 5'. When the cranked actuating shaft 23 is exerting no displacement force, the fluid control elements 5 and 5' are pressed by the return spring 22 with their abutment faces against the stops 7 and 7'.

The electric-motor-actuating apparatus is situated in the cavity 15 of the piston-rod unit 14 and is formed by an electric motor 1 and a transmission 2, while a drive-output shaft 3 is firmly connected with a coupling piece 24 which is connected fast in rotation with the cranked actuating shaft 23. On the drive-output-shaft end of the transmission 2 a contact arrangement 4 is provided, which in this example of embodiment is formed by sliding contacts co-operating with a slider forming the switch 10, this slider being secured on the drive-output shaft 3. In the unit consisting of electric motor and transmission a series resistor is arranged which, connected in parallel with the switch device formed from sliding contact and slider, lies in a current supply lead of the electric motor.

When the fluid control elements 5 and 5 are in the position as drawn in Fig. 1, no displacing moment is acting from the driveoutput shaft 3 upon the cranked actuating shaft 23, so that the fluid control elements 5 and 5' rest with their abutment faces 6 on the stops 7 and 7' and close both the upper outer passage cross-section 19 and the lower outer passage cross-section 20. In this setting on axial movement of the piston rod unit 14 both the first damping valve system 16 and the second damping valve system 1 7 are effective.When the electric motor 1 is switched on a displacing moment is exerted through the transmission 2 and the drive-output shaft through the coupling 24 upon the cranked actuating shaft 23, and in the one direction of rotation the lower crank entrains the lower fluid control element 5, through the abutment face 6, until the latter abuts at its other end on the stop 7, whereby the lower outer passage cross-section 20 is opened. In this position then only the first damping valve system 16 is effective, for the second damping valve system 17 is bridged over by the opened lower passage cross-section 20 and the central passage cross-section 21. In the other di rection of rotation of the electric motor 1 the cranked actuating shaft 23 entrains the upper fluid control element 5' against the force of the return spring 22, whereby the upper outer passage cross-section 19 is connected with the by-pass passage 18, while the lower fluid control element 5, situated in the zero posi tion, is situated in the zero position, that is it closes the lower outer passage cross-section 20. In this position the first damping valve system 16 is bridged over by the opened up per passage cross-section 19 and the central passage cross-section 21, so that only the second damping valve system 17 is in action.

For better understanding in the diagrammatic illustrations according to Figs. 2 to 4 the same references will be used which designate functionally the same parts in Fig. 1. In the electric-motor actuating apparatus as shown in Fig. 2 the electric motor 1 and the transmission 2 are combined into one construction unit, while the drive-output shaft 3 comprises a contact arrangement 4 which is formed by a switch cam disc secured thereon. The actuating element 5 is here firmly connected with the drive-output shaft 3 and co-operates with an abutment face 6 with a stop 7. The series resistor 9 is situated in the current supply lead 8, while the switch 10 actuated by the contact arrangement 4 bridges over the series resistor 9 when in the closed condition.In the position as illustrated the current supply to the electric motor 1 takes place by way of the current supply lead 8 and the series resistor 9. The switch 10 is in the opened position; the motor 1 is supplied with a holding voltage which suffices to keep the fluid control element 5 with its abutment face 6 in engagement with the stop 7. By reference to Fig. 3 the displacement movement of the fluid control element 5 and the switching action thereby effected according to Fig. 2 will be explained in greater detail. Starting from the zero position 0 of the fluid control element 5, the switch 10 is initially closed, so that the motor 1 is supplied with the full motor voltage.

At the end of the rotation angle x the switch 10 is opened by the switch cam disc secured on the drive-output shaft 3 and acting as contact arrangement 4, and thus the bridging-over of the series resistor 9 in the current supply lead 8 is eliminated, so that now the holding voltage is applied to the electric motor 1. In this case it is advantageous if in this position the full passage cross-section is already cleared by the fluid control element 5.

The further rotating movemet of the fluid control element 5 according to the angle ss as far as the abutment of the abutment face 6 on the stop 7 takes place with holding voltage, that is with substantially reduced motor moment, so that the stop 7 is approached gently. Due to the here effected switch-over from full motor voltage to holding voltage the motor current experiences a measurable reduction, and the reduction of the motor current can be taken for the recognition that the rotating movement of the fluid control element 5 has been executed.

In the embodiment according to Fig. 4 on the drive-output shaft 3 there is secured a slider forming the switch 10, which on rotation is electrically conductively connected with the contact arrangement formed by sliding contacts. In the zero position as shown there is no contact connection between the slider and the sliding contacts, so that the series resistor 9 is in circuit in the current supply lead 8, and starting takes place with holding voltage. As from a pre-determined angle of rotation the slider 10 comes on to the sliding contact 4 and thus bridges over the series resistor 9, so that the further rotating movement takes place with full motor voltage. At the end of the sliding contact 4 a switch-over is again made to holding voltage, and the remainder of the rotating movement until the fluid control element 5 lies on the stop 7 again takes place with holding voltage.This form of embodiment shows that on reversal of polarity of the current supply leads the electric motor, formed as direct current motor, carries out the displacement in the other direction of rotation in analogous manner, and at the end of this rotating movement the fluid control element 5' lies against the stop 7'.

In the diagram according to Fig. 5 the individual resistance characteristic curves are shown in dependence upon temperature. In this case R, designates the total resistance formed from the motor resistance R2 and the series resistance Ra. The characteristic curve of the motor resistance R2 shows that with rising temperature the resistance of the motor winding increases greatly. The series resistor is so selected that the resistance value decreases with rising temperature, namely in such a way that the total resistance R1 forms a weakly rising characteristic curve with rising temperature. In this case an analog evaluation of the current gives information as to the oil temperature in the damper and as to the damper condition, that is the position of the fluid control element.A further possibility consists in selecting the temperature-dependent resistance so that the total resistance is constant over the temperature. In this case the damper state can be read off temperature-independently from the total resistance.

As a result of the switching-over of the motor current in dependence upon the angle of rotation of the fluid control element 5 an unambiguous indication of the position in each case of the fluid control element 5 is rendered possible by way of the two supply leads of the electric motor 1. The two end positions are determined merely by current measurement and the polarity in each case in the supply leads, that is without additional leads to the vibration damper. If only a two-stage displacement of the vibration damper is required, the vibration damper can readily be used as earth lead, this earth lead being connected with the motor, while only one cable leads to the motor. On the other hand in the case of electrically insulated installation of the vibration damper in the vehicle it is possible to form this damper as pole-changeable supply lead and to connect it thus with the electric motor, so that in this case again only one lead, formed by a cable, has to be conducted to the motor.

Claims

1. Actuating apparatus for a vibration damper with variable damping power, in which in the vibration damper, as a result of movement of a vehicle body in relation to the vehicle axle, damping medium is forced by way of a damping device of variable damping power from one working chamber into a second working chamber, while for the damping power variation at least one fluid control element, subject to the action of a return spring and drivable by an electric motor, is provided which is rotatable against the force of the return spring out of its zero position against at least one stop defining an end position, characterised in that with the electric motor (1) there are associated, in a current supply lead (8), a series resistor (9) and a switch (4, 10) bridging over this series resistor (9), which switch connects the series resistor (9) into circuit in dependence upon at least one predetermined angle of rotation of the respective fluid control element (5, 5') and before the stop (7, 7') is reached.

2. Actuating apparatus according to Claim 1, characterised in that the switch (10) is actuatable, possibly in several positions in rotation, by an actuating apparatus (4) dependent upon the angle of rotation.

3. Actuating apparatus according to Claim 1 or 2, characterised in that the series resistor (9) is connectable into circuit in the region of the zero position and in the region of an end position.

4. Actuating apparatus according to Claim 1 or 3, characterised in that the switch (4, 10) is formed with at least one slider (10) and at least one sliding contact (4).

5. Actuating apparatus according to one of Claims 1 to 4, characterised in that the series resistor (9) is arranged in the region of the electric motor (1) in a cavity (15) of the piston rod.

6. Actuating apparatus according to one of Claims 1 to 5, characterized in that the series resistor (9) is formed by a resistor possessing electric resistance which decreases with rising temperature.

7. Actuating apparatus according to one of Claims 1 to 6, characterised in that the series resistor (9) displays a temperature-dependence such that the total resistance, formed from the sum of the motor resistance, which increases with temperature rise, and of the series resistance (9), forms a slightly rising characteristic curve with rising temperature.

8. Actuating apparatus according to one of Claims 1 to 7, characterised in that with at least one supply lead (8) of the electric motor (1) there is connected an evaluator device which receives an indication as to the temperature and'our the position of the fluid control element (5, 5').

9. An actuating apparatus for a vibration damper having variable damping power as claimed in Claim 1, substantially as described with reference to Fig. 1 of the accompanying drawings.