DE10130507A1 - Air spring particularly for use as road vehicle shock absorber comprises a piston and a roll-back bellows, with piezoelectric sensor that issues a signal when undergoing deformation - Google Patents

Abstract

The air spring comprises a piston and a roll-back bellows with at least one piezoelectric sensor that is located in the roll-back zone of the spring, to issue a signal when undergoing deformation. An Independent claim is also included for a method for control of the proposed air spring, involving use of signals from the sensor element in the role of an input to a control unit.

Description

The invention relates to an air spring, in particular for road vehicles, with a rolling piston and a bellows.

With air springs of the type mentioned, the problem of regulating the Air pressure in the bellows for height control and / or for regulating the Spring characteristic.

An air spring is known from DE 198 11 982 A1, in which the Height control takes place using an ultrasonic sensor. The ultrasonic sensor is used for detection the distance between the two ends of the air bellows, the ultrasonic sensor contains an ultrasonic transducer that is designed for a high frequency. The Ultrasonic transducer contains a piezoelectric transducer element and an adaptation layer, whose thickness R is the converter's own wavelength.

EP 188 289 describes a control system for rear axle suspension known in which a piezoelectric sensor accelerates the front tires detected. Depending on the determined acceleration value, the Spring characteristics of the suspension of the rear axle adjusted accordingly.

From DE 34 34 660 A1 an air spring is known in which a Gas pressure sensor for detecting and regulating the pressure in the rolling bellows. The sensor is there made of a piezoelectric foil or crystal that has a signal depending on that releases the air pressure acting on the sensor.

Furthermore, from DE 42 43 530 A1 an air spring with a bellows and a height sensor known. Are on the outer wall of the rolling piston Pressure sensors or contacts arranged in the axial direction. The pressure sensors are from the Roller fold actuated during a rolling movement and the corresponding output signals of Pressure sensors fed to a height regulation.

Fig. 1 shows an embodiment known from DE 42 43 530 A1 the air spring. The air spring has an elastomeric bellows 1 , which is attached to a rolling piston 2 . Flat, electrical pressure sensors 3 are arranged on the piston skirt of the rolling piston 2 . The pressure sensors 3 are aligned in the axial direction and arranged in two diametrically opposite groups.

During operation of the air spring, the rolling piston 2 plunges into the bellows 1 at different depths. This is indicated in Fig. 1, where the left side shows the rolling piston 2 immersed more than on the right side of the figure.

Depending on the immersion depth of the rolling piston 2 , the rolling fold 4 covers the piston skirt of the rolling piston 2 more or less. In the drawing of Fig. 1 on the right side are four pressure sensors 3 covered by the rolling fold 4 and thus switched to the logic "1", while the uncovered pressure sensors 3 have the switching state of logic "0". If the rolling piston 2 plunges further into the rolling bellows 1 (left side of FIG. 1), only the last two pressure sensors 3 are still logic "0" in the switching state.

The switched pressure sensors 3 give an electrical output signal to evaluation electronics, not shown in FIG. 1. The immersion depth of the rolling piston 2 in the bellows 1 is determined by the evaluation electronics by means of the respective logical switching states of the pressure sensors 3 . Depending on the immersion depth, the compressed air supply to the roller bellows 1 can be changed accordingly.

The invention has for its object an improved air spring and to provide an improved method of controlling an air spring.

The object underlying the invention is achieved with the features of independent claims each solved. Preferred developments of the invention are specified in the dependent claims.

The invention allows the use of deformable sensor elements for Determining the penetration depth of the rolling piston in the bellows of an air spring. As Sensor elements are preferably strain gauges, piezoceramics or piezoelectric foils, preferably made of a polymeric material, e.g. B. from Polyvinylidene fluoride (PVFD), for use.

According to a development of the invention according to claim 5 that is Sensor element formed triangular. For example, a triangular film can be made Polyvinylidene fluoride in a rolling area of the bellows on the rolling piston to be ordered. The slope is due to the triangular design of the sensor element of the sensor signal generated during a rolling movement is increased. This allows one more accurate measurement than, for example, a rectangular sensor element. Another advantage is that the film area required is reduced. Furthermore, one triangular sensor element advantageous that from the signal intensity to the Immersion depth of the rolling piston in the rolling bellows can be closed because of the signal intensity depends on the width of the film covered by the bellows. The advantage here is that a constantly changing signal is obtained when the immersion depth is changed and furthermore, only one sensor is required, ie a triangular sensor element can be one Replace cascade of rectangular sensor elements.

According to a development of the invention according to claim 6, the Air spring on several strip-shaped sensor elements. The strip-shaped sensor elements are preferably arranged one below the other in the axial direction. From the number of Sensor elements that are on the rolling piston during a rolling movement of the bellows are covered, the depth of penetration of the rolling piston into the bellows results.

According to a development of the invention according to claim 7, the several strip-shaped sensor elements of different lengths. The Sensor elements are preferably in turn arranged one below the other in the axial direction, wherein them along a direction of movement of the bellows on the rolling piston after their Length are sorted. The envelope of the sensor elements of different lengths can be used again give a triangular shape. A particular advantage of this embodiment is to be seen in the fact that they take advantage of triangular training with the advantages of Combination of multiple strip-shaped sensor elements allowed. In particular, an appropriate choice of the strip lengths of the sensor elements can be used non-linear, for example exponentially increasing total output signal of the Generate sensor elements depending on the depth of penetration of the rolling piston into the bellows.

According to a development of the invention according to claim 8 Sensor element at least partially embedded in an elastomer. This will make the sensor element well against external mechanical influences that are typical when operating a Road vehicles arise - such as falling rocks etc. - protected and the risk of Damage to the sensor element from such external mechanical influences significantly reduced.

Another advantage of this embodiment results in use of deformable sensor elements that are flat and that are elongated or compression are particularly sensitive. This is both at Strain gauges as well as the case with piezoelectric foils.

Such a flat sensor element preferably faces the Elastomer component a relatively small thickness, that is, preferably each Direction of expansion of the elastomer component at least five times the thickness of the Sensor element. Furthermore, the thickness of the sensor element is preferably significantly less than its width and height, so that the sensor element in the first approximation as a flat two-dimensional structure can be viewed.

By embedding the flat sensor element in the elastomer deformations of the elastomer due to an external mechanical pressure of the Roll bellows on the rolling piston during a rolling movement on the flat sensor element transferred so that this lengthens along with the elastomer can. The elastomer is preferably a rubber, rubber or gel material.

According to a development of the invention according to claim 10, the sensor element is surrounded on all sides by the elastomer and electrically insulated from the elastomer if the elastomer is electrically conductive. For this purpose, an electrically insulating adhesion promoter can advantageously be used, which improves the adhesion between the sensor element and the surrounding elastomer component and additionally electrically insulates the sensor element from the elastomer component. The advantage of this development can be seen in the fact that the adhesion promoter ensures good adhesion of the piezoelectric film to the surrounding elastomer component and thus good power transmission from the elastomer component to the sensor element. In addition, separate electrical insulation of the sensor element is then not necessary. Chemosil 211 , for example, can be used as the electrically insulating adhesion promoter.

According to a development of the invention according to claim 12 is at least the part of the sensor element which is embedded in the elastomer is corrugated. The advantage This development is to be seen in the fact that the sensor element deforms the Elastomer can absorb better due to the wavy shape and thus its Fatigue resistance and lifespan increased.

According to a development of the invention according to claim 13 that is Sensor element embedded in a non-conductive silicone gel, which is partially in a Recess of the rolling piston is arranged. The silicone gel also allows transmission of the mechanical movement acting on the rolling piston during a rolling movement of the rolling bellows Forces on the sensor element embedded in the silicone gel. In an advantageous manner the gel does not fit completely into the recess of the rolling piston, but instead has a game. This ensures that the sensor element is sufficient can deform. Such a game is necessary because rubber essentially is incompressible.

The invention allows the sensor elements both on the rolling piston as well as to attach to the bellows, or to integrate into the bellows. Is essential thereby that when the bellows rolls on the rolling piston, the Sensor elements are successively covered by the roller bellows, so that the corresponding mechanical force to a deformation and a corresponding output signal of the or Sensor elements leads. The corresponding deformation is caused by the embedding of the Guaranteed sensor elements in rubber.

According to a development of the invention according to claim 16, this is Sensor element for emitting an asymmetrical signal during a back and forth movement of the Rolled bellows trained. The asymmetrical signal can be used to determine whether the current direction of movement of the rolling piston into the bellows or is directed out. This information can be used in control electronics Further processing can be entered in order, for example, to match the spring characteristic adapt. Such an asymmetrical signal is obtained, for example, when it is used a trapezoid or T-shaped sensor element.

Furthermore, the invention also allows the relative speed of Roll-off piston and roller bellows to different by detecting the sensor signals To determine times. A resulting speed-dependent signal will also evaluated by the control electronics to make appropriate adjustments for example to make the spring characteristic.

An embodiment and further advantages of the invention are in Explained in connection with the following figures, shows:

Fig. 1 shows an air spring having a rolling bellows and a height sensor of the prior art,

Fig. 2 shows an inventive sensor element,

Fig. 3 shows several vertically arranged to a rolling strip-shaped sensor elements,

Fig. 4 is a triangle-shaped sensor element,

Fig. 5 comprise a plurality of strip-shaped sensor elements having different length and whose envelope is triangular,

Fig. 6 shows the output characteristic of the resulting signal of the sensor elements of FIG. 5,

Fig. 7 is an elastomeric member with a planar sensor element in a schematic representation;

Fig. 8 is an elastomeric member with a wavy sensor element in a schematic representation;

Fig. 9 shows an embodiment of the air spring of the invention with multiple embedded in an elastomeric strip-shaped sensor elements,

Fig. 10 is an asymmetric output of a single sensor element,

Fig. 11 is a flowchart for determining the direction of movement of the rolling piston and the rolling bellows, and

Fig. 12 is a flowchart for determining a speed course of the relative speed of the rolling piston and rolling lobe.

Fig. 2 shows a single sensor deformable member 5. The sensor element 5 can be a strain gauge or an arrangement of strain gauges. Furthermore, the sensor element 5 can be realized as a piezoelectric sensor, preferably by means of a polymeric material, for example a piezoelectric film, in particular made of polyvinylidene fluoride, or from a piezoceramic material. The sensor element 5 is preferably embedded in an elastic material, for example rubber or elastomer, in order to support the lateral deformation of the sensor element when a pressure is exerted by the rolling bellows. If the sensor element 5 is arranged in the area of the roll fold of the bellows instead of on the rolling piston, such embedding is not necessary.

The sensor element 5 has electrical connections 6 and 7 . Electrical connections 8 and 9 go from the connections 6 and 7 to a measuring instrument 10 . If the sensor element 5 is deformed, a corresponding signal is transmitted to the measuring instrument 10 via the lines 8 and 9 . The measuring instrument 10 carries out an analog or digital preprocessing of the signal and delivers an output signal via the line 11 to an electronic evaluation unit 12 .

The sensor element 5 is arranged in a rolling region of the rolling bellows on the rolling piston in such a way that the sensor element 5 is deformed during a rolling movement and thus a corresponding output signal is produced. An immersion of the rolling piston in the rolling bellows is registered by this output signal and evaluated accordingly by the evaluation electronics 12 . As a result of the evaluation in the evaluation electronics 12 , control or regulation processes can be initiated, for example an adaptation of the characteristic of the air spring by switching on an additional volume.

FIG. 3 shows a roll-off piston 13 of an air spring. A plurality of strip-shaped sensor elements 14 are arranged on the rolling piston in the axial direction perpendicular to a rolling movement of a rolling bellows (not shown in FIG. 3) on the rolling piston 13 . Each of the sensor elements 14 has a signal output 15 for outputting a deformation-dependent signal.

For example, a signal output 15 can be logically "1" if the relevant sensor element 14 is deformed, that is to say if a deforming pressure is exerted on the relevant sensor element 14 by the rolling bellows due to a penetration movement of the rolling piston. The signal outputs 15 are in turn fed to evaluation electronics which, for example, determine the depth of penetration of the rolling piston into the bellows from the individual logic signal outputs or carry out other additional evaluations, for example with regard to the speed or frequency of penetration, the direction of penetration or the like.

FIG. 4 shows the roll-off piston 13 with a triangular-shaped sensor element 16. The sensor element 16 has the shape of an acute-angled triangle, the acute angle of the triangle pointing in a direction opposite to the rolling movement. Alternatively, the acute angle can also point in the direction of the rolling movement. According to the embodiment of FIG. 2, the sensor element 16 has connections 6 and 7 as well as lines 8 and 9 in order to supply the output signal of the sensor element 16 to a measuring instrument, not shown in FIG. 4, which in turn emits a signal for evaluation electronics.

The advantage of the embodiment of FIG. 4 in comparison to the embodiment of FIG. 2 is a greater sensitivity with regard to the measurement of the penetration depth of the rolling piston. In particular, the triangular design of the sensor element 16 enables a greater signal steepness to be achieved. It is particularly advantageous that the immersion depth can also be inferred from the sensor signal.

FIG. 5 shows an arrangement corresponding to FIG. 3, the individual sensor elements 18 having different lengths. The sensor elements 18 are arranged such that the length increases from one sensor element 18 to the next by the same amount along the rolling movement. The envelope of the sensor elements 18 is therefore triangular. The individual output signals 19 of the sensor elements 18 can be added together in order to obtain the non-linear course of the resulting output signal shown in FIG. 6.

The X-axis of the diagram in FIG. 6 shows the penetration depth of the rolling piston into the rolling bellows and the Y-axis shows the resulting output signal, which results from adding the individual output signals 19 .

First, with a shallow depth of penetration, only the first sensor element 18 is covered by the bellows along the rolling movement. During the further rolling movement there is then an overlap of the subsequent sensor element 18 , which in comparison to the first sensor element 18 is longer by a defined amount. As a result, the resulting overall signal is not only doubled, but the resulting overall signal is additionally increased by a signal amount that corresponds to the additional defined length of the second sensor element 18 . The further rolling movement therefore results in the substantially exponentially increasing signal curve of the resulting output signal, which is shown schematically in FIG. 7.

Fig. 7a shows an elastomeric member 20, which can consist for example of rubber. The sensor element in the form of a piezoelectric film is embedded in the elastomer component in such a way that it is surrounded on all sides by the elastomer component 20 . The piezoelectric film 21 is flat and its thickness d is substantially smaller than the thickness of the elastomer component 20 and as the depth t and the width b of the film 21 (see FIG. 7b).

The piezoelectric film 21 in turn has connections 6 and 7 , from which electrical lines 8 and 9 lead to the measuring instrument 10 - as shown in FIG. 2. The piezoelectric film 21 is provided on all sides with an adhesion promoter, which is used for an adhesive connection between the film and the surrounding elastomer component and electrically isolating it, including its electrical connections 6 , 7, from the elastomer component 20 . As an alternative to an adhesion promoter, a more arid insulator can also be provided if the insulating effect of the rubber is insufficient. However, an adhesion promoter does not necessarily have to be used.

If a force is exerted on the elastomer component 20 , which acts in the direction of the arrows shown in FIG. 7a, it is compressed as a result of this force. When the force is lost, there is a corresponding relaxation of the elatom component 20 and the piezoelectric film 21 located therein.

During the compression, the elastomer component 20 expands to the side; this expansion disappears again during relaxation. The lateral expansion is transferred to the piezoelectric film 21 embedded in the elastomer component 20 . The film 21 is oriented in the elastomer component 20 such that its surface normal (i.e. the surface normal that is perpendicular to the plane spanned by b and t (see FIG. 1b)) runs parallel to the force acting on the elastomer component 20 that a particularly good transmission of the expansion of the elastomer component 20 to the piezoelectric film 21 is ensured.

In addition, the piezoelectric film 21 is preferably arranged in the vicinity of the edge of the elastomer component 20 . This has the advantage that the deformations of the elastomer component 20 in the edge region are only slight and the film 21 is therefore not destroyed by deformations of the elastomer component 20 which it cannot follow.

FIG. 8 shows an elastomer component 20 which is constructed essentially the same as the component shown in FIG. 7. The only difference is that the piezoelectric film 21 embedded in the elastomer component 20 is corrugated. This has the advantage that a deformation of the elastomer component 20 as a result of the force exerted by the rolling bellows on the rolling piston during a rolling movement can be absorbed by the piezoelectric film 21 without fatigue.

The Fig. 9 shows the roll-off piston 22 of an air spring with the rolling fold of the rolling bellows 23 24th A rubber layer 25 is located on the surface of the rolling piston 22 . Strip-shaped sensor elements 26 are arranged on the surface of the rubber layer 25 , as shown in FIG. 3 or FIG. 5.

A further rubber layer 27 follows the sensor elements 26 , so that the sensor elements 26 are surrounded on both sides by a rubber layer. The arrangement consisting of the rubber layers 25 and 27 and the sensor elements 26 can be implemented in a coherent elastomer component 28 .

Depending on the position of the roller fold 23 , different sensor elements 26 of the elastomer component 28 are acted upon by a pressure which acts essentially perpendicularly on the elastomer component 28 , so that this extends longitudinally, inter alia, in a direction perpendicular to the plane of the drawing in FIG. 10. This linear expansion is transmitted to the corresponding sensor elements 26 , which leads to a corresponding output signal. The output signals obtained in this way are fed to an electronic evaluation system as explained in relation to FIGS. 2, 3, 4 and 5. For example, the height and speed of the air spring can be determined.

It is of particular advantage in the embodiment of FIG. 9 that the elongation of the elastomer component 28 is at least partially transmitted to the sensor elements 26 , so that an appropriately accurate and easily evaluable output signal is obtained. Alternatively, the elastomer component 28 can also be integrated in a region of the rolling bellows 24 , which corresponds to the rolling fold 23 , or can be vulcanized in, for example, glued thereon. In the event that the bellows 24 consists of a material of a corresponding elasticity, one of the rubber layers 25 , 27 can be replaced by the surface of the bellows 24 .

Fig. 10 shows an output signal of a single sensor element, which was determined at a periodic oscillation of the air spring. As can be seen from FIG. 11, the waveform is asymmetrical. In particular, the waveform due to rollover during the upward movement of the roller fold is different from the signal shape during the downward movement. It can thus be determined from the signal curve which relative movement the rolling piston and the bellows execute at a given point in time.

If a plurality of sensor elements are arranged one above the other - as is the case, for example, in the embodiment of FIGS. 3, 5 and 10 - the individual sensor elements each give time-shifted signal profiles which correspond to the signal profile shown in FIG. 11. The direction of movement "roll up" or "roll down" can also be recognized from the time shift of the individual signals obtained in this way. The speed of the rolling movement can also be determined from this.

Fig. 11 shows a corresponding schematic flow chart. In step 121 , the signal shape of the output signal supplied by a sensor element is first detected.

In step 122 , the edge of the signal is compared with a typed waveform, which corresponds to the upward or downward movement, and is correlated therewith. Based on this correlation, a decision is then made as to whether it is an upward or downward movement. A corresponding signal is output to control electronics, which processes this signal in step 123 .

FIG. 12 shows a schematic flow diagram for determining the compression speed. In step 131 , a signal level S _{1 of} a sensor element is first detected at a first time T ₁ . The sensor element can be an element corresponding to FIG. 2 or FIG. 4; However, it may also be a plurality of superposed strip-shaped sensor elements corresponding to Fig. 3, act 5 and 10, wherein the signal level is then obtained by the addition of the individual signals of the sensor elements.

In step 132 , a corresponding detection of the signal level S _{2 takes place} at a subsequent time T ₂ . From the difference between the signal levels, a signal is then determined in step 133 which is proportional to the speed of movement of the rolling piston and the bellows.

This signal is fed to control electronics. The speed curve is determined in step 134 by continuous input of a corresponding speed-dependent signal. In step 135 , the spring characteristic is adjusted by the control electronics, for example by correspondingly increasing or decreasing the compressed air pressure in the air spring in accordance with the speed curve determined in step 134 . LIST OF REFERENCE NUMBERS 1 rolling bellows
2 rolling pistons
3 pressure sensors
4 roll fold
5 sensor element
6 connections
7 connections
8 lines
9 lines
10 measuring instrument
11 line
12 evaluation electronics
13 rolling piston
14 sensor element
15 signal output
16 sensor element
17 output signal
18 sensor element
19 output signal
20 elastomer component
21 piezoelectric film
22 rolling piston
23 roll fold
24 roller bellows
25 rubber layer
26 sensor element
27 rubber layer
28 elastomer component

Claims (18)

1. Air spring, especially for road vehicles, with
a rolling piston ( 2 ; 22 ) and a bellows ( 1 ; 24 ) and with
at least one sensor element ( 5 ; 14 ; 16 ; 18 ; 26 ), which is arranged in a roll-off area and emits an electrical signal when it is deformed. 2. Air spring according to claim 1, wherein the sensor element as a strain gauge is trained. 3. Air spring according to claim 1, wherein the sensor element as a piezoelectric Sensor element is formed. 4. Air spring according to claim 3, wherein the sensor element is a polymeric material, preferably a piezoelectric film, in particular a film Has polyvinylidene fluoride, and / or a piezoceramic material. 5. Air spring according to one of the preceding claims, in which the sensor element is triangular. 6. Air spring according to one of the preceding claims, with several in Essentially strip-shaped sensor elements. 7. Air spring according to claim 6, wherein the strip-shaped sensor elements have different lengths and perpendicular to a direction of movement of the Roll bellows are arranged with increasing length. 8. Air spring according to one of the preceding claims, wherein the sensor element is at least partially embedded in an elastomer ( 20 ). 9. Air spring according to claim 8, wherein the elastomer is rubber, rubber or a gel is. 10. Air spring according to claim 8 or 9, wherein the sensor element in such a way Is embedded elastomer that it is surrounded on all sides by the elastomer, and that Sensor element is electrically insulated from the elastomer when the elastomer is electrically conductive. 11. Air spring according to claim 8, 9 or 10 in the one surface of the sensor element is provided with an electrically insulating adhesion promoter, the liability between the surface and the elastomer improved and the sensor element electrically insulated from the elastomer. 12. Air spring according to one of claims 8 to 11, in which at least part of the Sensor element, which is embedded in the elastomer, is corrugated. 13. Air spring according to one of the preceding claims, wherein the sensor element in a non-conductive silicone gel is embedded, and the silicone gel partially in one Recess is arranged in the rolling piston. 14. Air spring according to one of the preceding claims, in which the sensor element the rolling piston is attached. 15. Air spring according to one of the preceding claims, in which the sensor element the roll bellows is attached, or is integrated in the roll bellows. 16. Air spring according to one of the preceding claims, wherein the sensor element for delivering an asymmetrical signal during a back and forth movement of the Roll bellows is formed. 17. A method for controlling an air spring according to one of the preceding claims, comprising the following steps: Detection of the signal shape of the signal emitted by the sensor element, - Determining the direction of movement of the bellows from the signal shape, and - Evaluation of the determined direction of movement in control electronics. 18. A method for controlling an air spring according to one of claims 1 to 16, comprising the following steps: Detection of a signal value of the signal emitted by the sensor element at a first point in time, Detection of the signal value at a second point in time, - Determination of a speed-dependent signal from the difference between the signal values at the first and the second point in time, and - Evaluation of the speed value in control electronics.