JPH0522803Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a capacitive cylinder displacement meter for detecting changes in vehicle height due to changes in the load of an automobile.

(Prior Art) Conventionally, as a device for detecting a change in vehicle height due to a change in the load of an automobile, a device that detects changes in the expansion and contraction of a shock absorber has been developed, for example, in 1983-
It is disclosed in No. 88609 and No. 57-177113.

In these conventional shock absorbers that detect changes in vehicle height, a coil is buried inside a cover made of non-conductive and non-magnetic material over the entire stroke detection area, separately from the shock absorber body. The displacement of the piston rod relative to the cylinder tube is detected by connecting it to an LC oscillator and detecting changes in the inductance of the coil. However, burying the coil in this way increases the number of parts and assembly man-hours, resulting in high costs. This has the disadvantage that changes in inductance cannot be detected accurately and stably due to the influence of noise from the sensor, resulting in low displacement detection accuracy.

In order to eliminate such drawbacks, the applicant of the present application proposed a shock absorber as shown in FIG. 4 in Japanese Patent Application No. 107685/1983. This shock absorber is of a so-called twin-inch tube type in which oil 3 is housed in tubes of different diameters in an inner cylinder 1 and an outer cylinder 2. An electrically insulated capacitor is constructed, and the relative position between the inner cylinder 1 and the piston rod 4 is detected by detecting the capacitance of this capacitor.

In FIG. 4, the inner cylinder 1 and the piston rod 4 are insulated by an insulating member 7 interposed between the piston 5 and the sliding ring 6 and an insulating member 9 interposed between the rod guide 8 and the piston rod 4. There is. The inner cylinder 1 and the outer cylinder 2 also have a chamber 11 formed in the upper part by a rod guide 8 and an oil seal 10 provided above it between the outer cylinder 2 and the piston rod 4, and a chamber 11 formed in the rod guide 8. It communicates via a bypass 12, and communicates via an orifice 13 and a constant plate 14 in the lower part. The detection circuit unit 15 is attached to the upper end of the shock absorber, and the inner cylinder 1 and the piston rod 4 are connected here.
A CR oscillation circuit whose parameter is the capacitance between the Based on the capacitance that changes as it moves up and down within the inner cylinder 1.
The oscillation frequency of the CR oscillation circuit is detected to detect the relative position between the inner cylinder 1 and the piston rod 4, and furthermore, the change in vehicle height is detected based on the relative position.

In such a shock absorber, a capacitor is formed by electrically insulating the inner cylinder 1 and the piston rod 4, which are originally provided in the shock absorber, and the inner cylinder is connected by detecting the capacitance of this capacitor. Since the structure is configured to detect the relative position between the piston rod 1 and the piston rod 4, the number of parts and the number of assembly steps are reduced, and costs can be significantly reduced. Furthermore, since it detects capacitance, it is less affected by external noise than conventional methods that detect coil inductance, and the amount of displacement can be detected more accurately. Furthermore, unlike the conventional method in which the coil is provided separately, there are no restrictions on mounting the sensing section, and it can be applied to shock absorbers of any structure as long as they are co-cylindrical. It also has the advantage of greatly expanding the range of applications.

(Problems to be Solved by the Invention) However, according to various experiments conducted by the present inventors, it has been found that the shock absorber shown in FIG. 4 has the following defects.

That is, when a shock absorber is mounted on a vehicle or the like, it is usually mounted via a rubber bushing in order to absorb vibrations and ensure stable shock absorber function. Carbon black is mixed into this rubber bushing to improve its durability, and therefore it exhibits conductivity, but the resistance value is too high to ground the outer cylinder 2 and the inner cylinder 1 through this rubber bushing, and the outer cylinder 2 and the inner cylinder 1 are difficult to reliably ground to the body, resulting in a problem that the capacitance cannot be stably detected. Further, since the shock absorber requires sufficient mechanical strength, the outer cylinder 2 is usually formed of a rolled steel plate, and its surface is provided with a coating layer of sufficient thickness in consideration of installation under the floor of the vehicle. However, forming the outer cylinder 2 from a rolled steel plate in this way requires mechanical processing, which increases costs, and if a coating layer is provided on the surface, since this is electrically insulating, There is also the problem that stray capacitance is formed through this paint layer, which causes detection errors. Furthermore, in the above-mentioned shock absorber, since the piston rod 4 is set at an opposite (positive) potential to that of the body arm, at the portion where it protrudes from the inner cylinder 1, the piston rod 4 and other members near the body that are grounded are An undesired stray capacitance is formed between the two, which causes a decrease in detection accuracy.

This idea was created by focusing on the above-mentioned problems. Rather than incorporating a displacement meter into the shock absorber, it can be made simple and inexpensive by configuring it exclusively for the displacement meter. The object of the present invention is to provide a capacitive cylinder displacement meter that can stably detect capacitance.

(Means for Solving the Problems) The capacitive cylinder displacement meter of the present invention includes an outer cylinder made of conductive resin that is electrically connected to the vehicle body, and an external cylinder inside the outer cylinder. A conductive inner cylinder provided insulated from the cylinder, an insulating piston slidably provided inside the inner cylinder, an upper end supported by the piston, and a lower end connected to the vehicle via a rubber bushing. an electrically conductive rod connected to a swinging portion of the piston so as to be movable relative to the piston while electrically insulating the inside of the inner cylinder from the inner cylinder; a retractable conductive dust boot whose other end is connected to the lower end of the rod and electrically connects the outer tube and the rod; , a detection means for detecting the displacement of the swinging portion with respect to the vehicle body by using the inner cylinder as a common electrode and detecting the capacitance formed between these electrodes; and an upper part of the outer cylinder communicating with the inside of the outer cylinder. a liquid chamber formed between an outer peripheral wall of the inner cylinder and an inner peripheral wall of the outer cylinder; , a communication hole that communicates with one liquid chamber and the other liquid chamber in the inner cylinder that are isolated by the piston, a communication hole that communicates between the outer cylinder and the storage tank, and a communication hole that is formed in the piston. , a communication hole communicating between one liquid chamber and the other liquid chamber in the inner cylinder separated by the piston.

(Function) In this configuration, the outer cylinder and the rod are electrically connected via the conductive dust boot.
Therefore, by attaching the outer cylinder directly to the automobile chassis, the outer cylinder and the rod can be reliably grounded to the body without interfering with the vertical movement of the rod due to the rocking of the vehicle. Even if there are other grounded members in the vicinity of the rod, undesired stray capacitance will not be formed, and detection accuracy can be effectively prevented from being degraded due to damage to the rod caused by flying stones. can. In addition, since the outer cylinder is made of conductive resin, it is easy to mold, so it can be done easily and inexpensively without requiring mechanical processing, and since the entire cylinder is conductive, it acts as a shield against external noise. also have

(Embodiment) FIG. 1 shows an embodiment of the present invention.
The outer cylinder 31 is molded from conductive resin. As the conductive resin, we use a material with a conductivity of 10 ⁰ to ^{10 1} Ω-cm, which is made of 6-nylon and mixed with brass pieces and has excellent corrosion resistance, mechanical strength, and heat resistance. Form to a thickness of 2 mm or more. A conductive inner cylinder 32 is provided inside this outer cylinder 31, and this inner cylinder 3
An electrically conductive rod 33 is provided which penetrates into and moves relative to each other.

The inner cylinder 32 is fixed at its lower end within the outer cylinder 31 by an insulating guide 34, and its upper end extends coaxially with an insulating member 35 interposed between the inner cylinder 32 and the outer cylinder 31 so as to be insulated from each other within the outer cylinder 31. make it exist Also, Rod 3
3 is slidably held on the guide 34 so as to be able to move coaxially within the inner cylinder 32, and the inner cylinder 3
An insulating piston 36 is provided at the tip that enters into the inner cylinder 32 so as to be able to slide on the inner circumferential surface of the inner cylinder 32.
2, so as to be movable relative to each other while being insulated from each other.

A seal 37 is provided at the lower end of the outer cylinder 31 between the outer cylinder 31 and the rod 33 below the guide 34, a cover 38 is provided below the seal 37, and a cover 38 is provided at the upper end above the insulating member 35. A storage tank 41 is provided.

The storage tank 41 has a bottom portion 41a formed integrally with the outer cylinder 31, and is integrally welded to the bottom portion 41a.
It is comprised of an outer cylinder 31 that is attached to the chassis of a vehicle and a container portion 41b made of the same material. As shown in FIG. 2A, which is a partial plan view, and FIG. 2B, which is a sectional view taken along the line II in FIG. Protrusions 44 are formed radially on the bottom surface 43 toward the bottom surface 43, and a ring-shaped member 45 is formed concentrically with the opening 42 above the bottom surface 43 at the tips of these projections 44.
A plurality of arc-shaped outlets 46a and a circular outlet 46b
and form.

Further, in this embodiment, a coil spring 47 is provided between the ring-shaped member 45 and the insulating member 35, which presses and biases the inner cylinder 32 toward the guide 34, thereby pushing the inner cylinder 32 in the direction of relative movement of the rod 33. The structure is such that the inner tube 33 is always positioned at a predetermined position within the outer tube 31 by absorbing expansion and contraction due to machining dimensional errors and temperature changes.

In this embodiment, oil 48 is contained in the outer cylinder 31 and the inner cylinder 32, respectively, and the oil 48 is contained in the outer cylinder 31 and the inner cylinder 32,
3 are used as electrodes, and the capacitance formed between them is measured to detect their relative positions. However, the space between the inner cylinder 32 and the rod 33 is always filled with oil 48 regardless of their relative movement. In order to
Oil 48 is also stored in the storage tank 41.
and the inner cylinder 32 are communicated with each other. Therefore, as shown in FIG. 2B, the insulating member 35 has an opening (communication hole) for communicating the inner cylinder 32 and the storage tank 41.
35a is formed. The amount of oil 48 accommodated in the outer cylinder 31, inner cylinder 32, and storage tank 41 is such that even when the rod 33 protrudes the most from the inner cylinder 32 in the vertical direction, the oil 48 remains in the storage tank 41. . In addition, in order to prevent reaction forces caused by the relative movement of the inner cylinder 32 and the rod 33, damping force of the oil 48, etc. from occurring, air may be mixed into the inner cylinder 32 due to the generation of these forces. In order to prevent this, the insulating member 35 is provided with a bypass (communication hole) 35b for communicating the upper and lower chambers in the outer cylinder 31, as shown in a partial plan view in FIG. Similarly, a bypass (communication hole) 34a is formed in the piston 34, and a through hole (communication hole) 36a is formed in the piston 36 for communicating the upper and lower chambers in the inner cylinder 32. The oil 48 is configured to flow smoothly in accordance with the relative movement of the rod 33.

On the other hand, the end of the rod 33 protruding from the inner cylinder 32 is movably provided with a mounting screw 49 for attaching it to the axle of a vehicle via a rubber bushing. In order to ensure that the outer cylinder 31 and the rod 33 are at the same potential to prevent the formation of undesirable stray capacitance, the rod should be connected to the lower end to prevent the formation of undesirable stray capacitance, and at the same time, to prevent the rod from being hit by stones etc. In order to prevent damage to the rod 33, a conductive dust boot 50 is provided as a means for electrically connecting the rod 33 and the outer cylinder 31. The dust boot 50 is made of a material having a conductivity of about 10 ⁰ to ^{10 1} Ω-cm, which is made by dispersing carbon black in a base resin made by polymerizing styrene-butadiene rubber and ethylene, and is formed into a bellows structure. It is configured to be able to expand and contract in accordance with the relative movement of 33.

Further, the outer cylinder 31 is provided with a detection circuit (detection means) 51 that detects the capacitance of the capacitor constituted by the inner cylinder 32 and the rod 33 and outputs a required signal corresponding to their relative positions. . In order to prevent the formation of undesired stray capacitance, this detection circuit 51 is connected to the inner cylinder 32 which forms a desired capacitance.
CR oscillation using the electrostatic capacitance between the inner cylinder 32 and the rod 33 as a parameter is mounted on the printed circuit board 51a in the same way as explained in FIG. 6. circuit,
A signal processing circuit or the like is provided that divides the oscillation frequency of this CR oscillation circuit and outputs a low frequency pulse signal.

In this embodiment, the rod 33 as one electrode forming the required capacitance is connected to the dust boot 50.
and the detection circuit 51 via the outer cylinder 31. In order to electrically connect the outer cylinder 31 and the detection circuit 51, one electrode wiring of the printed circuit board 51a should be in contact with the conductive pin 52. Then, the conductive pin 52 is attached to the receiver 31a formed integrally with the outer cylinder 31, thereby electrically connecting the outer cylinder and therefore the rod 33 to one electrode wiring of the detection circuit 51, and simultaneously printing. The substrate 51a and therefore the detection circuit 51 are fixed to the outer cylinder 31. In addition, the inner cylinder 32 as the other electrode forming the required capacitance is connected to the outer cylinder 31 and the printed circuit board 51.
It is connected to the other electrode wiring of the printed circuit board 51a via an electrode rod 53 that extends through a. For this reason: the outer cylinder 31 has a hole 3 into which the electrode rod 53 is loosely fitted.
1b, and a case 31c that protrudes to surround this hole 31b is integrally molded with the outer cylinder 31. Further, an insulating seal rubber 54 is hot-glued to the electrode rod 53 to form an integral structure, and this seal rubber 54 is attached to the case 31c by an insulating collar 55.
Press and hold inside. As a result, the tip of the electrode rod 53 can be attached to the inner tube 31 without touching the outer tube 31.
The oil leakage from the hole 31b is prevented. In addition, the printed circuit board 51a
Connect the cord 56 to the other electrode wiring and signal output terminal to which the electrode rod 53 is connected. After the detection circuit 51 is mounted on the outer cylinder 31 in this way, The mounting part including the part is molded with an insulating material.

In the above-mentioned configuration, the container portion 4 of the storage tank 41
1b is directly attached to the chassis of the vehicle, and the rod 33
When the mounting screw 49 is attached to the axle via the rubber bushing so that the rod 33 extends in a substantially vertical direction, the outer cylinder 31 and the rod 33 are dust-proof.
Since they are electrically connected via the boot 50, they are reliably earthed to the body. Therefore, by connecting the cord 56 connected to the electrode bar 53 to the other electrode terminal of the DC power supply mounted on the vehicle, the required voltage can be reliably applied between the inner cylinder 32 and the rod 33.

Here, if the inner diameter of the inner cylinder 32 is a, the outer diameter of the rod 33 is b, the penetration length of the rod 33 into the inner cylinder 32 is l, and the dielectric constant of the oil 48 is ε, then the inner cylinder 32 and the rod 33 are The capacitance C of the constituting capacitor is expressed by the following equation.

C=2πεl/log(a/b) As is clear from the above equation, the capacitance C changes depending on the penetration length l of the rod 33 into the inner cylinder 32. Therefore, by detecting the capacitance C in the detection circuit 51, the vehicle height and its changes can be stably detected from the relative position information between the inner cylinder 32 and the rod 33 based on the capacitance C. I can do it. Note that the dielectric constant of oil generally has a negative coefficient dependence on temperature, but this temperature dependence is
The oscillation resistance of the CR oscillation circuit can be offset by giving a part of the oscillation resistance a temperature characteristic that is opposite to the temperature dependence of the dielectric constant. Detection can be performed.

Note that the present invention is not limited to the above-described embodiments, and can be modified or changed in many ways. For example, the storage tank 41 can be configured with a bellows that separates oil from the outside air and is filled with oil, and whose volume can change according to the relative movement of the inner cylinder 32 and the rod 33. In this case, the storage tank 41 can be attached to any part of the outer cylinder 31. Furthermore, the capacitance of the capacitor composed of the inner tube 32 and the rod 33 can be detected not only by the CR oscillation circuit, but also by using other circuits such as an LC oscillation circuit, and by displacing the detection circuit 51. It can also be installed separately from the meter body.

(Effects of the invention) As described above, according to the invention, the outer cylinder is formed of a conductive resin, and the outer cylinder and the rod are electrically connected via a conductive dust boot. As a result, these can be reliably maintained at the same potential without interfering with the vertical movement of the rod due to the rocking of the vehicle. This effectively prevents the formation of undesired stray capacitance, and also effectively prevents the rod from being damaged by flying stones. Furthermore, since the entire outer periphery of the displacement meter is covered with an outer cylinder and dust boot made of conductive resin to maintain the same potential as the vehicle body, it is possible to provide a shielding effect against electromagnetic noise from the outside. Therefore, the capacitance between the inner cylinder and the rod can be stably measured, and thereby changes in the vehicle height of the automobile can be detected with high accuracy. Further, since the outer cylinder is made of conductive resin and can be obtained by molding, no mechanical processing is required, and therefore it can be made easily and inexpensively. Furthermore, since the present invention is constructed exclusively for the displacement meter, it can be used stably for a long period of time compared to when it is incorporated into a shock absorber, and it also prevents damage between the outer cylinder and the inner cylinder, and between the inner cylinder and the rod. can be easily insulated, and the overall process can be done simply and inexpensively. Furthermore, in the present invention, a storage tank for storing a liquid made of a dielectric substance that communicates with the inside of the outer cylinder and compensates for the volume of the liquid inside the outer cylinder is provided in the upper part of the outer cylinder, and a storage tank is provided in the upper part of the outer cylinder to store a liquid made of a dielectric material that communicates with the inside of the outer cylinder and compensates for the volume of the liquid in the outer cylinder. A communication hole that communicates between the liquid chamber and both liquid chambers in the inner cylinder separated by the piston, a communication hole that communicates between the outer cylinder and the storage tank, and a communication hole that communicates both liquid chambers in the inner cylinder through the piston. Since we provided a communication hole,
It can effectively prevent the generation of reaction force and damping force of the liquid due to relative movement between the inner cylinder and the rod, and therefore, it is effective to prevent air from entering from the seal part due to the generation of negative pressure inside the liquid, and the generation of air due to cavitation. In addition, it is possible to effectively compensate for changes in the volume inside the inner cylinder due to relative movement, and it is possible to constantly fill the portion constituting the capacitor with dielectric material.

Therefore, it is possible to effectively prevent the variable capacitance formed between the inner cylinder and the rod and the fixed capacitance formed between the outer cylinder and the inner cylinder from changing due to the inclusion of air. Since this can be prevented, the relative position between the inner cylinder and the rod, that is, the displacement of the swinging portion with respect to the vehicle body, can always be detected with high precision.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIGS. 2A, B, and 3 are partial detailed views thereof, and FIG. 4 is a diagram showing a shock absorber previously proposed by the applicant. 31... Outer cylinder, 32... Inner cylinder, 33... Rod, 34... Guide, 35... Insulating member, 36...
...Piston, 37...Seal, 38...Cover,
41...Storage tank, 47...Coil spring, 48...
Oil, 49...Mounting screw, 50...Dust boot, 51...Detection circuit.

Claims (1)

[Scope of claim for utility model registration] An outer cylinder made of conductive resin that is electrically connected to the vehicle body, and a conductive inner cylinder provided within the outer cylinder insulated from the outer cylinder. and an insulating piston that is slidably provided inside the inner cylinder, the upper end of which is supported by the piston, and the lower end of which is connected to a swinging part of the vehicle via a rubber bushing. a conductive rod that is electrically insulated from the inner cylinder and movable relative to the piston; one end of the rod is located at the lower end of the outer cylinder, and the other end is located at the lower end of the rod; an expandable and retractable conductive dust boot that is connected to the outer tube and the rod and electrically connects the outer tube and the rod; a detection means configured to detect the displacement of the swinging portion with respect to the vehicle body by detecting the capacitance of the body; a storage tank for storing a liquid made of a compensating dielectric; a liquid chamber formed between an outer peripheral wall of the inner cylinder and an inner peripheral wall of the outer cylinder; and one of the liquid chambers in the inner cylinder separated by the piston. A communication hole that communicates between the liquid chamber and the other liquid chamber, a communication hole that communicates between the outer cylinder and the storage tank, and a communication hole that is formed in the piston and is isolated by the piston. A capacitive cylinder displacement meter characterized by comprising a communication hole that communicates one liquid chamber with the other liquid chamber.