EP0353117A1 - Device to detect the position of a moving member inside a fixed member - Google Patents

Abstract

The invention relates to a device for measuring the position of a movable member relative to a fixed member, the fixed member being one of the walls of a booster housing (14) and the movable member being a piston means. (16) dividing the housing into a front chamber and a rear chamber, comprising a first movable means (42), movable with the movable member (16) and the displacement of which is identified with respect to a second fixed means (26) by relative to the fixed member (14). According to the invention, the second fixed means (26) is fixed to the fixed member (14) outside the housing (14) of the booster, the first mobile means (42) sliding relative to the second fixed means (26 ) so as to vary at least one electrical quantity as a function of the position of the first mobile means (42) relative to the second fixed means.

Description

The present invention relates to a device for detecting the position of a movable member inside a fixed member which surrounds it, and more particularly to a piston means of a pneumatically actuated servomotor, inside of this servo motor.

In the automobile industry, it has become common to assist various commands, actuated by the driver of a vehicle, such as braking, declutching, or other commands, by various force amplifying devices which, for a same exit effort, require only a limited effort from the driver.

Such amplifying devices are commonly constituted by pneumatic servomotors comprising a housing divided into a front chamber and a rear chamber by means of piston displaceable from a rest position close to the rear wall of the housing. These pneumatic actuators have fully satisfactory operation.

However, for reasons of safety and / or proper functioning, it is desirable to know at all times the state of these amplifying devices, in order to activate an alarm signal in the event of failure, to control other devices or to influence a feedback loop.

Document FR-A-2 509 883 discloses a declutching assistance servomotor comprising a meter for measuring the position of the actuator travel, consisting of a conductive strip extending in the direction of this travel, and a socket carried by the movable rod of the booster, the conductive strip and the socket together forming a linear potentiometer delivering a measurement signal to control the operation of the booster.

In this document, the metering device is integrated into the booster casing, which requires the latter to be of a special and relatively complex design, prohibiting its use on servomotors of conventional design.

To overcome this drawback, the invention aims to provide a device for measuring the position of the piston means in a pneumatically actuated servomotor, which is adaptable to housings of servomotors of known type without modification of the latter.

To this end, the invention provides a device for measuring the position of a movable member relative to a fixed member, the fixed member being one of the walls of a booster housing and the movable member being a means of piston dividing the housing into a front chamber and a rear chamber, comprising a first movable means, movable with the movable member and the displacement of which is identified with respect to a second fixed means with respect to the fixed member, characterized in that the second fixed means is fixed to the fixed member outside the booster housing, the first movable means sliding relative to the second fixed means so as to vary at least one electrical quantity as a function of the position of the first movable means compared to the second fixed plea.

• - la Figure 1 représente en coupe longitudinale un dispositif de détection selon un premier mode de réalisation de l'invention, et
• - la Figure 2 représente une vue analogue d'un deuxième mode de réalisation de l'invention.

Other characteristics and advantages of the present invention will emerge from the following description, given by way of illustration with reference to the appended drawing, in which:

• FIG. 1 shows in longitudinal section a detection device according to a first embodiment of the invention, and
• - Figure 2 shows a similar view of a second embodiment of the invention.

In FIG. 1, there is shown in section a detection device 10, according to a first embodiment of the invention, fixed on a servomotor 12. This booster is constituted in a known manner by a housing 14 internally divided by a piston means 16 into two chambers 18 and 20 selectively intercommunicating. The housing 14 has an opening 22 into which the detection device 10 is inserted in a leaktight manner by means of an elastic seal 24.

The detection device 10 is mainly constituted by a body 26 of electrically conductive material, and of cylindrical shape, of which a portion 28 of reduced diameter is provided on its periphery with annular grooves 30, the portion 28 being able to engage in the seal 24 in leaktight manner, the grooves 30 forming in a known manner a system for retaining the device 10 in the seal 24.

The body 26 is provided with a bore 32 into which opens another bore 34, of smaller diameter formed in the part 28 of reduced diameter. In the bore 32 is introduced an electrically insulating sleeve 36, and in the bore 34 is introduced a ring 38, electrically conductive, and of the same internal diameter as that of the sleeve 36, so as to define a continuous bore 40.

In the bore 40, formed subsequently of the bores made in the sleeve 36 and the ring 38, slides a rod 42, made of electrically conductive material, extending outside of the part 28, and therefore inside from chamber 18, to the piston means 16. The rod 42 is held in contact with the piston means 16 by spring 44, bearing on one side on the ring 38, and on the other on a shoulder 46 formed at the end of the rod 42. This rod has longitudinal grooves 48, connecting the chamber 18 and the interior of the bore 40.

In the sleeve 36 is formed a longitudinal groove 50, at the bottom of which is deposited an electrically conductive track 52, and resistive such as those used in the linear potentiometers. the end of the rod 42 penetrating into the bore 40 carries an elastic metal tongue 54, capable of rubbing on the track 52, so as to form a movable contact between the rod 42 and the track 52. The rod 42 also comprises, in the vicinity of the tongue 54, a finger 56, penetrating into the groove 50, and serving both to immobilize in rotation the rod 42 relative to the sleeve 36, and to form a stop preventing the rod 42 from coming out of the bore 40 under the effect of the spring 44.

The body 26 is finally closed in a sealed manner, at its end opposite to that which is fixed to the housing 14, by a plug 58 provided with a passage 60 for a conductive wire 62 electrically connected to the end closest to the track 52.

Thus, during the operation of the servomotor 12, that is to say when the piston means 16 moves, for example in the direction of the arrow F, the rod 42 moves at the same time as the piston means 16 thanks to the spring 44 now still applied to it by one of its ends. The other end therefore displaces the elastic tongue 54 on the track 52. The electrical circuit formed by the wire 62, the track 52, the tongue 54, the rod 42, the ring 38 and the body 26 therefore has a variable electrical resistance. as a function of the position of the piston means 16 thanks to the potentiometric track 52. An appropriate electronic circuit connected to the terminals of this variable resistance, will therefore provide a signal representative of the position of the piston means 16 inside the booster housing , this signal can be used to control other devices or for signaling purposes.

The detection device which has just been described requires for its assembly, the production of an opening in the booster housing, and therefore the use of a seal. The increase in the number of openings in a pneumatic device multiplies the risk of leaks, which can cause degradation, or even complete stoppage, of the operation of the pneumatic device.

This is why, according to a preferred embodiment of the invention shown in Figure 2, the device for detecting the position of the piston means is mounted in one of the openings already made in the booster housing and necessary for its operation. . These openings are connected, on one side of the booster, the air supply at atmospheric pressure, and on the other side, to a vacuum source.

Thus seen in Figure 2 a device for detecting the position of the piston means of a booster, similar to that of Figure 1, where the same elements are identified by the same mechanical references.

The body 26 of the device 10 is laterally provided with a hollow extension 70. An opening 72 is made in the body 26 so as to communicate the interior of the bore 32 with the interior of the extension 70, the sleeve 36 having also an opening 74 allowing communication between the interior of the bore 40 with the interior of the extension 70. On the extension 70 can be fixed a hollow end piece 76 allowing connection to a pneumatic pipe (not shown). In the case where this pneumatic pipe is connected to a vacuum source, provision is generally made for interposing a non-return valve ensuring the maintenance of a reduced pressure in the chamber 18 during periods of non-operation. Such a valve can advantageously be integrated into the detection device 10, the opening 72 constituting a first valve means by its edges 78 forming the seat of a second valve means 80, held in the rest position by a return spring 82 bearing on its end 76 from its other end.

In each of these embodiments, it is possible to provide an automatic adjustment system for the length of the rod 42, to take account of the play due to the manufacturing tolerances of the booster, that is to say variations in the distance at rest between the piston means 16 and the housing 14.

It can thus be seen that the invention provides a means of knowing at all times the position of the piston means in a booster without any modification of the latter, and therefore applicable to any type of existing booster.

It is obvious that the invention is susceptible of numerous variants without going out of its mind. Thus the body of the device can be made of molded plastic, the electrical contacts being made by crossings of sealed wires. Similarly, in cases where it is sufficient to identify only a few discrete positions of the piston means, the device of the invention can be simplified, as well as the associated electronic circuit. We can for example provide that the track 52 is discontinuous, that is to say formed of conductive pads arranged at appropriate distances corresponding to the positions to be identified, each pad being connected to an external electrical contact and therefore giving all or nothing the information of the passage of the piston means through a predetermined position, for example start of travel, intermediate position and end of travel. In this case, provision may be made for the end of the rod which enters the bore 40 to be provided with a permanent magnet, while flexible blade switches will be buried at different locations in the body 26 or the sleeve 36 and actuated by the passage of the permanent magnet at their level. It is also possible to provide for a winding or solenoid coaxially with the bore 40, the rod 42 then acting as a plunger and modifying the inductance of the winding, which can be measured at its terminals. We can also plan to make the rod 42 in dielectric material, and to have two conductive plates in the body 26 so as to form a capacitor whose capacity will depend on the position of the rod.

Finally, the invention is applicable to any type of booster, for braking assistance, declutching, whether simple or in tandem. For a brake booster, it could for example be provided that the start of race contact actuates brake warning lights ("stop" lights), one or more intermediate position contacts act on an anti-lock system wheels, and the limit switch signals excessive wear on the brake linings.

Claims (8)

1. Device for measuring the position of a movable member with respect to a fixed member, the fixed member being one of the walls of a housing (14) of a servomotor and the movable member being a piston means (16) dividing the housing into a front chamber and a rear chamber, comprising a first movable means (42), movable with the movable member (16) and the displacement of which is identified with respect to a second fixed means (26) with respect to the fixed member (14), characterized in that the second fixed means (26) is fixed to the fixed member (14) outside the casing (14) of the booster, the first mobile means (42) sliding relative to the second fixed means (26) so as to vary at least one electrical quantity as a function of the position of the first mobile means (42) relative to the second fixed means. 2. Device according to claim 1 characterized in that the second fixed means is located outside the booster housing on the side of the front vacuum chamber. 3. Device according to claim 2 characterized in that the second fixed means comprises a vacuum retaining valve. 4. Device according to claim 3 characterized in that the first movable means and the second fixed means constitute a potentiometer. 5. Device according to claim 4 characterized in that the potentiometer is linear. 6. Device according to any one of the preceding claims, characterized in that it comprises a system for adjusting the length of the first movable means (42). 7. Vacuum retaining valve for pneumatic servomotor, characterized in that it comprises a measuring device according to any one of claims 1 to 6. 8. Pneumatic booster, characterized in that it is equipped with a measuring device according to any one of claims 1 to 6.

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