CN110494657B

CN110494657B - Actuator for hydraulic or pneumatic control device

Info

Publication number: CN110494657B
Application number: CN201880016175.8A
Authority: CN
Inventors: 吉拉姆·艾伯特; 克里斯多夫·莫里尔; 让·菲利浦·瓦赞
Original assignee: Leicam Power Transmission Systems LLC; Peugeot Citroen Automobiles SA
Current assignee: Leicam Power Transmission Systems LLC; PSA Automobiles SA
Priority date: 2017-03-06
Filing date: 2018-03-05
Publication date: 2020-10-13
Anticipated expiration: 2038-03-05
Also published as: WO2018162380A1; FR3063526B1; FR3063526A1; CN110494657A; DE112018001186T5

Abstract

The invention relates to an actuator for a hydraulic or pneumatic control device, comprising: a cylindrical body (8); a piston (10) sliding in the body (8); a control rod (12) movable between an extended position and a retracted position, a stop (28) projecting radially from the control rod (12) and configured to interact with a stop surface (30) on the cylindrical body (8); a protective sleeve (16) which surrounds the control rod (12) and comprises in succession: a first end (17) attached to the body (8); a rigid portion (21) inside which the stopper (28) moves; a deformable portion (22) having a contracted state and an expanded state; and a second end (19) attached to the control rod (12), the piston (10) defining with the body (9) a third chamber (39) of variable volume, of variable volume to receive or supply fluid from or to the deformable portion (22).

Description

Actuator for hydraulic or pneumatic control device

Technical Field

The present invention relates to the field of actuators for assembling hydraulic or pneumatic control devices of motor vehicles. In view of this, the present invention relates to a cylinder for a control system of a clutch or a brake control system of a motor vehicle.

Background

Hydraulic or pneumatic cylinders for control devices are known in the prior art, comprising a cylindrical body provided with an internal bore in which a piston is slidably housed, so as to define a chamber of a hydraulic or pneumatic actuator of variable volume. The hydraulic or pneumatic cylinder has a control rod connected at one end to the piston and at the other end to an actuating member to control the movement of the piston. For example, in the context of a transmission control cylinder in a clutch system, such an actuating member is a clutch pedal of a vehicle.

In order to limit the movement of the control rod with respect to the cylindrical body, the control rod comprises a stop, for example in the form of a stop disc projecting radially around the control rod. The stop interacts with a cylindrical body, the end of the cylindrical body through which the control rod passes forming a stop surface that interacts with the stop on the control rod.

Furthermore, in order to protect the cylindrical body and the piston from dust in the environment, a bellows surrounds the control rod. In fact, such dust can reduce the seal between the piston and the body and can even reduce the performance of the piston and/or the cylindrical body. A first end of the bellows is mounted on the cylindrical body and a second end of the bellows is mounted on the control rod. During the movement of the control rod with respect to the cylindrical body, the bellows contracts or expands according to the direction of movement of the control rod, so as to remain around the control rod and prevent dust from entering the through hole of the cylindrical body housing the piston.

However, in order to protect the cylinder, the bellows must be sized to allow it to completely surround the control rod. The stop projecting radially from the control rod thus results in a bellows having a considerable minimum size. Due to this considerable minimum size, the bellows has a large change in its internal volume during contraction or expansion associated with movement of the control rod.

To allow such a large change in the internal volume of the bellows, the internal volume of the bellows is put into communication with its external environment. To this end, it is known to make openings in the bellows so that air can circulate between the external environment of the bellows and the internal volume of the bellows. However, even if this communication is limited to a simple opening, it still constitutes an inlet for outside air and therefore also an inlet for dust into the internal volume of the bellows.

Document US2004/0188199a1 describes an actuator of a control device which limits the risk of dust entering the internal volume of the bellows by connecting it to the external environment chosen for its low ash content. Thus, in this document, the communication between the internal volume of the bellows and the air source is through a conduit passing through the bellows attachment on the control rod, which conduit leads to an environment of limited exposure to dust. However, this solution only limits the penetration of dust into the inner volume of the bellows and does not prevent the entry of dust into the inner volume of the bellows. DE102013202767 discloses an actuator according to the preamble of claim 1.

Disclosure of Invention

An aspect of the present invention is to provide a control actuator with good reliability and wear resistance to overcome at least some of the drawbacks of the prior art.

In particular, the idea of the invention is to provide an actuator for a control device, which protects its inner space from external contamination.

According to one embodiment, the present invention provides an actuator for a hydraulic or pneumatic control device, comprising:

-a cylindrical body having an inner bore;

-a piston adapted to slide along a sliding axis inside the bore;

-a control rod having a first end coupled to the piston and a second end for coupling to the actuating element so as to move the piston within the inner bore during movement of the actuating element, the control rod being movable between an extended position and a retracted position, the stop member projecting radially from the control rod and being arranged to interact with the stop surface of the cylindrical body when the control rod is in the retracted position;

-a protective sleeve of the control rod, which protective sleeve surrounds the control rod and comprises in succession:

o a first end sealingly fixed on the cylindrical body;

a rigid portion defining a first chamber within which the stop member moves when the control rod moves between its extended position and its retracted position;

a deformable portion adapted to deform along the control rod when the control rod is moved and defining a second chamber of variable volume communicating with the first chamber, the deformable portion being deformable between a contracted state when the control rod is in the retracted position and an extended state when the control rod is in the extended position; and

a second end sealingly fixed on the control rod,

the piston (10) and the inner bore of the body (8) define a third chamber (39) of variable volume communicating with the first chamber (23), the volume of which varies according to the position of the piston (10) so as to receive, on the one hand, a certain volume of fluid resulting from the reduction in volume of the second chamber (24) when the control rod (12) is moved towards its retracted position and, on the other hand, supply the second chamber (24) with fluid when the control rod (12) is moved towards its extended position.

The rigid portion is defined as a portion having sufficient rigidity such that the rigid portion does not deform during movement of the control rod between its retracted and extended positions, thereby maintaining a substantially constant internal volume of the first chamber.

Such an actuator therefore has a variable volume boot, the internal volume of which varies independently of the size of the stop member of the control rod. Thus, the size of the second chamber can be minimised, thereby minimising the change in volume of the shield when the control lever is moved. By minimizing the variable volume of the protective sleeve, there is no longer a need to provide communication between the interior volume of the protective sleeve and its external environment. In particular, it is not necessary to supply external air to the protective sleeve when its internal volume increases, or to evacuate the air contained therein when the internal volume of said protective sleeve decreases. In fact, depending on the direction of movement of the control rod, it may be advantageous to absorb or supply the amount of air displaced by the change in the state of the second chamber by a third chamber formed in the cylindrical body, the volume of which varies according to the movement of the piston in the cylinder.

According to other advantageous embodiments, such an actuator may have one or more of the following features:

according to one embodiment, the internal volume of the second chamber when the deformable portion is in the extended state is between + 30% and-30%, in particular between + 10% and-10%, preferably between + 5% and-5% of the internal volume of the third chamber when the control rod is in the retracted position.

According to one embodiment, the internal volume of the second chamber when the deformable portion is in the extended state is equal to the internal volume of the third chamber when the control rod is in the retracted position.

According to a certain embodiment, the amount of decrease in the internal volume of the second chamber when the deformable portion changes from the extended state to the retracted state corresponds to the amount of increase in the internal volume of the third chamber when the control rod moves from the extended position to the retracted position. Conversely, the amount of increase in the internal volume of the second chamber when the deformable portion changes from the retracted state to the extended state corresponds to the amount of decrease in the internal volume of the third chamber when the control rod moves from the retracted position to the extended position.

According to one embodiment, the stop member is a stop disk projecting radially around the control rod.

According to one embodiment, the diameter of the deformable portion of the sheath is smaller than the diameter of the rigid portion.

According to one embodiment, the deformable portion of the shield comprises a bellows having an average diameter smaller than the largest radial dimension of the stop member.

According to one embodiment, the deformable portion of the shield comprises a bellows having a minimum diameter smaller than a maximum radial dimension of the stop member.

According to one embodiment, the mean diameter of the bellows is smaller than the diameter of the stopper disc.

According to one embodiment, the maximum diameter of the bellows is smaller than the maximum radial diameter of the stop member.

According to one embodiment, the bellows has a plurality of successive folds, the diameter of each fold of the bellows increasing from the second end of the protective sleeve towards the rigid portion. Due to these features, the deformable portion of the sheath remains coaxial with the control rod, including when the control rod is slightly tilted relative to the piston axis.

According to one embodiment, the deformable portion of the protective sleeve is made of an elastic material. Due to these features, the deformable portion has good deformation characteristics, allowing to simply modify the internal volume of the second chamber of the envelope.

According to one embodiment, the wall thickness of the rigid part of the shield is greater than the wall thickness of the deformable part of the shield.

According to one embodiment, the rigid portion of the protective sleeve has at least one stiffening member.

According to one embodiment, the reinforcement member is at least one axial reinforcement member extending parallel to the control rod.

According to one embodiment, the stiffening member is an insert associated with the rigid portion.

Due to these features, the rigid part has good mechanical characteristics. In particular, due to these features, the rigid portion has a good rigidity, ensuring that the internal volume of the first chamber is preserved. Thus, the deformable portion is preferably deformed at the rigid portion, thus the variable volume of the sheath is determined by the deformable portion.

According to one embodiment, the first end of the control rod is coupled to the piston with a degree of rotational freedom about a radial axis perpendicular to the sliding axis of the piston, the sheath further comprising a flexible portion between the rigid portion and the first end of the sheath, the flexible portion being adapted to allow the degree of rotational freedom of the rigid portion about the rigid portion. Due to these features, the rigid portion of the sheath remains coaxial with the control rod, including when the control rod is slightly tilted with respect to the piston axis.

The idea of some aspects of the invention is to have a bellows sealingly surrounding the control rod.

Aspects of the invention contemplate minimising the change in volume of the protective enclosure. The idea of some aspects of the invention is to separate the size of the variable volume of the protective sleeve from the size of the stop member of the control lever. The idea of some aspects of the invention is to divide the protective sleeve into a fixed volume in the movement of the stop member of the control rod and a variable volume that allows the deformation of the protective sleeve when the control rod is moved with respect to the cylinder body.

The concept of certain aspects of the invention is that the interior volume of the protective sleeve is not supplied with ambient air. Aspects of the present invention contemplate not allowing dust to penetrate the interior volume of the shield. The concept of certain aspects of the invention is to facilitate movement of the control lever despite the presence of the protective sleeve.

Drawings

Other objects, details, features and advantages of the present invention will become apparent from the following description of several particular embodiments thereof, given by way of non-limiting example only with reference to the accompanying drawings.

In the figure:

fig. 1 is a schematic diagram of a hydraulic control apparatus of a clutch for a motor vehicle.

Figure 2 is a perspective schematic view of a hydraulic cylinder according to the present invention including a control rod surrounded by a protective sleeve.

Figure 3 is a detailed cross-sectional view of figure 2 showing the protective sleeve of the control lever.

FIG. 4 is a partial axial cross-sectional view of the hydraulic cylinder of FIG. 2 when the control rod is in the extended position.

FIG. 5 is a partial perspective cut-away view of the hydraulic cylinder of FIG. 2 when the control lever is in an extended position.

FIG. 6 is a partial axial cross-sectional view of the hydraulic cylinder of FIG. 2 when the control rod is in the retracted position.

FIG. 7 is a partial perspective cut-away view of the hydraulic cylinder of FIG. 2 when the control lever is in a retracted position.

Fig. 8 is a partial axial cross-sectional view of a hydraulic cylinder according to a variant embodiment with the axis of the control rod aligned with the sliding axis of the piston.

Fig. 9 is a partial axial cross-sectional view of the hydraulic cylinder of fig. 8 with the axis of the control rod tilted relative to the sliding axis of the piston.

Detailed Description

In the description and claims, the terms "outer" and "inner" and the orientations of "axial" and "radial" should be used to refer to elements of the control device actuator according to the definitions given in the description. By convention, the "radial" orientation is orthogonal to the X axis along which the piston, which determines the "axial" orientation, slides in the cylinder body bore and away from that axis from the inside to the outside. The terms "outer" and "inner" are used to define the relative position of one element with respect to another element about the X-axis; thus, elements close to the X-axis are considered to be inner, as opposed to outer elements located radially at the periphery. Furthermore, the terms "rear" AR and "front" AV are used to define the relative position of one element with respect to the other in the axial direction, the element intended to be placed near the end of the control rod opposite the piston being designated rear, and the element intended to be placed near the end of the piston opposite the control rod being designated front.

In the following, the invention is described in the context of a transmission hydraulic cylinder of a hydraulic clutch control device, but applies in a similar manner to any cylinder actuator, hydraulic or pneumatic cylinder of a control device, such as a master cylinder of a brake system or the like.

Fig. 1 schematically shows a hydraulic control device 1 for a clutch 2. The hydraulic control device 1 has a transmission hydraulic cylinder 3 associated with an actuating element, such as a pedal 4, and a receiving hydraulic cylinder 5 associated with the clutch 2, for example via an actuating fork 6. The transmission cylinder 3 and the receiving cylinder 5 are interconnected by a hydraulic circuit 7 filled with fluid. The fluid is, for example, brake fluid or oil, such as transmission oil.

The transmission cylinder 3 and the receiving cylinder 5 each comprise a

body

8, 9 having an internal bore and a

piston

10, 11 adapted to slide within the bore and defining with the bore a variable volume hydraulic chamber connected to the hydraulic circuit 7. The piston 10 of the transmission cylinder 3 is connected to a control rod 12 articulated on the clutch pedal 4. The piston 11 receiving the hydraulic cylinder 5 is connected to a rod 13 supported on the control fork 6 of the clutch 2.

The actuating fork 6 is pivotally mounted on the vehicle chassis and interacts with the clutch stop 14 such that pivoting of the actuating fork 6 causes axial movement of the clutch stop 14 and thus movement of the clutch 2 between the engaged and disengaged positions.

When the user depresses the pedal 4, the control rod 12 moves so that the piston 10 of the transmission cylinder 3 slides from the extended position to the retracted position, back and forth, in the body 8 of the transmission cylinder 3, to force the fluid out towards the receiving cylinder 5. The piston 11 of the receiving cylinder 5 then slides into the body 9 of the receiving cylinder 5, which allows the clutch 2 to move from its engaged position to its disengaged position.

Fig. 2 is a perspective view of the transmission hydraulic cylinder 3 in fig. 1. The transmission hydraulic cylinder 3 has a control lever 12. A fluid reservoir 15 is mounted on the body 8 of the drive cylinder 3. This reservoir 15 constitutes a fluid reserve for the variable volume hydraulic chamber of the transmission hydraulic cylinder 3 and thus for the hydraulic circuit 7.

A protective sleeve 16, shown in more detail in figure 3, surrounds the control rod 12. The front end 17 of the sheath 16 is fixed to the rear end 18 of the body 8. The rear end 19 of the sheath 16 is sealingly secured to the rear portion 20 of the control rod 12. The sheath 16 comprises, from the front end 17 to the rear end 19, a rigid portion 21 and a deformable portion 22.

The deformable portion 22 has a bellows shape. The deformable portion 22 has a conical shape with the diameter of the folds of the bellows decreasing from the front of the bellows to the rear of the bellows. The deformable portion 22 is made of a deformable material, for example an elastomer, for example ethylene propylene diene monomer rubber (EPDM), Nitrile Butadiene Rubber (NBR), Hydrogenated Nitrile Butadiene Rubber (HNBR) or even silicone or a thermoplastic elastomer (TPE), such as a thermoplastic vulcanizate (TPV or TPE-V).

The rigid portion 21 is cylindrical in shape and surrounds the front portion 27 of the control rod 12. The rigid portion 21 is a non-deformable portion. To this end, the rigid portion 21 is made in any suitable way, allowing to maintain its shape during the movement of the control rod 12. For example, the rigid portion 21 may be made of the same material as the deformable portion 22, but with a greater wall thickness. In another embodiment, the rigid portion 21 may include at least one stiffening member, such as a stiffening rib (not shown) extending parallel to the control rod 12. In another embodiment, the material used to make the rigid portion 21 may be selected to have mechanical characteristics suitable for retaining the shape of the rigid portion 21. In another embodiment, the stiffening member may be an insert (not shown) associated with the rigid portion 21. These different embodiments allowing stiffening of the rigid part can be implemented alternatively or in combination. The rigid portion 21 and the deformable portion 22 may be co-manufactured, i.e. made in a single piece, for example by moulding, co-moulding or other means, or manufactured separately and subsequently combined to form the sheath 16.

The rigid portion 21 defines a first or forward chamber 23 of the sheath 16. The first chamber 23 has a constant volume regardless of the position of the control rod 12. The deformable portion 22 defines a second or rear chamber 24 of the sheath 16. The second chamber 24 has a variable volume. The first chamber 23 communicates with the second chamber 24.

As shown in fig. 2 to 7, the rear end 18 of the main body 8 of the transmission hydraulic cylinder 3 has an annular passage 25 on the radially outer face. The front end 17 of the sheath 16 has an annular leading edge 26 projecting radially towards the X axis. The leading edge 26 is received in the channel 25 to secure the front end 17 of the sheath 16 to the rear end 18 of the body 8. The leading edge 26 and the annular channel 25 interact to form a seal. The rear portion 20 of the control rod 12 has an annular groove 31. The rear end 19 of the sheath 16 includes ribs 32 that project radially toward the X axis. The rib 32 is received in the recess 31 to secure the rear end 19 of the sheath 16 to the rear 20 of the lever 12. Preferably, the interaction between the ribs 32 and the grooves 31 is fluid tight.

The front portion 27 of the lever 12 is separated from the rear portion 20 by a disc 28. The forward end of the forward portion 27 is mounted on the rearward end 29 of the piston 10 as described below in connection with fig. 4 and 5. The rear end of the rear portion 20 is hinged to the step 4. The disk 28 is circular in shape and projects radially from the control rod 12.

The rear end 18 of the body 8 has a rear face 30 facing the disc 28. The rear face 30 has a central opening coaxial with the axis X, through which passes the front portion 27 of the control rod 12. The diameter of the disc 28 is greater than the diameter of the opening in the back face 30 of the body 8. In other words, the disk 28 forms a stop member of the lever 12, which interacts with the rear face 30 of the body 8 forming a stop surface. As described below, the interaction between the disc 28 and the back face 30 allows the forward movement of the control rod 12 to be blocked when the disc 28 axially abuts the back face 30. Thus, disk 28 and back 30 can define the retracted position of lever 12.

The disk 28 is accommodated in the first chamber 23. The rigid part 21 has an internal diameter greater than the diameter of the disc 28 to allow the disc 28 to move in the first chamber 23. Furthermore, the average diameter of the second chamber 24, which is the arithmetic mean between the inner diameter (or smallest diameter) of the rigid portion and its outer diameter (or largest diameter), is smaller than the diameter of the disk 28. The average diameter of the second chamber 24 is preferably equal to or close to the diameter of the bore in the body 8 of the drive cylinder 3. In other words, the rigid portion 21 allows to house the stop member of the control rod 12 formed by the disc 28, while the deformable portion 22 of variable volume of the sheath 16 moves with respect to said stop member, so that the size of the deformable portion 22 of the sheath 16 is independent of the size of the stop member of the control rod 12.

Fig. 4 and 5 show the hydraulic cylinder of fig. 2 with the control rod in an extended position.

With the control rod 12 in the extended position, the piston 10 received in the bore of the body 8 of the drive cylinder 3 is pushed back by the control rod 12, with the rear end 29 of the piston 10 located in the bore of the body 8, near the rear end 18 of the body 8. The radially inner face 33 of the body 8, which defines the bore in which the piston 10 slides, has a groove in which a washer, in this case a lip washer 34, is accommodated. The lip gasket 34 provides a dynamic seal against the piston 10. In other words, this lip gasket 34 ensures that the hydraulic fluid chamber of the transmission cylinder is sealed and prevents fluid from escaping from the hydraulic circuit 7 through the rear of the body 8 of the transmission cylinder 3 when the piston 10 slides in the bore. The gasket can also be an O-ring.

It is important that the lip gasket 34 be kept dust free in order to maintain its integrity during the service life of the drive cylinder 3.

A bore in the body 8 of the drive cylinder 3 defines with the rear end 29 of the piston 10 a third chamber 39. The third chamber 39 communicates with the first chamber 23 and the second chamber 24 via an opening in the rear face 30 of the body 8. In other words, this third chamber 39 is delimited axially on the one hand by the rear end 29 of the piston 10 and the opening of the rear face 30 of the body 8, and radially on the other hand by the radially inner face 33 of the hole provided in the body 8 of the transmission cylinder 3.

With the control rod 12 in the extended position as shown in fig. 4 and 5, the third chamber 39 has a minimum internal volume and the rear end 29 of the piston 10 is located as close as possible to the opening in the rear face 30 of the body 8. In this position, the disc 28 is housed in the first chamber 23, close to the junction between the first chamber 23 and the second chamber 24. Also, in this position, the second chamber 24 has a maximum internal volume and the bellows is fully extended. Preferably, the dimension of the deformable portion 22, in particular its mean diameter, is such that the change in volume of the second chamber 24 between the contracted condition of the deformable portion 22 (see fig. 6 and 7) and the expanded condition of the deformable portion 22 (see fig. 4 and 5) corresponds to the change in volume of the third chamber 39 when the control rod 12 is in the extended position forcing the piston 10 in the body 8 to the advanced position (see fig. 4 and 5) and when the control rod 12 is in the retracted position (see fig. 6 and 7).

The control lever 12 is movable between an extended position, as shown in fig. 4 and 5, and a retracted position, as shown in fig. 6 and 7.

When the user presses on the clutch pedal 4, the clutch pedal 4 pushes the control rod 12 towards the body 8 of the transmission cylinder 3. By pushing the control rod 12 towards the body 8, the control rod 12 is moved axially forward so that the front end of the control rod 12 pushes the piston 10 from the rear of the body 8 towards the front thereof by sliding it into the bore of the body 8. The lip gasket 34 ensures a fluid-tight seal of the hydraulic chamber of the transmission cylinder while the piston 10 slides. In addition, the sliding of the piston 10 moves the rear end 29 of the piston 10 away from the opening in the rear face 30 of the body 8, thereby increasing the internal volume of the third chamber 39.

Moreover, the advancement of the lever 12 relative to the body 8 causes both the disc 28 and the rear portion 20 of the lever 12 to axially approach the rear face 30 of the body 8.

As shown in fig. 6 and 7, the disc 28 abuts a back face 30 of the body 8 to block further advancement of the lever 12. The disc 28 moves in the first chamber 23 from the position shown in fig. 3 to 5 to the position shown in fig. 6 and 7. The rigid portion 21 of the sheath 16 is fixedly mounted on the rear end 18 of the body 8 of the drive cylinder 3 and the deformable portion 22 of the sheath 16 is mounted on the rear portion 20 of the lever 12, the rear portion 20 of the lever 12 and the rear face 30 of the body 8 approaching one another, causing the deformable portion 22 to contract between the rear end 19 of the sheath 16 fixed to the rear portion 20 of the lever 12 and the rigid portion 21 of the sheath 16 fixed to the rear end 18 of the body 8. Due to the rigidity of the rigid portion 21, only the deformable portion 22 of the sheath 16 contracts, the internal volume of the sheath 16 varying only as a result of the variation of the internal volume of the second chamber 24 delimited by the deformable portion 22. In other words, this contraction of the deformable portion 22 causes the volume of the second chamber 24 to decrease, while the volume of the first chamber 23 remains constant due to the rigidity of the rigid portion 21.

By contraction of the deformable portion 22 of the sheath 16, the volume of fluid displaced from the second chamber 24 is absorbed by the third chamber 39, the volume of the third chamber 39 increasing as the piston 10 advances in the bore of the body 8.

A disc 28 forming a stop member limiting the movement of the control rod 12 with respect to the main body 8 is housed in the first chamber 23, so that the size of the deformable portion 22 is independent of the size of the disc 28. However, the volume of fluid displaced by the contraction of the deformable portion 22 is a direct result of the size of the deformable portion 22. As a result, the variable volume of the sheath 16 depends only on the change in volume of the deformable portion, becoming independent of the size of the stop member of the control rod 12. Therefore, the volume of the deformable portion 22 can be minimized so that the volume of fluid displaced during contraction of the deformable portion 22 is absorbed by the increased volume of the third chamber 39 formed in the main body 8 of the transmission hydraulic cylinder 3.

Preferably, the change in volume of the second chamber 24 between the extended position and the retracted position of the deformable portion 22 is equal to the change in volume of the third chamber 39 between the retracted position and the extended position of the control rod 12. However, depending on the mechanical characteristics of the sheath 16, the change in volume of the second chamber 24 may be slightly different from the change in volume of the third chamber 39, for example, by plus or minus 30%, preferably by plus or minus 10%, more preferably by plus or minus 5%, and ideally the same. Such differences in volume changes may be absorbed, for example, by slight deformation of jacket 16 or by slight pressure rises or drops in jacket 16.

Conversely, when the control rod 23 is moved from the retracted position shown in fig. 6 and 7 to the extended position shown in fig. 3 to 5, the piston 10 is moved back from the main body 8 of the transmission cylinder 3 by the control rod 12. This movement of the piston 10 causes the internal volume of the third chamber 39 to decrease. In addition, the rear portion 20 of the control rod 12 moves away from the rear face 30 of the body 8 of the drive cylinder, causing the deformable portion 22 of the sheath 16 to expand, thereby increasing the internal volume of the second chamber 24. This movement of the lever 12 also causes the disc 28 to move away from the back 30 of the body 8 such that the disc 28 moves into the first chamber 23, approaches the deformable portion and remains in the first chamber 23.

The volume of fluid displaced from third chamber 39 by the movement of piston 10 into body 8 supplies fluid to second chamber 24 when it transitions from the contracted state to the expanded state without supplying fluid from the environment external to sheath 16. In other words, the fluid contained in the sheath 16, on the one hand, in the first and

second chambers

23, 24 and, on the other hand, in the third chamber 39, is generally a constant volume that is not in communication with the fluid in the environment outside the transmission cylinder 3 and remains in the

chambers

23, 24 and 39 during the movement of the control rod 12 and the piston 10.

The jacket 16 thus constitutes a fluid-tight double-

chamber volume

23 and 24, in which dirt from the environment outside the transmission cylinder 3 cannot penetrate, thus protecting the lip gasket 34 received in the bore of the body 8 of the transmission cylinder 3 and interacting with the piston 10 to ensure the fluid-tightness of the transmission cylinder 3.

Fig. 8 and 9 show a variant embodiment of the transmission hydraulic cylinder 3, in which the sheath 16 comprises a flexible portion 40 between its front end 17 fixed to the rear end 18 of the body 8 and the rigid portion 21. The flexible portion 40 is formed in any manner suitable to allow the sheath 16 to be tilted with respect to the X-axis, as described below. In a variant embodiment, shown in figures 8 and 9, the flexible portion 40 is formed by a fold in the sheath 16.

The front end of the control rod 12 includes a ball joint 35 that is received in an insert 36. The insert 36 has resilient tabs that allow the ball joint 35 to be inserted into the insert 36 with some freedom in the radial direction relative to the X-axis and held in place, allowing the control rod 12 to tilt relative to the X-axis. The rear end 29 of the piston 10 comprises a chamber 37 into which the insert 36 is inserted. The insert 36 has a fir-tree fastener 38 which fits forcibly into an axial recess in the cavity 37 to hold the insert 36 in place in the cavity. Thus, the front end of the control rod 12 is connected to the rear end 29 of the piston 10. Such interaction between the control rod 12 and the piston 10 is for example described in document FR 2924185.

When the control rod 12 is coaxial with the X-axis, such as with the control rod 12 in the extended position, the rigid portion is also coaxial with the X-axis and the flexible portion 40 is in the rest position.

When the control rod 12 is tilted with respect to the X-axis, for example, during the movement of the clutch pedal 4 from the engaged position to the disengaged position or during the installation of the transmission hydraulic cylinder 3 in the vehicle, the flexible portion is deformed to keep the rigid portion 21 coaxial with the control rod 12. Keeping the rigid part 21 coaxial with the control rod 12 prevents the disk 28 from coming into contact with the wall surface of the rigid wall, thus facilitating the movement between the control rod 12 and the body 8 of the transmission cylinder 3 with respect to the X-axis.

Furthermore, the conical shape of the bellows contributes to the movement of the control rod 12 when it is moved by the clutch pedal 4, the bellows remaining coaxial to the control rod 12 and inclined with respect to the X-axis.

The invention has been described with reference to several particular embodiments, but it is obvious that the invention is not limited thereto, and that the invention comprises all technical equivalents of the means described and their combinations if they fall within the scope of the invention. Furthermore, the invention is described above in the context of a transmission hydraulic cylinder of a clutch system in connection with the accompanying drawings, but the invention is applicable to any type of cylinder, such as a master cylinder of a brake system, a hydraulic or pneumatic actuator, an electromechanical actuator, etc.

Use of the verbs "comprise," "comprising" or "comprising" … … and their modified forms do not exclude the presence of elements or steps other than those listed in a claim.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. An actuator for a hydraulic or pneumatic control device, comprising:

-a cylindrical body (8) having an inner bore;

-a piston (10) adapted to slide along a sliding axis (X) inside said inner bore;

-a control rod (12) comprising a first end coupled to the piston (10) and a second end for coupling to an actuating element (4) so as to cause the piston (10) to move within the bore when the actuating element (4) is moved, the control rod (12) being movable between an extended position and a retracted position, a stop member (28) projecting radially from the control rod (12) and arranged to interact with a back face (30) of the cylindrical body (8) when the control rod (12) is in the retracted position;

-a protective sleeve (16) of said control rod (12), said protective sleeve surrounding said control rod (12) and comprising:

o a first end (17) sealingly fixed on said cylindrical body (8);

o a second end (19) sealingly fixed to the control rod (12),

it is characterized in that the preparation method is characterized in that,

-said protective sheath (16) comprises, between its first and second ends, in succession:

o a rigid portion (21) delimiting a first chamber (23) within which the stop member (28) moves when the control rod (12) moves between its extended position and its retracted position;

a deformable portion (22) adapted to deform along the control rod (12) during the movement of the control rod (12) and defining a second chamber (24) of variable volume communicating with the first chamber (23), the deformable portion (22) being deformable between a contracted condition when the control rod (12) is in the retracted position and an expanded condition when the control rod (12) is in the extended position; and

the piston (10) and the inner bore of the body (8) define a third chamber (39) of variable volume communicating with the first chamber (23), the volume of which varies according to the position of the piston (10) so as to receive, on the one hand, a certain volume of fluid resulting from the reduction in volume of the second chamber (24) when the control rod (12) is moved towards its retracted position, and to supply the second chamber (24) with fluid when the control rod (12) is moved towards its extended position.

2. An actuator according to claim 1, wherein the internal volume of the second chamber (24) when the deformable portion is in the extended state is + 30% to-30% of the internal volume of the third chamber (39) when the control rod (12) is in the retracted position.

3. An actuator according to any of claims 1 to 2, wherein the amount of reduction of the internal volume of the second chamber (24) when the deformable portion (22) changes from the extended to the retracted state corresponds to the amount of increase of the internal volume of the third chamber (39) when the control rod (12) moves from the extended to the retracted position, and the amount of increase of the internal volume of the second chamber (24) when the deformable portion (22) changes from the retracted to the extended state corresponds to the amount of reduction of the internal volume of the third chamber (39) when the control rod (12) moves from the retracted to the extended position.

4. An actuator according to any of claims 1 to 2, wherein the internal volume of the second chamber (24) when the deformable portion is in the extended state is equal to the internal volume of the third chamber (39) when the control rod (12) is in the retracted position.

5. Actuator according to any of claims 1-2, wherein the deformable part (22) of the shield (16) has a smaller diameter than the rigid part (21) of the shield (16).

6. Actuator according to any of claims 1 to 2, wherein the stop member (28) is a stop disc radially protruding around the control rod (12).

7. Actuator according to any of claims 1-2, wherein the deformable portion (22) of the shield (16) comprises a bellows having an average diameter smaller than the maximum radial dimension of the stop member.

8. Actuator according to claim 7, wherein the deformable portion (22) of the shield (16) comprises a bellows with a minimum diameter smaller than the maximum radial dimension of the stop member.

9. The actuator of claim 7, wherein the bellows has a plurality of successive folds, the diameter of each fold of the bellows increasing from the second end of the shield toward the rigid portion.

10. Actuator according to any of claims 1-2, wherein the deformable part (22) of the protective sheath (16) is made of an elastic material.

11. Actuator according to any of claims 1-2, wherein the wall thickness of the rigid part (21) of the shield (16) is larger than the wall thickness of the deformable part (22) of the shield (16).

12. An actuator according to any of claims 1 to 2, wherein the rigid portion of the shield has at least one stiffening member.

13. Actuator according to any of claims 1 to 2, wherein a first end of said control rod (12) is coupled to said piston (10) with a certain degree of rotational freedom about a radial axis perpendicular to a sliding axis (X) of said piston (10), said shield (16) further comprising a flexible portion (40) located between said rigid portion (21) and a first end (17) of said shield (16), said flexible portion (40) being adapted to allow said rigid portion a degree of rotational freedom about said rigid portion.