EP0051014A1 - Device for continuously controlling the stroke of a piston of an actuator - Google Patents

Abstract

The present invention relates to a device for continuously adjusting the amplitude of the stroke of a piston (2). The movements of the piston (2) being controlled by a rod (7), this comprises an extension having the form of a differential piston (22) movable in a cylinder (21), said differential piston (22) having a cavity internal (25) in which is disposed a second rod (27) provided with a cam (34) whose opposite edges can uncover and seal cyclically at least two orifices (35, 36) connected to one and the other of the two chambers (23, 24) defined by the piston (22) in the cylinder (21). Application to the adjustment of the stroke of a differential piston.

Description

The present invention relates to a device allowing a continuous adjustment of the stroke of the piston of a jack, applicable in particular in the case of a differential piston.

There are currently several types of device for modifying the length of the stroke of a piston. For example, US Patent No. 2,898,890 describes such a device in which compressed air can be blown at each of the ends of the cylinder inside which the piston moves. Several discharge orifices, closed by valves, are distributed along this cylinder. The opening of one of these valves causes a vacuum on one side of the piston and, thanks to an appropriate system, compressed air is sent to the other side of the piston. It then moves back to the level of the selected orifice. A rough adjustment of the piston stroke is thus obtained by the choice of the outlet orifice. This device has a certain number of drawbacks: first of all, it does not allow a continuous variation of the amplitude of the displacement of the piston. In addition, the installation is quite complex, and therefore expensive, because the discharge orifices can be quite numerous and each of the shut-off valves is controlled by a solenoid.

The object of the present invention is precisely to eliminate these drawbacks by proposing a simple device which makes it possible to continuously vary the stroke of the piston.

According to the main feature of the stepless stroke adjustment device of a piston which is the subject of the invention, this piston forming part of a cylinder comprising a control member at least part of which is in the form of a rod, movable in rotation and in translation and cooperating with said piston, said rod has an extension having the shape of a differential piston movable in translation and in rotation inside a cylinder and defining in this one a chamber with large section and a chamber with small section, the latter being permanently in communication with a source of fluid under high pressure, said differential piston having an internal cavity in which is disposed a second rod immobilized in translation and which can be oriented angularly, said second rod being provided with a cam having two opposite edges which can uncover and seal cyclically, during the rotation of the differential piston, at least two orifices respectively connected to one and to the other of the two chambers.

According to another characteristic of this device, the second rod has a cavity which allows, thanks to one of said orifices, to put the large section chamber in communication with a fluid discharge.

Finally, according to a last characteristic of this device, said differential piston comprises an outer wall on which are hollowed out at least two grooves, the ends of one of these grooves opening into one of said orifices and into the chamber with a large section respectively , the ends of the other groove opening respectively into the other orifice and into the small section chamber.

The invention will appear better on reading the description which follows, given purely by way of illustration and in no way limiting, of an exemplary embodiment in which the device which is the subject of the invention is applied to a programmed control actuating cylinder itself comprising a differential piston controlled by a rod equipped with a cam.

The operating principle of such a jack being the same as that of the adjustment device which is the subject of the invention, we will first describe in detail the operation of this jack, then we will show how the stroke of the piston can be modified thanks to the device according to the invention.

• - la figure 1 est une coupe axiale schématique du vérin hydraulique d'actionnement à commande programmée,
• - les figures 2 et 3 reproduisent partiellement la figure 1 à deux positions différentes du piston mobile,
• - la figure 4 est une vue en perspective de la came portée par la tige de commande du vérin suivant les figures 1 à 3, et
• - la figure 5 représente un tel vérin associé à un dispositif de réglage conforme à l'invention.

This description will be made with reference to the accompanying drawings in which:

• FIG. 1 is a schematic axial section of the hydraulic actuator with programmed control,
• - Figures 2 and 3 partially reproduce Figure 1 at two different positions of the movable piston,
• FIG. 4 is a perspective view of the cam carried by the actuator control rod according to FIGS. 1 to 3, and
• - Figure 5 shows such a cylinder associated with an adjustment device according to the invention.

The jack shown in FIGS. 1 to 3 comprises a tubular cylindrical body 1 in the axial bore of which a piston 2 is slidably mounted which thus defines two opposite chambers respectively referenced 3 and 4. This piston 2 is itself provided in the form tubular, the axial housing 5 thus determined partially extending inside the motor member 6 operated by said piston. Inside the abovementioned blind housing 5 is engaged a shaft or rod 7 of smaller diameter, hollowed out with an axial channel 8, one end of which opens into the blind part of the housing 5 while the opposite end is connected by bores radials with two escape lights 10 which communicate quent themselves with the low pressure of the hydraulic system.

The drive member 6 having a diameter greater than that of the shaft 7, the piston 2 can be described as "differential". Although the two chambers are established at the same diameter, chamber 3 will hereinafter be called "small section" while chamber 4 will be "large section". It will be noted that the small section chamber 3 is permanently connected to a source of fluid under high pressure by means of two opposite radial slots 11. Furthermore, the shaft 7 extends beyond the discharge slots 10 to exit axially of the cylinder 1 of the jack and receive the drive of a motor 12 associated with an appropriate transmission 13.

The part of this shaft 7 which is engaged in the housing 5 is secured, by machining or by fixing, to a cam 14 whose FIG. 4 clearly shows the profile; in the example considered, it is a double sinusoidal profile which extends symmetrically in two parts around the cylinder formed by said shaft. This cam 14 opposes the communication of the large section chamber 4 with the discharge channel 8, and its two opposite edges are intended to form shutters for two pairs of radial orifices 15 and 16, drilled in the thickness of piston 2; each of the orifices 15 is connected by a peripheral groove 17 to the large section chamber 4, while similar grooves 18 ensure the communication of the orifices 16 with the small section chamber 3, it being understood that these two pairs of grooves 17 and 18 are profiled so as not to intersect.

The operation of this cylinder follows from the foregoing explanations and is easily understood.

In FIG. 1, it has been assumed that the motor 12 associated with the shaft 7 was stopped and that the cam 14 is was in an orientation such that the four holes 15 and 16 were covered by the edges of said cam and were therefore closed. The fluid under high pressure which, in this example, is a hydraulic liquid, penetrates well into the chamber with small section 3 and tends to push the piston 2 downwards, but since the opposite chamber 4 is separated by the cam 14 of the lights evacuation 10, said piston remains stationary.

If on the contrary, as shown in FIG. 2, the motor 12 is started and drives the shaft 7 and the cam 14 in the dextrorotatory direction, the edge or lower lip of said cam will discover the two orifices 16; the hydraulic fluid can thus pass from the chamber 3 to the chamber 4 through the aforementioned orifices and the grooves 18. The chamber 4 having a larger useful section, the piston 2 moves upwards. Of course, this axial displacement of the piston tends to bring the orifices 16 below the lower edge of the cam 14, but as the latter is rotated, said orifices remain uncovered as long as this cam has not rotated 90 °.

At this time and as illustrated in FIG. 3, the orifices 16 are closed by the lower edge of the cam 14, while the upper edge of the latter discovers the two orifices 15. The chamber 4 is thus placed in communication with the bass pressure through the grooves 17, the orifices 15, the channel 8 and the ports 10, while the high pressure is exerted on the upper face of the piston which, consequently, i moves downwards. This downward movement of the piston 2 and of the member 6 will continue for a time corresponding to a 90 ° rotation of the shaft 7, so that things will end up in the position of FIG. 1 and that 'a new operating cycle i can then occur.

It is of course necessary to provide sealing members capable of avoiding any parasitic communication between the chambers of the cylinder and the orifices of the piston 2 during the sliding thereof. Likewise, it is essential to associate angular immobilization means with this piston during its reciprocating movement. With these precautions, perfect operation of the jack is obtained, the member 6 of which is slaved to follow a well-defined law of movement, which is a function of the profile of the rotating cam 14.

FIG. 5 shows how such a jack can be associated with an adjustment device according to the invention.

In this figure, we find the cylinder 1 with its radial lights 10 and 11 for its connection with the hydraulic installation, the differential piston 2 pierced with radial holes 15-16 and hollowed out with communication grooves 17-18, and the cam rotary 14 which is carried by the shaft 7 rotatably mounted in the blind axial bore 5 of said piston. However, the shaft 7 which carries the cam 14 is here integral with a part 40 which extends axially downward to form the piston 22 of a second hydraulic cylinder with programmed control.

The piston 22 is similar to the piston 2; it is slidably mounted in a cylinder 21 provided with lights 31 and 30 respectively connected to the high and to the low pressures of the general installation. The piston 22 is a differential piston which delimits in the cylinder 21 a chamber 23 with a small section and a chamber 24 with a large section. In the blind housing 25 of the piston 22 is engaged a cam 34 carried by a second rod 27 which is not driven in a rotational movement: this shaft 27 protrudes beyond the free transverse face of the cylinder 21 to be equipped a member allowing the adjustment of its orientation, which organ has been shown diagrammatically in the form of a lever 19. Also found on the piston 22 are holes 35, 36 and grooves 37, 38 which play the same role as the holes 15, 16 and the grooves 17, 18 of the piston 2.

Of course, the extension 40 of the rod 7 must be rotated by the motor 12 without this drive being able to oppose its axial displacement under the effect of the piston 22. The transmission interposed between the motor 12 and the part 40 is therefore formed by two pinions or toothed wheels 41 with straight teeth.

The operation of the assembly shown in Figure 5 is easily understood. The upper cylinder works identically and under the same conditions as in Figures 1 to 3, so that the member 6 moves alternately up and down depending on the program set by the rotating cam 14. For the cylinder lower, the rotation of the piston 22 somehow replaces that of the cam and therefore said piston 22 slides axially; the lever 19 allows, by changing the angular position of the cam 34 in the piston 22, to adjust, not the amplitude of the stroke of the latter, but the precise moment when this stroke occurs. It is conceivable under these conditions that, according to the phase shift of the two jacks of the assembly shown in FIG. 5, it is possible to obtain that the travel of one adds to the travel of the other or is subtracted from it, so that the user is finally able to precisely adjust the amplitude of the movement of the member 6 carried by the piston 2.

As indicated above, the arrangement of the device according to FIG. 5 has been shown very schematically and in particular provision must be made for seals, seals or other means suitable for sealing the sliding of the pistons 2 and 22.

It is understood that the invention is not limited to the single example which has just been described, but variants can be envisaged without departing from the scope of the invention, in particular replacing certain execution details with all other equivalents. Finally, if a particular application has been described in which the device which is the subject of the invention is associated with a differential piston, this can be applied to any type of cylinder whose piston is provided with a ordered.

Claims (3)

1. Device for continuously adjusting the amplitude of the stroke of the piston (2) of a jack, the latter comprising a control member at least part of which is in the form of a rod (7) , mobile in rotation and in translation and cooperating with said piston (2), characterized in that said rod (7) has an extension having the form of a differential piston (22) mobile in translation and in rotation inside d '' a cylinder (21) and defining therein a large section chamber (24) and a small section chamber (23), the latter being permanently in communication with a source of fluid under high pressure, said differential piston ( 22) having an internal cavity (25) in which is disposed a second rod (27) immobilized in translation and which can be angularly oriented, said second rod (27) being provided with a cam (34), having two opposite edges which can uncover and seal cyclically, during the rotation of the piston differential (22), at least two orifices (35, 36) respectively connected to one and to the other of the two chambers (24, 23). 2. Device according to claim 1, characterized in that the second rod (27) has a cavity (28) which allows, thanks to one (36) of said orifices, to bring the large section chamber (24) into communication. with a fluid outlet (30). 3. Device according to any one of claims 1 or 2, characterized in that said differential piston (22) comprises an outer wall on which are hollowed out at least two grooves (37, 38), the ends of one (37 ) of these grooves opening into one (35) of said orifices and into the large-section chamber (24) respectively, the ends of the other groove (38) opening respectively into the other orifice (36) and into the small section chamber (23).

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