GB2403513A

GB2403513A - Hydraulic engine with stepped radial cylinders

Info

Publication number: GB2403513A
Application number: GB0420883A
Authority: GB
Inventors: Bernard Allart; Jean-Pierre Souply
Original assignee: Poclain Hydraulics Industrie
Current assignee: Poclain Hydraulics Industrie
Priority date: 2002-03-08
Filing date: 2003-03-05
Publication date: 2005-01-05
Anticipated expiration: 2023-03-05
Also published as: DE10392363B4; AU2003227811A1; WO2003076799A1; FR2836960B1; DE10392363T5; GB0420883D0; GB2403513B; FR2836960A1

Abstract

The invention relates to a hydraulic engine comprising a cylinder block (6) with stepped radial cylinders with two chambers (8A, 8B), a thrust body (4) and a fluid distributor (16). Each stepped cylinder can be connected to a connecting orifice (28) which connects to a distribution orifice (18A, 19A), each cylinder sleeve has a first and second line (24A, 24B) respectively permanently connected to the first and second working chamber of the cylinder (8A, 8B). The engine comprises a cylinder selector (30) which can be displaced between a first position, in which the first and second lines of the cylinder sleeve (24A, 24B) are connected to a connecting orifice (28) and a second position in which the first line (24A) is connected to a connecting orifice (28) and is isolated from the second line (24B) and the second working chamber (8B).

Description

Hydraulic motor with radial multistage cylinders The present invention

relates to a hydraulic motor comprising: - a cylinder block having at least one group of multistage cylinders, arranged radially relative to an axis of rotation and having a first and a second separate working chamber, each cylinder of said group cooperating with a piston designed to slide in this cylinder and having a cylinder pipe designed to be linked to a communication orifice located in a communication face, formed in a part of the motor integral to the cylinder block and at right angles to said axis of rotation, - a reaction unit mounted with rotation relative to the cylinder block about the axis of rotation, - a fluid distributor, which rotates as one with the cam and having a distribution face which is at right angles to the axis of rotation and which cooperates with said communication face, this distribution face having distribution orifices that are designed to be linked to a fluid feed or to a fluid outflow by distribution pipes and that are designed to communicate with said communication orifices.

A motor of this type is known, for example through the document FR 2 700 364 which discloses a motor with radial pistons having multistage cylinders, in other words comprising two separate chambers. In this particular case, it concerns a small diameter chamber which is near to the axis and a larger diameter chamber which is apart from it. The pistons are themselves multistage and comprise two parts of different diameters, respectively sliding in each of the two chambers.

This arrangement makes it possible to produce motors with high maximum cubic capacities, by making the best use of the space available in the cylinder block.

The invention is suited generally to a motor with radial pistons, which comprises at least one group of cylinders, each having two separate working chambers.

For example, the cylinder block can comprise a row of multistage cylinders and a row of non-multistage cylinders.

The object of the invention, based on this known motor, is to produce a hydraulic motor with radial pistons having at least two different active operating cubic capacities, the motor being extremely compact and the change of cubic capacity exploiting the existence of the two separate working chambers of at least certain cylinders.

This object is achieved through the fact that, for each cylinder of said group of multistage cylinders, the cylinder pipe comprises a first section permanently linked to the first working chamber and a second section permanently linked to the second working chamber, and the fact that the motor also comprises a cubic capacity selector and means of controlling this selector designed to move the latter between a first position in which, for each of said cylinders, the first section and the second section are linked to a communication orifice, and a second position in which, for each of said cylinders, the first section is linked to a communication orifice and is isolated from the second section and from the second working chamber linked to said second section.

The abovementioned FR 2 700 364 recommends the presence of a means of communication which provides permanent communication between the two working chambers of each cylinder of the group of multistage cylinders.

According to the present invention, the two working chambers are not permanently linked by such a communication means. In the first position of the cubic capacity selector, these two chambers intercommunicate - 3 through the fact that the first and second sections of the cylinder pipe are linked to a communication orifice. Thus, in this first position, it is the maximum cubic capacity of the group of multistage cylinders that is used to generate an engine torque.

Conversely, in the second position of the cubic capacity selector, only the first working chamber of each cylinder of the group of multistage cylinders is used to generate an engine torque by means of the link between the first section of the cylinder pipe of each of said cylinders and a communication orifice. At the same time, the second section of the cylinder pipe and the second working chamber are isolated from the communication orifice. The second working chamber is therefore isolated from the first and, since it is no longer connected to a communication orifice, it does not help to generate an engine torque.

Thus, according to the invention, it is the fact that the cylinders of the group of multistage cylinders each have two separate working chambers, that makes it possible, depending on whether the two chambers or only one of them are connected to a communication orifice, to operate the motor with different active operating cubic capacities. For this, the conformation of the cylinder pipe of each cylinder of the group of multistage cylinders is original in that it comprises both the abovementioned cylinder pipe sections.

An advantageous arrangement is defined by the fact that the cubic capacity selector is arranged in an axial cylinder bore of a part of the motor integral to the cylinder block, by the fact that, for each cylinder of the group of multistage cylinders, the first and second sections of the cylinder pipe are linked to said cylinder bore, respectively in a first and in a second connection area spaced axially and by the fact that the cubic capacity selector comprises, for each cylinder of the group of multistage cylinders, means forming a connecting axial groove designed, in the first position of the selector, to link said two connection areas and a means of separation designed to separate said two connection areas in the second position of the selector.

As will be seen in the description that follows, the axial cylinder bore can be implemented in the cylinder block or in an element such as a connecting ring that is integral to the cylinder block, at least with respect to the rotation about the axis of rotation. For each cylinder of the group of multistage cylinders, the first and second sections of the cylinder pipe are connected in two different areas of the axial cylinder bore. These sections can be extended at least partly substantially radially which, given that the motor has radial pistons, simplifies their geometry.

Advantageously, for each cylinder of the group of multistage cylinders, a communication orifice of the cylinder pipe is linked to said axial cylinder bore in a communication area and said connecting groove-forming means is designed to link said two connection areas and said communication area in the first position of the selector, while it is designed to link the first connection area and the communication area in the second position of the selector, in which the second connection area is separated from the first connection area.

In this second position of the selector, the second connection areas can be interlinked, all together or in groups.

They can thus all be connected to a sealed enclosed space or to an enclosed space linked to a non- pressurized tank, for example through the intermediary of the interior space of the motor, linked to such a tank by a leak return pipe. They can also be connected in groups to sealed enclosed spaces (such as grooves of the abovementioned cylinder bore), a group typically comprising the second connection areas of two cylinder pipes for which the pistons move in phase opposition.

According to an advantageous arrangement, the control means are designed to place the selector in a third position in which, for each cylinder of the group of multistage cylinders, the second section and a communication orifice are linked and are isolated from the first section of said pipe and from the first working chamber linked to said first section.

Thus, the motor presents three different active operating cubic capacities, in which, respectively, the two working chambers of each cylinder of the group of multistage cylinders are used to deliver the engine torque, or else only the first of these chambers used, or else only the second of these chambers is used.

In this case, advantageously, for each cylinder of the group of multistage cylinders, the communication section of the cylinder pipe is linked to said cylinder bore in the communication area, which is axially spaced from said first and second connection areas, and the cubic capacity selector comprises, for each cylinder of the group of multistage cylinders, connecting groove- forming means designed to link said communication area and the two connection areas in the first position of the cubic capacity selector, to link the communication area and the first connection area separated from the second connection area in the second position of the selector, and to link the communication area and the second connection area separated from the first connection area in the third position of the selector.

Advantageously, for each cylinder of the group of multistage cylinders, the cylinder pipe comprises, in addition, a third section which is permanently linked to the first working chamber and which is linked to the cylinder bore in a third connection area, the first connection area, the communication area, the second connection area and the third connection area being arranged successively in the axial direction and, for each cylinder of the group of multistage cylinders, the selector presents a first and a second connecting groove, arranged in such a way that: - in the first position of the cubic capacity selector, the first connecting groove links the communication area and the first connection area while the second connecting groove links the second and third connection areas, - in the second position of the selector, the first connecting groove links the communication area and the first connection area while the third connection area is isolated from the second connection area, and - in the third position of the selector, the first groove links the communication area and the second connection area while these two areas are isolated from the first connection area and from the third connection area.

Advantageously, the selector is a slide valve, arranged in the cylinder bore and integral to the cylinder block with respect to the rotation about the rotation axis, and the control means comprise a hydraulic control chamber and elastic return means cooperating with the slide valve in opposition.

When the selector is used to control only two different operating cubic capacities of the motor, it is sufficient for it to be able to be moved between two positions. In this case, it is sufficient for the fluid feed from the hydraulic control chamber to move the selector in a first direction to an end stop and for the connection of this chamber to an outflow to allow, - 7 - under the effect of the elastic return means, the selector to be moved in a second direction opposite to the first, to another end stop.

When, conversely, the selector is used to select three different cubic capacities, it must be able to occupy three positions in which, respectively, the two chambers are linked to a communication orifice, only the first chamber is linked to a communication orifice, or only the second chamber is linked to a communication Orlflce.

For this, all known control means, in particular mechanical, hydraulic or electronic, can be used. When hydraulic control means are to be used, those disclosed by documents FR 2 794 496, FR 2 781 532, FR 1 411 047 and EP 0 284 460 can be used as a basis. Thus, it could be possible to provide only one hydraulic control chamber for which the fluid feed up to a first feed pressure moves the selector in a first direction as far as a moving end stop, on encountering first elastic return means and for which the feed as far as a second feed pressure higher than the first moves said moving end stop in the same direction until it encounters second elastic return means, so enabling the selector to be moved over a longer travel as far as a first fixed end stop. When the chamber is linked to a fluid outflow, the selector is moved in the reverse direction as far as a second fixed end stop opposite to the first, under the effect of the first elastic return means, whereas, under the effect of the second elastic return means, the moving end stop can return to its initial position.

According to an advantageous arrangement, the cylinder bore is centered on the axis of rotation, the motor comprises a shaft which extends into this cylinder bore and the selector is a slide valve formed by a ring - 8 arranged around this shaft, the hydraulic control chamber then being formed around said shaft.

Advantageously, for each cylinder of the group of multistage cylinders, the two working chambers comprise a large-diameter working chamber and a small-diameter working chamber arranged between the axis of rotation of the motor and said large-diameter working chamber.

Said small- and large-diameter working chambers can be coaxial or noncoaxial.

The means of selecting the cubic capacity described above can be used to select the operating cubic capacity of the motor via the working chambers of the cylinders of the group of multistage cylinders.

As is known, a selection of the cubic capacity via the distribution orifices of the fluid distributor is known from the prior art. For this, a cubic capacity selector is interposed between the distributor and the main feed and outflow couplings to selectively interconnect the distribution orifices with the fluid feed or outflow.

When two successive distribution orifices are linked to the same main pipe (feed or outflow), the passage of a communication orifice in line with one and then the other of these orifices during the relative rotation of the cylinder block and of the distributor does not allow the working chamber linked to this communication orifice to stress its piston so as to generate an engine torque. This type of cubic capacity selector interposed between the distributor and the main couplings is, for example, known through document FR 2 794 496.

According to the invention, a first cubic capacity selector which selects the cubic capacity via the working chambers of the multistage cylinders and a second cubic capacity selector interposed between the distributor and the main couplings can be used - 9 - together. A large number of cubic capacity ratios can be obtained in this way. For example, if the first cubic capacity selector has three positions, while the second has only two, six different cubic capacity ratios can be obtained.

The invention will be clearly understood and its advantages will be better illustrated by reading the detailed description which follows, of an embodiment represented through non-limiting examples. The description refers to the appended drawings, in which: - figure 1 is an axial cross-sectional view of a hydraulic motor with radial pistons conforming to the invention; - figure 2 shows a design variant of the motor in figure 1; - figures 3 to 5 are half axial cross-sectional views showing design variants of a hydraulic motor according to the invention; and - figure 6 is an axial cross-sectional view showing another variant.

The motor in figure 1 comprises a fixed casing in four parts 1A, 1B, 1C and ID, assembled by screws 2.

The internal periphery 4 of the part 1B of the casing forms a reaction cam for the pistons of a cylinder block 6. The latter has cylinders arranged radially about an axis of rotation A which each comprise a first chamber 8A and a second chamber 8B. In this particular case, in the example of figure 1, the two chambers 8A and 8B of each cylinder are coaxial, in other words, they are centered on the same radius R originating from the axis A. Furthermore, for each cylinder, the first chamber 8A is the one that is furthest away from the axis A and which has the greatest diameter, whereas the second chamber 8B is nearer to the axis A. Inside each cylinder, a piston slides, each piston comprising a first part lOA which slides with seal tightness in the l - 10 - first chamber 8A of the cylinder concerned and a second part lOB which slides with seal tightness in the second chamber 8B of this cylinder. The piston ends cooperate with the cam 4 to turn the cylinder block relative to the motor casing. This cylinder block drives an output shaft 12 which is locked to it by axial salines 14.

The motors furthermore comprise an internal fluid distributor 16, which rotates as one with the cam 4 with respect to the rotation about the axis A and inside which are constructed distribution pipes 18 and 19 which, via grooves 20 and 21 of the distributor, are respectively linked to a main fluid feed coupling and to a main fluid outflow coupling. In this particular case, only the main coupling 22 to which the pipes 19 are connected via the groove 21 is represented in figure 1. The internal fluid distributor 16 has a distribution face 16A which is at right angles to the axis of rotation A and into which the distribution pipes open via distribution orifices, respectively 18A and 1 9A.

Each cylinder of the cylinder block has a cylinder pipe discharging into a communication orifice which, during the relative rotation of the cylinder block and the cam, is designed to communicate in turn with the different distribution orifices. More specifically, each cylinder pipe comprises a first section 24A, permanently connected to the first working chamber 8A and a second section 24B, permanently connected to the second working chamber 8B.

In the example in figure 1, a connecting ring 26 is arranged between the cylinder block 6 and the distributor 16. The first and second sections 24A and 24B of the cylinder pipes are formed in the cylinder block and they open into a connecting face 6A of the latter, respectively at orifices 23A and 23B. The connecting ring 26 has a connecting face 26B, in which - 11 a first and a second connecting orifice, respectively 23'A and 23'B, are arranged, and cooperates with the face 6A of the cylinder block. The connecting ring 26 comprises connecting holes, respectively 24'A and 24'B, which open into its connecting face 26B in the orifices 23 'A and 23 'B. Since the latter are in line with the orifices 23A and 23B, the connecting holes 24'A and 24 'B are respectively connected to the sections 24A and 24B of the cylinder pipes.

Each cylinder pipe is furthermore designed to communicate with a communication orifice 28, which is arranged in the radial face 26A of the connecting ring 26. This face 26A is at right angles to the axis A and presses against the distribution face 16A of the distributor, to allow communication between the communication orifices 28 and the distribution orifices 18A, IDA.

In this particular case, each cylinder pipe is permanently connected to a communication orifice 28, the connecting hole 24 'A extending, for each of these pipes, between the connecting orifice 23'A permanently connected to the first section 24A of the cylinder pipe and a communication orifice 28. The connecting ring 26 is made to rotate as one with the cylinder block, typically using spring pins 26' arranged between the orifices 23B and 23 'B. It is fixed axially by the fact of the axial stress exerted on the distributor in the direction of the cylinder block.

The motor in figure 1 further comprises a cubic capacity selector 30 which is arranged in an axial cylinder bore 26C of the connecting ring 26. The abovementioned connecting holes 24'A and 24'B link the connecting orifices 23'A and 23'B to the axial cylinder bore 26C in two connection areas, respectively 29A and 29B, which are axially spaced relative to each other. - 12

In its first position, represented in the top part of figure 1, the cubic capacity selector 30 is used to link the first and the second sections 24A and 24B of each cylinder pipe to a communication orifice 28. In its second position, represented in the bottom part of figure 1, the selector 30 isolates the first section 24A from the second section 24B and from the second working chamber 8B, whereas the first section 24A remains linked to the communication orifice 28 to connect the first working chamber 8A to this orifice.

In this second position, the two working chambers 8A and 8B of each multistage cylinder are therefore isolated from each other and, because of its link to a communication orifice, only the first working chamber 8A can be linked alternately to the fluid feed and to the fluid outflow, in such a way that the active cubic capacity is calculated according to the volumes of the first working chambers 8A of the various cylinders.

More specifically, the cubic capacity selector 30 comprises, for each cylinder of the group of multistage cylinders, a connecting groove 32 which, in its first position (top part of figure 1) links the two connection areas 29A and 29B. Given that, as has already been seen, the connecting hole 24'A is permanently linked to the communication orifice 28, this first position is effectively used to link the two sections 24A and 24B of the cylinder pipe concerned to its communication orifice 28. In figure 1, two diametrically opposed connecting grooves 32 can be seen.

In its second position, the selector separates the connection areas 29A and 29B of each cylinder pipe from each other. This separation is typically due to the fact that the connection area 29A is blanked off by the axial partition 30A of the selector. The connecting groove 32 linked to the cylinder pipe concerned is, for itself, in line with the connection area 29B. Thus, the - 13 - connecting holes 24 'B are isolated from the connecting holes 24'A and therefore from the communication orifices 28, in such a way that the second sections 24B of the cylinder pipes are not connected to a communication orifice.

In this second position, the second working chambers 8B are all linked to an enclosed space. In practice, the connecting ring 26, in its axial cylinder bore 26C, has an annular groove 26D which, in the second position of the selector, communicates with the connection areas 29B via the axial grooves 32. Thus, all the second working chambers 8B are interlinked via the enclosed space formed by the groove 26D. The latter can be sealed and simply be used to interlink the chambers 8B when, the selector being in its second position, they are "deactivated". It is important to note that it would also be possible to choose to link the second chambers 8B in groups in the second position of the selector, typically by choosing to interlink two chambers belonging to cylinders whose pistons are in phase opposition according to their position in the cylinder block.

It is, however, advantageous to provide for the enclosed space formed by the groove 26D to communicate permanently with the interior space 3 of the motor casing in such a way that, when the selector 30 is in its second position, it allows the working chambers 8B to be linked to the interior space of the motor. This is why a connecting pipe 27 can be provided in the ring 26. This interior space is advantageously linked to a non-pressurized tank through the intermediary of a leak return pipe that is not represented. Thus, the chambers 8B "deactivated" in the second position of the selector are not pressurized.

The selector 30 is a slide valve that is made to rotate with the cylinder block 6 about the axis A by a pin 31. - 14

The means of controlling this slide valve between its two positions comprise a hydraulic control chamber 34 and elastic return means 35 which cooperate with this slide valve in opposition. The control chamber 34 is linked to a control pipe 36 which can be fed with fluid or coupled to an outflow. In this particular case, a shaft 13 extends into the cylinder bore 26C in such a way that the selector 30 is a slide valve formed by a ring arranged around this shaft. The chamber 34 is itself formed around the shaft 13 by being sealed at its two opposing ends by gaskets, respectively 34A and 34B.

The shaft 13 which is arranged in the cylinder bore 26C is a brake shaft. In practice, it rotates as one with the cylinder block via splines similar to the abovementioned splines 14. This shaft passes inside a cylinder bore formed in the distributor and its end opposite to the cylinder block has annular brake disks 38. The part ID of the casing also has annular brake disks 39 which are inserted between the disks 38. The disks 38 and 39 are pressed against each other in the braking position by a piston 40, itself permanently returned to its braking position by elastic return means such as a Belleville spring washer 42. The disks 38 and 39 are arranged inside a brake release chamber 44 which can be fed with fluid via a brake release pipe 46 to move the piston 40 counter to the force exerted by the spring 42.

There now follows a description of figure 2, in which the elements that are unchanged from figure 1 retain the same references.

The variant in figure 2 differs from that in figure 1 on the one hand by the replacement of the connecting ring 26 by an extension 126 of the cylinder block 106 being as one with it and, on the other hand, by the 15 presence of an additional cubic capacity selector 148 in the internal fluid distributor 116.

The cylinder block 106 in practice has an axial extension 126 directed toward the distributor 116. The communication face 126A is formed by a radial face of this extension 126, pressing against the distribution face 116A of the distributor. The communication orifices 28 are formed in said face 126A. For each multistage cylinder, the cylinder pipe comprises a first section 124A and a second section 124B. The section 124A extends, in the extension 126, between the chamber 8A of the cylinder and the communication orifice 28 which is associated with it. As in the example in figure 1, a junction is used to connect this first section 124A to the axial cylinder bore 126A, in a first connection area 29A. The second section 124B extends between the second chamber 8B and a second connection area 29B.

In the variant in figure 1, the groove 26D ( linked or not to the interior space of the motor casing) was used to connect the chambers 8B in the second position of the selector 30.

In the variant in figure. 2, the axial cylinder bore 126C also has a groove, designated by the reference 126D.

It can be seen in the bottom part of figure 2 that, in its second position, the selector 30 connects the second connection areas 29B with this groove 126D, via the connecting grooves 32. The groove 126D permanently communicates with the interior space 3 of the motor via a connecting pipe 127 formed in the part 126 of the cylinder block.

- 16 - In its first position, the selector 30 connects, for each cylinder pipe, the first and second connection areas 29A, 29B, via the connecting grooves 32.

The means of controlling the selector, comprising the chamber 34 and the spring 35 are similar to those in figure 1.

In figure 2, the motor has an additional cubic capacity selector 148 which, in a manner known per se, is used to select several active motor operating cubic capacities by modifying the connection of certain distribution pipes to the fluid feed or outflow.

It is described briefly, by way of example, bearing in mind that, for this additional cubic capacity selector, any type of known cubic capacity selector inserted between the distribution pipes and the feed and outflow couplings can be considered.

In this particular case, the distributor 116 comprises three series of distribution pipes, respectively 117, 118 and 119, which are respectively linked to three grooves of the distributor, 120, 121 and 123. A main coupling 22 is permanently linked to the groove 123, while another main coupling is permanently linked to the groove 120.

The selector 148 has an axial cylinder bore 149, inside which is arranged a slide valve 150. This cylinder bore comprises three channels, respectively 151, 152 and 153, respectively permanently linked to each of the abovementioned three grooves 120, 121 and 123. The slide valve has a groove 154 which, in the position visible in figure 2, connects the channels 152 and 153 of the selector, and therefore interconnects thedistribution pipes coupled to the grooves 121 and 123, whereas the distribution pipes connected to the groove are isolated. The slide valve 150 is returned to - 17 its position represented in figure 2 by a spring 156.

By feeding fluid from a control chamber 158, from a control pipe 160, the slide valve 150 can be moved in the direction F until it reaches a position in which the groove 154 interlinks the channels 151 and 152.

For example, the main coupling linked to the groove 120 is an outflow coupling, such that the distribution pipes 117 are all outflow pipes, whereas the coupling 22 is linked to the feed, such that the pipes 119 linked to the groove 123 are all feed pipes. Two pairs of distribution pipes respectively comprise a pipe 117 and a pipe 118, and a pipe 117 and a pipe 119. Thus, in the position in figure 2, the slide valve 150 selects the maximum cubic capacity in which the abovementioned two pairs each have a distribution orifice linked to the feed and a distribution orifice linked to the outflow.

If the slide valve 150 is moved in the direction of the arrow F. the grooves 120 and 121 are interlinked whereas the groove 123 is isolated. In this case, one of the abovementioned two pairs of distribution pipes comprises a pipe 117 linked to the groove 120, therefore to the outflow, and a pipe 119 linked to the groove 123, therefore to the feed. Conversely, the other pair comprises a pipe 117 linked to the groove and a pipe 118 linked to the groove 121, both to the outflow. This second pair is therefore inactive, that is to say, when a communication orifice passes successively in line with the distribution orifice of each of the two pipes of this second pair, no pressure differential occurs in the cylinder of this communication pipe and no engine torque is generated by the piston contained inside this cylinder.

Thus, the selector 148 is used, according to its position, to ensure that all the pairs of two consecutive distribution orifices are active, and 18 - comprise an orifice linked to the feed and an orifice linked to the outflow, or conversely, that certain pairs are inactive comprising two orifices, both linked to the same pressure, either to the feed or to the outflow.

For its part, the selector 30 is used to ensure that, when a communication orifice comes into line with a distribution orifice, the two chambers 8A and 8B of the cylinder associated with this communication orifice are effectively linked to a distribution orifice or that only the chamber 8A is.

It is therefore understood that the selector 30 is used to select two active cubic capacities through the chambers 8A and 8B, whereas the selector 148 is used to - select two active cubic capacities through the distribution pipes. In each of the two positions of the selector 30, two positions are possible for the selector 148, such that four possible active cubic capacities are obtained.

The use of a cubic capacity selector cooperating with the distribution pipes to obtain three different cubic capacity ratios is known, for example from document FR 1 411 047. By combining a cubic capacity selector of this type with the cubic capacity selector 30 of the invention, six cubic capacity ratios can be obtained.

As will be seen in the description that follows

(figure 4), the invention can be used to select three different operating cubic capacities through the chambers of the multistage cylinders. In this case, the cubic capacity selector of the invention, combined with a selector cooperating with the distribution pipes, can be used to obtain six, even nine cubic capacity ratios.

- 19 - There now follows a description of figure 3, in which the elements that are unchanged from the preceding figures retain the same references. l

In figure 3, the interior axial cylinder bore of the cylinder block 206 is not provided with splines to drive a shaft. In practice, the output shaft of the motor 212 is formed in a single piece with the cylinder block and the cylinder bore 226C in which the cubic capacity selector 230 is positioned is formed by an axial void in the cylinder block, extending in the same axial segment as the cylinders.

The communication face 226A is a radial face of the cylinder block 206 formed in a radial plane near to the cylinders of the latter. Thus, the axial bulk of the motor is reduced compared to that in figures 1 and 2, since neither the ring 26 nor the extension 126 is needed.

The first and second sections 224A, 224B of each cylinder pipe discharge into the axial cylinder bore 226C, respectively in a first and in a second connection area, 229A, 229B.

The geometry of these pipe sections can be simplified compared to that in figures 1 and 2. In practice, as can be seen in figure 3, they can each be extended practically like a single pipe segment which is radial, respectively from the chambers 208A and 208B.

In figure 3, the connecting groove 232 formed axially at the outer periphery of the selector 230 for each cylinder pipe interlinks the connection areas 229A and 229B, such that the chambers 208A and 208B of the multistage cylinder represented are linked. -

In figure 3, the first section 224A of the cylinder pipe is permanently linked to the communication orifice 28.

Since the pipe sections 224A and 224B extend substantially radially, it is easier to choose, in the variant in figure 3, the first working chamber 208A to be the one which has a small diameter and which is therefore nearest to the axis A. In practice, in this case, the second section 224B which is connected from the cylinder bore 226C to the second working chamber 208B has larger dimensions than the first section and it is easier to arrange it such that the first section 224A is situated between the communication face 226A of the cylinder block and said second section 224B. This allows the connecting grooves 232 to be implemented in the form of axial grooves. It is, however, possible to provide grooves having a different form, for example a spiral portion, and to arrange the two sections of a cylinder pipe such that they are angularly offset from each other. It would also be possible to replace the grooves 232 with pipes, provided axially or substantially axially in the selector and open only at their ends.

In figure 3, the first section 224A of the cylinder pipe is permanently linked to the orifice 28 by a branch 225 which extends axially in the cylinder block.

If the selector 230 is moved in the direction F in figure 3, until the connecting groove 232 is positioned in line with the second connection area 229B, by separating the first connection area 229A from this second area by the axial partition 230A of the selector 230, a second active operating cubic capacity smaller than the first is obtained. In practice, in this case, only the chamber 208A remains connected to the communication orifice 28, via the abovementioned connecting section 225. Conversely, the second section - 21 224B of the cylinder pipe discharges simply into the cylinder bore 226C and the chamber 208B is not connected to a communication orifice. By forming, in the cylinder bore 226C, an annular groove similar to the groove 26D described with reference to figure 1, the selector 230, in its second position, can be made to connect all the chambers 208B with such a groove, via the connecting grooves 232.

However, in this particular case, the cylinder bore 226C permanently communicates with a communication pipe 227 which is connected to the interior space 3 of the motor casing, the latter possibly being in turn linked to a non-pressurized tank through the intermediary of a leak return pipe. It is understood that, in the second position of the slide valve 230, the second sections 224B of the cylinder pipes are all linked to this interior space of the motor via the communication pipe 227.

The selector 230 is arranged inside the axial cylinder bore in such a way as to separate inside the latter a hydraulic control chamber 234 from another chamber which contains a return spring 235. It is this other chamber which is linked to the interior space of the motor via the communication pipe 227. A control pipe 236 is linked to the chamber 234.

The selector 230 rotates as one with the cylinder block. For example, a rotating shim 231A is locked relative to the cylinder block (for example, by teeth around its external periphery) and features, on its internal periphery, a stud (in the cutting plane) which penetrates into an axial slot 231B on the outer periphery of the selector. Any other rotation locking means allowing a displacement, typically by a pin, can be considered. - 22

In figure 3, the additional cubic capacity selector 148 similar to that in figure 2 is used to obtain two different methods of linking the distribution pipes to the main fluid feed and outflow couplings, such that a total of four cubic capacities is possible.

There now follows a description of the motor in figure 4 for which the casing is in two parts, 301A and 301B.

The distributor 16 is similar to that in figure 1. The radial cylinders of the cylinder block 306 each have two different working chambers, respectively 308A and 308B. For each of these cylinders, the cylinder pipe comprises a first section 324A permanently linked to the chamber 308A and a second section 324B permanently linked to the chamber 308B. These two sections discharge into the axial cylinder bore 326C of the cylinder block 306, respectively in a first connection area 329A and a second connection area 329B.

The cylinder pipe also has a communication section 324C, which is separate from the first and second sections 324A, 324B and which is permanently linked to a communication orifice 28.

This communication section is linked to the cylinder bore 326C in a communication area 329C.

In the preceding figures, this communication section was permanently linked to the first section of the cylinder pipe, because it formed a part of this first section (for example, branch 225 in figure 3).

Thus, in the variants in figures 1 to 3, the abovementioned communication area was always formed by the first connection area, via which the first section of the cylinder pipe was linked to the cylinder bore.

- 23 - In figure 4, the communication area 329C is, conversely, separate from the two connection areas from which it is axially spaced. l

The cubic capacity selector 330 comprises connecting groove-forming means which, in the first position of this selector, link the communication area 329C and the two connection areas, 329A and 329B.

Conversely, in its second position, the selector 330 interlines only the communication area 329C and the first connection area 329A, which is separate from the second connection area 329B. In its third position, the selector 330 can link the second connection area 329B with the communication area 329C, isolating the second connection area from the first connection area 329A.

It is assumed that the useful volume of the first working chambers 308A and that of the second working chambers 308B are respectively designated VA and VB.

With this convention, the large cubic capacity of the motor determined by the first position of the selector corresponds to the sum VA + VB. In the second position of the selector, only the chambers 308A are "active", so that the cubic capacity is determined by the volume VA. In the third position, only the chambers 308B are "active", so that the cubic capacity is determined by the volume VB.

Based on the information contained in French patent No. 2 127 268, it would also be possible to provide a fourth cubic capacity which would correspond to the volume VA - VB. For this, it would be necessary at a given time for the chamber 308A to be linked to a first communication orifice while the chamber 308B is linked to a second communication orifice, the two communication orifices being, at that moment, respectively linked to the fluid feed and to the fluid outflow. The selector would then have a particular - 24 conformation because, for each pair of a first and a second working chamber of a cylinder, it would comprise a pair of communication sections respectively linked to a first and to a second communication orifice. There would then be a selector position in which the two chambers would be linked respectively to each of these two orifices.

This is not shown in figure 4, which is now described in greater detail. The cylinder pipe of the cylinder represented in this figure comprises a third section 324D which is permanently linked to the first working chamber 308A and which is linked to the cylinder bore 326C in a third connection area 329D.

It can be seen in figure 4 that the first connection area 329A, the communication area 329C, the second connection area 329B, and the third connection area 329D are in turn arranged in the axial direction F. For each cylinder of the group of multistage cylinders, the selector has a first and a second connecting groove, respectively 332A and 332B. In the first position of the cubic capacity selector visible in figure 4, the first connecting groove 332A links the communication area 329C and the first connection area 329A, whereas the second connecting groove interlines the second and third connection areas 329B, 329D.

In this situation, the first working chamber 308A is connected to the communication orifice 28 by the fact that the first section 324A of the cylinder pipe communicates with the communication section 324C via the groove 332A which links the areas 329A and 329C.

Also, the chamber 308B communicates with said chamber 308A by the fact that the second section 324B of the cylinder pipe communicates with the third section 324D of this pipe via the second groove 332B. Thus, all of the useful volume of the chambers 308A and 308B is - 25 exploited to generate an engine torque. This position is therefore that of the large cubic capacity.

In the second position of the selector 330, in which the latter is moved in the direction of the arrow F over a distance D1, the first connecting groove 332A continues to link the communication area 329C and the first connection area 329A, whereas the third connection area 329D is isolated from the second connection area 329B.

In this case, the first working chamber 308A of the cylinder is connected to the communication orifice 2B by the fact that the first section 324A of the cylinder pipe is linked to the communication section 324C by the groove 332A. Conversely, the second working chamber 308B is no longer linked to the first working chamber 308A, so that this chamber 308B, which is no longer linked to the communication area 329C, is no longer linked to the communication orifice 28. The result is that the second working chamber 308B is inactive.

Advantageously, in this situation, the chamber 308B is linked to an interior space of the motor. To this end, the selector 330 comprises, for each multistage cylinder, a connecting hole 360, which is arranged radially and which, in the second position of the selector, is in line with the second connection area 329B. This hole discharges into the interior space 331 of the slide valve, and all the second working chambers 308B can thus be interlinked.

In figure 4, this interior space of the slide valve permanently communicates with a part of the cylinder bore 326C which is itself permanently linked to the interior space of the motor casing by a communication pipe 327. Since this interior space can be linked to a nonpressurized tank through the intermediary of a motor leak return pipe, the second working chambers - 26 308B can thus all be set to the atmospheric pressure of this tank.

For some applications, it could be enough to deactivate the chambers 308B by setting them to the same pressure which would not necessarily be that of this tank. For example, it would be possible to link them all to a sealed enclosed space formed by the fact that the holes 360 would be replaced by a continuous groove open only on the outer axial face of the selector 330.

This selector rotates as one with the cylinder block.

In this particular case, a pin 331A is interlocked with the selector and is engaged in an axial slot 331B of the cylinder block in which it slides when the selector moves.

In the third position of this selector, in which it is moved in the direction F over an additional distance D2, the first connecting groove 332A links the communication area 329C and the second connection area 329B, whereas these two areas are isolated from the first connection area 329A and from the third connection area 329D. In this situation, the second working chamber 308B is linked to the communication orifice 28 by the link between the second section 324B of the cylinder pipe and the communication section 324C. Conversely, the chamber 308A ceases to be connected to the communication orifice 28.

In this situation, it is advantageous to ensure that the chambers 308A are interlinked. Since this is the case for the chambers 308B in the second position of the selector, they are advantageously linked to the interior space of the motor which is itself linked to the leak return pipe. In figure 4, this link can be provided by the second connecting groove 332B which, in the third position of the selector, connects the third connection area 329D to the part of the cylinder bore - 27 326C into which the pipe 327 discharges. As was indicated previously for the chambers 308B, the chambers 308A could be interlinked in a sealed enclosed space, without making them communicate with the interior space of the motor.

Naturally, the embodiment in figure 4 is compatible with the replacement of the distributor 16 by a distributor similar to the distributor 116 in figure 2, cooperating with an additional cubic capacity selector.

If this selector has at least two positions, a motor having a total of six different cubic capacity ratios can be obtained. If, as has been indicated previously, the selector 330 is replaced by a selector which, in a fourth position, can be used to obtain a cubic capacity corresponding to VA - VB, then with an additional selector of the type of the selector 148, eight different cubic capacity ratios can be obtained. By replacing this selector with a three-position, and therefore three- cubic capacity, selector, twelve cubic capacity ratios can be obtained.

It can be seen in figure 4 that the motor comprises a positive engagement brake. In practice, the first braking teeth 338 are integral with a radial face of the cylinder block 306, whereas the second braking teeth 339 are supported by a braking piston 340 which rotates as one with the motor casing. This piston is constantly returned to the braking position by elastic return means 342, and it can be forced to its brake release position by feeding fluid from a brake release chamber 344, via a brake release pipe 346. A brake of this type is known from document FR 2 765 637.

In figure 4, the means of controlling the movement of the selector 330 comprise a hydraulic control chamber 334 designed to be connected to a fluid feed and outflow via a control pipe 336. This chamber is - 28 arranged on a first side of the selector 330 formed by a slide valve.

Elastic return means have an opposing effect on the movement of the selector 330. In this particular case, such return means are arranged on the other side of the selector from the chamber 334, in other words in the space 331. These return means comprise two springs 335A and 335B. When the chamber 334 is fed with fluid under pressure to a limit pressure, the selector 330 moves in the direction F. over the distance D1, compressing the first spring 335A, until it presses against a moving end stop 337A which is constantly returned in the direction opposite to the direction F by the second spring 335B. If the pressure in the control chamber 334 increases beyond the abovementioned limit pressure, the selector moves more in the direction of the arrow F driving with it the moving end stop 337A, which compresses the spring 335B, until its movement is limited by a fixed end stop 337B.

Naturally, any control means enabling a selector to be moved between three positions can be used instead of those represented in figure 4.

There now follows a description of figure 5 in which the two parts of casing 301A, 301B, the distributor 16 and the brake 340, 342, 344, 346 are similar to those in figure 4. The cubic capacity selector 230 is itself similar to that in figure 3. Overall, the variant in figure 5 corresponds to that in figure 3, except that no additional cubic capacity selector cooperates with the distributor pipes. The cylinder block 406 differs only from the cylinder block 206 of figure 3 by the fact that the active chambers of the multistage cylinders, respectively 408A and 408B, are not coaxial.

In practice, the axis RA of the chamber 408A is offset relative to the axis RB of the chamber 408B toward the distributor 16. In comparison to the embodiment in - 29 - figure 3, this provides, on the side opposite from the chamber 408A relative to the distributor, for more space in the cylinder block to house the second section 424B of the cylinder pipe. Furthermore, this arrangement can be used to prevent the piston from pivoting on itself inside the cylinder, so a saving on additional devices used to avoid such pivoting can be achieved. The first section 424A of this pipe is, for itself, similar to the first section 224A of the pipe in figure 3 and, like it, it is permanently linked to a communication orifice by a branch 225. Because of the space available in the cylinder block alongside the cylinders opposite to the distributor, the communication pipe 227 can be replaced with a communication pipe 427 extending substantially radially alongside a cylinder.

The axes RA and RB of the chambers 408A and 408B can be formed by radii centered on the axis of rotation A of the motor. In figure 5, the motor output is formed by a flange 412 integral to the cylinder block 406.

The variant in figure 6 differs from the preceding variants in that it concerns a rotating cam motor.

The various external couplings of the motor are arranged in a fixed part of the latter, inside the distribution cover 501B. The cam 4 is formed at the interior periphery of a rotating casing part 501A and the motor is sealed on the side opposite to the distribution cover 501B by an also rotating casing part 501C. The internal fluid distributor 516 is made to rotate as one with this rotating casing part 501C by an interlocking shaft 513 with which it cooperates via splines 517. The cylinder block 506 is fixed with respect to the rotation about the axis A of the motor.

In practice, it can be fixed to a part of the chassis by screws positioned in tapped holes 502. This cylinder block has multistage cylinders which each comprise two - 30 - different working chambers, respectively a first chamber 508A and a second chamber 508B.

The different variants explained previously with respect to the selection of the cubic capacity by the selective communication of the working chambers of the cylinders of the communication orifices can be used.

To simplify, figure 6 shows a variant which is similar to that in figure 5. In practice, the first and second sections 524A and 524B of each cylinder pipe discharge into an axial cylinder bore 526C of the cylinder block in two connection areas, respectively 529A and 529B which are separate. These sections extend radially. The selector 530 has, for each multistage cylinder, an axial groove 532. In the first position of this selector represented in figure 6, the grooves 532 connect the first and second connection areas 529A and 529B of each cylinder pipe. Given that the first section 524A of the cylinder pipe is connected to a communication orifice 28 by an axial branch 525, this position is that of the large cubic capacity, in which the volumes of the chambers 508A and 508B are used to generate an engine torque.

The selector can be moved axially in the direction F by feeding fluid to a control chamber 534, and against the opposing effect of a return spring 535. It thus reaches a second position, in which the groove 532 is only in line with the second connection areas 529B, whereas the first connection areas 529A are isolated by the axial partition 530A of the selector. In this case, only the chambers 508A are connected to the communication orifices 28 and they alone contribute to the generation of the engine torque, whereas the chambers 508B are inactive. The second sections of the cylinder pipes 524B are each linked to the interior space of the motor by a groove 532. More specifically, in the second position of the selector 530, the grooves 532 connect - 31 - together all the second sections 524B and connect them with the interior space of the cylinder bore 526C of the cylinder block, on the side opposite to the control chamber 534, said interior space of which is isolated by the selector itself. The hole or holes 527 permanently connect this interior space of the cylinder bore to the interior space 503 of the motor casing, which is connected to a tank by a leak return pipe 505, a hole 503' formed in the part of the cylinder block which is located above the distribution cover enabling this communication. - 32

Claims

1. A hydraulic motor comprising: - a cylinder block (6; 106; 206; 306; 406; 506) having at least one group of multistage cylinders, arranged radially relative to an axis of rotation (A) and having a first and a second separate working chamber (8A, 8B; 208A, 208B; 308A, 308B; 408A, 408B; 508A, 508B), each cylinder of said group cooperating with a piston ( lOA, lOB) designed to slide in this cylinder and having a cylinder pipe designed to be linked to a communication orifice (28) located in a communication face (26A; 126A; 226A; 326A), formed in a part of the motor integral to the cylinder block and at right angles to said axis of rotation, - a reaction unit (4) mounted with rotation relative to the cylinder block about the axis of rotation, - a fluid distributor (16; 116; 516), which rotates as one with the cam (4) and having a distribution face ( 16A; 116A) which is at right angles to the axis of rotation and which cooperates with said communication face, this distribution face having distribution orifices (18A, l9A) that are designed to be linked to a fluid feed or to a fluid outflow by distribution pipes (18, 19; 117, 118, 119) and that are designed to communicate with said communication orifices, characterized in that, for each cylinder of said group of multistage cylinders, the cylinder pipe comprises a first section (24A; 124A; 224A; 324A; 424A; 524A) permanently linked to the first working chamber (8A; 208A; 308A; 408A; 508A) and a second section (24B; 124B; 224B; 324B; 424B; 524B) permanently linked to the second working chamber (8B; 208B; 308B; 408B; 528B), and in that it also - 33 comprises a cubic capacity selector (30; 230; 330; 530) and means of controlling this selector (34, 35; 234, 235; 334, 335A, 337A, 335B; 534, 535) designed to move the latter between a first position in which, for each of said cylinders, the first section (24A; 124A; 224A; 324A; 424A; 524A) and the second section (24B; 124B; 224B; 324B; 424B; 524B) are linked to a communication orifice (28), and a second position in which, for each of said cylinders, the first section is linked to a communication orifice (28) and is isolated from the second section and from the second working chamber (8B; 208B; 308B; 408B; 508B) linked to said second section.

2. The motor as claimed in claim 1, characterized in that the cubic capacity selector (30; 230; 330; 530) is arranged in an axial cylinder bore (26C; 126C; 226C; 326C; 526C) of a part (26; 126; 206; 306; 406; 506) of the motor integral to the cylinder block (6; 106; 206; 306; 406; 506), and in that, for each cylinder (8A, 8B; 208A, 208B; 308A, 308B; 408A, 408B; 508A, 508B) of the group of multistage cylinders, the first and second sections (24A, 24B; 124A, 124B; 224A, 224B; 324A, 324B; 424A, 424B; 524A, 524B) of the cylinder pipe are linked to said cylinder bore, respectively in a first and in a second connection area (29A, 29B; 229A, 229B; 329A, 329B; 529A, 529B) spaced axially and in that the cubic capacity selector (30; 230; 330; 530) comprises, for each cylinder of the group of multistage cylinders, means forming a connecting axial groove (32; 232; 332A; 332B; 532) designed, in the first position of the selector (30; 230; 330; 530), to link said two connection areas and a means of separation (30A; 230A; 330A; 530A) designed to separate said two connection areas in the second position of the selector. - 34

3. The motor as claimed in claim 2, characterized in that, for each cylinder (8A, 8B; 208A, 208B; 308A, 308B; 408A, 408B; 508A, 508B) of the group of multistage cylinders, a communication orifice (28) of the cylinder pipe is linked to said axial cylinder bore (26C, 126C, 226C; 326C; 526C) in a communication area (29A; 229A; 329C; 529A) and said connecting groove-forming means (32; 232; 332A, 332B; 532) is designed to link said two connection areas (29A, 29B; 229A, 229B; 329A, 329B; 529A, 529B) and said communication area (29A; 229A; 329C; 529A) in the first position of the selector (30; 230; 330; 530), while it is designed to link the first connection area (29A; 229A; 329A; 529A) and the communication area (29A; 229A; 329C; 529A) in the second position of the selector, in which the second connection area is separated from the first connection area.

4. The motor as claimed in claim 2 or 3, characterized in that said axial cylinder bore (126C; 226C; 326C; 526C) is formed in the cylinder block (106; 206; 306; 406; 506).

5. The motor as claimed in claim 2 or 3, characterized in that said axial cylinder bore (26C) is formed in a connecting ring (26) integral to the cylinder block (6), and in that, for each cylinder (8A, 8B) of the group of multistage cylinders, said first and second sections (24A, 24B) of the cylinder pipe open into a connecting face ( 6A) of the cylinder block ( 6) corresponding with, respectively, a first and a second connecting orifice (23'A, 23'B) provided in a connecting face (26B) of the connecting ring (26) which cooperates with said connecting face ( 6A) of the cylinder block, the communication face (26A) being formed by a face of said connecting ring opposite to the connecting face of said ring, and - 35 in that the connecting ring comprises connecting holes (24'A, 24'B) linking said first and second connecting orifices to said axial cylinder bore (26C) .

6. The motor as claimed in any one of claims 1 to 5, characterized in that, for each cylinder (8A; 8B; 208A, 208B; 408A, 408B; 508A, 508B) of the group of multistage cylinders, the first section (24A; 124A; 224A; 424A; 524A) of the cylinder pipe is permanently linked to a communication orifice (28) . l

7. The motor as claimed in any one of claims 1 to 5, characterized in that, for each cylinder (308A, 308B) of the group of multistage cylinders, the cylinder pipe also has a communication section (324C), separate from said first and second sections (324A, 324B) and permanently linked to a communication orifice (28).

8. The motor as claimed in any one of claims 1 to 7, characterized in that the control means (334, 335A, 337A, 335B) are designed to place the selector (330) in a third position in which, for each cylinder (308A, 308B) of the group of multistage cylinders, the second section (324B) and a communication orifice (28) are linked and are isolated from the first section (324A) of said pipe and from the first working chamber (308A) linked to said first section.

9. The motor as claimed in claims 3, 7 and 8, characterized in that, for each cylinder (308A, 308B) of the group of multistage cylinders, the communication section (324C) of the cylinder pipe is linked to said cylinder bore (326C) in the communication area (329C), which is axially spaced from said first and second connection areas (329A, - 36 329B), and in that the cubic capacity selector (330) comprises, for each cylinder of the group of multistage cylinders, connecting groove-forming means (332A, 332B) designed to link said communication area (329C) and the two connection areas (329A, 329B) in the first position of the cubic capacity selector (330), to link the communication area (329C) and the first connection area (329A) separated from the second connection area (329B) in the second position of the selector, and to link the communication area (329C) and the second connection area (329B) separate from the first connection area (329A) in the third position of the selector.

10. The motor as claimed in claim 9, characterized in that, for each cylinder (308A, 308B) of the group of multistage cylinders, the cylinder pipe also comprises a third section (324D) which is permanently linked to the first working chamber (308A) and which is linked to the cylinder bore (326C) in a third connection area (329D), the first connection area (329A) , the communication area (329C), the second connection area (329B), and the third connection area (329D) being arranged successively in the axial direction, and in that, for each cylinder of the group of multistage cylinders, the selector (330) has a first and a second connecting grooves (332A, 332B), arranged such that: - in the first position of the cubic capacity selector (330), the first connecting groove (332A) links the communication area (329C) and the first connection area (329A) whereas the second connecting groove (332B) links the second and third connection areas (329B, 329D), - in the second position of the selector, the first connecting groove (332A) links the communication area (329C) and the first connection - 37 area (329A) whereas the third connection area (329D) is isolated from the second connection area (329B), and - in the third position of the selector, the first connecting groove (332A) links the communication area (329C) and the second connection area (329B) whereas these two areas are isolated from the first connection area (329A) and from the third connection area (329D).

11. The motor as claimed in any one of claims 1 to 10, characterized in that it comprises means (32, 26D; 32; 126D; 232; 332B, 360; 532) for linking to an enclosed space the working chambers of the cylinders of the group of multistage cylinders which are isolated from the communication orifices (28) of the cylinder pipes of these cylinders according to the position of the cubic capacity selector (30; 230; 330; 530).

12. The motor as claimed in claims 2 and 11, characterized in that the cylinder bore has an enclosed space (26D; 126D; 331) which permanently communicates with the interior space ( 3; 503) of the motor and in that the selector is designed to link to said enclosed space of the cylinder bore the working chambers isolated from the communication orifices according to the position of said selector.

13. The motor as claimed in claim 2 and any one of claims 1 to 12, characterized in that the selector (30; 230; 330; 530) is a slide valve, arranged inside the cylinder bore (26C; 126C; 226C; 326C; 526C) and integral to the cylinder block (6; 106; 206; 306; 406; 506) with respect to the rotation about the axis of rotation (A) and in that the control means comprise a hydraulic control chamber (34; 234; 334; 534) and elastic return means (35; - 38 235; 335A, 335B; 535) cooperating with the slide valve in an opposing way.

14. The motor as claimed in claim 13, characterized in that the cylinder bore is centered on the axis of rotation, in that the motor comprises a shaft (13) which extends into this cylinder bore (26C), and in that the selector (30) is a slide valve formed by a ring arranged around this shaft and the hydraulic control chamber (34) is formed around said shaft.

15. The motor as claimed in any one of claims 1 to 14, characterized in that, for each cylinder (408A; 408B) of the group of multistage cylinders, the two working chambers comprise a large-diameter working chamber (408B) and a small-diameter working chamber (408A) arranged between the axis of rotation (A) of the motor and said large diameter working chamber (408B) and in that said small and large-diameter working chambers are not coaxial.