EP1612411B1 - Hydraulic motor - Google Patents

Description

The present invention relates to a hydraulic motor comprising a cam and a cylinder block able to rotate relative to each other about an axis of rotation, the cam comprising a plurality of cam lobes each having a rising ramp and a downward ramp and the cylinder block having a plurality of cylinders in which pistons adapted to cooperate with the cam are slidably mounted, the motor further comprising a fluid distributor, integral with the cam with respect to the rotation around the axis of rotation and comprising distribution ducts connected to a supply or an exhaust and able to communicate with the cylinders during the relative rotation of the cylinder block and the cam by distribution orifices each arranged in correspondence with a ramp of a cam lobe so that a cylinder whose piston cooperates with a rising ramp can be connected to the feed and that a cylinder whose foot ston cooperates with a down ramp can be connected to the exhaust, the instantaneous angular positions in which the pistons cooperate with the cam during the relative rotation of the cylinder block and the cam being such that the engine is substantially homokinetic.

A hydraulic motor of this type is known from the prior art. This is for example a radial piston hydraulic motor of the type described in French Patent Application No. 2,834,012.

The motor is substantially homokinetic, which means that, when the fluid feed rate is constant, the rotation speed of the rotating part of the engine (cylinder block or cam) is substantially constant. In other words, the rotation takes place smoothly. In a homokinetic motor, the fluid balance must be substantially zero, that is to say that at each moment, the amount of fluid entering the cylinders must be substantially equal to the amount of fluid leaving the cylinders.

In engines of this type, it is generally sought to distribute the rolls regularly in the cylinder block. In other words, the angular spacing between the cylinders of each pair of consecutive cylinders is constant. This regular distribution is particularly concerned with ensuring that the center of symmetry of the cylinder block is substantially located on its geometric axis, which is also its axis of rotation. Moreover, in general, when designing an engine, a compact embodiment is sought which, with regard to the cylinder block, notably leads to defining the minimum space required between two consecutive cylinders taking into account the size of these cylinders which is necessary to obtain the desired cubic capacity.

Starting from a basic engine, one can seek to achieve a slightly different engine, especially a motor having a reduced displacement. In this approach, for the sake of economy and rationalization, it is sought to use as much as possible for the engine of reduced capacity, parts already defined for the basic engine.

The displacement of an engine depends on the size of the cylinders and the maximum possible stroke of the pistons disposed in these cylinders. This stroke itself depends on the amplitude of the undulations of the cam, that is to say the depth of the cam lobes. Thus, starting from an existing engine, it is possible to define a reduced displacement engine by replacing the cam of this pre-existing motor with a new cam whose lobes have a reduced depth compared to those of the pre-existing cam. This being so, this technique has limitations. It returns to reduce the slope of the cam lobe ramps, which is only possible to a certain extent to preserve the essential qualities of the engine. It is thus considered that it is not generally suitable to reduce the stroke of the pistons by more than 50%.

It should be added that it is not always desirable, to define a hydraulic motor having a displacement smaller than that of a pre-existing engine, to design a motor whose elements have a size smaller than that of the corresponding elements of the engine. preexisting. In particular, the requirement for braking torque, sizing the bearing or bearings necessary to support the object rotated by the motor or speed of the latter may require the presence of sufficiently large components. In addition, it may be advantageous to keep for the engine with reduced displacement dimensions of space identical to those of the pre-existing engine, in particular to make it interchangeable.

The present invention aims to define an engine that can be derived from a pre-existing engine having a larger displacement by other methods than that, mentioned above, of reducing the depth cam lobes, and having a large number of parts in common with the original engine.

This object is achieved thanks to the fact that, in any relative position of the cylinder block and the cam, there is at least one unused cam lobe with which no piston cooperates and that the angular spacings between two consecutive cylinders are different. between them and different from a multiple of the smallest angular spacing between two consecutive cylinders, said angular spacings being determined such that the resultant of the forces exerted by the pistons on the cam is low or substantially zero.

In the engine according to the invention, it is by using a reduced number of cylinders always leaving at least one instantaneously unused cam lobe and by defining a particular distribution of these cylinders in the cylinder block that one manages to achieve a reduced displacement. In fact, this engine can be distinguished from an original engine only by its cylinder block, all other parts, and even the pistons, can be kept except that the number of pistons is obviously reduced.

When the engine is defined from a pre-existing engine, its cost is reduced compared to that of an engine of the same reduced displacement, obtained by reducing the depths of the cam lobes of the pre-existing engine. This decrease in cost comes from the reduction in the number of cylinders (fewer holes to machine, fewer pistons).

In the engine of the invention, the distribution of the rolls in the cylinder block is no longer regular as in the engines of the prior art and, contrary to the prior art, it is not sought to have a maximum of cylinders in the cylinder block taking into account the size of the latter. On the contrary, the rolls are distributed irregularly but to ensure that the motor is substantially homokinetic with this irregular distribution and that it is substantially balanced, that is to say that the resultant forces exerted by the pistons on the cam is weak or substantially zero.

In the engine of the invention, it is possible to obtain number of cylinder combinations on a number of cam lobes that can not be obtained for a homokinetic motor having a regular distribution of the cylinders.

The qualifier "weak" means that this resultant is sufficiently low to avoid premature wear of certain parts of the engine (in particular the bearings) that would result from the need to compensate for this resultant. In other words, the service life of the bearings is substantially the same for this reduced displacement engine as for a similar engine of origin but having the maximum of cylinders that can be housed in its cylinder block, and spaced from each other . In particular, it is considered that the resultant of the forces exerted by the pistons on the cam is small if it is at most of the same order of magnitude as the thrust force of a piston in its cylinder (between 0 and 1 to 1.3 times this effort).

For the purposes of the present patent application, the fact that a cam lobe is "unused" must be instantly appreciated: at a given moment, no piston is in contact with this cam lobe, which does not mean that this lobe does not contribute to the engine torque since, of course, a piston will be in contact with this cam lobe at another time, during the relative rotation of the cylinder block and the cam.

• pour un moteur fictif intermédiaire comprenant la came à Nc lobes de came et un bloc-cylindres fictif intermédiaire ayant un nombre Np de cylindres regroupés de sorte que l'espacement angulaire Ei entre deux cylindres regroupés consécutifs est égal à (360°.Nco/Nc)/Np et dans une position relative de référence du bloc-cylindres et de la came de ce moteur fictif intermédiaire, le piston de chaque cylindre occupe une position angulaire Pi, i variant de 1 à Np, sur l'un des Nc lobes de came, le nombre Nco étant le nombre des lobes de came consécutifs sur lesquels le moteur fictif intermédiaire est homocinétique,
• les Np cylindres du moteur hydraulique sont répartis dans le bloc-cylindres de telle sorte que, dans une position relative du bloc-cylindres et de la came correspondant à ladite position relative de référence du bloc-cylindres et de la came du moteur fictif, le piston de chaque cylindre occupe sur un lobe de came la même position angulaire Pi que dans le moteur fictif et que la résultante des efforts exercés par les pistons sur les lobes de came soit inférieure à la résultante de ces efforts dans le moteur fictif.

Advantageously, in the hydraulic motor comprising Np cylinders and Nc cam lobes, the angular spacings between the Np cylinders are determined as follows:

• for an intermediary dummy engine comprising the cam with Nc cam lobes and an intermediate dummy cylinder block having a number Np of cylinders grouped so that the angular spacing Ei between two consecutive grouped cylinders is equal to (360 ° .Nco / Nc ) / Np and in a relative reference position of the cylinder block and the cam of this intermediate hypothetical engine, the piston of each cylinder occupies an angular position Pi, i ranging from 1 to Np, on one of the Nc lobes of cam, the number Nco being the number of consecutive cam lobes on which the intermediate dummy engine is homokinetic,
• the Np cylinders of the hydraulic motor are distributed in the cylinder block such that, in a relative position of the cylinder block and the cam corresponding to the said relative reference position of the cylinder block and the cam of the fictitious engine, the piston of each cylinder occupies on a cam lobe the same angular position Pi as in the fictitious engine and that the resultant of the forces exerted by the pistons on the cam lobes is less than the resultant of these efforts in the fictitious engine.

The use of the fictitious intermediate engine makes it possible to define the positions of the pistons on the Nco of cam lobes of the engine on which the latter is homokinetic. This means that a motor having only these Nco cam lobes whose profile would be adapted and the Np cylinders spaced regularly from each other would be homokinetic. Another way of verifying the homokinetic character on Nco cam lobes is to note that the fluid balance is zero at each moment as long as the pistons of the Nc cylinders are in contact with Nco cam lobes.

The hypothetical intermediate engine is therefore used to define, in a given reference position, the position of the pistons on Nco consecutive cam lobes for the engine to be homokinetic. In the hydraulic motor, the object of the invention, the Np cylinders of the engine are distributed to maintain the same angular positions of cooperation of the pistons on the cam lobes, but making sure to obtain a resultant of the forces exerted by the pistons on the cam that is weak.

Advantageously, the angular spacings between two consecutive cylinders are at least equal to an angular spacing Eo equal to 360 ° / Npo, Npo being an integer greater than Np and representing the maximum number of cylinders, similar to those of the motor of the invention , which could be evenly distributed in the cylinder block.

For example, the original engine from which the motor of the invention may be defined may be a homokinetic motor in which the angular spacings between two rolls are equal to E 0.

• un moteur fictif intermédiaire ayant la came à Nc lobes de came et Np cylindres analogues à ceux dudit moteur, serait homocinétique sur Nco lobes de came,
• les nombres Npo et Nc ont un diviseur commun entier d, et
• le nombre m est tel que Nco est égal à Nc.m/d et Np est égal à Npo.m/d.

Advantageously, the engine having at least a small and a large active operating displacement, it comprises at least one group of Nc / m cam lobes whose cam lobes are inactive in the small engine displacement, m being an integer divider of Nc at least 2 defined as follows:

• an intermediate fictitious motor having the cam with Nc cam lobes and Np cylinders similar to those of said motor, would be homokinetic on Nco cam lobes,
• the numbers Npo and Nc have an integer common divisor d, and
• the number m is such that Nco is equal to Nc.m / d and Np is equal to Npo.m / d.

This makes it possible to define a reduced displacement engine having two operating cylinders such that, in each displacement, the engine is homokinetic and has a resultant of the forces exerted by the pistons of the cam which is weak.

As known to those skilled in the art, considering a cylinder whose piston is successively in contact with the rising and falling ramp of a cam lobe, a cam lobe is active if the cylinder is alternately connected to the feed and the fluid exhaust, respectively, which are at different pressures. It is inactive in the case where the cylinder is connected to the same pressure vessel.

• la figure 1 est une vue en coupe axiale d'un moteur du type celui de l'invention ;
• la figure 2 est une vue schématique en coupe radiale d'un moteur d'origine, avec sa came, son bloc-cylindres et ses pistons, ce moteur ayant six lobes de came et neuf pistons ;
• la figure 3 est une vue développée schématique montrant le profil des lobes de came et la position des différents pistons sur ce profil dans une position relative de référence du bloc-cylindres et de la came ;
• la figure 4 est une vue analogue à la figure 3, pour un moteur fictif intermédiaire ayant six lobes de came, six pistons et qui est homocinétique sur quatre lobes de came ;
• la figure 5 est une vue analogue à la figure 4 pour un moteur selon l'invention, comportant six lobes de came, six pistons et pour lequel deux lobes de came sont inutilisés dans toute position angulaire relative du bloc-cylindres et de la came ;
• la figure 6 est une vue schématique en coupe radiale, pour le moteur à six lobes de came et six pistons correspondant à la figure 5 ;
• la figure 7 est une vue développée schématique montrant les positions des pistons sur les lobes de came pour un moteur à dix lobes de came et à sept pistons, dans une position relative de référence du bloc-cylindres et de la came ;
• la figure 8 est une vue analogue à la figure 7 pour un moteur fictif intermédiaire ayant dix lobes de came, cinq pistons et qui est homocinétique sur sept lobes de came ;
• la figure 9 est une vue analogue à celle de la figure 8 pour un moteur selon l'invention, ayant dix lobes de came et cinq pistons ; et
• la figure 10 est une vue schématique en coupe radiale pour le moteur à dix lobes de came et à cinq pistons correspondant à la figure 9.

The invention will be better understood and its advantages will appear better on reading the description which follows, of an embodiment shown by way of non-limiting example. The description refers to the accompanying drawings in which:

• Figure 1 is an axial sectional view of a motor of the type of the invention;
• Figure 2 is a schematic radial sectional view of an original engine, with its cam, its cylinder block and its pistons, the engine having six cam lobes and nine pistons;
• Figure 3 is a schematic developed view showing the profile of the cam lobes and the position of the different pistons on this profile in a relative reference position of the cylinder block and the cam;
• Figure 4 is a view similar to Figure 3, for an intermediate dummy engine having six cam lobes, six pistons and which is homokinetic on four cam lobes;
• Figure 5 is a view similar to Figure 4 for an engine according to the invention, having six cam lobes, six pistons and for which two cam lobes are unused in any relative angular position of the cylinder block and the cam;
• Figure 6 is a schematic radial sectional view for the six-lobe cam engine and six pistons corresponding to Figure 5;
• FIG. 7 is a schematic expanded view showing the positions of the pistons on the cam lobes for a ten-lobed engine. cam and seven pistons, in a relative reference position of the cylinder block and the cam;
• Figure 8 is a view similar to Figure 7 for an intermediate dummy motor having ten cam lobes, five pistons and which is homokinetic on seven cam lobes;
• Figure 9 is a view similar to that of Figure 8 for an engine according to the invention having ten cam lobes and five pistons; and
• FIG. 10 is a schematic view in radial section for the ten-lobe cam and five-piston engine corresponding to FIG. 9.

The engine shown in Figure 1 is in this case a fixed cam motor and rotating cylinder block. Of course, the invention also applies to rotary cam motors and fixed cylinder block.

The engine of FIG. 1 comprises a housing 2 whose cam 10 forms a part, and a cylinder block 12 which rotates relative to this cam about an axis of rotation A. The cylinder block 12 has a plurality of cylinders 14 in which pistons 16 adapted to cooperate with the cam are slidably mounted. More precisely, the pistons 16 comprise, at their ends opposite to the axis of rotation A, rollers 16A which, during displacements of the pistons in their cylinder, roll on the cam. This comprises a plurality of cam lobes which, in Figure 2, are 6 in number and are respectively numbered L1 to L6. Each cam lobe has a rising ramp M and a descending ramp D. By convention, if it is considered that the cylinder block rotates relative to the cam in the direction R, the rising ramps of the lobes are those with which they cooperate. pistons when moved in the direction away from the axis of rotation A.

The engine comprises a fluid distributor 18 which is integral with the cam with respect to the rotation about the axis A. This distributor comprises distribution ducts 20 which are connected to a supply or an exhaust and which are adapted to communicate with the cylinders during the relative rotation of the cylinder block of the cam by distribution orifices 22. In this case, it is a planar distribution, the distribution orifices 22 being located in a distributor face 20A of the distributor which is perpendicular to the axis of rotation A. The cylinder block comprises meanwhile a communication face 12A in which are located communication orifices 13, this face of communication being also perpendicular to the axis A, the distribution and communication faces being in contact with each other and the distribution and communication orifices being arranged so that, during the rotation of the block cylinders relative to the cam, the communication orifices are successively in communication with the successive dispensing orifices.

In a manner known per se, for example from French Patent Application No. 2,834,012, each dispensing orifice is arranged in correspondence with a ramp of a cam lobe. Thus, in the direction of rotation R and if the engine is operating in full displacement, all the distribution orifices which are situated opposite the ramps are connected to the supply while all the distribution orifices which are located opposite a down ramp are connected to the exhaust. In the present case, the motor of FIG. 1 has two distinct displacements of operation. It has in fact a device for selecting the cubic capacity known per se (see, for example, FR 2,834,012) having a selection spool 30, arranged in a bore 32 of a housing part and adapted, in its position in FIG. 1, to communicate some distribution ducts, in which case the engine operates in reduced capacity. When the drawer 30 is moved in the direction of the arrow T, the distribution ducts are isolated from each other and the engine operates in large displacement.

In Figure 2, we see that the different cylinders are spaced regularly from each other. Thus, the cylinder block of the engine of Figure 2 comprising in this case 9 cylinders, the AC axes of these cylinders are spaced from each other by 40 °. A cylinder axis is the axis of symmetry of a cylinder, extending radially from the axis of rotation A.

In FIG. 3, which is a schematic representation of the development of the cam of the engine of FIG. 2, the different cam lobes L1 to L6 have been identified with their rising and falling ramps (these ramps being rectilinear on the schematic representation) . The angular spacing Eo = 40 ° between the cylinder axes has also been reported.

In the following, it will be considered that the angular spacing between two consecutive cylinders is the angular spacing between the cylinder axes of these two cylinders.

In FIG. 3, the cylinders are represented by their AC axes and referenced in circles.

As will be seen hereinafter, the cylinders and the pistons are divided into three groups and in FIG. 3, the cylinders are designated by the references I1 to III3, the Roman numeral which is the first part of this reference designating the group to which belongs to the considered cylinder, while the Arabic numeral which constitutes the second part is the calendar of the cylinder considered within this group.

Figure 6 is a view similar to Figure 2 for an engine according to the invention. It can be seen in this figure that, at any moment of the relative rotation of the cylinder block and the cam, that is to say for any relative position of these two elements, two cam lobes are unused because no piston is in instant contact with them. In this case, in the position shown in Figure 6, the cam lobes L2 and L5 are instantly unused. This is also visible on the developed cam of this motor, shown in Figure 5.

The engine of FIG. 6 can be obtained from that of FIG. 2, by modifying the cylinder block to eliminate certain cylinders and thus reduce the engine displacement, and by distributing the cylinders appropriately so that the engine is homokinetic and that the resultant of the forces exerted by the pistons on the cam is weak. More precisely, in the motor of FIGS. 2 and 3, the spacing E0 between the rolls is constant and is equal to 360 ° / Npo, Npo being the number of cylinders of the engine and being equal to 9, so that Eo is equal to at 40 °.

FIG. 4 shows the development of the cam of a hypothetical intermediate engine useful for determining the construction of the engine according to the invention, in the variant of FIGS. 5 and 6. In the present case, this hypothetical intermediate engine is constructed from the pre-existing engine, whose development is shown in FIG.

This intermediate fictitious engine includes the original engine cam, with its six cam lobes numbered L1 to L6.

In the relative position of the cylinder block of the cam shown in FIG. 4 (hereinafter relative reference position), these are the two lobes L5 and L6 which are unused. Indeed, compared to the original engine shown in Figure 3, the three cylinders III1, III2 and III3 of the third group, which were opposite these cam lobes, were removed. Cylinders I1 to II3 remain, they are spaced apart from each other by E0 = 40 ° and, in the position of Figure 4, are grouped opposite cam lobes L1 to L4.

This intermediate fictitious engine is homokinetic on four cam lobes and with its six cylinders I1 to II3. This means that, in the reference position of FIG. 4, the regular angular spacing between the grouped cylinders may be such that the cylinder which naturally follows the last cylinder II3 of the group of cylinders grouped together keeping the same spacing with respect to this The last cylinder would be exactly in the same position on the cam as the first cylinder I1 in this group, ignoring the unused lobes L5 and L6. In other words, considering, in the reference position, that only the lobes L1 to L4 are used, and insofar as the first cylinder I1 is on the first vertex of the first cam lobe L1, that is to say At the bottom of its rising ramp M, it is necessary that the cylinder I'1 which would naturally follow the cylinder II3 with the same spacing with respect to it as the spacing Eo which is between all the cylinders, is found on the first top of the L5 cam lobe, ie at the bottom of its rising ramp M. In this case, this is naturally respected with the 40 ° spacing of the original engine since we see that the cylinder III1 which was deleted in Figure 3 was well located there. This is due to the fact that the engine of FIGS. 2 and 3 is homokinetic, not only on the nine cylinders which it comprises, but also on each group I, II, III of cylinders which it comprises and this, in each case, on two cam lobes.

It can be seen that the first cylinder of each group I1, II1, III3 is opposite the first vertex of an odd cam lobe, L1, L3 and L5. In addition, the fluid balance of the motor of FIG. 4 is zero for each of the groups I and II because, if it is considered that the cylinder block rotates in the direction R with respect to the cam, the fluid leaving the second group cylinder (I2 or II2) is compensated by the fluid entering the third (I3 or II3) and no fluid enters the first cylinder (I1 or II1) nor comes out.

The intermediate hypothetical engine is not balanced since, in the reference position (in FIG. 4), these 6 cylinders are all facing the first 4 cams L1 to L4.

Referring to Figure 2, it is understood that the removal of the cylinders III1, III2, III3 would have the consequence that the resultant forces exerted by the pistons on the cam would have a relatively large value and would be substantially oriented according to the arrow F shown in Figure 2.

The engine according to the invention, according to the variant of Figures 5 and 6, is derived from the intermediate imaginary engine of Figure 4 by a different angular distribution of the cylinders. In FIG. 4, in the reference position, the six cylinders I1 to I3 were arranged such that their respective pistons cooperated with the used cams L1 to L4 in respective positions P1 to P6.

On the motor of Figure 5, in the reference position shown, it is the lobes of the cams L2 and L5 are instantly unused. The six cylinders are distributed so that the positions P1 to P6 are preserved on the other cam lobes. Thus, the cylinders I1 and I2 retain their original position and the positions P1 and P2 on the cam lobe L1 are thus preserved. The cam lobe L2 is unused. The third cylinder I3 of the first group is spaced from the cylinder I2 so that, in the reference position, its piston cooperates with the cam lobe L3 in the same position P3 as that in which it cooperates with the cam lobe L2 in the figure 4. Similarly, the cylinders of the second group II1 to II3 are moved as indicated by the arrows going from Figure 4 to Figure 5 so that, in the same reference position, their pistons cooperate with the cam lobes L4 and L6 in the same positions P4, P5 and P6 as those in which they cooperated with the lobes L3 and L4 of Figure 4.

FIG. 6 shows in radial section the cam of the engine according to this variant of the invention with its cylinder block having six cylinders, the cylinder block and the cam being in the same relative reference position as in FIG. 5. It is seen that the pistons cooperate with the cam lobes L1, L3, L4 and L6 in the positions P1 to P6.

As shown in FIGS. 5 and 6, for this engine with 6 cam lobes and 6 cylinders, and for which 2 cam lobes are unused in relative position of the cylinder block and the cam, the angular spacings between the consecutive cylinders are respectively substantially equal to 40 °, 100 °, 40 °, 40 °, 100 ° and 40 °. Of course, the machining constraints of the cylinder block and the manufacturing tolerances make these angular spacings may be slightly different from the aforementioned values, which is expressed by the adverb "substantially". The variations may be of the order of plus or minus 0.5 °. It can be seen that the spacing of 100 ° between the most spaced cylinders is not a multiple of the 40 ° spacing between the other cylinders.

It is understood by considering Figure 6 that the motor is substantially balanced, that is to say that the resultant forces exerted by the pistons on the cam is substantially zero. Indeed, with each piston occupying a given position on a cam lobe, corresponds to another diametrically opposed piston which occupies a similar position on another cam lobe. Thus, the pistons of cylinders I1 and II1 which are diametrically opposed each cooperate with a cam lobe top, the pistons of cylinders I2 and II2 which are diametrically opposed each cooperate with the middle region of the descending ramp of a cam lobe ; the pistons of cylinders I3 and II3 which are diametrically opposed each cooperate with the median region of the rising ramp M of a cam lobe.

The motor of FIGS. 5 and 6 is homokinetic on the 4 cam lobes which are instantaneously used in each relative angular position of the cylinder block of the cam.

An engine with a cylinder block having cylinders similar to those of the engine of Figure 6 and having six cam lobes none of which would be instantly unused, would be homokinetic on all of its six cam lobes, if, as the engine of Figure 2, it had a number Npo equal to 9 rolls evenly spaced spacing Eo equal to 360 ° / Npo or 40 °. Note that in the engine of Figures 5 and 6, the spacings between the consecutive cylinders are always at least equal to this spacing Eo.

As indicated with reference to FIG. 1, the motor of the invention may comprise several active operating displacements. This is particularly the case of that of Figures 5 and 6 which can be homokinetic in a large and a small displacement of operation.

More precisely, this engine comprises a number Nc equal to 6 of cam lobes, a number Np equal to 6 of cylinders; it is homokinetic on a number Nco equal to 4 of cam lobes and as indicated above, it could at maximum include a number Npo equal to 9 cylinders similar to hers, regularly distributed, being homokinetic on its Nc cams. The numbers Npo and Nc have a common divisor d equal to 3. There exists a number m equal to 2 such that Nco = 4 = Nc.m / d = 6 x 2/3 and such that Np = 6 = Npo. m / d = 9 x 2/3. Under these conditions, a group of Nc / m = 6/2 = 3 cam lobes can be inactive in the small engine displacement. In the present case, these considerations are easily verifiable on the engine of FIGS. 5 and 6 in which two of the three groups of cylinders of the original engine of FIG. 3 have been preserved.

It is recalled that to make the cam lobes inactive in small displacement, it should be ensured that the distribution ducts located in correspondence with the rising and falling ramps of these cam lobes are not alternately connected to the feed and at the fluid outlet. However, to avoid premature wear of the support bearings of the rotating part of the motor, it is advantageously chosen that the lobes that are inactive in small displacement are interposed between two active lobes. In other words, the 6 cam lobes L1 to L6 of the motor of FIG. 6 are distributed in two groups of 3 cam lobes, namely a group L1, L3 and L5, and another group L2, L4 and L6. and the lobes of the second group being inactive in small displacement.

Referring to Figures 7 to 10, there is now described an engine according to the invention, according to another variant.

Figure 7 shows the development of the cam and shows the positions of the cylinders for a conventional engine having 10 cam lobes, numbered from 1 to 10 and 7 cylinders, numbered C1 to C7. Thus, for this motor, Nc = 10 and Npo = 7. In FIGS. 7 to 9, the rising ramps M and descending D are indicated for a direction of rotation R of the cylinder block with respect to the cam.

The engine according to the invention, in the variant of FIGS. 9 and 10, is homokinetic on 7 of its 10 cam lobes.

FIG. 8 shows the development of the cam and the position of the cylinder for the intermediate hypothetical engine which is constant-velocity over 7 cam lobes grouped together, so that the number Nco is equal to 7. It can be seen in FIG. 8 that the fluid balance is zero, the fluid exiting the cylinders C3 and C5 being compensated by the fluid entering the cylinders C2 and C4, respectively, while no fluid feeds or escapes the cylinder C1.

In the reference position shown in FIG. 8, the first cylinder C1 is in a position such that its piston cooperates with the first top of the first cam lobe L'1, which determines the reference position of the cylinder block and of the the cam chosen for FIGS. 7 to 9. The rolls are grouped opposite the first seven cam lobes 1 to 7. Thus, the cylinders C1 to C5 of the engine of Figure 7 are retained while the cylinders C6 and C7 are removed.

In order for the motor of FIG. 8 to be homokinetic on seven cam lobes, with its cylinders grouped and spaced regularly, it is necessary that, if a cylinder C'1 were added after cylinder C5, respecting the same angular spacing between all cylinders together, then the piston of this additional cylinder C'1 would be in contact with the first top of the cam lobe L'8, in the same position as the cylinder C1 relative to the lobe L'1.

Contrary to the situation described with reference to FIGS. 3 to 6, that of FIGS. 7 to 10 requires a registration of the position of the rolls between the original engine corresponding to FIG. 7 and the intermediate imaginary engine corresponding to FIG. indeed, the first cylinder removed from the original engine C6 is not facing the first top of the cam lobe 8.

In the original engine, the cylinders are regularly spaced, the spacing Eo between two consecutive cylinders being equal to 360 ° / Npo, or about 51.4 °, Npo being equal to 7. In the reference position shown in FIG. 7, the first cylinder C1 is opposite the first apex of the cam lobe 1 and, because of the spacing Eo, the position of the cylinder C6 is located facing the cam lobe 8, being spaced apart a spacing ΔE with respect to the first vertex of this lobe.

To define the configuration of the hypothetical intermediate engine, it is therefore necessary to correct this spacing ΔE. This is achieved by regularly spacing the cylinders C1 to C5 of a spacing $$\mathrm{Ei}\mathrm{=}\mathrm{(}\mathrm{360}\mathrm{°}\mathrm{.}\mathrm{Nco}\mathrm{/}\mathrm{Nc}\mathrm{)}\mathrm{/}\mathrm{np}\mathrm{,}\mathrm{is}\mathrm{(}\mathrm{360}\mathrm{\times }\mathrm{7}\mathrm{/}\mathrm{10}\mathrm{)}\mathrm{/}\mathrm{5}\mathrm{,}\mathrm{is}\mathrm{50}\mathrm{,}\mathrm{4}\mathrm{°}\mathrm{.}$$

In this intermediate fictitious motor, and for the reference position shown in FIG. 8, the pistons of the cylinders C1 to C5 respectively occupy the cam lobes L'1, L'2, L'3, L'5 and L'' 6 angular positions P1 to P5. This engine is homokinetic on seven cam lobes. However, as explained with reference to the previous variant, inasmuch as all the cylinders are grouped, the engine is not balanced, that is to say that the resultant forces exerted by the pistons on the cam is too important. Consequently, to define the motor of FIG. 9, starting from the imaginary motor of FIG. 8 and considering the reference position of FIGS. 7 and 8, the cylinders are distributed on the different cam lobes so as to keep on the cam lobes respectively the angular positions that had these cylinders, while ensuring that the forces exerted by a piston on the cam is substantially compensated by the forces exerted by one or more pistons substantially opposite. In this case, the cylinder C3 is arranged facing the cam lobe 2 in the position P3 that it had with respect to the lobe L'3, the cylinder C5 is arranged opposite the cam lobe 7 in the position P5 that it had with respect to the lobe L'6, and the cylinder C2 is arranged facing the cam lobe L'9 in the position P2 that it had with respect to the lobe L'2. The positions of cylinders C1 and C4 are unchanged.

Thus, as can be seen in FIGS. 9 and 10, the engine according to the second variant comprises 10 cam lobes and 5 cylinders, the angular spacings between the consecutive cylinders being respectively substantially equal to 64.8 °, 86.4 °, 86.4 °, 64.8 ° and 57.6 °. In practice, given the manufacturing tolerances, the spacings may vary by plus or minus 0.5 ° with respect to the values announced above. It can be seen that the different spacings of 57.6 ° are not multiples of this value. In addition, these spacings are greater than the minimum spacing Eo which is 51.4 ° for the motor of FIG. 7.

To define the engine according to the invention, it is therefore advantageously from a pre-existing engine having Npo cylinders, as shown for example by the developed Figures 3 and 7. Retaining a reduced number of cylinders Np, then the number is defined Nco of cam lobes on which the engine must be homokinetic and, starting from this number Nco, the angular spacing between the grouped cylinders of the intermediate engine, according to Figures 4 or 8, is defined, so that motor is homokinetic on these Nco cam lobes. Then, the Np cylinders of the engine are distributed in the cylinder block so that their angular positions relative to the respective cam lobes are preserved, so as to ensure that the engine is homokinetic. This distribution is made so that the resultant forces exerted by the pistons on the cam is as small as possible.

To define a reduced displacement engine having several possible engine displacements, one starts from an original homokinetic engine (for example according to FIGS. 2 and 3) for which the numbers Npo of cylinders and Nc of cam lobes have a divider common whole d. An integer m is determined which is at least 2 and less than d, which is an integer divider of the number Nc, and the intermediate dummy engine is defined such that the number Nco of cam lobes on which this engine is homokinetic is equal to Nc.m / d and such that the number Np of its cylinders is equal to Npo.m / d. Finally, at least one group of Nc / m of cam lobes is determined whose cam lobes can be inactivated so as to operate the hydraulic motor in a small active displacement.

Advantageously, when the engine has at least a small and a large operating displacement, it comprises at least two groups of cam lobes, the cam lobes of one of the groups being inactive in the small displacement. In this case, it is possible to choose that the cam lobes of one and the same group all have an identical profile which is different from the profile of the cam lobes of the other group.

It has been indicated previously that the depth of the lobes of the cam is one of the parameters which determines the displacement of the engine. It is therefore possible to determine the depth of the cam lobes which are active in a given operating displacement so that the value of this displacement is precisely equal to a determined value.

Claims (11)

1. A hydraulic motor comprising a cam (10) and a cylinder block (12) that are suitable for rotating one relative to the other about an axis of rotation, the cam comprising a plurality of cam lobes (L1-L6) each of which has a rising ramp M and a falling ramp D, and the cylinder block having a plurality of cylinders (14; I1-II3; C1-C5) slidably receiving pistons (16) that are suitable for co-operating with the cam, the motor further comprising a fluid distributor (18) that is constrained to rotate with the cam about the axis of rotation (A) and that includes distribution ducts (20) connected via distribution orifices (22) to a feed or to a discharge and suitable for communicating with the cylinders while the cylinder block (12) and the cam (10) are rotating relative to each other, each distribution orifice being disposed in register with a ramp (M, D) of a cam lobe (L1-L6) such that a cylinder whose piston is co-operating with a rising ramp (M) can be connected to the feed and such that a cylinder whose piston is co-operating with a falling ramp (D) can be connected to the discharge, the instantaneous angular positions in which the pistons (16) co-operate with the cam (10) while the cylinder block (12) and the cam (10) are rotating relative to each other being such that the motor is a substantially constant-velocity motor;
   said motor being characterised in that, in any relative position of the cylinder block (12) and of the cam (10), there is at least one cam lobe that is unused and with which no piston (16) co-operates, and in that the angular spacings between two consecutive cylinders are mutually different and differ by a multiple of the smallest angular spacing between two consecutive cylinders, said angular spacings being determined so that the resultant of the forces exerted by the pistons on the cam is small or substantially zero.
2. A motor according to claim 1, comprising Np cylinders and Nc cam lobes, the angular spacings between the Np cylinders are determined as follows:

   - angular positions Pi are defined for an imaginary intermediate motor (Figure 4, Figure 8) comprising a cam that has Nc cam lobes and an imaginary intermediate cylinder block having a number Np of cylinders (I1-I3; C1-C5) that are grouped together so that the angular spacing Ei between two consecutive grouped-together cylinders is equal to (360°.Nco/Nc)/Np and, when the cylinder block and the cam of said imaginary intermediate motor are in a reference relative position, where the piston (16) of each cylinder (I1-II2, C1-C5) occupies an angular position Pi (for i in the range 1 to Np), on a respective one of the Nc cam lobes (L1-L6; L'1-L'10), and where the number Nco is the number of consecutive cam lobes over which the imaginary intermediate motor is a constant-velocity motor; and

   - the Np cylinders (I1-II3; C1-C5) of the hydraulic motor are distributed in the cylinder block (12) in such a manner that, when the cylinder block and the cam are in a relative position corresponding to said reference relative position of the cylinder block and of the cam of the imaginary motor, the piston (16) of each cylinder occupies, on a cam lobe (L1, L3, L4, L6; L'1, L'2, L'5, L'7, L'9), the same angular position Pi as in the imaginary motor, and in such a manner that the resultant of the forces exerted by the pistons on the cam lobes is smaller than the resultant (F) of the forces in the imaginary motor.
3. A motor according to claim 1 or claim 2, comprising Np cylinders (I1-II3; C1-C5) and Nc cam lobes (L1-L6; L'1-L'10), said motor being characterised in that the angular spacings between two consecutive cylinders are not less than an angular spacing Eo equal to 360°/Npo, where Npo is an integer number greater than Np and representing the maximum number of cylinders analogous to the cylinders of said motor that could be distributed uniformly in the cylinder block.
4. A motor according to claim 3, having at least one small and one large active operating cubic capacity, said motor being characterised in that it comprises at least one group of Nc/m cam lobes (L2, L4, L6) whose cam lobes are inactive when the motor is in its small cubic capacity, where m is an integer divisor of Nc and not less than 2, and is defined as follows:

   - an imaginary intermediate motor having the cam that has Nc cam lobes and Np cylinders analogous to those of said motor would be constant-velocity over Nco cam lobes;

   - the numbers Npo and Nc have an integer common divisor d; and

   - the number m is such that Nco is equal to Nc.m/d and Np is equal to Npo.m/d.
5. A motor according to any one of claims 1 to 4, characterised in that the cam (10) has a number of cam lobes Nc equal to 6, and in that the cylinder block (12) has 6 cylinders, the angular spacings between the consecutive cylinders being respectively equal to 40°, 100°, 40°, 40°, 100°, and 40°.
6. A motor according to claim 5, characterised in that the six cam lobes are distributed into two groups of three cam lobes (L1, L3, L5; L2, L4, L6), one lobe of each group being interposed between two lobes of the other group.
7. A motor according to any one of claims 1 to 4, characterised in that the cam has 10 cam lobes, and in that the cylinder block has 5 cylinders, the angular spacings between the consecutive cylinders respectively being substantially equal to 64.8°, 86.4°, 86.4°, 64.8°, and 57.6°.
8. A method of designing a hydraulic motor according to claim 2, and to any one of claims 2 to 7, said method being characterised in that it consists in:

   - defining an imaginary intermediate motor (Figure 4, Figure 8) comprising a cam having Nc cam lobes (L1-L6; L'1-L'10) of which a number Nco of cam lobes is chosen so that the imaginary intermediate motor is constant-velocity over Nco cam lobes, an imaginary intermediate cylinder block having a number Np of cylinders (I1-II3; C1-C5) grouped together so that the angular spacing Ei between two consecutive grouped-together cylinders is equal to (360°.Nco/Nc)/Np, and defining a reference relative position of the cylinder block and of the cam of said imaginary intermediate motor, in which reference relative position the piston of each cylinder (I1-II3; C1-C5) occupies an angular position Pi, on a respective one of the Nc cam lobes; and

   then defining the cylinder block of the hydraulic motor by distributing the Np cylinders (I1-II3; C1-C5) of the imaginary intermediate motor in said cylinder block in such a manner that, when the cylinder block (12) and the cam (10) are in the same relative position as the reference relative position of the cylinder block and of the cam of the intermediate motor, the set of angular positions (P1-P6; P1-P5) in which the pistons (16) of the hydraulic motor co-operate with the cam lobes (L1-L6; L'1-L'10) of said motor is identical to the set of angular positions Pi occupied by the pistons on the cam lobes of the imaginary intermediate motor, and in such a manner that the resultant of the forces exerted by the pistons on the cam lobes is less than the resultant of said forces in the imaginary intermediate motor.
9. A method of designing a hydraulic motor according to claim 2, and to any one of claims 2 to 7, said method being characterised in that it consists in:

   - starting from an existing design for an original constant-velocity motor (Figure 3, Figure 7) comprising a cam having Nc cam lobes (L1-L6; L'1-L'10), all of the lobes being active, and an original cylinder block having a number Npo greater than Np of cylinders (I1-III3; C1-C7) distributed uniformly at an angular spacing Eo equal to 360°/Npo;

   - defining an intermediate motor comprising the cam having Nc cam lobes of said original motor and of which a number Nco of cam lobes is chosen so that the imaginary intermediate motor is constant-velocity over Nco cam lobes, an imaginary intermediate cylinder block having a number Np of cylinders (I1-II3; C1-C5) grouped together so that the angular spacing Ei between two consecutive grouped-together cylinders is equal to (360°.Nco/Nc)/Np, and defining a reference relative position of the cylinder block and of the cam of said imaginary intermediate motor, in which reference relative position the piston of each cylinder occupies an angular position Pi, on a respective one of the Nc cam lobes; and

   then defining the cylinder block (12) of the hydraulic motor by distributing the Np cylinders (I1-II3; C1-C5) of the imaginary intermediate motor in said cylinder block in such a manner that, when the cylinder block (12) and the cam (10) are in the same relative position as the reference relative position of the cylinder block and of the cam of the intermediate motor, the set of angular positions in which the pistons of the hydraulic motor co-operate with the cam lobes of said motor is identical to the set of angular positions Pi occupied by the pistons on the cam lobes of the imaginary intermediate motor, and in such a manner that the resultant of the forces exerted by the pistons on the cam lobes is less than the resultant of said forces in the imaginary intermediate motor.
10. A method according to claim 9, characterised in that the Np cylinders (I1-II3; C1-C5) of the imaginary intermediate motor are distributed in the cylinder block of the hydraulic motor such that the angular spacings between two consecutive cylinders are at least equal to Eo.
11. A method according to claim 9 or claim 10, characterised in that a constant-velocity original motor is chosen for which the numbers Npo and Nc have an integer common divisor d, an integer number m is determined that is at least equal to 2 and less than d, and that is an integer divisor of the number Nc, the imaginary intermediate motor is defined such that the number Nco is equal to Nc.m/d and such that the number Np is equal to Npo.m/d, and at least one group of Nc/m cam lobes is determined whose cam lobes can be inactivated so as to cause the hydraulic motor to operate in a small active cubic capacity.

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