FR3137420A1 - Hydraulic machine comprising a cam and pistons - Google Patents

Abstract

The hydraulic machine (1) comprises: - a cam (14) having a cylindrical external face (30) and a main axis (X-X), and - at least one gauge (40) rigidly fixed to the face and arranged to detect a load of the face and/or a variation of a shape of the face. Abstract Figure: Fig. 3

Description

Hydraulic machine comprising a cam and pistons FIELD OF INVENTION

The invention relates to hydraulic machines.

STATE OF THE ART

We know from document CN203822539 a hydraulic machine equipped with a cam, pistons and a sensor for measuring a torque exerted on the cam.

One aim of the invention is to improve the control of hydraulic machines.

According to the invention, a hydraulic machine is provided comprising:

- a cam having a cylindrical external face and a main axis, and

- at least one gauge rigidly fixed to the face and arranged to detect a stress on the face and/or a variation in a shape of the face.

Thus, the detection of the stress or the shape variation takes place directly at the external face of the cam, therefore as close as possible to the cam itself and in real time. This detection is therefore carried out with good reliability. This eliminates load losses and friction. It makes it possible to improve the control of the machine by having particularly precise information on its operation and its condition. The invention provides access to information, some of which was previously difficult to obtain with precision. Depending on the embodiments, detection makes it possible to obtain its speed of rotation, its direction of rotation, the torque generated and its efficiency. In addition, detection on the external face of the cam therefore takes place outside the Faraday cage that certain hydraulic machines constitute. This allows wireless transmission outside the machine of detection information.

The machine may also have at least one of the following characteristics:

- the gauge or at least one of the gauges is arranged to detect a radial stress and/or a variation in a circumferential dimension of the face;

- the gauge or at least one of the gauges is arranged to detect an axial stress and/or a variation in an axial dimension of the face;

- the gauge or at least one of the gauges includes a piezoelectric sensor;

- the gauge or at least one of the gauges is a resistive gauge;

- the gauge or at least one of the gauges is a multiaxial gauge; And

- the machine includes at least two gauges extending in the same plane perpendicular to the axis.

The words “strain gauges” and “strain gauge” are considered synonymous here. The stress can be accessed if the extensometry gauge has been calibrated. For example, if we know the elongation of the material, we know the stress. Then, in a subcategory, “resistive gauge” and “piezoelectric gauge”, are two means of measuring extensometry.

It can be expected that, the cam having lobes, the gauge or at least one of the gauges extends in the median angular position of an angular sector formed by one of the lobes.

It can be envisaged that, the machine comprising a casing and members for fixing the cam to the casing, the gauge or at least one of the gauges extends in the median angular position of an angular sector formed by two fixing members. continuing around the axis.

So, in this case, the gauges are placed in the most flexible parts of the machine defined according to the fixing devices. This embodiment is particularly suitable when the fixing members are uniformly distributed around the axis.

It can be expected that the cam has at least one facet cutting into the cylindrical face, the gauge or at least one of the gauges extending to the right of the facet.

Thus, for a better response of the gauge, these facets form external thinnings (e.g. flats) in the cam to thin it, support the gauges and increase their sensitivity. We then obtain a better response thanks to a greater amplitude.

It can be envisaged that, the machine comprising pistons and piston housings, the cam has switching points arranged so that a fluidic switching of one of the housings takes place when the piston passes from this housing to the right from this point, the gauge or at least one of the gauges extending to the right of one of the switching points.

Thus, this situation of the gauge allows better detection. Indeed, the switching point is associated with greater stress and in particular often with an impulse as we will see later. Furthermore, there are machines in which the position of the switching point does not correspond to the thinnest part of the cam or even to the middle of the lobe. These are staggered power supply situations. For example, these are random offsets within the cam dish to reduce harmonic noise. This embodiment is well suited for such a situation.

It can be provided that the gauge or at least one of the gauges extends to the right of a zone of the cam presenting maximum flexibility with reference to all the zones of the cam.

This embodiment is particularly suitable for cams which are not bolted.

It can be expected that the machine comprises pistons and that at least four gauges are arranged in circumferential succession following a single file in an angular sector equal to the angle formed by the angular sector formed by two consecutive pistons in the circumferential direction.

Such an arrangement serves to measure speed and position in a much finer manner than with simple isolated gauges. It makes it possible to obtain a continuous or quasi-continuous measurement and to permanently monitor the passage of the pistons. In fact, the chain thus formed extends in an angular sector equal to the angle formed by the angular sector formed by two consecutive pistons. It is therefore called upon at all times during rotation. The finer the succession of the gauges in the chain, the more precise the indication of the engine position.

According to the invention, a machine is also provided comprising at least one machine according to the invention.

According to the invention, a method is also provided in which a stress on a cylindrical external face of a cam of a hydraulic machine and/or a variation in a shape of the face is detected, the detection taking place directly on the face.

The method according to the invention may also have at least one of the following characteristics:

- we detect a stress along a circumferential direction of the face and/or a variation of a circumferential dimension of the face, we determine if the stress or the deformation corresponds to a passage of at least one piston, and if the stress or the deformation corresponds to the passage of the piston, we determine at least one value among the following:

- a rotation speed of the machine,

- a direction of rotation of the machine,

- a torque generated by the machine, and

- machine performance;

- we determine an orientation of a peak associated with the stress or deformation and we deduce a direction of rotation of the machine;

- at least two stresses or two deformations are successively detected in the same predetermined zone of the cam and a rotation speed of the machine is determined by means of the two stresses or the two deformations;

- at least two stresses or two deformations are detected in two respective predetermined zones of the cam and a direction of rotation of the machine is determined by means of the two stresses or the two deformations;

. at least one amplitude of the stress or variation is measured and, by means of the amplitude, an intensity of a torque generated by the machine is determined;

. at least one amplitude of the stress or variation is measured and an output of the machine is determined by means of the amplitude and a hydraulic pressure at the input of the machine;

. amplitudes appearing simultaneously on two gauges are measured and the amplitudes are summed;

- we measure the amplitudes of at least two stresses or two deformations in two respective predetermined zones of the cam and we determine by means of the amplitudes at least one intensity of a force exerted on the machine from outside the machine;

- an axial stress and/or a variation of an axial dimension of the face is detected; And

. the machine is stopped during the detection step.

DESCRIPTION OF FIGURES

We will now present embodiments of the invention and variants by way of non-limiting examples in support of the drawings in which:

- there is an exploded view in longitudinal section of a hydraulic machine according to one embodiment of the invention;

- Figures 2 and 3 are views in axial section of the machine of the at the level of the cylinder block following plane II-II of the ;

- Figures 4 and 5 are perspective and elevation views of the cam with the rollers of the machine of the ;

- Figures 6 and 7 show two examples of the gauges fitted to the machine with the ;

- Figures 8 to 13 and 15 are diagrams illustrating the detection by the machine gauges of the ;

- Figures 14 and 16 are longitudinal sectional views of the same machine illustrating the implementation of the method of the invention, respectively during calibration and during use; And

- Figures 17 to 19 are views of a cam of a machine according to another embodiment of the invention.

Machine presentation

Figures 1 and 14 illustrate a hydraulic machine 1 forming one embodiment of the invention. It includes a casing 2 in two parts. It also includes a shaft 4 in two parts, a longitudinal axis XX of which forms a main axis of the machine. The left shaft part on the connects the cylinder block 8 (see below) to a mounting flange of a member to be driven, for example a wheel 51 of a vehicle or machine. The right shaft part corresponds to a brake and is optional. The two shaft parts are linked in rotation in the cylinder block by splines. The machine is generally rotationally symmetrical around the XX axis. Bearings 6 serve to support the shaft 4 to mount it rotatably in the casing 2. The bearings 6 are for example two in number and include bearings. The machine comprises a cylinder block 8 having housings 10 radial to the axis, the cylinder block being integral in rotation with the shaft 4. Pistons 12 are received in the respective housings 10 and mounted movable to slide radially at the axis in these accommodations. Overall, the hydraulic machine 1 can be assembled in sections, from left to right, a bearing section, a motor or pump section, a hydraulic supply section including a distributor, and a brake section.

The machine comprises a cam 4 also shown in Figures 2 to 5. The cam is rigidly fixed to the casing 2 and has an internal face 16 forming a rolling track for rollers 18 connected to the respective pistons 12. The pistons are supported on the cam 14 via the rollers. Track 16 has lobes 20 alternating around the axis, as illustrated in , corresponds to a back and forth movement of the pistons 12 during the rotation of the shaft 4 relative to the casing.

The machine includes a distributor 22. As illustrated in , the distributor 22 is able to put the housings 10 of the pistons in communication with a high pressure fluid circuit 24 and with a low pressure fluid circuit 26. The machine comprises discs 28 forming a brake of the shaft relative to to the crankcase.

As illustrated in , the cam 14 has a cylindrical external face 30 of axis XX. A thickness of the cam is measured in the direction radial to the axis between the two faces 16 and 30. This thickness is minimum at the bottom of the lobes 20 and maximum between them, namely in the zones 42 located between the lobes. When the machine rotates, the pistons equipped with rollers travel along the cam, and have an alternating path with bottom dead centers and top dead centers. The thinnest parts of the cam correspond to the top dead centers, and the thickest parts to the bottom dead centers. At places of maximum thickness, the cam has conduits 32 for receiving fixing members such as screws 34. These conduits and these members are parallel to the axis. Cam 14 is sandwiched between the two parts of the casing in the axial direction. Each fixing member 34 passes through the cam and the two parts of the casing in the present example.

Depending on the command applied to it, the machine can operate as a motor to produce a torque under the effect of hydraulic pressure or as a pump to provide hydraulic pressure under the effect of a torque, and this in one or more the other of the two possible directions of rotation.

In reference to the , assuming for example that the machine operates as a motor, certain pistons 12a are in communication with the high pressure circuit 24, others 12b are in communication with the low pressure circuit 26, the other 12c are in an intermediate situation, namely on the point of changing circuits, either because they are at the bottom of a lobe 20, or because they are exactly halfway between two lobes 20, in a zone 42. At each point top dead center or bottom dead center occurs a switching between one and the other of the two power circuits. At this moment, the supply port of the piston in the cylinder block leaves a high pressure or low pressure supply port of the hydraulic distributor, to join a supply port of the other supply circuit, respectively low pressure or high pressure. The figure shows the orifices 36 of the distributor conduits connected to the housings 10 of the pistons to put them in communication with the low and high pressure circuits.

In the present example, the machine 1 comprises eight pistons 12 and the cam 14 has six lobes 20, these numbers being not limiting. Over one revolution, a piston will present 12 switchings.

A more detailed description of these elements of the machine will be found in application FR-2 796 886.

Gauges

As illustrated in , the machine further comprises gauges 40 rigidly and directly fixed to the external face 30 of the cam and arranged to detect a stress on the face and/or a variation in its shape.

Each gauge 40 is for example a strain gauge arranged to detect a radial stress on the axis. This is, for example, a piezoelectric gauge. But we could alternatively use an extensometry gauge arranged to detect a variation in a circumferential dimension of the face, such as a resistive gauge. Alternatively, multiaxial gauges, such as rosettes, can be used.

The gauges are arranged in the same plane P perpendicular to the axis, the trace of which is visible on the . In this example there are as many gauges 40 as lobes 20. The gauges extend to the right of the respective lobes. Thus, each gauge extends in the median angular position of an angular sector formed by one of the lobes. This position corresponds to a thin part of the cam, and to the power switching zone, at the moment when a piston would be in the top dead center position. This position can be plus or minus 5° from top dead center. They are therefore also regularly distributed around the axis, in this case with a spacing of 60° between two consecutive gauges 40.

The fixing members 34 extend into the zones 42 located between the lobes 20 which are the thickest zones of the cam 14. These zones are stressed in the radial direction by the pistons 12 during their passage but deform very little under the effect of this stress so that this deformation is negligible. On the other hand, the zones corresponding to lobes 20 are the finest. And they do not include a fixing organ. They are stressed in the radial direction by the pistons 12 during their passage and are deformed significantly under the effect of this stress. This deformation is proportional to the intensity of the radial stress. The deformation 44 of the external face 30 of the cam as one of the pistons passes has been illustrated in an exaggerated manner on the .

40 gauges can be installed in the machine as follows.

We illustrated at two resistive gauges 40 serving as an extensometry gauge located on the face 30 to the right of the same lobe 20. Pairs of similar gauges are associated with the other lobes. One of the gauges 40 has its longitudinal direction oriented along the circumferential direction of the face 30. The other gauge 40 has its longitudinal direction oriented along the direction parallel to the axis. Each gauge here is monodirectional. The first measures the deformation of the external face 30 of the cam in the circumferential direction. The second measures the deformation of the same face in the axial direction.

We illustrated at alternatively, a gauge 40 of the rosette type serving as an extensometry gauge and located on the face 30 to the right of a lobe 20. Similar gauges are associated with the other lobes. This is a multidirectional gauge capable of measuring deformations of the face 30 of the cam both in the circumferential direction and in the axial direction.

Strain or extensometry gauges have an electrical resistance which increases with the deformation they undergo.

Alternatively, the gauges 40 may be strain gauges such as piezoelectric gauges. They deliver a tension representing the constraint they undergo. We can also use hybrid gauges which are of both types.

For example, we can use gauges or sensors supplied by the companies HBK or KYOWA.

In each case, all gauges are connected to an electronic circuit configured to receive signals from the gauges and perform the calculations presented below. These arrangements each make it possible to obtain the measurements for the implementation of the different functions presented in this mode of implementation of the process.

Detection of the passage of a piston and determination of the direction of rotation

Thanks to the gauges 40, in the present mode of implementation of the method of the invention, a stress on the face 30 in its circumferential direction and/or a variation in its circumferential dimension is detected directly on the external face 30. To do this, in this case, we determine whether the stress or deformation corresponds to a passage of at least one piston 12, and if so, we determine at least one value among the following:

- a rotation speed of the machine,

- a direction of rotation of the machine,

- a torque generated by the machine, and

- machine performance.

In particular, we determine an orientation of a measurement peak by gauge 40, associated with the stress or deformation, and we deduce the direction of rotation.

In addition, at least two stresses or two deformations are detected successively by means of the same gauge 40 and the rotation speed is determined by means of the two stresses or the two deformations.

In addition, at least two stresses or two deformations are detected by means of two gauges 40 and the direction of rotation of the machine is determined by means of the two stresses or the two deformations.

These detections and determinations are made by automated calculation means receiving the signals from the gauges and processing them in real time using appropriate programming.

We illustrated at the deformation of the face 30 of the cam due to the thrust of a piston 12 in the form of a three-dimensional map. This diagram illustrates:

- on the abscissa the position of the roller 18 relative to the cam 14 in degrees around the axis XX;

- on the ordinate the position of the gauge 40 around the axis, knowing that this position is fictitiously varied from 0 to 60° in the angular sector a of the , And

- in gray levels the ratio of circumferential dimension variation seen by the gauge.

This is a finite element simulation with cam 14 without casing 2 or bearings 6. In the left part, it is a first direction of rotation and in the right part the other direction.

Each diagram is divided into four vertical bands.

In the first two bands located between 0 and 15° and between 15 and 30° respectively, piston 12 is supplied by the high pressure circuit. The first band begins at bottom dead center and switching from the low pressure circuit to the high pressure circuit. The second band ends at top dead center and switching from the high pressure circuit to the low pressure circuit.

In the following two bands located between 30 and 45° and between 45 and 60° respectively, the piston is supplied by the low pressure circuit. The third band begins at top dead center and switching from the high pressure circuit to the low pressure circuit. The fourth band ends at bottom dead center and switching from the low pressure circuit to the high pressure circuit.

There shows on the left that the most deformed zone of the external face 30 corresponds to the passage of the roller at top dead center (middle of the lobe) with a slight angle offset. At this moment, we switch from a high pressure port to a low pressure port (in other words from the intake, forming an engine stroke, to the exhaust, forming a non-engine stroke). We see the deformation of the cam become maximum, then suddenly drop when switching to low pressure (at 30°).

The diagram on the right shows the same thing in a reversed rotation direction. This time, when switching from a low pressure orifice to a high pressure orifice, the deformation suddenly becomes maximum and then gradually drops.

It is when the gauge is located to the right of the lobe, therefore at 30°, that detection by the gauge is best. The 40 gauge is not point-specific, it has a certain surface and can therefore observe this phenomenon in both directions. A gauge that is a few degrees away from top dead center would see the phenomenon better in one direction, but less in the other. For an engine with a geometry of the type of Poclain's MS05 engine, the center of the gauge can be placed in an angular sector located between +5° and -5° around the center of the lobe, namely between 25° and 35°. This range is associated with particularly good detection, as shown in the diagram of the .

We therefore see that the highest stress (equivalent to the greatest deformation), takes place in the middle of lobe 20 at the level of the top dead center, that is to say the thinnest zone.

We have illustrated in the diagram of the :

- on the abscissa the angular displacement of a roller 18,

- on the left ordinate the oil flow, in liters per minute, in the piston housing; And

- on the right ordinate the deformation of the gauge in µm/m.

The left part of the diagram is the high pressure zone and the right part the low pressure zone. When the flow is positive, on the left, this is an engine time for the piston. When it is negative, on the right side, it is an escape time. The switch from high pressure to low pressure takes place in the middle of the lobe, at 30°. Here we are in the presence of an extensometry gauge 40 formed by a resistive gauge. The gauge provides its relative deformation of type ΔL/L, therefore measured in µm/m. The strongest deformation of the gauge is located just before the 30° point. The deformation rises suddenly then decreases more gradually. The flow in the feed hole of a piston which travels the lobe is positive from 0 to 30° which corresponds to an engine time. It increases then decreases in this interval. It is negative in the interval between 30 and 60°, in which it decreases then increases again, which corresponds to an escape time.

This diagram of oil flow on the piston and pressure on a lobe shows the shape of a typical measurement. A rising edge 46 is observed on the time warp measurement. This front indicates that we saw a piston passing in one direction. If we had seen a falling front, it would have indicated a rotation in the opposite direction.

In the switching zone, we observe a parasitic peak 41. In fact, the roller enters the cam plate, and the pressure is reversed. The piston supply port changes from a high pressure distributor port to a low pressure port, with a 2° seal gap. A sudden decompression or recompression occurs on the switches. This parasitic peak varies depending on the working pressure and the speed of the engine. We also observe another parasitic peak 43 to 45° which comes from the same phenomenon occurring on another piston on another lobe.

The sealing gap comes from the fact that an angular sector is provided, here of 2°, separating the position in which the piston housing is no longer in communication with the high pressure circuit and that in which it enters into communication with the low pressure circuit. This angular sector is larger than the angular sector occupied by the orifice of the piston housing, as illustrated in . It aims to prevent the low and high pressure circuits from being in direct communication via the piston housing. In this angular sector, the piston is on the zone called "cam plate", which is no longer sinusoidal but in an arc centered on the axis in order to temporarily immobilize the piston. The switches occur in the cam flats, and their length corresponds to the dimensions of the piston housing ports vis-à-vis the gap between two feed ports on the face of the distributor, including a seal gap.

We therefore observe that the preferred angular position of the gauge is located to the right of each lobe, therefore corresponds to the middle of a top dead center switching, that is to say substantially in the middle of a cam flat of the thinnest part of the cam. Generally speaking, for hydraulic machines of different sizes, depending on their geometry, the center of the gauge can be placed in an angular sector corresponding to the cam plate around the center of the lobe. If the gauge is located in the cam plate, but a few degrees before or after the switching point, the gauge will have a preferential operating direction to the direction of rotation of the machine. If the gauge is located substantially in the cam plate and centered over the switching points, the gauge will be indifferent to the direction of rotation.

We illustrated at a similar diagram indicating the angular position of the piston 12 on the abscissa and the measurement made by gauge 40 on the ordinate. We are at low speed in one direction of rotation then in the opposite direction for the machine operating in motor mode. (The same diagram would also illustrate, for the same direction of rotation, the machine operating first in motor mode, then in pump mode). We can ignore the spurious peaks in the figure. On the left, we see that the rising front occurs twice in a row, on the right the falling front occurs twice in a row. Each peak can be detected electronically, along with its orientation. On this engine, between the passage of two pistons at the same point, the cylinder block, therefore the engine shaft, rotated by 45°

A similar diagram is shown in with a greater number of peaks. This is a measurement on a motor that runs in one direction for a period of time, then stops and goes in the other direction.

We illustrated at a simplified form of the base peak forming these diagrams in one direction of rotation. This is an example of a typical time signal when going from high pressure to low pressure. High pressure is for example between 200 and 600 bars (one bar worth 10 ⁵ Pa), typically 400 bars, while low pressure is between 20 and 25 bars.

Thus, determining the orientation of the peak associated with the stress or deformation at one of the gauges 40 makes it possible to determine the direction of rotation of the machine. It is also possible to detect at least two stresses or two deformations in two respective predetermined zones of the cam and thus determine the direction of rotation of the machine. Furthermore, if at least two stresses or two deformations are detected successively at the same gauge, taking into account the time interval between the two detections makes it possible to determine the rotation speed.

Taking symmetry into account

In this example, the symmetry of the machine can be taken into account to further improve these detections and these calculations. Indeed, in this machine, in each pair of gauges 40 facing each other, the two gauges are stressed in substantially the same way at the same time. We can therefore sum the signals from these two gauges. Thus, we measure amplitudes appearing simultaneously on two gauges and we perform a sum of the amplitudes. Depending on the symmetry of the machines and the number of lobes, multiple concomitant signals can be obtained.

Thus, on the diagram of the , the signals from the gauges 40 have been represented in a manner similar to the previous ones.

If we number the six gauges from 1 to 6 around the X-X axis, on the first part of the diagram, we therefore have a signal representing the sum of the signals from gauges 2 and 5, a signal of the sum of the signals from gauges 3 and 6 and a signal of the sum of gauges 1 and 4. It can be observed that these signals are not of the same height, the gauges not having exactly the same calibration. In addition, the gauges are not placed in exactly the same angular position. Sometimes we have a 4° offset from TDC and sometimes 2°.

The other part of the diagram is similar for the opposite direction of rotation.

These steps can be implemented with a different number of gauges in the engine, for example 8 or 10 for as many lobes as gauges, provided that some of the gauges provide substantially identical signals at the same time.

The same determinations and the same calculations can be carried out using the signals thus summed for greater precision.

Torque determination

In another aspect of this mode of implementation of the method of the invention, at least one amplitude of the stress or deformation is measured with the gauges 40 and an intensity of a torque is determined by means of the amplitude. generated by the machine.

To this end, first of all, a torque calibration of the motor is carried out on a test bench during which the values provided by the gauges 40 corresponding to the torques measured elsewhere are measured. We thus establish a law, for example linear, of the torque as a function of the deformation or stress signal provided by the gauges, or even a correspondence table. Then, on the rolling machine, that is to say in use, we collect a stress or deformation value using the gauges 40, we consult the table, and we obtain the torque supplied by the motor.

This determination method provides an estimated torque as close as possible to the cam. This eliminates load losses and friction. This process allows instantaneous torque control on the rolling machine, which is more precise than pressure measurement and eliminates errors.

If we are in the presence of a machine comprising wheels 51 each actuated by a machine according to the invention, the torque measurement makes it possible to control the traction of the machine for each wheel, for example to control an anti-slip mode of the 'machine. Torque measurement by gauges is also useful for controlling operation at very low speed (or creep drive in English).

Determination of motor efficiency

In another aspect of this method of implementing the method, it is also possible to obtain an estimate of the efficiency of the machine. To do this, at least one amplitude of the stress or deformation is measured by means of the gauges and an efficiency of the machine is determined by means of the amplitude and a hydraulic pressure at the inlet of the machine.

More precisely, we can proceed as follows. We know the theoretical torque or the torque when the machine is new. Thanks to the process, we then measure the effective thrust exerted by the pistons in operation, which frees us from engine losses (friction losses and hydraulic losses). From this effective thrust and knowing the hydraulic pressure at the inlet of the machine and the geometry of the machine (in particular the slope of the cam ramps), we then calculate the real torque produced by the engine, this calculation being carried out from a way known to those skilled in the art.

Then, the yield is calculated by the following formula:

Efficiency = Actual (measured) torque/theoretical torque

Measuring performance makes it possible, for example, to know the state of wear of the machine. The efficiency can change depending on the temperature of the fluid or the mechanical components. Thanks to knowledge of output, machine operation can prioritize obtaining optimal output in real time. This efficiency reflects the level of break-in of the machine which is useful to indicate a level of maximum power usable on the machine without risk of damaging it. This measurement can also help detect wear or a malfunction of the machine.

Measurement of the overall deformation of the cam by several sensors

We have illustrated in Figures 14 and 16 the situation of the same machine 1 forming a wheel motor of a machine.

As the machine rests on the ground via its wheels 51, each motor receives external forces which apply to its structure and pass through the cam 14, passing on the one hand through the wheel 51 of the machine, the shaft 4 and the bearings 6 and on the other hand by the casing 2, the cam 14 and the frame 47 of the machine. This is on the one hand the weight of the machine and on the other hand the reaction of the ground. These external forces are axial and radial. They generally result in stresses on the cam in directions different from those of the piston stresses, namely in compression or extension of the cam, following the axial direction of the engine in particular but not only. The axial forces exerted on the hydraulic machine induce compressions or elongations of its structure, in particular of the casings along the X-X axis of the machine. The radial forces exerted on the machine induce bending of the structure of the machine, in particular of these casings.

It is also possible here to use gauges 40 to measure these forces, but on axes different from the piston passage measurements.

For this, the gauges 40 are arranged, as illustrated in Figures 6 and 7, to detect an axial stress or a variation of an axial dimension of the external face 30. Indeed, unlike the previous case in which each gauge serving to see the passage of a roller is oriented in a circumferential direction of the cam, this time, to see the external forces, the gauges are oriented in a direction parallel to the axis.

It is also possible to provide the two gauge orientations or a multidirectional gauge, for example a rosette gauge to measure the deformations resulting from external forces at the same time as the deformations due to the passages of the piston rollers. Electronic filtering then makes it possible to separate the axial measurement and the transverse measurement of the gauges. Indeed, for the detection of forces we need to analyze the continuous component of the signal unlike the speed where we can determine it using the dynamic component. For force detection, we do not look at the dynamic component, we therefore filter the signal.

Furthermore, thanks to the presence of several gauges at different locations on the cam, the amplitudes of at least two stresses or two deformations are measured in two respective predetermined zones of the cam and at least one intensity is determined by means of the amplitudes. of a force exerted on the machine from outside it. It is not necessary for the gauges to be in line with the lobes. We can predict that the machine is stopped during the detection step.

In reference to the , to measure external forces, we first carry out a calibration. To do this, calibrated radial forces Fr and axial forces Fa are exerted by means of two cylinders on the machine placed on a calibration bench. These forces are brought back onto the axis XX via a rolling member 48 and a lever arm 50. This assembly makes it possible to apply forces to the machine identical to those generated during its use. The machine can be stopped or running. We then acquire the signals provided by the gauges 40. This makes it possible to obtain a law or a correspondence table giving the forces as a function of the signals from the gauges.

Then, when using a motor of the same type mounted on a machine as on the , we obtain the measurements provided in real time by the gauges, we consult the law or the table and we derive the forces Fr and Fa received by the engine. We can thus deduce the state of charge of the motor and record its load. Knowing its endurance, we can determine its aging, that is to say its wear. We can identify the wheels 51 which are more or less loaded and manage traction (in particular in anti-slip mode). We can determine the loads seen by the motor and estimate its lifespan to manage its maintenance.

On the , we have shown the offset d of the wheel 51 relative to the flange 53 carrying the wheel and the offset d between the wheel and the closest bearing 6 on the shaft 4. The calibration assembly of the corresponds to the offset d . The external forces acting on the wheel include an axial thrust Fa and a radial thrust Fr. They induce on the carcass of the hydraulic machine 1 a bending moment M due to the offset d' and calculated according to the formula:

M = d’.Fr

The calibration assembly of the is used to reproduce the same forces on the hydraulic machine. This explains the shape of the lever which also produces the offset due to the end of the shaft and the shape of the rim of the machine. The offset between the point of application of the radial force and the point where a force is exerted on the carcass (the bearing bearing) induces a bending moment on the carcass of the machine, which results in compressions and extensions of the gauges in the axial direction.

The reliability of this process is illustrated by the diagrams of the . On each diagram, time is indicated on the abscissa. They indicate on the ordinate the amplitude of the axial force Fa, the radial force Fr and the torque. The measured and estimated quantities are represented each time. A close correspondence between the measured value and the estimated value is observed in each case. The percentage error is shown on the right y-axis.

Peaks are visible on these graphs. They do not represent the passage of the pistons. You would have to zoom in a lot more to see them. They simply show the reaction of the radial cylinder when the axial force is changed.

In the diagram on the axial force, we vary the latter from -2000 daN to 2000 daN. This means that we pull and push on the tree.

In the diagram on the radial force, we do not apply such a force here. Only parasitic forces appear resulting from the axial stresses applied. Without parasitic effort, we would be at 0 daN. In this case, the radial force applied is 0 and we only have a parasitic force.

We find it in the torque estimated by the model. For the torque diagram, we give the high pressure a value such as 100 bars, 200 bars, 300 bars or 400 bars. We do not vary it in this test. Only the axial force applied varies.

Chain embodiment

We present with reference to Figures 17 to 19 another embodiment of the invention. Only the characteristics which differ from those presented above will be described.

In this machine, at least four gauges 40 are arranged in circumferential succession on the external face of the cam 14 following a single file in an angular sector equal to the angle a formed by the angular sector formed by two consecutive pistons 12 in the circumferential direction . This angle a is illustrated in . These gauges form what is called here for convenience a chain 60. All the gauges 40 of the chain 60 are identical to each other and follow one another with the same spacing. They are electrically connected in series.

Such an arrangement is used to measure speed and position in a much finer manner than with the simple gauges described above. It makes it possible to obtain a continuous or quasi-continuous measurement and to permanently monitor the passage of the pistons. In fact, the chain extends in an angular sector equal to the angle formed by the angular sector formed by two consecutive pistons 12. It is therefore called upon at all times during rotation. The fact that there is always a roller on it allows you to know the precise position of the motor. The finer the succession of the gauges in the chain, the more precise the indication of the engine position. This is evident from the diagram of the giving the appearance of the signal provided by the chain gauges as a function of time.

The number of 40 gauges in the sector is at least four. In this case, the chain 60 includes 10 gauges in this angular sector, as illustrated in . This number could take other values such as 6, 8, etc. The chain can also include additional gauges beyond this angle.

In this case, the angle formed by the angular sector formed by two consecutive pistons in the circumferential direction is 45°. The chain therefore extends over 45° or more, so that there is always a piston permanently resting on the area covered by the chain. As a half-lobe is only 30°, the chain is longer than the lobe.

To be able to operate in both directions of rotation, the chain should cover the two half-lobes. However, as the chain contains gauges electrically connected in series, the more there are, the more the signal is attenuated. This is why, in this embodiment, the chain covers a half-lobe but not an entire lobe, which means that detection is only done in one direction of rotation which puts the half-lobe under high pressure. In addition, the remaining part covered by the chain outside the half-lobe, namely 45-30=15°, extends into a half-lobe at low pressure. In the opposite direction of rotation, detection is done on the other lobe, which will be at high pressure. With a chain of a length such that it extends in an angular sector equal to the angle formed by the angular sector formed by two consecutive pistons 12, we can finely measure the position of the motor in both directions of rotation.

In this embodiment, as illustrated in , the chain extends between a top dead center and the bottom dead center which immediately follows it (PMH6 and PMB1 in this case). The cam 14 also carries five gauges 40 arranged to the right of the other top dead centers (from PMH1 to PMH5 in this case). These other gauges make it possible to know the forces and torque, the direction of rotation and the speed at low frequency and with low precision. The 60 chain allows you to know the speed with greater precision.

The processing of the gauge signal takes place as explained above.

Alternatively, we can extend the chain over a larger angular sector and dispense with all or part of these other gauges.

Other considerations

We therefore see that we can use the deformations of the cam during the passage of the pistons to measure the speed, the angle and the direction of rotation of the engine, the real torque supplied, as well as the force supplied by each piston and the external efforts. The determination takes place in real time and from information obtained as close as possible to the cam, this information being net of load losses and friction. The gauges are stressed in particular at each passage of the piston by the force in contact with the roller on the cam. All the torque variable is concentrated on a reduced number of active pistons. This specific rather than global stress amplifies the stress very strongly, which creates a very amplified signal from the gauges and therefore very usable.

The instrumentation used is minimally intrusive, takes up little space, is easily integrated and does not pose any problems with sizing, compatibility with oil, resistance to pressure or sealing. The gauges in the examples presented above do not pose a problem of clogging due to metallic pollution. In addition, the use of gauges does not disrupt the chain of transmission of forces within the machine.

The placement of the gauges on the cam allows measurements to be taken on a unique and characteristic part of each machine model.

Numerous modifications can be made to the invention without departing from its scope. We can vary the number of pistons, lobes and gauges.

The invention can be applied to all or part of a hydraulic machine, in particular, to a hydraulic machine containing several sub-parts which can be deactivated to change its displacement, for example by selecting groups of lobes or groups of pistons capable of forming homokinetic machines, which makes it possible to change the displacement of the hydraulic machine. The calculation of speed and torque must then take this into account.

Claims (26)

Hydraulic machine (1) comprising:
- a cam (14) having a cylindrical external face (30) and a main axis (XX), and
- at least one gauge (40) rigidly fixed to the face and arranged to detect a stress on the face and/or a variation of a shape of the face. Machine according to the preceding claim in which the gauge or at least one of the gauges (40) is arranged to detect a radial stress and/or a variation in a circumferential dimension of the face (30). Machine according to one of the preceding claims in which the gauge or at least one of the gauges (40) is arranged to detect an axial stress and/or a variation in an axial dimension of the face (30). Machine according to one of the preceding claims in which the gauge or at least one of the gauges (40) comprises a piezoelectric sensor. Machine according to one of the preceding claims in which the gauge or at least one of the gauges (40) is a resistive gauge. Machine according to one of the preceding claims in which the gauge or at least one of the gauges (40) is a multiaxial gauge. Machine according to one of the preceding claims which comprises at least two gauges (40) extending in the same plane perpendicular to the axis (X-X). Machine according to one of the preceding claims in which, the cam having lobes (20), the gauge or at least one of the gauges (40) extends in the median angular position of an angular sector formed by one of the lobes . Machine according to one of the preceding claims comprising a casing and members for fixing the cam to the casing, the gauge or at least one of the gauges (40) extending in the median angular position of an angular sector formed by two fixing members following each other around the axis. Machine according to one of the preceding claims in which the cam has at least one facet engaging the cylindrical face, the gauge or at least one of the gauges extending to the right of the facet. Machine according to one of the preceding claims which comprises pistons and piston housings, the cam having switching points arranged so that fluid switching of one of the housings takes place when the piston passes this housing to the right of this point, the gauge or at least one of the gauges extending to the right of one of the switching points. Machine according to one of the preceding claims in which the gauge or at least one of the gauges extends to the right of a zone of the cam having maximum flexibility with reference to all the zones of the cam. Machine according to one of the preceding claims which comprises pistons (12) and in which at least four gauges (40) are arranged in circumferential succession in a single file in an angular sector equal to the angle formed by the angular sector formed by two consecutive pistons in the circumferential direction. Machine comprising at least one machine (1) according to one of the preceding claims. Method in which a stress on a cylindrical external face (30) of a cam (14) of a hydraulic machine (1) and/or a variation of a shape of the face is detected, the detection taking place directly on the face. Method according to the preceding claim in which a stress is detected in a circumferential direction of the face (30) and/or a variation in a circumferential dimension of the face. Method according to one of claims 15 to 16 in which:
- we determine whether the stress or the deformation corresponds to a passage of at least one piston (12); And
- if the stress or deformation corresponds to the passage of the piston, at least one value is determined among the following:
- a rotation speed of the machine,
- a direction of rotation of the machine,
- a torque generated by the machine, and
- machine performance. Method according to one of claims 15 to 17 in which an orientation of a peak associated with the stress or deformation is determined and a direction of rotation of the machine (1) is deduced. Method according to one of claims 15 to 18 in which:
- at least two stresses or two deformations are successively detected in the same predetermined zone of the cam (14); And
- a rotation speed of the machine (1) is determined by means of the two stresses or the two deformations. Method according to one of claims 15 to 19 in which:
- at least two stresses or two deformations are detected in two respective predetermined zones of the cam (14); And
- a direction of rotation of the machine (1) is determined by means of the two stresses or the two deformations. Method according to one of claims 15 to 20 in which:
- at least one amplitude of the stress or variation is measured; And
- an intensity of a torque generated by the machine (1) is determined by means of the amplitude. Method according to one of claims 15 to 21 in which:
- at least one amplitude of the stress or variation is measured; And
- an output of the machine (1) is determined by means of the amplitude and a hydraulic pressure at the inlet of the machine. Method according to one of claims 15 to 22 in which amplitudes appearing simultaneously on two gauges (40) are measured and a sum of the amplitudes is carried out. Method according to one of claims 15 to 23 in which:
- the amplitudes of at least two stresses or two deformations are measured in two respective predetermined zones of the cam (14); And
- we determine by means of the amplitudes at least one intensity of a force (Fr, Fa) exerted on the machine from outside the machine. Method according to one of claims 15 to 24 in which an axial stress and/or a variation of an axial dimension of the face (30) is detected. Method according to the preceding claim in which the machine is stopped during the detection step.