EP1756405B1 - Device for varying a compression ratio of an internal combustion engine and method for using said device - Google Patents

Abstract

The device (32) has a cam (42) housed between a crank pin (34) and a hole (44) provided in a connecting rod head (30). The cam has circular shape with geometric axis of the cam corresponding to its center axis, and a hole (46) with axis non coaxial with the geometric axis and merged with axis of the crank pin. The cam permits to vary compression rate of an internal combustion engine. An independent claim is also included for a method for varying compression rate of an internal combustion engine.

Description

The present invention relates to a device for varying the compression ratio of an internal combustion engine and to a method enabling the use of such a device.

It relates more particularly to a device that can change the compression ratio of this engine by changing the dead volume of the combustion chamber at the top dead center of the piston.

It is already known, by the document EP 0 297 904 , a device for varying the compression ratio of an engine in which the engine comprises a crankshaft, a cylinder inside which a piston slides in a reciprocating movement by means of a connecting rod connected to said piston and said crankshaft , this piston delimiting with the top of the cylinder a combustion chamber having a dead volume at the top dead center (TDC) of this piston, and a rotary eccentric, of drawn type, interposed between the connecting rod and the piston. This eccentric, in a first position, allows the piston to reduce the dead volume of the combustion chamber while increasing the compression ratio and increase this dead volume, for another position of this eccentric, while obtaining a rate of lower compression. To do this, the eccentric has a groove provided to cooperate with two locking pins each disposed symmetrically with respect to the axis of the piston for immobilizing the eccentric in one or other of its positions.

This device, although satisfactory, nevertheless has many disadvantages.

One of the drawbacks of such a device lies essentially in the lack of flexibility of the possibilities of adjusting the compression ratio which comprises only two possibilities of variation of this rate.

In addition, such a device requires a precise adjustment between the groove and the pin to prevent pinching phenomena of the pin in the groove.

He is also known, by the document US 5,165,368 , a device for varying the compression ratio in which the towed eccentric carries a jack which cooperates with the crankpin of the crankshaft so as to control the rotation of this eccentric.

This device has a major disadvantage in the sense that the eccentric towed comprises an element (the jack) which disturbs, or even opposes, the movement of the eccentric during its rotation which is generated by the torque from the resulting inertia force displacement of the piston and connecting rod assembly.

In another type of device for varying the compression ratio, as better described in the patent application DE-A-42 26 361 , the eccentric is not an eccentric towed type but a motorized eccentric through the cooperation of a gear sector of this eccentric with a worm.

This device has a major disadvantage in the sense that the worm must be motorized to control the rotation of the eccentric. This motorization is bulky and requires large powers to overcome the inertia of the mobile and the various friction.

The present invention proposes to overcome the above mentioned drawbacks by means of a device for variation of the compression ratio of simple and space-saving design which makes it possible to increase the possibilities of variation of the compression ratio.

For this purpose, the present invention relates to a device for varying the compression ratio of an internal combustion engine comprising at least one cylinder with a combustion chamber, a mobile unit comprising a piston displaceable in translation under the action of a connecting rod connected by an axis to said piston and connected to a crankpin of a crankshaft, said piston making a race between a top dead center and a bottom dead center leaving a dead volume at the top dead center of said piston, said device comprising an eccentric rotary tensioner housed between said crankpin and said connecting rod by making it possible to vary the compression ratio and means for controlling the displacement of the eccentric, characterized in that the control means comprise a fluidic jack carried by the connecting rod and comprising a slider placed in a housing formed in a slide support, in that the slide defines two fluidic chambers in communication with each other. at least one closed circuit and in that the slide comprises a toothed surface cooperating with a toothed sector carried by the periphery of the eccentric.

The fluidic chambers may be in communication with one another by at least one closed circuit.

The closed circuit may comprise at least one valve means for controlling the flow of fluid from one chamber to the other.

Advantageously, the valve means can be a valve with at least two channels.

Preferably, the valve means can be a piezoelectric device.

The piezoelectric device may comprise a needle and a piezoelectric actuator.

The piezoelectric device can be controlled by cooperation of pads and electrical tracks.

The circuit may comprise at least one metering device located downstream of the draining means.

The metering device may comprise a piston-cylinder assembly with a setting spring.

The elements of the closed circuit may be at least partly housed in the cylinder.

The variation device may comprise means for locating the position of the eccentric.

The locating means may comprise a transmitter-receiver set of signals.

The eccentric can include the transmitter and the receiver can be housed on a fixed part of the engine.

The eccentric may comprise means cooperating form with the slide.

The cooperation means may comprise a toothed sector carried by the eccentric and a toothed bearing carried by the slide.

An advantage of the present invention over devices of the state of the art lies in the fact that the energy loss of the bearing function between the connecting rod and the crankpin is lower. Indeed, when the compression ratio does not vary, the position of the eccentric relative to the connecting rod is fixed and the bearing function between the connecting rod and the crankpin is achieved by the relative displacement between the eccentric and crankpin crankpin . Therefore, the bearing function between the connecting rod and the crankshaft is made with a smaller bearing diameter, which is a significant advantage because as is experienced energy loss of a bearing, for a given load under normal operating conditions, is an increasing function of its diameter.

Another advantage of the present invention is easier control of compression ratio adjustment. Indeed, the present invention uses a reversible kinematic connection which continuously links the angular displacement of the eccentric to the translation of the slide. As a result, the angular setting of the eccentric and consequently the adjustment of the compression ratio is a continuous function of the position in translation of the slide defined by the mechanical construction of the device according to the invention. Thus, at no time can the compression ratio be varied without the translational position of the slide being modified and, thanks to the hydraulic device of the present invention, the control of the position of the slide is obtained easily.

Other additional advantages of the present invention are lower energy loss, higher accuracy and longer life. Indeed, the present invention uses a reversible kinematic connection to continuously link the angular displacement of the eccentric to the translation of the slide. Due to the reversibility of the kinematic link, the friction in this connection can be minimized by construction. Thanks to this, the energy loss by friction of this connection, the wear of this connection and the amplitude of the hysteresis phenomena may be all three smaller. In addition, the lowering of the amplitude of the hysteresis phenomenon leads to a better accuracy of the adjustment of the compression ratio. In addition, because of its reversibility, the kinematic connection of the present invention does not present a risk of jamming. This reversibility can be obtained by means of a toothed sector, preferably placed on the peripheral wall of the eccentric, which cooperates through an opening provided in the connecting rod head, with a toothed rack-type bearing, provided in a slider movable in a housing carried by a support connected to the connecting rod. This slider has a displacement tangential to the circumference of said eccentric.

Yet another advantage of the present invention lies in a greater simplicity of integration of the device in the engine and in its environment. Indeed, the present invention uses an eccentric housed between the crankpin and the bore of the crankshaft. Therefore, the distance between the axis of the crankshaft and the various peripherals of the engine, the camshaft, the starter, the alternator, the water pump, etc. does not vary and therefore does not lead to additional specific devices to compensate for variations in distances between the crankshaft and these different devices of the engine. Likewise, the alignment between the crankshaft and the transmission does not change. Thanks to the present invention, it is therefore not necessary to use specific device to compensate for the alignment variations between the engine and the transmission to which it is coupled.

In addition, the device of the present invention allows to have a weight and a smaller footprint and a greater responsiveness of the adjustment of the compression ratio. Indeed, because the eccentric is towed, the adjustment of the compression ratio does not require a drive motor of the eccentric and the device is not penalized by the weight, the space and by the response times of a specific motor and its kinematic links to rotate the eccentric to adjust the compression ratio.

In addition, this device has other advantages such as compatibility with a shorter distance between the crankshaft axis and the engine cylinder head, less vibration and a lower cost of implementation. Indeed, the cylinder whose function is to control the position of the eccentric placed between the crankshaft and crankpin crankpin is distinct from said eccentric, including its slider is distinct from all other parts and is movable with respect to all these other pieces. Thanks to this a wide choice of orientation of said cylinder relative to the connecting rod is allowed, which simultaneously optimizes the distance between the axis of the crankshaft and the cylinder head and the vibrations induced by the moving equipment and also the shapes to reduce manufacturing costs.

• la figure 1 qui montre, en coupe axiale, un moteur à combustion interne avec le dispositif de variation du taux de compression selon l'invention dans une première position,
• la figure 2 est une autre vue, en coupe axiale, montrant le moteur à combustion interne avec le dispositif de la figure 1 dans une autre position et dans une autre configuration,
• la figure 3 est une vue de détail dans une position extrême du dispositif de l'invention de la figure 1,
• la figure 4 est un schéma montrant le circuit de commande utilisé pour le dispositif selon l'invention,
• la figure 5 est une autre vue de détail du dispositif montrant les différents éléments du circuit de commande portés par le dispositif selon l'invention,
• la figure 6a est une autre vue de détail du dispositif montrant une variante d'un des éléments du circuit de commande du dispositif selon l'invention alors que les figures 6b à 6d sont une illustration des différentes positions de ce dispositif pendant la rotation du vilebrequin et
• les figures 7a à 7d sont une autre illustration d'un dispositif de localisation de la position angulaire de l'un des éléments du dispositif de variation du taux de compression selon l'invention.

The other features and advantages of the invention will become apparent on reading the following description, given solely by way of illustration and not limitation, and to which are appended:

• the figure 1 which shows, in axial section, an internal combustion engine with the variation device of the compression ratio according to the invention in a first position,
• the figure 2 is another view, in axial section, showing the internal combustion engine with the device of the figure 1 in another position and in another configuration,
• the figure 3 is a detailed view in an extreme position of the device of the invention of the figure 1 ,
• the figure 4 is a diagram showing the control circuit used for the device according to the invention,
• the figure 5 is another detail view of the device showing the various elements of the control circuit carried by the device according to the invention,
• the figure 6a is another detail view of the device showing a variant of one of the elements of the control circuit of the device according to the invention whereas the Figures 6b to 6d are an illustration of the different positions of this device during the rotation of the crankshaft and
• the Figures 7a to 7d are another illustration of a device for locating the angular position of one of the elements of the compression ratio variation device according to the invention.

We refer to Figures 1 to 3 which show an internal combustion engine with at least one cylinder 10 which comprises a bore 12 inside which slides a hollow piston 14 in an alternating translational movement under the impulse of a connecting rod 16. This piston delimits with its upper part , the side wall of the bore 12 and the upper part of this bore, generally formed by a portion of the yoke 18, a combustion chamber 20 in which the combustion cycle takes place. The piston carries two diametrically opposed radial bores 22 through which is housed a cylindrical axis 24 which connects an end 26 of the connecting rod, said small end, to said piston through, sliding, a bore 28 provided in the small end. The other end of the connecting rod, called the big end, is connected by a device for varying the compression ratio 32 to a crank pin 34 of a crankshaft 36. This crankshaft is subjected to a rotational movement about an axis. XX so that the crankpin 34 follows a circular path 38 about the axis XX. As is known, the piston 14, the connecting pin 24, the connecting rod 16, the crankshaft 36 with its crankpin 34 form the movable engine.

In conventional engines, during the rotational movement of the crankshaft 36 as the intake and expansion phases, the crank pin 34 passes successively from a high position, indicated 0 ° on the figure 1 at a low position, indicated 180 °. During this movement, the piston 14, which is connected to the crankpin 34 by the connecting rod 16, undergoes an alternating translational movement between an initial upward dead center (referenced PMHi on the figure 1 ) which corresponds to the high position of the crankpin and an initial low dead point (referenced PMBi on the figure 2 ) corresponding to the low position of the crank pin. Thus, the piston 14 has an initial stroke between its PMHi and its PMBi.

In these engines, when the piston is at the PMHi, either at the end of the compression phase or at the end of the exhaust phase, there remains a dead volume 40 in the combustion chamber 20. This volume is necessary to the operation of the engine during its phases of compression, combustion and relaxation.

As is well known to those skilled in the art, the compression ratio of an engine is a function not only of the extent of the cylinder volume delimited by the piston stroke but also the magnitude of the dead volume. To modify the compression ratio, simply modify one of these volumes and more particularly the size of the dead volume.

To do this, the compression rate variation device 32 comprises an eccentric 42 housed between the crank pin 34 and a bore 44 provided in the crank head 30. This eccentric has a generally circular shape with a geometric axis X1X1 which corresponds to its center axis and comprises a bore 46 of X2X2 axis not coaxial with the axis X1X1 but coincident with the axis of the crankpin 34. This eccentric is slidably accommodated in the receiving bore 44 made in the connecting rod head and on the peripheral wall of the crank pin 34.

This eccentric is said towed because during operation of the engine, it is likely to be rotated about the axis X2X2 under the effect of a torque generated by the inertial force resulting from the displacement of the engine. mobile equipment and more particularly the piston and the cylinder.

Indeed, the crankpin 32 travels a semicircular path for a phase, for example admission, ranging from 0 ° to 180 ° and another semicircular path (180 ° to 0 °) for another phase, as the compression phase. During these journeys, the piston 14 goes from its top dead center to its bottom dead point and then from its bottom dead center to its top dead center. During this movement, this piston and the connecting rod 16 undergo an acceleration that increases as one of its dead spots approaches. When the resulting force of this acceleration, called the inertial force, is sufficient to overcome not only the weight of the piston 14 and the connecting rod 16 and / or the resultant of the gas pressures on the piston and the connecting rod but also the friction forces. between this piston and the wall of the bore of the cylinder, it generates an increase in speed of the piston rod assembly relative to that transmitted to this assembly by the crankpin. Therefore, if the displacement of the eccentric is not impeded, there is an additional displacement of the piston and the rod relative to that induced by the crankpin. This movement takes place upwards when the piston is on the side of the top dead center and down when the piston is on the side of the bottom dead center. This additional drive can be made possible by the rotation, around the axis X2X2, of the eccentric 42 connected to the connecting rod 16. Thus, as shown by way of example on the Figures 1 to 3 , the eccentric has a rotational movement in a counter-clockwise direction for a decrease in the compression ratio when the piston stroke from its top dead center to its bottom dead point, and in a clockwise direction for an increase in the rate of compression during the stroke of this piston from its dead point down to its top dead center.

This eccentric comprises, preferably on its peripheral wall, a toothed sector 48, of angular extent SD, which cooperates, through an opening 50 provided in the connecting rod head 30, with a toothed surface 52, of rack-type, provided on a slide 54 movable in rectilinear translation in a housing 56 carried by a support 58 connected to the connecting rod head 30. Preferably, this support is integrated with the lower half-bearing 60 which usually comprises the connecting rod head 30 and which is assembled by screws 62 to the other half-bearing 64 carried by the body of the connecting rod. The slider 54 comprises a peripheral wall 66 of cylindrical section on which are placed seals 68 and this in the vicinity of its end faces 70 which preferably comprise axial recesses 72. This peripheral wall is interrupted by the rack 52 which is substantially rectilinear and which extends over a large part of the length of this slider. This rack has a length in length which corresponds at least to the developed sector toothed 48 of the eccentric 42. The housing 56 is of complementary shape to the cross section of that of the slide 54 and comprises two end walls 74. The distance between these two walls and the setting of the toothed sector of the eccentric with respect to the toothed range of the slide are such that the total length of the slide to which is added the total clearance of this slide, under the effect of the rotation of the eccentric , allows the geometric axis X1X1 of this slider to be located on the left of the axis of the cylinder, considering the figures, and this both at the top dead center at the bottom dead center of the piston. Preferably, the angular displacement of this eccentric is of the order of 120 ° between its two extreme positions. To execute the initial setting of the toothed sector during the mounting of the device, the midpoint M1 of the toothed sector of the eccentric is located halfway at the point M2 of the length of the rack in such a way that the axis X1X1 this eccentric is at the same height as the axis X2X2 of the crank pin at the top dead center and at the bottom dead center of the piston. So from this position nominal, the eccentric rotates counter-clockwise at an angle of about 60 ° to obtain a minimum compression rate which may be the nominal rate and arrived at the position of the figure 3 and, for a maximum rate, rotates, still from this initial setting position, by an angle of approximately 60 ° in the clockwise direction to arrive at the position of the figure 1 . When the maximum rate is reached, the eccentric rotates counter-clockwise at an angle of about 120 ° to reach the minimum rate and about 120 ° clockwise to obtain a maximum rate from its minimum rate. The volumes delimited by the peripheral wall of the housing, its end walls and the end faces of the slide thus form two sealed fluidic chambers 75a and 75b, respectively, which allow the movement of the slide in the housing to be authorized and controlled. There is thus formed a fluid cylinder 76 comprising the support 58 with its housing 56 in which the slide 54 moves rectilinearly under the effect of the fluid present in the chambers 75a, 75b. Thus, the variation device comprises a slider and a slider support separate from the eccentric. The relative position in translation of this slider relative to its support is continuously kinematically related to the angular displacement of the eccentric relative to the connecting rod by a kinematically reversible connection.

This housing is connected to a control circuit 77, as shown in FIG. figure 4 , which makes it possible to control the rotation of the eccentric thanks to the control of the movement of the slide.

This control circuit comprises at least one closed circuit in which a fluid circulates, for example oil. In the example of the figure 4 the control circuit comprises two closed circuits 78a and 78b for which each closed circuit connects the two chambers 75a and 75b. The chamber 75a is connected by a pipe 80a to a valve means 82a and more particularly to a 3-way valve, one of the channels is connected to the pipe 80a and the other of the channels is connected to a cover 84a by a channel 86a. This valve is controlled by a means 88a whose actuation is dependent on the demand for variation of the rate of compression. A pipe 90a then connects the outlet of the valve 82a to a metering device 92a comprising a cylinder 94a with a sealed piston 96a movable within the cylinder and which define two metering chambers 98a and 100a. The chamber 98a is connected to the pipe 90a while the chamber 100a, which comprises a spring 102a, is connected by a pipe 104a to the fluid chamber 75b. Advantageously, the pipes 80a and 104a carry check valves 106a and 108a respectively avoiding a return of fluid in the chamber 75a and a fluid outlet of the chamber 75b.

Additionally, this control circuit comprises means for filling and purging circuits 78a and 78b. These means comprise a hydraulic pump 110, pipes 112a, 112b each carrying a non-return valve and connected to the pipes 104a, 104b, purge valves 114a and 114 connected to the pipes 80a and 80b and purge devices 116a and 116b located on the metering devices 92a and 92b.

So, considering the figure 4 , the displacement of the slider 54 to the left is controlled by the opening control of the valve 82a which communicates, through the pipes 80a and 90a, the fluid chamber 75a with the metering chamber 98a. Under the effect of the pressure generated in the fluidic chamber 75a by the displacement of the slide under the impulse of the eccentric, the piston 96a is pushed against the spring 102a towards the metering chamber 100a and the fluid present in this chamber is introduced through the pipe 104a into the fluid chamber 75b. Thus, any decrease in the volume of a fluid chamber results in an increase in the volume of the other chamber. This spring is tared in such a way that it makes it possible to dose the progressive introduction of the fluid into the chamber 98a, which makes it possible to avoid jolts at the level of the slide. As soon as this slider has reached the desired position, the valve 82a is actuated in closing by the control 88a to hold the slider in the position where it arrived. During this action, on the one hand, the communication between the chambers 75a and 98a is closed and, on the other hand, the evacuation of the fluid present in the metering chamber 98a, under the impulsion of the spring 102a, is authorized by the pipes 90a and 86a to the tank 84a.

The volume of the metering chamber 98a is shaped in such a way that it corresponds to a determined displacement value of the slide, hereinafter referred to as the increment description, this increment being able to be used partly or entirely during the displacement. from this slider. To adjust the compression ratio to the desired value, the volume of fluid from the fluid chamber 75a, during movement of the slider, may be greater than this increment. In this case, the control 88a controls several sequences of opening and closing of the valve 82a to sequentially fill and empty the chamber 98a by keeping the slide in the reached position and then close this valve as soon as the eccentric has reaches the desired position.

The displacement of the slider 54 in the opposite direction, that is to the right, is controlled in the same way but by acting on the various elements of the closed circuit 78b.

Thus, to be able to impose the direction of travel of the eccentric clockwise or counterclockwise, it will act on one or other of the circuits.

As regards the filling of the circuits 78a, 78b and of their purge, the hydraulic pump 110 fills, via the conduits 112a, 112b, the metering chambers 100a, 100b and the pipes 104a, 104b. Through these pipes, the fluidic chambers 75a, 75b are also filled, as well as the pipes 80a, 80b through which the filling of the metering chambers 98a, 98b is ensured. During this filling, the purge valves 114a, 114b and the purges 116a, 116b are open to evacuate any air present in the circuits. Of course and as is usual, the pump and the pipes 112a, 112b will be used to compensate for any fluid losses during operation of the device.

In practice and as better visible on the figure 5 , the different lines, dosing devices, purge valves, purges, and check valves are housed in the support 58, the crankshaft with its crank pin and the eccentric.

As these different elements are placed in several parallel planes transverse to the axis of the crankshaft, only some of these elements have been shown to avoid complicating the figure. It can thus be seen that the supply of fluid for the filling of the circuits is carried out by axial and radial bores 120 in the crankshaft and the crank pin, by a circumferential groove 122, between the bore of the eccentric 42 and the peripheral wall. the crankpin 34, for communication with the bores 120, and radial bores 124 communicating the groove 122 with the pipe 112 (respectively 112b) provided in the support 58. This support also comprises the control valves 82a and 82b, the metering devices 92a and 92b, the non-return valves 106 and 108 (respectively 108a), the purge valves 114 (respectively 114a) and the pipes 80, 90, 104 (respectively 104a) for putting in communication these elements.

In operation, the compression rate variation device is in a determined configuration, as shown in FIG. figure 3 which corresponds, by way of example, to a minimum compression ratio, which may be the nominal rate, and the piston 14 is at its bottom dead center position (PMBv) as illustrated in FIG. figure 2 . In this configuration, the PMBi is confused with the PMBv and the piston 14 has a stroke from this dead point down to its top dead center to achieve the compression phase of the air or fuel mixture present in the combustion chamber, as shown in the figure 1 . During this race and as illustrated in Figures 1 to 3 , the crankpin 34 travels a semicircular path to go from its low point (180 °) to its high point (0 °). During this movement, the piston 14, the connecting rod 16 and the eccentric 42 first undergo a maximum acceleration at low dead point which decreases during the movement of the piston and the rod and then vanishes. This piston and this link then undergo a deceleration which increases as the piston 14 approaches the top dead center. When the resulting force of this deceleration is sufficient to overcome the resultant gaseous pressures exerted on the piston, the weight of the piston 14 and the connecting rod 16 and the different friction forces, a drive of the piston and the connecting rod is generated by this force of inertia in an upward movement in considering the figures. This movement is even more easily realized that the forces of inertia, friction and the resulting gas pressures are all directed upwards. These conjugate forces apply on the X1X1 axis and create a torque which tends to rotate the eccentric about the X2X2 axis in a clockwise direction in the position of the slide shown in FIG. figure 3 .

Thus, depending on the operating parameters of the engine, such as the load and the speed of this engine, it is determined a compression ratio to meet the demand. This compression ratio is determined by a control unit, for example the calculator that usually comprises the engine, and this calculator determines a deflection angle of the eccentric to obtain this rate. Referring back to figure 4 and in the event of an increase in the compression ratio, control instructions are sent, by the computer, to the control 88a of the 3-way valve 82a to put in communication, during a number of sequences, corresponding to an increment number and / or an increment part in displacement of the slider, and a duration determined by this calculator, the fluidic chamber 75a with the metering device 92a so as to allow the displacement of the slider by transfer of the fluid from a fluidic chamber 75a towards the other fluid chamber 75b via this metering device. Under the effect of the rotation of the eccentric and by the cooperation of the toothed sector 48 of the eccentric with the rack 52 of the slide, this slide has a displacement to the left, to increase the compression ratio. Thus, by precisely and continuously controlling the quantity of fluid leaving the fluidic chamber by the opening and closing operation of the valve, it is possible to control the movement of the slide so that the eccentric moves. in rotation according to the angular movement determined by the computer. At the end of the number of actuations of the valve 82a and the duration of the opening of this valve, it remains closed by isolating the chamber 75a of the chamber 75b and the slide is immobilized in its position thanks to the fluid isolated in these bedrooms. In this configuration, the eccentric has traveled the angular movement determined by the calculator. At closing of the valve 82a, the fluid present in the chamber 98a of the metering device 92a is discharged to the tank 84a by the pipes 90a, 86a and the piston 96a of this metering device is found in the initial state, that is to say say close to the 90a pipeline.

As a result of this angular deflection in the clockwise direction from the figure 3 , the piston 14 makes an overtravel S with respect to its PMHi to be in the position illustrated in FIG. figure 1 . In this position, the distance between the axis 24 of the piston 14 and the axis of the crankpin has increased and the piston 14 has lengthened its initial course while exceeding the PMHi and penetrating into the initial dead volume 40. In this position , this initial dead volume is decreased and a new dead volume 118 is created in the cylinder 12. As this new dead volume is smaller than the initial dead volume, it follows that the compression ratio of the engine is increased.

This configuration of the device is retained as long as it is desired to keep this modified rate.

Given the fact that the rotation of the eccentric is continuously controlled by a controlled movement of the slide by the circuits 78a and 78b, it is therefore possible to vary the value of the overtravel S PMHi up to PMHv, and therefore the size of the dead volume.

Thus, thanks to the controlled movement of the slide, which displacement is a function of the response time and the number of opening and closing of the valve 82a, it is possible to increment this displacement and to obtain a multitude of possibilities of compression through a multiplicity of angular positions of the eccentric.

As soon as the computer determines a new angular displacement of the eccentric which corresponds, for the example described below, to a new compression ratio lower than that reached, this new rate may be the initial compression ratio for which the we find the initial dead volume or a rate lower than that which was obtained in a previous phase of increase of this rate, the computer sends instructions to the control 88b of the valve 82b of the circuit 78b so that the eccentric 42 be in the position illustrated in the figure 3 or in a position approximating this figure to reduce the compression ratio obtained in an earlier phase.

To do this, an operating phase of the motor is used during which the crankpin 34 goes from its 0 ° to 180 ° position, as the intake or expansion phase.

During this phase, the forces as described above apply to the crankpin but in the opposite direction. This has the effect of applying a force on the X1X1 axis which tends to rotate the eccentric around the X2X2 axis in a counter-clockwise direction.

To allow this rotation of the eccentric, just allow the controlled movement of the slide in its housing. For this and referring to the figure 4 , the control opening / closing for a specified time and closing the 3-way valve 82b allows to communicate the fluidic chamber 75b with the metering device 92b so as to allow this movement of the slide while controlling the transfer of doses of fluid dosed by the metering device 92b from a fluid chamber 75b to the other fluid chamber 75a. Under the effect of the rotation of the eccentric generated by the inertia force and by the cooperation of the toothed sector 48 of the eccentric with the toothed bearing surface 52 of the slide, this slide has a displacement to the right to reach the position illustrated in the figure 3 .

Also, this displacement of the slider is continuously controlled by action on the valve 82b, which makes it possible to obtain a multiplicity of angular positions of the eccentric during its displacement in the counter-clockwise direction and consequently a multiplicity of possibilities of decreasing the overtravel piston, which has the effect of obtaining a multiplicity of possibilities of increasing the dead volume 118 to the initial dead volume 40.

Thus, by virtue of this device for varying the compression ratio, it is not only possible to obtain a multiplicity of possibilities of increasing the compression rate but also a multiplicity of possibilities of decreasing this rate from a rate which has undergone an increase.

We are now going back to figure 6a which shows an alternative embodiment of the invention.

This variant differs from the embodiment described above only in the fact that each 3-way valve is replaced by two piezoelectric devices 126 (respectively 126b) which make it possible to improve the response time and consequently to increase the accuracy of the adjustment the compression ratio. Each of these devices comprises a needle 128 subjected to the action of a piezoelectric actuator 130 and constitutes a two-way valve. One of these piezoelectric devices controls the passage of the fluid between the pipe 80 (respectively 80b) and the pipe 90 (respectively 90b) and the other of the piezoelectric devices controls the passage of the fluid between the pipe 90 (respectively 90b) and the 86. Thus, each 3-way valve 82a, 82b of the circuit shown in FIG. figure 4 is replaced by two 2-way valves each formed by a piezoelectric device.

To control the piezoelectric actuator acting on the movement of the needle, the support 58 carries two electrical pads 132 connected by electrical conductors (not shown) to this actuator. Electric tracks 134 are carried by a fixed element of the motor, like the motor casing, and are arranged in such a way that they are continually facing the pads 132 at least for a movement of the crank pin from its 0 ° point. at its 180 ° point, as illustrated on the Figures 6a to 6d . Of course and without departing from the scope of the invention, these tracks can extend over the entire rotation of the crankpin 360 °. These tracks are traversed by an electric current and induce a magnetic field which creates an electric current at the pads 132 for the control of the actuator. Advantageously, an electrical track 134 is assigned to the control of each of the piezoelectric devices and a fifth track is common for the control of the four piezoelectric actuators 130.

The operation of the device for varying the compression ratio 32 and the circuits 78a, 78b is the same as that described with respect to the Figures 1 to 5 the differences according to which the connection of the fluid passage between the fluidic chamber 75a, 75b and the metering chamber 98a, 98b is carried out by a first 2-way valve constituted by a piezoelectric device, the connection of the fluid passage between the chamber of dosing 98a, 98b and the tarpaulin 84a, 84b is made by another 2-way valve consisting of a piezoelectric device, and an electric current is sent in the tracks 134 to control the opening of the needle 128 during the request for variation of the compression ratio.

The embodiments of the control of the variation device described up to now provide for the use of two closed circuits to control the movement of the slide. But it can be envisaged to use only one circuit comprising a pipe communicating the chamber 75a with a valve means, such as the 3-way valve, which would then be replaced by a 2-way valve or the piezoelectric device described above , and a pipe connecting the valve means to the other fluid chamber 75b. Of course, the filling means with their hydraulic pump and the connecting pipes with the pipe connecting the valve means to the chamber 75b, as well as the purge valves can also be provided on this single circuit.

In order to be able to know at any moment the compression ratio of the motor, there is provided a means for locating the angular situation of the eccentric 42, as illustrated on the Figures 7a to 7d .

This means comprises a signal transmitter-receiver assembly 136, one of whose elements is carried by the eccentric 42 and the other of which elements is carried by a fixed element of the motor, such as a tab 138 coming from a wall of this case. Advantageously, the eccentric carries an index 140 which emits a signal by radiation, for example by magnetic radiation, and the tab 138 carries a receiver formed by a reading sector 142 of the signal emitted by the index 140 and which makes it possible to know the position of this index during the rotation of the crank pin 34. This reading sector is substantially in a circular arc, whose concavity is directed towards the crankshaft, with a substantially constant radial thickness E. This sector comprises a first reading region 144 located in its upper part for reading the signal emitted by the index 140 when the compression ratio is maximum or is increased and a second region 146 placed in the lower part of this sector for the reading the signal emitted by the index 140 when the compression ratio is nominal or is decreased.

During operation of the engine, the calculator that this engine usually comprises determines the angular setting C of the eccentric with respect to the longitudinal axis of the connecting rod ( figure 7a ) to obtain a defined compression ratio and that when the piston is at top dead center. To be able to verify the accuracy of the calibration measured with respect to the calibration determined by the computer, the latter takes into account the intensity of the signal received by the reading region 144. In the case of the figure 7a this signal is highest when the emission point 148 of the index 140 is substantially in the middle of the thickness E of this reading region and corresponds to a maximum compression ratio. Thus, the different values of the compression ratio can be controlled by taking into account the position of the emission point 148 of the index 140 relative to the middle of the thickness E of this reading region. Therefore, one of the closed circuits 78a, 78b will be operational so that the slider 54 moves to allow an angular displacement of the eccentric 42 to obtain such a positioning of the emission point 148. From that this angular setting is obtained, the piston leaves its top dead center to go towards its bottom dead point ( Figures 7b and 7c ) and the index 140 moves away from the central zone of region 144 ( figure 7b ) to finally arrive, in the vicinity of the bottom dead center, away from sector 142 ( Figure 7c ). Likewise, this calculator determines the angular setting Ci ( figure 7d ) of the eccentric with respect to the longitudinal axis of the connecting rod, when the piston is at low dead point, to obtain a nominal compression ratio or to reduce the compression ratio obtained during a previous phase. To arrive at this determination, this calculator takes into account the intensity of the signal received by the reading region 146 and, as previously mentioned, this signal is at the highest when the point of emission of the index 140 is substantially in the middle of the thickness E of this region. As a result, the circuits 78a, 78b will be actuated in such a way that the slider can allow an angular displacement of the eccentric to obtain such angular setting.

According to one variant, this reading sector 142 comprises insulative wires insulated from one another and arranged substantially radially with respect to its arcuate shape over its thickness E. These conducting wires constitute a plurality of receivers of the signals emitted by the index 140 , angularly distributed from the upper part of the reading sector 142 to its lower part. The index 140 describes at each rotation of the crankshaft a substantially circular curve of radius less than the radius of the substantially circular shape of the reading sector 142. The substantially circular curve described by the index 140 is translated according to the angular setting of the eccentric 42. This translation, the radius of the reading sector 142 and its position are such that the index 140 is next to the conductive son of the thickness E of the reading sector 142 in a circular arc whose position is characteristic of the angular wedging of the eccentric 42. As a result, the knowledge of the identity of the conducting wires on the thickness E of the reading sector informed by the index 140 during the rotation of the crankshaft makes it possible to know the angular position of the eccentric with a precision function of the pitch of the conductor wires.

According to another variant, the reading accuracy of the angular setting of the eccentric 42 is improved by the combined reading of the position and the intensity of the signals perceived by the conductive threads informed by the index 140 during the rotation of the crankshaft. When the index 140 is completely opposite the thickness E of the reading sector 142, for example on the Figures 7a and 7d at least one of the conductive wires receives a maximum information signal from the index 140. When the index 140 is partially facing the thickness E of the reading sector 142, for example for the figure 7b , the informed leads receive a weaker signal from the index 140.

Advantageously, it will be provided to progressively and continuously decrease the compression ratio by increasing the angular setting of C to Ci and vice versa to increase it from Ci to C and that, combustion cycle of the engine by combustion cycle of the engine.

Of course, the present invention is not limited to the embodiments described.

In particular, it can be envisaged that the device for varying the compression ratio is placed at the small end of the connecting rod 26 with an eccentric carried by the axis 24 of the piston 14.

Claims (15)

1. A device for varying the compression ratio of an internal combustion engine including at least one cylinder (10) with a combustion chamber (20), a movable unit comprising a piston (14) that is translationally displaceable under the action of a connecting rod (16) that is linked by a pin (24) to said piston and connected to a crankpin (34) of a crankshaft (36), said piston travelling between a top dead centre and a bottom dead centre whilst a clearance volume (40, 118) is left at the top dead centre of said piston, said device including a rotating driven eccentric (42) accommodated between said crankpin and said connecting rod allowing the compression ratio to be varied and means (32; 78a; 78b) for controlling the movement of the eccentric, characterised in that the control means include a fluid jack (76) borne by the connecting rod and comprising a slide (54) placed in a housing (56) formed in a slide support (58), in that the slide, together with said support, delimits two fluid chambers (75a, 75b) in communication with at least one closed circuit (77; 78a; 78b) and in that the slide includes a toothed span that cooperates with a toothed sector borne by the periphery of the eccentric.
2. The device for varying the compression ratio according to Claim 1, characterised in that the fluid chambers (75a, 75b) are in communication with one another via at least one closed circuit (77; 78a, 78b).
3. The device for varying the compression ratio, according to one of claims 1 or 2, characterised in that the closed circuit includes at least one valve means (82a, 82b; 126) allowing the flow of fluid from one chamber to the other to be controlled.
4. The device for varying the compression ratio according to claim 3, characterised in that the valve means is at least a two-path valve (82a, 82b).
5. The device for varying the compression ratio according to claim 3, characterised in that the valve means is a piezoelectric device (126).
6. A device for varying the compression ratio according to claim 5, characterised in that the piezoelectric device includes a needle (128) and a piezoelectric actuator (130).
7. The device for varying the compression ratio according to claim 5 or 6, characterised in that the piezoelectric device is controlled by cooperation of contacts (132) and electric tracks (134).
8. The device for varying the compression ratio according to the preceding Claim 3, characterised in that the circuit includes at least one dispensing device (92a, 92b) situated downstream of the valve means.
9. The device for varying the compression ratio according to Claim 8, characterised in that the dispensing device includes a piston-cylinder assembly (94a; 96a) with a calibrating spring (102a).
10. The device for varying the compression ratio according to Claim 1, characterised in that the elements of the closed circuit are at least partially accommodated in the jack (76).
11. The device for varying the compression ratio according to one of the preceding claims, characterised in that the varying device includes means for locating (136) the position of the eccentric (42).
12. The device for varying the compression ratio according to Claim 11, characterised in that the locating means include a signal transmitter-receiver assembly (136).
13. The device for varying the compression ratio according to Claim 12, characterised in that the eccentric (42) includes the transmitter (140, 148) and in that the receiver (142) is accommodated on a fixed part (138) of the motor.
14. The device for varying the compression ratio according to one of the previous claims, characterised in that the eccentric includes means (48, 52) for shape cooperation with the slide.
15. The device for varying the compression ratio according to Claim 14, characterised in that the cooperation means include a toothed sector (48) borne by the eccentric (42) and a toothed span (52) borne by the slide (54).

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