EP0407302A1 - Method for adjusting the valve play in an internal combustion engine and device for implementing this method - Google Patents

Abstract

Method and device for automatically adjusting the play of the rockers for an internal-combustion engine. By means of a preferably stepping motor (19), the adjusting screw (23), the lock nut of which has been slackened, is rotated in such a way as to lift the valve from its seat. When a sensor detects the stopping of the valve, corresponding to its return to the closing position, the adjusting screw is rotated through an additional angle predetermined and corresponding to the play to be obtained, and the lock nut (30) is then tightened again. Advantageously, a shim having parallel faces is inserted beforehand between the adjusting screw and the valve, and towards the end of the operation this shim is removed, and the additional angle just mentioned allows for the thickness of the shim. <IMAGE>

Description

The present invention relates to a method of adjusting the play of the rocker arms of an internal combustion engine, and an apparatus for implementing this method.

Most internal combustion engines are equipped with intake and exhaust valves each controlled by a camshaft, by means of a certain number of organs, such as a rocker arm and a tappet which will meet here under the name of "rocker assembly", even if, in the case of a direct attack, it does not include a rocker.

The assembly formed by the control cam, or the control member, of rocker assembly and the valve moves between two extreme positions, one where the valve is forced, under the action of the cam, to s '' move as far away from its seat (maximum lifting position) and the other where the valve is pushed by a spring against its seat, and where there is, between the cam and the rocker clearance, or in the rocker assembly , or between it and the valve, maximum play (maximum play position). This play, which can be of the order of 0.1 to 0.3 mm, is essential to compensate for the effect of the differences in expansion, but it must remain within defined limits for proper operation of the engine.

Usually the adjustment is done manually.

The operation is done in principle cold with a thickness gauge and the clearance is adjusted by modifying the length of one of the parts of the rocker assembly which comprises, for this purpose, a head mounted on an adjustment screw provided with a locking nut. This head, when the clearance is zero, comes to bear, depending on the type of engine, on the cam, on the valve, or on another part of the rocker assembly. The operation, when done manually, involves bringing the camshaft into the maximum play position, measuring the play, and, after loosening the lock nut, turning the screw at an angle suitable for bring the play to the desired limits, then tighten the lock nut.

Manual adjustment is long and delicate. Errors may occur, for example from confusion between the clearances prescribed for the intake and exhaust valves.

Document DE-A-30 02 015 has proposed a process which lends itself to automation, and which comprises the following operations:
a detector sensitive to the position of the valve relative to the engine block, that is to say to the seat of the valve, is installed, and a device for controlling the rotation of the adjusting screw,
- after having released the locking nut and brought the rocker arm to the position which corresponds to the maximum clearance, the detector locates the zero point, where the valve rests on its seat,
- the adjustment screw is advanced until the sensor signals that the valve is lifted by a height x₁ on its seat,
- the adjustment screw is moved back until the sensor signals that the valve is lifted by a height x₂, between O and x, and
- the adjustment screw is moved back by rotation by an angle corresponding to the distance x₂ + x₃, x₃ being the desired clearance.

It only remains to tighten the locking nut.

This process has the drawback that any deformations and clearances from the moment the zero point is determined are not taken into account, in particular those which may appear when the direction of movement of the adjusting screw is reversed. This results in an imprecision which is perhaps the reason why this process has not been widely developed.

The aforementioned document also describes an apparatus for implementing this process. This apparatus includes a sensor capable of continuously grasping the displacements of the valve, this sensor is carried by a base on which is also fixed the motor for which it is a question of adjusting the valves, and it is provided with a sensor which comes to bear on a cup secured to the valve stem. The apparatus further comprises two tools, each driven by a motor, and arranged to drive in rotation one, the adjusting screw, and the other, the locking nut.

The object of the present invention is to provide an automated process for adjusting valves which provides greater precision than that of the known method, and which makes it possible to use less expensive equipment.

• a) monter sur le moteur un dispositif apte à déterminer la position de la soupape par rapport à son siège,
• b) monter sur le moteur un dispositif de commande de rotation de la vis de réglage,
• c) amener l'arbre à cames dans une position correspondant normalement au jeu maximal entre lui et la soupape en appui sur son siège,
• d) prendre, pour origine des mesures du dispositif de détermination de la position de la soupape, une situation où celle-ci est en appui sur son siège,
• e) desserrer l'écrou de blocage,
• f) commander la rotation de la vis de réglage jusqu'à ce que la soupape s'écarte de son siège,
• g) commander la rotation de la vis de réglage en sens inverse, ce déplacement en sens inverse comprenant au-delà du passage par la position origine, une rotation de la vis de réglage d'un angle correspondant au jeu désiré,
• h) resserrer l'écrou de blocage,
  caractérisé en ce que, au cours de l'étape g), on repère, à l'aide du dispositif de détermination de la position de la soupape, le moment où ladite soupape cesse de se déplacer en direction de son siège, et ce moment constitue le point de départ de la mesure angulaire de la rotation de la vis de réglage correspondant au jeu désiré.

The invention consequently provides a method for adjusting the clearance of the rocker arms of the valves of an internal combustion engine, comprising a rocker assembly with at least one part, the length of which can be varied using a screw. adjustment provided with a locking nut, this method comprising the steps of:

• a) mounting on the engine a device capable of determining the position of the valve relative to its seat,
• b) mount on the motor a device for controlling the rotation of the adjusting screw,
• c) bringing the camshaft into a position normally corresponding to the maximum clearance between it and the valve resting on its seat,
• d) take, for the origin of the measurements of the device for determining the position of the valve, a situation where the latter is supported on its seat,
• e) loosen the lock nut,
• f) control the rotation of the adjusting screw until the valve moves away from its seat,
• g) controlling the rotation of the adjustment screw in the opposite direction, this displacement in the opposite direction comprising, beyond passing through the original position, a rotation of the adjustment screw by an angle corresponding to the desired clearance,
• h) tighten the lock nut,
  characterized in that, during step g), with the aid of the device for determining the position of the valve, the moment when said valve ceases to move in the direction of its seat is identified, and this moment constitutes the starting point for the angular measurement of the rotation of the adjusting screw corresponding to the desired clearance.

By "camshaft" is meant here not only a camshaft of the current type but any device intended to mechanically move the valve according to a defined law.

According to the method of the invention, the same successive displacements of the adjusting screw are carried out as in DE-A-3 002 015, but the sensor does not determine the "zero point", where the valve rests on its seat, before the valve moves away from its seat. On the contrary, it determines this "zero point" during the reversing stroke, when the valve stops because it comes to rest on its seat and it is this "zero point" which serves as a point of start with the measurement of the angle of rotation which corresponds to the desired clearance.

As a result, there is no intermediate step, nor change of the direction of rotation of the adjusting screw, between the determination of the zero point and the establishment of the desired clearance.

For the determination of the zero point, one can, as in the document DE-A-30 02 015, operate while keeping in contact the end of the locking screw and the element on which it comes to bear, but it has been discovered a possibility of further improvement in precision: direct contact at the end of the adjusting screw requires that one of the two contacting surfaces be as perfectly flat and perpendicular to the axis of the screw as possible. According to an advantageous variant of the process of the invention:
- Before step f), a shim of known thickness is introduced with precision between the adjustment screw and the element of the rocker assembly against which said adjustment screw comes to bear, by placing said shim perpendicular to the 'axis of the adjusting screw,
in step g), the adjusting screw is printed with a complementary rotation which corresponds to the desired clearance, minus the angular value which corresponds to the thickness of the shim,
- and the shim is removed after step g).

A wedge is a plate of solid material, bounded by two flat and parallel surfaces between them. Therefore, when the adjusting screw and the rocker element are in contact with the shim, the distance between them is fixed with precision, and cannot be affected by the relative position of the axes.

The improvement in precision comes from the high quality of the wedge surfaces that can be obtained.

For the determination of the zero point, it is possible to use, as in the document DE-A-30 02 015, to use a sensor able to capture continuously, or almost continuously, the displacements of the valve.

However, an appreciable reduction in the cost and complication of the apparatus can be obtained, in the case where a shim is used, by providing that the device for determining the position of the valve provided in step a) consists of the shim itself, the latter being associated with means for detecting the moment when it comes into simultaneous contact with the adjusting screw and said element of the rocker assembly, and the moment when said contact simultaneous ceases.

With this way of doing things, it is no longer necessary to provide feelers intended to come into abutment, one on a part of the engine secured to the valve seat and the other on a part secured to the valve itself, the sensor being sensitive to the relative movement of these feelers. The moments when the valve departs from or comes back into contact with its seat correspond precisely to the moment when the shim is tightened between the adjusting screw and the opposing element, and when it ceases to be tightened.

Several arrangements can be used for the implementation of the method just described of the process of the invention. According to a first, very simple method, the shim has an electrically insulating central part and two opposite conductive faces, the adjusting screw and said element of the rocker assembly with the same electrical potential, at least one of said opposite faces of the shim is brought to a different potential when it is not in contact with the adjusting screw or said element, and a sensor detects the moment when said face of the shim changes potential with respect to the adjusting screw and said element of the 'together.

According to another method, which is a little more complicated, but eliminates any risk of incident due to poor electrical contact between one face of the wedge and the part with which it comes into contact, it can be provided that inside of the shim is included a piezoelectric element making it possible to detect a compressive force applied to the shim. Advantageously in this case, a shim is used comprising a layer of metallized polyvinylidene fluoride on its two faces, these being insulated from the outside by layers of insulating material. and the two metallized faces being connected to an electrical voltage sensor.

According to another operating mode, provision may be made for the shim to be printed with oscillations in its plane, and the arrest of these oscillations is detected, which corresponds to the tightening of the shim between the adjusting screw and said element.

The invention also provides an apparatus for implementing the above method, and which comprises:
- a device, comprising a sensor capable of detecting the zero point, where the valve comes into contact with its seat,
- a device for controlling the rotation of the adjusting screw,
this device being characterized in that it further comprises a central control member, connected to the rotation control device and to the sensor, this member being arranged to control in step e) the rotation of the adjusting screw in a first direction along a first angle previously stored in memory, then, in step f), in the opposite direction until detection using the signals emitted by the sensor, of the stop of the movement of the valve, and then, after said stop detection, at a second angle, corresponding to the game, and previously stored in memory, to carry out step g).

Advantageously, the device for controlling the rotation of the adjusting screw comprises a stepping motor, and the instructions of the control member are stored and transmitted in the form of the number of steps of said motor.

In the case where, instead of using means for determining the position of the valve associated with the shim as provided above, a quasi-continuous displacement sensor is used, it is advantageously provided that the latter is of the incremental type, and transmits in digital form the signals transmitted to the control unit.

Also in the case where such a displacement sensor is used, the accuracy can be improved with respect to the apparatus of document DE-A-30 02 015, by providing a feeler mounted movably on the support and provided with a button intended to come into contact with the seat of the valve or with a part which is rigidly linked to it, the sensor being linked to one of the feelers and its sensitive member being in contact with the other.

In this case, preferably, the feelers are pivotally mounted on the support, a spring bearing on the support pushing one of the feelers to bring it into contact with the part on which its key must come to rest, and the other feeler being controlled by a jack mounted on the first support, the latter feeler being provided with an auxiliary member capable of driving the other feeler to put it out of action during assembly or disassembly of the support.

This cylinder can also be controlled by the central control member, for example by means of a solenoid valve.

• Figure 1 est une vue schématique d'ensemble d'un appareillage selon l'invention,
• Figure 2 est une coupe du dispositif de commande de la rotation de la vis de réglage et de l'écrou de blocage,
• Figure 3 du dispositif pour saisir les déplacements de la soupape,
• Figure 4 est une vue en plan du même dispositif,
• Figure 5 est une vue en coupe et en élévation d'une partie d'un appareillage,
• Figure 6 est une vue en coupe horizontale, suivant la ligne II-II de la figure 5,
• Figures 7 et 8 sont des schémas montrant deux structures différentes de la cale.

The invention will now be described in more detail with the aid of practical examples illustrated with the aid of drawings, among which:

• FIG. 1 is a schematic overall view of an apparatus according to the invention,
• FIG. 2 is a section through the device for controlling the rotation of the adjusting screw and the locking nut,
• Figure 3 of the device for capturing the movements of the valve,
• FIG. 4 is a plan view of the same device,
• FIG. 5 is a view in section and in elevation of part of an apparatus,
• FIG. 6 is a view in horizontal section, along line II-II of FIG. 5,
• Figures 7 and 8 are diagrams showing two different structures of the wedge.

In the figures, the elements which are common have the same references.

FIG. 1 shows the division of the apparatus between three units: the central control member 1, the screwing device 2 of the adjusting screw and the locking nut, and the device 3 for detecting movements of the valve.

Figure 2 shows the detail of the screwing device. A frame 10, provided with means not shown for fixing relative to the engine block, carries two coaxial sleeves 11 and 12, which can rotate independently of each other relative to the frame 10 by means of ball bearings 13. The sleeves 11 and 12 are connected by pins 15 and 16 to a screwdriver rod 17, intended for driving the adjusting screw and a hexagonal socket 18, intended for driving the locking nut.

The sheath 11 is rotated by a stepping motor 19, by means of pulleys 20, 21 and a toothed belt 22. The motor 19 thus drives the screwdriver 18, and, consequently, the adjusting screw 23 of a rocker arm 24. The sleeve 12 is rotated by a motor 25, which is a screwdriver motor, by means of a sleeve 26, two pulleys 27 and 28 and a toothed belt 29. The motor 25 is thus able to apply the torque necessary for tightening and loosening the locking nut 30 mounted on the adjusting screw 23. The springs 31-32 respectively push the screwdriver rod 17 and the socket 18 against the adjustment 23 and the locking nut 30.

In the example described, the adjusting screw is carried by one end of the rocker arm 24, the other end of which comes into contact with a cam 33 of a camshaft 34 (FIG. 1). It is clear that the invention is not limited to such a provision.

FIG. 3 shows the device intended to capture the movements of the valve. A button 40 is in contact with the upper cup 41 of the valve 42 which we want to adjust the rocker game. The key 40 is carried by a feeler 43 forming a lever, and articulated on an axis 44 carried by a support 45, itself provided with means 46 for fixing relative to the engine block. The end of the lever probe 43 carries another key 47, which is in contact with a flat key 48, located at the end of an incremental displacement sensor 49. This sensor is itself fixed on another lever 50 , pivotally mounted on an axis 51 carried by the same support 45. The end of the lever 50 opposite the sensor 49 carries a spherical key 52 which bears directly on a machined face of the cylinder head of the engine, as close as possible to the valve 42.

A jack 53 pushes the lever 50 and thus ensures contact between the key 52 and the cylinder head. A spring 54 is supported on the support 45, and pushes the feeler-lever 43 to ensure the contact of the key 40 on the cup 41 of the valve.

As best shown in Figure 4, the feeler lever 50 is actually formed of parallel plates, held by spacers 55, 56. The spacer 56 passes under the feeler lever 43, so that when the cylinder 53 lifts the opposite end of the lever 50 upwards, according to FIG. 3, the lever 43 is also lifted and put out of contact with the valve cup, against the force of the spring 54, which allows the setting in place of the assembly without risking damaging the keys 40, 52.

In the practice of adjustment on a production line, a motor, fixed on a plate, is immobilized in a fixed position at the adjustment station. Slides, fixed in the adjustment station, carry a frame 10 and a support 45. These are successively immobilized in line with all the valves arranged along the same line of the engine, for example the intake valves, for adjustment of the clearance that is specific to these valves. One or more other sets of slides, each carrying similar equipment, may be assigned to valves arranged along one or more other lines of the engine, for example the exhaust valves.

In FIG. 1, the main elements of the devices described in FIGS. 2, 3 and 4 have been represented symbolically, as well as the solenoid valve 60 for controlling the jack 53. The central control member 1 comprises a processor 61, whose functions have been explained above, and two memories 62, 63, which contain the numbers of steps of the motor 19, in steps e) and g) of the process. Of course, memories 62 and 63 can be parts of a single memory. The design of the processor, and in particular the moment when it detects, at the end of step f), the stop of the movement of the valve by comparison of numbers of successive counts of increments emitted by the sensor 49, is to the scope of the skilled person, so that it is not necessary to describe in detail the structure of this processor.

FIGS. 5 to 8 relate to a preferred variant The elements different from those of FIGS. 1 to 4 bear reference numbers equal to or greater than 100.

Figure 5 corresponds to the bottom left part of Figures 1 and 3 on a considerably enlarged scale, for clarity. In this figure, we can see, in section, a rocker arm 24, crossed by an adjustment screw 23. A screwdriver rod 17 is arranged to rotate the adjustment screw, and a hexagon socket 18 is intended to drive the nut blocking 30 of this adjusting screw. The figure also shows the stem of a valve 42 which, in the arrangement of the main patent, comes to bear directly on the end of the adjusting screw 23.

According to the invention, a shim 100 is interposed between the adjustment rod 23 and the valve 42. This shim is mounted, fixed in rotation, on a support rod 101 mounted in a bearing 102, carried by a plate 103, itself connected to the frame by two balusters 104. A control lever 105 is mounted, fixed in rotation, on the shaft 101. As can be seen better in FIG. 6, the lever 105 has the form of a horizontal arm and it is articulated on the rod of an actuator 106, the body of which is itself articulated on a support carried by the plate 103. The position of the actuator 106 is shown in solid lines, or in dashed lines, lever 105 and shim 100 which correspond to the actuation of this shim, that is to say in the position visible in FIG. 1. The positions 105A and 100A of the lever and of the shim in their inactive position, which allows the establishment of the valve. The cylinder 106 can be pneumatic or hydraulic, or electric.

To detect the tightening of the shim, provision may be made for an electronic oscillator (not shown) to be interposed between the support rod 101 and the shim 100. This oscillator causes an oscillating movement of small angular amplitude around the axis of the support rod 101 in the proper plane of the hold. The electronics associated with the electromagnet, which has a feedback winding, oscillates the system at its natural frequency (a few hundred Hertz). As soon as the wedge is hampered in its oscillating movement by the fact that it is tightened, the oscillations cease, which is instantly detected by the electronics and makes it possible to know precisely when the tightening starts or stops.

FIG. 7 shows another method of detecting the tightening of the shim 100. This consists of a sandwich of three layers: a layer 110 of treated steel, a layer 111 of alumina, and a layer 112 of carbide of tungsten and nickel. The two end faces of the sandwich are electrically conductive, but the alumina layer constitutes an insulator. We symbolized in Figure 3 a very simple electrical circuit, consisting of a voltage source 113, connected to the two layers conductive 110 and 112, and, in parallel, to a millivoltmeter 114. It is obvious that the indication of the millivoltmeter 114 corresponds to the voltage across the terminals of the source 113 as long as 110 and 111 are not in contact respectively with the valve 42 and with the adjusting screw 43. On the contrary, as soon as this contact takes place, the entire apparatus being metallic, the voltage across the terminals of the millivoltmeter 114 drops to zero.

FIG. 4 shows a different embodiment of the shim 100. A central film of polyvinylidene fluoride (PVDF) 120 and coated on each of its faces with a layer of aluminum 121, 122, deposited in the vapor phase, and the assembly is coated on each of its sides with a layer of zirconia 123, 124. The two layers of aluminum 121, 122 are connected to a charge amplifier 125. It is known that polyvinylidene fluoride is piezoelectric. It is therefore understood that, as soon as the shim is compressed, a voltage appears at the terminals of the charge amplifier 125. It is within the reach of the skilled person to convert the voltages supplied at the terminals of the millivoltmeter 114 or at output of the charge amplifier 125 into control signals for implementing the method which has been described above.

Claims (14)

1. A method for adjusting the clearance of the rocker arms of the valves of an internal combustion engine, comprising a rocker assembly with at least one part the length of which can be varied using an adjusting screw (23) provided with a locking nut (24), this method comprising the steps of: a) mounting a device (3) capable of determining the position of the valve relative to its seat on the engine, b) mount a device (2) for controlling the rotation of the adjusting screw, c) bringing the camshaft (34) into a position normally corresponding to the maximum clearance between it and the valve resting on its seat, d) take, for the origin of the measurements of the device for determining the position of the valve, a situation where the latter is supported on its seat, e) loosen the lock nut, f) control the rotation of the adjusting screw until the valve moves away from its seat, g) controlling the rotation of the adjustment screw in the opposite direction, this displacement in the opposite direction comprising, beyond passing through the original position, a rotation of the adjustment screw by an angle corresponding to the desired clearance, h) tighten the lock nut,
characterized in that, during step g), with the aid of the device (3) for determining the position of the valve, the time when said valve ceases to move in the direction of its seat is identified, and this moment constitutes the starting point for the angular measurement of the rotation of the adjusting screw corresponding to the desired clearance. 2. Method according to claim 1, characterized in that:
- before step f), a shim (100) of known thickness with precision is introduced between the adjusting screw (23) and the element (42) of the rocker assembly against which said adjustment screw comes to bear, by placing said shim perpendicular to the axis of the adjustment screw,
in step g), the adjusting screw (23) is printed with a complementary rotation which corresponds to the desired clearance, minus the angular value which corresponds to the thickness of the shim (100),
- and the shim is removed after step g). 3. Method according to claim 2, characterized in that the device for determining the position of the valve provided in step a) is constituted by the shim (100) itself, the latter being associated with means (114 , 125) to detect the moment when it comes into simultaneous contact with the adjusting screw and said element of the rocker assembly, and the moment when said simultaneous contact ceases. 4. Method according to claim 3, characterized in that the wedge comprises an electrically insulating central part (111) and two opposite conductive faces (110, 112), the adjusting screw (23) and said element (42) of the rocker assembly with the same electrical potential, at least one of said opposite faces of the shim is brought to a different potential when it is not in contact with the adjusting screw or said element, and a sensor (114) detects the moment where said face of the shim changes potential with respect to the adjusting screw and to said element of the assembly. 5. Method according to claim 3, characterized in that inside the shim is included a piezoelectric element (121) for detecting a compression force applied to the shim. 6. Method according to claim 5, characterized in that a wedge is used comprising a layer of polyvinylidene fluoride (121) metallized on its two faces (120, 122), these being isolated from the outside by layers insulating material (123, 124) and both metallized faces being connected a charge amplifier (125). 7. Method according to claim 3, characterized in that it prints oscillations in its plane, and it detects the cessation of these oscillations, which correspond to the tightening of the wedge between the adjusting screw and said element. 8. Method according to one of claims 1 to 7, characterized in that said element of the rocker assembly is constituted by the stem of the valve. 9. Apparatus for implementing the method according to one of claims 1 to 8, and comprising:
- a device, comprising a sensor (49) capable of detecting the zero point, where the valve (42) comes into contact with its seat,
- a device (2) for controlling the rotation of the adjusting screw,
this device being characterized in that it further comprises a central control member (1), connected to the rotation control device and to the sensor, this member being arranged to control in step e) the rotation of the screw adjustment in a first direction along a first angle previously stored in memory, then, in step f), in the opposite direction until detection using the signals emitted by the sensor, of the movement stop of the valve, and then, after said stop detection, at a second angle, corresponding to the clearance, and previously stored, to perform step g). 10. Apparatus according to claim 9, characterized in that the device for controlling the rotation of the adjusting screw comprises a stepping motor (19), and the instructions of the control member are stored and transmitted as a number of steps of said motor. 11. Apparatus according to one of claims 9 or 10, and wherein the sensor capable of detecting the zero point is a displacement sensor capable of grasping so quasi-continuous movement of the valve relative to its seat, characterized in that said sensor is of the incremental type, and transmits in digital form the signals transmitted to the control member. 12. Apparatus according to one of claims 9 or 10, and wherein the sensor capable of detecting the zero point is a displacement sensor capable of almost continuously capturing the movements of the valve relative to its seat, or according claim 11, and comprising:
- a support (45) capable of being immobilized in a fixed position relative to the internal combustion engine to be checked,
- a feeler (43) movably mounted on the support and provided with a key (40) intended to come into contact with the valve (42) or with a part (41) which is rigidly linked to it, and
- a sensor sensitive to the movement of the probe, characterized in that it further comprises:
- a feeler (50) movably mounted on the support and provided with a button (52) intended to come into contact with the seat of the valve or with a part which is rigidly linked to it, the sensor (49) being linked to one of the feelers whose sensitive organ (48) is in contact with the other. 13. Apparatus according to claim 12, characterized in that the feelers are pivotally mounted on the support, a spring (54) bearing on the support pushing one of the feelers to bring it into contact with the part on which its key must come in support, and the other feeler being controlled by a jack (53) mounted on the first support, this latter feeler being provided with an auxiliary member (56) capable of driving the other feeler to put it out of action during mounting or dismounting the support. 14. Apparatus according to claim 13, characterized in that the cylinder (53) is also controlled by the central control member.

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