EP0681092B1 - A valve control device for an internal combustion engine having a tappet clearance compensation device - Google Patents
A valve control device for an internal combustion engine having a tappet clearance compensation device Download PDFInfo
- Publication number
- EP0681092B1 EP0681092B1 EP95106560A EP95106560A EP0681092B1 EP 0681092 B1 EP0681092 B1 EP 0681092B1 EP 95106560 A EP95106560 A EP 95106560A EP 95106560 A EP95106560 A EP 95106560A EP 0681092 B1 EP0681092 B1 EP 0681092B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- tappet
- valve
- cam
- chamber
- bush
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000002485 combustion reaction Methods 0.000 title claims description 8
- 238000006073 displacement reaction Methods 0.000 claims description 7
- 238000005192 partition Methods 0.000 claims description 7
- 239000012530 fluid Substances 0.000 claims description 2
- 230000002093 peripheral effect Effects 0.000 description 7
- 238000013016 damping Methods 0.000 description 4
- 230000035939 shock Effects 0.000 description 4
- 230000008602 contraction Effects 0.000 description 2
- 125000004122 cyclic group Chemical group 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005461 lubrication Methods 0.000 description 2
- 125000006850 spacer group Chemical group 0.000 description 2
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
- F01L1/12—Transmitting gear between valve drive and valve
- F01L1/14—Tappets; Push rods
- F01L1/16—Silencing impact; Reducing wear
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
- F01L1/02—Valve drive
- F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
- F01L1/08—Shape of cams
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
- F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
- F01L13/0015—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque
- F01L13/0031—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque by modification of tappet or pushrod length
Definitions
- the present invention relates to a control device for a valve of an internal combustion engine, comprising:
- Such a valve control device forms the subject of European Patent Application No. EP-A-0 574 867 which is to be considered as part of the present description.
- the tappet clearance compensation device is constituted by a spacer pad of calibrated dimensions, interposed between the tappet and the valve. To adjust the tappet clearance, that is to say the relative position between cam and tappet, it is necessary to replace the spacer pad. Since such a system is subject to wear over time, which modifies the tappet clearance, it is necessary to perform periodic inspections for the purpose of checking if the tappet clearance is maintained within a predetermined range of values.
- the principal object of the present invention is that of providing a valve control device for an internal combustion engine of more efficient type than previously known systems by the use of an automatic hydraulic tappet clearance compensation device.
- the tappet clearance compensation device is of self adjusting hydraulic type and can be connected to the pressurised oil source of the hydraulic brake device by means of a first auxiliary duct formed in the body of the tappet and by a second auxiliary duct formed in the said bush, these auxiliary ducts being intended to assume a mutually aligned position in which the automatic compensation device and the hydraulic brake device are connected together, when the valve is in the said closure position, and positions out-of-alignment with one another, in which the automatic compensation device is isolated from the hydraulic brake device, when the valve is in a position other than the closure position.
- the device according to the invention allows automatic adjustment of the tappet clearance compensation by utilising a single source of pressurised oil for supplying both the hydraulic brake device and the automatic tappet clearance compensation device, in this way making available a large volume for effectively damping shock waves which propagate in the pressurised oil circuit in consequence of different phases of operation of the hydraulic brake device.
- the reference numeral 1 indicates a cylinder head of an internal combustion engine (only partially illustrated in the drawings).
- the reference numeral 2 indicates an induction duct associated with one of the cylinders, the outlet opening of which is controlled by a valve 3 which in its closure position is disposed in contact with a seat 3a.
- the valve 3 has a stem 4 displaceable axially along an axis D to control opening and closure of the duct 2.
- the stem 4 is guided by a sleeve 4a of type known per se, associated with the cylinder head 1.
- the displacement of the valve 3 is controlled cyclically by a cam 5 mounted on the internal combustion engine's camshaft, rotating in a direction indicated by the arrow E about the axis F of the camshaft.
- a tappet 6 the body of which is substantially cup-shaped.
- the tappet 6 is mounted axially slidably within a bush 8 coaxially of the axis D, connected rigidly to the cylinder head 1.
- a spring cap (disc) member 10 of type known per se is axially fixed to the valve stem 4 and is engaged by a coil spring 11 concentric with the stem 4, the function of which is to maintain the valve 3 urged towards its closure position of the duct 2.
- the tappet 6 includes a head 14 adjacent the cam 5, which has an active surface 15 cooperable with the cam profile 5.
- This active surface 15 comprises a first flat portion 15a substantially orthogonal to the axis D and a second, curved portion 15b joined to the portion 15a and having a constant radius of curvature in such a way as to present a convex zone towards the cam 5.
- the head 14, fixed to the tappet 6, is locked against relative rotation with respect to the bush 8 by means of a pair of guide shoulders 16 which have a shape corresponding to the shape of the adjacent edge of the head 14 and are formed on an element 16a rigidly connected to the cylinder head 1 by means of a screw 17 which also permits fixing of the bush 8 to the cylinder head 1.
- the cam 5 comprises an asymmetric cylindrical member the base of which is defined by a curved line which comprises a portion 5a having a cam base circle of radius R 0 and a cam lobe 5b projecting from the base circle, serving as a thrust head for the tappet 6.
- the curved line defines the profile of the cam 5 which is asymmetric with respect to a plane passing through the axis of rotation F and the apex of the lobe 5b, in such a way that the cam 5 has a "less steep" profile portion 5c and an opposite “steeper” profile portion 5d, where the term “steepness” means the variation of the radial coordinate with respect to the axis F for a given increment of the angular coordinate.
- the angular displacement of the cam 5 is greater than the angular displacement of the cam necessary to take the valve to its closure position.
- a predetermined threshold value for example corresponding to a speed of rotation of the engine of about 2500 revolutions per minute
- the law of closure of the valve 3 is determined solely by the mass of the movable components, the thrust of the spring 11 and the inertial and damping actions to which the valve 3 is subject.
- the active profile 15 of the tappet 6 is always in contact with the profile of the cam 5.
- Each bush 8 is surrounded by a respective peripheral chamber 22 supplied by the pressurised oil utilised for lubrication of the engine.
- annular chamber 26 forming part of a hydraulic brake device 23 the volume of which is variable in dependence on the position of the tappet 6 with respect to the bush 8.
- the chamber 26 extends radially between the tappet 6 and the bush 8 and is delimited in the axial direction by a portion 6a of greater diameter than the tappet 6 and, on the opposite side, by a portion 8a of smaller diameter than the bush 8.
- the chamber 26 therefore has a base area in the form of a circular ring concentric with the axis D and is delimited internally by a circumference of radius R 1 and externally by a circumference of radius R 2 .
- Each bush 8 has radial holes 24 for connecting the peripheral chamber 22 to the annular chamber 26, having a relatively short length with respect to their diameter, or rather which achieve thin wall opening conditions in such a way that the flow of fluid through them produces a damping effect causing a hydraulic brake action to slow the stroke of the valve in the last part of its closure phase so as to avoid sharp contact between the tappet 6 and the cam profile 5 during "ballistic" operation.
- exit apertures 28 close to the smaller diameter portion 8a, which extend between the chamber 22 and the chamber 26, the diameter of the holes 28 being significantly less than the diameter of the apertures 24 in such a way as to cause a more energetic damping action during the final phase of the closure of the valve 3, when the cylindrical outer wall of the tappet 6 closes the holes 24.
- the tappet 6 further includes a hydraulic device for automatically adjusting the tappet clearance compensation.
- This device generally indicated with the reference numeral 30, includes a cup-shaped member 32 mounted slidably along the axis D in a corresponding seat in the tappet 6 and substantially sealed in such a way that the bottom of the member 32 is disposed directly in contact with the end of the valve stem 4 closest to the cam 5.
- a circlip 32a prevents accidental separation of the member 32 from the seat defined in the tappet 6.
- the member 32 defines, with the inner wall of the cylinder head 14, a substantially cylindrical cavity 36 in which oil is present.
- a sleeve 37 which has a dividing partition 38, orientated transversely with respect to the axis D, which allows the cavity 36 to be separated into an upper chamber 36a and a lower chamber 36b (with reference to the drawings).
- a compression coil spring 48 is interposed between the partition 38 and the bottom of the cup-shaped member 32.
- the partition 38 is provided with a central through hole 40 on the lower edge of which engages a ball 42 of a non-return valve.
- the ball 42 is urged towards a position in which it closes the hole 40 by a conical coil spring 46 which rests on the bottom of a perforated cage 44 in such a way as to prevent the passage of the oil present in the chamber 36b towards the chamber 36a in normal conditions.
- a conical coil spring 46 which rests on the bottom of a perforated cage 44 in such a way as to prevent the passage of the oil present in the chamber 36b towards the chamber 36a in normal conditions.
- first auxiliary duct 50 which at one end is open to the exterior of the tappet and, at the opposite end, opens into the chamber 36a.
- second auxiliary duct 52 passing therethrough, one end of which opens into the peripheral chamber 22, whilst the opposite end faces towards the tappet 6.
- the ducts 50 and 52 can be disposed in a mutually aligned condition, illustrated in Figures 1 and 2, in which they put the peripheral chamber 22 into communication with the chamber 36 when the valve 3 is in its closure position closing the duct 2.
- the ducts 50 and 52 are in positions which are not aligned with one another ( Figure 3) in such a way that the chamber 36a is isolated from the chamber 22.
- the spring 48 automatically compensates for this clearance by separating the bottom of the member 32 from the partition 38 of the sleeve 37 and therefore from the head of the tappet 6 by a distance equal to the clearance which has arisen in the system.
- a depression is caused within the chamber 36b which causes opening of the non-return valve against the action of the spring 46 causing the passage of oil under pressure from the chamber 36a to the chamber 36b until achieving an equilibrium condition in which the clearance is completely nullified and the ball 42 is returned into the position covering the hole 40 thereby closing the non-return valve.
- the base area of the cavity 36 which corresponds to the area over which the pressure of the oil present in the peripheral chamber 22 is exerted when the ducts 50 and 52 are aligned with one another, corresponds to the area of a circular surface of radius R 3 , which is at least equal to but preferably greater than the base area of the annular chamber 26 defined by the difference between the areas of the circular surfaces defined by the radii R 2 and R 1 .
- the resilient characteristic of the spring 48 is chosen in dependence on the force acting in the chamber 26 defined by the product of the base area of the chamber 26 and the pressure of the oil present in it, in such a way that this resultant force is of a magnitude which predominates over the resilient force of the spring 48. In this way, in the absence of any tappet clearance to be compensated, unwanted extension of the spring 48 during the "ballistic" operation of the system is prevented.
- the cam 5 includes a pair of cylindrical abutment surfaces 7 the radius of which is equal to the radius of the base circle R 0 of the cam, disposed alongside and on opposite sides of the asymmetric cylindrical member of the cam 5.
- Figure 7 shows the cylinder head 1 which has a plurality of valves 4 with respective tappets 6 and bushes 8, each of which is surrounded by a respective peripheral chamber 22.
- the chambers 22 are supplied with pressurised engine lubrication oil via a common channel 20.
- a plurality of cylindrical reservoirs 55 (only one of which is visible in Figure 7) are connected by service channels 54 to the channel 20 and each contains an elastically deformable cylindrical member 56 of type known per se.
- the volume which each of the members 56 occupies within the respective reservoir 55 is variable as a function of the change of the oil pressure in the channels 20 and 54.
- the hydraulic brake device 23 performs its action slowing the valve 3 during the final phase of its rising stroke.
- the oil flows out from the chambers 26 in the contraction phase, through the respective apertures 24 and 28, accumulates in the reservoirs 55 to be returned to the chambers 26 during their subsequent phase of expansion which takes place simultaneously with opening of the valves 3.
- the flow of oil exchanged between the chambers 26 and the reservoirs 55, caused by the cyclic expansions and contractions of the chambers 26, generates shock waves which propagate in the oil through the channels 20.
- the volume of the reservoirs 55 and the channels 20 and 54 together with the additional volume defined by the ducts 50 and 52 is sufficiently great to minimise the effects of these shock waves and to render them negligible. Moreover, when the tappet clearance compensation devices 30 are connected to the peripheral chambers 22 by the ducts 50 and 52, these shock waves are effectively damped along the ducts 50 and 52 in such a way as not to propagate into the interior of the chambers 36a.
- the invention it is possible to utilise the same pressurised oil circuit already intended to operate the hydraulic brake device 23 to supply oil under pressure to the cavity 36 of the device 30 so that the tappet clearance compensation can take place correctly even when, as a result of inevitable escapes of oil through the imperfect seals between the bush 37 and the cup-shaped member 32 and between the member 32 and its seat in the tappet 6, the volume of oil contained in the chamber 36b diminishes.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Valve-Gear Or Valve Arrangements (AREA)
- Valve Device For Special Equipments (AREA)
Description
- The present invention relates to a control device for a valve of an internal combustion engine, comprising:
- a valve displaceable between a duct closure position and a duct open position, this valve being associated with resilient biasing means urging it towards its closure position,
- valve control means for displacing the valve towards its open position, including a rotary cam operable to engage an active surface of a tappet interposed between the cam and the valve, at least during the displacement of the valve towards its open position,
- a hydraulic brake device for slowing the movement of the valve during the last part of its closure stroke, including an annular chamber defined between the tappet and a bush coaxially of and external to the tappet, this chamber being in communication with a source of oil under pressure and having a volume which is variable as a consequence of the displacement of the tappet with respect to the bush, and
- a tappet clearance compensation device interposed between the tappet and the valve.
- Such a valve control device forms the subject of European Patent Application No. EP-A-0 574 867 which is to be considered as part of the present description.
- In the above-indicated known device the tappet clearance compensation device is constituted by a spacer pad of calibrated dimensions, interposed between the tappet and the valve. To adjust the tappet clearance, that is to say the relative position between cam and tappet, it is necessary to replace the spacer pad. Since such a system is subject to wear over time, which modifies the tappet clearance, it is necessary to perform periodic inspections for the purpose of checking if the tappet clearance is maintained within a predetermined range of values.
- Hydraulic devices which allow automatic adjustment of the tappet clearance in an internal combustion engine are known from US Patents US-A-4 367 701 and US-A-4 373 477.
- The principal object of the present invention is that of providing a valve control device for an internal combustion engine of more efficient type than previously known systems by the use of an automatic hydraulic tappet clearance compensation device.
- This object is achieved according to the invention in that the tappet clearance compensation device is of self adjusting hydraulic type and can be connected to the pressurised oil source of the hydraulic brake device by means of a first auxiliary duct formed in the body of the tappet and by a second auxiliary duct formed in the said bush, these auxiliary ducts being intended to assume a mutually aligned position in which the automatic compensation device and the hydraulic brake device are connected together, when the valve is in the said closure position, and positions out-of-alignment with one another, in which the automatic compensation device is isolated from the hydraulic brake device, when the valve is in a position other than the closure position.
- By virtue of these characteristics the device according to the invention allows automatic adjustment of the tappet clearance compensation by utilising a single source of pressurised oil for supplying both the hydraulic brake device and the automatic tappet clearance compensation device, in this way making available a large volume for effectively damping shock waves which propagate in the pressurised oil circuit in consequence of different phases of operation of the hydraulic brake device.
- Further characteristics and advantages of the present invention will become more clearly apparent from the following detailed description, made with reference to the attached drawings, provided purely by way of non-limitative example, in which:
- Figure 1 is a sectioned side view of a valve control device according to the invention;
- Figure 2 is a view on an enlarged scale of a detail indicated with the arrow II in Figure 1;
- Figure 3 is a view similar to Figure 2 at a different point in the operation of the device;
- Figure 4 is a perspective view of some of the elements of Figure 3;
- Figures 5 and 6 are partially sectioned front elevation views in the direction of the arrow V of Figure 4 in two different instants in the operation of the device; and
- Figure 7 is a schematic side view in the direction of the arrow VII-VII of Figure 1, which illustrates a cylinder head of an internal combustion engine provided with the control device of the invention.
- With reference to the drawings, the reference numeral 1 indicates a cylinder head of an internal combustion engine (only partially illustrated in the drawings).
- The reference numeral 2 indicates an induction duct associated with one of the cylinders, the outlet opening of which is controlled by a
valve 3 which in its closure position is disposed in contact with a seat 3a. Thevalve 3 has astem 4 displaceable axially along an axis D to control opening and closure of the duct 2. - The
stem 4 is guided by a sleeve 4a of type known per se, associated with the cylinder head 1. The displacement of thevalve 3 is controlled cyclically by acam 5 mounted on the internal combustion engine's camshaft, rotating in a direction indicated by the arrow E about the axis F of the camshaft. - Between the
cam 5 and the end of thevalve stem 4 closest to thecam 5 there is interposed atappet 6 the body of which is substantially cup-shaped. Thetappet 6 is mounted axially slidably within abush 8 coaxially of the axis D, connected rigidly to the cylinder head 1. - A spring cap (disc)
member 10 of type known per se is axially fixed to thevalve stem 4 and is engaged by acoil spring 11 concentric with thestem 4, the function of which is to maintain thevalve 3 urged towards its closure position of the duct 2. - The
tappet 6 includes ahead 14 adjacent thecam 5, which has anactive surface 15 cooperable with thecam profile 5. Thisactive surface 15 comprises a firstflat portion 15a substantially orthogonal to the axis D and a second,curved portion 15b joined to theportion 15a and having a constant radius of curvature in such a way as to present a convex zone towards thecam 5. - The
head 14, fixed to thetappet 6, is locked against relative rotation with respect to thebush 8 by means of a pair ofguide shoulders 16 which have a shape corresponding to the shape of the adjacent edge of thehead 14 and are formed on anelement 16a rigidly connected to the cylinder head 1 by means of ascrew 17 which also permits fixing of thebush 8 to the cylinder head 1. - The
cam 5 comprises an asymmetric cylindrical member the base of which is defined by a curved line which comprises aportion 5a having a cam base circle of radius R0 and acam lobe 5b projecting from the base circle, serving as a thrust head for thetappet 6. The curved line defines the profile of thecam 5 which is asymmetric with respect to a plane passing through the axis of rotation F and the apex of thelobe 5b, in such a way that thecam 5 has a "less steep"profile portion 5c and an opposite "steeper"profile portion 5d, where the term "steepness" means the variation of the radial coordinate with respect to the axis F for a given increment of the angular coordinate. - Because of the different "steepness" of the
profile portions valve 3 from the zero height to the maximum height, the angular displacement of thecam 5 is greater than the angular displacement of the cam necessary to take the valve to its closure position. In this way, when the speed of the camshaft which is well known to be proportional to the speed of the engine, exceeds a predetermined threshold value, for example corresponding to a speed of rotation of the engine of about 2500 revolutions per minute, theactive profile 15 of thetappet 6 loses contact with the "steeper"profile portion 5d of thecam 5, thus achieving an operation of the "ballistic" type. In these conditions the law of closure of thevalve 3 is determined solely by the mass of the movable components, the thrust of thespring 11 and the inertial and damping actions to which thevalve 3 is subject. For speeds of the camshaft less than the predetermined threshold value theactive profile 15 of thetappet 6 is always in contact with the profile of thecam 5. - Each
bush 8 is surrounded by a respectiveperipheral chamber 22 supplied by the pressurised oil utilised for lubrication of the engine. - Between the
tappet 6 and thebush 8 is defined anannular chamber 26 forming part of ahydraulic brake device 23 the volume of which is variable in dependence on the position of thetappet 6 with respect to thebush 8. In particular, thechamber 26 extends radially between thetappet 6 and thebush 8 and is delimited in the axial direction by aportion 6a of greater diameter than thetappet 6 and, on the opposite side, by aportion 8a of smaller diameter than thebush 8. Thechamber 26 therefore has a base area in the form of a circular ring concentric with the axis D and is delimited internally by a circumference of radius R1 and externally by a circumference of radius R2. - Each
bush 8 hasradial holes 24 for connecting theperipheral chamber 22 to theannular chamber 26, having a relatively short length with respect to their diameter, or rather which achieve thin wall opening conditions in such a way that the flow of fluid through them produces a damping effect causing a hydraulic brake action to slow the stroke of the valve in the last part of its closure phase so as to avoid sharp contact between thetappet 6 and thecam profile 5 during "ballistic" operation. - In the
bush 8 there are further formedexit apertures 28 close to thesmaller diameter portion 8a, which extend between thechamber 22 and thechamber 26, the diameter of theholes 28 being significantly less than the diameter of theapertures 24 in such a way as to cause a more energetic damping action during the final phase of the closure of thevalve 3, when the cylindrical outer wall of thetappet 6 closes theholes 24. - The
tappet 6 further includes a hydraulic device for automatically adjusting the tappet clearance compensation. This device, generally indicated with thereference numeral 30, includes a cup-shaped member 32 mounted slidably along the axis D in a corresponding seat in thetappet 6 and substantially sealed in such a way that the bottom of themember 32 is disposed directly in contact with the end of thevalve stem 4 closest to thecam 5. Acirclip 32a prevents accidental separation of themember 32 from the seat defined in thetappet 6. - The
member 32 defines, with the inner wall of thecylinder head 14, a substantiallycylindrical cavity 36 in which oil is present. To the interior of themember 32 is mounted, also slidably and substantially sealed, asleeve 37 which has a dividingpartition 38, orientated transversely with respect to the axis D, which allows thecavity 36 to be separated into anupper chamber 36a and alower chamber 36b (with reference to the drawings). Acompression coil spring 48 is interposed between thepartition 38 and the bottom of the cup-shaped member 32. - The
partition 38 is provided with a central throughhole 40 on the lower edge of which engages aball 42 of a non-return valve. Theball 42 is urged towards a position in which it closes thehole 40 by aconical coil spring 46 which rests on the bottom of aperforated cage 44 in such a way as to prevent the passage of the oil present in thechamber 36b towards thechamber 36a in normal conditions. When theball 42 is moved away from the edge of thehole 40 overcoming the biasing action of thespring 46, thechamber 36a and thechamber 36b are put into communication with one another, thereby permitting the transfer of oil from one to the other. - In the body of the
tappet 6 is formed a firstauxiliary duct 50 which at one end is open to the exterior of the tappet and, at the opposite end, opens into thechamber 36a. In thebush 8 there is formed a secondauxiliary duct 52 passing therethrough, one end of which opens into theperipheral chamber 22, whilst the opposite end faces towards thetappet 6. Theducts peripheral chamber 22 into communication with thechamber 36 when thevalve 3 is in its closure position closing the duct 2. When thevalve 3 is in a different position from the closure position theducts chamber 36a is isolated from thechamber 22. - When a clearance between the
tappet 6 and thecam 5 arises thespring 48 automatically compensates for this clearance by separating the bottom of themember 32 from thepartition 38 of thesleeve 37 and therefore from the head of thetappet 6 by a distance equal to the clearance which has arisen in the system. In these conditions a depression is caused within thechamber 36b which causes opening of the non-return valve against the action of thespring 46 causing the passage of oil under pressure from thechamber 36a to thechamber 36b until achieving an equilibrium condition in which the clearance is completely nullified and theball 42 is returned into the position covering thehole 40 thereby closing the non-return valve. - The base area of the
cavity 36, which corresponds to the area over which the pressure of the oil present in theperipheral chamber 22 is exerted when theducts annular chamber 26 defined by the difference between the areas of the circular surfaces defined by the radii R2 and R1. Consequently the force exerted on thedevice 30 by the pressure of the oil present in thechamber 22, when theducts member 32 and thetappet 6 in the absence of engagement between theactive surface 15 of the tappet and the profile of thecam 5, will be slightly predominant over the force due to the pressure of the oil which acts on the base surface of thechamber 26, in such a way that, thanks also to thespring 48, when thevalve 3 is in the closure position of the duct 2 adjustment of the clearance of the tappet takes place without causing any variation in the volume of thechamber 26. - During operation of the system in the "ballistic" mode, when the
active surface 15 of thetappet 6 loses contact with the "steeper"profile portion 5d of thecam 5 and therefore theducts tappet 6 and thecam 5 could cause unwanted extension of thespring 48, as a result of which the bottom of the cup-shaped member 32 could move to a position which is too greatly spaced from theactive surface 15 of thetappet 6 thereby preventing the correct closure of thevalve 3 on the seat 3a. The force due to the pressure present in thechamber 26, together with the inertial forces and the friction to which thetappet 6 is subjected, cause a resultant force which opposes the thrust exerted by thespring 48. In particular, the resilient characteristic of thespring 48 is chosen in dependence on the force acting in thechamber 26 defined by the product of the base area of thechamber 26 and the pressure of the oil present in it, in such a way that this resultant force is of a magnitude which predominates over the resilient force of thespring 48. In this way, in the absence of any tappet clearance to be compensated, unwanted extension of thespring 48 during the "ballistic" operation of the system is prevented. - Moreover, in order to prevent the
compensation device 30 from extending too much under the resilient action of the thrust of thespring 48 at the end of the closure stroke of thevalve 3, thecam 5 includes a pair ofcylindrical abutment surfaces 7 the radius of which is equal to the radius of the base circle R0 of the cam, disposed alongside and on opposite sides of the asymmetric cylindrical member of thecam 5. - Figure 7 shows the cylinder head 1 which has a plurality of
valves 4 withrespective tappets 6 andbushes 8, each of which is surrounded by a respectiveperipheral chamber 22. Thechambers 22 are supplied with pressurised engine lubrication oil via acommon channel 20. A plurality of cylindrical reservoirs 55 (only one of which is visible in Figure 7) are connected byservice channels 54 to thechannel 20 and each contains an elastically deformablecylindrical member 56 of type known per se. The volume which each of themembers 56 occupies within therespective reservoir 55 is variable as a function of the change of the oil pressure in thechannels - In operation of the engine, during closure of the duct 2 by the
valve 3, thehydraulic brake device 23 performs its action slowing thevalve 3 during the final phase of its rising stroke. In these conditions, and in a cyclic manner, the oil flows out from thechambers 26 in the contraction phase, through therespective apertures reservoirs 55 to be returned to thechambers 26 during their subsequent phase of expansion which takes place simultaneously with opening of thevalves 3. The flow of oil exchanged between thechambers 26 and thereservoirs 55, caused by the cyclic expansions and contractions of thechambers 26, generates shock waves which propagate in the oil through thechannels 20. - The volume of the
reservoirs 55 and thechannels ducts clearance compensation devices 30 are connected to theperipheral chambers 22 by theducts ducts chambers 36a. - Thanks to the invention it is possible to utilise the same pressurised oil circuit already intended to operate the
hydraulic brake device 23 to supply oil under pressure to thecavity 36 of thedevice 30 so that the tappet clearance compensation can take place correctly even when, as a result of inevitable escapes of oil through the imperfect seals between thebush 37 and the cup-shapedmember 32 and between themember 32 and its seat in thetappet 6, the volume of oil contained in thechamber 36b diminishes.
Claims (5)
- A device for controlling the valve of an internal combustion engine, comprising:- a valve (3) displaceable between a duct (2) closure position and a duct (2) open position, this valve (3) being associated with resilient biasing means (11) urging it towards its closure position,- valve control means for displacing the valve (3) towards its open position including a rotary cam (5) operable to engage an active surface (15) of a tappet (6) interposed between the cam (5) and the valve (3) at least during the displacement of the valve towards its open position,- a hydraulic brake device for slowing the movement of the valve (3) in the last part of its closure stroke, including an annular chamber (26) defined between the tappet (6) and a bush (8) coaxially of and external to the tappet (6), this chamber (26) being in communication with a source (22) of oil under pressure and having a volume which is variable as a consequence of the relative displacement of the tappet (6) with respect to the bush (8), and- a tappet clearance compensation device (30) interposed between the tappet (6) and the valve (3),characterised in that the tappet clearance compensation device (30) is of self-adjusting hydraulic type and can be connected to the pressurised oil source (22) of the hydraulic brake device by means of a first auxiliary duct (50) formed in the body of the tappet (6) and by a second auxiliary duct (52) formed in the said bush (8), these auxiliary ducts (50, 52) being intended to assume a mutually aligned position in which the automatic compensation device (30) and the hydraulic brake device (23) are connected together when the valve is in the said closure position, and positions out-of-alignment with one another, in which the automatic compensation device (30) is isolated from the hydraulic brake device (23) when the valve (3) is in a position other than the closure position.
- A device according to Claim 1, characterised in that between the tappet (6) and the valve (3) is interposed a cup-shaped member (32) slidable with respect to the tappet (6) along the axial direction (D) of movement of the valve (3), this cup-shaped member (32) defining with the tappet (6) a cavity (36) in which is present a movable dividing partition (38) disposed transversely with respect to the said axial direction (D) to subdivide this cavity (36) into a first chamber (36a) into which the said auxiliary duct (50) opens and a second chamber (36b) in which resilient thrust means (48) interposed between the partition (38) and the cup-shaped member (32) are provided, the partition (38) including a non-return valve (40, 42, 46) for impeding the passage of fluid present in the second chamber (36b) towards the first chamber (36a).
- A device according to Claim 1 or Claim 2, characterised in that the cross-sectional area of the said cavity (36), with respect to the said axial direction (D), is equal to or greater than the cross-sectional area of the said annular chamber (26).
- A device according to Claim 2 or Claim 3, characterised in that the elastic characteristic of the elastic thrust means (48) is such that the resultant forces which act on the tappet (6) when its active surface (15) is spaced from the cam (5), determined by the pressure in the annular chamber (26) and by inertial and friction forces to which the tappet (6) is subject, are predominant over the thrust force exerted by the elastic thrust means (48).
- A device according to any of Claims from 2 to 4, characterised in that the cam (5) with asymmetric profile comprises a cylindrical member the base of which is defined by a curved line which has a base portion (5a) delimited by a base circle (R0) of the cam (5) and from which extends a cam lobe (5b) of asymmetric form, and a pair of cylindrical surfaces (7) externally delimited by a radius equal to the radius of the base circle (R0) of the cam (5), these cylindrical surfaces lying alongside and on opposite sides of the said cylindrical member.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
ITTO940369A IT1273185B (en) | 1994-05-06 | 1994-05-06 | CONTROL DEVICE OF A VALVE OF AN INTERNAL COMBUSTION ENGINE WITH RECOVERY DEVICE OF THE TAPPING GAP |
ITTO940369 | 1994-05-06 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0681092A1 EP0681092A1 (en) | 1995-11-08 |
EP0681092B1 true EP0681092B1 (en) | 1997-02-26 |
Family
ID=11412515
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP95106560A Expired - Lifetime EP0681092B1 (en) | 1994-05-06 | 1995-05-02 | A valve control device for an internal combustion engine having a tappet clearance compensation device |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0681092B1 (en) |
DE (1) | DE69500161T2 (en) |
IT (1) | IT1273185B (en) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
IT1268193B1 (en) * | 1994-12-22 | 1997-02-21 | Fiat Auto Spa | CONTROL DEVICE OF A VALVE OF AN INTERNAL COMBUSTION ENGINE |
DE102004048288A1 (en) * | 2004-10-05 | 2006-05-04 | Ina-Schaeffler Kg | Variable valve train of an internal combustion engine |
GB2563064B (en) * | 2017-06-02 | 2022-05-18 | Camcon Auto Ltd | Valve actuators |
CN112267923B (en) * | 2020-09-28 | 2022-04-05 | 中国北方发动机研究所(天津) | Self-oil-supply energy-storage hydraulic tappet of engine |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE4035376C2 (en) * | 1989-11-16 | 2000-04-27 | Volkswagen Ag | Actuator for a lift valve |
DE4317607A1 (en) * | 1992-06-05 | 1993-12-09 | Volkswagen Ag | Variable valve drive for poppet valve in vehicle IC engine - uses working chamber in cup tappet controlled by throttle opening as valve moves position |
IT1257904B (en) * | 1992-06-19 | 1996-02-16 | Fiat Ricerche | CONTROL DEVICE OF A VALVE OF AN INTERNAL COMBUSTION ENGINE. |
DE4419768A1 (en) * | 1993-06-26 | 1995-01-05 | Volkswagen Ag | Variable valve gear for a lifting valve |
-
1994
- 1994-05-06 IT ITTO940369A patent/IT1273185B/en active IP Right Grant
-
1995
- 1995-05-02 DE DE69500161T patent/DE69500161T2/en not_active Expired - Fee Related
- 1995-05-02 EP EP95106560A patent/EP0681092B1/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
EP0681092A1 (en) | 1995-11-08 |
DE69500161T2 (en) | 1997-06-05 |
DE69500161D1 (en) | 1997-04-03 |
ITTO940369A1 (en) | 1995-11-06 |
ITTO940369A0 (en) | 1994-05-06 |
IT1273185B (en) | 1997-07-07 |
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