Spool Valve Control of an Electrohydraulic Camless Valvetrain

Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 721 058 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Intel e F01L 9/02 of the grant of the patent: 31.03.1999 Bulletin 1999/13

(21) Application number: 95309381.2

(22) Date of filing: 21.12.1995

(54) Spool valve control of an electrohydraulic camless valvetrain Schieberventilsteuerung fur eine elektro-hydraulische Gaswechselsteuerung ohne Nocken Commande de vanne a tiroir pour distribution electro-hydraulique sans came

(84) Designated Contracting States: (72) Inventor: Schechter, Michael DE ES FR GB Farmington Hills, Michigan 48331 (US)

(30) Priority: 06.01.1995 US 369459 (74) Representative: Messulam, Alec Moses et al A. Messulam & Co. (43) Date of publication of application: 24 Broadway 10.07.1996 Bulletin 1996/28 Leigh-on-Sea Essex SS9 1BN (GB)

(73) Proprietors: (56) References cited: • FORD MOTOR COMPANY LIMITED EP-A- 0 391 507 DE-A-3 619 956 Brentwood Essex (GB) US-A- 3 209 737 US-A- 5 255 641 Designated Contracting States: US-A- 5 456 222 GB • FORD FRANCE S. A. 92506 Rueil-Malmaison Cedex (FR) Designated Contracting States: FR • FORD-WERKE AKTIENGESELLSCHAFT 50735 Koln (DE) Designated Contracting States: DE • Ford Motor Company Dearborn, Ml 48126 (US) Designated Contracting States: ES

DO 00 o

CM Is- Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU

Printed by Jouve, 75001 PARIS (FR) 1 EP 0 721 058 B1 2

Description nected to a source of hydraulic pressure, a second port connected to a sump and a third port connected to the [0001] The present invention relates to a hydraulically valve actuator. All the hydraulic pressure is supplied operated valve control system for an internal combus- through the spool valve. tion engine. 5 [0007] In its embodiments, the present invention con- [0002] Reference is made to US-A-5 375 41 9, US-A- templates a hydraulically operated valve control system 5 373 817, US-A-5 419 301, US-A-5 410 994, US-A-5 for an internal combustion engine. The system includes 404 844, US-A-5 456 223, US-A-5 497 736 and US-A- a high pressure hydraulic branch and a low pressure hy- 5 456 221. draulic branch, having a high pressure source of fluid [0003] The increased use and reliance on microproc- 10 and a low pressure source of fluid, respectively. A cyl- essor control systems for automotive vehicles and in- inder head member is adapted to be affixed to the en- creased confidence in hydraulic as opposed to mechan- gine and includes an enclosed bore and chamber. An ical systems is making substantial progress in engine engine is valve shiftable between a first and a second systems design possible. One such electrohydraulic position within the cylinder head bore and chamber, and system is a control for engine intake and exhaust valves. is a hydraulic actuator has a valve piston coupled to the The enhancement of engine performance to be attained engine valve and reciprocable within the enclosed by being able to vary the timing, duration, lift and other chamber which thereby forms a first and a second cavity parameters of the intake and exhaust valves' motion in which vary in displacement as the engine valve moves. an engine is known in the art. This allows one to account A spool valve assembly is mounted to the cylinder head for various engine operating conditions through inde- 20 member and includes a valve body coupled thereto, with pendent control of the engine valves in order to optimise the valve body including a channel. The cylinder head engine performance. All this permits considerably great- member includes three ports, a first port connecting the er flexibility in engine valve control than is possible with valve body to the high pressure branch, a second port conventional cam-driven valve trains. connecting the valve body to the low pressure branch [0004] One such system is disclosed in U.S. Patent 25 and a third port connecting the valve body to the first Number 5,255,641 to Schechter (assigned to the as- cavity, with the three ports being oriented such that the signee of this invention). A system disclosed therein em- valve body can be moved so that the channel is aligned ploys a pair of solenoid valves per engine valve, one with the third and first ports, the third and second ports connected to a high pressure source of fluid and one or neither the first or second port. The cylinder head connected to a low pressure source of fluid. They are 30 member further includes a high pressure line extending used to control engine valve opening and closing. While between the second cavity and the high pressure this arrangement works adequately, the number of so- branch. The system further includes actuator means for lenoid valves required per engine can be large. This is moving the spool valve relative to the three ports. particularly true for multi-valve type engines that may [0008] An advantage to the present invention is that have four or five valves per cylinder and six or eight cyl- 35 it provides a hydraulically operated valve control system inders. A desire arises, then, to reduce the number of with reduced cost and less complexity by eliminating the valves needed in order to reduce the cost and complex- need for two solenoid valves per engine valve and em- ity of the system. If each pair of solenoid valves is re- ploying one spool valve to control an engine valve in a placed by a single actuator, then the number of valves system that incorporates a high pressure and a low is cut in half. 40 pressure branch selectively connected to a cavity above [0005] This same patent also disclose using rotary a piston mounted on the engine valve. distributors to reduce the number of solenoid valves re- [0009] The invention will now be described further, by quired per engine, but then employs an additional com- way of example, with reference to the accompanying ponent rotating in relationship to the crankshaft to prop- drawings, in which: erly time the rotary distributors. This tie-in to the crank- 45 shaft may reduce some of the benefit of a camless val- Fig. 1 is a schematic diagram showing a single en- vetrain and, thus, may not be ideal. Further, the system gine valve, from an engine valvetrain, and an elec- still employs a separate solenoid valve for high pressure trohydraulic system for selectively supplying hy- and low pressure sources of hydraulic fluid. A desire, draulic fluid to the engine valve; and then, exists to further reduce the number of valves con- so Figs. 2A - 2D are graphs showing the relative timing trolling the high and low pressure sources of fluid from of the engine valve lift, spool valve movement and the hydraulic system. the low and high pressure ball checkvalve opening, [0006] EP-A-391 507 discloses a hydraulic valve sys- respectively. tem to be used for driving an intake or exhaust valve in an internal combustion engine. An actuator for the valve 55 [0010] Fig. 1 shows a hydraulic system 8, for control- employs a piston which is actuated by hydraulic pres- ling a valvetrain in an internal combustion engine, con- sure admitted to the actuator by a cam driven spool nected to a single electrohydraulic engine valve assem- valve mechanism. The spool valve has a first port con- bly 10 of the electrohydraulic valvetrain. An electrohy-

2 3 EP 0 721 058 B1 4 draulic valvetrain is disclosed in U.S. Patent 5,255,641 [0017] The magnitude of the pressure at the inlet to to Schechter assigned to the assignee of this invention). high pressure pump 50 is determined by a small low [0011] An engine valve 12, for inlet air or exhaust as pressure pump 54 and its associated pressure regulator the case may be, is located within a sleeve 13 in a cyl- 56 which supply a small quantity of oil to the inlet of high inder head 14, which is a component of engine 11. A 5 pressure pump 50 to compensate for the leakage valve piston 16, fixed to the top of the engine valve 12, through leak-off passage 52. is slidable within the limits of piston chamber 18. [0018] In order to control the supply of the high pres- [0012] Hydraulic fluid is selectively supplied to a vol- sure and low pressure fluid to volume 20 above piston ume 20 above piston 1 6 through an upper port 30, which 16, hydraulic spool valve 34 is employed. It is actuated is connected to a spool valve 34, via hydraulic line 32. 10 by an electric motor 60, shown as a rotary motor, which Volume 20 is also selectively connected to a high pres- controls the linear motion and position of spool valve 34. sure fluid reservoir 22 through a high pressure check Motor rotation is converted into linear motion of spool valve 36 via high pressure lines 26, or to a low pressure valve 34 via threads or helical splines 62 on a central fluid reservoir 24 via low pressure lines 28 through a low shaft 64, which is coupled to motor 60. Motor 60 is elec- pressure check valve 40. A volume 42 below piston 16 ts trically connected to an engine control system 48, which is always connected to high pressure reservoir 22 via activates it to determine the opening and closing timing. high pressure line 26. The pressure surface area above Spool valve 34 would then be attached directly to the piston 1 6, in volume 20, is larger than the pressure area motor armature. below it, in volume 42. [0019] A spool valve body 66 is mounted in and rota- [0013] In order to effectuate the valve opening and 20 tionally fixed relative to cylinder head 14. It is coupled closing, a predetermined high pressure must be main- to central shaft 64 by means of mating internal threads tained in high pressure lines 26, and a predetermined or helical splines 72. With such an arrangement, rotation low pressure must be maintained in low pressure lines of central shaft 64 causes linear displacement of spool 28. The preferred hydraulic fluid is oil, although other valve body 66 relative to cylinder head 14. Cylinder head fluids can be used rather than oil. 25 14 includes three ports; a high pressure port 74 connect- [0014] High pressure lines 26 connect to high pres- ed between high pressure line 26 and body 66, a low sure fluid reservoir 22 to form a high pressure branch pressure port 76 connected between low pressure line 68 of hydraulic system 8. A high pressure pump 50 sup- 28 and body 66, and a third port 78 leading from body plies pressurised fluid to high pressure branch 68 and 66 to volume 20 above engine valve piston 16 via hy- charges high pressure reservoir 22. Pump 50 is prefer- 30 draulic line 32. Valve body 66 also includes an annular ably of the variable displacement variety that automati- channel 80 running about its circumference. When valve cally adjusts its output to maintain the required pressure body 66 is centrally positioned, which is its closed posi- in high pressure reservoir 22 regardless of variations in tion, spool valve 34 keeps third port 78 disconnected consumption, and may be electrically driven or engine from the other two, 74 and 76. Rotating motor 60 in one driven. 35 direction causes central shaft 64 to rotate, moving spool [0015] Low pressure lines 28 connect to low pressure valve body 66 downward. This connects third port 78 fluid reservoir 24, to form a low pressure branch 70 of with high pressure port 74 via annular channel 80. Ro- hydraulic system 8. A check valve 58 connects to low tation in the other direction causes third port 78 to con- pressure reservoir 24 and is located to assure that pump nect with low pressure port 76 via annular channel 80. 50 is not subjected to pressure fluctuations that occur 40 [0020] The timing of the process of engine valve in low pressure reservoir 24 during engine valve open- opening and closing for the system of Fig. 1 is graphi- ing and closing. Check valve 58 does not allow fluid to cally illustrated in Figs. 2A - 2D. Engine valve opening flow into low pressure reservoir 24, and it only allows is controlled by spool valve 34 which, when positioned fluid to flow in the opposite direction when a predeter- to allow high pressure fluid to flow from high pressure mined amount of fluid pressure has been reached in low 45 line 26 into volume 20 via hydraulic line 32, causes en- pressure reservoir 24. From low pressure reservoir 24, gine valve opening acceleration, and, when re-posi- the fluid can return directly to the inlet to pump 50 tioned such that no fluid can flow between line 26 and through check valve 58. line 32, results in engine valve deceleration. Again re- [0016] The net flow of fluid from high pressure reser- positioning spool valve 34, allowing hydraulic fluid in vol- voir 22 through engine valve 12 into low pressure res- so ume 20 to flow into low pressure line 28 via hydraulic ervoir 24 largely determines the loss of hydraulic energy line 32, causes engine valve closing acceleration, and, in system 8. The valvetrain consumes oil from high pres- when re-positioned such that no fluid can flow between sure reservoir 22, and most of it is returned to low pres- line 28 and 32 results in deceleration. sure reservoir 24. A small additional loss is associated [0021] Thus, to initiate engine valve opening, engine with leakage through the clearance between valve 12 55 control system 48 activates motor 60 to move spool and its sleeve 13. A fluid return line 44, connected to a valve body 66 so that annular channel 80 aligns with leak-off passage 52, provides a route for returning any high pressure port 74; 102 in Fig. 2B. The net pressure fluid which leaks out to an oil sump 46. force acting on piston 16 accelerates engine valve 12

3 5 EP 0 721 058 B1 6 downward; 100 in Fig. 2A. Engine control system 48 closed bore and chamber (18); then reverses the direction of motor 60, so that motor an engine valve (12) shiftable between a first 60 moves spool valve body 66 until annular channel 80 and a second position within the cylinder head no longer aligns with high pressure port 74, this is the bore and chamber (18); spool valve closed position; 1 08 in Fig. 2B. The pressure s a hydraulic actuator having a valve piston (16) above piston 1 6 drops, and piston 1 6 decelerates push- coupled to the engine valve (1 2) and reciproca- ing the fluid from volume 42 below it back through high ble within the enclosed chamber (18) which pressure line 26; 104 in Fig. 2A. Low pressure check thereby forms a first and a second cavity which valve 40 opens and fluid flowing through it prevents void vary in displacement as the engine valve (12) formation in volume 20 above piston 16 during deceler- 10 moves; ation; 1 06 in Fig. 2C. When the downward motion of engine valve 12 stops, low pressure check valve 40 closes characterised in that there is provided; and engine valve 1 2 remains locked in its open position; 110 in Fig. 2A. a spool valve assembly (34) mounted to the cyl- [0022] The process of valve closing is similar, in prin- 15 inder head member (1 4) including a valve body ciple, to that of valve opening. Engine control system 48 (66) coupled thereto, with the valve body (66) activates motor 60 to move spool valve body 66 so that including a channel (80); annular channel 80 aligns with low pressure port 76; 114 the cylinder head member (14) including three in Fig. 2B. The pressure above piston 16 drops and the ports (74,76,78), a first port (74) connecting the net pressure force acting on piston 16 accelerates en- 20 valve body (66) to the high pressure branch gine valve 12 upward; 112 in Fig. 2A. Engine control sys- (68), a second port (76) connecting the valve tem 48 then reverses the direction of motor 60, so that body (66) to the low pressure branch (70) and it moves spool valve body 66 until annular channel 80 a third port (78) connecting the valve body (66) no longer aligns with low pressure port 76, the spool to the first cavity (20), with the three ports valve closed position; 108 in Fig. 2B. The pressure 25 (74,76,78) being oriented such that the valve above piston 1 6 rises, and piston 1 6 decelerates; 1 1 8 in body (66) can be moved so that the channel Fig. 2A. High pressure check valve 36 opens as fluid (80) is aligned with the third and first ports, the from volume 20 is pushed through it back into high pres- third and second ports or neither the first or sec- sure hydraulic line 26 until valve 12 is closed; 116 in Fig. ond port, with the cylinder head member (14) 2D. 30 further including a high pressure line (26) ex- [0023] Varying the timing of spool valve activations tending between the second cavity and the high varies the timing of the engine valve opening and clos- pressure branch (68); and ing. Valve lift can be controlled by varying the duration actuator means (60) for moving the spool valve of the alignment of annular channel 80 with high pres- relative to the three ports, said actuator means sure port 74. Varying the fluid pressure in high pressure 35 (60) comprising a rotary motor (60) and a cen- reservoir 22 permits control of engine valve accelera- tral threaded shaft (64) coupled thereto, with tion, velocity and travel time. the central threaded shaft (64) coupled to the [0024] During each acceleration of engine valve 12, spool valve (34) such that rotation of the shaft potential energy of the pressurised fluid is converted into (64) in one direction will cause the spool valve kinetic energy of the moving valve 12 and then, during 40 to move a in first direction and rotation of the deceleration, when valve piston 1 6 pumps the fluid back shaft (64) in the opposite direction will cause into high pressure reservoir 22, the kinetic energy is con- the spool valve to move in a direction opposite verted back into potential energy of the fluid. Such re- to the first direction, to selectively couple the cuperation of hydraulic energy contributes to reduced first cavity with the high pressure branch (68) energy requirement for the system operation. 45 and the low pressure branch (70).

2. A hydraulically operated valve control system ac- Claims cording to claim 1 further including control means (48) cooperating with the rotary motor (60) for se- 1. A hydraulically operated valve control system for an so lectively coupling the first cavity to the high pressure internal combustion engine, the system comprising: and low pressure branches (68,70) via the spool valve body (66) to oscillate the engine valve (1 2) in a high pressure hydraulic branch (68) and a low timed relation to engine operation, where during pressure hydraulic branch (70), having a high each oscillation, some of the high pressure fluid pressure source (22) of fluid and a low pressure 55 used to reciprocate the engine valve (12) is returned source (24) of fluid, respectively; to the high pressure source, thereby allowing that a cylinder head member (14) adapted to be af- the net fluid flow between the high pressure and low fixed to the engine (11) and including an en- pressure sources may be substantially less than a

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volume swept by the valve piston (16). nung (74) den Ventilkorper (66) mit dem Hoch- druckzweig (68) verbindet, eine zweite Offnung 3. A hydraulically operated valve control system ac- (76) den Ventilkorper (66) mit dem Nieder- cording to any one of the preceding claims further druckzweig (70) verbindet, und eine dritte Off- including a high pressure check valve (36) mounted s nung (78) den Ventilkorper (66) mit dem ersten between the first cavity and the high pressure Hohlraum (20) verbindet, wobei die drei Off- source of fluid. nungen (74, 76, 78) so ausgerichtet sind, dal3 der Ventilkorper (66) derart bewegt werden 4. A hydraulically operated valve control system ac- kann, dal3 der Kanal (80) mit der dritten und der cording to any one of the preceding claims further 10 ersten Offnung fluchtet, mit der dritten und der including a low pressure check valve (40) mounted zweiten Offnung, oder mit keiner der beiden er- between the first cavity and the low pressure source sten oder zweiten Offnungen, wobei das Zylin- of fluid. derkopfglied (14) auBerdem eine Hochdruck- leitung (26) aufweist, welche sich zwischen 5. A hydraulically operated valve control system ac- 15 dem zweiten Hohlraum und dem Hochdruck- cording to any one of the preceding claims, wherein zweig (68) erstreckt; und the surface area of the valve piston (16) exposed to Stellantriebsmittel (60) zum Bewegen des the first cavity subjected to fluid pressure is larger Schieberventils in bezug auf die drei Offnun- than the surface area of the valve piston (16) ex- gen, wobei besagte Stellantriebsmittel (60) ei- posed to the second cavity subjected to fluid pres- 20 nen Drehmotor (60) und eine damit gekoppelte sure. mittige, mit einem Gewinde versehene Welle (64) aufweisen, wobei die mit einem Gewinde versehene mittige Welle (64) mit dem Schie- Patentanspriiche berventil derart gekoppelt ist, dal3 eine Dre- 25 hung der Welle (64) in eine Richtung eine Be- 1. Hydraulisch betatigtes Ventilsteuersystem fur eine wegung des Schieberventils in einer ersten Brennkraftmaschine, welches System folgendes Richtung bewirkt, und eine Drehung der Welle aufweist: (64) in der entgegengesetzten Richtung eine Bewegung des Schieberventils in eine der er- einen Hochdruck-Hydraulikzweig (68) und ei- 30 sten Richtung entgegengesetzten Richtung be- nen Niederdruck-Hydraulikzweig (70) mit je ei- wirkt, so dal3 der erste Hohlraum selektiv mit ner Hochdruckquelle (22) fur Druckmittel und dem Hochdruckzweig (68) und mit dem Nieder- einer Niederdruckquelle (24) fur Druckflussig- druckzweig (70) verbunden wird. keit; ein Zylinderkopfglied (14), welches zur Befesti- 35 Hydraulisch betatigtes Ventilsteuersystem nach gung am Motor (11) ausgelegt ist und eine ge- Anspruch 1, weiterhin Steuermittel (48) aufwei- schlossene Bohrung und Kammer (18) auf- send, die mit dem Drehmotor (60) zusammenwir- weist; ken, so dal3 der erste Hohlraum iiber den Schieber- ein Motorventil (12), welches zwischen einer ventilkorper (66) selektiv mit dem Hochdruckzweig ersten und einer zweiten Stellung innerhalb der 40 und dem Niederdruckzweig (68, 70) verbunden Zylinderkopfbohrung und Kammer (18) ver- wird, so dal3 das Motorventil (12) in zeitlicher Ab- stellbar ist; stimmung mit dem Motorbetrieb hin- und herge- einen hydraulischen Stellantrieb mit einem mit hend bewegt wird, wobei bei jeder Schwingung ein dem Motorventil (12) gekoppelten und in der Teil der Hochdruckflussigkeit, die dazu verwendet geschlossenen Kammer (18) hin- und herbe- 45 wird, das Motorventil (12) hin- und herzubewegen, wegbaren Ventilkolben (16), in welcher Kam- zur Hochdruckquelle zuruckgeleitet wird, so dal3 mer so ein erster und ein zweiter Hohlraum ge- der Netto-Flussigkeitsdurchsatz zwischen der bildet wird, dessen Rauminhalt sich mit den Be- Hochdruckquelle und der Niederdruckquelle we- wegungen des Motorventils (12) andert; da- sentlich kleiner ist, als ein vom Ventilkolben (16) durch gekennzeichnet, dal3 folgendes vorgese- 50 verdrangtes Volumen. hen ist: eine Schieberventileinheit (34), welche im Zy- Hydraulisch betatigtes Ventilsteuersystem nach ei- linderkopfglied (14) eingebaut ist und einen da- nem beliebigen der vorangehenden Anspruche, mit verbundenen Ventilkorper (66) aufweist, weiterhin ein Hochdruck-Ruckschlagventil (36) auf- wobei der Ventilkorper (66) einen Kanal (80) 55 weisend, welches zwischen dem ersten Hohlraum aufweist; und der Hochdruck-Druckmittelquelle angeordnet wobei das Zylinderkopfglied (14) drei Offnun- ist. gen aufweist (74, 76, 78), wobei eine erste Off-

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4. Hydraulisch betatigtes Ventilsteuersystem nach ei- aligne avec les troisieme et premier orifices, les nem beliebigen der vorangehenden Anspruche, troisieme et second orifices ou bien ni le pre- weiterhin ein Niederdruck-Ruckschlagventil (40) mier ni le second orifice, I'element de culasse aufweisend, welches zwischen dem ersten Hohl- (14) comprenant en outre une conduite haute raum und der Niederdruck-Druckmittelquelle ange- 5 pression (26) s'etendant entre la seconde cavi- ordnet ist. te et la branche haute pression (68), et un moyen d'actionnement (60) destine a depla- 5. Hydraulisch betatigtes Ventilsteuersystem nach ei- cer le tiroir cylindrique relativement aux trois nem beliebigen der vorangehenden Anspruche, in orifices, ledit moyen d'actionnement (60) com- welchem der Flacheninhalt der Ventilkolbenflache 10 prenant un moteur electrique rotatif (60) et un (16), welche dem ersten mit Hydraulikdruck beauf- arbre filete central (64) couple a celui-ci, I'arbre schlagten Hohlraum zugekehrt ist, groBer als der filete central (64) etant relie au tiroir cylindrique Flacheninhalt der Ventilkolbenflache (16) ist, wel- (34) de facon que la rotation de I'arbre (64) che dem zweiten mit Hydraulikdruck beaufschlag- dans un premier sens amene le tiroir cylindri- ten Hohlraum zugekehrt ist. 15 que a se deplacer dans une premiere direction et que la rotation de I'arbre (64) dans le sens inverse amene le tiroir cylindrique a se deplacer Revendications suivant une direction opposee a la premiere direction, afin de relier selectivement la premiere 1. Systeme de commande hydraulique de soupape 20 cavite a la branche haute pression (68) et la destine a un moteur a combustion interne, le syste- branche basse pression (70). me comprenant : 2. Systeme de commande hydraulique de soupape une branche hydraulique a haute pression (68) selon la revendication 1, comprenant en outre un et une branche hydraulique a basse pression 25 moyen de commande (48) cooperant avec le mo- (70), comportant une source a haute pression teur electrique rotatif (60) afin de relier selective- (22) de fluide et une source a basse pression ment la premiere cavite aux branches a haute pres- (24) de fluide, respectivement, sion et a basse pression (68, 70) par I'intermediaire un element de culasse (1 4) concu pour etre fixe du tiroir cylindrique (66) afin de faire osciller la sou- au moteur (11) et comprenant un alesage et 30 pape de moteur (1 2) de facon synchroniser avec le une chambre incorpores (18), fonctionnement du moteur, ou durant chaque os- une soupape de moteur (12) pouvant etre de- cillation, une partie du fluide haute pression utilise placee entre une premiere et une seconde po- pour faire aller et venir la soupape de moteur (12) sition a I'interieur de I'alesage et de la chambre est renvoyee vers la source haute pression, en per- de la culasse (18), 35 mettant ainsi que le debit net de fluide entre les un actionneur hydraulique comportant un pous- sources a haute pression et a basse pression soit soir de soupape (16) associe a la soupape de sensiblement inferieur au volume deplace par le moteur (1 2) et pouvant etre deplace en mouve- poussoir de soupape (16). ment alternatif a I'interieur de la chambre incor- poree (18), laquelle forme ainsi une premiere 40 3. Systeme de commande hydraulique de soupape et une seconde cavite dont le volume varie lors- selon I'une quelconque des revendications prece- que la soupape de moteur (12) se deplace, dentes, comprenant en outre un clapet anti-retour haute pression (36) monte entre la premiere cavite caracterise en ce que sont prevus et la source a haute pression de fluide. 45 un ensemble de distributeur a tiroir cylindrique 4. Systeme de commande hydraulique de soupape (34) monte sur la culasse (14), comprenant un selon I'une quelconque des revendications prece- tiroir (66) associe a celui-ci, le tiroir (66) com- dentes, comprenant en outre un clapet anti-retour prenant un canal (80), basse pression (40) monte entre la premiere cavite I'element de culasse (14) comprenant trois ori- so et la source a basse pression de fluide. fices (74, 76, 78), un premier orifice (74) reliant le tiroir (66) a la branche haute pression (68), 5. Systeme de commande hydraulique de soupape un second orifice (76) reliant le tiroir (66) a la selon I'une quelconque des revendications prece- branche basse pression (70) et un troisieme dentes, dans lequel I'aire de surface du poussoir de orifice (78) reliant le tiroir (66) a la premiere ca- 55 soupape (16) exposee a la premiere cavite soumise vite (20), les trois orifices (74, 76, 78) etant a la pression de fluide est superieure a I'aire de sur- orientes de facon que le tiroir (66) puisse etre face du poussoir de soupape (16) exposee a la se- deplace de telle maniere que le canal (80) soit conde cavite soumise a la pression de fluide.

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FIG. 2D