Automatic timing variation device for an internal combustion engine

Abstract: The proposed device comprises a cylinder (16) rigid with a camshaft drive pulley (15), and a piston (33) restrained to said cylinder (16) and camshaft (13) by helical groove connections and prismatic pair connections which, on command, allow said camshaft (13) to undergo rotation relative to said pulley (15).

Description: This invention relates to a device far automatically varying the timing, or angular position, of a camshaft relative to the crankshaft of an internal combustion engine. In internal combustion engines the timing of the camshafts and hence of the intake and exhaust valves is normally optimised for a determined engine speed, and in the case of fixed timing it is hardly adequate and sometimes only just acceptable at other speeds. Consequently either a compromise value is adopted or devices are used which enable it to be automatically varied in either a continuous or discrete manner. Devices able to continuously vary the timing are generally fairly complicated, while the discrete variation types are more simple but still fairly satisfactory because they enable timing values to be used which are optimised for one or another region of the engine operating range. At idling and at low loads the cross-over (simultaneous opening of the intake and exhaust valves) must be short to prevent the exhaust gas flowing back into the explosion chamber or into the intake ducts by virtue of the intake vacuum and/or the exhaust overpressure. The main advantage obtained by short cross-over is reduction in fuel consumption, reduction in harmful exhaust emission, and uniform engine idling. At high speed under full admission conditions a long cross-over is necessary to improve cylinder filling by utilising the inertia and resonance of the fluids in the intake and exhaust ducts. Finally, at close to maximum speed under full admission conditions it is advantageous to considerably retard the closure of the intake valves to exploit the inertia and resonance of the fluid in the intake ducts. The benefits are a higher torque, high maximum power and optimised fuel consumption. Discrete control devices of this type are described in US-A-4 231 330 and FR-A-2 526 858. A further device is known from EP-A-0 147 209 and has the features of the preamble of claim 1. In this known device the end of the camshaft carries a driven member which is secured frontally to said end and has a portion rotatably supporting the annular end wall of the cylinder and another portion having a quadrangular cross section progressively rotated about the central axis of the driven member. Said latter portion mates with a quadrangular bore of the piston extending straight in the axial direction, so defining a helical groove coupling by which the axial displacement of the piston under pressure fluid causes a relative rotation between the crankshaft and the camshaft. Owing to the construction of this known device, considerable labour is required for machining the helically developing coupling with the necessary precision and for orderly assembling the numerous parts of which the complete device is composed. DE-A-3 126 620 discloses a valve timing device wherein the journal of the camshaft has integral projecting portions including an end portion and an intermediate portion, the end portion being externally coupled with the piston and being internally hollow to rigidly house an axial appendix of the annular end wall which rotatably supports the cylinder with the pulley rotated by the crankshaft. The same end wall frontally supports a control device controlling operation of the piston by a centrifugal mass responsive to the rotational speed of the camshaft. The piston is coupled both with the cylinder and with said end portion by toothed couplings. Also this device is of complex construction and assembling. The object of the present invention is to provide an automatic timing variation device for an internal combustion engine which as in the case of those of the cited prior documents is particularly efficient and reliable but which is considerably simpler in its design and assembly, is of reduced overall size, weight and cost, and provides considerable timing accuracy. This is attained by a device having the features of claim 1. Characteristics and advantages of the invention are described hereinafter with reference to the accompanying Figures 1 to 4 which show a preferred embodiment of the invention by way of non-limiting example. Figure 1 is a partial axial section through a timing variation device according to the invention; Figure 2 is a partial section on the line II-II of Figure 1; Figure 3 is a partial section on the line III-III of Figure 1; Figure 4 is a modification of the detail of Figure 2. In Figure 1 the reference numeral 10 indicates overall an internal combustion engine head, only part of which is shown. In the engine head there is provided a bearing 11 which supports a journal 12 of the camshaft, which is indicated overall by 13 and is also shown only partly. The camshaft 13 is for example that which controls the engine intake valves. The reference numeral 15 indicates a toothed pulley which is rotated by the crankshaft, not shown, by way of a toothed belt, also not shown. The reference numeral 16 indicates overall a cylinder formed from an annular supporting end wall 18 and a cylindrical side wall 19 welded at 17, for example by a laser process. This enables the inner surfaces of the wall 19 to be machined to design precision and tolerances before fixing to the wall 18. The cylinder 16 is housed in a suitable seat 20 of the pulley 15 by way of a seal ring 21, and the pulley 15 is fixed axially onto a front face of the end wall 18 by screws such as that indicated by 22, by way of a safety plate 23 between the screw heads and the pulley 15. The pulley 15 comprises slots 24 such as that shown in Figure 1, which correspond to threaded bores 25 in the wall 18 and holes 26 in the safety plate 23 to allow precise adjustment of the timing of the camshaft 13 with respect to the pulley 15. To ensure that the timing obtained on locking the cylinder 16 to the pulley 15 is maintained, the plate 23 is upset after assembly into a suitable seat 14 in the pulley 15. The cylinder 16 is supported rotatably in a cantilever manner by an end portion 27 of the journal 12 of the camshaft 13 by way of the annular end wall 18, which is rotatably supported on the end portion 27 externally around thereof and is fixed axially to said camshaft 13 by a screw 28 and a washer 29. The cylindrical side wall 19 of the cylinder 16 is provided internally with helical grooves 30 which engage with corresponding helical grooves 31 provided in the skirt 32 of a piston 33, to form a helical groove coupling. The head portion 34 of the piston 33 is annular and is provided with a bore 35 for being axially slidable on an intermediate portion 36 of the journal 12 of the camshaft 13. As visible in Fig. 1, the portions 27 and 36 are integral projecting portions of the journal 12 of the camshaft 13. The bore 35 comprises preferably at least two diametrically opposite flat walls 37 which slidably engage corresponding diametrically opposite flat walls 38 of the intermediate portion 36 to form a prismatic coupling, as shown in Figure 2. The two diametrically opposite flat walls 37, 38 can be connected by respective opposite portions of a cylindrical wall, each of said portions directly connecting both the opposite flat walls 37, 38. The bore 35 and portion 36, which have transverse dimensions greater than the portion 27, can be provided with several engageable flat walls, such as those indicated respectively by 39 and 40 in Figure 4, which shows an embodiment in which said bore 35 and portion 36 are of hexagonal cross-section. The reference numeral 41 indicates elastic means in the form of a spring, interposed between the head 34 of the piston 33 and a shoulder 42 on the camshaft 13, to urge said piston 33 axially into a first stroke end position against the end wall 18 of the cylinder 16, the reference numeral 43 indicating a further shoulder on the camshaft 13 acting as a travel stop for the piston 33 in a second stroke end position. A variable-volume chamber indicated by 44 is enclosed between the head 34 of the piston 33 and the walls 18 and 19 of the cylinder 16. The chamber 44 is sealed by virtue of the tolerance used for the contacting surfaces of the walls of the bore 35 and portion 36 and for the surfaces of the wall 19 of the cylinder 16 and an annular projection 45 on the skirt 32 of the piston 33. In addition, any seepage of oil to the outside of the cylinder 16 is retained by a ring (of "corteco" oil lip seal type) 75 fixed in a suitable seat in the head 10. The chamber 44 communicates with a diametrical duct 46 provided in the camshaft 13 and branching from an axial duct 47 also provided in said camshaft 13. The duct 47 communicates by way of a duct 48 and an annular chamber 49 with a duct 50 provided in the engine head 10 as shown in Figure 3. The duct 50 can be connected to a feed duct 51 which receives pressurised oil iron the engine lubrication circuit, and to a discharge duct 52. In Figures 1 and 3 the reference numeral 53 indicates a lubrication circuit duct which feeds oil to the bearing 11. The ducts 50, 51, 52 communicate with corresponding ducts which open into a cylindrical cavity indicated by 54 and provided in a structure 55 fired to the head 10 by way of a seal gasket 56. A slide valve indicated overall by 57 is slidingly mounted in the cavity 54 to control communication between the ducts 50, 51, 52. The slide valve 57 comprises an internal cylindrical chamber 58 which communicates with annular chambers 62, 63, 64, by way of radial ducts 59, 60, 61. The slide valve 57 is balanced because the forces exerted by the oil on its walls have a zero resultant. The slide valve 57 is engaged by a spring indicated by 65 and a push rod indicated by 66 and operationally connected to the armature, not shown, of an electromagnet indicated overall by 67. The electromagnet 67 is fixed to the structure 55 by a rubber-metal sleeve 68 and screws 69. The electromagnet 67 is operationally connected, by a line 71, to a control centre 70 in the form for example of a programmed microprocessor. Signals indicative of chosen engine operating parameters such as engine r.p.m., throttle valve angle or angles, intake vacuum and intake air throughput, these being represented by the arrow 72 and 73, are fed to the control centre 70. The control centre 70 feeds no control signal to the electromagnet 67 until it senses that the chosen engine parameters, such as r.p.m, throttle valve angle or angles or air throughput are below predetermined threshold values. While the electromagnet 67 is deactivated the push rod 66 remains in its retracted position and the slide valve 57, under the action of the spring 65, assumes a first operating position as shown in Figure 3, in which it connects the duct 50 to the discharge duct 52. Thus the chamber 44 of Figure 1 is also connected to discharge and the piston 33 is urged axially by the spring 41 against the wall 18 of the cylinder 16, to assume the first stroke end position, as shown in Figure 1. Under these conditions the piston 33 effects a first timing, or angular position, between the camshaft 13 and pulley 15. Preferably this first timing is optimised for low r.p.m. values and reduced loads, and if the camshaft 13 is that which controls the engine intake valves, it can be chosen to provide minimum cross-over with the exhaust valves, so regularising the engine operation under these conditions. The control centre 70 feeds a control signal to the electromagnet 67 when it senses that the chosen engine parameters exceed said predetermined threshold values. The electromagnet 67 is activated and its armature urges the push rod 66 outwards so that it moves the slide valve 57 into a second operating position against the action of the spring 65, to connect the duct 50 to the feed duct 51 by way of the annular chamber 63. The chamber 44 of Figure 1 is thus connected to the pressurised oil feed and the action of the oil urges the piston 33 axially against the shoulder 43, overcoming the action of the spring 41. When the piston 33 slides axially to the cylinder 16 and camshaft 13, it also rotates within the cylinder 16 relative thereto because of the connection formed by the helical grooves 30 and 31, until it reaches its second stroke end position against the shoulder 43. As the piston 33 rotates, it rotates the camshaft 13 because of the connection formed by the engaging flat walls 37, 38 or 39, 40. Under these conditions, the piston 33 effects a second timing, or angular position, between the camshaft 13 and the pulley 15. This second timing value can for example be optimised for high-load r.p.m. values corresponding to maximum torque. Thus if the camshaft 13 is that which controls the intake valves, this value can be chosen to provide lengthy cross-over with the exhaust valves to exploit the inertia and resonance of the fluid column passing through the intake and exhaust ducts, to improve cylinder scavenging and filling with fresh charge under said conditions. With the proposed device it is possible to effect a third timing, equal to said first, for r.p.m. values and loads corresponding to maximum power. In this case the control centre 70 senses passage through further predetermined threshold values of the chosen engine parameters and interrupts the feed of said control signal to the electromagnet 67, so that the slide valve 57 returns to its first operating position under the action of the spring 65, to connect the chamber 44 to discharge 52. The piston 33 is urged by the spring 41 against the well 18 of the cylinder 16, and the camshaft 13 returns to assume said first timing value. This timing results in a retardation in the closure of the intake valves, which enables the inertia and resonance of the fluid present in the intake ducts to be exploited to increase cylinder filling under said maximum power conditions. The described device has various advantages by virtue of its very simplified design and assembly, its minimised size, weight and cost, its efficiency, a particularly rapid response and its reliability. It also allows very precise adjustment of the timing between the camshaft 13 and pulley 15. A further advantage of the device is its considerable flexibility, enabling it to be used on engines in which the camshaft is driven either by a toothed belt or by a chain.

Claims: A device for automatically varying the timing, or angular position, of a camshaft (13) relative to the crankshaft of an internal combustion engine, comprising a cylinder (16) rigid with a pulley (15) rotated by the crankshaft, and a piston (33) provided with restraint means which keep said piston (33) normally rotationally rigid with said cylinder (16) and with said camshaft (13) while allowing it to undergo axial movement relative to said cylinder (16) and camshaft (13) thereby causing a relative rotation between said cylinder (16) and said camshaft (13), the device also comprising elastic means (41) engaged with said piston (33) to urge it into a first stroke end position and valve means (57) arranged to feed and discharge pressurised fluid to and from said piston (33) in order to move it between said first stroke end position and a second stroke end position, said valve means (57) being controlled by a control centre (70) in accordance with chosen engine parameters and said restraint means consisting of a helical groove coupling (30,31) and a prismatic coupling (37, 38 or 39, 40), and wherein said cylinder (16) has an annular supporting end wall (18), characterised in that the journal (12) of the camshaft (13) has integral projecting portions including an end portion (27) and an intermediate portion (36), and in that said annular supporting end wall (18) is rotatably supported on said end portion (27) of the journal (12) externally around said end portion (27), in that said pulley (15) is fixed axially onto a front face of said annular supporting end wall (18), and in that an annular head portion (34) of said piston (33) is axially slidable on, and coupled by one of said couplings (30, 31; 37,38 or 39,40) to, said intermediate portion (36) of the journal (12). A device as claimed in claim 1, characterised in that the helical groove coupling (30,31) is provided between a skirt (32) of the piston (33) and a cylindrical side wall (19) of the cylinder (16), and the prismatic coupling (37, 38 or 39,40) is provided between a bore (35) of the annular head portion (34) and said intermediate portion (36) of the journal (12) of the camshaft (13). A device as claimed in claim 2, characterised in that the bore (35) of the annular head portion (34) of the piston (33) has at least two diametrically opposite flat walls (37 or 39) slidably engaging corresponding diametrically opposite flat walls (38 or 40) of said intermediate portion (36) of the journal (12) of the camshaft (13). A device as claimed in claim 3, characterised in that the bore (35) of the annular head portion (34) and the intermediate portion (36) of the journal (12) of the camshaft (13) each have a hexagonal cross section. A device as claimed in claim 3, characterised in that said two diametrally opposite flat walls (37; 38) are connected by respective opposite portions of a cylindrical wall, each of said portions directly connecting both said opposite flat walls (37; 38).

Inventors: COGHI GIOVANNI, LANATI PAOLO, SCAPECCHI PIER LUIGI, COGHI, GIOVANNI, LANATI, PAOLO, SCAPECCHI, PIER LUIGI
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1989
Main classification: F01L1
IPC codes: F01L1