A valve control system for a variable-timing internal combustion engine, particularly for an engine with several valves per cylinder

Abstract: A control system (1) for valves (2) for a variable-timing internal combustion engine, particularly for an engine with several valves (2) per cylinder (6), of the type in which a camshaft (3) carries at least one cam (4) having a profile which varies along the axis of the shaft, and a control device (5) interposed between the cam (4) and at least one duty valve (2) of a cylinder (6); the control device (5) is constituted by a cam follower (14) cooperating with a peripheral surface (15) of the cam (4) and a substantially T-shaped rocker (18) which includes a central portion (21) having a support saddle (16) for the cam follower (14) on its upper surface and beneath it a seat (22) for fixing to a fulcrum (25) for the rocker (18) carried by a head (11) of the engine, and a pair of side arms (31) which bear against the stems (34) of respective homologous valves (2) of the cylinder (6).

Description: The present invention relates to a valve control system for a variable-timing internal combustion engine, particularly for an engine having several valves per cylinder. Valve control systems for internal combustion engines are known e.g. from EP-A-0 263 794 and JP-A-59 103 907, which enable the lift of the valves to be adjusted in dependence on the running condition of the engine (variable timing systems) and/or to control more than one valve with the same cam. For example, the camshaft may have conical cams with linear profiles which vary along the axis of the camshaft; an axial movement of the camshaft, by means of a power-assisted control system, alters the cam-profile in contact with the valve stem, thereby altering the lift pattern of the valve. Although they are highly efficient, such control systems have the disadvantage of requiring the insertion of an adaptor element between the cam and the valve stem and its associated tappet so as to compensate for the conical shape of the cam itself. The need for this adaptor element makes the valve-control mechanism more complicated to manufacture, often increases the reciprocating masses thereby making the dynamic response of the valves less rapid and also makes it difficult, if not impossible, to use automatic systems to compensate for any clearances that may form as a result of wear between the cams and tappets. The object of the present invention is to provide a valve control system for a variable-timing internal combustion engine which is free of the disadvantages described and which, in particular, enables the reciprocating masses involved in the opening and closing movements of the valves to be minimized, enables the number of control members to be reduced relative to the total number of valves to be controlled and enables automatic clearance-compensation systems to be fitted easily. On this basis, the present invention provides a valve control system for a variable-timing internal combustion engine, particularly for an engine with several valves per cylinder, of the type disclosed in Claim 1. In order better to understand the invention, there follows a non-limitative description of one embodiment, with reference to the appended drawings, in which: Figure 1 is a sectioned side elevation of a valve control system for a variable-timing internal combustion engine constructed according to the present invention; Figure 2 is a partial front elevation of the valve-control system illustrated in Figure 1; and Figure 3 is a plan of a detail of the valve-control system illustrated in Figure 2. With reference to Figures 1 to 3, a system is indicated 1 for the control of the valves 2 of a variable-timing internal combustion engine, of which only one head 11 is illustrated for the sake of simplicity. The control system 1 is made up substantially of a camshaft 3 having at least one cam 4 with a profile which varies along the axis of the camshaft 3 itself, and of a control device 5 interposed between the cam 4 and a duty valve 2 of a cylinder 6 of the engine, each of the valves 2 being arranged in a respective valve seat 7 in direct communication with the cylinder 6 and being provided with a return spring 8 packed between the head 11 of the engine and a washer 12 securely fixed to the valve 2 itself by respective clamping cotters 13. The control device 5 includes in turn a cam follower 14 which cooperates with a peripheral surface 15 of the cam 4 and with a support saddle 16 for the cam follower 14. According to the present invention, the control device 5 is constituted essentially by a substantially T-shaped rocker 18 which includes a central portion 21 on the upper surface of which is formed the support saddle 16 for the cam follower 14 and on the underside of which is a seat 22, constituted by a hemispherical recess 23 formed at one end 24 of the central portion 21, for fixing to a fulcrum 25 defined by a ball-headed pin 26 engaging the seat 22 and carried by the head 11 of the engine; also at the end 24, the rocker 18 has an axially-projecting rudder element 27 engaged in a cooperating guide element 28 formed on the head 11 of the engine. As well as the central portion 21, the rocker 18 includes a pair of side arms 31 which project in opposite directions from an end 32 of the central portion 21 opposite the end 24 and the connection seat 22; each arm 31 bears against an upper end 33 of a stem 34 of a respective homologous valve of the cylinder 6. According to the invention, the support saddle 16 extends along the entire length of the central portion 21 and is defined by a substantially semi-cylindrical recess 35 having an axis of symmetry A parallel to and coincident with a longitudinal axis of the central portion 21 of the rocker 18. The cam follower 14 is defined essentially by a pad 36 having a flat upper surface 37 which cooperates with the conical peripheral surface 15 of the cam 4, while a convex lower surface 38, which is substantially semi-cylindrical, cylindrical, has a profile which matches the recess 35 of the support saddle 16. According to the present invention, the ball-headed pin 26 is fixed securely to a hydraulic tappet 41 mounted in a seat 42 in the head 11, and having an axis of symmetry B which is substantially parallel to a corresponding axis of symmetry C of one of the stems 34 of the valves 2. An hydraulically-sealed supply duct 44 is formed in a portion 43 of the head 11 intermediate the guide element 28 for the rudder element 17 and the hydraulic tappet 41 for supplying lubricating oil under pressure both to the guide element 28 and to the hydraulic tappet 41. In use, as the hydraulic tappet 41 is fixed in its seat 42 formed in the head 11, it does not contribute its mass to the overall mass in reciprocating motion, but acts exclusively as a self-adjusting support for the ball-headed pin 26 onto which the rocker 18 for operating the valves 2 is fixed by means of the seat 22. The advantages provided by the present invention are apparent from the above description: besides providing automatic compensation for any clearance created through wear, thanks to the presence of the hydraulic tappet, such a valve control system for a variable-timing internal-combustion engine takes up less space and the masses in reciprocating motion are greatly reduced. The hydraulic tappet is in fact fixed in a suitable seat in the engine head instead of being fixed securely to a valve stem; this leads to a considerable reduction in the masses in reciprocating motion with the result that the valves accelerate faster making it possible to employ a cam with a highly defined profile, and thereby improve the filling of the cylinder with the air and fuel mixture and, as an end result, the performance of the engine itself.

Claims: A control system (1) for the valves (2) of a variable-timing internal combustion engine, particularly for an engine with several valves (2) per cylinder (6), of the type which includes a camshaft (3) with at least one cam (4) having a profile which varies along the axis of the camshaft (3), and a control device (5) interposed between the cam (4) and at least one duty valve (2) of a cylinder (6) of the engine, the control device (5) including in turn a cam follower (14) which cooperates with a peripheral surface (15) of the cam and a support saddle (16) for the cam follower (14), the control device (5) including a central portion (21) having the support saddle (16) for the cam follower (14) on its upper surface and a pair of side arms (31) projecting in opposite directions from the central portion (21), each of the arms (31) bearing against an upper end (33) of a stem (34) of a respective homologous valve (2) of the cylinder (6) whereby an end (24) of the central portion (21) of the control device (5) has an axially-projecting rudder element (27) engaged in a corresponding guide element (28) formed in the engine head (11) of the engine characterised in that the control device (5) consists of a rocker (18) which is substantially T-shaped, the pair of side arms (31) projecting in opposite directions from a first end (32) of the central portion (21), the central portion (21) has a seat (22) beneath it for fixing to a fulcrum (25) for the rocker (18) carried by a head (11) of the engine, this seat (22) being located in a second end (24) of the central portion opposite the first end (32), the rudder element (27) is located at said second end (24) of the central portion (21) of the rocker arm (18) in correspondence with the fulcrum (25). A control system (1) for valves (2) according to Claim 1, characterized in that the fixing seat (22) consists of a hemispherical recess (23) formed in said second end (24) of the central portion (21) of the rocker (18), the fulcrum (25) being defined by a ball-headed pin (26) engaged in the seat (22). A control system (1) for valves (2) according to Claim 2, characterised in that the support saddle (16) extends along the entire length of the central portion (21) and is defined by a semi-cylindrical recess (35) having an axis of symmetry (A) parallel to and coincident with the longitudinal axis of the central portion (21) of the rocker (18); the cam follower (14) being defined by a pad (36) having a flat upper surface (37) cooperating with a conical peripheral surface (15) of the cam (4) and a convex lower surface (38) which is substantially semi-cylindrical and has a profile which matches the semi-cylindrical recess (35) of the saddle (16). A control system (1) for valves (2) according to any one of Claims 2 and 3, characterised in that the ball-headed pin (26) is fixed securely to a hydraulic tappet (41) mounted in a seat (42) in the head (11), the said seat (42) having an axis (B) parallel to a corresponding axis of symmetry (C) of the stems (24) of the valves (2). A control system (1) for valves (2), according to Claim 4, characterised in that the engine head (11) of the said engine has a supply duct (44) for pressurised lubricating oil, the duct (44) being formed in a portion (43) intermediate the guide element (28) and the hydraulic tappet (41) and being hydraulically connected to both the latter.

Inventors: MARTINELLI PAOLO, MOLINARI GIUSEPPE
Applicants: FERRARI SPA, FERRARI S.P.A.
Application year: 1993
Main classification: F01L1
IPC codes: F01L1, F01L13, F02F1