Seal for a rod sliding against the action of elastic means, in particular an internal combustion engine valve stem

Abstract: A seal (1) for a rod (2) sliding against the action of elastic means (22), in particular the stem (2) of an internal combustion engine valve (3); the seal (1) presenting a sleeve-shaped elastomeric element (5) consisting of a sealing portion (6) cooperating with the stem (2), and an assembly portion (7); and a stiffener (12) formed integral with the assembly portion (7); the stiffener (12) presenting a portion (21) for supporting and centering the elastic means (22) and extending radially and axially outwards of the elastomeric element (5) and on the opposite side in relation to the sealing portion (6).

Description: The present invention relates to a seal for a rod sliding against the action of elastic means, in particular an internal combustion engine valve stem. Known elastomeric seals for preventing leakage of the supply system lubricating oil into the combustion chamber of the engine substantially consist of a substantially sleeve-shaped sealing portion, and a sleeve-shaped assembly portion fitted in a seat formed externally on the valve stem guide. To reinforce the assembly portion and so ensure effective seating of the seal, the assembly portion normally presents a rigid metal stiffener, normally outside the co-molded assembly portion, and which provides for ensuring correct positioning of the seal. To prevent wear on the cylinder head, the ends of the valve stem contrast springs facing the cylinder head normally rest on metal caps in turn resting directly on the cylinder head. The above solutions are not without drawbacks. Due to vibration and/or particularly after prolonged use, the seal tends to work out of the seat, thus resulting in impaired sealing performance, while the metal caps, by virtue of not being fitted to the cylinder head, are a frequent cause of noise and vibration. Also the seal known from EP-A-0 459 022 though simpler, is not free from the described drawbacks. It is an object of the present invention to provide a seal designed to overcome the aforementioned drawbacks, and which provides for troublefree, low-cost, even automated, assembly. According to the present invention, there is provided a seal for a rod sliding against the action of elastic means, as claimed in Claim 1 and a device for the guide and the sealing of a stem as claimed in claim 3. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Fig.1 shows a front section of a sliding rod seal in accordance with the present invention; Fig.2 shows an enlarged front section of a detail on the Fig.1 seal. Number 1 in the accompanying drawings indicates a seal for a sliding rod 2, and particularly in the example shown for the stem 2 of an intake or exhaust valve 3 (shown only partially in Fig.1) of an internal combustion engine of which the cylinder head 4 is shown partially. Seal 1 comprises a substantially sleeve-shaped elastomeric element 5, in turn comprising a sealing portion 6 cooperating with stem 2 of valve 3, and an assembly portion 7 designed to fit inside a substantially cylindrical seat 8 on the guide element 11 of stem 2. A stiffener 12 is provided inside and formed integral with assembly portion 7. Sealing portion 6 presents two inner projecting sealing lips 13 cooperating in sliding manner with the outer surface 14 of stem 2 of valve 3, for preventing oil from leaking towards cylinder head 4 and into the engine through guide element 11 of stem 2. To improve sealing between lips 13 and surface 14 of stem 2, sealing portion 6 presents an outer annular pressure element, e.g. an annular spring 15, for exerting predetermined radial pressure on sealing lips 13 between which an oil collecting chamber 16 is formed. According to the present invention, stiffener 12 is co-molded with elastomeric element 5, and comprises, outside element 5, a portion 21 for supporting and centering a spring 22 contrasting axial movement of stem 2 of valve 3. Supporting and centering portion 21 extends radially and axially outwards in relation to elastomeric element 5, and on the opposite side in relation to sealing portion 6. According to the present invention, supporting and centering portion 21 in turn presents a first substantially flat supporting surface 23 designed to rest on a corresponding flat surface 24 of cylinder head 4; while a second surface 25, opposite surface 23, supports end 26 of contrast spring 22. In use (Fig.2), supporting and centering portion 21 is thus gripped between cylinder head 4 and end 26 of spring 22, and, via stiffener 12, provides for maintaining assembly portion 7 in the design position inside seat 8 and, consequently, for maintaining sealing portion 6 contacting surface 14 of stem 2. In particular, supporting and centering portion 21 presents a substantially S-shaped radial section, and comprises a first portion 31 blending with stiffener 12 and projecting radially from elastomeric element 5, a second cylindrical portion 32 for centering spring 22 and substantially coaxial with sealing portion 7, and a peripheral supporting portion 33 substantially perpendicular to cylindrical centering portion 32 and having surfaces 23 and 25 on either side. The advantages of the present invention will be clear from the foregoing description. In particular, the portion of the seal for supporting and centering the coil spring is fixed directly to the assembly portion stiffener and co-molded directly with the elastomeric element, thus enabling the seal (which is gripped inside the seat by the spring) to be maintained in the required position, and automatic centering of the coil spring. The supporting portion also provides for dispensing with the spring caps, thus enabling low-cost automated assembly of the seal, and overcoming the noise problem typically associated with spring caps.

Claims: A seal (1) for a rod (2) sliding against the action of elastic means (22), in particular the stem (2) of an internal combustion engine valve (3); the seal (1) comprising: a substantially sleeve-shaped elastomeric element (5), in turn comprising a sealing portion (6) cooperating with said stem (2), and an assembly portion (7) designed to fit inside a seat (8) on a guide element (11) for said stem (2); and a stiffener (12) formed integral with said assembly portion (7); said seal (1) further comprising a cylindrical centering portion (32) substantially coaxial with said sealing portion (6), for centering said elastic means (22) and, in combination, a peripheral supporting portion (33) substantially perpendicular to said cylindrical centering portion (32) and comprising a first shoulder surface (23) faced in the direction of introduction of said assembly portion (6) in said seat (8) and a second shoulder surface (25), opposite to the first one, able to receive and support said elastic means (22); said supporting and centering portions (33,32) being a one piece with the stiffener (12) of the assembly portion (7); said portions (33,32) being connected to said stiffener (12) via a blending portion (31) projecting radially from said elastomeric element (5) and forming therewith a portion (21) of the stiffener (12) having substantially S-shaped radial section and extending radially and axially outwards in relation to said elastomeric element (5), and on the opposite side in relation to said sealing portion (6); characterized in that said stiffener (12) is co-molded with said elastomeric element (5) and embedded inside the same; said substantially S-shaped portion (21) of the stiffener (12) extending outwards of said elastomeric element (5). A seal (1) as claimed in Claim 1, characterized by the fact that said supporting and centering portion (21) presents said first (23) and second (25) surfaces on either side. Device for the guide and the sealing of a stem (2) of an internal combustion engine valve (3), comprising a guide element (11) fitted integrally inside a cylinder head (4) of the engine, a coil spring (22) coaxial with said stem (2) and with said guide element (11) and resting on said cylinder head (4), said stem (2) sliding within said guide element (11) against the action of said coil spring (22), and a seal (1) comprising an elastomeric sealing element (5), in turn comprising a sealing portion (6) cooperating with said stem (2), and an assembly portion (7) designed to fit inside a seat (8) on said guide element (11) and a stiffener (12) for reinforcing said elastomeric element (5); said seal (1) further comprising a cylindrical centering portion (32) substantially coaxial with said sealing portion (6), for centering said coil spring (22) and, in combination, a peripheral supporting portion (33) substantially perpendicular to said cylindrical centering portion (32) and comprising a first shoulder surface (23) faced in the direction of introduction of said assembly portion (7) in said seat (8) and a second shoulder surface (25), opposite to the first one, able to receive and support said elastic means (22); said portions (33,32) being connected to said stiffener (12) via a blending portion (31) projecting radially from said elastomeric element (5) and forming therewith a portion (21) having substantially S-shaped radial section and extending radially and axially outwards in relation to said elastomeric element (5), and on the opposite side in relation to said sealing portion (6); characterized in that said supporting and centering portions (33,32) are a one piece with the stiffener (12), which is formed integral with the assembly portion (7), said stiffener (12) being co-molded with said elastomeric element (5) and embedded inside the same; said substantially S-shaped portion (21) of the stiffener (12) extending outwards of said elastomeric element (5) so as to be gripped between said cylinder head (4) of said engine and said coil spring (22).

Inventors: GAMBINO GIUSEPPINO, VIAZZI ROBERTO, GAMBINO, GIUSEPPINO, VIAZZI, ROBERTO
Applicants: RFT SPA, RFT S.P.A.
Application year: 1993
Main classification: F01L3
IPC codes: F01L3