Abstract:
A valve spring assembly includes a hollow valve spring plate and a locking element retained by a retainer both received in the interior of the hollow valve spring plate. The locking element is removable from the valve spring plate while the retainer is received by the valve spring plate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a valve spring assembly. 
     Known valve spring assemblies include a valve spring plate which can be mounted to a valve stem and which supports a valve spring. The valve spring plate is retained on the valve stem by means of locking means, such as clamping cones or retaining rings, etc. Such valve spring assemblies, valve spring plates and installation methods are used in the manufacture of drives, machines or vehicles. 
     German patent 44 21 408 shows a valve spring assembly with a hollow valve spring plate and a valve spring that engages a rim region of the valve spring plate, which can be attached to the stem of a valve of an internal combustion engine. In order to secure the valve spring plate to the valve stem, the valve spring assembly is provided with a locking element that is formed by clamping cone halves. Retaining projections or brackets are provided on the valve spring plate to secure the locking element in an inner region of the valve spring plate against loss. 
     SUMMARY 
     Accordingly, an object of this invention is to provide a valve spring assembly which can be easily installed. 
     These and other objects are achieved by the present invention, wherein a valve spring assembly includes a hollow or sleeve-like valve spring plate and a locking element retained by a retainer. The valve spring plate and the retainer form a pre-assembled unit. These components can be installed in a single assembly cycle or together on a valve stem and just as simply removed from it again. It is not necessary to install the valve spring plate first, then to attach the locking element and then to secure these to the valve stem, for example, by a positive locking, connection or a non-positive locking connection. Instead, the valve spring assembly is installed on the valve stem and conducted along it until the locking element makes a locking connection with the valve stem. The valve spring plate is secured to the valve stem and is loaded by a valve spring. The valve spring plate is moved towards the locking element and can be secured by the locking element on the valve stem in the axial direction. In order to disassemble the valve spring assembly or the valve spring plate, the plate can be loaded against the force of the valve spring so that the locking element exits from the sleeve and thereby becomes accessible for the disassembly, for example, with the use of tools, such as a screwdriver. 
     The retainer may comprise a hinge and/or a spring which can fold over as a function of the load applied to it, so that the locking element can be withdrawn from the valve spring plate. Preferably, at least a portion of the retainer comprises an elastic component, such as a simple and low cost elastic plastic element or rubber element. 
     The retainer may be a removable component which may be clamped to the valve spring plate or otherwise secured. The retainer can be formed onto the valve spring plate, such as in the form of an elastic sheet metal component. Alternatively, the retainer may be permanently connected to the plate by adhesive, or welding, or the like. The retainer may be a one-piece component or a multi-piece unit. Preferably, it has an inwardly projecting lip clamped in a groove formed in an inner surface of the plate. 
     Preferably, the valve spring plate has a contact surface which engages the locking element to prevent axial movement of the valve spring plate in one direction. Preferably, the contact area is formed by a shoulder on the plate. The shoulder may be a gradual or abrupt transition. 
     The valve spring plate may not interact directly with the valve spring, but instead with further components arranged between the valve spring and the valve spring plate. However, the valve spring plate includes a contact area for the valve spring. The contact area is preferably arranged in a rim region of the valve spring plate, or is formed by it, since the valve spring is usually configured as a helical spring through which a valve stem can extend. 
     Preferably, the valve spring plate includes means for securing the valve spring, so that the valve spring is integrated into the valve spring assembly in such a way that it can be installed together with the valve spring plate and the locking means. Preferably, the plate has a hook-shaped rim which surrounds an opening which receives the valve spring, so that the plate engages and is clamped to an end of the valve spring plate. Alternatively, the spring may be non-removably coupled to the plate, such as by welding, soldering or the like. The spring may also be retained by a simple and cost effective conventional retaining ring, or by retaining disks or snap rings or by corresponding components that preferably interact with an encircling groove in the valve stem. 
     Preferably, the valve spring assembly includes a valve stem seal which is removably fastened to the valve spring plate so that the valve stem seal can be installed together with the valve spring assembly. Later, it can be separated from the valve spring plate and placed in an operating position. 
     The valve spring plate includes a recess which releasably receives the valve stem seal. Alternatively, the valve spring plate may have a projection which is releasably received by a recess formed in the valve stem seal. The recess is designed so that the valve stem seal is released when it has reached its operating position on the cylinder head, wherein the valve stem seal is secured on the cylinder head by a clamped connection, by friction locking, or in other ways. 
     The valve spring plate may be a single individual part and can be combined with the remaining components of the valve spring assembly in a pre-assembly station and then applied together with these other components as an installation unit on a valve stem of an internal combustion engine. 
     The valve spring assembly may be manually or automatically installed. By combining several components in a valve spring assembly which can be brought to an installation site, the installation process can be accelerated or performed by means of a robot, for example, with a magazine or an automated supply arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial sectional view of a valve spring assembly with a valve stem extending through a cylinder head of an internal combustion engine; and 
     FIGS. 2-5 are partial sectional views of the valve spring assembly of FIG. 1, showing individual stages during installation of the valve spring assembly on the valve stem. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a valve stem  10  of an intake or exhaust valve (not shown in any further detail), extends through a portion of the cylinder head  12  of an internal combustion engine (not shown). Above the valve stem  10  a valve spring assembly  14  is shown as removed from or not installed on the valve stem  10 . 
     The valve spring assembly  14  includes a valve spring  16 , a valve stem seal  18 , a valve spring plate  20 , a locking element or locking ring  22 , as well as an elastic retainer  24 . The retainer  24  is a hollow annular member and surrounds a bore or opening which extends completely through retainer  24 . The valve spring  16  in the installed condition is brought into contact at one end with the cylinder head  12  and at the other end with an underside  25  of the valve spring plate  20 . 
     The valve spring plate or sleeve  20  is a collar-shaped, rotationally symmetrical shaped component, and has a central, approximately circular recess  26 . Recess  26  has a diameter, in the region  28  facing the valve stem  10 , which provides a sliding fit with the valve stem  10 . Region  30  of recess  26  has a diameter which is greater than the first diameter, thereby forming a shoulder or a contact surface  27  therebetween. The diameter of recess  26  preferably increases with increasing distance from the contact surface  27 . 
     An outer rim  32  of the valve spring plate  20  engages and supports the valve spring  16  on the valve spring plate  20 , and has a hook-shaped cross-section which surrounds an annular opening which faces downwardly towards bottom surface  25  of the valve spring plate  20 . An end  34  of the valve spring  16  engages the rim  32  and is clamped on the valve spring plate  20 . 
     A recess  36  or circular depression is formed in the bottom surface  25  of valve spring plate  20 . The recess  36  has a diameter so that there can be a releasable clamped connection between the recess  26  and the valve stem seal  18 . Preferably, the valve stem seal  18  is made from an elastic material or an elastic plastic material so that it performs a desired sealing function. 
     The valve stem  10  and the cylinder head  12  are configured in the usual manner, where the valve stem  10  includes an encircling groove  38  in an upper region facing away from the cylinder head  12 . 
     A method for installing the valve spring assembly on the valve stem  10  is as described in connection with FIGS. 2 through 5. 
     Referring now to FIG. 2, the valve spring assembly  14  has been applied to the valve stem  10 , so that the valve spring  16  is brought into contact with the cylinder head  12 , where no further force is applied. In this first position the locking element  22  is located above the groove  38 , it is arranged within the sleeve-shaped valve spring plate  20 . 
     Referring now to FIG. 3, the valve spring plate  20  is moved towards the cylinder head  12  against the force of the valve spring  16 . The locking element  22  also moves downward since it is carried along by the retainer  24 . 
     If the valve spring  16  is compressed in such a way that the locking element  22  is brought to the groove  38  of the valve stem  10 , then the locking element  22  is brought into engagement with the groove  38  upon a further movement of the valve spring plate  20  in the direction of the cylinder head  12 . The locking element  22  is preferably configured in the form of a retaining ring or a spring ring. This engagement generates an audible click that, in the case of a manual installation, can indicate to an operator that the locking element  22  has been brought into position. In order to move the valve spring plate  20  further, a force must now be applied which is sufficient to deflect the elastic retainer  24  so that the locking element  22  can be moved past it without being brought out of engagement with the groove  38 . This further movement of the valve spring plate  20  is performed in order to move the valve stem seal  18  further towards the cylinder head  12  so that it can clampingly engage a correspondingly portion of the cylinder head  12 . 
     Referring now to FIG. 5, the valve stem seal  18  remains engaged with the cylinder head  12  after the valve spring plate  20  has moved away from the cylinder head  12 . The valve spring assembly  14  is now in its operating position wherein the valve spring plate  20  is released form valve stem seal  18 . If the valve spring  16  urges the valve spring plate  20  away from the cylinder head  12 , then the locking means  24  is again moved into contact with the locking element  22 . The valve spring  16  and the retainer  24  are preferably dimensioned to assure that the retainer  24  deflects and allows the locking element  22  to move past it and enter into the interior region of the plate  20 . The valve spring  16  moves the valve spring plate  20  on the valve stem  10  contact surface  27  of the valve spring plate  20  engages the locking element  22 . Further expansion of the valve spring  16  would result in movement of the valve stem  10  relative to cylinder head  12 , and the valve spring assembly  14  is ready for operation. 
     To un-install the valve spring assembly  14  from the valve stem  10 , the valve spring plate  20  is moved against the force of the valve spring  16  and towards the cylinder head  12 , until the locking element  22  is removed from the valve spring plate  20 . The locking element  22  is now accessible and can be removed easily from the valve stem  10 , for example, with the use of a screwdriver or another appropriate tool. Now, the valve spring assembly  14  and, in particular, the valve stem seal  18  can be taken off or removed from the valve stem  10  or the cylinder head  12 . 
     The process described above can be performed manually. But it could also be performed automatically, since the valve spring assembly  14  includes in a pre-assembled unit all components that are to be attached to the valve stem  10 . 
     While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.