Title of Invention

"HYDRAULIC TENSIONING DEVICE FOR A TRACTION MECHANISM DRIVE"

Abstract

The invention relates to a hydraulic tensioning device for a traction mechanism drive, in particular for a chain or belt drive of an internal combustion engine, comprising a tensioning piston which is guided in a displaceable manner in a cylinder, a pressure chamber which is determined by the tensioning piston and the cylinder and which is used to receive hydraulic fluid, and a pressure-relief valve which defines the pressure in the pressure chamber. The pressure-relief valve (8) comprises, at least partially, a pre-mounted component which can be inserted or is inserted (10) into the tensioning piston (4).

Full Text

Title of the invention Hydraulic tensioning device for a traction mechanism drive Field of the invention The invention relates to a hydraulic tensioning device for a traction mechanism drive, in particular for a chain drive or belt drive of an internal combustion engine, having a tensioning piston which is moveably guided in a cylinder, having a pressure space, which is defined by the tensioning piston and the cylinder, for holding hydraulic fluid, and having an overpressure valve which limits the pressure in the pressure space. Background of the invention DE 40 35 823 Cl describes a hydraulic tensioning device for traction mechanism drives such as chain drives or belt drives in internal combustion engines. A tensioning piston which is pressed against the chain is held in a longitudinally displaceable manner in a cylinder. The tensioning piston and the cylinder delimit a pressure space for holding hydraulic fluid. Tensioning movements of the tensioning piston in the direction of the chain cause an enlargement of the pressure space, with a non-return valve being opened, and it being possible for engine oil to flow into the pressure space, as a result of the vacuum generated therein. Under chain tension, the tensioning piston is pressed inwards, that is to say away from the chain, with the pressure space being reduced in size. As the tensioning piston moves inwards, engine oil is forced out of the pressure space through a leakage gap. The damping behavior of the tensioning device can be influenced by the size of the leakage gap. if the pressure in the pressure space becomes too great, the overpressure valve opens. A similar chain tensioner is known from DE 100 38 606 Al. The overpressure valve of said chain tensioner is composed substantially of a valve ball which is pressed by a pressure spring against a valve seat which is formed on a sleeve in the interior of the tensioning piston. If the pressure in the interior of the pressure space exceeds a defined limit, the valve ball is displaced counter to the force of the valve spring, so that the engine oil can escape out of the piston. As the chain tensioner is assembled, the piston is situated in the vertical position and the valve spring is inserted into the interior of the piston. Since the valve spring is not preloaded in this state, the valve ball must be balanced on the valve spring until further components are mounted. It is therefore very difficult to assemble a chain tensioner of said type using automated assembly machines without disruptions occurring. Summary of the invention The invention is therefore based on the problem of specifying a hydraulic tensioning device for a traction mechanism drive which can be assembled in a simple and reliable way. In order to solve said problem, in a hydraulic tensioning device for a traction mechanism drive of the type specified in the introduction, it is provided that the overpressure valve is composed at least partially of a pre-assembled modular unit which can be or is inserted into the tensioning piston. As a result of the use of the modular unit according to the invention which comprises at least parts of the overpressure valve, it becomes unnecessary to balance the valve ball on the valve spring during assembly. At the same time, it is automatically ensured as a result of the modular unit that the ball bears correctly against the valve spring; a further advantage is that the modular unit can be assembled using automated assembly machines. In a further embodiment of the invention, it can be provided that the modular unit comprises a holding body as a fixed valve element which can be or is connected to a cage which holds a moveable valve element. The modular unit therefore comprises the holding body, the cage and the moveable valve element; said components are pre-assembled and inserted as a modular unit into the tensioning piston. Here, the modular unit is designed such that it always bears correctly against the valve spring. In the tensioning device according to the invention, it is preferable for the moveable valve element to be embodied as a valve ball. Further embodiments are also conceivable,- the moveable valve element could, for example, be embodied as a cone. Particularly high reliability of the tensioning device according to the invention is obtained if a valve seat is formed on the holding body for the cage, which valve seat can be sealed off by the moveable valve element. In conventional tensioning devices, the valve seat is usually formed by a further separate component; it is possible in contrast thereto to dispense with an additional component in the tensioning device according to the invention, since the holding body both holds the cage for the moveable valve element and has the valve seat. In this context, it is also particularly advantageous for the tensioning device according to the invention to be able to have a throttle bore on the holding body. Said throttle bore has hitherto been formed by means of a separate part, which can now be dispensed with. Successful functioning of the tensioning device according to the invention can be ensured in that the cage has, at least on one side, one or more projections, by means of which the moveable valve element is held in the interior of the cage. As the modular unit is assembled, the moveable valve element can be pressed into the cage by means of the projections. The cage has no influence on the functioning of the moveable valve element but serves merely to secure the valve element during assembly. In a further embodiment of the invention, it can be provided that the cage is preferably of annular design and has two oppositely-situated projections at least on one side of the cage. The two projections prevent the moveable valve element from moving out of the cage. In order to further simplify the assembly of the modular unit of the tensioning device according to the invention, it can be provided that the oppositely-situated projections are formed on both sides of the cage. Since the cage is symmetrical about its central plane, it is possible to dispense with a complex positioning operation before inserting the moveable valve element. In the tensioning device according to the invention, the cage can be fastened in the holding body in such a way that the cage can be or is inserted into the holding body in a force-fitting and/or form-fitting manner. It is possible for the outer contour of the cage to be of non-circular, in particular polygonal, design, making it possible to dispense with further fastening elements.. In other embodiments, the cage can have retaining projections or retaining lugs on its outer side. It is alternatively or additionally possible for a securing element such as a securing ring to also be used to hold the modular unit, which comprises the holding body and the cage, in its position in the tensioning piston. It is particularly preferable for the cage of the tensioning device according to the invention to be composed of a plastic material. The holding body can be composed of metal, preferably of steel. Brief description, of the drawings Further advantages and details of the invention can be gathered from the following description of an exemplary embodiment and on the basis of the figures. The figures are schematic drawings, in which: Figure 1 shows a partially sectioned assembly drawing of the hydraulic tensioning device according to the invention; Figure 2 shows an exploded view of the tensioning device shown in figure 1; Figure 3 shows a modular unit having a holding body, a cage and a valve ball; and Figure 4 shows the modular unit shown in figure 3 after assembly. Detailed description of the drawings Figure 1 shows a partially sectioned assembly drawing of a hydraulic tensioning device. The tensioning device illustrated is a chain tensioner and serves to tension the chain drive of an internal combustion engine. The hydraulic tensioning device 1 is composed substantially o£ a housing 2 in which a tensioner hydraulic element housing 3 is inserted. A tensioner piston 4 is held in an axially displaceable manner in the interior of the tensioner hydraulic element housing 3. During operation, the front face of the tensioning piston 4 bears against the chain drive. The tensioner hydraulic element housing 3, which serves simultaneously as a cylinder for the tensioning piston 4, and the tensioning piston 4 form a pressure space which is filled with hydraulic fluid, usually engine oil. A main tensioner spring 5 is arranged in said pressure space, which main tensioner spring 5 is embodied as a pressure spring and presses the tensioning piston 4 outward against the chain to such a degree that equilibrium is obtained between the spring force and the pressing force. If the tensioning piston is displaced in the direction of the chain, the pressure space is enlarged; as a result of the vacuum generated therein, a non-return valve 6, which is indicated in figure 1, opens, so that engine oil can flow into the pressure space. If the chain becomes tense again, the tensioning piston 4 is pressed into the tensioner hydraulic element housing 3, causing the pressure space to be reduced in size. Engine oil is forced out of the pressure space through a leakage gap 7 between the tensioning piston 4 and the tensioner hydraulic element housing 3. During normal operation, the tensioning piston 4 therefore performs an oscillating movement, with it being possible for the piston displacement to be in the region of approximately 5/10 mm. Since the chain extends as it continues to age, the tensioning piston 4 is gradually pushed outward out of the tensioner hydraulic element housing 3, so that even a chain which has become elongated with age can be reliably If the pressure in the pressure space becomes too great, an overpressure valve 8 opens, so that engine oil can escape through an axial opening in the tensioning piston 4. The overpressure valve 8 comprises a pre-assembled modular unit 10, composed of a holding body, a cage and a valve ball, and an overpressure spring 9. Situated in the holding body is a throttle bore whose size influences the damping behavior of the tensioning device. Figure 2 shows an exploded view of the tensioning device 1 shown in figure 1. During assembly of the tensioning device 1, the overpressure spring 9 is inserted into the vertically aligned tensioning piston 4; the pre-assembled modular unit 10, composed of the holding body, the cage and the valve ball, can subsequently be placed onto the overpressure spring 9. The outer contour of the modular unit 10 is matched to the inner shape of the tensioner piston 4, so that the modular unit 10 is guided in the tensioner piston 4. In this way, the valve ball is automatically positioned and centered on the overpressure spring 9. The pre-assembled modular unit 10 can be assembled with the overpressure spring 9 to form the overpressure valve 8 using automated assembly machines. Figure 3 shows a modular unit having a holding body, a cage and a valve ball. The holding body 11 is of substantially annular design and is open at one side. The opposite side (in figure 3, the rear side) of the holding body 11 is closed off with the exception of a throttle bore 12. The outer contour of the holding body 11 is matched to the inner contour of the tensioner piston 4. A cage 13 can be inserted into the interior of the holding body 11, into which cage a valve ball 14 can be inserted. The valve ball 14 is preferably produced from steel, though the materials glass, ceramic or plastic are also conceivable. The cage 13 has, at one side or on both sides, two oppositely-situated radial projections which must be overcome as the valve ball 14 is inserted into the cage 13. The cage 13 can be produced from a plastic material, so that the projections 15 are pressed elastically to the side as the valve ball 14 is pressed in, before subsequently returning to their original position. In the illustrated exemplary embodiment, projections are also provided on the opposite side of the cage 13, so that the valve ball 14 can be assembled from both sides of the cage 13. In order to ensure that the cage 13 is held securely in the holding body 11, the cage 13 has a plurality of projecting retaining lugs 16 distributed over the periphery, which retaining lugs 16 lead to a form-fitting and force-fitting connection. In other embodiments, the outer contour of the cage 13 can be of non-circular, for example approximately polygonal, design. Figure 4 shows the modular unit 10 shown in figure 3 after assembly. The cage 13 serves merely to facilitate the assembly of the ball 14 by securing the latter. After assembly, the cage 13 does not fulfill any function. As a result of the cage 13. the ball 14 is automatically centered, so that the latter seals off a valve seat 17 which is formed in the interior of the holding body 11. The cage 13 is formed such that it does not impede the axial movement of the ball 14 as the valve opens and closes. Since the modular unit 10 is compact, it can also be used in small tensioner pistons. List of reference symbols 1 Tensioning device 2 Housing 3 Tensioner hydraulic element housing 4 Tensioning piston 5 Main tensioner spring 6 Non-return valve 7 Leakage gap 8 Overpressure valve 9 Overpressure spring 10 Modular unit 11 Holding body 12 Throttle bore 13 Cage 14 Valve ball 15 Projection 16 Retaining lug 17 Valve seat Patent claims 1. A hydraulic tensioning device for a traction mechanism drive, in particular for a chain drive or belt drive of an internal conibustion engine, having a tensioning piston which is moveably guided in a cylinder, having a pressure space, which is defined by the tensioning piston and the cylinder, for holding hydraulic fluid, and having an overpressure valve which limits the pressure in the pressure space, characterized in that the overpressure valve (8) is composed at least partially of a pre-assembled modular unit (10) which can be or is inserted into the tensioning piston (4). 2. The tensioning device as claimed in claim 1, characterized in that the modular unit (10) comprises a holding body (11) as a fixed valve element which can be or is connected to a cage (13) which holds a moveable valve element. 3. The tensioning device as claimed in claim 2, characterized in that the moveable valve element is embodied as a valve ball (14). 4. The tensioning device as claimed in one of claims 2 to 3, characterized in that a valve seat (17) is formed on the holding body (11), which valve seat (17) can be sealed off by the moveable valve element. 5. The tensioning device as claimed in one of claims 2 to 4, cTaaxacterized in that a throttle bore (12) is formed on the holding body (11). 6. The tensioning device as claimed in one of claims 2 to 5, characterized in that the cage (13) has, at least on one side, one or more projections (15), by means of which the moveable valve element is held in the interior of the-, cage (13). 7. The tensioning device as claimed in claim 6, characterized in that the cage (13). is preferably of annular design and has two oppositely-situated projections (15) at least on one side of the cage. 8. The tensioning device as claimed in claim 6 or 7, characterized in that the projection(s) (15) are formed on both sides of the cage. 9. The tensioning device as claimed in one of claims 2 to 8, characterized in that the cage (13) can be or is inserted into the holding body (11) in a force-fitting and/or form-fitting manner. 10. The tensioning device as claimed in one of claims 2 to 9, characterized in that the outer contour of the cage is of non-circular,, in particular polygonal, design. 11. The tensioning device as claimed in one of the preceding claims, characterized in that the cage (13) is composed of a plastic material. 12. The tensioning device as claimed in one of the preceding claims, characterized in that the holding body (11) is composed of metal, preferably of steel.

Documents:

1303-delnp-2007-abstract.pdf

1303-delnp-2007-Claims-(14-09-2012).pdf

1303-delnp-2007-claims.pdf

1303-delnp-2007-Correspondence Others-(14-09-2012).pdf

1303-delnp-2007-Correspondence Others-(20-08-2014).pdf

1303-delnp-2007-correspondence-others 1.pdf

1303-DELNP-2007-Correspondence-Others.pdf

1303-delnp-2007-Description (Complete)-(20-08-2014).pdf

1303-delnp-2007-description (complete).pdf

1303-delnp-2007-Drawings-(14-09-2012).pdf

1303-delnp-2007-drawings.pdf

1303-delnp-2007-Form-1-(14-09-2012).pdf

1303-delnp-2007-form-1.pdf

1303-delnp-2007-form-18.pdf

1303-delnp-2007-Form-2-(14-09-2012).pdf

1303-delnp-2007-form-2.pdf

1303-delnp-2007-Form-3-(14-09-2012).pdf

1303-delnp-2007-form-3.pdf

1303-delnp-2007-form-5.pdf

1303-delnp-2007-GPA-(14-09-2012).pdf

1303-delnp-2007-pct-210.pdf

1303-delnp-2007-pct-304.pdf

1303-delnp-2007-pct-306.pdf

1303-delnp-2007-pct-308.pdf

1303-delnp-2007-Petition-137-(14-09-2012).pdf

Form-1 (12-10-2012).pdf

Form-2 (12-10-2012).pdf

GPA (12-10-2012).pdf

Others (12-10-2012).pdf