Tensioning device for a chain drive

Abstract

A hydraulic tensioning device for a chain drive of an internal combustion engine, having a receptacle and having a tensioning piston which is guided in displaceable fashion in a cylindrical hollow space of the receptacle and which has a piston hollow space, wherein the piston hollow space together with the cylindrical hollow space of the receptacle forms a pressure chamber, and having a pressure relief valve unit arranged in the piston hollow space. The pressure relief valve unit is a preassembled structural unit and comprises a spring, a closing body and a valve seat and also a valve receptacle which surrounds the valve seat in a first subsection, wherein the valve receptacle forms an interference fit with the valve seat, and wherein the valve receptacle or the valve seat in a second subsection form an interference fit with the inner shell surface of the tensioning piston.

Claims

1. A hydraulic tensioning device for a chain drive of an internal combustion engine, the hydraulic tensioning device comprising: a housing with a receptacle having a cylindrical hollow space; a tensioning piston that is guided in the cylindrical hollow space of the receptacle, the tensioning piston including a piston hollow space; a pressure chamber formed by the piston hollow space and the cylindrical hollow space of the receptacle; a pressure relief valve unit arranged in the piston hollow space, the pressure relief valve unit comprises a preassembled structural unit including a spring, a closing body, a valve seat comprising a first sub-section and a second sub-section, and a valve receptacle surrounding the valve seat only in the first sub-section, the valve receptacle forms an interference fit with the valve seat, and the valve receptacle in the first sub-section forms an interference fit on a radially outer surface of the valve receptacle with an inner lateral surface of the tensioning piston.

2. The tensioning device according to claim 1, wherein the valve receptacle is comprised of plastic or metallic, non-hardened material.

3. The tensioning device according to claim 1, wherein the tensioning piston comprises a molded component.

4. The tensioning device according to claim 1, wherein the pressure relief valve unit includes a supply end and a discharge end, valve receptacle on the discharge end includes a recess and a surface for supporting the spring, and the valve receptacle holds the valve seat by the supply end.

5. The tensioning device according to claim 4, wherein the valve seat includes a recess on the supply end and a sealing surface for the closing body.

6. The tensioning device according to claim 1, wherein the valve seat has, in the first sub-section, a smaller outer diameter than in the second sub-section.

7. The tensioning device according to claim 1, wherein the closing body is a spherical shaped or plate shaped.

8. The tensioning device according to claim 1, wherein the valve receptacle has an engagement position on an end thereof holding the valve seat.

9. The tensioning device according to claim 1, wherein the tensioning piston or an inner lateral surface of the piston hollow space has a hardened construction and the valve seat is made from a metallic material, and the valve seat or a surface of the valve seat has a hardened construction.

10. The tensioning device according to claim 1, wherein the pressure relief valve unit comprises a ball as a closing body and an inner guide, and the inner guide is held by a base of the valve receptacle.

11. A hydraulic tensioning device for a chain drive of an internal combustion engine, the hydraulic tensioning device comprising: a housing with a receptacle having a cylindrical hollow space; a tensioning piston that is guided in the cylindrical hollow space, the tensioning piston including a piston hollow space; a pressure chamber formed by the piston hollow space and the cylindrical hollow space of the receptacle; a preassembled pressure relief valve unit arranged in the piston hollow space, the pressure relief valve unit comprises a preassembled structural unit including a spring, a closing body, a valve seat, and a valve receptacle surrounding at least a portion of the valve seat with an interference fit; wherein the valve seat has a first sub-section and a second sub-section, and the valve receptacle only surrounds the valve seat in the first sub-section, at least one of the valve receptacle or the valve seat form an interference fit with an inner lateral surface of the tensioning piston.

12. The hydraulic tensioning device of claim 11, wherein the valve receptacle is comprised of plastic or metallic, non-hardened material.

13. The hydraulic tensioning device of claim 12, wherein the inner lateral surface of the tensioning piston is formed of a hardened material.

14. The hydraulic tensioning device of claim 13, wherein the valve seat is made from a metallic material and at least a surface of the valve seat is hardened.

15. The hydraulic tensioning device of claim 11, wherein the valve receptacle engages with the interference fit with the inner lateral surface of the tensioning piston, and the plastic or metallic, non-hardened material permits an increased tolerance between an outside surface of the valve receptacle and the inner lateral surface of the tensioning piston in comparison to an interference fit between two hardened surfaces.

16. The hydraulic tensioning device of claim 11, wherein the valve seat includes a recess on a supply end and a sealing surface for the closing body on a discharge end.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in more detail with reference to embodiments, wherein reference is made to the drawings. Functionally identical elements of the explained embodiments are marked with the same reference symbols.

(2) FIG. 1 shows a hydraulic tensioning device in the longitudinal section,

(3) FIG. 2 shows a second embodiment of a hydraulic tensioning device,

(4) FIG. 3 shows a first embodiment of a pressure relief valve unit from FIG. 1,

(5) FIG. 4 shows an alternative embodiment of the pressure relief valve unit from FIG. 3,

(6) FIG. 5 shows a second embodiment of a pressure relief valve unit, and

(7) FIG. 6 shows an alternative embodiment of the pressure relief valve unit from FIG. 5.

DETAILED DESCRIPTION

(8) In FIG. 1, a hydraulic tensioning device 1 is shown for a chain drive of an internal combustion engine in a longitudinal section. A chain drive comprises a drive sprocket connected to the crankshaft, a driven sprocket connected to a camshaft, and a timing chain that connects the drive sprocket to the driven sprocket (not shown). Via the tensioned section of the drive timing chain, the driving moment of the crankshaft is transmitted to the camshaft. The timing chain is tensioned on its slack section, in order to be able to guarantee its functionality throughout its operating period. For this purpose, the timing chain is loaded with a tensioning force by the tensioning device.

(9) The hydraulic tensioning device 1 includes a receptacle 2 and a tensioning piston 3 that is guided so that it can move axially in a cylindrical hollow space 4 of the receptacle 2 and is held by a securing wire 33 in a transport position. The tensioning piston 3 is constructed with a piston hollow space 5 that forms, together with the cylindrical hollow space 4 of the receptacle 2, a pressure chamber 6. The tensioning piston 3 and receptacle 2 are constructed as a mechanical piston locking unit 25. A recess 7 is arranged at the end of the receptacle 2 that is opposite the opening for assembling the tensioning piston 3. The supply of hydraulic medium into the pressure chamber is realized via the recess 7. At the end of the tensioning piston 3 that is at a distance from the receptacle 2, there is another recess 8, by which some part of the hydraulic medium can be discharged. The ends form the supply and the discharge end 9, 10 of the tensioning device.

(10) At the supply end 9 of the tensioning device 1, within the pressure chamber 6 there is a check valve 11 that releases the hydraulic agent flow in the supply direction and prevents the discharge from the pressure chamber 6. At the discharge end 10 of the tensioning device, a pressure relief valve unit 12 is arranged within the piston hollow space 5. The pressure relief valve unit forms, with the inner lateral surface of the tensioning piston 3, which is hardened according to the purpose of the application, an interference fit, wherein the tensioning piston is constructed as an extruded part. The pressure relief valve unit further comprises a seat 13 for a main spring 14, whose pretensioning force acts on the receptacle 2 on one hand, which is connected rigidly to a component of the internal combustion engine (not shown), and whose pretensioning force acts, on the other hand, on the tensioning piston 3, whose discharge end 10 contacts a tensioning rail 26 of a chain drive (see, for example, FIG. 2).

(11) Such tensioning devices 1 for the chain drive of an internal combustion engine are used to tension the timing chain (not shown) and to damp oscillations that occur in the chain drive. For this reason, the cylindrical hollow space 4 of the receptacle 2 and the piston hollow space 5 of the tensioning piston 3 form the pressure chamber 6 that is filled with hydraulic medium when the chain drive is being operated. The hydraulic medium is usually supplied as engine oil from the general hydraulic medium circuit. A slow response under dynamic loading forms the return side of the hydraulic damping. Sudden tensioning of the slack section therefore can lead to excessive loading of the timing chain. The pressure relief valve unit 12 weakens the described effect and is simultaneously used for venting.

(12) A comparable tensioning device 1 is shown in FIG. 2. The pressure relief valve unit is pressed into a piston hollow space. The tensioning piston 12 is located in contact with a tensioning rail 26.

(13) In FIG. 3, the pressure relief valve unit 12 from FIG. 1 is shown in longitudinal section as a first embodiment. The pressure relief valve unit 12 includes a valve receptacle 15 that holds a valve seat 16, a valve plate 17 as a closing body, and a spring 18; in this way, a structural unit that can be preassembled is formed. The pressure relief valve unit exhibits a recess 19 on the valve seat 16 and another recess 20 on the valve receptacle 15, whereby a supply end and a discharge end 21, 22 of the pressure relief valve unit 12 are defined. On the discharge end 22, the valve receptacle 15 forms a spring seat 23 against which the spring 18 is supported. The spring loads the valve plate 17 with a pretensioning force, so that the valve plate 17 is supported against a sealing surface 24 of the valve seat 16; the recess 19 on the valve seat is closed in this way and released only in an operating state in which the pressure in the pressure chamber exceeds a predefined value.

(14) The valve seat 16 is formed of a metallic material and can have a hardened surface. The valve seat 16 is held on the supply end 21 by the valve receptacle 15, supported on the discharge end 22 against the valve receptacle and is surrounded by this after its assembly in a first sub-section 27. A second sub-section 28 connects to the first sub-section 27 of the valve seat 16, wherein the first sub-section 27 of the valve seat 16 has a smaller diameter than the second sub-section. In the first sub-section 27, the valve receptacle 15 forms, with the inner lateral surface of the tensioning piston 3, an interference fit, wherein the valve receptacle 15 has an engagement position 29 on the end holding the valve seat 16.

(15) In FIG. 4, an alternative construction of the pressure relief valve unit 12 is shown. The valve seat 16 has a first sub-section 27 and a second sub-section 28, wherein the valve seat 16 forms, in a second sub-section 28, an interference fit with the inner lateral surface of the tensioning piston 3. Otherwise, the construction corresponds to the design described in FIG. 3.

(16) An alternative construction is shown in FIG. 5. A pressure relief valve unit with a ball 32 as a closing body and with an inner guide 30 is shown, wherein the inner guide 30 is held by a base of the valve receptacle 15. The inner guide 30 is arranged along the entire axial length of the inner periphery of the valve receptacle 15 and has three axially extending connecting pieces 31. Otherwise, the construction corresponds to the design described in FIG. 3.

(17) In FIG. 6, another alternative construction is shown. A pressure relief valve unit with a ball 32 as the closing body and an inner guide 30 according to the embodiment of FIG. 5 is shown. Otherwise, the construction corresponds to the design described in FIG. 4.

LIST OF REFERENCE SYMBOLS

(18) 1 Tensioning device

(19) 2 Receptacle

(20) 3 Tensioning piston

(21) 4 Cylindrical hollow space of the receptacle

(22) 5 Piston hollow space

(23) 6 Pressure chamber

(24) 7 Recess

(25) 8 Recess

(26) 9 Supply end of the tensioning device

(27) 10 Discharge end of the tensioning device

(28) 11 Check valve

(29) 12 Pressure relief valve unit

(30) 13 Seat for a main spring

(31) 14 Main spring

(32) 15 Valve receptacle

(33) 16 Valve seat

(34) 17 Valve plate

(35) 18 Spring

(36) 19 Recess

(37) 20 Recess

(38) 21 Supply end of the pressure relief valve unit

(39) 22 Discharge end of the pressure relief valve unit

(40) 23 Spring seat

(41) 24 Sealing surface

(42) 25 Piston locking unit

(43) 26 Tensioning rail

(44) 27 First sub-section

(45) 28 Second sub-section

(46) 29 Engagement position

(47) 30 Internal guide

(48) 31 Connecting piece

(49) 32 Ball

(50) 33 Securing wire