WO2014026798A1

WO2014026798A1 - Automatic hydraulic tensioner

Info

Publication number: WO2014026798A1
Application number: PCT/EP2013/063983
Authority: WO
Inventors: Vladimir Baranov; Marco Kowalski; Bernd Hartmann
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2012-08-13
Filing date: 2013-07-03
Publication date: 2014-02-20
Also published as: DE102012223329A1

Abstract

The invention relates to an automatic hydraulic tensioner comprising - a tensioner housing (2) with a cylinder (8), - a piston (10) which is guided in the cylinder in a longitudinally movable manner and which delimits a hydraulic pressure chamber (11) together with the cylinder, - a hydraulic storage chamber (13) which is delimited by the tensioner housing and by the cylinder, - a non-return valve (12) which connects the storage chamber to the pressure chamber, said non-return valve closing when the pressure in the pressure chamber exceeds the pressure in the storage chamber, - and a pressure relief valve (15) which connects the pressure chamber to the storage chamber, said pressure relief valve opening when the pressure in the pressure chamber exceeds a specified threshold pressure. The automatic tensioner comprises a control valve (20) which can be switched between an open and a closed position and which allows a flow via the pressure relief valve in the open position and blocks the flow via the pressure relief valve in the closed position.

Description

Hydraulic automatic tensioner

The invention relates to a hydraulic automatic tensioner. This includes:

a tensioner housing having a housing bottom and a cylinder extending therefrom,

a piston which can be moved longitudinally in the cylinder and which delimits a hydraulic pressure chamber with the cylinder,

a hydraulic reservoir bounded by the tensioner housing and by the cylinder,

a non-return valve which runs on the housing bottom and connects the storage space with the pressure chamber, the check valve closing when the pressure in the pressure chamber exceeds the pressure in the storage space,

- And a pressure relief valve which connects the pressure chamber with the reservoir, wherein the pressure relief valve opens when the pressure in the pressure chamber exceeds a predetermined limit pressure.

Background of the invention

Such automatic tensioners are typically belt tensioners, which pretension the belt of the accessory drive of an internal combustion engine by means of a tensioning roller actuated by the belt tensioner. While the biasing force is generated by the force of a tensioner spring between tensioner housing and piston, the hydraulic part of the tensioner damps the vibrations of the belt drive by means of so-called leakage gap damping. When Einfahrbewe- movements of the piston in the cylinder and corresponding increase in pressure in the pressure chamber, a portion of the hydraulic fluid therein is pressed through the small leakage gap between the piston and cylinder back into the storage space. The case to be overcome throttle resistance corresponds to the damping of the tensioner.

In order to limit the maximum pressure in the pressure chamber and consequently to limit the operating maximum tension of the belt, it is known to make the piston hollow cylindrical and with a recess on the part of the pressure chamber. ren, in which a pressure relief valve is used. This opens when a limiting pressure in the pressure chamber is exceeded, so that the hydraulic fluid can relieve the pressure in the reservoir via the pressure relief valve and the pressure in the pressure chamber is essentially limited to this limit pressure. A hydraulic belt tensioner with limited reaction forces as a result of such a pressure relief can be seen, for example, from DE 10 2010 034 290 A1 and EP 2 101 082 A2.

Object of the invention

Proceeding from this, the present invention seeks to provide a hydraulic automatic tensioner of the type mentioned with an improved characteristic of the pressure relief. Summary of the invention

The solution to this is that the automatic tensioner comprises a switchable between an open and a closed position control valve, which allows in the open position, the flow through the pressure relief valve and prevents the flow through the pressure relief valve in the closed position. In other words, the pressure relief of the tensioner according to the invention can be locked as needed during operation, wherein in the locked state, the force-displacement map would correspond to the map of a comparable tensioner without pressure relief.

The adjustability of the pressure relief allows, for example, that the tensioner is operated during the starting process of the internal combustion engine like a tensioner without pressure relief with high reaction forces and accordingly high damping. This is particularly advantageous in internal combustion engine with start-stop function and consequently numerous restarting operations.

Another application may be the belt drive of an internal combustion engine with a starter generator, short RSG. In this case, the boot process of the Internal combustion engine swapped by means of the RSG train and idler belt of the belt drive, which then located in Zugtrum tensioner should also be operated with high damping, ie without pressure relief. In a constructional borderline case, the piston is still longitudinally movable, but fitted with such a small guide clearance in the cylinder that the leakage gap is hydraulically almost and theoretically completely impermeable. This dimensioning of the leakage gap would result in the tensioner being virtually blocked or locked in the retraction direction when the pressure relief is blocked. Such a high rigidity of the tensioner hydraulics may be desirable in the aforementioned starting processes of the internal combustion engine. The characteristic of the open pressure relief is then suitably tuned so that it takes over the function of the leakage gap damping when the tensioner is in the normal operating mode following the starting process of the internal combustion engine.

The switch-off pressure relief of the tensioner may also be useful if the belt drive is operated in a speed range of the internal combustion engine with pronounced vibration excitation and in this operating range a strong vibration damping from the tensioner with correspondingly high tension forces should go out.

BRIEF DESCRIPTION OF THE DRAWINGS Further features of the invention emerge from the following description and from the drawings, in which an exemplary embodiment of an automatic tensioner according to the invention for an accessory belt drive of an internal combustion engine is represented. The invention is nevertheless not limited to belt tensioners, but can also be used in automatically adapted form in automatic tensioners in chain drives. In this case, for example, the hydraulic reservoir in the tensioner housing omitted if the chain tensioner - as usual - is connected to the hydraulic fluid circuit of the internal combustion engine. Show it: 1 shows a known belt tensioner with rigid pressure relief in a longitudinally sectioned overall view; Figure 2 shows the piston of a belt tensioner according to the invention with flexible

Pressure relief;

Figure 3 shows the series connection of the control valve and pressure relief valve as a hydraulic circuit symbol;

FIG. 4 shows an enlarged section of the piston according to FIG. 2 with the control valve closed;

FIG. 5 shows the enlarged section of the piston according to FIG. 4 with the control valve open;

FIG. 6 shows the valve seat of the control valve in perspective detail view. Unless otherwise stated, the same or functionally identical features or components are provided with the same reference numbers.

DETAILED DESCRIPTION OF THE DRAWINGS The invention will be elucidated on the basis of FIG. 1, which shows a known hydraulic automatic tensioner 1, which pretensions the belt of an auxiliary belt drive of an internal combustion engine. Essentially, the tensioner comprises the following components: a tensioner housing 2, a piston part 3 movable longitudinally thereto, an elastomer bellows 4 sealing the tensioner hydraulics to the environment, and a helical compression spring acting on the piston part and the tensioner housing in the direction of extension of the tensioner Piston part and the tensioner housing are provided with fastening eyes 6 and 7, at which the tensioner on the Brennkraft- machine on the one hand and on a (not shown) clamping lever with belt tensioner on the other hand is articulated.

The tensioner housing 2 is pot-shaped and provided with a cylinder 8 which extends upwards from a housing bottom 9. The piston part 3 comprises a hollow cylindrical piston 10, which is guided longitudinally movably in the cylinder and limits with the cylinder a hydraulic fluid filled pressure chamber 1 1. The latter communicates via a check valve 12 extending at the bottom of the housing with a reservoir 13, which is bounded externally by the tensioner housing and internally by the cylinder in the form of an annular space partially filled with hydraulic fluid. The check valve is designed as a ball valve, wherein the valve ball is closed when the hydraulic fluid pressure in the pressure chamber is greater than in the reservoir. This is the case when the tensioned by the belt tensioner shortened, wherein the piston retracts into the cylinder and a portion of the compressed hydraulic fluid is displaced over the small guide and leakage gap 14 between the piston and cylinder from the pressure chamber into the reservoir. The throttle resistance to be overcome thereby dampens the relative movement of the piston and cylinder and consequently the vibrations in the belt drive. The extension following the shortening of the tensioner causes an expansion of the pressure chamber, wherein hydraulic fluid is sucked in with open valve ball of the check valve from the storage space into the pressure chamber to the pressure equalization.

In order to limit the pressure in the pressure chamber 1 1 to an upper limit pressure, the pressure chamber 1 1 is also connected via a pressure relief valve 15 and the bore 16 in the piston 10 to the reservoir 13. The pressure relief valve is designed as a conical seat valve, wherein the valve cone 17 is clamped between the limit pressure prescribing the valve spring 18 and a valve seat ring 19 in the piston and lifts off the valve seat ring when the pressure in the pressure chamber exceeds the limit pressure.

FIGS. 2 to 5 show a piston part 3 according to the invention which, upstream of the pressure relief valve 15, is provided with an operationally switchable control element. Erventil 20 is provided. As it is also shown by the switching symbol in Figure 3, the control valve is a 2/2-way valve, which is actuated electromagnetically and is normally closed. According to FIG. 4, in this closed position, a pressure-relieving hydraulic fluid flow from the pressure chamber 11 via the pressure relief valve into the reservoir 13 is prevented. In the energized open valve position according to FIG. 5, the control valve allows the hydraulic fluid flow from the pressure chamber via the pressure relief valve into the reservoir, wherein the pressure relief valve opens when the pressure in the pressure chamber exceeds the predetermined limit pressure. The pressure relief valve is designed here as a plate valve, the valve plate 17 is acted upon by the limit pressure presetting valve spring 18 in the closing direction.

The control valve 20 extends including the solenoid of the electromagnet 21 in the longitudinal direction of the piston 10 completely between the pressure chamber 1 1 and the pressure relief valve 15 and closes in the closed position, the electromagnet passing through the inflow bore 22 to the pressure relief valve in the piston. This is done by a solenoid plate acted upon by the electromagnet 23, which is pressed sealingly against the energized in the pressure chamber against a valve seat inserted in the inflow valve seat part 25 (see FIG. 4) when the electromagnet is de-energized.

To open the control valve 20, the electromagnet 21 is energized via line 26, so that the armature plate 23 is attracted away from the valve seat part 25 to the electromagnet. In this valve position, the anchor plate releases openings 27 in the valve seat part for flow to the pressure relief valve 15, as shown by the arrows in Figure 5.

As can be seen in Figure 6, the valve seat member 25 is formed with a substantially T-shaped cross-section as a hollow body which is opposite to the ren renförmigen openings 27 by the anchor plate 23 by means of a cover 28 to the pressure chamber 1 1 out. LIST OF REFERENCE NUMBERS

1 tensioner

2 tensioner housing

3 piston part

4 elastomer bellows

5 helical compression spring

6 fixing eye

7 fastening eye

8 cylinders

9 caseback

10 pistons

1 1 pressure chamber

12 check valve

13 pantry

14 leakage gap

15 pressure relief valve

16 hole in the piston

17 valve cone / valve plate

18 valve spring

19 valve seat ring

20 control valve

21 electromagnet

22 inflow bore

23 anchor plate

24 wave spring

25 valve seat part

26 power line

27 openings in the valve seat part

28 lids

Claims

claims

1 . Hydraulic automatic tensioner, comprising

a tensioner housing (2) having a housing bottom (9) and a cylinder (8) extending therefrom,

- A longitudinally movable in the cylinder (8) guided piston (10) which defines a hydraulic pressure chamber (1 1) with the cylinder (8),

a hydraulic reservoir (13) delimited by the tensioner housing (2) and by the cylinder (8),

- A check valve (12) extending on the housing bottom (9) and the reservoir (13) with the pressure chamber (1 1) connects, wherein the check valve (12) closes when the pressure in the pressure chamber (1 1) the pressure in the Vor - Council room (13) exceeds,

- And a pressure relief valve (15) which connects the pressure chamber (1 1) with the reservoir (13), wherein the pressure relief valve (15) opens when the pressure in the pressure chamber (1 1) exceeds a predetermined limit pressure,

characterized in that the automatic tensioner (1) comprises a switchable between an open and a closed position control valve (20) which allows in the open position the flow through the pressure relief valve (15) and in the closed position, the flow through the pressure relief valve (20). 15) prevented.

2. Hydraulic automatic tensioner according to claim 1, characterized in that the pressure relief valve (15) is designed as a plate valve whose valve plate (17) is acted upon by a limiting pressure predetermined valve spring (18) in the closing direction.

3. A hydraulic automatic tensioner (1) according to claim 1, characterized in that the control valve (20) is designed as electromagnetically actuated 2/2-way valve, which in the longitudinal direction of the piston (10) including lent of the solenoid (21) largely or completely between the pressure chamber (1 1) and the pressure relief valve (15) and in the closed position closes the inflow from the pressure chamber (1 1) to the pressure relief valve (15).