CN107743558B - Independent tensioning device - Google Patents

Abstract

The invention relates to a separate tensioning device, in particular for a drive chain of a combustion motor, having a housing and a tensioning piston which is guided in a displaceable manner in a piston bore of the housing, wherein a high-pressure chamber and a low-pressure chamber for a hydraulic medium are formed in the piston bore and the tensioning piston separates the high-pressure chamber from the low-pressure chamber. A piston rod is arranged on the tensioning piston, which extends out of the tensioning piston through the low-pressure chamber. In addition, a hydraulic medium reservoir with a volume compensation mechanism and a damping mechanism for the inward movement of the tensioning piston into the piston bore are provided.

Description

Independent tensioning device

Technical Field

The invention relates to a separate tensioning device, in particular for a drive chain of a combustion motor, which comprises: has a housing; a tensioning piston which is guided in a movable manner in a piston bore of the housing, wherein a high-pressure chamber and a low-pressure chamber for a hydraulic medium are formed in the piston bore and the tensioning piston separates the high-pressure chamber from the low-pressure chamber; and having a piston rod extending from the tensioning piston through the low pressure chamber; a reservoir for hydraulic medium; a check valve; a volume compensation mechanism; and has a damping mechanism for the displacement movement of the tensioning piston into the piston bore. The invention also relates to a chain drive for a combustion motor having such a separate tensioning device.

Background

A simple tensioning device for use as a chain tensioner or belt tensioner in a combustion motor has a pressure chamber between the tensioning piston and the tensioner housing, which pressure chamber is filled with a hydraulic medium for damping the inward movement of the tensioning piston and which pressure chamber is under high pressure during damping. Furthermore, a compression spring for prestressing the tensioning piston is usually also arranged in the high-pressure chamber. Through a throttle gap between a piston bore in the housing and the tensioning piston or through a corresponding throttle opening in the end face of the tensioning piston, the hydraulic medium can escape from the pressure chamber upon a pressure increase in the high-pressure chamber by the inward movement of the tensioning piston for damping the inward movement of the tensioning piston. The high-pressure chamber is connected to the oil circuit via a check valve for displacing the escaping hydraulic medium.

The pressurized hydraulic medium in the high-pressure chamber prevents a too far displacement of the tensioning piston into the housing even when relatively strong and powerful vibration shocks act on the tensioning piston. Depending on the installation position of the tensioning device and the supply of hydraulic medium to the high-pressure chamber via the oil circuit, a partial or complete emptying of the pressure chamber may occur. As a result, in particular when starting the motor, a virtually undamped inward movement of the tensioning piston can occur, as a result of which not only can an undesirable rattling noise of the combustion motor occur, but also an even tripping of the control chain or toothed belt (Ü berspringen) can occur. This effect becomes severe when the working area of the tensioning piston in the tensioning direction moves due to wear.

In order to prevent undesired inward displacement of the tensioning piston into the housing, in addition to tensioning devices having purely mechanical locking mechanisms which prevent the inward displacement of the piston by means of spring-loaded latching elements, tensioning devices are also provided which have hydraulically actuated readjusting mechanisms which enable continuous displacement of the working area of the tensioning piston. These solutions with continuous displacement of the working area of the tensioning piston also always require the supply of hydraulic medium from the outside to the high-pressure chamber.

In addition, there are separate tensioning devices with closed hydraulic systems, for which a drastic drop in the pressure of the hydraulic medium and leakage of light from the high-pressure chamber in the interior of the closed clamping device are prevented. Such a separate hydraulic tensioner is already known from DE 102008016654 a 1. Such a self-tensioning device, which is closed in itself, comprises a cylindrical housing with a tensioning piston guided in a piston bore of the housing, on which a piston rod is integrally formed, and a free piston, wherein the piston rod extends through the free piston. The piston bore of the housing is divided by the tensioning piston into a high-pressure chamber and a low-pressure chamber, wherein the free piston delimits a hydraulic reservoir of the low-pressure chamber with respect to an air region at atmospheric pressure outside the tensioning device. Since the volume of the high-pressure chamber changes during the inward or outward movement of the tensioning piston, the low-pressure chamber must receive the hydraulic medium from the high-pressure chamber or be supplied accordingly in order to compensate, the free piston moving relative to the housing. Due to the bottom-oriented (bodenientier) design, the piston rod of such a separate hydraulic tensioner tends to tilt, thus allowing only small tolerances in addition to the expensive sealing of the free piston, thereby resulting in overall higher expenditure for the production of such a separate hydraulic tensioner.

DE 19510681 a1 describes a self-contained tensioning device of the type mentioned, in which an oil tank is arranged on the side of the tensioning piston at the tensioning end of the device, which oil tank is sealed off from air by a membrane. The diaphragm is held by a cup-shaped closure and is tensioned against the container by a spring-biased piston. The hydraulic medium under pressure can flow from the tank into the high-pressure chamber of the tensioning device through an opening in the piston rod and a supply channel and a check valve in the tensioning piston. In order to avoid too large a volume flow of the hydraulic medium and thus an insufficient damping effect in such a tensioning device, the width of the leakage gap is limited, but this results in a small damping effect and a very strong response behavior of the tensioning device at high operating temperatures.

DE 102011079188 a1 shows a further tensioning device with a tensioning piston guided in a displaceable manner in a piston bore and a reservoir for hydraulic medium arranged on the side of the tensioning piston, wherein the tensioning piston is sealed off from the piston bore and exits the housing on the tensioning side. The reservoir chamber is connected via a plurality of channels to a non-return valve at the bottom of the piston bore for feeding hydraulic medium to the high-pressure chamber. Instead of a leakage gap, several throttle openings are provided on the tensioning piston, from which throttle openings the hydraulic medium can escape directly from the high-pressure chamber into the reservoir. The spring-biased piston in the container should compensate for the large volume changes that occur during operation. Due to the high pressure in the high-pressure chamber, the high number of load changes, the high temperature and the high sliding speed of the tensioning piston, a reliable and durable seal between the piston bore and the tensioning piston cannot be ensured during operation. In the event of a failure of this seal, the entire function of the separate tensioning device is jeopardized.

Disclosure of Invention

In this respect, the object of the invention is to provide a self-contained tensioning device which can be produced easily with a small number of components and avoids or reduces the disadvantages of the tensioning devices known from the prior art.

This object is achieved according to the invention in a separate tensioning device of the type mentioned by the following: the damping mechanism includes a leakage gap between the tensioning piston and the piston bore and a separate aperture port (blend ribbon) between the high pressure chamber and the reservoir. The aperture openings provided in addition to the leakage gap enable good damping properties of the separate tensioning device, which are hardly dependent on viscosity, to be achieved by turbulence through the aperture with a simultaneously relatively small change in the volume of the hydraulic medium in the reservoir by the narrow piston rod. In particular, a damping of the inward movement of the tensioning piston can thereby be achieved, which damping is more independent of the viscosity of the hydraulic medium, i.e. the temperature of the hydraulic medium. While in the case of conventional tensioning devices the damping characteristic drops undesirably strongly with increasing operating temperature, in the case of the tensioning device according to the invention only small changes in the damping characteristic occur with simultaneous small changes in the volume of the hydraulic medium in the reservoir. The reservoir for receiving the hydraulic medium directly in fluid connection with the low-pressure chamber, but outside the piston bore, can easily receive the hydraulic medium from the high-pressure chamber and supply it without a free piston via a movable reservoir wall when the tensioning piston moves in the piston bore, wherein a large stroke of the tensioning piston can be achieved despite a comparatively short overall length compared to conventional independent hydraulic tensioners with a free piston. The movable container wall of the volume compensation device also makes it possible to adapt the volume of the container to the position of the exterior of the tensioning piston and to use it for preloading the drive train of the combustion motor with a large tensioning travel. In addition to being used as a chain tensioner, this independent tensioning device can also be used as a belt tensioner in the same way. The separate tensioning device according to the invention does not require an external supply and therefore also does not need to be connected to the oil circuit of the combustion motor once it has been filled with the hydraulic medium once. In the bottom region of the piston bore, the hydraulic medium, which is at a high pressure in the high-pressure chamber during the inward movement of the tensioning piston, escapes through the leakage gap or the bore opening between the tensioning piston and the piston bore into the low-pressure chamber on the opposite side of the tensioning piston in the piston bore or directly into the reservoir. Since the low-pressure chamber is in fluid connection with the container, the volume increase of the hydraulic medium can be compensated by the volume compensation mechanism, wherein the movable container wall correspondingly enlarges the volume of the container without a pressure increase occurring in the low-pressure chamber or in the container. For a reliable fluid supply and pressure maintenance of the high-pressure chamber, a non-return valve is provided on the bottom of the piston bore of the housing, which is directly connected to the container.

A special embodiment of the separate tensioning device provides that the aperture opening is arranged in a side wall of the housing and can be closed by means of the tensioning piston. The arrangement of the aperture opening in the side wall of the housing not only allows easy production, but also the use of special throttle inserts made of different materials and having special aperture openings. In order to provide a damping which intensifies the inward movement of the tensioning piston in the final position of the tensioning piston, the bore opening can be arranged in the vicinity of the bottom of the piston bore and can be closed by means of the tensioning piston. When the tensioning piston is pushed far into the piston bore, the tensioning piston closes the bore opening provided in the side wall of the piston bore, so that the damping is significantly increased when the tensioning piston is pushed further in the direction of the bottom of the piston bore. Thus, rattling of the drive train can be prevented by the residual stress of the tensioning piston and a more severe damping by the leakage gap.

An advantageous embodiment provides that the aperture opening is configured as an aperture, wherein the aperture opening preferably has a diameter of 0.1 to 1.0mm and a length of 0.5 to 2.0 mm. In addition to the easy production of the aperture opening, the preferred dimensioning enables the damping characteristics to be adjusted appropriately to the respective design of the tensioning device.

For a large individual resistance against the inward movement of the tensioning piston, the leakage gap between the piston bore and the outer wall of the tensioning piston can be between 5 μm and 30 μm. When the pressure in the high-pressure chamber increases, the hydraulic medium flows in only a small volume flow through the narrow and long annular leakage gap between the tensioning piston and the piston bore, while a main volume flow of the hydraulic medium flows through the bore opening. Even in the case that the individual resistance of the leakage gap depends on the viscosity of the hydraulic medium, the bulk flow through the aperture is not dependent on the viscosity of the hydraulic medium due to the turbulence. Accordingly, no individual change in resistance occurs at the bore diameter as the operating temperature rises despite the temperature dependence of the viscosity of the hydraulic medium. In a tensioning device according to the invention, the combination of a very narrow and very long leakage gap and a separate aperture opening can be adjusted accordingly in such a way that the damping behavior is essentially independent of the viscosity despite the viscosity-dependent individual resistance of the leakage gap.

In a preferred embodiment, the movable container wall of the volume compensation means is designed as an elastic membrane. Such a resilient membrane is on the one hand impermeable to the hydraulic medium and on the other hand enables an easy sealing of the movable container wall with respect to the container. Preferably, the elastic diaphragm can be arranged on the housing without prestress for substantially maintaining the hydraulic medium in the reservoir at a hydrostatic pressure during operation. The elastic diaphragm can thereby transmit the surrounding hydrostatic pressure uniformly to the hydraulic medium in the reservoir. Since the elastic membrane as a flexible element, which is sealed off from the housing, requires a certain base stress, the pressure in the container is not equal to the hydraulic pressure outside the container, but is only substantially the same, and in the rest state has a pressure difference between 0 and 0.2 bar. In addition, during operation of the tensioning device, pressure peaks occur due to a certain inertia of the elastic membrane, which may reach values between-0.2 and 1.2 bar relative to the hydrostatic pressure, in particular in the channel leading to the low-pressure chamber.

In an advantageous embodiment, the volume compensation device has a spring-loaded compensation piston for prestressing and restoring the movable container wall. Such a spring-loaded compensation piston makes it possible to easily adjust the hydraulic medium content in the reservoir and to define the volume of the reservoir appropriately. In addition, the spring-loaded compensation piston prevents air or hydraulic medium from the environment from being unintentionally sucked into the container or the low-pressure chamber which is in fluid connection with the container. In order to limit the stroke of the spring-loaded compensation piston and to prevent too great a loading of the movable container wall, the volume compensation mechanism can have an upper stop and a lower stop for the spring-loaded compensation piston.

In one embodiment, the movable container wall of the volume compensation device is designed as a resilient diaphragm, which in this embodiment can transmit the pressure of the spring-loaded compensation piston uniformly to the hydraulic medium in the container even in the event of an uneven loading of the diaphragm by the spring piston. The spring-loaded compensation piston can simultaneously serve to guide and support the elastic diaphragm, in particular when the pressure in the container increases.

In a further embodiment, the container is at least partially formed in the housing of the tensioning device. In addition to the reduction of the components of the tensioning device, the partial or integrated design of the container in the housing of the tensioning device also makes it possible to arrange the container along a flange surface of the tensioning device, by means of which flange surface heat generated during operation in the separate tensioning device as a result of throttling processes can be dissipated to adjoining motor components.

The piston rod, which is arranged on the tensioning side of the tensioning piston, extends through the low-pressure chamber and emerges at the end side from the housing, can be expediently connected fixedly to the tensioning piston. The fixed arrangement of the piston rod or the tapering of the tensioning piston into a piston rod on the side of the low-pressure chamber makes it possible firstly to form a high-pressure chamber and a low-pressure chamber in the piston bore once and to separate the high-pressure chamber from the low-pressure chamber by the tensioning piston. In addition, the volume change in the interior of the separate tensioning device is reduced during the displacement of the tensioning piston into and out of the piston bore or the displacement of the piston rod into and out of the low-pressure chamber. To this end, the diameter of the piston rod can be between 40% and 70%, preferably between 50% and 60%, of the diameter of the piston bore.

For a good sealing of the low-pressure chamber with respect to the piston bore of the housing and with respect to the piston rod, the housing can be provided at the end side with a plug, wherein the piston rod extends through the plug. This also enables a good guidance of the piston rod in the stopper and a relatively small sealing surface between piston rod and stopper. Since the piston rod moves relative to the stopper when the tensioning piston or piston rod is moved out of and into the housing, a rod seal is advantageously provided in the stopper through which the piston rod extends and which seals the low-pressure chamber relative to the sealing surface.

In order to be able to fill the tensioning device in an auxiliary manner and to vent the high-pressure chamber, the piston rod can have a vent which extends from the high-pressure chamber up to the end face of the piston rod. Such a ventilation opening, which is closed during operation by a closing plug and a pressure plug on the end face of the piston rod, is not necessary in principle for a separate tensioning device, but in the installed position and operation of the tensioning device, an air cushion can be formed in the high-pressure chamber by the tensioning piston, which is usually of hollow cylindrical design, and can be easily ventilated via the ventilation opening. Furthermore, the ventilation opening enables an additional filling if a filling opening provided for this purpose is not available.

In a special embodiment, the effective compensation area of the movable container wall is greater than the difference between the cross-sectional area of the piston bore minus the cross-sectional area of the piston rod. The effective compensation area of the movable container wall, due to the correspondingly large design of the area of the elastic shaped wall part of the elastic diaphragm, enables the necessary stroke of the movable container wall to be reduced relative to the stroke of the tensioning piston or piston rod, and thus also the necessary container volume for the separate tensioning device. The cross-sectional area is in this case viewed perpendicularly to the tensioning device of the tensioning piston or piston rod.

An alternative refinement provides that the cross-sectional area of the piston rod is between 1% and 50%, preferably between 3% and 30%, in particular between 5% and 15%, of the effective compensation area of the movable container wall. The relatively small cross-sectional area of the piston rod, which is proportional to the compensation area of the movable container wall, minimizes the necessary container volume and thus the structural size of the separate tensioning device, which is proportional to the possible working stroke of the tensioning piston or piston rod.

When the movable container wall is prestressed and reset by the spring-loaded compensation piston, the pressure difference between the low-pressure chamber and the hydrostatic pressure of the hydraulic medium in the container relative to the environment can also be only between-0.2 bar and 2.0 bar during operation. Such a small pressure difference relative to the hydrostatic pressure makes it easier to seal the separate tensioning device from the environment, depending on the tightness of the rod seal and the pressure of the spring-loaded compensation piston acting on the movable diaphragm wall. In operation, a slight overpressure is usually present here. The small negative pressure in the low-pressure chamber and the container is only produced when the tensioning piston is rapidly moved out due to the inertia of the system. In addition, the comparatively easy sealing of the separate tensioning device, in particular the sealing between the piston rod and the stopper, also includes the following possibilities: as soon as the spring-loaded compensation piston bears against the upper or lower stop, the hydraulic medium content in the reservoir is compensated. In the absence of volume compensation due to the compensating piston bearing against the upper or lower stop, the pressure in the hydraulic medium reservoir fluctuates considerably more strongly relative to the atmospheric pressure and can be drawn into or discharged from the reservoir via the seal between the piston rod and the housing or the stopper and thus serves to compensate for a too large or too low hydraulic medium content in the reservoir.

The invention further relates to a chain drive for a combustion motor, having a drive chain which connects a drive sprocket and at least one driven sprocket to one another, and having a separate tensioning device which tensions the drive chain according to one of the embodiments described above. By virtue of the independent design of the tensioning device, this chain drive of the combustion motor does not need to be connected to the oil circuit. As a result, a reliable function of the tensioning device can be ensured even in the event of a pressure drop in the oil circuit. This also makes it possible to lubricate the combustion motor on the side of the oil circuit driven by the oil pump. The separate tensioning device in the previously described embodiment can also be used in much the same way for a combustion motor belt drive.

Drawings

The invention is explained in detail below with the aid of the figures. In the drawings:

figure 1 shows a schematic view of a chain drive according to the invention together with a separate tensioning device according to the invention,

figure 2 shows a perspective cross-sectional view of a separate tensioning device according to the invention,

FIG. 3 shows a perspective sectional view of a further independent tensioning device according to the invention together with a hydrostatic container, and

fig. 4 shows a perspective sectional view of a further independent tensioning device according to the invention together with a hydrostatic container.

Detailed Description

The timing chain drive 1 of the combustion motor, which is shown in fig. 1, comprises two camshaft sprockets 2 located above, a crankshaft sprocket 3 located below, a timing chain 4 wound around them, a guide rail 5 for guiding the timing chain 4 in the slack side of the timing chain drive 1, and a pivotably arranged timing rail 6, which presses against the timing chain 4 in the slack side of the timing chain drive 1. The tensioning rail 6 is pressed onto the control chain 4 by means of a separate tensioning device 8 which is fixed in the combustion motor. The separate tensioning device 8 is designed as a flange tensioner and is flanged to the motor component 7 via the fastening means 12, see also fig. 2. In this case, the piston rod 9 of the tensioning device 8 presses against the pressing region 10 of the pivotably arranged tensioning rail 6 and thereby tensions the control chain 4 in the slack side of the control chain drive 1.

Fig. 2 shows the design of a tensioning device 8 according to the invention by means of a sectional view through the separate tensioning device 8 designed as a flange tensioner. The tensioning device 8 comprises a housing 11, which is designed as a bore and milling element, which is fastened to the motor component 7 by means of a plurality of fastening means 12. The housing 11 has a cylindrical piston bore 13, in which the tensioning piston 14 is guided in a displaceable manner together with the piston rod 9, which projects in the tensioning direction on the tensioning piston 14. As shown in fig. 1, an end plug 15 on the tensioning-side end of the piston rod 9 is pressed against the drive region 10 of the tensioning rail 6 for prestressing the control chain 4 by means of the tensioning rail 6.

The tensioning piston 14 is designed as a hollow piston and has a compression spring 16 in its interior, which presses against an end face 17 of the hollow cylindrical tensioning piston 14 and pretensions the tensioning piston 14 in the tensioning direction. The piston rod 9 is connected to the end face 17 in the tensioning direction, wherein a hydraulic medium channel 18 is provided in the piston rod 9, which hydraulic medium channel is closed by the end plug 15. On the bottom of the piston bore 13, a non-return valve 19 is arranged, which is pressed into its seat at the bottom of the piston bore 13 by the pressure spring 16.

In the piston bore 13, a high-pressure chamber 20 is formed between the bottom of the piston bore 13 and the hollow cylindrical tensioning piston 14, to which hydraulic medium is supplied via the non-return valve 19. In the operating state, the high-pressure chamber 20 is charged with a hydraulic medium at a certain operating pressure for hydraulically damping the displacement movement of the tensioning piston 14 when the tensioning piston 14 is displaced into the piston bore 13. On the side of the tensioning piston 14, at the open end of the tensioning side of the piston bore 13, there is a low-pressure chamber 21 in which there is a hydraulic medium with a low overpressure relative to the atmospheric pressure. A plug 22 is provided at the open end of the tensioning side of the piston bore 13, in which plug an annular rod seal 23 is arranged and the piston rod 9 extends through the plug 22 out of the low-pressure chamber 21, wherein the rod seal 23 seals the low-pressure chamber 21 with respect to the piston rod 9 extending out through the plug 22. The low-pressure chamber 21 is connected fluidically (fluidically) via a connecting channel 24 to a reservoir 25 for the hydraulic medium, typically oil of an associated combustion motor. The hydraulic medium reservoir 25 extends along a flange region 26 of the housing 11 from the connecting channel 24 at the end on the tensioning side of the housing 11 to the low-pressure chamber 21 to the housing bottom 27, in which a fluid feed 28 to the check valve 19 is provided. During the displacement movement of tensioning piston 14, hydraulic medium is supplied to high-pressure chamber 20 via fluid inlet 28 and check valve 19, wherein check valve 19 only allows hydraulic medium to flow through in the direction of high-pressure chamber 20 and closes the valve channel in the opposite direction, in order to enable damping of vibrations of tensioning device 8.

On the housing bottom 27, a volume compensation 29 is provided for defining the hydraulic medium reservoir 25. In this embodiment, the volume compensation means 29 is designed as a separate component which is attached to the housing 11 for the purpose of forming the container 25, but the volume compensation means 29 can also be designed as part of the housing 11. The volume compensation means 29 is formed by a one-sided open hollow body 30, preferably a hollow cylindrical base body, which is dimensioned and shaped according to the housing base 27. In the region of the opening of the hollow body 30, a resilient membrane 31 extends, which forms a movable container wall of the volume compensation means 29 and at the same time also creates a seal between the hollow body 30 and the housing bottom 27.

In the embodiment of the inventive tensioning device shown in fig. 2, the elastic diaphragm 31 rests on the side facing away from the container 25 on the compensation piston 32, which prevents unintentional bulging and unilateral overloading of the elastic diaphragm 31. Accordingly, the elastic membrane 31 can be made of a very flexible material and with a small wall thickness. The compensation piston 32 is prestressed by means of a helical spring 33 in the direction of the elastic diaphragm 31 and serves to advance the movable container wall, i.e. the elastic diaphragm 31, when the volume of the hydraulic medium in the container 25 decreases, and thus also to maintain the pressure of the hydraulic medium in the container 25, which is essentially determined by the pressure-dependent permeability of the rod seal 23 relative to the piston rod 9. The compensation piston 32 is guided in a sleeve 34 of the hollow body 30, wherein the sleeve 34 forms a lower stop 35 and an upper stop 36 together with the mushroom-shaped compensation piston 32.

In the region of the high-pressure chamber 20, a bore opening 37 is provided in the side wall of the piston bore 13, from which opening the hydraulic medium can escape directly from the high-pressure chamber 20 into the hydraulic medium reservoir 25 during the inward movement of the tensioning piston 14 into the piston bore 13, in order to specifically dampen the inward movement of the tensioning piston 14 in this way.

Fig. 3 shows a further tensioning device 8 according to the invention, which differs from the embodiment shown in fig. 2 primarily by an unstressed elastic membrane 31, so that the hydraulic medium in the reservoir 25 is under a substantially hydrostatic pressure. The tensioning device 8 in fig. 3 comprises a housing 11 with a cylindrical piston bore 13 in which the tensioning piston 14 is guided in a displaceable manner together with the piston rod 9 projecting in the tensioning direction. The tensioning piston 14 has a compression spring 16 in its interior, which presses against an end face 17 of the hollow cylindrical tensioning piston 14 and pretensions the tensioning piston 14 in the tensioning direction. The piston rod 9 is connected to the end side 17 in the tensioning direction, wherein a hydraulic medium channel 18 for venting the high-pressure chamber 20 is provided in the piston rod 9, which hydraulic medium channel is closed by an end plug 15. An end plug 15 on the tensioning-side end of the piston rod 9 rests during operation on the pressing region 10 of the tensioning rail 6 for prestressing the control chain 4 by means of the tensioning rail 6. On the bottom of the piston bore 13, a non-return valve 19 is arranged, which is pressed into its seat in the bottom of the piston bore 13 by the pressure spring 16 and supplies the high-pressure chamber 20 with hydraulic medium.

On the side of the tensioning piston 14, a low-pressure chamber 21 is present at the tensioning-side open end of the piston bore 13, into which hydraulic medium flows when the tensioning piston 14 is displaced into the piston bore 13 via a leakage gap 38 between the tensioning piston 14 and the piston bore 13, in order to generate a hydraulic damping of the displacement movement of the tensioning piston 14. A plug 22 is provided at the open end of the tensioning side of the piston bore 13, in which plug an annular rod seal 23 is arranged and through which the piston rod 9 extends outward from the low-pressure chamber 21, wherein the rod seal 23 seals the low-pressure chamber 21 with respect to the piston rod 9 extending outward through the plug 22. The low-pressure chamber 21 is connected via a connecting channel 24 to the reservoir 25 for hydraulic medium, so that a pressure equalization takes place here.

In order to define the hydraulic medium reservoir 25, a volume compensation 29 is again provided on the housing base 27 for this tensioning device 8, which is mounted as a separate component on the housing 11. The volume compensation 29 is formed by a one-sided open hollow body 30, preferably an arched flange part, which is dimensioned and shaped according to the housing bottom 27. In the region of the opening of the hollow body 30, a resilient membrane 31 extends, which forms a movable container wall of the volume compensation means 29 and at the same time also creates a seal between the hollow body 30 and the housing bottom 27. For pressure compensation with the environment, the arched section of the hollow body 30 is provided with a hole (not shown) so that an atmospheric ambient pressure exists between the hollow body 30 and the elastic membrane 31.

The arched section of the hollow body 30 simultaneously serves as a lower stop 35 for the elastic diaphragm 31 in order to prevent an excessively violent or uneven expansion and overloading of the elastic diaphragm 31. When the elastic membrane 31 rests against the arched section of the hollow body 30, the volume of the container 25 is at its maximum. When the volume of the hydraulic medium in the reservoir 25 decreases as a result of the tensioning piston 14 being moved out of the piston bore 13, the elastic diaphragm 31 is arched in the direction of the housing base 27, as a result of which the volume of the reservoir 25 decreases. In this case, air at atmospheric pressure flows through openings (not shown) in the hollow body 30 into the region between the arched section of the hollow body 30 and the elastic diaphragm 31, as a result of which the pressure of the hydraulic medium in the reservoir 25 is substantially maintained at hydrostatic pressure.

Fig. 4 shows a further embodiment of a tensioning device 8 according to the invention, which has an elastic membrane 31 that is not prestressed. In the section of the separate tensioning device 8 embodied as a flange tensioner in fig. 4, it can be seen that the elastic diaphragm 31 and the associated reservoir 25 for hydraulic medium are not arranged in series (autoflash) in relation to the high-pressure chamber 20, the piston bore 13 and the tensioning piston 14, but are arranged laterally on the housing 11. The tensioning device 8 in turn comprises a housing 11 with a cylindrical piston bore 13, a tensioning piston 14 guided in a displaceable manner in the piston bore 13, and a piston rod 9 projecting on the tensioning piston 14 in the tensioning direction. The hollow cylindrical tensioning piston 14 has a compression spring 16 in its interior, which pretensions the tensioning piston 14 in the tensioning direction. The piston rod 9 is connected to the end side 17 in the tensioning direction, wherein a hydraulic medium channel 18 for venting the high-pressure chamber 20 is provided in the piston rod 9, which hydraulic medium channel is closed by the end plug 15. On the bottom of the piston bore 13, a non-return valve 19 is arranged, which is pressed into its seat in the bottom of the piston bore 13 by the pressure spring 16 and supplies the high-pressure chamber 20 with hydraulic medium.

In this tensioning device 8, a low-pressure chamber 21 is also provided between the piston bore 13 and the piston rod 9, into which the hydraulic medium flows through a leakage gap 38 between the tensioning piston 14 and the piston bore 13 when the tensioning piston 14 is moved into the piston bore 13, in order to hydraulically damp the movement of the tensioning piston 14 in. A plug 22 is provided at the open end of the tensioning side of the piston bore 13, in which plug an annular rod seal 23 is arranged and through which the piston rod 9 extends outward from the low-pressure chamber 21, wherein the rod seal 23 seals the low-pressure chamber 21 with respect to the piston rod 9 extending outward through the plug 22. The low-pressure chamber 21 is connected via a connecting channel 24 to the reservoir 25 for hydraulic medium, so that a pressure equalization takes place here.

In contrast to the embodiment shown in fig. 2 and 3, with such a tensioning device 8, the volume compensation 29 is not arranged on the housing base 27, but rather on the side on the housing 11 itself. The volume compensation 29 for defining the hydraulic medium reservoir 25 is mounted on the housing 11 as a separate component and is formed by a single open hollow body 30, preferably an arched flange part, and an elastic membrane 31 extending in the region of the opening of the hollow body 30. The elastic membrane 31 forms a movable container wall of the volume compensation 29 and simultaneously seals the container 25 between the hollow body 30 and the side wall of the housing 11. For pressure compensation with the environment, the arched section of the hollow body 30 is provided with a hole (not shown) so that an atmospheric ambient pressure exists between the hollow body 30 and the elastic membrane 31.

The arched section of the hollow body 30 simultaneously serves as a lower stop 35 for the elastic diaphragm 31 in order to prevent an excessively violent or uneven expansion and overloading of the elastic diaphragm 31. When the elastic membrane 31 rests against the arched section of the hollow body 30, the volume of the container 25 is at its maximum. When the volume of the hydraulic medium in the reservoir 25 decreases as a result of the tensioning piston 14 being moved out of the piston bore 13, the elastic diaphragm 31 is arched in the direction of the side wall of the housing 11, as a result of which the volume of the reservoir 25 decreases. In this case, air at atmospheric pressure flows through openings (not shown) in the hollow body 30 into the region between the arched section of the hollow body 30 and the elastic diaphragm 31, as a result of which the pressure of the hydraulic medium in the reservoir 25 is substantially maintained at hydrostatic pressure.

In the embodiment of the separate tensioning device 8 according to the invention, which is shown in fig. 2 to 4, a separate bore opening 37 is provided in the side wall of the piston bore 13 in the region of the high-pressure chamber 20 in addition to a leakage gap 38 between the tensioning piston 14 and the piston bore 13, from which bore opening 37 the hydraulic medium can escape directly from the high-pressure chamber 20 into the hydraulic medium reservoir 25 during the insertion movement of the tensioning piston 14 into the piston bore 13. The additional individual aperture openings 37, which can be designed both as simple holes (not shown) and as inserts made of special materials and provided with precisely dimensioned holes, can be provided with only very narrow leakage gaps 38. The narrow leakage gap 38 in combination with the additional aperture opening 37 reduces the temperature dependence of the hydraulic damping for the inward movement of the tensioning piston 14 and thus enables a significant improvement in the targeted adjustment of the damping.

The manner of functioning and working of the above described independent tensioning device 8 is explained in detail below.

The embodiment of the individual tensioning device 8 according to the invention, which is shown here in fig. 2 to 4, is preferably used for a chain drive 1 of a combustion motor. In operation, the tensioning piston 14 of the tensioning device 8 is pressed by means of the prestress of the compression spring 16 via the piston rod 9 and the end plug 15 of the piston rod 9 against the pressing region 10 of the tensioning rail 6 for tensioning the drive chain 4 of the chain drive 1. In the embodiment of the tensioning device 8 as a belt tensioner, the piston rod 9 is pressed onto the drive belt by means of a corresponding pressure roller. Independent of the use of the tensioning device 8, when the tensioning piston 14 is disengaged from the piston bore 13, hydraulic medium flows from the reservoir 25 through the fluid inlet 28 in the housing bottom 27 and the check valve 19 into the high-pressure chamber 20, filling up the volume of the high-pressure chamber 20 which has expanded as a result of the disengagement of the tensioning piston 14.

During a vibration movement of the tensioning rail 6 or pressing roller, for example, when pressure is applied to the tensioning piston 14 via the end plug 15 and the piston rod 9, an inward movement of the tensioning piston 14 into the high-pressure chamber 20 takes place, which is damped by the hydraulic fluid in the high-pressure chamber 20. Since the oil of the combustion motor, which is normally used as a hydraulic medium, cannot flow back into the reservoir 25 via the check valve 19, the inward movement of the tensioning piston 14 increases the fluid pressure of the hydraulic medium in the high-pressure chamber 20. When the pressure in the high-pressure chamber 20 rises, the hydraulic medium flows through a narrow, long annular leakage gap 38 between the piston bore 13 and the outer wall of the hollow cylindrical tensioning piston 14, which in the embodiment shown is only between 5 μm and 30 μm. This narrow and long leakage gap 38 generates a very high resistance against the inward displacement movement of the tensioning piston 14 and thus a very strong damping by the small volume flow flowing through the leakage gap 38 from the high-pressure chamber 20 into the low-pressure chamber 21. In addition, the damping by the leakage gap 38 between the tensioning piston 14 and the piston bore 13 depends very much on the viscosity of the hydraulic medium and thus also on the temperature of the hydraulic medium.

In order to improve the hydraulic adjustment of the tensioning device 8 according to the invention and to obtain a damping which is as independent of viscosity as possible, an additional separate aperture opening 37 is provided in the high-pressure chamber 20 in the side wall of the piston bore 13, through which opening hydraulic medium can escape with turbulence from the high-pressure chamber 20 directly into the hydraulic medium reservoir 25 during the inward movement of the tensioning piston 14. By suitable dimensioning of the aperture 37 and the leakage gap, the damping characteristics of the separate tensioning device 8 according to the invention can be achieved, which are influenced primarily by turbulence through the aperture 37 and are therefore substantially independent of the viscosity of the hydraulic medium. For this purpose, the aperture opening 37 in the embodiment shown here is formed as a hole having a diameter of 0.1 to 1.0mm over a length of 0.5 to 2.0 mm.

Furthermore, the arrangement of the bore opening 37 in the side wall of the piston bore 13 and at a distance from the bottom of the piston bore 13 makes it possible to achieve what is known as end position damping for the tensioning piston 14. As soon as tensioning piston 14 moves beyond a critical end position point determined by the position of aperture opening 37 during the retraction movement, the outer wall of tensioning piston 14 covers aperture opening 37, so that during the further retraction movement of tensioning piston 14 into piston bore 13, only a strong damping of leakage gap 38 between piston bore 13 and tensioning piston 14 is still active and the further retraction movement of tensioning piston 14 is damped more strongly. In the moved-in state of the tensioning piston 14, the rattling or jerking of the drive chain 4 is thereby reduced in particular.

During the displacement movement of the tensioning piston 14 into the piston bore 13, the hydraulic medium flows from the high-pressure chamber 20 through the leakage gap 38 between the piston bore 13 and the tensioning piston 14 into the low-pressure chamber 21 and from there through the connecting channel 24 into the hydraulic medium reservoir 25, and directly from the high-pressure chamber 20 through a separate aperture opening 37 in the side wall of the piston bore 13 into the hydraulic medium reservoir 25, whereby the volume of the hydraulic medium in the reservoir 25 is increased. The increased volume of the hydraulic medium in the reservoir 25 presses against the elastic diaphragm 31 and moves the movable reservoir wall outwards into the hollow body 30 of the volume compensation mechanism 29, possibly against the prestress of the compensation piston 32. Since the cross-sectional area of the piston rod 9 which is moved into the housing 11 of the tensioning device 8 is smaller than the cross-sectional area of the tensioning piston 14 which is moved into the high-pressure chamber 20, the movable wall of the volume compensation 29 only has to compensate for the volume displaced by the piston rod 9, since the volume of the low-pressure chamber 21 is simultaneously increased when the high-pressure chamber 20 is reduced, in proportion to the difference of the cross-sectional area of the piston bore 13 minus the cross-sectional area of the piston rod 9 divided by the cross-sectional area of the piston bore 13. Accordingly, a relatively small stroke of the movable container wall or of the elastic membrane 31 enables a relatively large movement stroke of the piston rod 9 or of the tensioning piston 14. This ratio is improved by the increase in the effective compensation area of the movable container wall or the elastic membrane 31. In fig. 2 and 3, the entire movement stroke of tensioning piston 14 is depicted by the spacing arrows between the bottom of piston bore 13 and tensioning piston 14 and between tensioning piston 14 and plug 22.

The preloaded volume compensation 29, which is shown in fig. 2, of the separate tensioning device 8 according to the invention has a lower stop 35 and an upper stop 36, which together prevent an excessively high loading of the elastic diaphragm 31. In addition, the stops 35, 36 regulate the hydraulic medium content of the reservoir 25. If, during operation, the volume of the hydraulic medium decreases due to wear, the elastic diaphragm 13 may no longer completely compensate for the volume change, so that, during the displacement movement of the tensioning piston 14, the pressure in the hydraulic medium reservoir 25 and in the low-pressure chamber 21 connected thereto drops below ambient pressure, usually atmospheric pressure, the separate tensioning device 8 can suck hydraulic medium into the low-pressure chamber 21 between the rod seal 23 and the piston rod 9 and compensate for the lack of hydraulic medium. However, if the tensioning device 8 draws in too much hydraulic medium, the pressure of the hydraulic medium in the reservoir 25 and the low-pressure chamber 21 increases significantly relative to the ambient pressure when the compensation piston 25 impacts the lower stop 35 and hydraulic medium can escape between the piston rod 9 and the rod seal 23.

In contrast to the preloaded volume compensation 29 shown in fig. 2, the separate tensioning device 8 according to the invention according to fig. 3 and 4 has an unstressed elastic diaphragm 31 which is fastened to the housing 11 by means of the hollow body 30 and seals the container 25. If, during the displacement movement of the tensioning piston 14, the volume of the hydraulic medium in the reservoir 25 rises during operation, the elastic diaphragm 31 is arched in the direction of the arched section of the hollow body 30, wherein the pressure in the hydraulic medium reservoir 25 remains substantially constant at a hydrostatic pressure which is predetermined by the atmospheric pressure between the hollow body 30 and the elastic diaphragm 31. The non-prestressed elastic diaphragm can thereby transmit the surrounding hydrostatic pressure uniformly to the hydraulic medium in the reservoir. Since the elastic membrane as a flexible element which is sealed off from the housing requires a certain base stress and has a certain inertia, the pressure in the container is not necessarily equal to the atmospheric pressure outside the container but is only substantially the same and can have a pressure difference of between 0 and 0.2bar in the rest state. Additionally, pressure peaks occur during operation of the tensioning device due to the inertia of the elastic membrane and the contour of the container 25, which pressure peaks, in particular in the channel leading to the low-pressure chamber, can reach values between-0.2 and 1.2 bar relative to the hydrostatic force.

The movement of the tensioning piston 14 or the piston rod 9 out of the separate tensioning device 8 is effected by the prestress of the pressure spring 16 in the high-pressure chamber 20. As soon as no external force is applied any longer to the end plug 15 of the piston rod 9, the compression spring 16 presses the tensioning piston 14 together with the piston rod 9 in the direction of the open end of the piston bore 13, i.e. in the tensioning direction. Due to the displacement movement of the tensioning piston 14, the internal pressure of the hydraulic medium in the high-pressure chamber 20 drops, so that the check valve 19 on the bottom of the piston bore 13 can open and allow the hydraulic medium to flow from the reservoir 25 into the high-pressure chamber 20. The displacement movement of the tensioning piston 14 or the piston rod 9 is therefore carried out without damping.

In the damping of the inward movement of tensioning piston 14, heat is generated by the pressure drop at leakage gap 38 between piston bore 13 and tensioning piston 14 and at additional bore opening 37, which is given to the hydraulic medium and the surrounding components of tensioning device 8. During the intensified damping of the chain drive, the entire individual tensioning device 8 heats up with the hydraulic medium. Since in the present design of the individual tensioning devices 8 a large part of the hydraulic medium reservoir 25 is located in the flange region 26 of the housing 11, the heat generated as a result of the damping of the inward movement can be dissipated to the motor component 7 via the large contact surface of the hydraulic medium and the flange region 26.

List of reference numerals:

1 control chain drive

2 camshaft sprocket

3 crankshaft sprocket

4 control chain

5 guide rail

6 tensioning rail

7 Motor component

8 independent tensioning device

9 piston rod

10 area of compression

11 casing

12 fixing device

13 piston hole

14 tensioning piston

15 end plug

16 pressure spring

17 end side

18 hydraulic medium channel

19 check valve

20 high pressure chamber

21 low pressure chamber

22 plug

23-bar seal

24 connecting channel

25 container

26 flange region

27 bottom of the housing

28 fluid input

29 volume compensation mechanism

30 hollow body

31 elastic diaphragm

32 compensating piston

33 helical spring

34 sleeve

35 lower stop

36 top stop

37 aperture opening

38 leakage gap

Claims (19)

1. A separate tensioning device (8) which is connected to the frame

-a tensioning piston (14) having a housing (11), which is guided in a movable manner in a piston bore (13) of the housing (11), wherein a high-pressure chamber (20) and a low-pressure chamber (21) for a hydraulic medium are formed in the piston bore (13) and the tensioning piston (14) separates the high-pressure chamber (20) from the low-pressure chamber (21),

-having a piston rod (9) arranged on the tensioning side of the tensioning piston (14), the piston rod (9) extending through the low-pressure chamber (21) and emerging at the end side out of the housing (11),

-having a container (25) for the hydraulic medium, wherein the container (25) is in fluid connection with the low pressure chamber (21) and a check valve (19) is arranged between the high pressure chamber (20) and the container (25),

-having a volume compensation means (29) for adapting the volume of the container (25), which volume compensation means (29) is constructed in the form of a movable container wall, and

-having a damping mechanism for the movement of the tensioning piston (14) into the piston bore (13),

characterized in that the damping mechanism comprises a leakage gap (38) between the tensioning piston (14) and the piston bore (13) and a separate aperture opening (37) between the high-pressure chamber (20) and the container (25).

2. Independent tensioning device (8) according to claim 1,

characterized in that the aperture opening (37) is arranged in a side wall of the housing (11) and can be closed by means of the tensioning piston (14).

3. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the aperture opening (37) is configured as a hole having a diameter of 0.1 to 1.0mm and a length of 0.5 to 2.0 mm.

4. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the width of the leakage gap (38) between the tensioning piston (14) and the piston bore (13) is between 5 μm and 30 μm.

5. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the movable container wall of the volume compensation means (29) is designed as an elastic membrane (31).

6. Independent tensioning device (8) according to claim 5,

characterized in that the elastic diaphragm (31) is arranged on the housing (11) without prestress for maintaining the hydraulic medium in the reservoir (25) at a substantially hydrostatic pressure during operation.

7. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the volume compensation means (29) has a spring-loaded compensation piston (32) for prestressing and restoring the movable container wall.

8. Independent tensioning device (8) according to claim 7,

characterized in that the volume compensation mechanism (29) has an upper stop (36) and a lower stop (35) for the spring-loaded compensation piston (32).

9. Independent tensioning device (8) according to claim 7,

characterized in that the pressure difference between the low-pressure chamber (21) and the hydraulic medium in the reservoir (25) is between-0.2 bar and 2.0 bar relative to atmospheric pressure.

10. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the piston rod (9) is fixedly connected with the tensioning piston (14).

11. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the diameter of the piston rod (9) is between 40% and 70% of the diameter of the piston bore (13).

12. Independent tensioning device (8) according to claim 11,

characterized in that the diameter of the piston rod (9) is between 50% and 60% of the diameter of the piston bore (13).

13. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the piston rod (9) has a ventilation opening, wherein the ventilation opening extends from the high-pressure chamber (20) up to the end side of the piston rod (9).

14. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the effective compensation area of the movable container wall is larger than the cross-sectional area of the piston bore (13) minus the cross-sectional area of the piston rod (9).

15. Independent tensioning device (8) according to claim 1 or 2,

characterized in that the cross-sectional area of the piston rod (9) is between 1% and 50% of the effective compensation area of the movable vessel wall.

16. Independent tensioning device (8) according to claim 15,

characterized in that the cross-sectional area of the piston rod (9) is between 3% and 30% of the effective compensation area of the movable vessel wall.

17. Independent tensioning device (8) according to claim 15,

characterized in that the cross-sectional area of the piston rod (9) is between 5% and 15% of the effective compensation area of the movable vessel wall.

18. Independent tensioning device (8) according to claim 1,

characterized in that the separate tensioning device (8) is used for the drive chain (4) of the combustion motor.

19. Chain drive (1) for a combustion motor, having a drive sprocket (3), at least one driven sprocket (2), a drive chain (4) connecting the drive sprocket (3) and the at least one driven sprocket (2) to one another, and a separate tensioning device (8) according to any one of claims 1 to 18 for tensioning the drive chain (4).

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