The present invention concerns a hydraulic tensioner for use in traction drives, particularly in chain drives of internal combustion engines. The tensioner comprises a pot-shaped housing forming a cylinder in which a piston is guided for longitudinal movement. In the installed state, the piston is elastically suspended for longitudinal movement against a traction element, and adjusting movements of the piston are damped by a damping device. For this purpose, depending on the adjusting movement of the piston, a fractional quantity of a hydraulic fluid, particularly lubricating oil from the internal combustion engine, can flow out of the pressure chamber through a leak gap or, on reversal of the adjusting movement, flow back into the pressure chamber through a one-way valve.
A hydraulic tensioner of the pre-cited type is known, for instance, from the document DE 40 35 823 C1. This hydraulic tensioner particularly intended for chain drives in internal combustion engines comprises a piston that is guided for longitudinal movement in the cylinder and is indirectly connected to the traction element, i.e. the chain. The piston and the cylinder together define a pressure chamber for receiving the hydraulic fluid. Movements of the tensioner and, thus also, adjusting movements of the piston toward the chain enlarge the pressure chamber, so that a partial vacuum is formed enabling a re-flow of hydraulic fluid into the pressure chamber through a one-way or non-return valve. An opposite movement of the piston in the direction of the cylinder diminishes the pressure chamber which causes a fractional quantity of the hydraulic fluid to be displaced out of the pressure chamber through a leak gap. The configuration of the leak gap has a substantial influence on the damping characteristic of the hydraulic tensioner. If the tensioner is configured for a large leakage, the tensioner becomes softer, i.e. vibrations and impacts of the traction element resulting from large adjusting movements of the piston are substantially damped. A small leak gap permitting only a weak flow of fluid limits the damping action to small adjusting movements of the piston which disadvantageously lead to an introduction of higher forces into the traction drive.
The damping behavior of a hydraulic tensioner is generally optimally tuned to a particular point of operation. A soft damping is suitable for reducing noise development in the chain drive in a lower engine speed range. At higher speeds of rotation, the internal combustion engine manifests a different operational behavior through which, with a soft damping, a larger quantity of hydraulic fluid is displaced out of the pressure chamber through the leak gap. In this case, a situation can occur in which the time for re-suction of hydraulic fluid into the pressure chamber is insufficient, so that malfunctions of the hydraulic tensioner can occur.
It is an object of the present invention to provide a configuration for a hydraulic tensioner of the pre-cited type such that the tensioner can be economically manufactured and possesses a high degree of functionality.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the housing and the piston are made without chip removal by a deep drawing method. The deep drawing method used by the invention makes finishing work superfluous, so that these components can be made at low cost in large series. After assembly, i.e. when the piston has been inserted into the housing, a separate securing element forms an end stop for the piston. The position and the shape tolerances of all the components of the tensioner of the invention are designed such that a defined leak gap determining the damping characteristic of the damping device is formed between the piston and the housing or between the piston and the securing element.
Further advantageous features of the invention will be discussed in the following.
According to one advantageous feature of the invention, an effective securing element is constituted by a separate bushing that is fixed in the housing after the piston has been mounted. The bushing is designed with regard to its wall thickness and length such that a functionally required, defined leak gap is formed that, at the same time, also defines the guiding lash between the piston and the bushing.
The bushing provided as a securing means is inserted into the housing, so that its front end forms an end stop for the piston which comprises a radial step.
Preferably, the bushing is positioned in the housing through a press or interference fit. Alternatively, joining by a fusion of material is also feasible, for instance, by soldering or gluing the bushing to the housing for obtaining its permanent positional fixing.
An alternative to a bushing as a securing element, the invention also includes a locking ring fixed by positive engagement on the piston and cooperating with a radially stepped portion of the housing. The design of the locking ring and an associated annular groove for this ring in the piston is such that the piston with inserted locking ring can be pushed into the housing or cylinder. After passing the leak gap between the piston and the housing, the locking ring expands automatically and forms an anti-disintegration feature between the housing and the piston.
A suitable locking ring is, for example, a radially pre-tensioned circlip. Alternatively, a closed steel ring or a plastic ring with adequate elasticity and wear resistance may likewise be used as a locking ring. In the case of plastic rings, the choice is limited to plastics having the required wear resistance and fatigue strength. Preferably, the locking rings used have a circular cross-sectional profile, but locking rings having a square or rectangular cross-sectional profile and cooperating with annular grooves of appropriate configuration in the piston may also be used.
The one-way or non-return valve of the hydraulic tensioner of the invention is a disk valve likewise made without chip removal. For this purpose, a disk-shaped, elastic, sluing valve plate may be used. This valve plate positioned, for example, in the region of the housing bottom can be directly associated to a supply bore through which the hydraulic fluid can re-flow into the pressure chamber. Through the proposed configuration of the valve plate that is centered in the housing, for example, through centering lugs and loaded by a force of the compression spring of the hydraulic tensioner, the assembly of the one-way valve is simplified and, moreover, this one-way valve is integrated in the tensioner without need of additional design space.
In another suitable embodiment, the disk valve is a valve comprising two parts made without chip removal, one part being a valve body in the form of a disk that is guided and secured against loss in a housing configured as a retaining element. This structure enables a short reaction time for opening and closing the valve already at the slightest differences in pressure or upon a reversal of flow of the hydraulic fluid, which has an advantageous effect on the mode of operation of the hydraulic tensioner.
For a better understanding of the invention, examples of embodiment are described more closely below with reference to the appended drawings.
For realizing an anti-disintegration feature between the housing 2a and the piston 3a, the housing 2a comprises a radially stepped end portion 11 on which the piston 3a is guided. The deep drawing method used for making the housing 2a and the piston 3a assures quality of production without additional finishing. At the same time, the production method also assures the defined guiding lash required between the housing 2a and the piston 3a, which guiding lash, in turn, defines the leak gap 9a and the damping characteristic of the tensioner 1a. For realizing an effective anti-disintegration feature of the inter-inserted components, a securing element 12a in the form of a locking ring 13 is positioned in an end region of the piston 3a to cooperate with an end stop 15a of the radial step 11 of the housing 2a. The locking ring 13 is preferably a radially pre-tensioned circlip inserted into an annular groove 14 of the piston 3a. The annular groove 14 is configured such that, during insertion of the piston 3a into the radial step 11 of the housing 2a, the locking ring 13 yields sufficiently in radial direction to enable an unobstructed assembly. When the locking ring 13 has passed the radial step 11, the pre-tensioned locking ring 13 is displaced radially outwards producing an overlap between the locking ring 13 and the radial step 11 which together form an end stop 15a.
The hydraulic tensioner 1b of
For achieving an exact guidance of the piston 3b, the bushing 16 has a length (S1) of =0.4 of the length “S2” of the piston 3b. An optimal leak gap is an annular gap having a dimension of =0.08 mm and arranged between the outer peripheral surface of the piston 3b and the inner contour of the bushing 16.
An efficient anti-disintegration feature between the housing 2b and the piston 3b is assured through the end stop 15b in that an end annular portion 18 of the piston 3b cooperates with a front end of the bushing 16. The one-way valve 10b is arranged in the region of the housing bottom 4 and force-loaded directly by a spring end of the compression spring 5 so as to bear against the bottom 4 and cooperate with the supply bore 8 for the hydraulic fluid.
The structure of the one-way valve 10b can best be seen in
Number | Date | Country | Kind |
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10 2006 055467.1 | Nov 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/061969 | 11/7/2007 | WO | 00 | 5/22/2009 |