Patent Grant
8763573
This application claims the priority of DE 10 2009 054 049.0 filed Nov. 20, 2009, which is incorporated by reference herein.
The invention relates to a camshaft adjusting arrangement for varying the angular position of a camshaft relative to a crankshaft of an internal combustion engine, the camshaft adjusting arrangement comprising a drive element, which is driven by the crankshaft and is supported so that it can rotate in relation to the camshaft, at least two hydraulic chambers, to which a hydraulic fluid can be admitted in order to set a defined relative rotational position between the drive element and the camshaft, being formed between the drive element and the camshaft, the camshaft adjusting arrangement comprising a first component and a second component, the first component having a cylindrical receiving face which is designed to receive a cylindrical seating face of the second component.
Camshaft adjusting devices, particularly those working hydraulically, are sufficiently well-known in the prior art. In the hydraulic camshaft adjuster there is a vane impeller, in which vanes are formed or arranged. The vanes are situated in hydraulic chambers, which are incorporated in an external rotor. The internal rotor (connected to the camshaft) can be adjusted relative to the external rotor between an ‘advanced stop’ and a ‘retarded stop’ by way of corresponding admission of hydraulic fluid to the respective side of the hydraulic chambers. The flow of hydraulic oil is here controlled by an electrically actuated directional valve.
The rotary motion of the crankshaft is generally transmitted to the external rotor via a gearwheel, which is rotationally fixed to the external rotor. In the prior art there are known solutions in which the gearwheel is embodied as a chain sprocket and is arranged at the outer circumference of the external rotor or rotationally fixed to the external rotor.
A camshaft adjusting device of generic type is described in DE 10 2004 038 695 A1. Here the drive element has a laterally attached and fixed covering element. An axial end section of the drive element or its housing in this case has a cylindrical receiving face.
The covering element is seated on the receiving face by way of a corresponding seating face. In order to afford the covering element sufficient grip on the axial end section of the drive element or its housing, a press-fit is here provided between the cylindrical receiving face and the cylindrical seating face.
DE 10 2006 039 371 A1 shows a similar solution. Here too, the camshaft adjuster has a drive element, which is rotationally fixed to the crankshaft. An output element, which is rotationally fixed to the camshaft, is rotatable relative to the drive element. The device is axially limited by a side cover at each side.
A torsion spring in the form of a flat spiral spring is also provided. A first end of the torsion spring acts on the output element. The other end of the torsion spring is fixed to the drive element. The torsion spring is here under a pre-tension, so that it can exert a torque on the output element relative to the drive element. The torsion spring serves to compensate for a friction torque, which acts on the camshaft and pushes the output element towards retarded timings. The torsion spring is further provided in order to move the output element into a basic position in which the output element can be mechanically locked to the drive element should the hydraulic medium supply to the device become insufficient.
The torsion spring is arranged in a spring compartment, which is delimited on the one hand by the side cover and on the other by the aforementioned covering element (spring cover). The covering element grips radially and axially over the side cover and is provided with a positively interlocking element.
A disadvantage of the hitherto known solutions is that although the first component and the second component, that is to say, in particular, the front or side cover of the drive element and the covering element, are cost-effective to produce, the production tolerances mean that the press-fit between the two parts, that is to say the radial compressive stress between the two cylindrical contact faces between said parts, which constitute a transverse press-fit, cannot be kept sufficiently precisely within a predefined tolerance band.
The object of the present invention therefore is to develop a camshaft adjusting arrangement of the aforementioned type so that it is possible to purposely keep the radial compressive stress, which in the assembled state results between said first and second component, particularly between the front or side cover and the covering element, within an admissible range. The intention is thereby to keep the press-fit between the parts within a defined range without special precautions for the production of the parts. At the same time it is intended to fully maintain cost-effective production of the parts.
This object is achieved by the invention, which is characterized in that in order to reduce a radial compressive stress between the first component and the second component at least one compensating element is arranged in the cylindrical receiving face of the first component and/or in the cylindrical seating face of the second component.
The compensating element is preferably embodied as a groove-like recess, which extends over a defined angle over the circumference of the first component and/or the second component. The angle here is preferably between 10° and 25°. The axial extent of the compensating element is preferably the entire contact area between the two components along the cylindrical receiving or seating face.
Two, three or four compensating elements are preferably arranged over the circumference of the cylindrical receiving face and/or the cylindrical seating face. These are preferably arranged equidistantly over the circumference.
The groove-like recess is preferably let into the cylindrical receiving face of the first cornponent.
In axial section the groove-like recess may have largely radially extending lateral boundaries. These boundaries may merge via a rounding into a base section of the groove-like recess.
The first component is preferably a front cover of the drive element. The second component is preferably a covering element of the drive element. This may be produced as a thin sheet-metal component.
The invention is here geared to the concept that the compensating element in the cylindrical receiving face of the first component and/or in the cylindrical seating face of the second component will make it possible to match the circumferences of the cylindrical receiving face and the cylindrical seating face. This serves to reduce the radial compressive stress.
According to the invention at least one compensating element is proposed, which on the outer and/or inner component generates an elastic-plastic spring action in the transverse press-fit. This elastic-plastic variation of the circumferential faces of the two interacting components has a corresponding influence on the compressive stress between the components. The compensating element may be formed as a radial impression inwards or outwards. Given the minimal overlap of the components, residual stresses resulting from the manufacturing process will cause the compensating element to generate a minimum, essential residual pre-tensioning force in the transverse press-fit. With a greater overlap the compensating element allows an elastic or even plastic deformation in a circumferential direction, producing a variation in the effective circumferential length of one of the two components. The transverse press-fit is correspondingly limited to a maximum admissible radial compressive stress.
In a transverse press-fit with a thin-walled cylindrical component a predefined overlap is therefore very easy to establish. This is therefore an easy way of compensating for production tolerances.
The invention serves to compensate for an increased overlap in the transverse press-fit between the cylindrical components, which are joined to one another axially to the transverse press-fit (that is to say by pressing on axially). The residual force pre-tensioning in the transverse press-fit and hence also the axial joining force can thereby be more readily controlled and/or limited.
In the case of a zero overlap in the transverse press-fit the two components will theoretically have the same circumferential lengths at the joining face. The compensating element in the form of a radial segmental recess constitutes an enlargement or a reduction of the effective circumferential area of one of the two interacting components which is approximately equal to the circumferential length of the one component at maximum admissible overlap.
The compensating elements in this respect constitute elastic spring elements in the circumferential direction of the transverse press-fit, which, depending on the size of the overlap in the circumferential direction, allow a radial deformation inwards or outwards, which leads to a variation in the effective circumferential length of the component.
The compensating characteristic may also be plastically deformed locally. In this case the necessary residual pre-tensioning force in the transverse press-fit is produced by a residual elasticity of the compensating element.
The radial impression of the compensating element may be formed by shallow radial transitions to the basic body of the component.
In order to allow the radial expansion in the area of the compensating element, a radial segmental recess may be provided in the other component opposite the compensating element. The minimum depth of the recess is determined according to the necessary radial deformation of the compensating element.
The design configuration of the compensating elements with verification of the stress state and the expansion of the compensating element can be undertaken by a finite element analysis and supported by corresponding tests.
The axial joining force during assembly may be force-travel controlled in order to produce the optimum transverse press-fit.
The proposed invention therefore serves purposely to produce a maximum admissible overlap in the transverse press-fit of the thin-walled components without having to sacrifice economic production of the joining faces. The joining forces in the assembly line are thereby reduced while ensuring the fatigue strength of the components in the transverse press-fit at no additional cost.
Exemplary embodiments of the invention are represented in the drawings, in which:
a and
b schematically show two joined parts, which form a transverse press-fit,
a and
b again schematically show two joined parts, which form a transverse press-fit, one of the parts now being provided with compensating elements for controlling the magnitude of the compressive stress between the parts,
a again schematically shows two parts joined to give a transverse press-fit, and
b again schematically shows two joined parts, which form a transverse press-fit, the other part, compared to
An essential constituent part of the camshaft adjusting arrangement 1 is a drive element 2, which incorporates a hydraulic adjusting device, which is capable of bringing about an angular rotation between an outer annular part (stator) and a rotor 15, in order to influence the timings of the internal combustion engine in a known manner. The rotor 15 is rotationally fixed to the camshaft 14. The drive element 2 is driven by the crankshaft of the internal combustion engine, a gearwheel 16 being shown which is fixedly connected to the drive element 2. The crankshaft is connected to the gearwheel 16 by way of a chain (not shown).
Hydraulic chambers, one of which is denoted by 17, are located in the camshaft adjusting arrangement 1. The hydraulic chamber 17 is here delimited radially inwards by the rotor 15 and radially outwards by the stator or drive element 2; laterally the hydraulic chamber is delimited by two side covers, that is to say by a front cover 3, which is here referred to as the first component, and by a rear cover 18.
Multiple hydraulic chambers 17, to each of which hydraulic fluid can be admitted in order to be able to adjust said rotation, are effectively located between the drive element 2 and the rotor 15. Multiple pairs of hydraulic chambers are here arranged over the circumference.
Connected to the front cover 3 is a covering element 4, which is here referred to as the second component. The covering element 4, relative to the front cover 3, defines a receiving space 19, in which a torsion spring 20 is arranged, the purpose of which has already been described above.
As can be seen from a comparison of
In order to purposely influence the level of the radial compressive stress in the transverse press-fit, the exemplary embodiment provides for a design configuration as shown to best advantage in
According, to these, three compensating elements 7, 8 and 9 in the form of groove-like recesses are let into the first component 3.
Each compensating element 7, 8, 9 extends over a circumferential section, which is specified by the angle α (see
In the exemplary embodiment the groove-like recesses 7, 8, 9 have largely radially extending lateral boundaries 10 and 11 (see
In
a and
It can be seen from
The same applies to the solution according to
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| Number | Date | Country | |
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