EP1418011A1

EP1418011A1 - A method for the assembly of a motor-vehicle wheel

Info

Publication number: EP1418011A1
Application number: EP20030025223
Authority: EP
Inventors: Mario Roetto
Original assignee: Esam SpA
Current assignee: Esam SpA
Priority date: 2002-11-06
Filing date: 2003-11-05
Publication date: 2004-05-12
Also published as: ITTO20020955A1

Abstract

In order to assemble a motor-vehicle wheel (30), a wheel rim (10) and a wheel disc (20) are provided, the eccentricities of the rim and of the disc are measured, and the angular positions of the eccentricities are determined. The rim and the disc are oriented relative to one another in a angular position such that the eccentricities of the rim and of the disc are disposed on opposite sides of the axis of rotation of the wheel so as to minimize the overall eccentricity of the wheel disc/rim unit (20, 10), to the extent permitted by the wheel or motor-vehicle manufacturer's specifications. The disc (20) is then force-fitted coaxially in the rim (10). Finally, the disc and the rim are welded together.

Description

The present invention relates to a method for the assembly of a motor-vehicle wheel of the type in which the wheel comprises a disc which is force-fitted and welded in a rim. The invention is equally applicable to both steel wheels and aluminium wheels.
For a better understanding of the prior art and of the problems inherent therein, a conventional assembly method will be described first of all with reference to Figures 1a-1d of the appended drawings.
Conventionally, a wheel disc 20 is force-fitted in a wheel rim 10 with radial interference (Figure 1c) by means of a press (not shown), after which the rim and the disc are joined together by welding by means of apparatus indicated S. Some motor-vehicle manufacturers require the wheel rim 10 and the wheel disc 20 to be oriented angularly relative to one another prior to coupling so as to align the valve hole 11 of the wheel rim 10 in a substantially radial plane with one of the through-holes 21 for the stud bolts (not shown) for the mounting of the wheel on the hub (not shown) or with one of the ventilation openings 22 of the wheel disc 20.
It is known that wheels are critical components of a motor vehicle; if the wheels are not balanced per se, premature wear of the tyre takes place and vibrations which may give rise to further problems are produced.
Errors of shape and in particular ovality of the individual rim and disc components of a wheel of the above-mentioned type adversely affect the resulting eccentricity of the disc-rim unit once it has been assembled.
The current trend amongst wheel manufacturers is to reduce the depth of the shoulders of the tyres and at the same time to increase the diameter of the disc-rim unit. Theoretically, this increase in dimensions leads to a greater incidence of overall eccentricity of the wheel due to errors of shape of the wheel disc and of the wheel rim.
The object of the present invention is therefore to assemble a wheel of the type specified above whilst addressing mainly the problem of minimizing the resulting eccentricity of the wheel composed of the disc-rim unit, to the extent permitted by the motor-vehicle or wheel manufacturers' specifications.
This and other objects and advantages which will be understood further from the following description are achieved, according to the invention, by an assembly method as defined in Claim 1. Preferred embodiments of the invention are defined in the dependent claims.
A preferred embodiment of the invention will now be described purely by way of non-limiting example with reference to the appended drawings, in which:
Figures 1a-1d show schematically the main steps of an assembly method according to the prior art,
Figures 2 and 3 are an axial section and a front elevational view, respectively, of a motor-vehicle wheel to which the present invention relates,
Figures 4a-4e show schematically the main steps of an assembly method according to the present invention, and
Figure 5 is a graph showing the radial distances, from the respective centres, of points of two surfaces of a disc and of a rim which make up a motor-vehicle wheel.
With reference now to Figures 2 and 3 of the drawings, a wheel unit, generally indicated 30, comprises a wheel rim 10 and a wheel disc 20 which is fitted completely in the rim 10 in accordance with the present invention.
The structural characteristics of the rim 10 and of the disc 20 shown in Figures 2 and 3 may be considered generally known and will not therefore be described in greater detail herein. It will suffice to note here that the rim 10 has a valve hole 11 (Figure 3) and two opposed and facing radial portions 12, 13 suitable for engaging the sides of the beads of a tyre (not shown) in order to hold the tyre on the rim; each portion 12, 13 is connected to a respective substantially cylindrical or slightly frustoconical portion 14, 15 for the engagement of the opposed inner edges of the tyre. The rim 10 also has an inner, substantially cylindrical portion 16 which constitutes the seat in which the wheel disc 20 is force-fitted and welded.
The wheel disc 20 forms a substantially cylindrical outer peripheral edge 23, which is force fitted coaxially in the inner cylindrical portion 16 of the rim 10, and a central opening 24 for receiving a projecting end of a hub (not shown) when the wheel unit 30 is mounted on a vehicle. The central opening 24 is surrounded by a pair of concentric ridges 25, 26 between which four or five circumferentially spaced-apart holes 21 (four in this embodiment) are formed for housing respective stud bolts (not shown) projecting from the hub of the vehicle for fixing the wheel unit 30 and the tyre (not shown) to the vehicle. A plurality of ventilation openings, uniformly spaced apart circumferentially, are indicated 22.
An important characteristic of the assembly method according to the present invention is, very briefly, that the eccentricities of the rim 10 and of the disc 20 are measured separately. These two components are then coupled in a relative angular position such as to minimize the resulting eccentricity of the wheel unit once it is assembled.
As shown schematically in Figure 4a, the rim 10 is clamped on a rotating chuck, schematically indicated M1, and is rotated about the central axis X1. In the embodiment shown, the chuck M1 clamps the rim 10 by means of jaws or cones acting against the inner cylindrical surface 16 of the rim. In this embodiment, three radial jaws are provided, arranged at 120° relative to one another.
A pair of feelers or sensors, schematically indicated F14, F15, are connected to an electronic measuring instrument, schematically indicated EM1. The chuck M1 is rotated about its own axis, as indicated by the arrow A, rotating the rim 10. Whilst the rim is rotating about the axis X1, the feelers or sensors F14, F15 detect any variations, relative to the theoretical design values, of the radial distances of a plurality of points on the outer surfaces of the portions 14 and 15 from the centre of the circle. The above-mentioned points are disposed on closed lines resulting from the intersection of the disc and of the rim with respective radial planes (perpendicular to the axis of rotation). Owing to working inaccuracies, these closed lines are in fact never perfect circles.
The constructional and operating characteristics of the sensors or feelers in question (which may be of any known type) are known in the art and do not therefore need to be described in detail herein.
The radial position data of the portions 14 and 15 are transmitted by the measuring instrument E to an electronic processing unit, schematically indicated EPU, - typically a PLC or Programmable Logic Controller, or a PC (personal computer) - which supervises the operation of the measuring apparatus as a whole.
The measuring apparatus correlates the radial position values of the above-mentioned points that are disposed on the outer surfaces of the portions 14 and 15 with respective angular position values of the rim with the use of an encoder (schematically indicted E1) which is fixed for rotation with the chuck M1 and associated with a detection device SD1 which detects the angular position data for the chuck and transmits these data to the unit EPU. Both the encoder and its detection device are known in the art and do not need to be described in detail herein.
The processing unit EPU correlates the angular position data for the chuck with the radial positions of the various points of the portions 14 and 15 in order to obtain information which is represented herein in the form of a graph (or "harmonic"), indicated D10 in Figure 5, which gives the deviation, relative to the theoretical design values, of the radial distances from the centre of the circle of a plurality of points disposed on a closed line given by the intersection of the outer surface of the portion 14 (or 15) with a radial plane.
In exactly the same way as described above with reference to the rim 10, a graph D20 is also obtained for the wheel disc 20 and in particular for its cylindrical surface 23 which is to be fitted with radial interference inside the inner cylindrical portion 16 of the wheel rim 10. As shown in Figure 4b, the disc 20 is mounted on a chuck M2 and rotated about an axis X2 extending through the centre of the central opening 24. Whilst the disc 20 is rotating about the axis X2, a feeler or sensor F23 (which may be of the same type as those indicated F14 and F15 above) detects any variations, relative to the theoretical design value, of the radial distances of a plurality of points of the portion 23 from the centre of the disc. The radial position data for the portion 23 are transmitted by the measuring instrument E2 to the electronic processing unit EPU and are correlated with the corresponding angular position data supplied by a detection device SD2 associated with an encoder E2 fixed for rotation with the chuck M2.
The electronic processing unit EPU is provided with applications software for processing the data represented schematically by the graphs D10 and D20 and making results available in the form of data which represent, for each of the components 10 and 20, the extent or absolute value of the eccentricity and its angular position.
The processing unit then determines the relative angular positions in which the rim and the disc are coupled in order to minimize the overall eccentricity of the rim/disc unit, possibly also taking account of the motor-vehicle manufacturer's particular specifications.
In other words, the unit EPU calculates the value of the angle α (Figure 4c) by which the rim and the disc must be angularly offset in order to be coupled in a manner such as to achieve the least eccentricity of the assembled unit.
According to the characteristics of the component-handling apparatus and of the press (not shown) which performs the force-fitting, the unit EPU may bring about a further rotation of one or other of the chucks M1 and/or M2 on which the rim or the disc is mounted in order to position them angularly in the relative position determined by the unit EPU.
Basically, the errors of eccentricity of the disc and of the rim are compensated by orienting these two components angularly relative to one another in a manner such that their respective eccentricities are substantially opposed with respect to the axis of rotation of the wheel or at least are arranged on opposite sides of the axis of rotation.
In this description and in the appended claims, the expressions "substantially opposed" and "on opposite sides" are also intended to indicate situations in which a motor-vehicle manufacturer requires the valve hole 11 of the rim to be aligned with one of the ventilation openings 22 or with one of the wheel-mounting holes 21. Naturally, in these situations, the overall eccentricity of the assembled wheel will be greater than the minimum eccentricity which would be obtained by diametrically opposing the eccentricities of the rim and of the disc with respect to the axis of rotation. In order to keep to constructional constraints of the above-mentioned type, the unit EPU may be programmed so as to control the rotation of the chucks in order to align the valve hole 11 with the ventilation opening 22 or with the fixing hole 21 which is closest to the ideal position calculated.
The disc 20 is then fitted in the rim 10 in a manner known per se (see Figure 4d) and, finally, welding apparatus S (Figure 4e) welds the disc to the rim in conventional manner, for example, by spot welds or discontinuous bead welds 40 distributed uniformly around a circumference of the wheel.
As will also be appreciated, as well as achieving the objects mentioned in the introductory portion of the description, the assembly method according to the present invention enables the dimensional tolerances of both of the components of the wheel to be checked, thus enabling parts that are clearly defective to be discarded. It will also be appreciated that the invention advantageously permits monitoring of the diameters of the two components to be fitted together and checking of the interference value required by the assembly method.

Claims

A method for the assembly of a motor-vehicle wheel (30), comprising the steps of:

a) providing a wheel rim (10),

b) providing a wheel disc (20),

d) force-fitting the wheel disc (20) coaxially in the wheel rim (10), and

e) welding the wheel disc (20) and the wheel rim (10) together,
characterized in that the force-fitting step is preceded by the steps of:

a1) measuring the eccentricity of the wheel rim (10),

a2) determining the angular position of the eccentricity of the wheel rim (10),

b1) measuring the eccentricity of the wheel disc (20),

b2) determining the angular position of the eccentricity of the wheel disc (20), and

c) orienting the wheel rim (10) and the wheel disc (20) relative to one another in an angular position such that the eccentricities of the wheel rim and of the wheel disc are disposed on opposite sides of the axis of rotation of the wheel so as to minimize the overall eccentricity of the wheel disc/rim unit (10, 20), to the extent permitted by the wheel or motor-vehicle manufacturer's specifications.
An assembly method according to Claim 1, characterized in that at least one of the measurement steps a1) and b1) comprises the step of measuring the radial distances from the centre of the wheel rim (10) or of the wheel disc (20) of a plurality of points of a closed line resulting from the intersection of a radial plane with a substantially cylindrical or slightly frustoconical surface (14, 15, 23) of the wheel rim (10) or of the wheel disc (20).
An assembly method according to Claim 2, characterized in that the measurement step a1) comprises the step of measuring the radial distances from the centre of the wheel rim (10) of a plurality of points of a closed line resulting from the intersection of a radial plane with a substantially cylindrical or slightly frustoconical surface (14, 15) for the engagement of one of the inner edges of a tyre.
An assembly method according to Claim 3, characterized in that the measurement step a1) comprises the step of measuring the radial distances from the centre of the wheel rim (10) of a plurality of points of two closed lines resulting from the intersection of two radial planes with two respective substantially cylindrical or slightly frustoconical surfaces (14, 15) for the engagement of the two opposed inner edges of a tyre.
An assembly method according to Claim 2, characterized in that the measurement step b1) comprises the step of measuring the radial distances from the centre of the wheel disc (20) of a plurality of points of a closed line resulting from the intersection of a radial plane with at least one substantially cylindrical or slightly frustoconical surface (23) which can be force-fitted in a cylindrical seat (16) of the wheel rim (10).
An assembly method according to any one of Claims 1 to 4,
characterized in that it further comprises the steps of:

centring and clamping the wheel rim (10) on a rotatable chuck (M1),

rotating the chuck (M1) in order to rotate the wheel rim about its own central axis (X1),

measuring, during the rotation step, the radial distances from the centre of the wheel rim (10) of a plurality of first points of at least one closed line resulting from the intersection of a radial plane with at least one substantially cylindrical or slightly frustoconical surface (14, 15) of the wheel rim (10), by means of measuring instruments (F14, F15, EM1) which can make available to an electronic processing unit (EPU) first data indicative of the radial positions of the first points,

detecting, by means of detection means (E1, SD1) associated with the chuck (M1), angular positions adopted by the chuck during the rotation stage in order to make available to the processing unit (EPU) second data indicative of the angular positions of the first points, and

correlating and processing the first and second data by means of the processing unit (EPU) in order to calculate the eccentricity of the wheel rim (10) and to determine the angular position of the eccentricity of the wheel rim (10).
An assembly method according to any one of Claims 1, 2 or 5, characterized in that it further comprises the steps of:

centring and clamping the wheel disc (20) on a rotatable chuck (M2),

rotating the chuck (M2) in order to rotate the wheel disc about its own central axis (X2),

measuring, during the rotation step, the radial distances from the centre of the wheel disc (20) of a plurality of second points of at least one closed line resulting from the intersection of a radial plane with at least one substantially cylindrical or slightly frustoconical surface (23) of the wheel disc (20), by means of measuring instruments (F23, EM2) which can make available to an electronic processing unit (EPU) first data indicative of the radial positions of the second points,

detecting, by means of detection means (E2, SD2) associated with the chuck (M2), angular positions adopted by the chuck during the rotation stage in order to make available to the processing unit (EPU) second data indicative of the angular positions of the second points, and

correlating and processing the first and the second data by means of the processing unit (EPU) in order to calculate the eccentricity of the wheel disc (20) and to determine the angular position of the eccentricity of the wheel disc (20).
An assembly method according to Claims 6 and 7,
characterized in that it further comprises the steps of:

correlating, by means of the unit (EPU) the eccentricity data of the wheel rim and of the wheel disc and the respective angular position data of those eccentricities, and

determining, by means of the unit (EPU), the value of the angle (α) through which the wheel rim (10) and the wheel disc (20) should be oriented in order to couple them in a manner such as to minimize the overall eccentricity of the wheel disc/rim unit (20, 10) as a whole.
An assembly method according to Claim 1 or Claim 8,
characterized in that the orientation step comprises the step of orienting the wheel rim (10) and the wheel disc (20) relative to one another in an angular position such that the eccentricities of the wheel rim and of the wheel disc are diametrically opposed with respect to the axis of rotation of the wheel.
An assembly method according to Claim 1 or Claim 8,
characterized in that the relative angular position between the wheel rim (10) and the wheel disc (20) is selected in a manner such that a valve hole (11) formed in the wheel rim (10) is aligned radially with a hole (21) for a fixing stud bolt or with a ventilation opening (22) in the wheel disc (20).
An assembly method according to any one of Claims 2 to 10, characterized in that the first or second points detected on the said closed lines are spaced apart uniformly.