WO1998052009A1

WO1998052009A1 - Method and apparatus for balancing wheels with pneumatic tyres

Info

Publication number: WO1998052009A1
Application number: PCT/IB1998/000699
Authority: WO
Inventors: Norbert Seitz
Original assignee: Carnehammar, Lars, Bertil
Priority date: 1997-05-12
Filing date: 1998-05-11
Publication date: 1998-11-19
Also published as: DE19719886A1; AU7071198A

Abstract

A method for balancing automobile wheel assemblies comprising pneumatic tyres, said method comprising introducing a viscous balancing composition into the tyre; mounting the wheel on a rotatable assembly; pressing a rotatable drum and the tread surface of the wheel in the rotatable assembly against one another with a static force F, the axes of rotation of the drum and the wheel assembly being essentially parallel; and driving the drum and/or the wheel assembly to rotation for a time period T; the force F and the time T being sufficient to cause the balancing composition to be distributed inside the tyre, thereby balancing the wheel assembly. The method may preferably be carried out on an apparatus comprising a rotatable assembly on which a wheel assembly comprising a rim and a pneumatic tyre may be mounted; a rotatably mounted drum having an axis of rotation essentially parallel to that of the rotatable wheel assembly, the axes drum and/or the rotatable wheel assembly being capable of being moved in a direction towards and away from one another; driving means for rotating the rotatable wheel assembly and/or the drum; spring means and dampening means for providing static force and dampening in a direction between the axes of rotation of the drum and the rotatable wheel assembly, respectively, and essentially at right angles to said axes; and spring means and/or dampening means mounted between the axis of rotation of the rotatable wheel assembly and the ground and/or between the axis of rotation of the drum and the ground.

Description

METHOD AND APPARATUS FOR BALANCING WHEELS WITH PNEUMATIC TYRES

FIELD OF THE INVENTION

The present invention concerns a method for balancing wheel comprising pneumatic tyres containing a viscous balancing composition, as well as an apparatus capable of carrying out the method.

BACKGROUND OF THE INVENTION

US patent 4,867,792 describes a thixotropic tyre balancing composition which is spread on the inner surface of the tyre prior to mounting on the rim. It is described that after driving a vehicle with tyres treated in this manner, any imbalances in the wheel assemblies should be balanced out through the balancing composition being distributed. The tyre balancing composition changes its position by itself in order to maintain the wheels in a balanced condition.

However, it has turned out that when performing the initial distribution of thixotropic balancing compositions by simply driving the vehicle in question, and if the composition has been spread manually on the inner tyre surface prior to mounting or, in particular, if it has been injected through the valve stem on an already mounted tyre, can lead to very severe and uncomfortable vibrations of the vehicle wheel suspension systems which may endanger road safety.

DE 38 23 926 Al describes a method for carrying out quality control of tyre manufacture, the method involving mounting the tyre on a measuring rim comprising measuring means, pressing the tyre at a fixed distance against a measuring drum comprising force measuring means, and rotating the rim/tyre combination together with the drum by driving one of them with a motor. However, the document does not envisage using the procedure for balancing tyres, just as there is no description of introducing a balancing composition into the tyre during the procedure .

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a method for balancing a wheel using a viscous balancing composition so that an initial driving distance, with its reductions in road safety and drive comfort, can be eliminated. A further object is to provide an apparatus useful in carrying out the method of the invention.

Thus, one aspect of the invention is a method for balancing automobile wheel assemblies comprising pneumatic tyres, said method comprising

introducing a viscous balancing composition into the tyre;

mounting the wheel on an a rotatable assembly; pressing a rotatable drum and the tread surface of the wheel in the rotatable assembly against one another with a static force F, the axes of rotation of the drum and the wheel assembly being essentially parallel; and

driving the drum and/or the wheel assembly to rotation for a time period T;

the force F and the time T being sufficient to cause the balancing composition to be distributed inside the tyre, thereby balancing the wheel assembly.

In a second aspect, the invention concerns an apparatus comprising a rotatable assembly on which a wheel assembly comprising a rim and a pneumatic tyre may be mounted; a rotatably mounted drum having an axis of rotation essentially parallel to that of the rotatable wheel assembly, the axes drum and/or the rotatable wheel assembly being capable of being moved in a direction towards and away from one another;

driving means for rotating the rotatable wheel assembly and/or the drum;

spring means and dampening means for providing static force and dampening in a direction between the axes of rotation of the drum and the rotatable wheel assembly, respectively, and essentially at right angles to said axes; and

spring means and/or dampening means mounted between the axis of rotation of the rotatable wheel assembly and the ground and/or between the axis of rotation of the drum and the ground.

DETAILED DESCRIPTION OF THE INVENTION

In the method of the invention, the balancing composition introduced into the tyre is suitably of the thixotropic types described the above-mentioned US patent 4,867,792 as well as in US patent 5,431,726, the content of both hereby being incorporated by reference.

When effecting contact between the wheel assembly and the drum, the wheel and the drum can have one of at least two relative arrangements. In a first arrangement, the axis of the drum is outside the circumference of the tyre and the axis of the tyre is outside the circumference of the drum, i.e. that the tyre tread is in contact with the outside surface of the drum; this is the preferred embodiment and will be described in more detail below. The second possible arrangement is that where the entire tyre is inside a hollow drum, and the tyre tread is in contact with the inside surface of the drum. Skilled persons in the field of automobile and tyre testing equipment will be able to envisage other possible ways of effecting contact between a tyre and a drum intended to simulate the tyre moving along a road surface, and all such arrangements are comprised within the scope of the present invention.

In the first of the above discussed arrangements, the diameter of the drum may in principle be from a fraction of the tyre diameter, such as a roller of 5-10 cm diameter, to several times the diameter of the tyre such as the road wheel drums used in the testing of car suspension systems and having diameters of up to 5 meters . In a preferred embodiment, the drum/wheel diameter ratio is in the range from 0.1 to 1.

The rotational speed of the wheel is preferably so that the peripheral speed is at the most 70 m/s, preferably at least 10 m/s such as 30-40 m/s. Since thixotropic balancing compositions primarily exert their balancing effect when the tyre is subjected to vibrational forces that exceed the flow limit of the composition in question, the speed at which the wheel assembly rotates should be such that the imbalances of the wheel cause it to be subjected to strong harmonic oscillations. The exact speed for that condition will depend on a number of factors such as weight and size of the wheel/tyre assembly, stiffness of the tyre, etc. The skilled art worker will be able, through simple experimentation, to determine the conditions at which the harmonic oscillations appear.

The force F with which the tyre and drum act on one another can vary widely but is preferably of a magnitude which simulates the wheel loading of an actual vehicle and is then in particular dependent on whether the tyre in question is for a passenger vehicle or for a truck or cargo vehicle. In the present context, the term "simulates" is intended to mean that the force F between the tyre and the drum is between 50% and 200% of the weight load on each of the wheels of the vehicle for which the wheel is being balanced. In the case of a passenger vehicle or a light cargo vehicle, a typical load force will be from around 1500 N to around 8000 N, and in the case of a truck or bus a typical load force may be in the range from 20000 N to 50000 N.

The force may be produced by any means known to the skilled person such as hydraulic means; arrangements using weights; springs; pneumatic means; magnetic, e.g. electromagnetic, means; electromechanical means or the like.

As indicated above, the time period T is of a length which allows the wheel assembly to become balanced by the balancing composition inside the tyre. Although it will, for economic reasons, obviously be advantageous to minimize T as much as possible, the actual magnitude of T will depend on a number of factors, i.a. to what extent oscillations of the wheel assembly are obtained under the actual method conditions. However, experiments have indicated that T can be brought down to as short as 2 minutes or less.

In a preferred embodiment, rotatable wheel assembly and/or the drum are suspended using spring means and/or dampening means .

In the present context, the term "spring means" is intended to mean any device capable of providing a spring action, i.e. an increase in a force as a result of an increase in translational shift of the object suspended. Thus, as examples of the spring means may be mentioned spiral or disc springs made from steel or fibre-reinforced plastics; pneumatic cylinders; magnetic repulsion devices; or the like. To the extent that the means producing the force F are constituted by devices producing a spring action, it is conceivable that the spring means of the suspension can form part of the means producing the force F. The spring characteristics of the spring means may suitably be in the range of 10-1000 N/mm, preferably in the range of 50-100 N/mm.

Furthermore, the term "dampening means" is intended to mean any device or arrangement capable of performing a dampening effect on vibrations of object to be dampened such as the wheel assembly or drum. As examples of dampening means may be mentioned oil-based viscosity dampers such as those commonly used in the wheel suspension in automobiles, or suitable electromagnetic arrangements.

The characteristics of the dampening means may suitably have dampening characteristics providing a dampening factor between the drum and the tyre of from 500 to 5000 Ns/m, preferably from 800 to 2000 Ns/m, such as around 1000 Ns/m for a passenger vehicle; and a dampening factor of from 800 to 8000 Ns/m for a truck.

Also, the wheel assembly suspension unit and the drum suspension unit may each be suspended in relation to a base using spring and dampening means as described above.

In order to determine when the balancing procedure of the method is completed, it is preferable that the balance properties of the wheel assembly is monitored by a measuring means connected to the suspension of the wheel assembly. Such a measuring means may be a device measuring the acceleration or movement of the wheel shaft or the forces acting on the wheel shaft. Thus, the measuring means may be an accelerome- ter device, a mechanical, electromechanical or optical displacement measurement device, or a strain gauge or piezoelectric force measurement device.

In a particularly preferred embodiment of the method of the invention, it is envisaged to induce vibrations to the system in order to create the vibrational forces that assist in distributing the balancing composition as mentioned above. Thus, while the drum and the tyre are being pressed against another, the vibrations may be applied to the wheel assembly and/or the drum and are intended to superimpose a dynamic force F_d on the static force F. If vibrations are applied to both the wheel assembly and the drum, the vibrations may be applied to them independently of one another. Furthermore, the vibrations on any one of the wheel and the drum may be applied independently in two directions at right angles to one another. It is envisaged that vibrations may be at a frequency of at the most 100 Hz, preferably at the most 50 Hz, in particular at the most 30 Hz, and an amplitude of at the most ±50 mm. Typically, useful amplitudes are up to around ±0.1 mm at 100 Hz, up to ±10-20 mm at 30 Hz, and up to ±50 mm at 10 Hz.

The vibrations may suitably be induced in a direction essentially parallel with a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes, and/or being induced essentially at right angles with a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes.

The vibrations may be induced by any conventional vibration- inducing means known to the skilled person.

Since the rheological properties of the balancing composition inside the tyre is usually dependent on the temperature of the composition, and the speed at which balancing is attained would therefore be expected to be greater at increased composition temperature, a further embodiment of the invention is contemplated in which the composition inside the tyre is subjected to heating, e.g. by means of microwaves emitted from a standard microwave transmitter or by means of radio frequency heating. It is contemplated that the balancing composition may suitably be heated to a temperature typical of the operating temperature of a tyre, such as around in the range of 70-90°C.

In the second aspect relating to the apparatus, a preferred embodiment is that which further comprises measuring means for monitoring the balance of the wheel assembly. Such measuring means may be as described above.

It is further advantageous if the apparatus comprises means for inducing vibrations, the nature of the vibrations being as described above. Examples of useful vibration- inducing means include mechanical means such as an excentric linkage mechanism; hydraulic means comprising a piston and cylinder arrangement and associated hydraulic pumps and valves as well as pump control means; electromagnetic means. A preferred type of vibration- inducing means are excentric linkage mecha- nisms, such as those in which a cylindrical rotary member having a non-circular generator curve, e.g. an elliptical, cylindrical rotary member, is arranged between the two assemblies between which a relative vibrating movement is to be induced. By rotating the member, the two assemblies are cyclically forced away from one another and allowed to approach one another (usually under the influence of spring means and optionally associated dampening means) , thereby inducing a vibrating relative movement. The characteristics of the vibrations are preferably as described above.

By way of example only, the invention is illustrated further with reference to the drawings in which figs 1-3 show different embodiments. Like items on the figures are designated with the same references.

Fig 1 shows a wheel 3 comprising a pneumatic tyre 3' mounted on a rim 3''. Prior to mounting, the tyre has had a viscous balancing composition placed inside it. The wheel 3 is mounted on a rotatable assembly mounted on a base, and the wheel is driven by a motor (M) 6 via a belt or chain drive or similar. A rotatable drum 4 is pressed against the tread surface of the tyre with a force F. The assembly 8 comprising the drum 4 is able to move in the direction of the force F using bearing elements indicated by means of the rollers 7. The generally vertical member 10 supporting the drum 4 is journalled on an axis 9 and is further supported relative to the assembly 8 through spring and dampening means indicated schematically and symbolically at 5. Similarly, the assembly 2 is connected to the ground or base plate 1 through spring and dampening means 5' .

The embodiment in fig 2 corresponds to that of fig 1 with the difference that instead of the wheel assembly 3 being driven by a motor 6, it is the drum 4 being driven by the motor.

In the embodiment in fig 3, the base plate 1 is subdivided into a plate 1' and another, separate plate 1' ' . Each of these are connected to a base plate or the ground 12 through spring means 13. Between the assembly 8 and a block 14, a vibrating means 11 is placed, here shown schematically as an elliptical rotary member rotating at an angular speed of ω. Similarly, between the plate 12 and the plate 1' and between the plate 12 and plate 1'', vibrating means 11' and 11'', respectively, are placed, here also shown schematically as elliptical rotary members rotating at an angular speed of ω' and ω' ' , respectively. The various elliptical rotary members are driven by respective motors (not shown) .

It is clear that the apparatuses described on the above figures are by way of example only and that the person skilled in the art will be able to propose many variants without departing from the principle and scope of the attached claims .

Claims

1. A method for balancing automobile wheel assemblies comprising pneumatic tyres, said method comprising introducing a viscous balancing composition into the tyre;

driving the drum and/or the wheel assembly to rotation for a time period T;

2. A method according to claim 1, wherein the peripheral speed V of the tyre is at the most 70 m/s, preferably at least 10 m/s, such as 30-40 m/s.

3. A method according to claim 1 or 2 wherein the force F between the tyre and the drum is selected to be of a magnitude simulating the wheel load of an actual vehicle.

4. A method according to claim 3 wherein the force F between the tyre and the drum is between 50% and 200% of the weight load on each of the wheels of the vehicle for which the wheel is being balanced, such as between 1500 and 8000 N for a passenger vehicle or light cargo vehicle, and between 20000 and 50000 N for a truck.

5. A method according to any of claims 1-4 in wherein the suspension means of the rotatable wheel assembly and/or the drum comprises spring means and/or dampening means.

6. A method according to claim 5 wherein the dampening characteristics of the dampening means between the drum and the tyre provide a dampening factor of from 500 to 5000 Ns/m, preferably from 800 to 2000 Ns/m, such as around 1000 Ns/m for a passenger vehicle; and a dampening factor of from 800 to 8000 Ns/m for a truck.

7. A method according to any of claims 1-6 wherein attainment of balancing of the wheel assembly is determined by measuring means connected to the shaft of the wheel assembly.

8. A method according to any of claims 1-7 wherein the drum, while being pressed against the tyre tread during the rotation, and/or the rotatable wheel assembly is being subjected to induced vibration so that a dynamic force F_d is superimposed on the static force F.

9. A method according to claim 8 wherein the vibration is at a frequency of at the most 100 Hz, preferably at the most 50 Hz, and an amplitude of at the most ±50 mm.

10. A method according to claim 9, said vibrations being induced in a direction essentially parallel with a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes, and/or being induced essentially at right angles with a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes.

11. An apparatus for performing the method according to of claim 1, comprising a rotatable assembly on which a wheel assembly comprising a rim and a pneumatic tyre may be mounted;

a rotatably mounted drum having an axis of rotation essentially parallel to that of the rotatable wheel assembly, the axes drum and/or the rotatable wheel assembly being capable of being moved in a direction towards and away from one another;

driving means for rotating the rotatable wheel assembly and/or the drum;

12. An apparatus according to claim 11 which further comprises measuring means for monitoring the balance of the wheel assembly.

13. An apparatus according to claim 11 or 12 which further comprises means for inducing vibrations in the drum and/or the rotatable wheel assembly during the rotation.

14. An apparatus according to claim 13 wherein the vibrations are at a frequency of at the most 100 Hz, preferably at the most 50 Hz, and an amplitude of at the most ±50 mm.

15. An apparatus according to claim 13 or 14 wherein said vibrations are being induced in a direction essentially parallel with a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes, and/or being induced essentially at right angles to a line connecting the centre of the axis of rotation of the wheel assembly and the centre of the axis of rotation of the drum, and essentially at right angles with said axes.

16. An apparatus according to any of claims 13-15 wherein the vibration is induced by mechanical, electromechanical or hydraulic means.