METHOD FOR BALANCING MOTOR VEHICLE WHEELS

Abstract

A method for balancing motor vehicle wheels, comprising mounting the wheel onto the rotating spindle of a balancing machine, using a probe of known type, selecting balancing planes and diameters, providing the data to the balancing machine, spinning the wheel, calculating the value of imbalance, calculating an entity and angular position for balancing weights to be applied in the balancing planes and diameters previously selected by the operator; during the spinning of the wheel, measuring an acceleration time between two predetermined speeds of the wheel; calculating an imbalance threshold value and applying the balancing weight only if it is above the calculated threshold value.

Description

The aim of the present invention is to provide a method which enables, by use of a single parameter, to determine the threshold values for the static imbalance, the dynamic imbalance and the overall imbalance of a motor vehicle wheel.

This aim is attained by the invention by means of a correlation between the overall moment of inertia of the wheel and the threshold values.

As an indicative parameter of the moment of inertia of the wheel, the invention teaches adopting the time of acceleration of the wheel between two preselected rotation speeds.

It has been found to be advantageous to select the time for acceleration between 25 and 50 rpm, given that the torque of the electric motors used in balancing machines is practically constant during this interval.

It has been found that the function linking the threshold values of the various types of static, dynamic and overall imbalance to the acceleration time is practically linear, and is expressed by the following equation:

W _B =K _S ×T _ACC +S ₀

Where

W_B is the threshold level of the balancing weight expressed in grams (g)

K_S is a threshold constant expressed in grams per millisecond (g/ms)

S₀ is the minimum threshold value expressed in grams (g)

T_ACC is the acceleration time expressed in milliseconds (ms).

The same equation is suitable for calculating the threshold values of the balancing weights for the overall imbalance W_BD; the static imbalance W_BS and the dynamic imbalance W_BM.

The values of the constants K_S and S₀ are determined by testing, for each type of imbalance.

By way of example, for a light alloy wheel of size 8″×16″, experimental tests led to the determination of the following threshold constants:

* overall imbalance constants:

K_SD=6.25 g/s

S_OD=1.5 g

* static imbalance constants

K_SS=16.25 g/s

S_OS=1.5 g

* dynamic imbalance constants

K_SC=15 g/s

S_OC=1.5 g

With a wheel acceleration time going from 25 to 50 rpm of T_ACC=0.4 s. By applying the equation of the present invention, the following threshold values were calculated

*W_BDi=W_BDe=6.25×0.4+1.5=4 g

*W_BS=16.25×0.4+1.5=8 g

*W_BMi=W_BMe=15×0.4+1.5=7.5 g

The following symbols will be used in the following description.

W_BD is the threshold value of the correcting weights for overall imbalance;

W_BS is the threshold values of the correcting weights for static imbalance;

W_BM is the threshold value of the correcting weights of the dynamic imbalance;

W_S is the static imbalance;

W_M is the dynamic imbalance;

W_D is the overall imbalance;

W_Di and W_De are the overall imbalances calculated in the two balancing planes

W_S1=W_S−W_BS (vectorial subtraction);

W_M1i=W_M1e=W_M−W_BM are vectorial subtractions in the balancing planes of the internal and external wheel.

The functioning procedures of a balancing machine operating according to the invention are as follows:

• • A. The machine takes account of the threshold value W_BD of the overall imbalance, calculated as specified above.

The following might emerge:

A1. The overall imbalance W_D measured by the balancing machine is smaller than or equal to W_BD (W_D<=W_BD);

The machine tells the operator not to apply any weight.

A2. The overall imbalance W_D measured by the balancing machine is greater than W_BD (W_D>W_BD); the machine subtracts W_BD from W_D and for each balancing plane calculates the values of W_D1i and W_D1e, where W_D1i=W_Di−W_BD, and W_D1e=W_De−W_BD.

• • B. The machine takes account of the threshold values W_BS and W_BM of the static and dynamic imbalances, calculated as specified above.
  • B1. The static imbalance WS measured by the machine is greater than W_BS (W_S>W_BS); and the dynamic imbalance W_M measured by the machine is greater than W_BM (W_M>W_BM);the machine calculates W_S1; W_M1i and W_M1e and calculates the resultants W_Di and W_De in the two balancing planes, displaying them on the machine's screen.

B2. The static imbalance W_S measured by the machine is greater than W_BS (W_S>W_BS); and the dynamic imbalance W_M measured by the machine is less than or equal to W_BM (W_M<=W_BM);

the machine calculates W_S1 and indicates which balancing plane the weight has to be applied in to minimise W_M, displaying the result on the machine's screen.

B3. The static imbalance W_S measured by the machine is less than or equal to W_BS (W_S<=W_BS); and the dynamic imbalance W_M measured by the machine is greater than W_BM (W_M>W_BM);

the machine calculates W_M1i and W_M1e and displays the results on the screen.

B4. The static imbalance WS measured by the machine is less than or equal to W_BS (W_S<=W_BS); and the dynamic imbalance W_M measured by the machine is less than or equal to W_BM (W_M<=W_BM);

the machine tells the operator not to apply any weight.

Claims

1) A method for balancing motor vehicle wheels, comprising following operations: mounting the wheel onto a rotating spindle of a balancing machine;using a probe of known type, selecting balancing planes and diameters, providing data relating to the planes and diameters to the balancing machine; spinning the wheel;calculating the value of imbalance W;calculating an entity and angular position for balancing weights to be applied in the balancing planes and diameters previously selected by the operator;characterised in that it comprises following further activities; a. during the spinning of the wheel, measuring an acceleration time TACC between two predetermined speeds of the wheel;b. calculating an imbalance threshold value WB with the equation as follows: WB=KS×TACC+S0

2) The method of claim 1, characterised in that the values of KS and S0 are determined experimentally.

3) The method of claim 1, characterised in that calculations are made of at least one of the threshold values, WBS of the balancing weight of static imbalance, WBM of the balancing weight of the dynamic imbalance and WBD of the balancing weight of the overall imbalance.

4) The method of claim 3, characterised in that the machine calculates the threshold value WBD of the balancing weight for the overall imbalance, and when the overall imbalance WD measured by the machine is less than or equal to WBD (WD<=WBD), no weight is applied.

5) The method of claim 3, characterised in that the machine calculates the threshold value WBD of the balancing weight of the overall imbalance, and when the overall imbalance WD measured by the machine is greater than WBD (WD>WBD), the machine subtracts WBD from WD for each balancing plane and calculates the values of WD1i=WDi−WBD, and WD1e=WDe−WBD and displays them on the screen of the machine.

6) The method of claim 3, characterised in that the machine calculates the threshold values WBS and WBM of the balancing weight for the static and dynamic imbalances, and when the static imbalance WS measured by the machine is greater than WBS (WS>WBS); and the dynamic imbalance WM measured by the machine is greater than WBM (WM>WBM), the machine calculates WS1, WM1i and WM1e and calculates the resultants WDi and WDe in the two balancing planes, and displays them on the machine's screen.

7) The method of claim 3, characterised in that the machine calculates the threshold values WBS and WBM of the balancing weight of the static and dynamic imbalances, and when the static imbalance WS measured by the machine is greater than WBS (WS>WBS) and the dynamic imbalance WM measured by the machine is less than or equal to WBM (WM<=WBM), the machine calculates WS1 and indicates the plane in which the weight must be applied in order to minimise WM, and displays the result on the machine's screen.

8) The method of claim 3, characterised in that the machine calculates the threshold values WBS and WBM of the balancing weight for the static and dynamic imbalances, and when the static imbalance WS measured by the machine is less than or equal to WBS (WS<=WBS); and the dynamic imbalance WM measured by the machine is greater than WBM (WM>WBM), the machine calculates WM1i and WM1e and displays the results on the screen.

9) The method of claim 3, characterised in that the machine calculates the threshold values WBS and WBM of the balancing weight of the static and dynamic imbalances, and when the static imbalance WS measured by the machine is less than or equal to WBS (WS<=WBS) and the dynamic imbalance WM measured by the machine is less than or equal to WBM (WM<=WBM), the machine tells the operator not to apply any weight.