Method and apparatus for balancing vehicle wheels by means of balance weights

Abstract: The vehicle wheel balancing method comprises determining, by electronic computing means, the position of the application plane (Q1, Q2) and the angular position (Z1, Z2) or each weight within a range about prechosen balancing planes (P1, P2), computed on the basis of weight values (N1, N2) chosen by the operator.

Description: For balancing motor vehicle wheels, machines are known comprising a rotary shaft on which the wheel is fixed, and means for determining wheel unbalance data. These machines are basically arranged to compute the values of the balance weights (two weights are usually required) after the operator has predetermined the position of the planes in which he intends to fit the weights (balancing planes). The machine must therefore be informed of the axial position of the chosen balancing planes, ie the axial distance between a reference plane and the balancing planes themselves, plus the radial distance between the axis of rotation and the point (in the balancing plane) at which the balance weight is to be applied. In traditional steel wheel rims, the balance weight application plane was assumed to coincide with the rim edges with the result that the chosen geometrical identification parameters were generally the distance between the inner side of the rim and the side of the machine casing (reference plane), the wheel rim width and its diameter. With the increasing use of light alloy wheel rims, unsuitable for receiving traditional balance weights on their outer edges, there has arisen the requirement for applying weights to wheel rims in intermediate positions between their outer edges, with a corresponding need for machines able to implement such application. For this purpose it is known to determine and memorize firstly the position of the chosen planes in which the relative balance weights are to be applied, and the radial distance between the point of application and the axis of rotation, all by means of a suitable geometrical position measurement device integrated into the machine. An electronic computing unit then computes the exact value of the balance weights to be applied in the prechosen planes and their exact angular position in these planes. The same measurement device can advantageously be used for this purpose. The feeler member of the measurement device is moved along the surface on which the balance weights are to be applied, an acoustic/visual indicator indicating when the feeler has reached the computed position. The described method has however the drawback that the determined balance weight values generally do not coincide with the balance weights available to the operator in practice, because these latter are necessarily finite in number, and of a value usually a whole multiple of five grams. Hence in practice the operator is compelled to round off the weight value in order to be able to use one of the weights available, with consequent balancing inaccuracy. US 5,355,729 discloses a method for overcoming the above drawback comprising the step of splitting the balancing weight in each application plane into two weights chosen from a finite number of values available in practice. According to the state of the art, to achieve a perfect balance two balancing weights chosen from a finite number of values available in practice must therefor be applied in each balancing plane. The object of the present invention is to overcome the said drawback without splitting the balancing weight, to achieve a perfect balance by applying a single weight chosen from a finite number of values available in practice in each balancing plane. Said object is achieved by a method and an apparatus having the features recited in the claims. According to the present invention the position of the application plane for each balance weight is determined and memorized, this being advantageously achieved by a geometrical position measuring device forming an integral part of the machine. The balancing planes, which essentially represent the planes in which the machine computes the balance weights, are preferably determined according to the invention by determining two ranges within which the weight application planes must lie, the balancing planes being the central planes of said ranges. After this, according to the invention, using electronic computing means the position of the plane of application of each balance weight within the range about the relative prechosen balancing plane is determined on the basis of weight values chosen by the operator from those available to him, ie generally in multiples of five grams. In a possible embodiment of the method according to the invention, after determining and memorizing the position of the range about the prechosen balancing planes for the balance weights (by means of said measurement device), a first computation is effected by electronic computing means to determine the value of the weights to apply in the relative prechosen planes. A second computation is then effected by said computing means to determine the position of the planes of application of the balance weights within the range of the previously chosen balancing planes, on the basis of fixed weight values close to the values determined by the first computation and chosen from those available. The invention is described in detail hereinafter with reference to the accompanying figures, which illustrate a non-exclusive embodiment thereof. Figure 1 is a perspective view of a wheel mounted on a balancing machine. Figure 2 is an axial section through a portion of the wheel of Figure 1. Figure 3 is a possible block diagram of the machine. The machine, indicated overall by 1, comprises a fixed structure (or machine body) 2 from which the device for locking the wheel 10 (shown in Figure 2) projects. The wheel 10 comprises a rim 11 having a hub 12 with an axial hole 13 by which the wheel is fixed to the vehicle members. The rim 11 has a radial portion (disc) 14 positioned closer to the outer side of the wheel (ie the side facing outwards when the wheel is mounted on the vehicle). The hub 12 has a surface 12a exactly perpendicular to the axis of the wheel 10, acting as a reference surface in coupling the wheel to the relative vehicle members. The substantially cylindrical portion (ring) of the rim 11 on which the tyre 16 is positioned is indicated by 15. The locking device comprises a motorized shaft 20 of horizontal axis A on which the wheel 10 is fixed, projecting from the machine body 2. The shaft 20 is rigid with a motorized coaxial support shaft 23 emerging from the body 2. By the use of clamping means 30, 31, 32 the wheel 10 is made rigid with the shaft 20 and positioned exactly centered on and perpendicular to it. To the side of the locking device there is positioned a geometrical position measuring device 40 comprising a rod 41 arranged to the side of the wheel 10 and a a second rod 42 fixed to the free end 41' of the rod 41. The rod 41 is parallel to the shaft 20 and is projectingly connected to the fixed structure 2 in such a manner as to be able to slide axially and to rotate about its own axis. The rod 42 is positioned to the front of the wheel 10 and carries parallel to the shaft 20 a stem 44, at the free end of which there is arranged a feeler means 50 in a known fixed geometrical position relative to the rod 41. The stem 44 can penetrate axially into the cavity within the wheel rim such that the feeler 50 can reach almost any point on the inner cylindrical surface 15. Within the machine casing 43 there are positioned the measurement means 60 for measuring the axial position and the angular position of the rod 41 relative to the machine fixed structure 2. The data provided by the measurement means 60 are fed to a processor unit 71 comprising inter alia a central memory 72 and a computing unit 73 connected to a display unit 74 (Figure 3). According to the invention, after fixing the wheel 10 on the shaft 20, the geometrical positions of the two planes P1 and P2 prechosen as balancing planes, within a range about which the balance weight application planes Q1 and Q2 must lie, are determined and memorized. Advantageously according to the invention, two ranges known as P1MIN-P1MAX and P2MIN-P2MAX are determined, of each of which P1 and P2 are the central planes. Preferably these planes or ranges are chosen through cylindrical surface parts of the portion 15 on which the balance weights 8 can be easily located, in regions free from discontinuities which could hinder application of the weights 8. The axial position of the planes P1 and P2, or of the relative ranges, is advantageously but not exclusively determined by the measurement device 40, by manually moving the feeler means 50 against the wheel rim surface in correspondence with each plane P1 and P2 or P1MIN, P1MAX, P2MIN, P2MAX and then recording in the memory 72 the data provided by the means 60, ie the geometrical parameters of the device 40 to which the distance of the defined planes from the reference plane R and the radial distance of the rim surface from the axis A correspond. At this point the wheel is rotated and the computing means 73 determine (by well known relationships linking the various geometrical parameters and the unbalance force vectors measured by the usual transducers provided on the machine, to the value of the balance weights) the values M1 and M2 of the balance weights which need to be positioned in the planes P1 and P2 to balance the wheel, and the correct angular positions T1, T2 of these weights within the respective planes P1 and P2. As normally these weight values M1, M2 are different from the values of the weights available to the operator (any coincidence would be fortuitous), this latter, or the machine automatically, feeds into the computing unit other weight values N1 and N2 (close to the computed values M1 and M2) representing weights actually available to the operator, ie pertaining to a discrete series of weights the values of which are multiples for example of five grams. The computing unit then effects a new computation to determine (on the basis of the said relationships linking the various geometrical parameters to the value of the balance weights) the geometrical position - ie the axial distance from the reference plane R - of other planes Q1 and Q2 in which to apply the balance weights of value N1 and N2, and their angular positions Z1, Z2 in these planes. In short, new groups of weight-position-plane values N1-Z1-Q1, N2-Z2-Q2 are recomputed to replace the groups of values M1-T1-P1, M2-T2-P2 obtained by the first computation using traditional methods. As the value N1, N2 of the weights to be applied to the wheel rim is chosen by the operator or by the machine, in some cases the planes Q1 and Q2 may fall outside the range P1MIN-P1MAX and/or P2MIN-P2MAX. If this happens the operator (or the machine) must repeat the procedure choosing two new weights N'1 and N'2 from those available to him. Because of this, not only are the application planes always within those regions of the wheel rim surface on which the balance weights can be easily applied, but it is also possible to apply balance weights having exactly the theoretical balancing value. Advantageously, the geometrical position of the application planes Q1 and Q2 can be identified by the said measurement device 40. This is achieved by manually moving the feeler means 50 carrying a balance weight 8 in front of the surface of the portion 15. When the weight 8 reaches the axial position of the application plane Q1, Q2, determined on the basis of the weight 8 and memorized in 72, the display unit 74 emits an optical signal. The operator then fixes the weight 8 within this plane in the correct angular position, also identified by a signal on the display unit. Numerous modifications of a practical and applicational nature can be made to the invention, but without leaving the scope of the inventive, idea as claimed hereinafter. The description of the computation systems has been omitted, as these are well known to the expert of the art.

Claims: A method for balancing vehicle wheels (10) by means of at least one balance weight (8) to be applied to the wheel rim (11), comprising determining and memorizing the position of a prechosen balancing plane (P1, P2) for each balance weight (8), characterized by attributing to each balancing plane (P1, P2) a range (Pimin-P1max, P2min-P2max) in which the weight application plane (Q1, Q2) must lie, determining by electronic computing means (71) the position of the weight application plane (Q1, Q2) within said range (P1MAX-P1MIN; P2MAX-P2MIN), and the angular position (Z1, Z2) of each balance weight (8; N1, N2) computed on the basis of weight values chosen from a finite number of values available in practice. A method as claimed in claim 1, characterised in that the position of the prechosen planes (P1 and P2) is defined by choosing the two ranges (P1MAX-P1MIN and P2MAX-P2MIN) of which P1 and P2 are the central planes. A method as claimed in claim 1, characterised by comprising, after determining and memorizing by a measurement device (40) the position of the ranges (P1MAX-P1MIN; P2MAX-P2MIN) within which the planes (Q1, Q2) of application of each balance weight are to lie: a first computation, by electronic computing means, to determine the weight values (M1, M2) to apply in the central planes of the ranges (P1MAX-P1MIN; P2MAX-P2MIN), a second computation, by said electronic computing means, to determine the position of the plane of application (Q1, Q2) and the angular position (Z1, Z2) of the balance weight within the aforesaid ranges, said second computation being effected on the basis of a weight value (N1, N2) close to the value (M1, M2) determined by the first computation and chosen from said finite number of values available in practice. A method as claimed in claim 1, characterised by comprising, after determining and memorizing by a measurement device (40) the position of a prechosen balancing plane (P1, P2) for each balance weight: a first computation, by electronic computing means, to determine the weight value (M1, M2) to apply in the relative prechosen plane (P1, P2), a second computation, by said electronic computing means, to determine the position of the plane of application (Q1, Q2) and the angular position (Z1, Z2) of the balance weight within a range about the prechosen balancing plane (P1, P2), said second computation being effected on the basis of a weight value (N1, N2) close to the value (M1, M2) determined by the first computation and chosen from said finite number of values available in practice. A method as claimed in at least one of the preceding claims, characterised in that said measurement device (40) is used to find the position of the plane (Q1, Q2) of application of the balance weight. An apparatus for balancing vehicle wheels (10) by applying at least one balance weight (8), comprising a rotary shaft (20) on a base (2), means (30, 31, 32) for clamping the wheel (10) onto said rotary shaft (20), means for measuring the vibrations of said rotary shaft (20) in at least two reference planes, computing means for computing unbalance, and processing means (73) for computing balance weights to be applied in two application planes (Q1 , Q2) of the wheel (10) in two angular positions (Z1 , Z2) computed by the processing means (73), said computing means comprising a memory for memorizing the unbalance data, characterised in that said processing means are arranged to compute said application planes (Q1 , Q2) to lie within a range around a prechosen balancing plane (P1 , P2), and to compute said angular positions (Z1 , Z2) and said application planes (Q1 , Q2) on the basis of weight values (N 1, N2) chosen from a finite number of values available in practice. An apparatus according to claim 6 characterised in that said processing means (73) is connected to a position transducer (50) arranged to indicate said application planes (Q1 , Q2) and said angular positions (Z1 , Z2).

Inventors: CORGHI REMO, CORGHI, REMO
Applicants: CORGHI SPA, CORGHI S.P.A.
Application year: 1996
Main classification: G01M1
IPC codes: G01M1