WO2010069015A1

WO2010069015A1 - Trackform measuring machine

Info

Publication number: WO2010069015A1
Application number: PCT/BR2008/000396
Authority: WO
Inventors: Josoé Rosa DA SILVA; Leandro Maria; Charles Muller
Original assignee: Gkn Do Brasil Ltda
Priority date: 2008-12-19
Filing date: 2008-12-19
Publication date: 2010-06-24

Abstract

The present invention relates to an apparatus for measuring pressure angle (10), conformity and vertex clearance (11) of tracks of constant velocity joint components. The principle associated with the apparatus consists in the use of locating means on the track, such locating means having a diameter identical to that of the functional ball (5) of the constant velocity joint, causing the same to simulate with exactitude the position and the center of the ball on the said track such that the profile and the deviations thereof are exactly referenced by the center of the ball as defined in the design specification of the constant velocity joint.

Description

"TRACKFORM MEASURING MACHINE"

Technical Field

The present invention refers to a trackform measuring machine, in general to the design and construction of a complete measuring equipment intended for dimensional control of the characteristics relative to the elliptical or gothic track shape used in the various types of constant velocity joints presently manufactured. The invention refers particularly to an apparatus for measuring pressure angle, conformity and vertex clearance of constant velocity joint ball tracks.

Brief Description of the Drawings

For a fuller understanding of the present invention there should be made reference to the attached drawings, which are merely illustrative and not limitative to the scope of the invention, wherein:

Figure 1 shows the most common embodiment of a constant velocity semi-axle;

Figure 2 illustrates constant velocity joints wherein this invention is applied, where the torque is transmitted from an external component to an internal component or vice-versa by means of balls;

Figure 3 shows an example of a CV joint component designated as an outer ring wherein the tracks are represented in perspective, exemplifying plunging-type CV joint tracks; Figure 4 represents the characteristics to be measured by the measuring apparatus according to the present invention; and,

Figures 5A and 5B show, respectively, a side view and a top view of the fastening and measuring mechanisms that make up the apparatus for measuring pressure angle, conformity and vertex clearance according to the present invention.

Prior Art

Constant velocity joints are mechanical components which main function is to transmit torque between two mutually spaced points with a capacity for angular articulation. They are used in a wide variety of types of automobiles and their main purpose is to transmit torque from the transmission gearbox to the vehicle wheel intended to be driven. The most common configuration of these components, such as depicted in Figure 1, is that of a constant velocity semi-axle 1 which is composed by a fixed type constant velocity joint 2, which is applied to the side of the vehicle wheel due to not being capable of axial displacement, a plunging-type constant velocity joint 3, which is applied to the transmission gearbox side and is capable of axial displacement, and an axle 4 which provides the connection between the two joints.

Such joints are named "constant velocity joints" or "homokinetic joints" due to the fact that even when operating angularly they maintain constant rotation at their ends. Such characteristic is important due to the oscillation of the suspension when encountering potholes and uneven pavement and also due to the steering motion of the wheel when the car changes direction. This causes the constant velocity joints to operate under constant angle variations in order to absorb these oscillations at their ends.

The constant velocity joints whereto the present invention applies are mainly characterized by transmitting the torque from an external component to an internal component or vice-versa by means of spherical balls 5 such as illustrated in Figure 2.

This property is achieved due to the fact that the torque is transmitted by means of spherical balls 5 that join the internal element 6, named the internal ring, to the external element 7, named the external ring, in a constant velocity joint. These balls, generally six (6) in number, are maintained in a bisecting plane during the imposition of load to the joint at various angles, however displacing themselves always along ball tracks both of the external element, external ring 8 (shown in Figure 3) and of the internal element, internal ring. Therefore all load requirements are transmitted mainly by the balls and by way of the ball tracks of both the internal element and the external element.

There are thus generated efforts and stresses between the balls and the tracks both of the internal ring and of the external ring with resulting friction between the parts and consequently more intense wear between such regions. The characteristics to be measured by the measuring apparatus are illustrated in Figure 4, and the purpose thereof is to improve the performance of the joint as well as to reduce the wear of the tracks 9 resulting from the friction thereof against the balls. In the illustration to the right side of Figure 4, the tracks 9 are configured with an elliptical shape in order that the contact 10 between the track 9 and the ball 5 is always defined at two contact points instead of a contact surface.

It is as important as the existence of two points of contact to define which will be the angle of contact between the track 9 and the ball 5 with regard to the reference axis defined by a pair of tracks, in this case the track in question and the one opposite thereto. Such importance stems from the fact that the said angle will determine the position in which the loads will be applied to the track thereby resulting in a better distribution of the load components, that is, more balanced or less balanced. One other characteristic that should be both specified and checked regarding the shape of the said tracks is the ratio of the radius of the ellipse at the point of contact to the radius of the working ball in the joint, called track conformity. This characteristic presupposes how will be distributed the stresses between the track and the ball resulting from the torque applied to the joint while at work. This reflects an important design and control parameter to predict the wear to be expected at the region under load. The third and last characteristic, both regarding the design and control of a track of elliptical shape, is called the clearance at the bottom of the track 11 (Vertex Clearance - VC). This is characterized by the distance between the track in the central position with relation to the respective contact points and the ball.

All the above characteristics are achieved by specific milling processes and tools developed exclusively for this purpose. This is due to the fact that one has to deal with very small magnitudes, often requiring less than micrometric resolutions of μm = 10 m for performing control thereof. Note: There exist tracks that have Gothic profiles (as illustrated to the left side in Figure 4) instead of elliptical profiles (as illustrated to the right side in Figure 4), however the control and design characteristics are similar and are applicable to such cases in the same manner.

Disclosure of the Invention

Consequently, it is of the utmost importance that the characteristics of the track profile of a constant velocity joint be present in the product according to the design specifications thereof. Therefore, the object of the present invention becomes quite important since the apparatus disclosed herein will constitute the instrument able to ascertain such characteristics in the components of the constant velocity joint throughout the various manufacturing steps of those components, and in this regard a preferred embodiment of the apparatus according to the invention is illustrated in Figures 5 A and 5B.

Thus, the present invention provides an apparatus for measuring pressure angle, conformity and vertex clearance in tracks of constant velocity joints, comprising:

a means for moving a measuring probe along a path identical to the track surface;

a means for scanning the entire track surface having as a reference the center of the functional ball;

a means for measuring only the track surface form deviation in relation to the functional ball;

a means for using as an alignment and positioning axis of the part to be measured the center of the two diametrically opposite tracks by means of elements that represent identically the functional ball when positioned on the constant velocity joint tracks;

a means for measuring the internal and external components of constant velocity joints without requiring adjustments;

a means for performing the track scan automatically collecting the data from the track measuring probe simultaneously with the respective angular position thereof given by a angular encoder device assisted by computer, hardware and motor; and,

a means for generating, by means of software, the data file comprising the respective radial and angular positions for subsequent analysis by a specific software.

The fundamental principle of the invention is based on the measurement of the previously described characteristics by measuring the track form deviations of the track to be measured with regard to a circle with a diameter equal to the diameter of the ball used to assemble the constant velocity joint. This occurs, as illustrated in Figures 5 A and 5B, when rotating an electronic measuring probe 12 by the center of a ball of identical diameter to that of the ball used to assemble the constant velocity joint, whereupon is performed a subsequent analysis of the data gathered via hardware and software. It should be noted that simultaneously with the rotation of the said electronic measuring probe 12, the same is in constant contact with the track surface.

There is thus created a device of electromechanical construction that reproduces the above described principle in a simple and automatic manner with a motor drive both for positioning and for performance of the measurement.

Initially there is provided a mechanical base supporting the fastenings of the two balls as well as the supporting base of the part to be measured. Since the part will be secured by means of the two opposite tracks there is therefore an axial motion in one of them 13 serving to offset the track diameter variations as well as to maintain the part under pressure to avoid movement thereof while the measurement is being performed. Opposite thereto there is provided the axle 14 comprising an LVDT type electronic measuring probe 12, which will probe the track surface upon the said axle rotating during the scanning of the track. At the upper part of this axle there is concentrically secured a ball segment with a diameter 15 identical to that of the ball mounted on the joint. This is provided to locate the part track according to the center of the rotating axle and consequently at the center of the ball segment. Therefore, upon securing the part to the device there are obtained the following results:

- correct alignment of the part since two tracks are aligned or parallel with the straight line generated by the center of the ball and of the ball segment; and, - the center of the track to be measured is concentric with the rotational center of the measurement axle;

Coupled to this same assembly there is an electronic sensor (LVDT type) 12 oriented in the radial direction of the semi-ball which purpose is to measure the track profile when caused to rotate along the rotating axle 14 by directly probing the surface. The orientation of the probe axis is the same orientation of the straight line generated by the center of the ball and of the ball segment that secure the part by way of its two tracks. There is thus obtained as a result the fact that the sensor readout corresponds to the exact deviations of form of the track surface when secured compared to the reference circle, which in this case has the same diameter of the ball used to assemble the constant velocity joint (balls 5 shown in Figure 2). Consequently, it is possible to perform a complete scan of the track profile, that is, from end to end, using as the rotational center the actual center of the track and thereby simulating the actual condition of the ball when in contact with the track of the constant velocity joint.

Since the rotational motion of the above referred axle is provided by an electronic command via software and hardware, the gathering of signals from the electronic sensor (LVDT type) 12 and the angular encoder device commences at once, thereby warranting the synchronism between the angular position and the radial position throughout the scan to be performed on the track of the constant velocity joint. For purposes of control and gathering of data there has been developed an electronic interface for motor control and for gathering the signals from both the electronic sensor (LVDT type) 12 and the angular encoder device 16, where all of these are connected to a PC type computer. The control of the motor is provided by direct supply of direct current such that the rotating axle follows a course in the shape of an arc from approximately +65° to -65°. The ends of course are limited by position sensors 17 mechanically positioned on the body of the apparatus. The inversion of the movement occurs by means of inversion of the polarity of the supply voltage. The interface board of the electronic sensor (LVDT type) 12 operates to supply and excite the sensor as well as to read the electronic signal thereof to subsequently send the same to the CPU that controls the apparatus. The interface board of the angular encoder device 16 operates to supply the same with a TTL signal with a voltage of ± 5 V as well as to read the value and send the same to the CPU that controls the apparatus.

The CPU that controls the system is a PC type computer that may be provided, for example, with a Windows® operating system. There are installed therein the drivers that control the above mentioned interface boards, the measuring program that controls the movements and the tasks of measurement and calibration and the program that calculates the results.

The main functions of the measurement software are the following:

- Positioning the system at the Zero Degree position

- Start of measurement; start of scan

- Gathering and storage of the measured points in a data file with a specific format

- Calibration of the reference radius according to a specific standard The main functions of the results calculating software are the following:

- Calculation of the angle of contact/pressure of the track on the left and right sides

- Calculation of conformity of the track on the left and right sides

- Calculation of clearance at the bottom of the track/vertex clearance; distance between the ball and the track bottom.

In Figure 5B, reference 18 shows a top view of the securing and measuring mechanisms that make up the apparatus for measurement of pressure angle, conformity and vertex clearance.

As previously mentioned, Figure 4 shows a representation of the characteristics to be measured by the measuring apparatus, particularly shown by references 9, 10 and 11. In these representations there is shown the profile of a circle of known diameter being placed on a track surface with an elliptical profile (a situation depicted on the right side) and on a track surface with a gothic profile (a situation depicted on the left side). It is clear that in this situation there are created two points of contact 10 between the ball represented herein by the circle and the track of elliptical or gothic shape, designated as PA {Pressure Angle). There is also represented the clearance 11 between the ball and the track bottom, designated as VC {Vertex Clearance). The conformity Ψ is the ratio of the radius at the point of contact to the radius of the measuring/assembly ball, that is, the result of the division between the radius of the ellipse at the point of contact, R, and the radius of the ball, r, given by the expression:

Ψ = R / r. Specifically regarding the reference 18 in Figure 5B,it is noted that the same shows a top view of the securing and measuring mechanisms that make up the apparatus for measuring pressure angle, conformity and vertex clearance according to the invention. By observing the reference 18, it is noted that the part is supported on a base with a flat face, however inclined with the same magnitude of the tracks of the outer ring. The support of the part is provided by two diametrically opposite tracks. Therefore, in the securing/supporting mechanism, there is on one side a ball 13 (shown in Figure 5A) with movement in the radial direction provided by a linear bearing 19 and compressed by a spring 20; and on the other side there is a fixed cylinder 14 (shown in Figure 5A) with only rotational motion. Two discs 15 with diameters identical to the diameter of the ball 5 are concentric with the cylinder and attached thereto. The electronic measuring sensor (LVDT type) 12 is also attached to this cylinder and positioned between the above mentioned discs. A bearing 21 is coupled to this cylinder and allows rotational motion thereof, such motion being generated by the electric motor 22 and the gearbox 23 thereof. Next to these components there is an angular encoder device 16 which informs the angular position of the respective cylinder. This motion is restricted at the ends by two induction type position sensors 17.

The evaluation of the track characteristics is provided by a software named TAS^® developed and distributed by GKN England for exclusive use of its factories throughout the world. However, for this to occur it is necessary that the track profile be copied as accurately as possible and digitized for later analysis with the said software. For this purpose there was therefore developed this electromechanical mechanism that copies exactly the profile and generates a data file comprising the angular position and its respective dimension. This occurs by way of the gathering and storage of the points via hardware and software having been developed for this purpose.

The purpose of the electronic sensor (LVDT type) 12 is to indicate the radial position of the track profile since its probe tip is in direct contact with the track surface. The reference thereof is corrected via software where the zero point of the sensor is equivalent to the exact value of the radius of the functional ball. Thus, the values of this sensor are stored upon performance of the scan along the track profile. Since the track profile is not circular, there is a deviation observed relatively to the ball radius, however where the ball contacts the track the value observed in the sensor will be the same as the radius of the ball or very close thereto.

Simultaneously with the time when the position values of the position sensor are stored, there are also gathered by means of the angular encoder device 16 the values of angular position of the axle to which the LVDT type sensor of Fig. 12 is attached. Therefore, it is possible to obtain both the radial position and its respective angular position, such that these are both stored simultaneously by means of a specific software associated with a PC type computer.

For driving the apparatus and for gathering and processing the signals, there is a specific software installed in the measuring apparatus computer. The apparatus is driven to perform the functions of: measurement; provision of reference to the probe; and linearization of the probe, as explained below.

- Provision of Reference to the Probe: The probe tip is placed at the 0° position to use a circular pattern with a radius identical to the radius of the functional ball to be measured.

- Linearization of the Probe: There is conducted a test with the electronic measurement sensor (LVDT type) 12 in order to regularize the gain of its signal and maintain the same true to the scale of measurement when compared with references both known and tracked as well as to correct the linearization of its signal along the range of measurement of approximately ± 500 μm.

- Measurement: The motor 22 is driven to cause the angular displacement of the axle comprising the electronic sensor (LVDT type) 12 following a course in the shape of an arc of approximately 140° counterclockwise. There is further started the gathering of the signals in synchronized manner and in real time. At the end of the measurement the software automatically builds a data file of specific format able to be used with the TAS ® calculation software. At this time it becomes possible to run the TAS® software, which performs the specific calculation routines for provision of the results of pressure angle 10, of conformity and vertex clearance of the track 11 based on the previously created data file.

Claims

1. An apparatus for measuring pressure angle (10), conformity and vertex clearance (11) of tracks of constant velocity joints, characterized by comprising: means (14) to move a measuring probe (12) along a trajectory identical to that of the track surface (9); means to scan the entire track surface (9) having as its point of reference the center of the functional ball (5); means to measure only the deviations of form of the track surface (9) with regard to the functional ball (5); means (14, 13) to use as the axis for alignment and positioning of the part to be measured the center of two diametrically opposite tracks by means of elements (15, 13) that represent identically the functional ball (5) when positioned on the tracks (9) of the constant velocity joint; means to measure the internal and external components of constant velocity joints without requiring adjustments; means to perform the scan of the track automatically by gathering the data from the track measuring probe (12) simultaneously with its respective angular position given by an angular encoder device (16) with the assistance of a computer, hardware and motor; and, means to generate via software the data file comprising the respective radial and angular positions for later analysis by a specific software.