Single row deep grooved radial ball bearing

(Fig. 6.12) These bearings are basically designed for light to medium radial load operating conditions. An additional feature is the depth of the grooves combined with the relatively large size of the balls and the high degree of conformity between balls and grooves which gives the bearing considerable thrust load carrying capacity so that the bearing will operate effectively under both radial and axial loads.

These bearings are suitable for supporting gearbox primary and secondary shafts etc..

Single row angular contact ball bearing (Fig. 6.13) Bearings of this type have ball tracks which are so

(a) Excessive slackness |b) Zero slackness

(a) Excessive slackness |b) Zero slackness

Id} Heavy preload

(c) Light preload

Id} Heavy preload

(c) Light preload

Fig. 6.11 (a-e) Bearing radial and axial load distribution

Fig. 6.12 Single row deep groove radial ball bearing

Fig. 6.13 Single row deep angular contact ball bearing disposed that a line through the ball contact forms an acute angle with the bearing shaft axes. Ball to track ring contact area is elliptical and therefore with the inclined contact angle this bearing is particularly suitable for heavy axial loads. Adjustment of these bearings must always be towards another bearing capable of dealing with axial loads in the opposite direction. The standard contact angle is 20°, but for special applications 12, 15, 25 and 30° contact angle bearings are available. These bearings are particularly suited for supporting front and rear wheel hubs, differential cage housings and steering box gearing such as the rack and pinion.

Double row angular contact ball bearings (Fig. 6.14) With this double row arrangement, the ball tracks are ground so that the lines of pressure through the balls are directed towards two comparatively widely separated points on the shaft. These bearings are normally preloaded so that even when subjected to axial loads of different magnitudes, axial deflection of the shaft is minimized. End thrust in both axial directions can be applied and at the same time very large radial loads can be carried for a relatively compact bearing assembly.

A typical application for this type of bearing would be a semi- or three-quarter floating outer

Fig. 6.14 Double row angular contact ball bearing
Fig. 6.15 Double row self-alignment ball bearing

half shaft bearing, gearbox secondary output shaft bearing etc.

Double row self-aligning ball bearing (Fig. 6.15) This double row bearing has two rows of balls which operate in individual inner raceway grooves in conjunction with a common spherical outer raceway ring. The spherical outer track enables the inner ring and shaft to deflect relative to the outer raceway member, caused by the balls not only rolling between and around their tracks but also across the common outer circular track. Thus the self-aligning property of the bearing automatically adjusts any angular deflection of the shaft due to mounting errors, whip or settlement of the mounting. It also prevents the bearing from exerting a bending influence on the shaft. The radial load capacity for a single row self-aligning bearing is considerably less than that for the deep groove bearing due to the large radius of the outer spherical race providing very little ball to groove contact. This limitation was solved by having two staggered rows of balls to make up for the reduced ball contact area.

Note that double row deep groove bearings are not used because radial loads would be distributed unevenly between each row of balls with a periodic shaft deflection. They are used for intermediate propellor shaft support, half shafts and wherever excessive shaft deflection is likely to occur.

Single row cylindrical roller bearing (Fig. 6.16) In this design of roller bearing, the rollers are guided by flanges, one on either the inner or outer track ring. The other ring does not normally have a flange. Consequently, these bearings do not take axial loads and in fact permit relative axial deflection of shafts and bearing housing within certain limits. These bearings can carry greater radial loads than the equivalent size groove bearing and in some applications both inner and outer ring tracks are flanged to accommodate very light axial loads.

Bearings of this type are used in gearbox and final drive transmissions where some axial alignment may be necessary.

Single row taper roller bearing (Fig. 6.17) The geometry of this class of bearing is such that the axes of its rollers and conical tracks form an angle with the shaft axis. The taper roller bearing is therefore particularly adaptable for applications where large radial and axial loads are transmitted simultaneously. For very severe axial loads, steep taper angle bearings are available but to some extent this is at the expense of the bearing's radial load carrying capacity. With taper bearings, adjustment must always be towards another bearing capable of dealing with axial forces acting in the opposite direction. This is a popular bearing for medium and heavy duty wheel hubs, final drive pinion shafts, the differential cage and crownwheel bearings, for heavy duty gearbox shaft support and in-line injection pump camshafts.

Double row taper roller bearing (Fig. 6.18) These bearings have a double cone and two outer single cups with a row of taper rollers filling the gap between inner and outer tracks on either side. The compactness of these bearings makes them particularly suitable when there is very little space and where large end thrusts must be supported in both axial directions. Thus in the case of a straddled final drive pinion bearing, these double row taper bearings are more convenient than two single row bearings back to back. Another application for these double tow taper roller bearings is for transversely mounted gearbox output shaft support.

Double row spherical roller bearing (Fig. 6.19) Two rows of rollers operate between a double

Fig. 6.18 Double row taper roller bearing Fig. 6.19 Double row spherical roller bearing

grooved inner raceway and a common spherically shaped outer raceway ring. With both spherical rollers having the same radii as the outer spherical raceway, line contact area is achieved for both inner and outer tracks. The inner double inclined raceway ring retains the two rows of rollers within their tracks, whereas the outer spherical track will accommodate the rollers even with the inner track ring axis tilted relative to the outer track ring axis. This feature provides the bearing with its self-alignment property so that a large amount of shaft deflection can be tolerated together with its capacity, due to roller to track conformity, to operate with heavy loads in both radial and axial directions. This type of bearing finds favour where both high radial and axial loads are to be supported within the constraints of a degree of shaft misalignment.

Single row thrust ball bearing (Fig. 6.20) These bearings have three load bearing members, two grooved annular disc plates and a ring of balls lodged between them. A no-load-carrying cage fourth member of the bearing has two functions; firstly to ease assembly of the bearing when being installed and secondly to evenly space the balls around their grooved tracks. Bearings of this type operate with one raceway plate held stationary while the other one is attached to the rotating shaft.

In comparison to radial ball bearings, thrust ball bearings suffer in operation from an inherent increase in friction due to the balls sliding between the grooved tracks. To minimize the friction, the groove radii are made 6-8% larger than the radii of the balls so that there is a reduction in ball contact area. Another limitation of these bearings is that they do not work very satisfactorily at high rotative speeds since with increased speed the centrifugal force pushes the balls radially outwards, so causing the line of contact, which was originally in the middle of the grooves, to shift further out. This in effect increases ball to track sliding and subsequently the rise in friction generates heat. These bearings must deal purely with thrust loads acting in one direction and they can only tolerate very small shaft misalignment. This type of bearing is used for injection pump governor linkage axial thrust loads, steering boxes and auxiliary vehicle equipment.

Needle roller bearings (Fig. 6.21) Needle roller bearings are similar to the cylindrical roller bearing but the needle rollers are slender and long and there is no cage (container) to space out the needles around the tracks. The bearing has an inner plain

Fig. 6.20 Single row thrust bearing

Fig. 6.21 Needle roller bearing

raceway ring. The outer raceway is shouldered either side to retain the needles and has a circular groove machined on the outside with two or four radial holes to provide a passageway for needle lubrication. The length to diameter ratio for the needles usually lies between 3 to 8 and the needle roller diameter normally ranges from 1.5 to 4.5 mm. Sometimes there is no inner raceway ring and the

needles operate directly upon the shaft. To increase the line contact area, and therefore the load carrying capacity, needles are made relatively long, but this makes the needle sensitive to shaft misalignment which may lead to unequal load distribution along the length of each needle. Another inherent limitation with long needles is that they tend to skew and slide causing friction losses and considerable wear. The space occupied by a complete needle roller bearing is generally no more than that of a hydrodynamic plain journal bearing. Bearings of this type are well suited for an oscillating or fluctuating load where the needles operate for very short periods before the load or motion reverses, thereby permitting the needles to move back into their original position, parallel to the shaft axis.

Because the needles are not separated from each other, there is a tendency for them to rub together so that friction can be relatively high. To improve lubrication, the needle ends are sometimes tapered or stepped so that oil or grease may be packed between the ends of the needles and the adjacent raceway shoulders.

Needle roller bearings are used for universal joints, gearbox layshafts, first motion shafts, mainshaft constant mesh gear wheel bearings, two stroke heavy duty connecting rod small bearings etc.

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