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Steering_Column-Rolling Bearings and Components forPassenger Car Chassis_API.pdf

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STEERING_COLUMN ROLLING BEARINGS AND COMPONENTS FORPASSENGER CAR CHASSIS_API
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Steering Column Rolling Bearings and Components for Passenger Car Chassis Automotive Product Information API 04 134 136This publication has been produced with a great deal of care, and all data have been checked for accuracy. However, no liability can be assumed for any incorrect or incomplete data.Product pictures and drawings in this publication are for illustrative purposes only and must not be used for applications incorporating INA products. Applications must be designed only in accordance with the technical information, dimension tables and dimension drawings. Due to constant development of the product range, we reserve the right to make modifications. The sales and delivery conditions in the relevant valid price list and on order confirmations apply for deliveries and other commercial transactions. Produced by: INA W?lzlager Schaeffler oHG 91072 Herzogenaurach (Germany) Mailing address: Industriestrasse 1–3 91074 Herzogenaurach (Germany) ? by INA · August 2000 All rights reserved. Reproduction in whole or in part without our authorization is prohibited. Printed in Germany by: mandelkow GmbH, 91074 Herzogenaurach3 Seite 4 Aims of development 4 Application areas for rolling bearings 5 Steering system 5 Demands on the steering system 6 Steering column 7 Types of steering column 8 Demands on steering column bearings 8 Safety considerations 10 Bearing arrangements 10 Bearing types 10 Opposed angular contact ball bearing arrangement 11 Clamping rings 12 Angular contact ball bearings SKL 13 Opposed needle roller bearing arrangement 14 Needle roller bearings LEN 15 Opposed four point contact ball bearing arrangement 16 Four point contact ball bearings KLX 17 Four point contact ball bearing and needle roller bearing arrangement 18 Rigidity 18 Opposed angular contact ball bearings SKL/SKL 19 Opposed needle roller bearings LEN/LEN 20 Opposed four point contact ball bearings KLX/KLX 21 Four point contact ball bearing KLX and needle roller bearing LEN 22 Comparison of rigidity values 23 Friction 25 Test procedures 26 Frictional torque in four point contact bearings KLX 27 Frictional torque 27 Rating life 28 Breaking load 29 Noise 30 Fitting dimensions 30 Design of bearing seating surfaces 33 Bearing selection matrix 35 Addresses Contents4 Aims of development Application areas for rolling bearings The aims of further developments and optimization in the field of passenger car chassis are primarily: the improvement of driving comfort by means of – low vibration levels, – more straightforward handling of components relevant to operation and – improved steering comfort the improvement of active safety to minimize the effects of emergency situations (see Demands on the steering system, page 5) the improvement of the passive safety by means of measures to reduce the results of accidents such as – safety steering columns, collapsible and energy absorbing steering wheels. Considerable advancements have been achieved by fine adjustment of the axle kinematics and suspension, e.g. multi-link suspension and axle integrated systems. The future belongs to “intelligent chassis” which obviously will automatically adjust themselves to the relevant driving conditions. Adjustment of the chassis is not limited to just the individual suspension and damping components but includes the associated areas of: drive and braking, driving comfort and driving safety and steering stability and road holding. Current chassis regulation systems such as ABS (anti-lock systems) and ASR or ETC (traction control) improve driving comfort and safety considerably. Further developments will make increased use of electronic components, and hydraulic elements will gradually be superseded. The increasing functionality of the complete component gives rise to increased importance of the rolling bearings. The most significant application areas for rolling bearings in the chassis are: the steering column, the steering gear, the suspension and the McPherson strut bearings and the braking system – without or with ABS. Figure 1 · Chassis with steering 134 1455 Steering system Demands on the steering system The steering system must: convert the angle of the steering wheel into a specific steering angle of the wheels and provide the driver with information on the vehicle’s condition of movement through the steering wheel. Safety requirements If a steering component is faulty or if it were to fail during operation, this has an effect on the function of the steering system. Compromised steering can lead to severe accidents. In order to prevent injury to people and damage to objects, the steering system must meet extremely high safety standards. Functional safety is therefore fundamental for all steering components. Economic requirements Economy of design and production play a large part in determining the competitiveness of a vehicle. Steering systems must therefore: comprise only a few components, be easy to produce and fit, have a low space requirement and be maintenance-free for the life of the vehicle. Technical driving requirements The technical driving requirements are influenced by the physics of driving and the steering kinematics and are also determined by the driver’s demands on comfort. The steering system must therefore: be easy to move and provide a high level of efficiency with a low energy requirement, have an acceptable steering torque but not hinder the self-centring return of the arrangement, damp out unevenness from the road surface and wheel oscillations and ensure directional stability and smooth coupling. Figure 2 · McPherson strut front axle with collapsible steering column 134 1616 Steering column The steering column basically consists of: the outer tube which is screwed to the bodywork and the steering shaft. The steering shaft connects the steering wheel to the steering gear and is supported in an outer tube. It transmits the steering torque. Steering columns have to satisfy the following requirements: ensure high rotational rigidity for the steering shaft, ensure smooth steering, damp out noise, prevent our reduce injury to driver in the event of an accident, have low frictional losses and ensure the vehicle is safe from theft. Figure 3 · Steering column – outer tube, steering shaft, steering gear 134 1627 Types of steering column The following design principles are used in general for steering columns. Rigid steering column – Figure 4 The classic design is a rigid steering column. The steering wheel has a rigid connection to the steering shaft which is usually a single-piece item. Steering column with angular adjustment – Figure 5 The angle of the steering wheel can be adjusted with this design. The tilting point is usually in the joint. Steering column with adjustable height Steering columns with adjustable height can be adjusted telescopically. The position of the steering wheel with respect to the driver can thus be altered in an axial direction. Combined adjustment mechanism – Figure 6 Steering columns with only angular or height adjustment are both compromise solutions. The most favourable position of the steering wheel with respect to the driver is achieved through a combination of both angular and height adjustment. Figure 4 · Rigid steering column Figure 5 · Steering column with angular adjustment Figure 6 · Steering column with adjustable height 134 109 134 110 134 1118 Demands on steering column bearings Safety considerations Bearings used in steering columns must satisfy the following requirements: clearance-free support of the steering shaft, effective damping of noise and oscillations, high rigidity and extremely low friction. Body impact test – Figure 7 There is a legal specification for: the maximum displacement distance of the upper end of the steering column into the passenger compartment and the impact force of a test piece on the steering wheel. Test conditions: displacement distance of 127 mm with frontal impact at a speed of 48,3 km/h maximum impact force of 11000 N; impact at 24,1 km/h. The impact force of 11000 N is limited by: the design of the steering shaft (e.g. corrugated tube) the use of spring elements or similar energy absorbers. The steering shaft bearings must be designed such that they take the load which occurs under specific test conditions. The shaft must display only indentations from the rolling elements and only slight deformation of the individual bearing components is permissible. The steering shaft must still be able to rotate. Anti-theft test – Figure 8 The anti-theft test defines: the safety limits of the steering lock. A torque of up to 240 Nm is applied to the steering wheel. This torque produces high residual radial forces on the upper and lower bearings via the circumferential force on the locking pin. The upper bearing on the steering wheel end is therefore subjected to high loads. The bearings must have a high static load safety factor. Indentations in the raceways from the balls are permissible but cracks or fractures may not occur in the bearing components. The steering function of the vehicle must be unaffected. The maximum permissible effect from the indentations is a reduction in the degree of steering comfort. Figure 7 · Body impact test Figure 8 · Anti-theft test 134 107 134 1089 Shake test – Figure 9 This test describes: the load on the bearing during tilting of the steering wheel caused by tensile or compressive movement. The driver leans all his or her body weight on the steering wheel, causing a bending moment with high reaction forces on the bearings. The force on the upper bearing is normally between 1 000 N and 1 500 N. Under these loading conditions, neither indentations nor deformations may occur in the bearings. Other tests: rigidity, frictional moment, tilting strength, operating life, vibration and noise. The bearing requirements and design recommendations are given on pages 18–29. Figure 9 · Shake test 134 10610 Bearing arrangements Bearing types Opposed angular contact ball bearing arrangement – Figure 10 This bearing arrangement is a proven solution. It is used by many vehicle manufactures as it: has only a low frictional torque, has a relatively high rigidity, is easy to fit and economical. The bearing are preloades clearance-free by cylindrical compression springs (variant I, ) or wave spring washers (variant II, ). The design and location of the springs is dependent on the bearing surroundings. The spring force determines the rigidity of the bearing arrangement as well as the frictional torque and some of the variations in the frictional torque. Very high axial forces occur if the springs are preloaded to full compression. The bearings must support these forces. Although the drawn and induction hardened ball bearings have a very high static load safety fact or, the forces must be limited so that raceway damage does not occur e.g. due to ball indentations. Figure 10 · Opposed angular contact ball bearing arrangement 1 1 Variant I Variant II 1 2 2 1 2 1 Z Z 134 12011 Clamping rings – Figure 11 A push fit is required on the shaft for fitting the bearings. Clamping rings are therefore used between the bearing and the shaft. These rings centre the shaft in the bearing and provide friction locking due to the spring preload. Clamping rings are produced in three design variants: solid ring made from deep drawn steel – these rings require a very high preload force and are used predominantly in trucks coiled rings made from thin-walled sheet steel plastic ring – TN clamping rings . Variants and are used in preference in passenger cars. In the production of the steel clamping rings, a blunt point is formed on the end of the wedge “s”. The gap between the shaft and the bearing inner ring must be greater than the dimension “s” in order to ensure shaft centring. Figure 11 · Clamping rings 1 2 3 2 3 Z 1 Z R Z s s Z Z 2 3 134 12212 Bearing arrangements Angular contact ball bearings SKL – Figure 12 Angular contact ball bearings SKL are drawn i.e. non-machined bearings which are subdivided by the type of rolling element guidance – full complement or cage guided ball set. Full complement angular contact ball bearings The full complement ball set provides rolling characteristics with greater variations in the frictional torque. This design is therefore not suitable for steering systems with high comfort requirements. Cage guided angular contact ball bearings Cages retain the rolling elements at a distance from each other as well as guiding them, thus reducing friction. The raceways can be honed in order to improve steering comfort. Angular contact ball bearing variants INA produces angular contact ball bearings SKL in the following variants: basic design with integral seals – these protect the bearings from contamination, with integral tolerance rings , , – these damp out noise and vibrations and bridge larger tolerances and with integral spring – these simplify steering column assembly. Figure 12 · Angular contact ball bearings SKL – selection 5 4 1 2 3 2 1 3 4 5 2 134 12413 Opposed needle roller bearing arrangement – Figure 13 For rigid steering systems with angular adjustment, the steering shaft can be axially fixed in the steering gear. Needle roller bearings of type LEN are frequently used in this instance. These bearings: do not have an inner ring – the needle rollers run directly on the steering shaft, provide clearance-free support for the steering shaft, damp out noise and vibrations, compensate tolerances in the surrounding structure – the steering shaft and the outer tube are usually cold- formed, are not remachined and are therefore economical components, have low friction and are easy to fit. Preloading The rubber tolerance ring provides the preload in the needle roller bearings. When the bearings are pressed into the outer tube, the split outer ring and the rolling elements are subjected to a defined preload by the tolerance ring. The preload is set such that: sufficient rigidity is achieved and the displacement force for the shaft is not too high. The limiting of displacement force is particularly necessary if the position of the steering shaft has to be adjusted during assembly. Figure 13 · Opposed needle roller bearing arrangement 1 1 2 1 2 134 12614 Bearing arrangements Needle roller bearings LEN – Figure 14 A single bearing of this series consists of: a rubber tolerance ring, a split outer ring, a needle roller and cage assembly (cage with rolling elements) and a thrust washer. The NBR hardness of the rubber tolerance rings is 65 to 80 Shore A (matched to the required rigidity). The precisely specified rubber mixture and the derived technical delivery conditions ensure uniform NBR quality throughout the operati
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