WHEEL ALIGNMENT Basics

Transcription

1 WHEEL ALIGNMENT Basics Bernhard Hoffmann Business Unit Manager Wheel Service 19. November Die NUSSBAUM Gruppe

2 Wheel alignment what for? When and why is a wheel alignment necessary? The complete geometry of the chassis is directly effecting the driving safety, road holding, the wear of the tires and the steering. To get the ideal characteristics, all tires steered and unsteered have to have a certain position to the road and driving direction. If the geometry of the chassis is not properly adjusted, the following will happen: Unusual high wear of the tires Steering is starting to shimmy The vehicle is pulling to one side 2

3 Table of contents Wheel alignment what for? Fundamental terms of wheel alignment Runout compensation How to detect a faulty chassis Different technologies wheel alignment Particularities of the car manufacturer 3

4 Fundamental terms of wheel alignment Midplane of tire is the upright midplane of the tire to the rotating axis Center point of tire is the point of intersection of the midplane and the rotating axis Symmetry axis of the vehicle is going from the middle of the rear to the middle of the front axle = = Radmittelebene Radaufstandspunkt Fahrzeugsymmetrieachse, in diesem Fall = geometrische Fahrachse = =

5 Measured values during a wheel alignment procedure Toe: Is the tire turning to the inside, then it is positive toe / toe in (effect: the tire is pushing to the inside) Is the tire turning to the outside, then it is negative toe / toe out (effect: the tire is pushing to the outside) Toe of the rear tires is the angle between midplane of tire and symmetry axis Geometric axis is the bisecting line of both toes of the rear axle Thrust angle is the angle between symmetry axis and the geometric axis Pos. toe (toe hier + inside) = Vorspur Einzelspur Neg. hier - toe = Nachspur (toe ouside) = = Fahrachswinkel Thrust angle + + = = 5

6 Measured values during a wheel alignment procedure Toe of the front tires is the angle between midplane of the tire and the geometric axis Total toe is the sum of both half toes (e. g. left positive toe = + 0,10 and right negative toe = - 0,07 = total toe +0,03 ) The toe is measured with the alignment heads. A infrared beam is send from each head to the other (along and across). A scale within the head is measuring, where the beam is impinging - + 6

7 Measured values during a wheel alignment procedure Function and effect: With the adjustment of toe the tire gets more grip to the road, thus the vehicle gets a stable and parallel straightforward drive. Without positive or negative toe, the tires are either falling to the inside or outside. The vehicle is not constantly driving straight on, the steering starts to shimmy. Also the tires would etch on the road and wear off much faster as normal. hier + Toe = Vorspur in Einzelspur hier - = Toe Nachspur out 7

8 Measured values during a wheel alignment procedure Steering difference angle is the angle from the inside to the outside tire when steered Steer. diff. angle is measured during the steering wheel procedure Spurdifferenz 20 - X Function and effect: The steered tires shall turn around the center point of the curve. Only then the tires will roll normally without squeaking and without abnormal wear. X 20 Lenkeinschlag 8

9 Measured values during a wheel alignment procedure Camber is the addiction of the tire to the perpendicular of the road Is the tire leaning to the top inside, you have negative camber (effect: tire tears to the inside). Is it leaning to the top outside, you have positive camber (effect: tire tears to the outside) Camber is measured with the alignment heads (inclinometer) Function and effect: Like toe the camber shall effect a stable chassis driving straight on without the steering to shimmy negativer Sturz Negative camber positiver Sturz Positiv camber 9

10 Measured values during a wheel alignment procedure Caster is the angle between the perpendicular of the center point of the tire and the axis of panning / steering. You have a positive caster (also called pulled tire) when the center point of the tire is behind the axis of panning / steering. You have a negative caster (also called pushed tire) when the center point of the tire is ahead the axis of panning / steering. Caster is measured during the steering wheel procedure Function and effect: A positive caster anticipates the shimmy of the steering and provides at the same time (together with king pin) that the steering wheel is getting back into straight position. 10

11 Measured values during a wheel alignment procedure King pin is the angle between axis of panning / steering across to the symmetry axle of the car. King pin is mostly always positive. King pin is measured during the steering wheel procedure. Function and effect: King pin together with caster are responsible for the smooth working of the steering. If king pin and caster would be zero, the steering would not come back on its own, but also you would need no power to steer the car into a curve. 11

12 Chassis data With 8-sensor-technology you can gain information about the chassis situation of the vehicle. These dates are giving a quick information if a car is bent or not. Especially when buying a used car or for the body shop, this information is needed. Set back of front / rear axle Track difference Wheelbase difference Axle offset Side offset 12

13 Quick view on all measuring results After the first alignment all results are shown on one screen. To get an impression of toe and camber a graphic in the center is shown. tears the yellow bar to left or right you can see the toe of the tire drops the yellow bar to inside (negative) or outside (positive) you can see the camber of the tire Toe Camber Caster KPI Included Angle Steering angle difference Max steering angle Rear Toe Rear Camber 13

14 Table of contents Wheel alignment what for? Fundamental terms of wheel alignment Runout compensation How to detect a faulty chassis Different technologies wheel alignment Particularities of the car manufacturer 14

15 Runout compensation The challenge: you want to measure the alignment of the axis of the vehicle, most suitable as the plane of camber / caster. But you are only able to measure the plane of the rim, exceptional case is e.g. MB, Smart, BMW where you measure at the hub or the rim center (Porsche) Von oben: D2 D1 D3 Schlagwinkel s r s D, M D Wahre Spur-Sturz-Ebene The runout and its position is measured when the tire has been turned. For mathematic reasons you need at least two points where to measure the position on the plane of the rim. At these two points the system measures toe and camber as well as the angle the rim has been turned between these two points. 15

16 Table of contents Wheel alignment what for? Fundamental terms of wheel alignment Runout compensation How to detect a faulty chassis Different technologies wheel alignment Particularities of the car manufacturer 16

17 How to detect a faulty chassis Unusual wear of the tires: Wear on edges - inside: toe out - outside: toe in Wear on edges like Saw tooth - inside: negative camber - outside: positive camber Wear on inside and outside - to much positive caster - tyre pressure to low Wear in the center - tire pressure to high 17

18 How to detect a faulty chassis Shimmy of the steering: - at low speed: caster to positive - unbalanced tires - buffer of the steering not ok - to much play in the steering gear Vehicle tears to one side: - to much difference in camber left / right - to much difference in caster left / right - hanging road - tire: difference in weight or pressure - brakes: one is better than the other, or the is stuck - defect in power steering 18

19 Table of contents Wheel alignment what for? Fundamental terms of wheel alignment Runout compensation How to detect a faulty chassis Different technologies wheel alignment Particularities of the car manufacturer 19

20 Different technologies of wheel alignment Optical, with mirror and cord Optical, with mirror and laser CCD-Infrared-Systems (6-/8-sensor-technology) 3D -Systems Robotic non touch systems without any preparations on the vehicle 20

21 Table of contents Wheel alignment what for? Fundamental terms of wheel alignment Runout compensation How to detect a faulty chassis Different technologies wheel alignment Particularities of the car manufacturer 21

22 Particularities of the car manufacturer Toe pressure bar: e.g. Mercedes-Benz. To push the tires to the outside to eliminate the play in the steering gear and other buffers. Load simulations: e.g. BMW, Porsche, Mercedes-Benz. To simulate the real driving situation on the road with loaded condition. 22

23 Particularities of the car manufacturer Fuel level: e.g. BMW, Porsche, Mercedes-Benz and others. Also with the declaration of the fuel level, the real driving situation on the road shall be as realistic as possible. Romess: Mercedes-Benz only. Device to measure the declination of the car. The desired value for adjustment is then calculated. 23

24 Particularities of the car manufacturer Ride height: e.g. Peugeot, VW and others. The ride height has to be measured at certain points defined by the manufacturer. Either, the user can choose between different heights, or he has to load / unload the car. 24

25 Particularities of the car manufacturer Special toe adjustment: VAG only multilink axles Special VAG tool, to measure the front toe of the vehicle in different heights (loading conditions). 25

26 Particularities of the car manufacturer Runout-compensation: e.g. Mercedes-Benz, Porsche, BMW, Smart do not allow to do the ROC Not all manufacturers allow the ROC, because the vehicle either has to be lifted or to be moved forward / backward. Doing this, toe, camber will not any more have the same situation as on the road. To avoid the ROC, you have to use special clamps with adapters going directly to the hub. Thus, mistakes made by wrong clamping are eliminated. 26

27 Otto Nußbaum GmbH & Co. KG Korker Strasse 24 D Kehl-Bodersweier Tel.: +49 (0) / Fax: +49 (0) / info@nussbaum-group.de November Die NUSSBAUM Gruppe