Reimpell / Stoll / Betzler The Automotive Chassis: Engineering Principles

2. Auflage 2001
ISBN: 978-0-08-052773-4
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 457 Seiten

This comprehensive overview of chassis technology presents an up-to-date picture for vehicle construction and design engineers in education and industry. The book acts as an introduction to the engineering design of the automobile's fundamental mechanical systems. Clear text and first class diagrams are used to relate basic engineering principles to the particular requirements of the chassis. In addition, the 2nd edition of 'The Automotive Chassis' has a new author team and has been completely updated to include new technology in total vehicle and suspension design, including platform concept and four-wheel drive technology.

Autoren/Hrsg.

Reimpell, Jornsen

Stoll, Helmut

Betzler, Jurgen

Inhaltsverzeichnis

1;Front Cover;1
2;The Automotive Chassis: Engineering Principles;4
3;Copyright Page;5
4;Contents;6
5;Preface;12
6;Chapter 1. Tyres of suspension and drive;14
6.1;1.1 General characteristics of wheel suspensions;14
6.2;1.2 Independent wheel suspensions–general ;20
6.3;1.3 Rigid and semi-rigid crank axles;35
6.4;1.4 Front-mounted engine, rear-mounted drive;43
6.5;1.5 Rear and mid engine drive;54
6.6;1.6 Front-wheel drive;58
6.7;1.7 Four-wheel drive;77
7;Chapter 2. Tyres and wheels;99
7.1;2.1 Tyre requirements;99
7.2;2.2 Tyre designs;102
7.3;2.3 Wheels ;123
7.4;2.4 Springing behaviour;129
7.5;2.5 Non-uniformity ;131
7.6;2.6 Rolling resistance;134
7.7;2.7 Rolling force coefficients and sliding friction;137
7.8;2.8 Lateral force and friction coefficients;141
7.9;2.9 Resulting force coefficient;151
7.10;2.10 Tyre self-aligning torque and caster offset;153
7.11;2.11 Tyre overturning moment and displacement of point of application of force;157
7.12;2.12 Torque steer effects;159
8;Chapter 3. Wheel travel and elastokinematics;162
8.1;3.1 Purpose of the axle settings;163
8.2;3.2 Wheelbase ;164
8.3;3.3 Track ;164
8.4;3.4 Roll centre and roll axis;173
8.5;3.5 Camber;188
8.6;3.6 Toe-in and self-steering;200
8.7;3.7 Steer angle and steering ratio;221
8.8;3.8 Steering self-centring–general;231
8.9;3.9 Kingpin inclination and kingpin offset at ground;234
8.10;3.10 Caster;243
8.11;3.11 Anti-dive and anti-squat mechanisms;268
8.12;3.12 Chassis alignment;273
9;Chapter 4. Steering ;279
9.1;4.1 Steering system;279
9.2;4.2 Rack and pinion steering;284
9.3;4.3 Recirculating ball steering;291
9.4;4.4 Power steering systems;294
9.5;4.5 Steering column;301
9.6;4.6 Steering damper;307
9.7;4.7 Steering kinematics;307
10;Chapter 5. Springing;320
10.1;5.1 Comfort requirements;320
10.2;5.2 Masses, vibration and spring rates;327
10.3;5.3 Weights and axle loads;331
10.4;5.4 Springing curves;341
10.5;5.5 Spring types;353
10.6;5.6 Shock absorbers (suspension dampers);360
10.7;5.7 Spring/damper units;388
10.8;5.8 McPherson struts and strut dampers;388
10.9;5.9 Variable damping;394
11;Chapter 6. Chassis and vehicle overall;399
11.1;6.1 Vehicle and body centre of gravity;399
11.2;6.2 Mass moments of inertia;407
11.3;6.3 Braking behaviour;410
11.4;6.4 Traction behaviour;423
11.5;6.5 Platform, unit assembly and common part systems;432
12;Bibliography;435
13;Glossary of symbols;437
14;Index of car manufacturers;446
15;Index of car suppliers;448
16;Subject index;450

Leseproben

1 Types of suspension and drive
This chapter deals with the principles relating to drives and suspensions. 1.1 General characteristics of wheel suspensions
The suspension of modern vehicles need to satisfy a number of requirements whose aims partly conflict because of different operating conditions (loaded/unloaded, acceleration/braking, level/uneven road, straight running/cornering). The forces and moments that operate in the wheel contact area must be directed into the body. The kingpin offset and disturbing force lever arm in the case of the longitudinal forces, the castor offset in the case of the lateral forces, and the radial load moment arm in the case of the vertical forces are important elements whose effects interact as a result of, for example, the angle of the steering axis. Sufficient vertical spring travel, possibly combined with the horizontal movement of the wheel away from an uneven area of the road (kinematic wheel) is required for reasons of ride comfort. The recession suspension should also be compliant for the purpose of reducing the rolling stiffness of the tyres and short-stroke movements in a longitudinal direction resulting from the road surface (longitudinal compliance, Fig. 1.1), but without affecting the development of lateral wheel forces and hence steering precision, for which the most rigid wheel suspension is required. This requirement is undermined as a result of the necessary flexibility that results from disturbing wheel movements generated by longitudinal forces arising from driving and braking operations. Fig. 1.1 A multi-link rear axle – a type of suspension system which is progressively replacing the semi-trailing arm axle, and consists of at least one trailing arm on each side. This arm is guided by two (or even three) transverse control arms (Figs 1.62 and 1.77). The trailing arm simultaneously serves as a wheel hub carrier and (on four-wheel steering) allows the minor angle movements required to steer the rear wheels. The main advantages are, however, its good kinematic and elastokinematic characteristics. BMW calls the design shown in the illustration and fitted in the 3-series (1997) a 'central arm axle'. The trailing arms 1 are made from GGG40 cast iron; they absorb all longitudinal forces and braking moments as well as transfering them via the points 2 – the centres of which also form the radius arm axes (Figs 3.158 and 3.159) – on the body. The lateral forces generated at the centre of tyre contact are absorbed at the subframe 5, which is fastened to the body with four rubber bushes (items 6 and 7) via the transverse control arms 3 and 4. The upper arms 3 carry the minibloc springs 11 and the joints of the anti-roll bar 8. Consequently, this is the place where the majority of the vertical forces are transferred between the axle and the body. The shock absorbers, which carry the additional polyurethane springs 9 at the top (Fig. 5.50), are fastened in a good position behind the axle centre at the ends of the trailing arms. For reasons of noise, the differential 10 is attached elastically to the subframe 5 at three points (with two rubber bearings at the front and one hydro bearing at the back). When viewed from the top and the back, the transverse control arms are positioned at an angle so that, together with the differing rubber hardness of the bearings at points 2, they achieve the desired elastokinematic characteristics. These are: • toe-in under braking forces (Figs 3.64 and 3.82); • lateral force compliance understeer during cornering (Figs 3.79 and 3.80); • prevention of torque steer effects (see Section 2.10.4); • lane change and straight running stability. For reasons of space, the front eyes 2 are pressed into parts 1 and bolted to the attachment bracket. Elongated holes are also provided in this part so toe-in can be set. In the case of the E46 model series (from 1998 onwards), the upper transverse arm is made of aluminium for reasons of weight (reduction of unsprung masses). For the purpose of ensuring the optimum handling characteristics of the vehicle in a steady state as well as a transient state, the wheels must be in a defined position with respect to the road surface for the purpose of generating the necessary lateral forces. The build-up and size of the lateral wheel forces are determined by specific toe-in and camber changes of the wheels depending on the jounce and movement of the body as a result of the axle kinematics (roll steer) and operative forces (compliance steer). This makes it possible for specific operating conditions such as load and traction to be taken into consideration. By establishing the relevant geometry and kinematics of the axle, it is also possible to prevent the undesirable diving or lifting of the body during braking or accelerating and to ensure that the vehicle does not exhibit any tendency to oversteer and displays predictable transition behaviour for the driver. Other requirements are: • independent movement of each of the wheels on an axle (not guaranteed in the case of rigid axles); • small, unsprung masses of the suspension in order to keep wheel load fluctuation as low as possible (important for driving safety); • the introduction of wheel forces into the body in a manner favourable to the flow of forces; • the necessary room and expenditure for construction purposes, bearing in mind the necessary tolerances with regard to geometry and stability; • ease of use; • behaviour with regard to the passive safety of passengers and other road users; • costs. The requirements with regard to the steerability of an axle and the possible transmission of driving torque essentially determine the design of the axis. Vehicle suspensions can be divided into rigid axles (with a rigid connection of the wheels to an axle), independent wheel suspensions in which the wheels are suspended independently of each other, and semi-rigid axles, a form of axle that combines the characteristics of rigid axles and independent wheel suspensions. On all rigid axles (Fig. 1.23), the axle beam casing also moves over the entire spring travel. Consequently, the space that has to be provided above this reduces the boot at the rear and makes it more difficult to house the spare wheel. At the front, the axle casing would be located under the engine, and to achieve sufficient jounce travel the engine would have to be raised or moved further back. For this reason, rigid front axles are found only on commercial vehicles and four-wheel drive, general-purpose passenger cars (Figs 1.3 and 1.4). Fig. 1.2 An extremely compact four-bar twist beam axle by Renault, with two torsion bar springs both for the left and right axle sides (items 4 and 8). The V-shape profile of the cross-member 10 has arms of different lengths, is resistant to bending but less torsionally stiff and absorbs all moments generated by vertical, lateral and braking forces. It also partially replaces the anti-roll bar. At 23.4 mm, the rear bars 8 are thicker than the front ones (Ø 20.8 mm, item 4). On the outside, part 8 grips into the trailing links 1 with the serrated profile 13 and on the inside they grip into the connector 12. When the wheels reach full bump, a pure torque is generated in part 12, which transmits it to the front bars 4, subjecting them to torsion. On the outside (as shown in Fig. 1.63) the bars with the serrated profile 11 grip into the mounting brackets 7 to which the rotating trailing links are attached. The pivots also represent a favourably positioned pitch centre Or (Fig. 3.159). The mounting brackets (and therefore the whole axle) are fixed to the floor pan with only four screws. On parallel springing, all four bars work, whereas on reciprocal springing, the connector 12 remains inactive and only the thick rear bars 8 and the cross-member 10 are subject to torsion. The layout of the bars means soft body springing and high roll stability can be achieved, leading to a reduction of the body roll pitch during cornering. To create a wide boot without side encroachments, the pressurized monotube shock absorbers 9 are inclined to the front and therefore are able to transmit forces upwards to the side members of the floor pan. Fig. 1.3 Driven, rigid steering axle with dual joint made by the company GKN – Birfield AG for four-wheel drive special-purpose vehicles, tractors and construction machinery. The dual joint is centred over the bearings 1 and 2 in the region of the fork carriers; these are protected against fouling by the radial sealing rings 3. Bearing 1 serves as a fixed bearing and bearing 2 as a movable bearing. The drive shaft 4 is also a sun gear for the planetary gear with the internal-geared wheel 5. Vertical, lateral and longitudinal forces are transmitted by both tapered-roller bearings 6 and 7. Steering takes place about the steering axis EG. Fig. 1.4 Top view of the dual joint...