Pic. 13.3. Elements of the front suspension of the Fiesta car: 1 - McPherson shock absorber strut; 2 - stabilizer bar; 3 – a rotary fist with a nave in gathering; 4 - subframe; 5 - L-shaped transverse levers
The front suspension of the Fiesta has a high «elasticity» when cornering. Excellent suspension behavior is ensured by shock absorbers 1 (pic. 13.3) McPherson, anti-roll bar 2, which improves the behavior of the car when cornering, and L-shaped wishbones 5 independent suspension, guiding the front wheels in the longitudinal and lateral directions.
Independent wheel suspension.
McPherson type front wheel suspension (patented in 1949) consists of a shock absorber, a spring and a steering knuckle with a wheel hub.
Shock absorber.
It combines the functions of a guide apparatus and a damping element and consists of a coiled coil spring and a telescopic shock absorber that operates inside the coils of the spring. Internal strut stops limit downward movement of the wheel, such as in the event of a hard impact or hitting a pothole, while preventing spring lockup and sudden shock failure.
strut dome (in the wheel wing).
The upper part of the shock absorber is attached to the dome. From above, it is made in the form of a rubber support with a thrust bearing, which rests on the upper and lower disc disks with a centering ring. A shock absorber rod is attached to the thrust bearing.
swivel support (ball joint).
It is attached to the bottom of the shock absorber with two bolts and connects the steering knuckle to the lower wishbone of the independent suspension. The wishbone of the independent suspension is fixed in the axle beam and perceives lateral forces.
Anti-roll bar.
An anti-roll bar is attached to the wishbones of the independent suspension, which is a suitably bent rod made of spring steel. It works like this: if the wheel on the inside of the corner moves away from the car while cornering, the stabilizer will twist. This resulting elastic force supports the shock absorber strut, which is located on the outer turning radius, which, together with the springs, increases the rigidity of the strut. The result of the stabilizer is a significant reduction in vehicle roll when cornering.
Steering with gear rack.
It is fixed on the axle beam behind the engine. The two-piece steering shaft directly acts on the rack, to the ends of which the left and right steering rods are respectively attached. Swivel movements are transmitted through the tie rod ends to the steering knuckle and wheels.
TECHNICAL DICTIONARY
Front wheel alignment
Pic. 13.4. Front wheel alignment
Wheel alignment has a significant effect on vehicle stability, tire wear and fuel consumption (pic. 13.4, 13.5).
Pic. 13.5. The angles of the front wheels: A - the angle of the longitudinal inclination of the axis of rotation; B - collapse; C - the angle of the transverse inclination of the axis of rotation of the wheel
Convergence — the difference in the distances between the side flanges of the rims, measured behind and in front of the wheels at the level of their centers. Positive toe means that the wheels in front are closer together than in the rear (at the level of their centers). Convergence affects the straightness of the vehicle and its handling. Due to toe-in, the front wheels rotate in parallel. When the vehicle turns, due to the trapezoid arrangement of the steering rods, the wheel located on the inner turning radius turns a larger angle than the wheel located on the outer turning radius. This is due to the fact that when turning, the inner wheels must move in a circle of a smaller radius than the outer ones. This automatically maintains cornering forces and vehicle trajectory. In addition, toe-in prevents wheel vibration and tire wear.
collapse is the angle between the plane of rotation and the vertical of the wheel. It can be positive, as in the Fiesta, if the wheels are tilted outward, or negative if the wheels are tilted inward. A properly set camber angle reduces the impact of bumps on the steering, reduces steering effort and affects the uniformity of front tire wear. If the camber angle of one wheel is positive and the other is negative, then the car will pull to the side when driving in a straight line.
The transverse angle of inclination of the axis of rotation of the wheel- this is the angle between the axis of inclination of the steering knuckle and the vertical drawn through the wheel attachment point in the longitudinal plane of the car. Distance from centerline across the wheel (the middle point of contact of the tire with the surface) is the turning radius. To reduce the effect of negative forces in the steering, the turning radius should be as small as possible. Due to the camber angles and the transverse inclination of the axis of rotation, the points of contact of the wheels with the road are located closer to the axis of the steering knuckle. This supports the so-called running-in shoulder. The smaller the break-in shoulder, the easier it is to drive the car. This leads to the fact that when the wheels are turned out, the car rises slightly. When you release the steering wheel, the wheels spontaneously return to the middle position (restoring moment). In addition, bumps from uneven surfaces are less transmitted to the steering.
Angle of longitudinal inclination of the axis of rotation - this is the angle between the axis of inclination of the steering knuckle and the vertical drawn through the wheel attachment point in a plane perpendicular to the longitudinal axis of the car. The axis about which the wheel turns is placed in space so that its lower part is tilted forward. Such an angle of longitudinal inclination is called positive. With a positive value of the angle, the best stability and stabilization of the steered wheels in a straight line is provided.
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