The steering system consists of components which allow the driver to guide the steered wheels or steered wheel conveniently so he can direct the vehicle by turn
Types of steering system
Centerpinsteeringsystem (figure 1):
Such direction is only used in trailers. Not being used in motor vehicles for the following reasons:
- Great efforts on the shaft due to the distance between the wheels and the point of support;
- High instability in tight corners, due to the large decrease in the support area.
Such direction eliminates the above drawbacks, since the shaft remains fixed only by moving the wheels via bolts. The disadvantage is the fact that both the wheels have a steering angle equal that causes imbalance to the vehicle (slippage).
In this system the steering angles are different, which makes both the steered wheels and the rear axle have a common turning center point. This system uses the principle of Ackermann, where the inside wheel angle becomes larger than the outside (the system is currently used in all vehicles).
To achieve this it’s used a set of two risers and a steering bar, which together with the shaft form a trapezium (figure 2).
Organsof the steering system:
In vehicles with four or more wheels:
- steering wheel and steering column shaft;
- tie rods, tie rods, steering rods, steering arms and bearings;
- stub shafts, bolts and wheels.
In vehicles with two or three wheels:
- handlebar steering or advances;
- shaft and bearings of the steering column, T's suspension;
- sheaths, jars and wheel guideline.
Steering wheel and shaft of the steering column:
The steering wheel is fixed to the upper end of the shaft of the steering column. This shaft is surrounded by a support shield or within which rotates supported by bearings or bushings.
Its main function is to convert the rotary motion of the steering wheel rotation and translation in some other cases (such as cash). It also has the secondary function greatly expand the force required to turn the wheels.
Steering boxes types:
Worm screwand nut with antifriction slides:
This box consists of a worm screw which is fixed to the housing body, and which axially displaces a nut. The movement of this nut is transmitted to the steering hanger by a fork.
The transmission of motion is linear.
Wormscrewandscrewed sector(or sprocket) box:
The area (or sprocket) is connected to an articulated arm with a rod, which connects to the rod direction. The worm is responsible for transmitting the movement of the steering wheel to the sector (or sprocket).
Worm screwandscrewedsectorwith circulating spheresbox:
In this case the worm screw runs on spheres, these spheres that circulate between it and an axis with rings for the spheres. The movement of the worm is transmitted to the toothed sector, which in turn transmits a hanger. This box has the advantage of having a very low wear. The transmission of motion is linear.
Worm screwand roller box:
Has the same operating principle of the worm screw and screwed sector box, but in this case the sector is replaced by a roller and the worm screw has a cylindrical shape, having a less diameter in the center.
Worm screw and pin steering box:
In this case a pin slides along a worm screw with variable thread pitch, this means that the box becomes gradual. The worm screw is connected to the steering column and the hanger to a tumbler.
Unassisted rack and pinion box:
In this kind of boxes there are two versions, one with a constant thread pitch rack and other with a variable thread pitch, the latter has the advantage of making the gradual box. The pinion is connected to the shaft of the steering column and engages the rack, the assembly then transforms rotary motion into linear motion of the steering wheel. This box takes the place of the steering bar on the trapeze Ackermann.
Assistedrack and pinion box (figure 3):
This box has the main difference from the previous for having a hydraulic circuit or an electric motor which reduces the force that causes the driver to turn. This case began to be used in heavy vehicles and industrial and agricultural machinery, but is now used in all vehicles. The hydraulic system can also be of assistance in other cases, although currently this type is more widely used.
Fully hydraulic box:
In this case there are no mechanical connection between the steering wheel and wheels, the movement is transmitted only by the action of a hydraulic system. This box has the drawback that not to allow the return direction (position line), so it is only used in agricultural tractors and industrial machines.
Connecting rods, tie rods, steering rods, steering arms and tie rod ends:
They are a whole set of components that make the transmission of motion from the gearbox to the shaft sleeve. The steering bars also have the function to narrow the angle of convergence.
Stub shafts and pins:
São as ligações finais às rodas directrizes, que lhes transmitem o movimento dado ao volante da direcção após ter percorrido todo o sistema de direcção.
This is where the driver applies the effort to turn, these elements are more used in two wheel vehicles but are used also in cultivators, ATV's, etc.. The steering handlebars are fixed at top suspensiontriple tree.
Shaft and bearings of the steering column, suspension triple trees:
A whole set of organs that transfer the movement of the steering handlebars to the wheel (or wheels) and support the steering system.
Inner fork tubes , outer fork tubes and directrix wheel:
These elements belong simultaneously to the steering and suspension, having as function to transmit the movement of the road direction.
Note: In motorcycles and at high speeds direction changes are not made through the steering system, but by changing the masses position.
Can be placed on any type of vehicle and has the function absorb the direction vibrations.
For the steering has good qualities, tire wear is normal and there driving safety, it is necessary to accurately verify the following angles, properly calculated by the builders, who were given the name of the alignment angles:
- Caster angle:;
- Camber angle;
- Tilt angle of the pin;
- Convergence and divergence angles.
Is the angle that the pin normally tilted forward as to the vertical, in four-wheeled vehicles. In bikes is the angle between a vertical line and fork tubes.
From an improper angle of advance can result the following consequences:
If the angle is small, the direction has no fixed position, it is too "loose."
If the angle is large, the direction can shake causing unpleasant and dangerous oscillating on the wheels and steering wheel.
If it is negative the direction becomes hard and dangerous.
Camberangle (figure 4):
Is the angle between the wheel surface and a vertical line.
If the angle is positive have a smaller influence of the force on the steering wheel.
If the angle is negative the center of gravity of the vehicle decreases.
Tilt angle of the pin (figure 5):
Is the angle that the pin forms with the vertical. This influences the speed which the wheels returning to the position of a straight line.
Negative angle: The braking forces cause the inclination of the wheels inwards, causing instability during braking.
Positive angle: The higher this is, the greater the ease with which the wheels turn. In wheels braking situation underwent a tilt out.
Zero angle: The direction becomes extremely heavy. In braking the wheels do not suffer from any inclination.
Convergence and divergence angles (figure 6):
Is the angle that would form two horizontal lines drawn along the height axis according to the plane of the wheel and extended until they meet.
In practice, the convergence is obtained by measuring the height axis, the distance between the wheels back (B) and front (A) and finding the difference between the two measurements (see illustration). This difference generally varies between 1 and 6 mm.
Four-wheel steering System (4WS):
In vehicles fitted with this system there is a steering gearbox completely hydraulic or electric on the rear axle, which depending on the steering angle of the front wheels, vehicle speed and sometimes the speed at which rotates the steering wheel to turn the rear wheels.