- Car Care & Maintenance
The suspension is the elastic connection between the vehicle and the ground and that its function is to release that same vehicle from road irregularities.
Springs: Through its elongation and contraction allow the axles go up and down, thus absorbing the irregularities of the floor.
Types of springs:
- Leaf springs;
- Helical springs;
- Torsion bars;
- Rubber Springs;
- Pneumatic springs;
- Hydropneumatic springs.
Leaf springs (Figure 1):
Are generally composed of several steel sheets, of different lengths mounted on each other, forming what is called a leaf spring.
The ends of the larger sheet (master sheet - 3) are wound to form an eye (1). In one of the bearings are placed eyelets through which the pins or screws connecting the spring to the chassis.
On the other ring master sheet binds to the chassis by means of a device called shackle (2), which allows for contraction and distention of the leaf springs.
This bundle is held together by clamps side (4) and fixed to the shaft by fixing clamps (5).
Helical springs (Figure 2):
They are formed by a steel bar helically wound.
They are usually fixed by one end to the chassis and the other to an independent pivot arm or the bottom of the damper (Macpherson).
These springs are the most currently used due to its light weight, quiet and easy adjustment wheel independent suspension.
The coil springs may be of two types: linear (1) or progressive (2).
The linear type has a constant diameter and thus compress always the same value with the same increase of load.
The progressive type have a variable diameter or distance between the turns varies, but for the same increase with a higher load is less than the offset.
Torsion bars (Figure 3):
Are formed by a bar (1) of steel having one end firmly fixed to the vehicle chassis (2) and the other fixed to a lever or suspension of the lower triangle (3) on whose end is exercised force of the suspension . Road irregularities are absorbed by the twist of that bar.
This type of springs are mainly used in trailers, having a current due to very small and their cost is low. The rubber springs can work in several situations: in compression, tension and compression.
Stabilizer bars (Figure 4):
Counter to the effect of centrifugal forces in curves which tends to tilt the vehicle to the outside. For example when the centrifugal force in a curve tends to rise the body from the left and download it by right, the bar suffers a twisting effect in the opposite direction, reducing the slope and stabilizing the vehicle.
Are essentially formed by steel bars at the ends rigidly secured to two arms which are articulated on the axle of the vehicle and secured centrally to two lugs to the body.
Consist in a rubber balloon with high strength that is placed in the same location and position of a coil spring. This type of springs used to change the distance of the vehicle to the ground.
We also find this type springs being attached to helical springs, acting as auxiliary.
Consist of a sphere with two compartments separated by a membrane, one of the compartments there is a gas oil alone and the other with connection to a chamber of a cylinder that connects to the wheel by a shaft.
This type of springs dispense shock absorbers.
They have the function of regulating the oscillatory motion of springs, transforming the mechanical energy into heat.
Shock absorbers can be of two types:
Mechanical shock absorbers:
Its principle of operation of the compression coil springs and the friction disc made of a material with high friction coefficient (fiber or termóide).
They are generally formed by two arms, one of which is connected to the chassis and the other corresponding to the axle by means of joints themselves.
These shock absorbers are now practically abandoned.
Hydraulic shock absorbers:
Based on a system of valves which controls the speed of passage of oil through them.
These shock absorbers can be of three types: rotary (disused), piston (disused) and telescopic.
Telescopic Hydraulic shock absorbers:
May be one or two tubes with or without a pressurized gas.
Shock absorbers with two tubes without pressurized gas (Figure 5):
Have as main components: two concentric cylindrical pipes (1 and 2), a rod with an outer ring (3), a plunger (4) and a lid provided with several holes of valves, three oil chambers (5) and a housing cylindrical.
These shock absorbers are connected to the chassis of the rod ring and the axle or wheel ring for a cylindrical tube which has at the outer end.
The passage of oil through the holes of the piston and the cover is controlled so that the separation and alignment of eyelets is done at a rate such that the movement of the cushion spring.
Shock absorbers with one tube and pressurized gas (Figure 6):
These shock absorbers have the main differences from the above, the fact that only consist of a cylindrical tube (1) and having two pistons, one piston moves freely and separates the oil from the pressurized gas (2).
The pressurized gas (3) exists in the buffer in order to keep the oil (4) at a constant pressure in order to avoid the phenomenon of cavitation (foam), which reduces the effectiveness of shock absorbers.
Alternatively to this system are suspensions that have a separate reservoir of shock absorber, where there is pressurized gas and oil separated by a membrane.
Shock absorbers with two tubes and pressurized gas (Figure 7):
This shock absorber is coupled the two preceding types, and their performance identical to that of two tubes without pressurized gas, only using an improvement in terms of no formation of cavitation.
The main differences with the damper tube with a pressurized gas have the fact that the oil (1) and the pressurized gas (2) not having a physical separation (piston), as in the above.
Shock absorbers variables:
In this case the attenuation level is variable, ie depending on the vehicle load.
This variation can be made in several ways:
- For the driver, by actuating the damper.
- By the driver by means of a selector on the carrier.
- Automatically, the electronic unit of the vehicle.
This variation is achieved only by changing the section of passage of the oil, ie, by changing the section or the number of valves.
It consists of several parts such as tread, sidewalls, heel, etc..
Its main function at the level of the suspension is to absorb small surface irregularities.
Types of suspension:
- Shaft rigid suspension;
- Independent suspension;
- Air suspension;
- Hydropneumatic suspension;
- Hydrolastic suspension.
Suspension rigid shaft (Figures 8,9 and 10):
This suspension is characterized, as the name indicates, on a rigid axle having wheels that connects together two by two.
This type of suspension is currently only used by heavy vehicles.
The main advantages of this type are: the low cost of construction, no changes of the angles of the wheels and a good cornering stability. Being the main disadvantages that they become too heavy (less comfort) and the influence that has a wheel on the other.
The figures are examples of suspensions of the rigid shaft with different types of springs and solutions of construction. Since the first and second axes of traction and a third simple axle.
In this type of suspension does not exist a rigid axle so that the wheels do not communicate with each other the suffer shocks and vibrations.
Currently the use of independent wheel suspension by cars is generalized both in front and in rear.
May be used any kind of springs previously seen in independent suspensions, although the most common are coil springs and torsion bars
Currently the most used systems are:
- Suspension Macpherson;
- Overlapping triangles;
MacPherson strut suspension (Figure 11):
The damper (1) in this case is mounted within the helical spring (2), this being positioned between a flexible coupling existing in the body and a plate (3) belonging to the shock. The stub axle (4) connects superiorly and inferiorly to the shock to an arm anchor (5). Often a stabilizer bar is added to this system.
The main advantages are a reduced footprint and easy maintenance.
Suspension overlapping triangles (Figure 12):
The springs, helical in this case, are connected to two triangular arms (1) which are articulated on the base frame (2) and the vertices on the wheels (3). The whole forms what is called a trapezoid articulate.
The spring support is generally from above on a support (4) which forms part of the chassis.
The damper may be mounted within the spring or the top joint.
It is also common place in this type of a suspension stabilizer bar (5).
The advantages of it are: reduced size in height and a small change in angles of the wheels.
The main disadvantage of this type of suspension is the high cost of construction.
Multi-link suspension (Figure 13):
This type of suspension has some similarities to the MacPherson type, such as the position of the damper (1) and the spring (2) and connected to the sleeve axis. But this suspension employs, as its name indicates, multiple connections to the chassis, namely an upper arm (3) and two lower arms (4).
The advantage of this system is that to achieve an excellent compromise between comfort and performance.
In this system air springs are used which contain a certain mass of compressed air. This mass of air within the springs constantly varies depending on vehicle load and surface irregularities, keeping it level and a constant ground clearance.
Control is achieved via pneumatic valves which in turn are controlled in a mechanically or electronically.
When there is made a tie rods mechanically connected to the axes causing the air inlet of the deposits and their escape into the atmosphere.
When it is done electronically there is a unit that performs the electronic management of the suspension.
In both cases the driver has the possibility to change the height of the vehicle.
The advantages are: comfort, the height and greater stability of the vehicle.
How have the disadvantage of high cost.
Hydropneumatic suspension (Figure 14 and 15):
In this type of suspension is used a "spring" Hydraulic (1) that resembles the one hydraulic cylinder, the plunger (2) can be of two types, with or without valves, when this spring is also assumes the functions of shock absorber . The spring has two openings an upper (3) which connects an accumulator control valve ball and the vehicle height and a lower hole (4) which is also connected to the height control valve (5).
The spherical accumulator (9), which is slightly away from the spring or can be situated directly above, contains a membrane (6) which separates the oil inside (7) of the gas (8).
The absorption of the irregularities is then made by the inlet and outlet oil reservoir spherical aid in damping gas is constantly opposed to the movement of the spring asterisk.
Hydrolastic suspension (Figure 16):
In this type of suspension for each wheel there is connected a drive hidragás (1), consisting of a reservoir with two zones separated by a membrane (2), the upper portion (3) contains a gas and the bottom (4) contains a liquid to water-based and alcohol.
The units are linked to each other two by two, the front and rear of the same hand, this greatly reduces the effect of the oscillatory body forward and backward tilt and curve due to centrifugal force.
The first effect is achieved because that when a unit is by compression of the wheel (5) of the liquid contained therein is transferred to another unit which is connected by a pipe (6) increasing the amount of liquid therein, against the said movement.
Damping this suspension is made by the passage of liquid valves each own (7).