Wheel steering mechanisms - Independent systems

Wheel guidance mechanisms

Before describing possible embodiments of the Independent Suspension System, this issue will describe the basic kinematic principles and some of the basics of the operation of Independent Suspension Systems.

The way the wheels are moved in relation to the body of the vehicle is an influential factor in terms of steering ability and the behavior of the vehicle on the road. The displacement, that is, the kinematics of the wheels, is conditioned by the construction and type of mechanism for steering the wheels and is generally independent of the other elements of the suspension system (elastic supports and dampers). The provision of wheel kinematics is the primary task of the wheel guidance mechanism. Wheel guidance mechanisms must minimize the size changes that define the optimal rolling conditions during vehicle movement across different types of substrates. It is especially important that the wheel slope values ​​do not change with the steering wheels. It is also undesirable to move the wheels in the transverse direction, as well as to change the value of the wheels.

Figure 2. Six degrees of freedom in space

The reliance system should assume the security of the said tasks. Independent systems make it possible to fully meet the above requirements and conditions to achieve optimal static and dynamic deflection values ​​and ensure proper steering wheel kinematics.

Some of the benefits of an independent steering system are:
• Reduced values ​​of unmolested mass
• moving one wheel on the same axle does not affect the movement of the other wheel
• a large number of kinematic configurations when constructing
• Simple isolation of vibrations and acoustic effects from the substrate
• there is no self-management effect
• Better lying on the road due to the lower center of gravity - the motor can be positioned lower because there is no transverse rigid shaft element

Figure 3. Types of joints

Some of the disadvantages:
• axle connection and clearance from the ground are limited (may be a disadvantage for ATVs)
• The tendency to equalize the load on wheels on the same axle in a curve is only possible by using a stabilizer (rod balance)
• robustness less than that of rigid shafts

Due to the cost and complexity of many manufacturers, their smaller vehicles are equipped with an independent front axle suspension system and the rear axle is made by a dependent or semi-independent suspension system. However, the share of vehicles using independent suspension systems is steadily increasing.

Kinematics of Independent Suspension Systems
Each independent suspension system consists of kinematic connections that connect the body to the elements to which the wheels attach. The individual elements in the linkage system are joined by joints. The joints are most commonly found at the ends of the elements. The wrist type determines the freedom of movement of the bonded elements. There are six degrees of element freedom (rotation about each of the three axes, and displacement along all three axes), and independent suspension guidance systems should limit the degree of freedom of the wheel carrier to one (two control axle services).

An unlimited degree of freedom should be a shift in the direction normal to the ground. However, none of the systems used today fully complies with the five-degree limit on freedom.

A second degree of freedom is required for the control which is performed by means of clamps that are attached to the control mechanism. In the continuation of the article, the explanations will be under the assumption that the control system is locked in the neutral position, so we will assume that the wheel carriers have only one degree of freedom.

The kinematic lever system that binds the wheel mounts to the body consists of rigid joints with the joints. Springs and shock absorbers make up an elastic element that restricts movement in the vertical direction (sixth degree of freedom). This elastic element does not affect the kinematics of the suspension system unless the suspension system is designed as a rotary sliding joint (spring leg).

The number of ties required to control the movement of the wheel depends on the kinematic characteristics of the various types of links built into the suspension system.

Figure 4. Independent suspension systems with 2-5 connections

The simplest type of suspension connection is a two-point connection (Figure 3a). The two-point coupling has either a spherical joint or a rubber bushing as an element of connection. Each clamp with two attachment points reduces the number of degrees of freedom of the wheel carrier by one. If the wheel carrier is attached to a five-link body with two attachment points, only one degree of freedom of the wheel carrier remains (for vertical movement). This solution is known as multilink (5 clamps).

Two degrees of freedom can be limited by using a 3-point link (triangular shoulder, Figure 3b), with one point of attachment on the wheel carrier and two points of attachment on the body. A single triangular shoulder functions as two fasteners with two attachment points. If one triangular arm and three two-point linkages are used, a four-link system is obtained (Figure 4).

If two triangular shoulders are used, only one two-point fastening is required.

This configuration is called a double triangular shoulder or a three-link system. In this configuration, the triangular shoulders are oriented transversely.

A four-point linkage (trapezoidal linkage) is used to limit four degrees of freedom (Figure 3c). If another two point attachment is added, the wheel carrier will have only one degree of freedom. This configuration is known as a two-clamp suspension system.

Figure 5. Orientation of ties: a) transverse b) longitudinal c) hair

Single-clamp retraction is also possible. This solution is implemented by tying the rear axle wheel mounts to the body using an axle which is also the axis of rotation of the wheel mount. Thus, each wheel carrier has only one degree of freedom. The movement of the wheel carrier is determined by the position of the axis of rotation or the axis (Figure 5).

Another example of this solution is the rotary sliding joint. An example of such a solution is a shock absorber whose piston can be rotated and vertically moved relative to the shock absorber housing (Figure 3d). Two degrees of freedom are limited by mounting the shock absorber housing to the wheel carrier and tying the shock absorber piston to the body using a spherical joint or rubber bushing (upper link, on "shock absorber cups").

This configuration is called the spring leg. Three more two-point fasteners (or one triangular shoulder and two two-point fasteners) are needed to reduce the number of degrees of freedom to one. The spring can be coaxially positioned relative to the shock absorber for space savings (Figure 6). Such systems require either two fasteners with two attachment points or one lower triangular shoulder. The suspension brackets can be positioned transversely, longitudinally and diagonally with respect to the direction of travel of the vehicle (Figure 5). Depending on the positioning, the clamps transmit forces in the transverse, longitudinal or in both directions. The support should generally be as circular in the lateral direction as possible and softer in the vertical direction.

Figure 6. Coaxial (left) and separately (right) mounted spring

The points of intersection of the axis of the joints in the suspension system determine the behavior of the suspension. The movement of the clamp system can be planar (planar), spherical or three-dimensional (Fig. 7).

The rotational axes of the planar clamping system are parallel to each other. Therefore, the axis of rotation of the carrier wheel is parallel to the axis of rotation of the clamp. The wheel moves about an axis in one plane. Although the axis of rotation of the wheel carrier changes as it moves the guiding elements, it remains parallel to the line "m".

If the axes of rotation of the lower clamps are not parallel to each other, and intersect at one point in space, then all points of the wheel carrier will make a spherical motion around that center point (Z). Unlike the planar system, the axis of rotation of the wheel carrier will not remain parallel to the original position, but the axis of rotation of the wheel carrier will rotate freely around the center point.

If the rotation axes are not parallel and do not intersect, the wheel carrier moves in a curved path around the 's' axis.

This movement is a three-dimensional movement in space.

Figure 7. Movement of the suspension system with the traezoidal clamp a) planar b) spherical and c) three-dimensional

Text by Vanja Dragosavljevic
Retrieved from: www.vrelegume.rs

Mladen

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