Meshing on the suspension Assembly

AIM:

       Meshing and implementing connections to the car rear suspension model.

ABSTRACT:

                In this project, I have taken a half section of a car rear suspension system where the meshing will be done on different components with 3D, 2D & 1D elements. Also for the particular areas connections will be implemented. The components with a uniform thickness of less than 5 mm are captured by the mid-surface technique (2D-elements), spring with 1D elements, and rest are captured using 3D elements(Tetra elements).

METHODOLOGY:

To capture the geometry we need to follow these steps.

• Import geometry & Topological cleanup
• Parts segregation under different property ID 
• Quality parameter and Mesh parameter setup as per the requirements given
• Construction line adjustment and defeaturing
• Mid-surface extraction if the components with a uniform thickness of less than 5 mm  
• Shell meshing and mesh correction.
• Volume definition and 3D mesh generation for other than mid-surfaced components.  
• Implementation of connections at required areas.

QUALITY PARAMETERS:

  The following quality criteria should be followed for the particular given model.                         

INTRODUCTION:

Vehicle Suspension System

The suspension system must provide proper steering control and ride quality. Performing these functions is extremely important to maintain vehicle safety and customer satisfaction. For example, if the suspension system allows excessive vertical wheel oscillations, the driver may lose control of the steering when driving on an irregular road surface. This loss of steering control can result in a vehicle collision and personal injury. Excessive vertical wheel oscillations transfer undesirable vibrations from the wheel(s) to the passenger compartment, which causes customer dissatisfaction with the ride quality. The suspension system and frame must also position the wheels and tires properly to provide normal tire life and proper steering control. If the suspension system does not position each wheel and tire properly, wheel alignment angles are incorrect and usually cause excessive tire tread wear. Improper wheel and tire position can also cause the steering to pull to one side.

When the suspension system positions the wheels and tires properly, the steering should remain in the straight-ahead position if the car is driven straight ahead on a reasonably straight, smooth road surface. However, if the wheels and tires are not properly positioned, the steering can be erratic, and excessive steering effort is required to maintain the steering in the straight-ahead position. The steering system is also extremely important to maintain vehicle safety and reduce driver fatigue. For example, if a steering system component is suddenly disconnected, the driver may experience a complete loss of steering control, resulting in a vehicle collision and personal injury. Loose steering system components can cause erratic steering, which causes the driver to continually turn the steering wheel in either direction to try and keep the vehicle moving straight ahead. This condition results in premature driver fatigue.

The suspension system contains three major parts: a structure that supports the vehicle’s weight and determines suspension geometry, a spring that converts kinematic energy to potential energy or vice versa, and a shock absorber that is a mechanical device designed to dissipate kinetic energy.

An automotive suspension connects a vehicle’s wheels to its body while supporting the vehicle’s weight. It allows for the relative motion between the wheel and vehicle body; theoretically, a suspension system should reduce a wheel’s degree of freedom (DOF) from 6 to 2 on the rear axle and to 3 on the front axle even though the suspension system must support propulsion, steering, brakes, and their associated forces. The relative motions of the wheels are its vertical movement, rotational movement about the lateral axes, and rotational movement about the vertical axes due to the steering angle.

Function of a Suspension System

As previously mentioned, it is mostly assumed that the only function of a suspension system is the absorption of road roughness; however, the suspension of a vehicle needs to satisfy a number of requirements with partially conflicting aims as a result of different operating conditions. The suspension connects the vehicle’s body to the ground, so all forces and moments between the two go through the suspension system. Thus, the suspension system directly influences a vehicle’s dynamic behavior. Automotive engineers usually study the functions of a suspension system through three important principle are;

 Ride Comfort: Ride comfort is defined based on how a passenger feels within a moving vehicle. The most common duty of the suspension system is road isolation—isolating a vehicle body from road disturbances. Generally, ride quality can be quantified by the passenger compartment’s level of vibration. There are a lot of inner and outer vibration sources in a vehicle. Inner vibration sources include the vehicle’s engine and transmission, whereas road surface irregularities and aerodynamic forces are the outer vibration sources. The spectrum of vibration may be divided up according to ranges in frequency and classified as comfortable (0–25 Hz) or noisy and harsh (25–20,000 Hz).

 Road Holding: The forces on the contact point between a wheel and the road act on the vehicle body through the suspension system. The amount and direction of the forces determine the vehicle’s behavior and performances, therefore one of the important tasks of the suspension system is road holding. The lateral and longitudinal forces generated by a tire depend directly on the normal tire force, which supports cornering, traction, and braking abilities. These terms are improved if the variation in the normal tire load is minimized. The other function of the suspension is supporting the vehicle’s static weight. This task is performed well if the rattle space requirements in the vehicle are kept minimal.

 Handling: A good suspension system should ensure that the vehicle will be stable in every maneuver. However, perfect handling is more than stability. The vehicle should respond to the driver’s inputs proportionally while smoothly following his/her steering/braking/accelerating commands. The vehicle behavior must be predictable, and behavioral information should accordingly be communicated to the driver. Suspension systems can affect vehicle handling in many ways: they can minimize the vehicle’s roll and pitch motion, control the wheels’ angles, and decrease the lateral load transfer during cornering.

Types of Suspension System

 Independent suspension system: 

This system means that the suspension is set-up in such a way that allows the wheel on the left and right side of the vehicle to move vertically independent up and down while driving on an uneven surface. A force acting on the single wheel does not affect the other as there is no mechanical linkage present between the two hubs of the same vehicle. In most of the vehicles, it is employed in front wheels.

This type of suspension usually offers better ride quality and handling due to less unsprung weight. The main advantages of independent suspension are that they require less space, they provide easier steerability, low weight, etc.. Examples of Independent suspension are

• Double wishbone
• Macpherson strut

 Dependent Suspension System:

In Dependent Suspension there is a rigid linkage between the two wheels of the same axle. A force acting on one wheel will affect the opposite wheel. For each motion of the wheel caused by road, irregularities affect the coupled wheel as well. It is mostly employed in heavy vehicles. It can bear shocks with a great capacity than independent suspension. Example of this system is solid axle. 

Semi-Dependent Suspension System:

This type of system has both the characteristics of a dependent as well as independent suspension. In semi-independent suspension, the wheel move relative to one another as in independent suspension but the position of one wheel has some effect on the other wheel. This is done with the help of twisting suspension parts. Example of semi-independent is twisted beam.

The difference between Dependent & Semi-independent suspension system figures are mentioned below:

Components of the car suspension system

Steering Knuckle:

Steering knuckle support the wheel and tire, brakes and sprung weight of the vehicle. A steering knuckle can be mounted in a variety of ways for both front and rear suspensions. In figure it shows an example of a common steering knuckle configuration. The steering knuckle also has an attachment point for the outer tie rod end. A wheel bearing or set of bearings mount to the steering knuckle to provide the mounting of the wheel hub. Steering knuckles are also sometimes called spindles. The spindle portion of the steering knuckle is where the wheel bearings and brake components are mounted. The spindle supports those components and allows the wheel to rotate on the wheel bearings.

Control Arm:

Control arms are used to control wheel movement. Used on both front and rear suspensions, they are commonly referred to by their position, such as the upper and lower control arms. Common control arm configurations are shown in figure below Control arms are also called A-arms or wishbones due to their similarity to being A- or wishbone-shaped.A-arms typically have two connections to the frame and a ball joint for connecting to the steering arm. The control arm are mounted with hub. These bushings allow for up and down movement of the arm while controlling back and forth motion.

Ball joint

Ball joints allow the steering knuckle to pivot for steering while providing a tight connection to the control arms and preventing any unwanted up and down or sideways movement. Ball joints use a ball-and-socket joint to allow a wide range of motion, similar to a shoulder or hip joint.

Ball joints can be one of two types 

•    Load carrying ball joints
•    Non-load carrying ball joints

Load-carrying ball joints support the weight carried by the springs. Because of this, these joints tend to wear faster and need replacement more often than non-load-carrying joints.

Non-load-carrying ball joints provide a steering pivot and component connection with a wide range of movement just like load carrying joints, but without the sprung weight applied to them.

Wheel Hub:

Wheel hubs must provide a secure mounting surface for the wheel rim and tire assembly. Wheel hub also contain the wheel bearings that provide smooth wheel rotation with reduced friction. Wheel bearings must have a minimum amount of end play to  reduce the wheel lateral movement. The wheel hub and bearing assemblies must carry the load supplied by the vehicle weight and these assemblies must also guide the wheel and tire assembly.

Spring:

The springs in the suspension have two important functions. Springs support the vehicle weight and absorb the bumps and movements that occur when driving. There are four types of springs used in suspension systems

• Coil spring 
• Leaf spring 
• Air spring 
• Torsion bar

Shock Absorber:

Shock absorbers are actually dampers, meaning that they reduce or make something less intense. The springs do the shock-absorbing while the shocks dampen the spring oscillations. Without the shocks absorber, our vehicles would continue to bounce for a long time after every bump, dip, and change in body movement. The most common type of shock absorber is the direct double-acting hydraulic shock absorber. This means that the shocks are used to directly act on the motion; double-acting means that they work in both compression and extension modes, and hydraulic means that fluid is used to perform work. Compression is upward wheel travel, also called jounce. The extension is downward wheel motion and is also called rebound.

PROCEDURE:

Import geometry & Topological cleanup

We need to import the CAD model into the ANSA interface. Once the file is loaded, switch on the TOPO mode. Then go for a geometry check and fix all the topological errors.

Segregate the parts under different property ID

Once all the errors are ficxed, we can segregate different parts under various property ID, Then we can proceed part by part for the process of pre-processing.   

As per the requirements given setup the mesh & quality parametrs for Tire & Rim(Ortho & Ortho Tria)

Then for the all given components, set the mesh & quality parameters(Ortho & Ortho Tria)

Set the quality parameter for the component with uniform thickness less than 5mm. For solid quality parameter Tetra element collapse value should be 0.2 

Construction line adjustment and defeaturing

So we need to capture the component properly and have to defeature, toggle off few construction lines and check the geometry before meshing the component. Few of the areas are shown below:

Mid-surface extraction should be done if the components with a uniform thickness of less than 5 mm  

There are only 3 parts that have a length less than 5 mm(uniform thickness) for those, we have to extract the mid-surface.

Shell meshing for all the components

Tire & Rim:

 Steering knuckle, Ball joint pin & Ball joint knuckle:

Wheel Hub & Brake Disc:

Brake Caliper & Upper Strut Mount:

Shock Absorber & Pendulum Bar:

Wish Bone & Car Frame:

Sway Bar & Tie Rods:

Connectors & Bush Link Mountings:

Volume definition and 3D mesh generation for other than mid-surfaced components. 

The next step we need to do is define the volume and generate Tetra elements through the volume but before defining, we need to make sure the part is properly meshed and closed. Also, the part should not contain any overlapping surface. Define them one by one and set different PID type Solid as shown below figure. Used Rapid Tetra mesh algorithm to auto-generate the Tetra element inside the volume. 

There are some section view which illustrates Tetra Solid elements inside the volume.

Implementation of connections at required areas.

There are specific areas that need connections representing bolt, weld, and rigid connections. In the below figures attached it can be easily seen where and why these connections required.

CONCLUSION:

All the components of a suspension system are captured quite decently with solid elements(Tetra) and shell element (Quad+Tria) as per the quality requirements. The sufficiently required connections are given with the RB2 cluster and two-node RB2. There is a total to 870020 tetra element under the volume meshing (3D) free from any Tetra collapse. The curved areas were mainly captured with the ortho Tria element during shell meshing on solid objects which helped to capture the feature correctly. The meshed final model has a smooth surface free from any dip or kinks and can be considered further processing.     

LEARNING OUTCOME: 

• Geometry check and cleanup.
• 1D, 2D(shell), and 3D(solid) meshing.
• Implementation of connections. 
• Car suspension system components and their purpose.