C-tech chassis stabilizer bar
why c-tech?
chassis in general :
Most street driven cars are manufactured using a construction technique known as unibody spaceframe chassis construction. This means that the body itself provides the stiffness and structure of the vehicle. Many older vehicles had separate stiffening structures and bodies, the body being solely designed as an aesthetic exterior and as a safety and environmental housing for the passengers. This technique is both heavier and requires more materials raising costs. Modern vehicle chassis are made entirely out of formed sheet metal sections which are usually spot welded together to form the structure of the vehicle. Designing these chassis is no easy task, the geometries being incredibly complex. Making these designs both cost effective, lightweight, stiff and safe is always a tradeoff.
Production vehicle chassis vary substantially in the degree to which they maximize the variables previously mentioned. Higher performance vehicles are often designed with maximum stiffness and lightweight in mind. A lighter weight chassis promotes an overall lower vehicle weight and better performance. Chassis stiffness though is also important for vehicle performance.
As a vehicle is driven, various forces are applied by the suspension on the chassis. This occurs under braking, cornering, driving surface variations, or any other vehicle movement. In higher these loads are, the more is demanded of a chassis. The chassis obviously has to be strong enough not to fail under these loads, but beyond that it must not deflect appreciably. Suspensions are carefully designed to position the wheels and tires of the vehicle for optimum performance under all conditions of vehicle use. If the chassis deflects when the forces are high, it causes suspension mounts and attachment points to temporarily shift, which destroys the careful suspension design when it is needed most. Chassis stiffness is most important in high performance or racing cars, where suspension loads are at their highest and suspension adjustment is most critical.
To combat chassis flex, many people desiring improved performance out of their unibody cars fit chassis stiffening devices onto their vehicles. The belief is that these bars, often fitted between the strut towers of the vehicle, and/or across the engine bay or connecting the front cross member with the floor pan, improve chassis rigidity and reduce flex under high load driving.
chassis development :
Throughout the development of the motor vehicle, many different types of chassis have been designed and tested. Through the years many advances have been made in chassis technology, and many old technologies have been thrown out as inferior. Here are some of the basic types which were or are in common use:
Ladder Chassis
Major structure of chassis is supported by central rails connected by cross braces. Used in vehicles of the 60s, and still used in trucks and SUVs due to good isolation between passenger cabin and road vibration. Since it is two dimensional it is not very stiff, and needs to be built heavier than a good space frame.
Tubular Space Frame
Very strong chassis construction technique, often used in race cars and ultra high performance ($$$) sports cars. The structure is formed from individual tubes, usually welded into a web of supports. Actually cheaper to build for small production runs, since hand production is involved. This technique is not feasible for general production vehicles due to the fact that automated production is next to impossible.
Unibody Chassis
This type of chassis is constructed of formed sheet metal pieces all spot welded together to form a metal box which makes up the structural and functional body of the car. Usually the metal used is steel, but some newer vehicles use aluminum to reduce material cost. Steel is usually formed by stamping with dies. Aluminum can be formed by stamping, but newer cars are using advanced hydroforming techniques to form panels. These structures are usually relatively stiff, although they are not necessarily designed to optimize this. They are generally heavier than a tubeframe structure, but also safer. These types of chassis are usually more feasible for large production vehicles, as tooling is very expensive.
Composite Monocoque Chassis
The lightest, most advanced performance vehicles ($$$$$$) employ this strategy for their chassis. Similar to unibody in form, but many different advanced materials are employed, such as fiberglass, carbon fiber, Kevlar, or glass fiber reinforced polymer (GFRP). These chassis are light, stiff, and expensive to produce. Making composite structures is very labor intensive, and the materials themselves are expensive. However the end product if correctly designed is the lightest and stiffest possible. The most advanced racecars use these structures, as do some supercars (such as the Porsche 959 or the Mclaren F1).
unibody chassis test :
The Model
A simple chassis model was designed in Pro/Engineer then imported into Abaqus as a shell. The face which represents the trunk was removed in Abaqus, and the geometry was stitched and reduced until the program was happy. The Pro/E model is visible in the attached drawing.
The Abaqus model was meshed using primarily quad-dominant shapes. Large rectangular areas were redefined as quad, and areas of irregular shape were redefined as tri. The Abaqus shell, mesh and model are visible in the following figures.
Equal and opposite forces of 1000 pounds each were applied to each of the strut towers. The chassis was held by the back of the chassis. This boundary condition and the loading is visible in the following figures.
What is Abaqus
ABAQUS is a highly sophisticated, general purpose finite element program, designed primarily to model the behavior of solids and structures under externally applied loading. ABAQUS includes the following features:
The Brace
Only one type of brace was tested in the analysis. This is because Abaqus was getting very quarrelsome and time was limited. The brace tested was the strut tower brace, depicted in the following figure. It attaches between the towers (where the load is applied). The same loads were then applied… and the results were amazing.
The Results
Both tests were run, and the stiffness of the model was far higher than expected. The exact reason for this is unknown, but it is probably due to some unpredicted idealization made in the model. The stiffness obtained was around 20,000 ft-lbs per degree of deformation, whereas most car chassis obtain 2000-3000 ft-lbs in a very well designed car. This difference does not make much difference however, as the study is mostly concerned with the increase in stiffness obtained from bracing, not with what the stiffness actually is. First we will look at the deformation pictures, then view some comparative graphs. Both graphs are displayed at 25 times deformation scale.
It is very plainly visible that the deformations are much lower. To get concrete numbers, some plots have been made to show the change in deformations. The plots ending in NB stand for No Bracing, and the ones which end in TB are for with Tower Brace. The plot of FrontEdge is the deformation of the bottom front edge of the chassis, and shows the angular twist of the chassis. The plot of CrossMember is a plot of the deformation along the member which runs between the wheel wells at the bottom of the vehicle. This graph is more indicative of how much effect the deformation of the chassis is having on the suspension geometry, as the suspension is often mounted to this member. Finally, the Tower plot is a plot of the left and right tower displacements, which also is a good indication of suspension movement caused by chassis flex. Here they are:
The unbraced deformations are clearly much higher. On the front edge around 75% higher, and about four times higher on the cross member. Tower displacement went from .9 to 2.1 mm, and increase of over twice.
Conclusions
The benefits of the strut tower brace seem to be validated. Chassis flex at the key suspension points went down considerably. Many experienced drivers claim to be able to feel the stiffness increase in a chassis when such a brace is added, and from my results it seems as if that may be possible.
for more details please visit http://www.ctechtuners.com/
why c-tech?
chassis in general :
Most street driven cars are manufactured using a construction technique known as unibody spaceframe chassis construction. This means that the body itself provides the stiffness and structure of the vehicle. Many older vehicles had separate stiffening structures and bodies, the body being solely designed as an aesthetic exterior and as a safety and environmental housing for the passengers. This technique is both heavier and requires more materials raising costs. Modern vehicle chassis are made entirely out of formed sheet metal sections which are usually spot welded together to form the structure of the vehicle. Designing these chassis is no easy task, the geometries being incredibly complex. Making these designs both cost effective, lightweight, stiff and safe is always a tradeoff.
Production vehicle chassis vary substantially in the degree to which they maximize the variables previously mentioned. Higher performance vehicles are often designed with maximum stiffness and lightweight in mind. A lighter weight chassis promotes an overall lower vehicle weight and better performance. Chassis stiffness though is also important for vehicle performance.
As a vehicle is driven, various forces are applied by the suspension on the chassis. This occurs under braking, cornering, driving surface variations, or any other vehicle movement. In higher these loads are, the more is demanded of a chassis. The chassis obviously has to be strong enough not to fail under these loads, but beyond that it must not deflect appreciably. Suspensions are carefully designed to position the wheels and tires of the vehicle for optimum performance under all conditions of vehicle use. If the chassis deflects when the forces are high, it causes suspension mounts and attachment points to temporarily shift, which destroys the careful suspension design when it is needed most. Chassis stiffness is most important in high performance or racing cars, where suspension loads are at their highest and suspension adjustment is most critical.
To combat chassis flex, many people desiring improved performance out of their unibody cars fit chassis stiffening devices onto their vehicles. The belief is that these bars, often fitted between the strut towers of the vehicle, and/or across the engine bay or connecting the front cross member with the floor pan, improve chassis rigidity and reduce flex under high load driving.
chassis development :
Throughout the development of the motor vehicle, many different types of chassis have been designed and tested. Through the years many advances have been made in chassis technology, and many old technologies have been thrown out as inferior. Here are some of the basic types which were or are in common use:
Ladder Chassis
Major structure of chassis is supported by central rails connected by cross braces. Used in vehicles of the 60s, and still used in trucks and SUVs due to good isolation between passenger cabin and road vibration. Since it is two dimensional it is not very stiff, and needs to be built heavier than a good space frame.
Tubular Space Frame
Very strong chassis construction technique, often used in race cars and ultra high performance ($$$) sports cars. The structure is formed from individual tubes, usually welded into a web of supports. Actually cheaper to build for small production runs, since hand production is involved. This technique is not feasible for general production vehicles due to the fact that automated production is next to impossible.
Unibody Chassis
This type of chassis is constructed of formed sheet metal pieces all spot welded together to form a metal box which makes up the structural and functional body of the car. Usually the metal used is steel, but some newer vehicles use aluminum to reduce material cost. Steel is usually formed by stamping with dies. Aluminum can be formed by stamping, but newer cars are using advanced hydroforming techniques to form panels. These structures are usually relatively stiff, although they are not necessarily designed to optimize this. They are generally heavier than a tubeframe structure, but also safer. These types of chassis are usually more feasible for large production vehicles, as tooling is very expensive.
Composite Monocoque Chassis
The lightest, most advanced performance vehicles ($$$$$$) employ this strategy for their chassis. Similar to unibody in form, but many different advanced materials are employed, such as fiberglass, carbon fiber, Kevlar, or glass fiber reinforced polymer (GFRP). These chassis are light, stiff, and expensive to produce. Making composite structures is very labor intensive, and the materials themselves are expensive. However the end product if correctly designed is the lightest and stiffest possible. The most advanced racecars use these structures, as do some supercars (such as the Porsche 959 or the Mclaren F1).
unibody chassis test :
The Model
A simple chassis model was designed in Pro/Engineer then imported into Abaqus as a shell. The face which represents the trunk was removed in Abaqus, and the geometry was stitched and reduced until the program was happy. The Pro/E model is visible in the attached drawing.
The Abaqus model was meshed using primarily quad-dominant shapes. Large rectangular areas were redefined as quad, and areas of irregular shape were redefined as tri. The Abaqus shell, mesh and model are visible in the following figures.
Equal and opposite forces of 1000 pounds each were applied to each of the strut towers. The chassis was held by the back of the chassis. This boundary condition and the loading is visible in the following figures.
What is Abaqus
ABAQUS is a highly sophisticated, general purpose finite element program, designed primarily to model the behavior of solids and structures under externally applied loading. ABAQUS includes the following features:
The Brace
Only one type of brace was tested in the analysis. This is because Abaqus was getting very quarrelsome and time was limited. The brace tested was the strut tower brace, depicted in the following figure. It attaches between the towers (where the load is applied). The same loads were then applied… and the results were amazing.
The Results
Both tests were run, and the stiffness of the model was far higher than expected. The exact reason for this is unknown, but it is probably due to some unpredicted idealization made in the model. The stiffness obtained was around 20,000 ft-lbs per degree of deformation, whereas most car chassis obtain 2000-3000 ft-lbs in a very well designed car. This difference does not make much difference however, as the study is mostly concerned with the increase in stiffness obtained from bracing, not with what the stiffness actually is. First we will look at the deformation pictures, then view some comparative graphs. Both graphs are displayed at 25 times deformation scale.
It is very plainly visible that the deformations are much lower. To get concrete numbers, some plots have been made to show the change in deformations. The plots ending in NB stand for No Bracing, and the ones which end in TB are for with Tower Brace. The plot of FrontEdge is the deformation of the bottom front edge of the chassis, and shows the angular twist of the chassis. The plot of CrossMember is a plot of the deformation along the member which runs between the wheel wells at the bottom of the vehicle. This graph is more indicative of how much effect the deformation of the chassis is having on the suspension geometry, as the suspension is often mounted to this member. Finally, the Tower plot is a plot of the left and right tower displacements, which also is a good indication of suspension movement caused by chassis flex. Here they are:
The unbraced deformations are clearly much higher. On the front edge around 75% higher, and about four times higher on the cross member. Tower displacement went from .9 to 2.1 mm, and increase of over twice.
Conclusions
The benefits of the strut tower brace seem to be validated. Chassis flex at the key suspension points went down considerably. Many experienced drivers claim to be able to feel the stiffness increase in a chassis when such a brace is added, and from my results it seems as if that may be possible.
for more details please visit http://www.ctechtuners.com/
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