29-08-2016, 03:17 PM
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INTRODUCTION
Suspension used in an automobile is a system mediating the interface between the vehicle and the road, and their functions are related to a wide range of drivability such as stability, comfort and so forth. Since the total optimization of such contents requires much of design freedom, a multilink suspension system, that is principally a parallel six-bar universal linkage, is getting installed to passenger cars, mainly to high-grade cars. On the other hands, such design freedom makes the design process for determining link geometry, etc. more complicated, and it is not so easy to design the suspension system with promising insights. This leads the necessity of a new generation of design methodology that can realize a potential of the complicated system toward total optimality. Since this problem includes many evaluation items, and multi-link suspension system has interconnected behaviour, the optimization is so complicated.
• The main objectives of the suspension system in a vehicle are:
Analyze the effect of mass on the CG of a small car.
Effect of speed on the roll angle of the small car.
Analyze the Effect of Roll Angle over the Lateral force.
Compare the Sprung Mass V/s Un-sprung Mass frequency of small Car.
To isolate the chassis and passengers from the road shocks and vibration that arises due to the irregularities on the road surface
To maintain the stability of the vehicle by resisting the weight transfer (longitudinal and lateral) during acceleration, braking a cornering and to maintain a proper steering geometry.
To maintain good traction by maintaining a constant contact patch of the tyre with the road (good road holding capability).
• SELECTION OF SUSPENSION SYSTEM:
The selection of the suspension system was based on different factors like their
• Kinematic response to the road loads,
• Simplicity in design,
• Ease of adjustability of the wheel alignment parameters,
• Manufacturability,
• Weight,
• Packaging space,
• Cost.
• DESIGN
Considering the above factors, double wishbone suspension was chosen for the front and the swing arm suspension was chosen for the rear as there is a single wheel in the rear and as both The types satisfy the above mentioned requirements.
• DESIGN TARGETS OF SUSPENSION SYSTEM:
To maintain adequate ground clearance (a minimum of 2 inches as per the rulebook).
• To maintain sufficient wheel travel for encounter with the bumps (a minimum of 2 inches as per the rulebook).
• To maintain proper geometry that ensures stability and proper steer.
• To achieve the natural frequency (and its distribution in front and rear) which provides a good comfort.
• To design the components with a fair factor of safety.
• To achieve a low unsprung mass.
• To achieve the above targets at a lower cost by careful material selection.
• Spring rate:
The spring rate (or suspension rate) is a component in setting the vehicle's ride height or its location in the suspension stroke. When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The spring rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where the loading conditions experienced are more extreme.
Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road. Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. Riding in an empty truck used for carrying loads can be uncomfortable for passengers because of its high spring rate relative to the weight of the vehicle. A race car would also be described as having heavy springs and would also be uncomfortably bumpy. However, even though we say they both have heavy springs, the actual spring rates for a 2,000 lb (910 kg) race car and a 10,000 lb (4,500 kg) truck are very different. A luxury car, taxi, or passenger bus would be described as having soft springs. Vehicles with worn out or damaged springs ride lower to the ground which reduces the overall amount of compression available to the suspension and increases the amount of body lean. Performance vehicles can sometimes have spring rate requirements other than vehicle weight and load.
• Calculation of the spring rate:
Spring rate is a ratio used to measure how resistant a spring is to being compressed or expanded during the spring's deflection. The magnitude of the spring force increases as deflection increases according to Hooke's Law. Briefly, this can be stated as
K=F/X
where
F is the force the spring exerts
k is the spring rate of the spring.
x is the deflection of the spring from its equilibrium position (i.e., when no force is applied on the spring Spring rate is confined to a narrow interval by the weight of the vehicle, load the vehicle will carry, and to a lesser extent by suspension geometry and performance desires.
K=500/56
K=8.92mm
INTRODUCTION
Suspension used in an automobile is a system mediating the interface between the vehicle and the road, and their functions are related to a wide range of drivability such as stability, comfort and so forth. Since the total optimization of such contents requires much of design freedom, a multilink suspension system, that is principally a parallel six-bar universal linkage, is getting installed to passenger cars, mainly to high-grade cars. On the other hands, such design freedom makes the design process for determining link geometry, etc. more complicated, and it is not so easy to design the suspension system with promising insights. This leads the necessity of a new generation of design methodology that can realize a potential of the complicated system toward total optimality. Since this problem includes many evaluation items, and multi-link suspension system has interconnected behaviour, the optimization is so complicated.
• The main objectives of the suspension system in a vehicle are:
Analyze the effect of mass on the CG of a small car.
Effect of speed on the roll angle of the small car.
Analyze the Effect of Roll Angle over the Lateral force.
Compare the Sprung Mass V/s Un-sprung Mass frequency of small Car.
To isolate the chassis and passengers from the road shocks and vibration that arises due to the irregularities on the road surface
To maintain the stability of the vehicle by resisting the weight transfer (longitudinal and lateral) during acceleration, braking a cornering and to maintain a proper steering geometry.
To maintain good traction by maintaining a constant contact patch of the tyre with the road (good road holding capability).
• SELECTION OF SUSPENSION SYSTEM:
The selection of the suspension system was based on different factors like their
• Kinematic response to the road loads,
• Simplicity in design,
• Ease of adjustability of the wheel alignment parameters,
• Manufacturability,
• Weight,
• Packaging space,
• Cost.
• DESIGN
Considering the above factors, double wishbone suspension was chosen for the front and the swing arm suspension was chosen for the rear as there is a single wheel in the rear and as both The types satisfy the above mentioned requirements.
• DESIGN TARGETS OF SUSPENSION SYSTEM:
To maintain adequate ground clearance (a minimum of 2 inches as per the rulebook).
• To maintain sufficient wheel travel for encounter with the bumps (a minimum of 2 inches as per the rulebook).
• To maintain proper geometry that ensures stability and proper steer.
• To achieve the natural frequency (and its distribution in front and rear) which provides a good comfort.
• To design the components with a fair factor of safety.
• To achieve a low unsprung mass.
• To achieve the above targets at a lower cost by careful material selection.
• Spring rate:
The spring rate (or suspension rate) is a component in setting the vehicle's ride height or its location in the suspension stroke. When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The spring rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where the loading conditions experienced are more extreme.
Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road. Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. Riding in an empty truck used for carrying loads can be uncomfortable for passengers because of its high spring rate relative to the weight of the vehicle. A race car would also be described as having heavy springs and would also be uncomfortably bumpy. However, even though we say they both have heavy springs, the actual spring rates for a 2,000 lb (910 kg) race car and a 10,000 lb (4,500 kg) truck are very different. A luxury car, taxi, or passenger bus would be described as having soft springs. Vehicles with worn out or damaged springs ride lower to the ground which reduces the overall amount of compression available to the suspension and increases the amount of body lean. Performance vehicles can sometimes have spring rate requirements other than vehicle weight and load.
• Calculation of the spring rate:
Spring rate is a ratio used to measure how resistant a spring is to being compressed or expanded during the spring's deflection. The magnitude of the spring force increases as deflection increases according to Hooke's Law. Briefly, this can be stated as
K=F/X
where
F is the force the spring exerts
k is the spring rate of the spring.
x is the deflection of the spring from its equilibrium position (i.e., when no force is applied on the spring Spring rate is confined to a narrow interval by the weight of the vehicle, load the vehicle will carry, and to a lesser extent by suspension geometry and performance desires.
K=500/56
K=8.92mm