SUSPENSION BASICS

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SUSPENSION BASIC


The Objective of any automotive Suspension system is to...
·        Supports the weight.
·         Provides a smooth ride.
·         Allows rapid cornering without extreme body roll.
·         Keeps tires in firm contact with the road.
·         Prevents excessive body squat & body dive.
·         Improves body control & vehicle mobility.
·         Allows front wheels to turn side-to-side for steering.
·         Works with the steering system to keep the wheels in correct alignment.

BASIC TERMINOLOGIES


  • SPRUNG MASS

Mass of all the components which are supported by the spring and half the mass of the links of the suspension system. 

  • UNSPRUNG MASS

Mass of all the components which are not supported by the spring and remaining half the mass of the links of the suspension system. 

  • TRACK WIDTH AND WHEEL BASE

The distance between the center line of the front tire when seen from the front is the tack width of the vehicle[Ref. fig  A below] and the distance between the center line of the front and rear tire when viewed from the side is known as the wheel base of the vehicle [Ref. fig  B below].

  • JOUNCE AND REBOUND
During bump there is Vertical displacement of entire sprung mass or specifically the tire. The Upward movement is jounce and downward movement is rebound.




  • CAMBER  
It is the Front View tilt of the tire with respect to wheel axis. Helps in maintaining the tire to stay vertical while jounce and rebound. Mostly all the racing cars have negative camber angle which helps them while cornering.
  • KING-PIN INCLINATION
It is Axis about which the wheel or tire rotate about during steering inputs is known as King- pin inclination. It is also known as “Steering axis inclination”

  • SCRUB RADIUS

It is the distance on the ground obtained by extending both the steering axis and the center line of the tire. As scrub radius increases the effort of the driver increases .Scrub radius can be controlled by the king – pin inclination.[Refer the above fig.]   
  •  CASTER

It is the Side view tilt of the steering axis. It creates camber change with steering input. Caster is also responsible for creating a restoring force for centering steering wheel.

  •  CASTER TRAIL

It is the Side view distance between the point of intersection of steering axis with ground and the contact patch center point of tire. It creates a restoring force for centering steering wheel. Increasing caster trail will increase the return ability of steering wheel.

  •   TOE
It is the angle made by the tires when viewed from the top in static condition. When the tires tilt inwards with respect to the center line of car when viewed from top. Turning the front of the tire in is referred to as adding “toe in” It is important for both front and rear tires.

  •  SLIP ANGLE
The angle between the direction of heading of vehicle and the direction in which the wheels are pointing is known as the slip angle. It is advantageous for the vehicle between 6-8 degrees in which the cornering force increases linearly with the slip angle. But after that cornering force decreases with the increase in slip angle.
  • UNDER STEER
Handling characteristic of an automotive vehicle that causes it to turn less sharply than the driver Intends because the front wheels slide to the outside of the turn before the  rear wheels lose traction.
  • OVER STEER
Handling characteristic of an automotive vehicle that causes it to turn more than the driver intends because the rear wheels slide to the outside of the turn  before the front wheels lose traction.

  •  DIVE
The condition arising at the time of braking resulting in weight transfer from rear to front causes front part of the vehicle to lower and rear to rise is Dive. Anti-Dive characteristics are made with suspension design.

  •  SQUAT
The condition arising at the time of sudden acceleration resulting in weight transfer from front to rear causes rear part of the vehicle to lower and front part to rise is squat.Anti-squat characteristics are made with suspension design.
  • g- FORCES
Tire and handling performance is described in terms of g-force. One g is simply the force equal to gravity here on Earth. If an object is said to weigh 100 pounds, the force of gravity on it equals 100 pounds.

  • WHEEL RATE 
Depending on the suspension design, springs are installed a certain distance away from the wheel, which determines the ratio of wheel travel to spring travel, or wheel rate. For example, if a coil spring is mounted on the midpoint of a control arm, or halfway between the center of the wheel and the arm pivot points, it compresses approximately 1 inch when the wheel travels vertically 2 inches. On a strut-type suspension, the coil spring has a more direct ratio because it is closer to the wheel, so when the wheel of a strut travels vertically 2 inches, the spring also compresses 2 inches. This means that a coil spring used on a strut-type suspension is less than half the spring rate of a coil spring used on suspensions that use control arms.






Comments

  1. HS10 December 2020 at 04:14

    this is awesome! very helpful to understand the fundamental stuff. thank you

    ReplyDelete

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