Suspension system

• The suspension system is used to provide passenger comfort, improve vehicle stability & control.
• suspension system classification:
1. dependent:
When the first wheel moves up and down, the second wheel is affected by the movement of the first wheel .
Advantage Disadvantage
1. Smaller number of parts. 1. higher vibration
2. Durable enough for heavy-duty 2. non comfort because the
use. unsprung weight is great.

2. independent:
When the first wheel moves up and down, the second wheel is not affected by the movement of the first
wheel.
Advantage Disadvantage
1. The unsprung weight is low. 1. Complex The construction.
2. The springs only support the body. 2. wheel alignment change with the
3. More comfort for passenger. up-and-down movement of the
wheels.
3. Wear of tire tread.

• Function of Suspension system:

1. Support the body on the axle.
2. Transmit the driving and braking force.
3. The vehicle wheel must be able to move up and down.
4. Absorb road surface irregularities.
▪ Functional requirements of suspension system:
1. Comfortability: provide passenger comfort.
2. Safety: provide vehicle stability and safe driving.
3. Durability: long life.
4. Maintainability: easy and non-expensive.
▪ Suspension principle:
▪ Oscillation and riding comfort:
1. Sprung weight:
It is the weight of the vehicle body and component above
The suspension system. (body, engine &chasse….)
2. Un sprung weight:
It is the every component under the suspension system (brakes, wheel, axle& tire)
▪ Vehicle motion:

Component of suspension system

▪ Suspension spring:
▪ The springs fitted between the wheels and the frame.
▪ Function:
1) Allows the wheels to move up and down without causing a similar movement of the frame.
2) It protects the frame from transmitting movement to it.
▪ Classification of spring:
1. Metallic: (coil spring, torsion bar spring, leaf spring)
2. Nonmetallic: (rubber spring, air spring)

1- Coil spring:
It expands and compresses to absorb the tire motions.
▪ Used in many types of vehicles.
2- Leaf spring:
Many metal layers are bound tightly as one unit to absorb the shock.
▪ Used in heavy duty vehicles and trucks.
3- Torsion bar:
When the wheel moves up or down, the torsion bar rotates and absorbs the shock.
▪ This system was used extensively in Europe.
4- Rubber spring:
It is very flexible, so it does not support heavy loads.
▪ So, the rubber springs are used as assisted springs or bushings, etc.

▪ Damper- shock absorb:

▪ Purpose:
1. Absorbs the energy stored in the spring.
2. Reduce the number of vibrations made between the initial bump and the final return of the spring to
normal position.

▪ Control Arm:
▪ purpose:
1. Free to move up and down with suspension.
2. Movable lever that fastens the steering knuckle to the vehicle’s body.
3. Connects the steering knuckle to the frame.
▪ The spindle supports the wheels and attaches to the control arm with ball joints.

▪ Ball joint:
▪ Purpose:
1. Swivel joints that allow control arm and steering knuckle to move up and down and side to side.
2. Front wheel Drive: Allows the Stub Axle Carrier to be turned by the steering system.
3. The drive shaft must allow for suspension and steering movement.
4. Ball joints provide the freedom of movement necessary for steering and suspension movements.

▪ stabilizer bar:
▪ purpose:
1. Prevents excessive body lean when turning.
2. When cornering, the outside of body drops
and twists the bar to limit sway.
3. The bar’s resistance to twisting motion limits
body lean in corners.
▪ strut rod:
▪ purpose:
1. Are attached between the lower control arm at one end and the frame of the vehicle with rubber
bushings.
2. Provide forward/backward support to the control arms.
3. A strut rod is the longitudinal support to prevent
front-to-back wheel movement.

▪ steering knuckle:
part of the suspension or as part of the wheel.
▪ purpose:
1. To join the suspension to the wheel Usually includes the spindle.
2. To provide pivot points between the suspension and wheel.

▪ Solid axle:
- A solid axle front suspension is very strong in heavy trucks.
- A axle the trucks used a solid front axle to support the front wheels.
- The main disadvantage of less quality.

▪ Kingpin:
- Allow the front wheels to rotate for steering.
 Air suspension system

This system is operated by an air pump or compressor that is either electric or engine drive.
➢ Types of air suspension system:
1. Bellow air suspension (spring):
2. Piston air suspension (spring):
▪ Air suspension main component:
1. Air compressor:
The air source in an air suspension system is
typically, an air compressor. It is responsible
for supplying compressed air to the system.

- A single piston in the air compressor is moved up and down in the cylinder by a crankshaft and connecting
rod.
- The armature is connected to the crankshaft, and therefore the rotating action of the armature moves the
piston up and down.

2. Air spring (Pneumatic bellow):

In an air suspension system, the air springs replace the coil
springs in conventional suspension systems. The air springs
are inflated or deflated to provide a constant vehicle trim height.
➢ The solenoid actuators in the struts have up to four suspension modes that may be selected by the driver:
1. Comfort—provides a smooth luxurious ride.
2. Dynamic—stiffest, most aerodynamic suspension mode.
3. Automatic - The suspension computer provides the best possible combination of comfort and handling
based on speed and driver style.
4. Life—for rougher roads.
3. Height sensor:

Function: is a component that measures the distance between

the suspension and the ground.

Height sensors send an electric signal to the control module in relation

to curb riding height.

Advantage air suspension Disadvantage air suspension

1. Reduce body roll and pitch. 1. Low Durability & Hight Cost.
2. It improves aerodynamic efficiency. 2. Heavy and complicated
3. Lowers the ride height at higher speeds. 3. Slow response

Semi active suspension

Semi-active suspension that constantly adjusts damping levels according to road conditions and vehicle
dynamics, providing comfort without sacrificing safety and control.

▪ type of semi active damping control:

1. Servo/Solenoid valve dampers:
- A damper consisting of a hydraulic actuator in conjunction with an electro-hydraulic servo-valve
modulating the controlling orifice area.
- Solenoid valves do not have as fast or accurate responses as servo-valves.
 2. Magnetorheological (MR)/electrorheological (ER) dampers:
- MR damper is a hydraulic damper consisting of a hydraulic cylinder containing micron-sized particles in
an MR fluid (usually oil).
- MR fluids are non-Newtonian fluids that change their properties in the
presence of a magnetic or electric field.

Steering system
▪ Purpose:
The purpose of the steering system is to allow the driver to control the direction of the vehicle by turning the
front wheels with the minimum amount of driver's effort.

▪ Steering methods:
a. Front wheel steering system.
b. Rear wheel steering system.
c. Four-wheel steering system.

▪ Functional requirement steering system:

A. Maneuverability.
B. Proper Steering Effort.
C. Smooth Recovery.
D. Minimum Transmission of Shock from Road Surface.

▪ Steering system Ackerman layout:

▪ Types of Steering System
1. Manual:
a. Pitman Arm “Parallelogram steering”
- It is used for light vehicles with an independent suspension system,
and for heavy vehicles with dependent suspension.
- The “Steering box”:
transmits steering box movement to the wheels.

b. Rack and Pinion:

1- Steering wheel: It is the control wheel to steer a vehicle by the driver.
2- Steering column:
- Provides the force to turn the steering gear.
3- Tie rod ends:
- connects the rack with steering knuckles.
- transmit motion from the rack to the steering knuckle.
- allow for up & down movement thru bumps & potholes & turns
2. Power Steering system :
1. Hydraulic assisted steering
2. Electrohydraulic assisted steering
3. Electric power steering
(A) Power-Steering With integral Control Valve.
(B) Power-Steering With Rack and Pinion.

▪ The steady-state handling characteristics may be classified into three categories:

A. Neutral Steering: When it is accelerated in a constant radius turn, the driver should maintain the same
steering wheel position.
B. Understeering: When it is accelerated in a constant radius turn, the driver must increase the steer angle.
C. Oversteering: When it is accelerated in a constant radius turn, the driver must decrease the steer angle.