In-Service suspension systems Flashcards
What is the secondary purpose of suspension?
To provide stability under all conditions e.g.
- Acceleration
- Braking
- Cornering
What is the primary purpose of suspension?
To provide a flexible support for MSE whilst isolating imperfections in the road
What methods of reducing inner plate friction are there?
- Synthetic rubber buttons
- Inner leaf plates
- Reduce the amount of leaves
If the amount of leaves are reduced, what happens to the remaining springs?
The remaining leaves have increased width
What are road springs used for?
To absorb bumps and shocks to prevent them from reaching the body of the equipment
What is sprung and unsprung weight?
- Sprung: Anything supported by the spring
- Unsprung: Mass supported by the wheel up to the spring
Why are leaves graduated in length?
To give constant stress throughout spring
What are the two semi-elliptical methods of attachment?
Fixed shackle and swinging shackle
What is spring rate governed by?
- Length of spring: Shorter spring = Higher rate
- Width of leaf: Wider leaf = Higher rate
- Thickness of leaf: Thicker spring = higher rate
- Number of leaves: Greater number = Higher rate
- Low spring rate: Spring deflects a lot = Softer ride
What does the equipment load determine on a semi elliptical leaf suspension system?
- Number of springs
- Length of springs
- Thickness of springs
What cross sectional shape can torsion bars be?
- Straight bar
- Square
- Circular
What are properties of helper leaf springs?
- Fitted to some HGV’s
- Overcome variations in laden and unladen rolling conditions
- Shorter leaf spring, clamped directly above the main spring
- No permanent contact with chassis
- Acts with main spring to increase spring rate when under load
What maintenance do you do on a leaf spring?
- Cracking of spring
- Missing or broken rebound clips
- Loose, cracked or corroded ‘U’ bolts
- Security of mountings
- Perished or worn bushes
What is spring rate?
The amount of deflection of the spring for a given load
What is a property of a semi elliptical one leaf spring and why?
Leaf is tapered (thicker in the middle)
To avoid overstressing the centre of the leaf
What are benefits of a low unsprung weight?
- Suspension system works less to control the movement of unsprung weight
- Body of equipment will shake less over road surfaces
What is the purpose of a progressive spring?
To accommodate unladen and laden weight
Why can spring deflection occur in a helical spring?
- Road conditions
- Off road terrain
- Weight of driver and passengers
- Cargo
What 3 designs of ends of a helical spring are there?
- 2 flat tail
- 1 flat tail and 1 tangent tail
- 2 pigtail
What changes spring rate in a helical coil?
- Length
- Diameter
- Number of active coils
What 3 types of torsion bar adjuster are there?
- Internal jacking screw
- Trunnion mounted jacking screw
- Lockable eccentric cam
How does a torsion bar work?
- Road wheel travels up
- End of torsion bar travels up
- Upwards travel induces a twist in the torsion bar
- Twist is a result of the bar absorbing energy
How is spring rate set by a torsion bar?
- Length
- Diameter
What 2 areas of the vehicle is a torsion bar connected to?
(Can be tapered)
- Anchored at the body or chassis
- Connected to suspension arm or lever
What are the purposes and applications of rubber suspension?
- Has a tendency to settle down in early phases of use
- Common on heavy equipment and tandem axle bogies
- Can store more energy for its size than any other type of suspension
- Energy released is significantly less than what’s absorbed
- Can be used as the main suspension spring
- an be fitted in conjunction with metal springs to modify suspension characteristics
- Can be used as a bump stop to stiffen springs at max defleciton
- On MSE ‘indespension units’ are used
How does rubber suspension operate?
- Suspension arm pivots up or down on bolt
- Causes arm to extend, expanding the rubber element
- Rubber element then continues to expand and retract to absorb road shocks
What are 3 designs of rubber bump stop?
- Solid conical
- Hollow conical
- Hollow cylindrical
What 3 designs of ends of a helical spring are there?
- 2 flat tail
- 1 flat tail and 1 tangent tail
- 2 pigtail
What is a disadvantage of coil over leaf suspension?
- Requires additional suspension members
What are advantages of coil suspension over leaf suspension?
- No inter plate friction
- Superior energy storage
What suspension is most commonly used on light vehicles?
Helical coil spring
Why can spring deflection occur in a helical spring?
- Road conditions
- Off road terrain
- Weight of driver and passenger
- Cargo
What changes spring rate in a helical coil?
- Length
- Diameter
- Number of active coils
What is the purpose of a progressive spring?
To accommodate laden and unladen weight
What are the 3 rates of springs in a coil suspension system?
- Linear rate
- Variable rate
- Dual rate
Where a stiff spring is needed but there isn’t enough room, what can be done?
Place one spring inside the other
What does coil bound mean?
Where a spring is fully compressed
What does changing spring shape achieve and how?
- More stability
- Increases the length of travel
Achieves because the springs become telescopic
Why are rubber isolators fit to coil springs?
To reduce noise
What checks should be done on coil springs?
- Cracking
- Corrosion
- Serviceability of rubber components
- Check securely located
Why do we use air suspension?
- It’s free
- Readily compressible
- Ride comfort is affected little by load
- Excellent for fitting to HGV’s
What are advantages of air suspension?
- Smoother ride
- Fragile cargo is better predicted
- Provides height control for easier trailer coupling
- Allows constant height to be maintained
- Allows for the provision of a lift axle
What are the 4 main components of air suspension?
- Compressor (reciprocating piston)
- Receiver
- Rubber air bellows
- Levelling valves
How does air suspension operate?
- Ignition on
- Compressor starts charging receiver and supplies bellows
- ECU and electronics set the suspension height (driver can override)
- Trailing arm sets the spring rate to ensure ride comfort regardless of conditions
What is the purpose of the lost motion connection?
To provide a time delay and allows trailing arm to ignore normal ride motions
What’s the purpose of lift axles?
To lift and retain a non driven axle
What are advantages of lift axles?
- Extends tyre life
- Reduces fuel consumption
- Temporarily transfers weight to driven axle improving traction
What common checks do we do on air suspension?
- Check for air leaks
- Check for signs of perishing of air bellows
- Check for any corrosion of pipes and correct routing of pipes
What are the main differences between hydro-pneumatic suspension and spring suspension?
- H-P is supported by a mass of gas
- Mass of gas remains constant irrespective of load
- Springs can be hydraulically connected together to improve vehicle stability
What are the main components of a hydro-pneumatic suspension system?
- Reservoir
- Pump
- Accumulator
- Pressure regulator
- Height corrector
- Control rod
- Rubber diaphragm
- Piston suspension
- Anti-roll bar
What is hydro-pneumatic suspension also known as?
Fixed mass air springs
What is the delay device in a hydro-pneumatic system also known as?
A dashpot
What is the purpose of a dashpot, and where is it located?
- To prevent rapid flow of oil past the slide valve when the vehicle goes over a bump or dip
- Incorporated in the height corrector/levelling valve
