Suspension

Suspension type is unequal length double A arm push-rod suspension.

Below the two blue lines intersect in the top rear of the car. This is the instant center the front suspension mechanism revolves around. This is done the create an anti-dive characteristic e.g. during braking the suspension will create an reaction force to counter the front spring compression. Simulation of the suspension is a must to determine if these angles need to be corrected. For now these values will be used as input for the first suspension simulation before any simulation design iteration is done.


full Ackerman steering in static position

Ackerman loss due to bump / kinematics / dynamics and suspension geometry = undetermined

steering angle is plus 35 degrees and minus 35 degrees. Turning circle = roughly 9,2 meters. Anything below 10 meters is very good.

rear axle steering e.g. behind the axle line of the front wheels. Not rear wheel steering ! and in-between the top and bottom A arm.

front toe out on full bump = undetermined

rear toe in on full bump = undetermined

static camber angle = undetermined

camber compression bump gain = undetermined

Camber compression extension negative gain = undetermined

Camber gain and loss due to steering angle input = undetermined. (caused by caster and kingpin angles)

Top A arm (side view) / (anti-dive) angle is 15 deg.

Bottom A arm (side view) / (anti-dive) angle is 20 deg.

Kingpin angle is 4 deg

scrub radius is positive 20 mm

Caster angle is 5 deg

Caster bump increase = undetermined (caused by anti-dive geometry)

suspension travel is 210 mm 82 mm compression hitting bump stop up to 92 mm hitting end of bump-stop and 118 extension hitting end of bump-stop.

damper spring type is KW Competition TTRSPW4A

The left of the section view shows the suspension in normal ride-height position and on the right of the section view the suspension is in full 92 mm compression at the end of the bump stop (rubber block on 15 mm damper push rod) . At the end of suspension travel there will be a hard end-stop on the chassis to prevent damage of the suspension mechanism. the hard end stop will hit the damper rocker arm.

above figures show front view, top view and side view respectively.

suspension 82 mm compressed just before hitting rubber endstop

Suspension 82 mm extended. this is normal expected road extension.

suspension in neutral position

Push rod design

material used is 25Crmo4 steel tube of 20 mm diameter by 1,5 mm wall thickness. spherical bearing 10 mm rod ends with locknuts and M10 threaded ends welded into the tube.

simulation is nessecary to determine the dynamic buckling and response of the push rod design e.g. A dynamic FEA to check if the push rod is strong and stiff enough.

Push rod hinge location.

the location is important not to cause any moment force on the upright to be combated by the drivers steering input.

not to cause a high moment load on the bottom A arm.

not to case a high bending force on the bottom A arm

the push rod angle should be kept to a minimum (straight up would be ideal but not possible) to optimize wheel spring rate to damper spring assembly rate


A custom upright design is chosen over an of the shelf component to increase stiffness and decrease weight as well as fully controlling the ackerman steering, caster and kingpin angles. This is the only way to make sure the correct scrub radius as well as all other characteristics are acquired .

Simulation of the suspension will determine if the no power-steering rack and pinion has a sufficient wheel angular speed to steering wheel rotation (not to many lock to lock turns) as well as a steering moment force below 25 Nm standing still and 10 Nm whiles driving.

in combination with the 20 mm scrub radius and all other geometric and kinematics of the suspension

Construction:

  • The hollow spindle and hollow sheet metal upright design makes sure the suspension is as light, stiff and as strong as possible. welded sheet metal upright construction will cut costs and decrease weight.

  • The bearings used are angular contact bearings from SKF type 7010_CD in O configuration low preload with custom 30 mm bearing separators .

  • The inner shaft seal is a low cross sectional height of type G70x78x5 from SKF

  • The outer shaft seal is a 65x80x8 HMS5 RG from SKF

All-though a spline on the spindle of the front hub is not needed since there will be no four wheel drive one is still in the current design. later a simpler version of the front spindle will be modeled.


This is done to keep the front hub design as close as possible to the rear hub design.