1801RX
Automotive
- Nov 15, 2018
- 1
Hello everyone,
[first post, so here goes!] We are currently designing the suspension for a new AWD vehicle, used for gravel-only [rallycross]. Think 550bhp 1000kg, very much like FIA WRX supercar.
I've spent quite some time reading up on websites like this, as well as RCVD etc. but currently find myself lost in details and need some "higher-level pointers" that help me understand what steps to take to arrive at some sensible goals.
My question is actually twofold:
A - is it possible for us to ballpark some spring/ARB values that approach a neutral handling car in steady state cornering, without having tire data available?
We will be using the same tire/rim combo on all 4 corners. We fully appreciate the need and use of testing to arrive at a desired setup, but the thing I'd like to avoid is starting out with a car that needs to be patched up because of some fundamental issues.
MAIN concern at this point is questioning integrating ARB's at either front or rear, or none at all
B - perhaps people with some experience with related cars would like to comment on some of our design parameters below? Would be greatly appreciated!
A - stuck in design process
The entire car is modeled out in 3D CAD, including weights.
AWD car, double wishbone on all 4 corners. Direct actuated spring/damper unit on lower control arm.
The suspension kinematics have been engineered iteratively using base Solidworks models combined with excel / VSUSP to arrive at what I think we want. Rates/frequencies/roll stiffness/load transfer have been evaluated using excel sheets (RCVD formula). So basicaly input spring/ARB choices and evaluate the outputs.
The steps I took so far:
-select suspension kinematics using models, to arrive at desired values
-extract sprung/unsprung weights and CoG locations from model
-Total weight distribution [56% front]
-select/trial spring rates to arrive at supension frequencies [1.74hz F / 1.79hz R]
-select/trial ARB and include tire vertical stiffness estimate to arrive at ride rate and total roll rate/stiffness
-roll stiffness distribution [60% front]
-use CoG vs neutral roll axis to arrive at load transfer F/R and TLLTD [58% front]
-calculate roll sensitivity [2.3 deg/G]
-input estimated max latG, verify:
--max steady state roll
--wheel travel used, travel reserve to bump stops for track irregularities
--actual wheel loads
This is where I'm stuck. Is it possible without tire data to say something usefull about steady state cornering balance?
B - car data, feel free to comment!
-AWD gravel, rallycross
-1020kg inc driver/fluids
-double wishbone all corners
-direct acting spring/shock on lower control arm, linear [Motion Ratio 1.49 to 1.51]
-uniball joints on every pickup, pickup points triangulated to feed forces into tube spaceframe (for compliance red.)
-total weight distribution [56% fr]
-design max latG: 1.3G
-wheelbase 2350mm
-tracks 1720/1720mm
-tire dia 640mm
-RCH 98mm fr / 118mm rr (1mm vertical change in roll, no gradient change in roll)
-roll sensitivity [2.3 deg/G]
(-tire vertical stiffness assumption: 300N/mm)
-susp frequencies [1.74hz F / 1.79hz R]
-currently small front ARB included
-roll stiffness distribution [60% fr]
-TLLTD [58% fr]
-jounce travel 140mm
-rebound travel 100mm
-static camber -1* fr / -1.5rr
-approx 50% camber recovery fr+rr
-caster -7* fr / 0* rr
-KPI 9*
-anti's: design includes multiple inboard pickups, one setting for 0% anti's all round, will be including pickups to accomodate approx 40% antidive and 20% antisquat.
-roll angle @ 1.3G: 3.0deg
-chassis stiffness not evaluated yet, but read somewhere proper design goal is >10x total roll stiffness
Many thanks for anyone commenting!!
regards,
Tom
[ps non native english speaker, hope everything makes sense!]
[first post, so here goes!] We are currently designing the suspension for a new AWD vehicle, used for gravel-only [rallycross]. Think 550bhp 1000kg, very much like FIA WRX supercar.
I've spent quite some time reading up on websites like this, as well as RCVD etc. but currently find myself lost in details and need some "higher-level pointers" that help me understand what steps to take to arrive at some sensible goals.
My question is actually twofold:
A - is it possible for us to ballpark some spring/ARB values that approach a neutral handling car in steady state cornering, without having tire data available?
We will be using the same tire/rim combo on all 4 corners. We fully appreciate the need and use of testing to arrive at a desired setup, but the thing I'd like to avoid is starting out with a car that needs to be patched up because of some fundamental issues.
MAIN concern at this point is questioning integrating ARB's at either front or rear, or none at all
B - perhaps people with some experience with related cars would like to comment on some of our design parameters below? Would be greatly appreciated!
A - stuck in design process
The entire car is modeled out in 3D CAD, including weights.
AWD car, double wishbone on all 4 corners. Direct actuated spring/damper unit on lower control arm.
The suspension kinematics have been engineered iteratively using base Solidworks models combined with excel / VSUSP to arrive at what I think we want. Rates/frequencies/roll stiffness/load transfer have been evaluated using excel sheets (RCVD formula). So basicaly input spring/ARB choices and evaluate the outputs.
The steps I took so far:
-select suspension kinematics using models, to arrive at desired values
-extract sprung/unsprung weights and CoG locations from model
-Total weight distribution [56% front]
-select/trial spring rates to arrive at supension frequencies [1.74hz F / 1.79hz R]
-select/trial ARB and include tire vertical stiffness estimate to arrive at ride rate and total roll rate/stiffness
-roll stiffness distribution [60% front]
-use CoG vs neutral roll axis to arrive at load transfer F/R and TLLTD [58% front]
-calculate roll sensitivity [2.3 deg/G]
-input estimated max latG, verify:
--max steady state roll
--wheel travel used, travel reserve to bump stops for track irregularities
--actual wheel loads
This is where I'm stuck. Is it possible without tire data to say something usefull about steady state cornering balance?
B - car data, feel free to comment!
-AWD gravel, rallycross
-1020kg inc driver/fluids
-double wishbone all corners
-direct acting spring/shock on lower control arm, linear [Motion Ratio 1.49 to 1.51]
-uniball joints on every pickup, pickup points triangulated to feed forces into tube spaceframe (for compliance red.)
-total weight distribution [56% fr]
-design max latG: 1.3G
-wheelbase 2350mm
-tracks 1720/1720mm
-tire dia 640mm
-RCH 98mm fr / 118mm rr (1mm vertical change in roll, no gradient change in roll)
-roll sensitivity [2.3 deg/G]
(-tire vertical stiffness assumption: 300N/mm)
-susp frequencies [1.74hz F / 1.79hz R]
-currently small front ARB included
-roll stiffness distribution [60% fr]
-TLLTD [58% fr]
-jounce travel 140mm
-rebound travel 100mm
-static camber -1* fr / -1.5rr
-approx 50% camber recovery fr+rr
-caster -7* fr / 0* rr
-KPI 9*
-anti's: design includes multiple inboard pickups, one setting for 0% anti's all round, will be including pickups to accomodate approx 40% antidive and 20% antisquat.
-roll angle @ 1.3G: 3.0deg
-chassis stiffness not evaluated yet, but read somewhere proper design goal is >10x total roll stiffness
Many thanks for anyone commenting!!
regards,
Tom
[ps non native english speaker, hope everything makes sense!]