north american pick-up ride analysis•Reduction in target vehicle axle mass will reduce excitation energy 196 179 211 180 8.0 9.0 10.0 11.0 12.0 13.0 14.0 Benchmark 1 Benchmark 2

north american pick-up ride analysis

Matthew Taylor - Principal Engineer Vehicle Dynamics

Contribution by Ricardo Prado of Metalsa

introduction

•Requirement to understand ride limitation of large US pick-up trucks

•High volume strong selling vehicle –competitive market place

–domestic product

–imported vehicles

•Do we understand the cause of the ride deficiencies

introduction

•Decision drivers for truck chassis

–direction from suppliers

–perception of consumer

–performance

where are the opportunities?

•Two ways to gain a financial advantage

–better product for same money (less than competition)

–same product for less money (less than competition)

functionality

tota

lco

st

budget

prestige

what is our direction?

•Our aim was to match the competition for less money

–understand the system

–do not just follow the crowd

objective

functionality

tota

lco

st

budget

prestige

benchmark

•Ride and handling comparison of six trucks

–three domestic market, three imported

•Goal of this report –ride performance

–target vehicle perceived worse primary ride

–target vehicle perceived worse secondary ride

5

5.5

6

6.5

7

7.5

8

Benchmark1

Benchmark2

Benchmark3

Benchmark4

Benchmark5

Target

Sub

ject

ive

Rat

ing

primary ride comparison

•Benchmarks 4 and 5 were thought to have car-like ride when unladen

•Ride centres of most US trucks were not axle aligned

–significant spread of ride frequencies

–axle centred strategy improves accuracy of front / rear type ride frequencycalculation

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

'Front' RideFrequency

'Rear' RideFrequency

Frequency 1 Frequency 2

Freq

uen

cy(H

z)

Benchmark 1Benchmark 2TargetBenchmark 3Benchmark 4Benchmark 5

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

Frequency 1 Frequency 2 Mean Frequency Frequency Ratio

Freq

uen

cy(H

z)/

Freq

uen

cyR

atio

(:1

)


primary ride comparison

•Benchmarks 4 and 5 were thought to have car-like ride when unladen

•Ride centres of most US trucks were not axle aligned

–significant spread of ride frequencies

–axle centred strategy improves accuracy of front / rear type ride frequencycalculation

–problems with primary ride strategy of target vehicle apparent

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

Frequency 1 Frequency 2 Mean Frequency Frequency Ratio

Freq

uen

cy(H

z)/

Freq

uen

cyR

atio

(:1

)


-6 -4 -2 0 2 4 6 8 10Ride Position (m)

Benchmark 2 Target Benchmark 3 Benchmark 4 Benchmark 5

primary ride conclusion

•Potential to improve axle centre strategy limited by vehicle’s mass, inertia andwheelbase ratio (dynamic index)

•Modification of wheelbase outside scope of project

–modification of spring tune

–significant recalibration of dampers

0.75 0.75

0.81

0.870.89

0.80 0.79

0.83

1.00

0.96

0.91

0.70

0.80

0.90

1.00

1.10

Benchmark1

Benchmark2

Target Benchmark3

Benchmark4

Benchmark5

Dyn

amic

Ind

ex(D

I)

LadenUnladen'Ideal' DI

secondary ride –overview of concern

•Secondary ride (shake) identified as much more significant problem

–dominated by axle roll and hop (in- and out- of phase wheel hop)

–in phase of particular problem

•Strong couple to vehicle chassis –common to all beam axle trucks tested

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

Calcu latedHeave

Calcu late Roll Heave First Roll Second Roll

Freq

uen

cy(H

z)

Benchmark 1Benchmark 2TargetBenchmark 3

secondary ride –modal strategy

•Axle bending frequency clearly not contributory

•Repositioning of chassis modal behaviour impractical

–below 6Hz to separate from axle heave

–above 13Hz to separate from axle bounce

•One vehicle attempted to lower chassis frequency

–subjective appraisal notes persistent shake

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

Calcu latedHeave

Calculate Roll Heave First Roll Second Roll

Freq

uen

cy(H

z)

Benchmark 1Benchmark 2TargetBenchmark 3

58.5

56

50.5

49.5

45

50

55

60

Benchmark 1 Benchmark 2 Target Benchmark 3

Freq

uen

cy(H

z)

secondary ride –operating shapes

•Operating shape analysis confirms similarity

–modal positioning of vehicles very similar

–amplitude of target vehicle significantly greater than benchmark

30mph –axle acceleration

Target: Green


Target: Green






Target: Green


Target: Greenroll

heave





•Solution is to understand cause of higher amplitude


Target: Green


Target: Greenroll

heave

secondary ride –differences

•Modal decoupling is not cost effective

–lower axle mode too low

–high axle mode too high

•Reduction in target vehicle axle mass will reduce excitation energy

196

179

211

180

8.0

9.0

10.0

11.0

12.0

13.0

14.0

Benchmark 1 Benchmark 2 Target Benchmark 3

Freq

uen

cy(H

z)

0

50

100

150

200

250

Mas

s(k

g)

Calculated Heave FrequencyCalculated Roll FrequencyAxle Assembly Mass

secondary ride –reduced axle weight

•Nothing in findings to support removal of Hotchkiss system

•Combination of two concepts

–low cost, low complexity Hotchkiss

–minimised weight, rigid beam De-Dion

secondary ride –reduced axle weight

•Beam no longer carries differential device

•Reduced weight, large section beam pressing

•Improved camber and toe stiffness

•‘Unsprung’mass reduced by 25%

•Excitation energy reduced by 3dB

result of modification

•Subjective ride rating improved by 1.5 points

•Objective results show significant reduction in axle energy

•As anticipated, modal behaviour unaltered

0.01

0.10

1.00

10.00

100.00

0 5 10 15 20

Frequency (Hz)

Acc

eler

atio

n^2

((m

/s^2

)^2

/Hz)

Modified - LH Axle AccelerationOriginal - LH Axle Acceleration

further work

•Increased acceleration response at seat rail dominated by front axle activity

–modifications to chassis have altered front axle coupling

–opportunity to re-tune mass damper

0.00

0.00

0.01

0.10

1.00

0 5 10 15 20

Frequency (Hz)

Acc

eler

atio

n^2

((m

/s^2

)^2

/Hz)

Modified - LH Seat Rail AccelerationOriginal - LH Seat Rail Acceleration

conclusions

•Primary ride compromised by poor inertia mass relationship

–can be improved in limited sense by damping

•Axle activity and modal behaviour of chassis not realistically separable

•Secondary ride subjectively improved by reduced mass axle

•Simple solution represents cost effective fix

Documents

north american pick-up ride analysis•Reduction in target vehicle axle mass will reduce excitation energy 196 179 211 180 8.0 9.0 10.0 11.0 12.0 13.0 14.0 Benchmark 1 Benchmark 2