rally car driver behaviour Weeee!

Transcription

1 rally car driver behaviour Weeee!

2 presentation map Motorsport Goals World Rally Environment Driver Behaviour

3 motorsport goals Most valuable sponsorship space minimum lap/stage time Most events are a series of connected corners (except drag racing) Getting round corners quickly is a key aspect of good motorsport performance Engine engineers see things differently!

4 motorsport goals - cornering Anatomy of a corner maximum deceleration transition to maximum lateral acceleration transition to maximum longitudinal acceleration Mid-corner speed determines maximum path curvature Longitudinal Acceleration Lateral Acceleration /r = A/v V

5 motorsport goals - cornering Sounds simple so far Line described was symmetric turn-in phase was as long as turn-out phase (blue, below) Non-intuitive result but known to many drivers: slow in, fast out is better (red) 1 6 Longitudinal Acceleration.5 Lateral Acceleration Longitudinal Acceleration Lateral Acceleration Asymmetric Symmetric Hot Cold

6 motorsport goals - cornering Lower entry speed, later but more rapid turn-in Earlier application of power Sometimes described as late apex 1 6 Longitudinal Acceleration.5 Lateral Acceleration Longitudinal Acceleration Lateral Acceleration Asymmetric Symmetric Hot Cold

7 motorsport goals - cornering Time from A to B is the response measure of interest 5.6 seconds 5.4 seconds.2 seconds/corner might be 2 seconds/lap typical short circuit No additional deceleration or mid-corner speed time is in the line 1 12 Longitudinal Acceleration.5 Lateral Acceleration Longitudinal Acceleration Lateral Acceleration Asymmetric Symmetric B Hot Cold A

8 presentation map Motorsport Goals World Rally Environment Driver Behaviour

9 world rally environment Around 5 bends/km WRC average 35 stage km per event 1 kph WRC average Unrehearsed, unpredictable reconnaissance run on Tuesday event on Friday, Saturday, Sunday weather and other cars since recce loose surface pace notes compiled by the driver: 8m until (caution) 5 th gear right over crest into 4 th gear left tightens

10 presentation map Motorsport Goals World Rally Environment Driver Behaviour

11 driver behaviour Driver has the front wheels fairly directly in their hand* Control bandwidth for front tyre slip angle about 5 Hz Rear wheels are bolted to the car Steering Angle Spectrum (degrees) 1 Normal Road Driving Professional Rally Driver Frequency (Hz) rear wheel steer forbidden Control bandwidth for rear wheels dependent on yaw-sideslip behaviour falls away with speed phase delays become significant Control gains rise with speed * Some drivers use both hands response frequency phase frequency

12 driver behaviour Yaw-sideslip behaviour frequency-capped by rough and loose surfaces Yaw-sideslip behaviour blunted by taut driveline Events take place in very limited space Risk-reward balance

13 driver behaviour Accurate control requires large and rapid steer inputs Car has numerically low ( fast ) steering, high levels of assistance Historically, steering technique defends against limited yaw-sideslip frequency Scandinavian Flick Handbrake when speed is too low (yaw-sideslip damping too high)

14 driver behaviour Scandinavian Flick is forced by low vehicle bandwidth Feed-forward manoeuvre with feedback trim in the later stages Goal is to rotate car on corner entry Once car is rotated, is quite safe Too fast in, throttle lift car tucks to inside of corner Too slow in, throttle apply car takes new, wider line Surprisingly instinctive with some practice and with a well-behaved car Consumes a lot of space/time

15 driver behaviour On-centre, handwheel controls yaw and sideslip in a coupled way In a corner, combination of throttle and handwheel gives control of both yaw and sideslip Most easily understood by thinking about Rear Wheel Drive in drift situation

16 driver behaviour Steering is reversed ( opposite lock ) Yaw control throttle and steer in opposition for more yaw, either more throttle or less steer Sideslip control throttle and steer together for more sideslip, more throttle and more countersteer

17 driver behaviour 2 controls, 2 outcomes Coupled control strategies for each outcome All wheel drive produces more complex effects but logic is broadly similar Both handwheel and driveline/brake are high bandwidth actuators No need to wait for rear of car to move to modify forces Works on different kinds of vehicle, too

18 driver behaviour Controls are somewhat non-linear in their operation Vehicle design & setup task is to deliver useful linearity Modelling separate regimes is not especially difficult Joined up model which switches strategies is more elaborate I have the same problem!

19 driver behaviour New generation of cars show less dramatic behaviour than old Drive up, turn in is preferred style Coupled control behaviour still in evidence balance more like front-wheel-drive brakes yaw more, throttle yaws less Great deal of emphasis on vehicle bandwidth Even more emphasis on control bandwidth yet faster steering extraordinarily responsive brakes/driveline load management with elaborate dampers

20 conclusions Limit driving requires a multi-mode approach Some modes blend control inputs in a way you ll never read in a book Nothing particularly difficult about modelling individual modes Switching modes a little more difficult for both people and models

21 rally car driver behaviour Weeee!