Ok I’ve mentioned this before but in order to truly understand chassis dynamics we must understand both sides of the Car vs Driver partnership. We must essentially listen to the chassis’s side of the story and then the driver’s side of the story. When we get this right we produce a capable chassis that is easily exploitable by the intended driver.
The human element of chassis dynamics is without doubt the most important and the hardest aspect for engineer’s to understand, the consequence is that this area of the science is often totally ignored and leads to drivers being blamed for poor skills or lack of commitment, either that or an acceptable outcome is eventually totally fluked via hours of trail and error.
The driving process:
• Step one: A driver looks at the oncoming road and estimates the required inputs to complete the task at hand, we make this estimate based on a model of the car held in our memory, the more accurate this model the more accurate our initial guess.
• Step two: An “Open Loop” input is made according to our guess
• Step 3: Then “Closed Loop” trimming modifies these inputs to take account of emerging conditions or errors in the initial guess
There are 3 main channels of feed back used for “Closed Loop” driving
1. Visual feedback
2. Inner ear (yaw rate, lateral acceleration etc) feedback
3. Muscle tension or Steering wheel torque feedback
It is through these communication channels that a car can speak to a driver.
Ok firstly, the drivers eyes….
Processing visual stimuli is actually quite a complex procedure and incurs a delay of around 600msec in most people between seeing and understanding, so that’s a maximum update rate of around 1.8Hz
Driving by your eyes alone is only possible if no quick action is required.
• If the roads and bend radiuses are known and learned
• And of course as long as no chassis control task’s are required
The inner ear….
Processing the yaw and latt acc information from the inner ear is a far simpler process and is therefore faster but even so this feed-back process still suffers a delay of around 300msec so this loop can actually update at around 3.2Hz which is pretty fast.
Muscle tension in the drivers body….
The task of moving the steering wheel is a function carried out by the brain stem, the brain stem works automatically to maintain the correct steering angle by varying your arms muscle tension. Changes in the steering resistance cause the brain stem to get confused and flag up the problem to a higher part of the brain that is responsible for processing the overall task of driving the car. This form of feedback is extremely fast at around 100msec so this can provide you feedback at 10Hz (ten times per second).
Some interesting points to note:
• A driver’s in-head car model is almost exclusively linear
• Excessive anxiety in a driver can easily cause the steer torque mechanism to be completely “swamped” by muscle tension and therefore useless.
• Inexperienced drivers are frequently unable to interpret inner ear signals or are too confused to act on them so they are discarded by the brains automatic information filters in the brain stem
• A surprising level of confusion exists in the inner ear between yaw and chassis roll, this lead some drivers to “dislike” body roll
• Many drivers are found to revert back to an entirely visual driving strategy in emergency circumstances
• Many drivers are overwhelmed and lose control even though the car was capable of completing the maneuvre
• A maximum practicable hand steering wheel rate is around 1100 degrees / second –but not for long
• Typical hand wheel rates are much slower - < 100 degrees / second in “Sensible” driving
If your thinking to yourself "yeah and" don't worry I am going somewhere with this
