MotoGP
All MotoGP bikes use control systems to help make to bikes easier to ride therefore go faster around the track. All teams use a form of ride by wire throttle control, traction control, engine braking control, launch control and anti wheelie. All necessary parameters are measured using a suitable data logger that will be measured through sensors that feed information on to the ECU and the engineers to make these systems work correctly.
This assignment looks at how these systems work and some of the variations used by different teams to achieve the same results.
Data Logging
Data logging is the key to all of the motoGP control systems, without logging wheel speeds with wheel speed sensors and GPS, bank angle, and gyroscopes none control systems can be controlled and understood. The data logger is a control system in itself and is an important tool measuring every measurable parameter on a modern GP bike. The engines are monitored constantly and the chassis measurements30 are an important part of getting the bikes handling finely tuned for the ride, track and conditions.
A bike without any sophisticated control systems, the data logger clearly shows when the bikes front wheel is in the air and the throttle has to be shut to drop the front again. It also shows when the rear wheel brakes traction and follows the same pattern as the RPM trace in 5th gear!
Heavy engine braking is shown as the rear wheel spins significantly slower than the front when entering a corner. This causes the bike to slide and hop making it difficult to tip into the corner.
These are the main symptoms modern electronic systems attempt to fix by carefully controlling the throttle and ignition. Development has sped up considerably in resent years with electronics making more things possible to the engineers. The tools to use and create these control systems has been made possible with sophisticated ECUs, ride by wire throttle control and data logging.
Ride by wire
Ride by wire throttle control has been one of the main reasons why development of other control systems has progressed in recent years. Ride by wire essentially allows the engineers to programme how the bike is going to behave by taking some of the control away from the rider. There early systems had two cylinders controlled by throttle cables via the throttle from the rider and two cylinders controlled by the ECU to maintain a direct feel for the rider. Now the throttle openings are entirely controlled via the ECU after measuring the required input from the rider. The ECU then sends signal to a motor that opens the throttle to the correct position.
The advantages of ride by wire are obvious when other control systems such as traction control are being developed as throttle opening is an important part of making the system work correctly to its full potential.
Traction Control
Traction control is a system that prevents, limits or corrects the amount of rear wheel spin the bike has when accelerating. When the wheel is spinning there is less drive meaning the bike is not accelerating as fast as it could be as the rider has the back off the throttle to regain grip at the tyre. Traction control optimises the power delivery so the tyre does not break traction and the greatest acceleration from any situation. This is true when accelerating hard out of slow corners, very fast but tight corners and wet track conditions.
Here are two different ways that Yamaha and Ducati go about traction control systems on there bikes.
Yamaha
Yamaha uses a system that corrects the amount of wheel spin when it happens. Yamaha measure accurately the speed of both wheels of the bike with wheel speed sensors as well as the overall speed of the bike with a GPS unit. When the rear wheel spins faster than the front wheel power is limited to regain traction at the tyre. The GPS could be used to step in if front wheel is in the air. Lean angle must be measured as the tyres have different circumferences as different lean angles which may give misleading results. The tyres circumference can be matched which the lean angle and programmed into the system giving very accurate wheel speed signal needed for traction control.
The preferred power control is by closing the throttle butterflies of two or more cylinders as this is possible with the ride by wire, Retarding the ignition is also a smooth and efficient way to lose power. If lots of power needs to be lost the spark is cut at varying number of cycles, but stating at nine cycles then a spark is missed on one or more cylinders. The problem with cutting the sparks is that the rider can feel the cut because the bike misfires and the bike will pump as the power is cut then comes in again while exiting a corner. Also cutting cylinders uses a lot of fuel which is a problem because of the limited amount of fuel allowed
Ducati
Ducati prevents wheel spin altogether by knowing how much traction the tyre and the track have and the area of the contact patch of the tyre on the ground at every lean angle. With this information the optimum amount of power can be fed to the rear wheel by limiting the throttle openings giving very smooth power delivery. This method does have some difficulties. The engineers must know the exactly the co-efficient of the tyres and the track. Most of what is known is from previous testing and does not take into account that the tyres maybe inconstant as well as the track surface and weather conditions. The traction control must be preset to be very close to the point of traction loss for maximum performance or the bike will be underpowered so it is very important that the information collected is as accrete as possible. A lot of trust is put into this system from the rider as in theory 100% throttle can applied by the rider out of a slow corner and the traction control will fire him out as fast as is possible with no wheel spin or high-side but not all riders have that level of trust.
Engine Breaking Control
Four stroke bikes have a lot of engine braking which can cause the bike to lock the rear wheel or hop into a corner which causes difficulties when braking. Slipper clutches have been used for a long time and are used on four stroke motoGP bikes. Slipper clutches mainly help control the rise in rpm with the downshift. Many bikes are electronically assisted, the current GP bike use a system that opens the throttle slightly when braking meaning that the engine braking can be eliminated. This can be done because the ECU knows when the throttle is closed and the speeds of the front and rear wheel. Similarly to the Yamaha type traction control the ECU calculates the difference between the front and rear wheels but this time the rear wheel will be slower than front wheel. Power must be applied so that the rear wheel speed matches the front wheel speed. The ECU can do this because of the freedom the ride by wire gives. This again has be carefully controlled as if there is a fine l ine between no engine braking and trying to accelerate the bike forwards while braking which would be very dangerous.
Ducati was developing a system that completely electronically disengaged the clutch on entry into a corner and then smoothly re-engaged when the throttle was applied. This system had no engine braking to make the bike feel similar to how a two stroke used to feel.
Anti Wheelie
When the bike wheelies power often has be laid off by the rider or the rear brake applied which slows the bike down. A wheelie is seen by the logger as the front wheel speed slowing and then speeding up when its grounded to match the new speed, as shown above in the 2D traces. Also when the front suspension is fully extended the wheel is often off the ground. When the front wheel slows the ECU will close the throttle slightly and this can be to maintain a small amount of wheel lift or closed enough to put the wheel firmly back on the ground.
Launch Control
Launch control is a system that is used for a race start that ensures the rider gets the best possible start by holding the engine at a curtain RPM set by the rider to get the best start possible. Its a combination of traction control and anti wheelie and would be best using a Ducati style of traction control for a launch as the bike is upright and the tyres are always new. Assumptions are made of tyre and track co-efficient easier and this could be easily set in the few hours before a race. If the front wheel lifts the anti wheelie kicks in and engages the traction control even more. This gives reliable consistent starts and is now even available in basic race kits for street bikes and is set when the rear wheel is not moving and in first gear.
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