Shift without lifting - how it works!

 by Mark Cipolloni and David Cipolloni
August 2, 2000

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Whereas F1 allows a driver to change gears using paddles on the steering wheel, CART does not.  A Champ Car driver must still take their right hand off the steering wheel for gear changes.  Although not as automated as F1, CART's engine manufacturers have developed systems that allow a driver to upshift without lifting off the throttle, all within the rules allowed by CART.

When a driver momentarily lifts off the accelerator to change gears the car is no longer accelerating.  That is time lost.  Studies have shown that the best drivers take 100 to 200 milliseconds to complete a gear shift.  However, as a race wears on the driver gets tired and these times can double or triple without the driver even realizing it.

The shift-without-lift technology allows a driver to complete an upshift in 30 to 50 milliseconds.  If you assume a driver makes 20 to 30 upshift's per lap on a course such as Long Beach, it's easy to compute how many upshift's are made over a 100 lap distance.  Let's assume, for arguments sake, that a driver makes 2000 upshift's in a race and the shift-without-lift technology saves 150 milliseconds per shift, that equates to 300 seconds of lost acceleration.  Note, that's lost acceleration, not lost time, a big difference.  

We must run the math to compute what the driver may gain in those 300 seconds.  Assuming a Champ Car accelerates from 0 to 60 mph in 3.6 seconds, the average rate of acceleration through its entire power band is somewhere in the neighborhood of 15 to 20fps2.   15fps2 x 150ms = 2.25fps.  In theory the car should be going 2.25fps faster after every shift vs. manual shifting.  

Going up through the gearbox from 1st to 6th is five gear changes.  In theory, 5 gear changes x 2.25 = 11.25fps faster, or about 7.6 mph faster at the instant of the last shift.  With either method the car will reach the same terminal velocity, however, the car with the shift-without-lift mechanism will get there faster.  For the short period of time the car is being shifted, the car with the shift-without-lift mechanism should be anywhere from 2.25 to 7.6mph faster (2.25 for 1 upshift, 7.6 for 5 upshifts), depending on the number of upshifts the driver executes in any one given maneuver.  Racing is sometimes a game of inches.  In some cases the gain may be just enough to make the pass.

Team Rahal was kind enough to run the data through their simulator and it resulted in a gain of 0.25 seconds per lap using the numbers above.  In a 100 lap race with no cautions, that can amount to a 25 second gain, which is quite significant.

FIGURE 1. Sequential Shift mechanism.  Note the spring loaded micro-switch that sends an electrical signal to the transmission and Engine Control Unit (ECU) when the driver moves the lever back (to the right in picture) Click to enlarge

How it works
In the cockpit the driver will pull the shift lever to the rear (see Figure 1) in order to upshift the transmission. This is done without lifting from the accelerator. To downshift the transmission the driver will push the shift lever forward and blip the throttle to assist in the gear change by relieving load on the drivetrain.  The clutch is not used on downshifts either.

The shift-without-lift process starts when the driver moves the shift lever and triggers a series of electrical events. Attached to the shift lever is a spring loaded micro-switch that responds to the drivers inputs and sends a signal to a sensor located on the transmission. The sensor rides on a cam inside the transmission that allows it to identify which gear the transmission is in (see Figure 2). 

Simultaneously a signal is then sent to the vehicles Electronic Control Unit (ECU - see Figure 3) that will in turn momentarily interrupt the engines ignition and fuel system to one or more cylinders (sorry we can't say how many - manufacturers secret). The gears in the transmission are momentarily unloaded enabling the synchronizers to lock a different gear to the transmission's main shaft. In a street car the load is removed from the transmission by depressing the clutch pedal and momentarily disconnecting the engine from the transmission's input shaft. The driver then can change gears and release the clutch, thereby reconnecting the engine to the transmission.  In a Champ Car the clutch mechanism is used only when moving from a standstill. 

FIGURE 2.  The black wire shown connects to a sensor in the transmission that connects to a camshaft type mechanism that tells the ECU what gear it is in at all times (click to enlarge)

The Electronic Control Unit shown below in Figure 3 will interrupt the engines ignition system for 30 to 50 milliseconds allowing for the upshift or downshift to take place. The amount of delay and other system parameters are programmed differently depending on the type of track the car will be used on and the gear ratios chosen. This is one of the reasons you will see the engineers toting their laptops around the garage area and connecting them to the cars ECU's at various times. 

From the drivers seat the transition between gears occurs in rapid succession with little notice of the systems intricacies. From the engineers standpoint the gear change must be made in the shortest possible time. To give you an example of the importance of this, consider that combustion takes place in each of the engines cylinders in 3 milliseconds or less. When this burn time is interrupted there is loss of power from that cylinder. Combustion pressure is lost and can only be regained when the piston arrives to complete it's next compression and power strokes. When the engineers deal with this system the relevance of 50 milliseconds of ignition and/or fuel system interruption means power is lost in the interrupted cylinders for as many as 3 'combustion' cycles each (assuming around 16,000 rpm). The trade-off of lifting off the throttle, however, is even worse.

FIGURE 3.  Electronic Control Unit (ECU)

One benefit of the shift-without-lift technology is that we no longer see engines ruined due to over-revving on upshifts when a driver misses a gear.  Unless the shift mechanism fails, it simply no longer happens due to driver error. That means less blown engines and money saved.  All over-revs you hear about today are done on downshifts.

While all of this high tech hardware might provide for faster lap times than the old clutch and shift method the driver must still properly time the upshifts and downshifts to optimize power output. No easy task on some of the big road and street courses at the speeds Champ Cars run and the vibration and g-force loading they are experiencing.  A healthy dose of respect is given to the drivers and engineers that prepare and drive these cars on race day.

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