[Engineering Feature]
The Indianapolis 500 Electronic Edge
IndyCar Series race cars all must use the same engine and semi-automatic transmission, so teams look to electronics and telemetry to give them the extra advantage needed for a trip to victory lane.
Surely most racing fans have May 24, 2009, circled on their calendars. For the non-gearheads, this Memorial Day marks the 93rd running of the Indianapolis 500. The event will pit 33 cars and drivers against each other in a grueling 500-mile race around a 2.5-mile track. The fastest average speed is more than 185 mph with top speeds cresting at about 235 mph.
The front and back straightaways are only five-eighths of a mile long, so drivers spend a good deal of time in the 9° banked turns. Trying to drive the optimum path with 32 other cars on the track is a real challenge, since each driver wants to be on the optimum line.
The race is more impressive when you consider that it’s more of a test of drivers and their teams than the best open-wheel race car. There are always variances, but the Indy Racing League (IRL), known as IndyCar, sets the specifications for the cars, making them nearly identical (see “IndyCar Specifications”).
Teams do have a wider range of discretion when it comes to brakes, tires, and suspension, but even they have some strict limits. However, teams can augment the sensor and telemetry system used in the car (Fig. 1). These modifications can often provide the edge that a team needs to win, whether it’s in selecting the best time to enter the pits or choosing what kind of tires to use.
THEY’RE ALL THE SAME Well, almost. There are strict limits on dimensions, weight, and all sorts of details such as the size and placement of the wings found on the front and rear of the cars. The engine and transmission/ gearbox are the same in each car. They can’t be tweaked, although they can be controlled. That means no playing around with the engine control unit (ECU).
Likewise, the RPMs are limited to 10,300. Go above the limit, and the engine will slow down by 9500 RPM, so there’s an incentive to push the limit but not exceed it. This can be tough when operating near the limit because bumps, wind, and drafting all affect the load on the engine and, hence, its speed.
It’s possible to make faster cars, but 225 mph is the turning point at which human reaction time turns a safe race into collision city. The cars are designed for safety, so drivers usually walk away from spectacular crashes, though fatal accidents have occurred at the Indianapolis Motor Speedway, also known as the Brickyard.
To reach this speed, the cars use a 650-hp, 3-l Honda V8 engine that costs about $2.9 million per car. The engine is smaller than the 3.5-l engine used a few years ago, and its smaller power band forces drivers to shift more often. The engines are designed to last at least 1200 miles between rebuilds, but this is definitely not stop-and-go traffic.
The engines run on 100% ethanol. The designers looked to minimize engine failures under demanding race loads while also cutting operating costs. A new engine will come into play next year. Thus, several additional suppliers are considering support for IndyCar.
SEMI-AUTOMATIC TRANSMISSION Adam Schaechter, chief engineer at AJ Foyt Racing, says that one of the biggest changes in the race over the past few years has been the switch to the current six-speed, all-forward-gears, semi-automatic transmission. It eliminates the clutch pedal and provides electronic control to synchronize timing and torque requirements, resulting in a smooth, efficient transition.
The drivers only have to contend with a paddle shifter that toggles up or down one gear. The shift control incorporates strain gauges to determine when a driver desires a transition. This has led to a “shift without lift” approach to driving, where the driver always has the “pedal to the metal.”
During a transition, the ECU will interrupt the fuel flow and ignition to the engine, providing a smoother shift. All of this accounts for the current speed and load on the engine. The transition occurs in 30 to 60 ms. The parameters are adjustable, but they’re set by IndyCar, not the teams.
The clutchless, semi-automatic transmission meshes with the IndyCar requirements because drivers would normally shift up and down. Jumping over gears is not a good idea. Over-revving an engine due to improper shifting can cost tens of thousands of dollars in wear and tear.
The semi-automatic transmission is relatively new for IndyCar, but so far it’s been well received. It tends to narrow the gap between drivers because manual shifting is an art, especially when moving at over 200 mph. The new transmission makes it easier to shift more if warranted. The shift paddles are mounted on the steering wheel for easy access.
Two Fig. 4's, and 2nd Fig. 4 and Fig. 5 should be 5 & 6.
Chip -May 08, 2009
In regards to automatic transmissions at Indy I remember that either A.J. Foyt and/or Dan Gurney used them in at least one race. I also remember that the Hall Chapparel (not Indy) race cars used automatic transmissions. This is not new technology just additional gears and better control in my opinion.
Anonymous -May 07, 2009
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