The elements of extracting maximum pace from racecars are many and varied, ranging from power output to a myriad of both major and minor components. One of these elements is transmission shift times.
Geartronics is working with Penny+Giles, a business group of Curtiss Wright Controls, to improve shift times and reliability of its motorsport paddleshift system for semi-automatic gearboxes. Penny+Giles is a designer and manufacturer of precision sensing technology, and Geartronics is applying its Hall-effect rotary sensors to achieve both goals.
Geartronics’ closed-loop control system uses a gearbox control unit (GCU) in conjunction with the sensor (designated SRH280DP) inputs to modify operation in real time. Geartronics’ Managing Director, Neil Wallace, explained: “In the context of semi-automatic gear selection, the closed-loop system monitors the gear position sensor to determine the precise angular position of the gearbox selector barrel. This information is fed back to the GCU control algorithm so the pneumatic actuator, engine torque reduction, or throttle blip can be turned on and off as necessary to effect the fastest and most reliable shifts.”
The pneumatic shifter mechanism directly controls the gearbox cam-drum or barrel and eliminates the need for driver-operated shift linkages.
An open-loop system has no feedback mechanism and depends on fixed timers to govern shifts. It applies the same engine cut or throttle blip duration for every shift, regardless of whether those times are appropriate for each individual shift requirement, explained Wallace.
But a closed-loop system relies absolutely on sensor feedback from the gearbox; this is where Penny+Giles’ system plays a key role. The sensor uses a 38-mm (1.5-in) flange housing with an environmental protection rating of IP68. The noncontact technology used with Hall-effect sensors is not affected by vibration, an important plus compared to resistive contacts in a motorsport environment.
“The strategy to successfully get out of one gear and engage the next as quickly as possible is not just a case of cutting the engine, or blipping the throttle for a few milliseconds and hoping for the best!” said Wallace.
He added that for any semi-automatic shift system to work consistently and reliably under all conditions, the GCU needs “as an absolute minimum” to measure the gearbox barrel position, throttle position, and engine speed, which is what the Penny+Giles sensor helps achieve.
Geartronics’ systems are used in various motorsport disciplines, including open-wheel and GT car racing, rally hill climbing, and also on the road-going Ariel AtomV8, which has a Sadev six-speed sequential gearbox with adjustable limited-slip differential and gearsets. Gear change is via a paddle airshift system that makes up-changes in 40 milliseconds and down-changes in 50 milliseconds, with the capability of five downshifts in less than a single second. The system is programmable and is available with auto upshift and cued downshift capability.
The car’s 3.0-L engine produces 373 kW (500 hp), and maximum power is achieved at 10,600 rpm. The Atom V8 weighs 550 kg (1213 lb). The company describes its performance as being “the most remarkable acceleration seen in a production vehicle ever”: 0-97 km/h (60 mph) in 2.5 s and to 160 km/h (100 mph) in 5 s.
The Penny+Giles sensor is factory-programmable, permitting specification of signal type, the measurement range (0-20° to 0-360° in 1° increments), and the output direction (clockwise or counterclockwise). It has a 12-bit resolution over the selected measuring range and operates from -40 to +140°C (-40 to +284°F) when powered at 5 Vdc.