The technology that automakers have been adding to improve safety and fuel economy, as well as maintain emissions compliance, also can provide high-performance modes, thanks to the sensors and high-speed data buses already in place. The 2015 Chrysler 200 demonstrates a sophisticated new example with its Sport Mode for models with all-wheel drive (AWD) and the 3.6-L V6. Sport Mode is a transmission-selectable position on the console shift knob.
Like many sport-oriented choices, the Sport Mode on the 200 retunes the accelerator pedal map, firms up and revises the transmission shift points, and has a manual shift mode with steering wheel paddles. Compared with the Normal (Drive) mode, it also provides more road feel with a specific steering assist curve (less assist) as road speed goes up.
High-speed CAN algorithms
Sport Mode also introduces a number of specific new performance algorithms using a group of electronic modules on the car's high-speed CAN (Controller Area Network). This data bus is the one that regulates engine/transmission/drivetrain operation, emissions, and safety systems.
The nine-speed front-wheel-drive automatic transaxle, introduced on Jeep Cherokee, is capped at seventh gear (still an overdrive gear) in Sport Mode on the 200, and the shift points are automatically selected from a map for maximum torque.
The transmission control module holds the lowest possible gear requested when the driver is holding the "-" paddle during paddle shifting, and will allow higher rpm in each gear than the Normal mode map. It will not do automatic upshifting—going only from 1st to 2nd gear at wide-open throttle. The paddle shifters are depicted on an instrument panel graphic, and as the engine approaches the rev limit, the "+" paddle graphic will glow red as an upshift indicator. If the driver doesn't upshift, he next gets a Shift Up arrow display as the engine rpm approaches fuel cutoff.
AWD has separate strategies for Normal and Sport modes. In Normal, the system prefers front-drive for fuel economy, but may switch automatically to AWD under certain conditions, including detection of a low-traction road surface and driver operation of the throttle. At road speeds under 9 mph (15 km/h), AWD also automatically engages to anticipate a possible sudden hard acceleration or any acceleration if the road surface traction drops, as detected by vehicle chassis electronics. When AWD is engaged, the split is 60-40 front-rear, although the dynamic multi-map electronics can push it to a maximum of 50-50.
AWD is an always-on, key part of Sport Mode, and the electronic stability control (ESC) broadens the allowable yaw range. As managed by the Drivetrain Control Module, AWD is engaged both front-to-rear and at the rear axle; no rear axle disconnect is possible as as it is in Normal mode.
There's always some rear torque bias in Sport Mode, derived from the accelerator pedal position and the delta from the previous position. The actual Sport Mode torque transfer to the rear is based on the available torque from the engine, vehicle speed, yaw rate, and vehicle grade. The system uses an enhanced torque map for launch modes, although there is no specific launch control system for the driver to select on the 200.
Engine braking, adaptive cruise, and ESC
When the driver lifts his/her foot from the accelerator in Sport, a specific algorithm closes the throttle plate a bit more than by a simple proportion. This increases engine braking and adds to the overall performance dynamics of the car.
The adaptive cruise control, which has four possible gap settings from the car ahead, not only switches to the minimum distance in Sport Mode, but the cruise control itself becomes much more aggressive. That is, when it resumes after deactivation, the acceleration to cruise speed is much greater, adding to the performance feel of the car. It won't be a full-throttle-to-tailgate a car ahead, but it does provide a contrast with Normal mode, for which the default is the maximum gap of the four settings.
Unlike some performance cars (such as SRT models) with a turn-off provision for traction control and electronic stability control (ESC), Sport Mode never allows a complete disconnect. In Sport there's always an ESC partial, which turns off the traction control and as noted earlier, increases the amount of yaw that it will allow before it intervenes. However, if the driver prefers to have full ESC even in Sport, pressing the ESC button on the control stack provides it.Continue reading »