'Drive By Wire'
by Jim Kerr

Over the last few years, "drive by wire" has become a common feature on many vehicles. Drive by wire can mean many things: electronic steering, electronic braking, or electronic throttle control. Honda is using electric steering on some vehicles, as is GM on the rear wheel steering on its Quadrasteer systems. Mercedes is using electronic braking in their SL and E-series cars.

But while these systems are electronically controlled and operated, there is still a mechanical backup system if an electrical problem develops. On the other hand, throttle systems are going to complete electronic control, doing away with throttle cables and mechanical backup systems. If a throttle control system malfunctions completely, the vehicle's engine simply returns to an idle, but redundant electronics mean the systems seldom fail completely. A warning on the dash tells the driver to have the vehicle repaired if a problem did develop.

Electronic throttle control may sound complicated but it really simplifies vehicle design construction and operation. Instead of a throttle cable and mechanical linkage at the gas pedal and engine, the link is done with wires. The gas pedal is still used, but all it moves is an electrical sensor. Springs provide the force that make a driver think the pedal is still connected to the engine, and on most vehicles the driver will not notice any difference between conventional throttle systems and drive by wire.

The pedal sensor sends a varying voltage to the engine computer, which controls an electric motor connected directly to the engine's throttle plates. Step on the gas pedal and the computer instantly opens the throttle.

Electronic throttles offer many advantages. Cruise control is an easy addition. So is traction control. If the engine computer senses wheel spin, it can close the throttle until spin is no longer detected. Varying the throttle rate electronically with programming can make the vehicle smoother and more responsive to drive. The first several degrees of pedal movement may allow slow acceleration, while the next several degrees of movement cause the vehicle to accelerate quickly.

SUV's are taking advantage of electronic throttle to change the responsiveness of the pedal from high to low range in the transfer case. When the vehicle is shifted into low range, the pedal responsiveness is reduced, allowing drivers better control over rough terrain and at very slow speeds. With mechanical throttles, this was always a compromise.

Throttle control is also integrated with transmission shifting. With electronic control, the throttle can be closed slightly to reduce engine output during a shift, providing smoother vehicle operation.

The latest in electronic throttle control comes in Lincoln's 2003 LS sedan. Just arriving at the dealers, the Lincoln LS is the first vehicle to take throttle control to a new level. Existing systems could be called a "pedal-follower" design. The throttle basically moves in relationship to the pedal input. The computer may decrease throttle opening during shifts or traction control intervention, but these systems basically look after engine torque output. The new Lincoln LS system looks at the complete vehicle to control throttle opening.

Here is an example how this new design works. When a driver is accelerating, the computer calculates torque delivered to the rear wheels instead of just engine output as other systems do. To calculate torque output at the rear wheels, the computer must monitor slip in the torque converter, transmission gear ratio, rear axle ratio, and engine output.

With a regular drive by wire throttle, the engine RPM drops when the transmission shifts and the computer moves the throttle plates to a position signaled by the pedal position. The Lincoln system uses the engine computer to move the throttle plates so rear axle torque output stays constant during a shift. The engine rpm will change, but the computer will move the throttle plates to a calculated position for constant torque rather than basing it only on pedal input.

The difference between the two systems seems small, as it is based only on electronic programming, but the real difference is in the driving. A few kilometres in the Lincoln LS demonstrates the smooth operation this programming provides. Shifts are smooth and vehicle acceleration is linear.

One day, all vehicle controls may operate electronically, but we probably won't recognize it. Pedals, steering wheels, and switches will remain for a long time, giving drivers the illusion the vehicle controls are still the same.

Originally posted by TL_Type_S
my 2k3 Max has it .. don't like it so far... it's too intelligent sometimes, and it refuses to drop me into 1st when I floor it after light accel. from a stop .. it may just be the transmission design, but I don't buy it. I can definitely see all the advantages the electronic throttle offers per this article, so I'm not complaining too much.