DEARBORN, Nov. 15, 2005 — Beneath the hood of a Ford hybrid vehicle is a system of electronic controls that continuously monitors the interaction between the driver, the vehicle and the road to deliver class-leading fuel economy. Utilizing drive-by-wire (or direct drive) technology, the hybrid s electronic controls add a new degree of precision to the communication between driver and vehicle.
Drive-by-wire technology refers to the replacement of mechanical components with electronic controls. While the technology it’self is not new, drive-by-wire has gained a newfound importance in hybrid technology.
“In the Ford hybrids, we use a brake-by-wire system,” said Tom Gee, manager, Hybrid Controls. “It s part of the regenerative braking system that manages friction braking to maximize braking energy recovered to charge the hybrid s battery. During normal use, a computer controls the hydraulic system. There is no connection between the brake pedal and the hydraulics.”
Brake-by-wire means there is no mechanical connection between the brake pedal and the hydraulic brakes during normal operation. This lets the system electronically optimize braking for maximum fuel economy and braking performance.
“When the driver steps on the brake in our hybrids, the pedal is attached to a spring to provide the feel of braking,” Gee said. “A sensor monitors the amount of pedal movement and relays the information to the Brake System Control Module (BSCM). The BSCM coordinates with the Vehicle System Controller to identify the amount of power the battery can absorb.”
If enough power can be absorbed by the battery for safe braking, none of the energy needs to be wasted by friction braking.
Whether in a hybrid or conventional powertrain, the benefit’s of drive-by-wire systems are greater precision in controlling the vehicle s performance. The greater precision results in better fuel efficiency and the related benefit’s of reduced emissions.
Along with the braking system, the hybrids utilize another form of drive-by-wire technology, the electronic throttle control. As with the brake pedal, when the driver steps on the gas pedal, a sensor monitors the movements. In turn, the Vehicle System Control balances the driver s input with the amount of power required to propel the vehicle, keep the battery charged and power accessories like air conditioning that may be running.
“Unlike a typical transmission, the hybrid s transmission contains no hydraulics except for an oil pump,” Gee said. “The Vehicle System Control sets engine speed and performance to optimize efficiency based on what the driver is doing.”
In developing the Escape Hybrid, Ford s engineers examined different types of hybrid systems before settling on the current technology. “For this type of system, you need a torque-based throttle by wire system to balance power flows through the hybrid systems,” Gee said.
Since the vehicle is making so many decisions affecting the vehicle s performance, Ford s engineers created a number of fail-safe measures in case the electronics should malfunction.
For example, that spring mentioned earlier that is attached to the brake pedal does more than give the driver the feel of stepping on the brakes. If the electronics were to fail, the driver stepping on the brakes would press through the spring and hydraulic braking could take place.
Similar fail-safe mechanisms monitor the vehicle and take action if the hybrid s actions go out of the normal range.
If all this sounds like robocar taking control away from the driver, the reality is quite different.
“The driver s actions influence the efficiency of the system,” Gee said. “That s why we encourage drivers of a hybrid to use a very smooth touch on the brake pedal. Normally most of the power dissipated by braking is absorbed into the battery. Hitting the brakes hard, howe’ver, requires more power than the battery can absorb, causing the vehicle to make up the difference in regular friction braking, which affects fuel economy.”
Drive-by-wire technology may be essential to the hybrid s functioning, but the technology has also found a home in some of Ford s non-hybrid vehicles. For instance, the 2004 Ford Explorer introduced electronic throttle control with the 4.0-liter V-6 and the 4.6-liter V-8 engines while the redesigned F-150 also incorporated electronic throttle control.
In Europe, a number of Ford vehicles have been utilizing drive-by-wire throttle controls for a number of years on both gas and diesel engines.