Frost & Sullivan Market Insight   Published: 14 Nov 2001
Are You Ready for Drive-by-Wire?
Date Published: 14 Nov 2001
By Joerg Dittmer
Automakers are forever seeking ways to reduce vehicle weight, because lower weight means less fuel consumption, which in turn means lower emissions. As a rule of thumb, reducing the weight of a vehicle by 100 pounds adds one mile per gallon (MPG) to fuel economy. Over 100,000 miles, increasing fuel economy from 25 MPG to 26 MPG saves 154 gallons of fuel.
Electronic systems have helped automakers toward this goal because these are often lighter than the mechanical systems that they replace. Additionally, electronic systems have proven to be precise in their functioning, reliable, and low maintenance. Thus, engines, transmissions, airbags, brakes, and many other systems are now controlled electronically on many vehicles.
The electronic revolution is not over - other vehicular systems may benefit from this technology. On future vehicles, steering and braking systems may be not just controlled electronically, but become completely electronic systems, just as throttle control already is going electronic. Collectively, these technologies are called "drive-by-wire".
Electronic Throttle Control
At one time, a cable linked the accelerator pedal to the carburetor, opening a butterfly valve when the driver stepped on the pedal. This mechanical system already is being replaced by wires. With this newer technology, a sensor measures the position of the accelerator pedal to determine the driver's intentions. This sensor sends a signal to the engine management electronic control unit (ECU), which sends a signal to an actuator that appropriately sets the fuel injection system (which has replaced the carburetor).
Similarly, the mechanical linkages of a steering system could be replaced by sensors, wires, an electric motor, and an ECU. Without the mechanical linkages, the steering wheel could be replaced by a joystick - a large steering wheel is only needed to give the driver sufficient leverage should it be necessary to steer without power assist. Without mechanical linkages, leverage is not an issue.
A steer-by-wire system has a position sensor at the steering wheel or joystick which provides input to the steering ECU. The ECU controls an electric motor that sets the position of the front wheels. Substantial weight savings results from the elimination of the steering column. However, it might take drivers a while to get used to the notion that they no longer have a mechanical backup should a problem develop in the electronic system. With redundant components and electronic self-diagnosis, steer-by-wire systems should be as safe as current systems.
Today's power steering systems get power assist from a hydraulic system, but electric power steering (EPS) systems have been developed. This is an enabling technology for steer-by-wire, because electric motors are easy for ECUs to control. EPS has advantages in addition to allowing a related technology to advance. By eliminating the hydraulic pump, which puts a full-time load on the engine, in favor of an electric motor that draws power only when needed, fuel economy is boosted. EPS systems are easier to install in vehicles on the assembly line because hydraulic lines do need to be fitted, and the elimination of power steering fluid is an environmental plus. In mass production, they should be cost-competitive with hydraulic power steering systems.
Similarly, braking systems may go electric. Instead of calipers and wheel cylinders actuated by the pressure of hydraulic brake fluid, electric brake actuators would be used. These would be controlled by an ECU that gets input from a brake pedal sensor.
Electrically actuated brakes are particularly suited for use with technologies such as antilock braking and stability control, because electric actuators can be controlled very precisely by the brake system ECU.
Shift-by-wire technology combines the benefits of manual transmissions (lower cost, weight, and fuel consumption) with the benefits of automatic transmissions (easier driving and less stress on the drivetrain). Shift-by-wire refers to automated manual transmissions, in which computer-controlled actuators handle the shifting. Shifting occurs at the optimal moment, and each shift is perfect.
Enabling Technologies
Steer-by-wire and brake-by-wire have been in development for years, but have not yet appeared on North American production vehicles. Acceptance by automakers is one issue - automakers are concerned about reliability, warranty, safety, and liability issues whenever they are offered new technology. Thus, drive-by-wire technologies must fully prove themselves before they will be widely used. Public acceptance is also an issue - automakers are reluctant to take steps that are too big for the vehicle-buying public to follow.
However, certain dynamics suggest that these technologies eventually will be introduced on North American vehicles. Not only do they advance goals such as better fuel economy and easier vehicle assembly, they may advance safety despite concerns over the lack of mechanical backup should power assist fail - for example, electric systems can function even when the engine stalls, drawing power from the battery. Hydraulic power assist fails if the engine stalls, making steering and braking more difficult.
Electrically powered equipment places additional load on a vehicle's alternator, which must provide extra electricity. Vehicles are expected to transition from 12/14-volt electrical systems to 36/42-volt systems, which make more electricity available because they are more efficient. Additionally, substantially more electricity can be generated by crankshaft-mounted integrated starter-alternators than today's belt-driven alternators can provide.
As 36/42-volt systems and integrated starter-alternators are introduced, automakers can be expected to take advantage of new opportunities opened up by the sudden increase in available onboard electric power.
In the longer term, fuel cells may become practical for mobile applications. With an electric motor propelling the vehicle, it only makes sense for other vehicular systems to be electrically powered.
When Will It Happen?
The key question, of course, is when will these new technologies appear on the road? Drive-by-wire systems are already appearing in Europe. For example, electro-hydraulic brake-by-wire appeared on the Mercedes-Benz S-Class in August 2001. This is a strong indication that drive-by-wire technologies will also come to North American vehicles. Europe tends to be ahead of North America in automotive technology.
Electro-hydraulic power steering (EHPS) systems are one step to full electric power steering, which in turn will be followed by steer-by-wire systems. EHPS drives the power steering pump by an electric motor rather than by a belt tied to the engine. This intermediate technology was used in some low-volume vehicles years ago.
A kind of steer-by-wire technology, called Quadrasteer, will appear on the 2002 GMC Sierra Denali. Quadrasteer is a four-wheel steering system developed by Delphi Automotive Systems. By allowing the rear wheels to turn up to 12 degrees, maneuverability is enhanced. Rear-wheel steering is accomplished with by-wire technology.
Similarly, anti-lock brake systems and electronic stability systems are steps toward brake-by-wire systems. Drivers are already familiar with anti-lock brakes, and awareness of stability systems is increasing. Electric-over-hydraulic braking systems may be introduced before full electric brakes are introduced.
Such gradual introduction facilitates the acceptance of new technologies.
However, the availability of more electric power will be key to the wide application of full electric systems. Automakers have been considering 36/42-volt systems, which would allow more vehicular systems to go electric. But automakers have delayed committing to 36/42-volt systems as the costs and challenges of their introduction have become clearer. Automotive use of this technology is still several years off.
Cost-effective fuel cells for electric vehicles may become available late in this decade. However, fuel cells may appear earlier as auxiliary power units that supplement or replace the alternator on conventionally powered vehicles. This technology would also facilitate the introduction of additional electrically powered vehicular systems.