Suppliers expand use of electrohydraulic brakes
Electrohydraulic braking, a technology developed to meet the needs of hybrid-powered vehicles, is poised for wider use in conventional cars and trucks.
TRW Automotive Holdings Corp. and Continental AG -- which have developed electrohydraulic brakes for hybrids and electric vehicles -- each has confirmed that it is adapting its system for use in conventional gasoline vehicles.
"Many automakers are trying to mainstream this technology, and not just use it for hybrids or EVs," said Dan Milot, TRW's Detroit-based chief engineer of advanced systems.
Automakers want to use the same brakes for all powertrains, which minimizes disruptions when they add hybrids. "We call that 'future-proofing,'" Milot said.
Here's how the technology works: Electric motors power the push rod within the master brake cylinder. The push rod, in turn, forces fluid through hydraulic lines to activate the brake calipers.
Because electric motors activate the brakes, there's no need for a vacuum booster, a standard part of regular brakes, to augment the force applied by the driver's foot on the brake pedal.
But the brake pedal and the master cylinder are still mechanically linked to provide stopping power in case of a failure of the main system.
Suppliers originally developed electrohydraulic brakes for EVs, whose powertrains could not accommodate vacuum boosts. Vehicles with small, turbocharged engines and direct injection also don't generate much vacuum boost for conventional brakes.
TRW introduced its electrohydraulic brakes in 2007, when General Motors installed them on hybrid versions of its full-sized pickups and SUVs.
TRW has lined up a development contract with a European automaker, and hopes to sign contracts with two American automakers this fall.
If the deals are completed, Milot expects production to begin in 2016.
Meanwhile, Continental produces electrohydraulic brakes for hybrid versions of the Ford Escape and Fusion. The German megasupplier also has three development contracts for global automakers, which could lead to volume production.
Here are some key advantages of electrohydraulic brakes:
They are as much as 6.6 pounds lighter and are more compact than conventional brakes on a compact sedan.
The same brakes can be used on vehicles with hybrid or conventional powertrains.
They don't require high-voltage electrical systems, unlike "pure" brake-by-wire systems, which use electrical impulses rather than hydraulic fluid to activate the brakes.
They can be activated 50 to 100 milliseconds more quickly than conventional brakes during panic stops.
That last item could be a decisive advantage, now that automakers are designing collision avoidance systems with automatic braking. If the brakes can be activated more quickly, the vehicle's onboard computer can wait longer to evaluate the likelihood of a crash.
That, in turn, reduces the chance of a false alarm that would needlessly bring the vehicle to a halt.
"By delaying your warning, the brakes have to respond much faster," notes Christian Schumacher, Continental's North American director of engineering systems. "That is why high-speed brake systems will be requested very soon for collision mitigation."
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