Honda’s New 2WD and Regen Braking Designs for Bikes

One of the key technologies used by virtually every electric and hybrid car on the market is regenerative braking—or reversing the flow of power to recharge the batteries when you’re slowing down—as a way to boost range. But the same idea has yet to be fully exploited on motorcycles for one simple reason: We do almost all of our braking with the front wheel, and send drive exclusively to the rear.

In cars, the braking effort is more evenly spread, and many put their power down though the front wheels, making the job of using electricity regeneration much easier than it is on bikes. However, the rewards of regen are potentially significant. Every time you hit the brakes, the forward motion that you burned fuel (or used electricity) to create gets converted into heat and dissipated into the air. If you can recover that energy and reuse it later, it’s a much more efficient way of operating.

A motorcycle’s weight transfers significantly to the front during braking, and the rear brakes are barely used in most cases. But that weight transfer also means using the rear wheel for regen-braking-to-drive isn’t always most efficient. Honda has been pondering precisely this problem, and it’s come up with a solution that involves making a hybrid or all-electric bike that’s two-wheel drive.

The obvious solution here—and one that’s been experimented with by various bike firms already—is to add a small electric motor/generator in the front wheel hub. But with such a vast amount of braking done with the front wheel, it’s unlikely that such a design could efficiently recover the maximum possible energy. Honda’s solution doesn’t use any electric connection to the front wheel but relies on hydraulics instead.

Hydraulic drive isn’t new to Honda. The firm used the system on the oddball DN-01 15 years ago, albeit driving the rear wheel instead of the front, creating a continuously variable transmission with no need for a clutch or any belts, gears, or chains. The system involves two angle-drive, axial-piston hydraulic pump/motor units—one at the wheel, the other at the bike’s engine (or electric motor).

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Honda’s patent shows one of these pump/motor units built into the front wheel of the bike. Multiple small pistons are mounted in a circular pattern around the axle, attached to a variable-angle swash plate at one end. These pistons pump hydraulic fluid, or are moved by the same fluid, depending on whether the unit is acting as a pump (during regenerative braking) or as a motor in 2WD mode. An actuator alters the angle of the swash plate to change the volume of fluid being moved. When the swash plate is parallel with the wheel, there’s no drive, but when it’s angled the incompressible fluid is moved through the system.

Because the drive/regen system is hydraulic, it only needs two flexible hoses to transfer drive to and from the front wheel—solving the usual problems in the design of 2WD motorcycles or how to turn the wheel without harming steering or suspension operation. It’s basically the same as the Öhlins-developed 2WD system used on the tiny number of Yamaha WR450F 2-Trac machines sold in 2004 and 2005 (but also experimented with on a vast array of bikes, including the Yamaha R1 and Ducati 996).

At the other end of the hoses there’s another variable hydraulic motor/pump unit to convert the fluid’s movement during regen braking back into a rotary motion. On Honda’s design, this acts on a planetary gearset that’s connected to an electric motor/generator unit and works like the CVT transmission and electric drive/regen system on a Toyota Prius. The system could be used along with a conventional combustion engine or on a pure electric bike design and gives entirely variable drive and regenerative braking effect from both the front and rear wheels, all controlled by the electronics. At its most extreme, the system would be able to deal with the vast majority of the braking, though Honda’s design also includes a conventional disc brake as a backup. The design could alter the percentage of drive taken to either wheel, going from conventional rear-drive only all the way to a setup that puts a significant amount to the front instead.

Will the patent ever become a viable production machine? Your guess is as good as ours at the moment, but given the potential increase in range and efficiency that effective regenerative braking offers, there’s a significant carrot dangling in front of the company that can crack this conundrum, particularly as ever more bikes move to electric power.