A few motorcycling websites are abuzz with news of a new Honda two-stoke motor that some say will power a motorcycle – but don’t hold your breath. “Hope springs eternal in the human breast,” wrote Alexander Pope, and ever since the age of dinosaurs, when two-strokes last roamed the earth, there’s been a clamour for their return.
The last two-stroke street-legal motorcycle offered by the Big Four in North America was Kawasaki’s KE100, discontinued around 2001. Even that bike was fairly tame, a far cry from the homicidal offerings of preceding decades. In the 1980s, machines like Honda’s NSR250 and Yamaha’s RD350 and RZ350 offered a blend of speed and handling that hasn’t been seen since. Before that, in the mid-70s, the Kawasaki H2 earned a legacy of raw power so lasting that the company dug it up for its new supercharged four-stroke H2R.
The main reason two-stroke motors fell from grace was their emissions; the two-strokes of past years burnt oil but were also bad at burning all the gas, emitting a lot of hydrocarbons out the pipe as a result.
However, the new Honda motor drawings that were recently unearthed seemingly address the issue of emissions; including a fuel injection system to make for a cleaner-burning two-stroke motor.
According to Honda’s patent filing, the fuel injection system (Parts 70, 71, 74) is attached to the scavenging port system, and is designed to inject fuel in a manner to cool the piston, which means you can reduce the need for lubricating oil. There is seemingly no mention of lubricating oil though, and even if the fuel spray to piston and cylinder is sufficient to keep the top end cool, there is no mention of how the surfaces and bearings keep lubricated (though the doc is so complex, we could have missed that bit).
However, Honda seem to have addressed the unburnt fuel quandary with the EFI squirting into one of three ports, allowing the other two scavenger ports to clear the burnt gases without having unburnt fuel spewing out of the exhaust port at the same time (a traditional problem of two-strokes).
And that exhaust is now taken care of by a very four-stroke like poppet valve located in the combustion chamber. This valve open as the piston descends and most of the power of the burning gas has been used to push it. Closing shortly after the air from the non injected scavenger ports chases out the last of the exhaust gases.
Or at least that’s what we think. Here’s the original PDF – we know there are a few very bright engineers out there that read CMG. Please feel free to correct/add to the operation as your lunch break allows.
Oh, and those extra connections around the crank? We’re assuming that they supply a rather trick way of tweaking the regular geometry of a crank to make the con-rod drop and rise closer to a vertical axis, thus reducing its fore and aft movement. Why? We’ll leave that to the CMG engineers …
Given the legacy of two-stroke power, a new two-stroke motorcycle would be an exciting development, but it’s probably not happening. Honda’s patent, when examined closely says the motor is designed for gas, diesel, kerosene or liquid propane use. That sounds like a powerplant for a generator or other stationary use, not a motorcycle, but we can hope.
Here’s the extract from the patent doc pertaining to the engine’s operation (good luck!):
When the piston position is at 0 degrees (top dead center), the fuel in the combustion chamber 44 burns, and the gas within the combustion chamber 44 expands, thereby forcing the piston 22 downward from the top dead center. Until the piston position reaches position A1, the lower end of the piston 22 is located above the upper edge of the second scavenging orifice 42d, and the second scavenging port 43b communicates with the part of the cylinder bore 3a located below the piston 22.
Once the piston position reaches position A1, the lower end of the piston 22 coincides with the upper edge of the second scavenging orifice 42d. During the time the piston position is between position A1 and position A2, the second scavenging orifice 42d is progressively closed by the downward stroke of the piston 22.
Once the piston position reaches position A2, the lower end of the piston 22 coincides with the lower edge of the second scavenging orifice 42d so that the communication between the second scavenging port 43b and the part of the cylinder bore 3a below the piston 22 is closed.
The piston 22 continues the downward movement, and when the piston position has reached position A3, the exhaust valve 48 opens, and the combustion gas begins to be expelled. When the piston position A4 has been reached, the upper end of the piston 22 coincides with the upper edge 42d of the second scavenging orifice 42d, and the communication between the second scavenging port 43b and the part of the cylinder bore 3a above the piston 22 is established.
After reaching the piston position of 180 degrees (bottom dead center), the piston 22 starts moving upward, and once the piston position AS is reached, the upper end of the piston 22 coincides with the upper edge of the second scav enging orifice 42d, and the communication between the sec ond scavenging port 43b and the part of the cylinder bore 3a above the piston 22 is shut off. The piston position range of A4 to AS corresponds to the open period for the first and second scavenging ports 43a and 43b.
When the piston 22 reached position A6 following the subsequent upward stroke of the piston 22, the exhaust valve 48 is closed. The piston position range of A3 to A6 corresponds to the open period for the exhaust port 46.
When the piston 22 has moved upward to position A7, the lower end of the piston 22 coincides with the second scavenging orifice 42d, and this starts the communication between the second scavenging port 43 and the part of the cylinder bore 3a under the piston 22. When the piston 22 is in the range of positions A7 to AS, the upward stroke of the piston 22 causes the second scavenging orifice 42d to be opened, and once the piston position reaches AS, the lower end of the piston 22 coincides with the upper edge of the second scavenging orifice 42d, thereby fully opening the second scavenging orifice 42d.
Seems to me that they are employing double-crank technology and that the crank axis is actually the axis of little dashed circle #11 in the picture above. Benefits of double crank can be many; you can find additional information here: http://www.mce-5.com/ and here: http://www.gomecsys.com/. Please note that Gomecsys claims patent on their system (issued in 1999); however, their patent application is just a copy of my publication made in 1990 making it public domain technology.