The core of Pinnacle’s technology resides in the engine architecture and what it calls the Cleeves Cycle. (James (Monty) Cleeves is the Founder, President, and CTO of Pinnacle.) As it is just emerging from stealth mode, with more IP work to be done, the company is still somewhat guarded about details on the Cleeves Cycle and the engine, Cleeves and Tom Covington, Pinnacle’s VP marketing and special projects, said in an interview.

(The company has had one US patent awarded (#7,921,817, on 12 April 2011) on the basic engine architecture, and has a number of other patent applications filed and pending.)

The reason you do opposed pistons is that the surface area to volume ratio of the combustion chamber is small. The heat that you waste trying to cool valves and stems [in a conventional engine] isn’t relevant.

The adiabatic engine guys in the 80s had the same concept—keep the heat in [for more efficiency]. But they didn’t do anything special with the heat that they kept in; that’s what we’re doing differently. We have a big expansion ratio compared to a traditional spark engine and so we can do something with this heat that we’ve saved. We still have the same sort of power densities as the traditional engines. We don’t have the hit that the Atkinson cycles do. We net diesel-like efficiencies on this teeny gasoline engine.

—Monty Cleeves

Using a four-stroke architecture is inherently easier from an emissions perspective, Cleeves said, noting that by using this design, Pinnacle can isolate the lubrication circuit from the air flow, which is traditionally a problem with opposed piston designs. The Pinnacle engine using a sliding sleeve valve system: intake liner, exhaust liner, spark plug in the middle.

The sleeve valve fits between the piston and the cylinder wall in the cylinder where it rotates and/or slides. The sleeve valve moves independently from the piston so that openings in the valve align with the inlet and exhaust ports in the cylinder at proper stages in the combustion cycle.

The company does say broadly that the Cleeves cycle operates on the Otto cycle (constant volume combustion) or Diesel cycle (constant pressure combustion) depending on operating conditions. Additional efficiency improvements will be realized through incorporation of variable valve timing, direct injection, turbocharging, and Pinnacle’s own low-cost variable compression ratio mechanism.

Pinnacle, says Cleeves, uses various attributes resulting from the design of its engine such as optimized breathing applied to turbulence generation and the retention of heat to cause the engine to run in an operating mode differing from conventional engines.

We’re not interested in the real high power efficiency, because if you look at a drive cycle, you never run there. That 10 hp engine is running at 4 hp most of the time. Having a high peak efficiency at 10 hp doesn’t help you if your efficiency at 4 hp isn’t very good. We focus on making it efficient where people use it. Our peak numbers at those lighter loads are not the big 42% numbers, but that’s where we get 30-50% difference between a conventional engine and us. We’ve moved our peak efficiency down where it’s usable.

—Monty Cleeves

The engine, notes Covington, doesn’t require a lot of “whizz bang” technology; the first application is a single-cylinder, single carburetor engine. “It doesn’t require magic.”

In terms of emissions, Cleeves said that Pinnacle was close to being able to hit Euro 5 on light vehicles in the developing world markets (the data out of the test cell shows achieving the spec, but Pinnacle is allowing for degradation).

Automotive applications will also likely happen more rapidly in the developing markets, than in the US, Pinnacle suggests.

It’s a lot less expensive to get these engines into production in developing markets, as we can do it a lot faster. We love this engine for automotive, but that’s a totally different ball of wax. It takes a lot more money and a lot more time.

—Tom Covington

Despite the simplicity of the initial single-cylinder application of the architecture, the design offers the opportunity to add in a number of advanced features, such as a variable compression ratio (VCR) mechanism, that are complementary to the technology that is already in the engine.

Today, VCR mechanisms have to worry about interacting with a single crankshaft. Because [the crankshaft] wants to be fixed in position, there are some pretty wild mechanisms [to achieve VCR]. With the opposed piston, we have a fixed crankshaft, and another crankshaft. We can do all sorts of things with that other crankshaft to change the distance between the two pistons. We can make terrific VCR mechanisms that allow us to run a 5:1 compression ratio, put huge amounts of energy into the turbo, boost the inlet manifold pressure to 3, 4, 5 bar, and put out 500 hp in the back of Porsche but actually deliver 50 mpg because you never need that 500 hp. Then you crank up the compression ratio to some huge number and adjust the valve timing, and we can do the Atkinson cycle at those conditions, and deliver net 50 mpg in the 500 hp Porsche turbo. It’s a pretty exciting engine when you get to put all the bells and whistles on.

—Monty Cleeves

Pinnacle says it will publish technical papers during the coming year, and plans to present at the SAE 2012 World Congress.

Resources

• US Patent #7,921,817: Internal Combustion Engine