Pinnacle Engines – Cleeves Cycle Ultra Efficient Combustion Engine

Pinnacle Engines - Ultra Efficient Combustion Engine

Pinnacle Engines - Ultra Efficient Combustion Engine

Well, here's another entrant in the opposed piston, super efficient engine sweepstakes, it's called the Ultra-Efficient Combustion Engine and it's from Pinnacle Engines. As with many, if not most other designs, this engine is in the "we're almost there" category. It looks like it has a lot of potential, but will it be superior to the many other opposed piston variants? Until the engine can be independently tested and compared to whatever others are available, all we have to go on is the press release.

The core of Pinnacle’s technology resides in its unique engine architecture and its Cleeves Cycle. 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. The result is a fundamentally more fuel efficient and scalable engine design, and one that is compatible with most fuels including gasoline, diesel, natural gas, propane and their biofuel replacements (e.g., ethanol).

The multi-fuel capability is a plus, but that seems to be a standard feature of these types of engines, so let's hope one of these is running soon and we can see how they really perform.

Press release follows:

Pinnacle Engines today unveiled plans to commercialize a breakthrough ultra-efficient engine by 2013. The new engine design enables significant reductions in fuel consumption and greenhouse gas emissions without increasing vehicle cost. Pinnacle also announced it has raised $13.5 million in venture funding from NEA, Bessemer Venture Partners and Infield Capital.

Advancing the Internal Combustion Engine
While electrification of the worldwide vehicle fleet presents a promising long-term solution, the costs of wide-scale deployment are high. As a result, the global vehicle fleet in 2050 is expected to rely mostly on the internal combustion engine as its prime mover.

Leveraging years of research and development and more than 500 hours of dynamometer testing, Pinnacle Engines’ ultra-efficient engine is based on a four-stroke, spark-ignited (SI), opposed-piston, sleeve-valve architecture. In drive cycle simulations performed by Pinnacle Engines, it achieves 30 – 50% better fuel economy in various drive cycle comparisons without the large cost penalty normally associated with dramatic fuel economy improvement. The performance of the Pinnacle Engines design has been independently verified by FEV, Inc., a globally recognized leader in engine development and a Pinnacle Engines development partner.

“Engines that can deliver significant efficiencies within 5 – 10 years are critical as the global demand for vehicles places a strain on both natural resources and the environment,” said Rohini Chakravarthy, Pinnacle Board member and a Partner at NEA. “We believe Pinnacle Engines is in a unique position to have a major impact in that timeframe, by delivering exceptional efficiency gains at the lowest possible cost.”

The core of Pinnacle’s technology resides in its unique engine architecture and its Cleeves Cycle. 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. The result is a fundamentally more fuel efficient and scalable engine design, and one that is compatible with most fuels including gasoline, diesel, natural gas, propane and their biofuel replacements (e.g., ethanol).

The patented Pinnacle Engines architecture and the innovative Cleeves Cycle are the culmination of over 100 years of combustion engine design, and forty years of research and innovation by founder and CTO Monty Cleeves – a long-time innovator in multiple fields, and a dedicated student of engine design. “This engine technology provides the fuel economy and CO2 emissions of a hybrid at a price that the whole world can afford,” says Cleeves.

Global Opportunity
The company is in the process of commercializing its technology through a joint development and licensing agreement with an Asian vehicle OEM. Production is slated to commence in Q1 2013. Further developments, including plans for expansion into the global automotive market, will be revealed later this year.

“By 2016, more than 200 million combustion engines will be manufactured globally. Pinnacle technology could make them considerably more efficient while dramatically reducing the costs required to achieve those efficiencies,” states Ron Hoge, Pinnacle’s new Chairman and CEO. “Monty Cleeves’ lifelong dream to design a much more efficient internal combustion engine is becoming a reality. The opportunity to be a part of this exciting new engine company with its game-changing technology and capability to scale quickly and affordably was something I couldn’t pass up.”

Hoge has forty years of business experience with executive leadership roles in eight different companies, from Fortune 500 firms to venture-backed startups. His background includes positions as the president and CEO of Cummins Power Generation (Onan), president and CEO of Magnetek, and president of a $1.5 billion aerospace division of Allied Signal. He has led businesses on three continents through their startup, growth, reorganization and disposition phases. He is also a director at two other energy efficiency startups, Glacier Bay, Inc., and NovaTorque, Inc.

About Pinnacle Engines
Pinnacle Engines is a Silicon Valley-based technology company founded to address the immediate need for a more efficient internal combustion engine. Its founders pioneered the ultra efficient Pinnacle Engines’ architecture and its Cleeves Cycle while leveraging traditional low-cost engine materials and manufacturing techniques. Pinnacle’s novel engine design addresses the growing need for more efficient internal combustion engines and will have a significant global impact on the transportation sector’s fuel consumption and CO2 emissions.

Link: Pinnacle Engines via Autobloggreen


  1. says

    “sleeve-valve architecture”–The more things change, the more they stay the same. I believe Sterns Knight used sleeve valves in their engines back in the 1920s or 1930s. The Bristol Centaurus aircraft engine is probably the ultimate development of a sleeve-valve design, with over 2,600HP on tap from its later variants.

    It’s interesting to see designers returning to old technology in order to improve, and ultimately, find solutions to today’s challenging internal combustion engine market.

    • Ken says

      It makes you wonder if the engineers of yesterday had the technology of today, how much further their work would have progressed. It also makes me wonder if the stories told to me the old timers I used to work with about how the oil companies purchased the rights to the patents concerning anything fuel efficient hold any truth…

      • says

        Engineers are usually 25 years ahead of what is possible in terms of metallurgy and production costs. It is usually in wartime, when money flows into research labs, that the great technological strides forwards are made.

    • Chris Walker says

      Sleeve Valve engines are very efficient, but sufferred cooling & fueling/throttle or induction control issues. So they made good aero engines, but poor land vehicle engines where revs rise & fall continually. New computer control technology, would be able to get round the throttle/induction issues & electronic fuel injection would sort the fueling issues. That that leaves cooling, which as an opposed piston engine should not be a problem as the whole liner can be wetted & modern sealing materials will contain the collant, allowing for the contant rotation of the “sleeves” or liners to you & me.

  2. Nicolas says

    constant volume or constant pressure combustion … with pistons … uh ? I need to get back to school

    • JR says

      Otto (spark) engines combust (almost) instantaneously, so fast that the piston is (almost) not moving (constant volume in the combustion chamber).

      Diesel engines inject and combust fuel as the piston is already heading down. Combusting at (almost) constant pressure. Pressure rises from combustion while volume grows… approximately maintaining pressure.

  3. Paulinator says

    Whenever I hear the term “multi-fuel” I think U.S. military cash injection for development..and that makes me suspicious already. The big British sleeve-valve engines benefited from low specific power output, ample cylinder spacing and cylinder heads that could wick away a lot of heat. I suspect that placing a sleeve-valve in the hottest region of the cylinder, where it is clustered tightly with other very hot cylinders, will prove very challenging if not unworkable. Has anyone seen an actual video?

  4. todd says

    I wonder if this is something Subaru is interested in. They may be the “Asian OEM” they refer to. Who else in Asia uses horizontally opposed 6 cylinder engines?


    • Stats says

      I somehow doubt it. Subaru has neither the capital nor the time to invest in something so new. When you consider that they are STILL running a 4-speed slushbox on most of their vehicles and they JUST introduced their first new (very similar) engine in 20 years, they’re not exactly on the cutting edge of crazy new things. Their specialty is taking a proven design and improving incrementally, with reliability and practicality at the top of the priority list.

      I’d guess Honda or Mazda if we’re talking about Japanese OEMs, but you can never discount the Chinese or Koreans, especially these days.

      • Tom says

        I have a “Encyclopedia of Motorcycles”, copyright 1996. It has entries for hundreds of small and now defunct American and European marques but doesn’t even mention the majority of today’s dozen largest volume motorcycle manufacturers (Lifan, Zongshen, Hero, Bajaj, PT Astra, etc.). Welcome to 2011.

        That “Asian vehicle OEM” is more likely to be an outfit like Geely, Chery or Tata. They’re huge, and you’ve never heard of them.

  5. tim says

    You could just take your Subaru 3 litre boxer six, cut it in half, turn it round, and away you go you mean?

    Couple of points from a laymans perspective: Must be a bitch to cool…. where you’d want the coolant is right where it’s hottest, and that is where all the intake and exhaust plumbing is, correct?

    How do you couple it to anything to make the vehicle go forward? the two crankshafts must be rotating in opposite directions, and are there issues in using only one?

    You guys will know: I’ve never had a techy question go unanswered!

    • JR says

      Tim, I agree that cooling is going to be an issue, but it’s not like our current engines and engineers designing them are having trouble keeping things cool. They will just have to make sure the car has the cooling capacity and that the “head” area is designed well. Durability testing should flush out these issues.

      They can gear or chain couple these crankshafts together. As long as they are connected and coupled to a transmission, no problemo. Very little is lost through gear coupling, and as long as things are synced and balanced well, vibes shouldn’t be too bad either.

      Hopefully helpful… but who knows what kinds of knew issues they will be up against… that’s the fun part!

  6. says

    Back in the 60’s I served my apprenticeship working on Commer diesel trucks from the UK that had opposing piston engines, 2 stroke, supercharged, single crank connected via rocker arms, so nothing new here other than the sleeve valves, cooling and noise (exhaust) were the issues of the day. Compact with high output is still the holly grail of modern design, back to the future for sure

  7. B50 Jim says

    Looks like the sort of thing that turns up in the pages of Popular Science from time to time — all kinds of potential, fabulous economy, mondo power, efficient….and all it needs to work is a few parts made of Kryptonite.

    Still, it’s a good idea and might be made to work with the right materials and engineering. Would it be any better than a standard engine? If not, the extra complexity of twin cranks and all that gearing would certainly doom it.

    ALCO did this in their diesel locomotives back in the late 40s to overcome problems with head-gasket sealing (no heads, no problems). The idea worked well but there were issues with those twin cranks, and pretty soon the engineers figured out how to keep the gaskets in place. A few still are running, and train buffs get all nostalgic when they talk about them.

  8. Scotduke says

    This design uses a combination of ideas previously seen elsewhere – no bad thing but as some comments say – cooling might be an issue. The French Voisin cars used sleeve valves in the 30s. They were powerful for the day but high revs would cause damage quicker than with conventional designs. Opposed pistons were also used in the Deltic two stroke diesel locomotive engines in the UK – high power to weight ratio for the day but noisy and not so reliable. The Bristol Centaurus was a great engine as anyone who has seen a Hawker Sea Tempest fly can attest – I think a couple have been very competitive at the Reno Air Races in the open class.

  9. Gazberzu says

    OMG, this architecture is sooooooooooo old I can’t really believe someone is trying to convince anybody he has just patented it !
    (for info, this architecture has been intented in 1907 by Raymond Koreyvo)

  10. says

    Relative to the lubrication and cooling problems of the sleeve valves (or the sleeve liners, doesn’t matter how you call it) you are talking about:

    If Pinnacle borrows the two side crankshafts of Achates (to eliminate the thrust loads from the piston skirt onto the cylinder wall), it may not solve the problems altogether but will reduce the cooling and lubrication needs, because the pistons will no longer thrust onto the sleeve-valve-liner and therefore the friction heat will decrease and the oiling of the rings will be easier.
    Besides, the sleeve valves are no longer squeezed between the piston skirt and the cylinder wall.

    In case the new sleeve valves are so good, why not to use them in the conventional four-stroke long-stroke engines, as well?

    On the other hand, please take a look at the opposed-piston four-stroke PatFour engine at the bottom of .
    The PatFour engine has conventional poppet valves, a single-crankshaft, is full-balanced, its main crankshaft bearings are permanently unloaded, it provides additional time for the combustion, etc.

    In a similar way, the OPRE two-crankshaft two-stroke opposed-piston engine (shown in the video at the bottom of running on Diesel fuel and driving two counter-rotating air propellers) can change to a four stroke engine.

    Manousos Pattakos

  11. DnA says

    Marine diesel engines have used similar duel crankshaft engines for years. They produce massive torque at low rpms which is perfect for large ships.

  12. says

    Some issues of the Pinnacle engine:
    the sealing, the lubrication and the wear of the sleeve valves;
    the actuation of the sleeve valves,
    the cooling of the cylinder;
    the lubricant control (the same problem with the two stroke port engines).

    The question is:
    does the Pinnacle combine the advantages of the four-stroke engines with the advantages of the two-stroke opposed-piston engines,
    or does it combine their disadvantages?

    The PatFour engine at the bottom of is:
    a four-stroke,
    single-crankshaft engine,
    having conventional poppet valves.

    Do you see any advantage of the Pinnacle engine over the PatFour?

    Manousos Pattakos

  13. gildasd says

    2 stroke – even more efficient – in 1932

    No sleeve, no valves, no problems. Quote:
    “The lower crankshaft ran eleven degrees behind the upper, meaning that the exhaust ports opened and, even more importantly, closed first, allowing proper scavenging. This system made the two-stroke Jumos run as cleanly and almost as efficiently as four-stroke engines using valves, but with considerably less complexity.”


    • says

      Would you mind to add to the advantages wikipedia writes about the Junkers Jumo design:
      an about 35% increase of the time for the injection, penetration, vaporization and combustion of the fuel,
      as well as the crosshead architecture that liberates the piston skirts and the cylinder liners from the thrust loads, enabling way lower lubricant consumption?

      This is what the OPRE engine at does.

      Would you mind to, additionally, remove the one crankshaft and the synchronization gearing?

      This is what the PatOP engine at does.

      Manousos Pattakos

      • gildasd says

        Brilliant, really nice architecture.

        But I do have a slight (foolish) preference for the “balancing trick” on the Junkers, using 2 cranks, one having all the engine loads (pumps etc) and the other destined to produce 70/60 of the power. Resulting of only a 30/40% cross load.

        And the only reason the did not turbo it was the lack of high temp alloys.

        Do you have any more reference material about opposed engines? I’m thinking of making a miniature 2 combustion chamber 50cc to power a moped as a uni prodject in one year’s time.

        • says

          For divided load application,

          like an OPRE range extender for electric cars, having two counter-rotating electic generators secured at its crankshafts,

          or like an OPRE power propulsion unit having two counter-rotating propellers on its two crankshafts (for small airplanes, parapante, portable flyers etc), as shown at

          the synchronizing gearing of the OPRE stays permanently rid of loads.

          More important, the basis of the single cylinder OPRE engine is not only perfectly rid of inertia vibrations of any kind (forces, moments and torques of any order), but it is also perfectly rid of combustion vibrations, too.

          The OPRE with its volumetric built-in scavenging pumps can operate with and without a phase difference between the two crankshafts.

          “Do you have any more reference material about opposed engines?”
          Email me (go to “pattakon Contact”)

          Manousos Pattakos

  14. Neale Clarke says

    Direct injected fuel is very cool. Has anyone ever tried to direct inject air as well? It would do away with the inlet valve completely, leaving only the exhaust valve.