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New engine-making tool should result in more fuel-efficient cars


October 8, 2012

Fraunhofer's cylinder bore hole honing tool

Fraunhofer's cylinder bore hole honing tool

You may think that the pistons in your car’s engine slide in and out of the cylinder bore holes smooth as silk, but according to researchers from Germany’s Fraunhofer Institute for Machine Tools and Forming Technology, the process could be smoother. If it was, your car would burn less gasoline, and require less oil for lubrication. Well, those researchers have developed an engine-building tool, designed to minimize engine cylinder friction.

There are two types of bore hole distortion that lead to the friction – static and thermal. Static distortion occurs when the engine is being assembled, with mechanical stress from activities such as the tightening-down of screws causing the bore holes to subtly change their shape. Thermal distortion occurs once the engine is running, as heat causes the bore holes to warp. In either case, the result is that the pistons rub against the inside of the bore holes, in the places where they’re distorted.

The researchers start by removing the cylinder head from a sample engine, to see what static distortions have been caused by the assembly process. They then simulate the operating temperature of the engine by heating it to 90º C (194º F), then measuring what thermal distortions have occurred. Their tool comes into play next.

It’s a cylindrical honing tool, used to carve out the inside of the bore holes. Due to integrated piezo actuators, however, it can expand or contract its diameter as required. When the dimensions of the distortions are fed into the system, the tool can be inserted into a bore hole, then take on the required shape as it’s turning, grinding the distortions away.

A prototype of the tool is now being tested with auto manufacturers. The Fraunhofer team believes that it could result in fuel savings of two to three percent, along with less oil consumption and longer engine life.

Source: Fraunhofer

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

The way it sounds, each block will have to be heated to operating temperature so that the thermal distortions of each can be known and accommodated. This is basically making every block bespoke since each blocks thermal distortion will be different and will have to handled accordingly.

Saving gas would be great but how much would a bespoke block add to the price of a vehicle?


not surprised, 90% of engine wear takes place during warmup, the faster warmup is, the less wear and fuel use, hence why cooling systems are getting smaller, (less coolant to warm up, faster warm up, oil warmed by coolant in the oil cooler) auto A/C systems the same they all used to be around 1KG, now in the .56KG range, machining the cylinder bores with the block hot makes sense, I always laugh at my neighbors starting their cars in the AM with the engine idling for 20 minutes getting 0 MPG in cold weather who then Whine about their MPG

Bill Bennett

Woah - this is old technology! You heat up the block with water at 180°F and then install "deck plates" with the head bolts torqued to spec. Head bolts, main bearing bolts, water pump bolts, and other bolts can also slightly affect the distortion of the block. But literally, guys have been doing this for decades. Maybe not in a production facility, but certainly at hot-rod facilities. (The deck plate simulates the stiffness of a cylinder head but allow the cutter to cut the cylinder bores. Some Honda engines have an open deck, with floating cylinders, so they are free to move as necessary and cannot be improved by this method)


@RT1583 It sounds to me like the shape of the cylinder is measured when the block is heated with all of the high and low spots mapped. In production a shape that when heated and torqued becomes a circle is honed into the cylinder walls. Pretty incredible tool when you think about it. Every engine can now be blueprinted from the factory. Piston rings can be smaller , lighter. Less leaking allows oil to last longer. @Grunchy I was aware of using deck plates but I never heard of engine shops actually heating the block up before machining. Neat to hear of the tricks used by the top builders.


In my early days at the Rover company, we had chrome plated bores on the LandRover vehicle engines. They were so slippery they were hardly run-in by the time most engines would be ready for a re-bore. The only problem was the oil consumption due to it leaking past the 'as new' piston rings, which obviously did not seal properly.

Take the above chrome plating process and apply the materials knowledge we have gained over the last fifty or so years to the piston rings and perhaps they can be made with an 'as run-in' surface finish. That would make today's engines last as long without the down side of the oil consumption suffered in the past.

Mel Tisdale

Lindsay Kent of Kent Engineering in Cape Town designed, patented and built a pressure testing system which some shops modified to do this, by running hot water through the block while it was being bored.


You still have pumping losses which is a much bigger problem for efficiency in a petrol engine. This is the force it takes to pull a piston down during the intake stroke when the throttle is mostly closed. It creates a partial vacuum which resists the piston movement. Diesels don't have throttles in the air flow which is partially (mostly) why they use almost no fuel at idle. I suspect pumping losses are a fact of life for petrol engines though.


This process tightens up everything, heats it up then measures the cylinder distortions.

Next step is to take everything off, let the block cool down then dynamically distort the honing tool to make an out of whack bore that becomes straight when the engine is assembled and warmed up.

What a way to make engines cost more. Far easier and cheaper to bolt on all the bits like crankshaft bearing caps and deck plates, heat the block up to running temperature then bore and hone the cylinders perfectly round.

No expensive new boring and honing tools required because that's the way shops that build high performance engines have done it for a long time.

The Fraunhofer guys need to spend a bit more time in the shops of NASCAR and NHRA teams.

Gregg Eshelman

Just check your tire pressure and you'll save 2x as much.


@Gregg I think your missing the point. for production you set up with 30 blocks , find the distortions and come up with a "best fit" program. Then that program can be used on the unheated / untorqued blocks. The only additional cost would be the machine tools which can be amortized over hundreds of thousands of blocks. If you can get 2-3% efficiency improvement I think that is huge.


Perhaps, if we could muster a coordinated effort among all those who have worked in this field, we might achieve more positive results and clearer understanding much sooner. Nah!


@ Captain - A "best fit program" is what they use right now. Machine all parts to the same deminsions. You cannot map every block the same for the simple reason that each one is a unique casting, even if they are all cast from the same lot of material. This doesn't even take into account the variances inherent in all the various parts that go into the structure of the engine, each of which brings its own unique characteristics to the finished product. There is no way for a manufacturer to do this economically.


@Rt1583 Using this tool may not result in as good as a custom build engine from a speed shop but I am sure there would be an improvement. True no two parts are exactly alike but they will distort in similar manner it looks like this tool can compensate for it. I would bet that there are some pretty bright people working on this project that have some familiarity with engine assembly lines and that they have taken production requirements into consideration. Do you really think that they propose to torque and heat up every block before machining? If this does give a 2-3 improvement in fuel economy then I can see it being adapted in a lot of factories. Electric steering gives about the same amount of savings and now look a the number of vehicles being equipped with them. Wait a few years and see what happens. As for no way to do it here are a few of the things that at one point in time I would have said no way to Engines that turn off at a stop light and then start instantly manual transmissions that shift like an automatic Launch control Stability control Voice activated control A 600+ horsepower Mustang for sale from a dealer A 300+ horsepower V6 Cooled seats GPS Self driving cars 5$ gas CNC controlled Pizeo actuators on a hone to bore out of round cylinders The Canadian and US dollar at par A Windows OS that I like The return of GM The internet The Maple Leafs wining another Stanley Cup OK the last one I don't believe :)


all of those benefits are going to the consumer.... this is so not going to make it out the door.

Michiel Mitchell

Triple efficiency with electric motors and laying wire in the roads.

Ross Nicholson

racer's have been doing this for years using block plates, some racer's go to extremes to make sure everything is square when that motor is running. One famous racer never used engine stands, as he felt the engine stand put to much stress at the back of the motor, hanging on the stand. This is all good stuff, but we still have most of the power going out the exhaust, if we could keep that heat in the motor by developing better materials, then we would have it all clean, economical power. But my bets on the electric motor, which are all ready 80 to 90 percent efficient, with better batteries and ranges in the 300-600 mile, there will be no turning back. but not to worry, the internal combustion engine will be around for a long time in one form or another, for the simple reason, they work pretty good.

Thomas Lewis

I would think a "wet sleeve" engine (like the old triumph and various other cars and many diesel engines) would sidestep this problem, because the cylinders are structurally independent of the block and don't get distorted. They are also nice because when doing a rebuild you don't rebore you just replace the worn cylinders with new ones.

There also is a reality that most engines will suffer a boil over event and the need for stability must far exceed running temperatures. A hole in a radiator hose should not result in a ruined engine. I do like cylinder inserts as with the inserts more care can be taken and more processes applied by dealing with each cylinder individually. To me the big defect in modern engines is the excessive costs of removing and rebuilding the engines as well as many other parts. One day we may have engines that dealerships simply swap out regularly as a couple of bolts and a very easy rebuild make an engine swap as easy as an oil change. Jim Sadler

Triple efficiency with electric motors and laying wire in the roads.

Facebook User

Now THAT"S funny!! When public utilities routinely bury power transmission lines, your idea might have merit.

Noel K Frothingham
Car makers do not want to produce cars that are efficient and easy to repair. The treatment of the Tesla cars is proof that the big three will suppress progress if they are allowed to get away with it. Back in 1959 the Volkswagon Beetle was promoted as a car that could have the entire drive train out of the car and on a bench in less than five minutes. And even that design could have been made easier to remove and rework. Jim Sadler
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