The movable section comprises a cylinder head and a cylinder block.
The base section comprises a crankcase, or a casing in general. There are projections of the crankcase into the cylinder head to provide supports for receiving the forces applied to the cylinder head from the high-pressure gas into the combustion chamber. These projections comprise pillars starting near the crankshaft base bearings and enter, through proper openings, into the cylinder head, they also comprise bridges firmly interconnecting the free ends of the pillars to strengthen the structure and to provide supports to a control shaft.
In the conventional cylinder block the narrowing between neighboring cylinders is an available free area for the pillars. Bearing the cylinder head, the pillars are loaded purely in tension and connect, as directly as desirable, the tightening screws of the crankshaft bearing caps to the tightening screws of the bridges. Limited to the bridges, the bending loads are no heavier than those in the crankshaft bearing caps, i.e. there is nothing special regarding the size or the design of the bridges.
The control shaft has eccentric pins or cams or toothed gears etc. The crankcase bears the control shaft and the control shaft bears the cylinder head, longitudinally.
The architecture of the crankcase projections fits the direction of the gas pressure forces on the cylinder head, resulting in pure tensile loading of the pillars.
There are sliders on the cylinder block, at the height where the piston skirts thrust the cylinder walls. These sliders thrust on respective crankcase sliders in order to pass the thrust loads of the cylinder block onto the crankcase. These loads are several times weaker than those on the cylinder head. The pillars of the crankcase projections can serve as the crankcase sliders, too. The bridging of the free ends of the pillars and the small distance of the thrust loads from the crankcase side of the pillars enables the structure to withstand heavy thrust loads.
The cylinder block, free from transferring to the crankcase the forces applied on the cylinder head, becomes lighter and distortion free. The forces tending to separate the cylinder head from the cylinder are small enabling the reliable sealing of the combustion chamber. The union of the cylinder head with the cylinder block in a single piece is a further option, better as regards the cooling, the simplicity, the robustness, the cost and the reliability.
The control shaft is pivotally mounted either on the cylinder head or on the crankcase projections. The control shaft supported on the crankcase projection directly, or by connecting means like connecting rods or sliders, receives the forces applied on the cylinder head and supports the cylinder head. The angular displacement of the control shaft varies the compression ratio by displacing the cylinder head relative to the crankshaft.
In a first embodiment, on top of the cylinder head 9 of the movable section 7, a control shaft 13 is pivotally mounted in the space between the two camshafts, leaving area for a centrally located spark in the combustion chamber 12.
The crankcase 2, of the base section 1, has projections 6 comprising pillars and bridges.
The control shaft has eccentric pins 14.
The connecting rods 15 are pivotally mounted at one end on said eccentric pins 14 and at the other end on the crankcase projections 6.
The movable section 7 is slidably fitted on the crankcase 2 by means of the cylinder sliders 10 and the crankcase sliders 5. The trust loads of the cylinders pass through the cylinder sliders 10 to the crankcase 2.
The angular displacement of the control shaft displaces the cylinder head, relative to the crankshaft, varying the compression ratio. The control shaft receives the forces applied to the cylinder head and passes them, through the connecting rods 15, to the bridges, then to the pillars and finally to the lower crankcase. Compared to the gas pressure force carried by the connecting rod to the crankshaft 4, each pillar carries less than a quarter and each short connecting rod 15 carries less than half.
In a second embodiment, the control shaft 13 is pivotally mounted on the cylinder head by means of needle roller bearings and has eccentric pins 14. First slider means 16 are pivotally mounted on the eccentric pins 14, they are also slidably fitted into second slider means 17 formed in the bridges of the free ends of the pillars. The angular displacement of the control shaft 13 displaces the cylinder head 9 relative to the crankcase varying the compression ratio. All heavy loaded pivot joints and sliders can be of the needle roller bearing type to avoid lubrication issues.
The geometry of the arrangement of the timing belt shown in
In another variation of the second embodiment,
The sealing is easy, for instance by means of a rubber seal 18 inserted into a groove formed in the crankcase and being in touch to a properly shaped surface 19 around the cylinder head. The angular displacement of the control shaft can be manual, mechanical, hydraulic, electrical etc. Knock sensors and feedback control enables HCCI operation.
In the prior art, like SAAB's PCT/SE91/818 and Toyota's U.S. Pat. No. 7,047,917, a pair of connecting shafts is arranged at the two sides of the cylinder block, laterally, to connect the upper and lower sections of the engine. The rotation of a control shaft displaces the cylinder head relative to the crankcase to vary the compression ratio. The inevitable long distance between the two connecting shafts generates heavy bending loads, flexing and noise, making the reinforcement of the two sections inevitable. In this patent, a variable compression ratio internal combustion engine comprises a base section and a movable section slidably fitted to each other.