patcrank Variable Compression Ratio (patcrank VCR)
Intellectual Property: patent GB 2,473,334
patent US 8,267,055
On a single cylinder:
In the following animation, between the crankpin of the crankshaft (gray) and the big-end bearing of the connecting rod (green) is interposed an eccentric ring (blue).
Although the eccentricity between the inner and the outer cylindrical surfaces of the eccentric ring is more than 20 times smaller than the piston stroke, it provides a range of compression ratios wider than any application may need.
The eccentric ring is secured on a secondary connecting rod which is rotatably supported, at its other end, on two "free" crankshafts (red) of same throw as the main crankshaft.
The eccentric ring performs a parallel to itself motion.
Rotating for an angle the control frame (cyan), where the secondary crankshafts are rotatably supported, the eccentric ring rotates about the crankpin for the same angle, changing the compression ratio.
On a three-inline:
The following slide shows the three connecting rods (green) of a three-inline, it shows also the three secondary connecting rods (blue) having eccentric rings at their ends, at a low (left), a medium (center) and a high compression ratio.
The necessary moving parts to modify the conventional three-inline into an engine with continuously (in a wide range) variable compression ratio are (per cylinder): a secondary slim and lightweight connecting rod (blue) and the 1/3 of the secondary thin and lightweight crankshaft. The secondary connecting rod and the secondary crankshaft "deal" with a slight part of the pressure and inertia loads of the piston.
The rotation of the crankshaft (not shown) causes, through the three secondary connecting rods, the rotation, at the same direction and with the same instant angular velocity, of the secondary crankshaft. The secondary connecting rods together with their eccentric rings move parallel to themselves.
On a conventional eight cylinder in Vee:
The following slide shows at left the connecting rods of a conventional V-8, 90 degrees modified to a continuously variable compression ratio engine. At right they are shown the additional moving parts that make the modification: in total four slim and lightweight secondary connecting rods and a thin and lightweight crankshaft, i.e. 0.625 moving parts per cylinder.
The rotation of the crankshaft causes, through the four secondary connecting rods, the rotation at the same direction and with the same angular velocity of the secondary crankshaft.
There are two eccentric rings per secondary connecting rod, at 90 deg angular offset to each other.
The angular displacement, for an angle f, of the rotation axis of the secondary crankshaft about the rotation axis of the crankshaft causes the angular displacement of all eight eccentric rings for the same angle f. This way the dead volume changes for the same quantity in all eight cylinders.
In brief:
In order to change the compression ratio into a wide range, the necessary displacement of the piston is about 1/10 of the piston stroke.
Interposing an eccentric ring, of eccentricity about 1/20 of the piston stroke, between the crankpin of the crankshaft and the big-end bearing of a connecting rod, and controlling the angular position of the eccentric ring, the variable compression ratio is realized.
In order to keep the eccentric ring parallel to itself, a secondary connecting rod and a secondary crankshaft is all it takes.
The ratio of the eccentric ring eccentricity (some 5mm, for 100mm piston stroke) to the "length" of the secondary connecting rod (some 100mm) equals to the ratio of the force from the connecting rod on the eccentric ring, to the force from the secondary connecting rod to the secondary crankshaft. For instance, with a force of 20,000 Nt (2 tons) on the piston from the high pressure into the cylinder, the secondary crankshaft is loaded with only 1,000 Nt (100 Kp). Therefore the secondary crankshaft and the secondary connecting rod are several times weaker and lighter than the main crankshaft and the main connecting rod of the engine, and the resistance of the control frame to move is small.
The parallel to themselves motion the secondary connecting rods perform, allows the same balance quality with the original engine (no need for any additional balance shaft). For instance, a modified patcrank-VCR V-8 engine is as vibration free as the original conventional V-8 engine.
The angular velocity of the eccentric ring on the crankpin equals to the angular velocity of the crankshaft journals on the crankshaft main bearings. The diameter of the big-end bearing of the connecting rod necessarily becomes bigger to make room for the eccentric ring, but the angular velocity of the big-end bearing of the connecting rod on the eccentric ring equals to the angular velocity of the wrist pin, which is some six times slower than the angular velocity of the crankshaft main bearings. I.e. the linear velocity of the big-end bearing of the connecting rod is small.
Animations
Click on any image below to download the relevant animation (first check the size).
A single cylinder with one secondary connecting rod and two secondary cranks.
After opening the animation press the . key of the keyboard to enter in "step-by-step" mode. Press a few times the . key to move the piston to the TDC and then press (or keep pressed) the Space Bar key to change the compression ratio. Press , key to get back to "animation" mode. Move the mouse above the animation to change the rhythm. Double click the mouse, or press ESC key, to quit the animation.
A three-inline with the patcrank-VCR, from various viewpoints.
A three-inline patcrank-VCR at operation in three different compression ratios. Press Space Bar for the next available compression ratio. With the . key move the piston to TDC and then keep pressed the Space Bar key.
The crankshaft is removed to show the rest parts of the mechanism of the three-inline patcrank-VCR from various viewpoints at a low, a medium and a high compression ratio. Press . key a few times to see the desirable slide. Press ESC key to quit.
The crankshaft and the secondary crankshaft, of the three-inline, with the secondary connecting rods interconnecting them. Press Space Bar to displace the secondary crankshaft (i.e. to change the compression ratio). Press . to get into step-mode. Press a few times . to get to a TDC. Keep pressed the Space Bar and look at the eccentric rings. Press , to return to animation-mode. Press D key to see the disassembly. Move mouse to slow down the rhythm. Press ESC key to quit.
A conventional eight cylinder in 90 degrees Vee, modified to patcrank-VCR, shown at three compression ratios.
Press H key to hide / unhide the crankshaft and the control frame.
Press C key or Space Bar key to change the compression ratio.
Press 1 or 2 or . . or 6 to see details of the secondary connecting rod.
Press . key and then keep pressed Space Bar.
Press H and keep pressed Space Bar key.
Press . key a few times.
Press ESC to quit animation.
Click on the above animated image to download the full-size / controllable "exe" (11MB) animation. This "packaging" comprises two independent secondary crankshafts (yellow) rotatably supported on a compact control frame.
With the animation running, press a few times the SpaceBar key to change the compression ratio and move the mouse around the animation window to get the desirable "rhythm".
Press the S key once and then keep pressed the SpaceBar key.
Press the D key and then press the S key a few times.
Press the C key, then press the S key a few times, then press the A key and move the mouse around the window.
Press ESC or DoubleClickMouse on the animation window to quit animation.
Video-animations (wmv format)
Click here to download the patcrankVCR.wmv video-animation (6MB)
Click here to download the patcrankV8.wmv video-animation (8MB)