The invention relates generally to internal combustion engines and, more particularly, to a variable-compression engine with a piston helically rotatable about an adapter connected to an end of a connecting rod.
Dynamically varying the compression ratio of an engine with load can increase the engine's efficiency, which leads to better gas mileage and reduced emissions. The compression ratio can be varied in a number of ways, including: (1) raising and lowering the cylinder relative to the crankshaft; (2) rotating the cylinder relative to the crankshaft; (3) opening or closing the entrance to an auxiliary combustion chamber; (4) raising and lowering the crankshaft via eccentric bearings; and (5) changing the effective length of the connecting rod with adjustable intermediate linkages. But most of these examples are hydraulically operated and require that the engine be running or otherwise need a separate battery-operated pump. Most also move against the working direction of the piston.
One version of a variable-compression engine overcoming these shortcomings and embodying features of the invention comprises a piston movable back and forth in a cylinder. A piston skirt extends between a closed top end of the piston and an open bottom end. The skirt forms an interior face with a helically threaded portion and an exterior face having a toothed structure in the form of circumferentially spaced teeth extending parallel to the axis of the cylinder. An adapter for connecting to an end of a connecting rod has helical threads that engage the threaded portion of the interior face of the piston skirt. Compression adjustment means engage the teeth on the exterior face of the piston skirt to rotate the piston helically on the helical threads of the adapter to adjust the compression ratio of the cylinder. The compression adjustment means may be realized, for example, as a rack gear having teeth meshing with the teeth on the exterior face of the skirt or as a timing belt extending partway around the piston with teeth regularly spaced to mate with the teeth on the exterior face of the skirt. The compression adjustment means could alternatively be realized as a collar with an outer periphery and a central bore receiving the piston. Internal teeth bounding the bore mate with the toothed structure on the exterior face of the piston skirt. External teeth are formed on the periphery of the collar. A gear having teeth engaging the external teeth on the collar rotates the collar and, consequently, the encircled piston to adjust the compression ratio of the cylinder.
Another version of a variable-compression engine comprises a cylinder and a piston that can reciprocate in the cylinder along the cylinder's axis. The piston has a cylindrical skirt that extends between a closed top end and an open bottom end of the piston. The skirt bounds a threaded interior bore and has a geared exterior. An adapter for connecting to an end of a connecting rod has helical threads and is received in the threaded interior bore. An adjustment gear meshes with the geared exterior of the piston skirt. The adjustment gear is selectively actuated to apply a tangential force to the piston skirt to rotate the piston in the cylinder helically on the helical threads of the adapter. In this way, the adjustment gear adjusts the compression ratio of the cylinder.
In yet another version of a variable-compression engine, a piston is reciprocatable in a cylinder having a closed head end. The piston travels in a stroke direction between a top dead center position nearer the head end of the cylinder and a bottom dead center position farther from the head end. The piston has a top end nearer the head end of the cylinder and a cylindrical skirt bounding a threaded interior bore that terminates in a blind end at the top end of the piston. The skirt has an exterior with a plurality of circumferentially spaced elongated teeth extending parallel to the stroke direction. Parallel channels are formed between consecutive teeth. A cylindrical adapter for connecting to an end of a connecting rod has threads on a cylindrical periphery. The adapter is received in the threaded interior bore of the piston. Drive lugs separated by gaps are arranged to engage the exterior of the piston skirt. One or more of the drive lugs are each received in an individual channel on the skirt. One or more of the teeth are each received in an individual gap between consecutive drive lugs. In this way, the piston can reciprocate in the stroke direction along the drive lugs. The drive lugs are selectively moved to apply a tangential force on the piston skirt by pushing against the elongated teeth. The tangential force causes the piston to rotate in the cylinder and ride along the threads of the cylindrical adapter to change the top and bottom dead center positions of the piston.
Yet another version of a variable-compression engine comprises a piston reciprocatable in a cylinder along the cylinder's axis. The piston has a cylindrical skirt that extends between a closed top end of the piston and an open bottom end. The skirt bounds a threaded interior bore and has a plurality of teeth forming a spur gear centered on the cylinder axis. An adapter for connecting to an end of a connecting rod has helical threads and is received in the threaded interior bore of the position. An adjustment gear meshing with the spur gear is selectively actuated to rotate the piston in the cylinder helically on the helical threads of the adapter to adjust the compression ratio of the cylinder.
Yet another version of variable-compression engine comprises a cylinder, a crankshaft, a connecting rod, a piston, and an adapter. The connecting rod is connected at a first end to a wrist pin on the adapter and at a second end to the crankshaft. The piston includes a skirt that forms a spur gear surrounding a threaded piston bore. The piston is threaded onto the threaded periphery of the adapter and received in the cylinder. The second end of the connecting rod extends from the bore in the cylinder to the crank shaft. Rotation of the spur gear causes the piston to ride along the threads of the adapter to adjust the distance between the piston and the second end of the connecting rod.
In another version of a variable-compression engine, a piston defines an axis and includes a skirt with a helically threaded region formed along an interior of the skirt. An adapter for attaching to an end of a connecting rod has a threaded periphery engaged with the helically threaded region of the piston skirt. The adapter can be displaced axially relative to the piston in the threaded region by rotation of the piston about the axis and the threaded movement of the piston on the adapter.
According to another aspect of the invention, a piston for a variable-compression engine, the piston comprises a piston head at one end and an open bottom at the other end. A piston skirt extends axially between the piston head and the open bottom and has an interior face with a helically threaded portion and an exterior face with a toothed structure in the form of parallel, circumferentially spaced teeth separated by axial channels.
In another aspect of the invention, a method for varying the compression ratio of an engine comprises: providing the skirt of a piston in an engine with internal threads; coupling one end of a connecting rod to the piston by pinning the end to an adapter threaded with the internal threads of the piston skirt; and rotating the piston to move it along the threads to change its position relative to the adapter and the end of the connecting rod.
These features and aspects of the invention, as well as its advantages, are better understood by reference to the following description, appended claims, and accompanying drawings, in which:
One version of a variable-compression engine embodying features of the invention is shown in
Each piston has a cylindrical skirt 30 that extends from a closed top end 32, or head, to an open bottom end 33. An interior face 34 of each piston skirt has a helically threaded portion 36 near the top end to form a threaded interior bore. A cylindrical adapter 38 has external threads 40 on its periphery that engage the threads on the interior face of the piston skirt. The interior face has more threads to give the adapter a range of axial positions along the piston in the direction of the cylinder axis 42. The adapter includes a diametrically arranged wrist pin 44 with a central journal rotatably received in a bore 46 at the piston end of the connecting rod.
The piston skirt includes a geared exterior face 35 in the form of circumferentially spaced, elongated teeth 48 extending parallel to the cylinder axis. The tooth structure on the skirt exterior defines a spur gear with parallel channels 50 between consecutive teeth. The external teeth on the piston skirt, together with the threaded connection of the piston to the adapter, permit the piston to be rotated on the adapter to adjust the stroke of the piston in the cylinder. One way this is done is with the rack gear 52 shown in
The compression ratio of the engine is adjusted by the rack gear. In
As shown in
Another compression adjustment means is shown in
In the version shown in
Another version of the variable-compression engine is shown in
A piston 17 is shown in
The piston 17 of
Thus, the invention provides means for adjusting the compression ratio of an engine either dynamically as the engine is running or while the engine is turned off. A vehicle's computer system can take various engine sensor readings and increase or decrease compression by sending appropriate signals to the stepper motor.
Although the invention has been described in detail with a few exemplary versions, other versions are possible. For example, the compression adjustment schemes shown can be adapted for use with other cylinder arrangements, such as with the banks of V-engines or with opposed-piston engines, or even with engines having circularly arranged cylinders. As another example, individual master spur gears engaging the pistons at each cylinder and driven separately or geared together could be used to adjust the compression ratio. So, as these few examples suggest, the scope of the invention is not meant to be limited to the example versions described in detail.