GB2320058A

GB2320058A - Piston engine with twin counter-rotating crankshafts and two connecting rods per piston

Info

Publication number: GB2320058A
Application number: GB9721289A
Authority: GB
Inventors: Edward Allen
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-12-06
Filing date: 1997-10-09
Publication date: 1998-06-10
Also published as: GB9721289D0

Abstract

A piston engine comprises a cylinder 1, a piston 2 which reciprocates within the cylinder, a pair of cranks 4A and 4B supported for rotation in opposite directions as mirror images of each other, and a pair of con-rods 6A and 6B each connecting a crank to the piston. This arrangement cancels out side forces on the piston to reduce friction and improve efficiency. The cranks 4A, 4B rotate with respective crankshafts carrying flywheels 5A, 5B which have meshing circumferential teeth to maintain synchronism. The con-rods 6A, 6B may be connected to the piston 2 through a triangular plate 7 having a pivot at each apex. The invention may be applied to i.c. engines with one or more cylinders. The two cranks may provide two outputs, eg for twin propeller shafts in a boat.

Description

IMPROVED PISTON ENGINE The present invention is concerned with an improved piston engine, and in particular with an improved internal combustion engine.

In most piston engines there is, for each cylinder, a piston connected to a crank by a single connecting rod or conrod, the crank being part of a crankshaft. This system is not fully efficient since, when the crank is at 90 degrees to its "top dead centre" position during both the power and compression strokes, part of the force on the piston is translated into a side force due to the angle of the con-rod to the piston. This side force creates friction, and hence a waste of energy, between the piston and the cylinder wall.

It is an object of the present invention to obviate or mitigate this problem.

According to the present invention there is provided a piston engine comprising a cylinder, a piston which reciprocates within the cylinder, a pair of cranks supported for rotation in opposite directions as mirror images of each other, and a pair of con-rods each connecting a crank to the piston.

In one embodiment of the invention the cranks form part of respective crankshafts and a flywheel is provided on each crankshaft, the two flywheels being interconnected to rotate in opposite directions in synchronism.

The flywheels may be interconnected by interengaging circumferential teeth.

The con-rods may be connected to a plate which pivots relative to the piston.

Preferably the plate is generally an isosceles triangle in shape, with the apex of the triangle connected to the piston and the other corners connected to the con-rods.

An embodiment of the present invention will now be described, by way of example with reference to the accompanying drawing in which: Fig. 1 is a cross-section of the cylinder and piston of an engine with the piston near top dead centre on the downstroke; and Fig. 2 is a similar cross-section with the piston at the bottom of its stroke.

Referring now to the drawing, there is shown in cross section a cylinder 1 and a piston 2 of an engine, the piston reciprocating in the cylinder. A pair of piston rings 3A and 3B are provided to create a seal between the piston and the cylinder wall.

Two cranks 4A and 4B form part of, and rotate with respective crankshafts each of which carries a respective flywheels 5A and 5B. Each crankshaft is supported for rotation in the engine about an axis coincident with the centre of its associated flywheel. Crank 4A rotates in the opposite direction, as shown by the arrows, to crank 4B, and the flywheels 5A and 5B are, in this embodiment, connected by circumferential teeth. The teeth ensure that the flywheels 5A and 5B, the crankshafts and the cranks 4A and 4B always rotate in synchronism in opposite directions as mirror images of each other, and in mirror image positions.

A pair of con-rods 6A and 6B connect the respective cranks 4A and 4B to the piston 2 through a plate 7 which is in the form of an isosceles triangle. The corners 7A and 7B of the plate 7 are pivotally connected to the con-rods 6A and 6B respectively. The plate 7 has its apex 7C pivoted on the piston 2. The pivoted connection of the plate to the piston helps to take up any "play" which may occur as the engine is used or worn.

In use, as the piston moves up and down in the cylinder the con-rods always oppose each other at the same angle. Thus any side force exerted by one con-rod on the piston is cancelled out by an opposite force from the other con-rod.

This reduces the friction between the piston and the cylinder wall thus improving efficiency. Also better balance is created.

It should be noted that in terms of the rotation of the crankshafts the downstroke of the piston is longer than the upstroke. This is because both top dead centre and bottom dead centre of the piston occur when each con-rods 6A and 6B is aligned with the centres of its associated flywheel and crank.

Thus considering Fig.l, it can be seen that the piston is slightly beyond its top dead centre and has commenced its downstroke, whereas in Fig.2 it is clear that the piston is at bottom dead centre. Further, by comparing Figs.l and 2, it can be seen that the the positions of the crank 4A are 180 degrees apart so that the downstroke is greater than 180 degrees and the upstroke is correspondingly less than 180 degrees.

In the embodiment shown the ratio of the length of the con-rods to the throw of the cranks is about 3 to 1 and this gives a downstroke of about 200 degrees and an upstroke of 160 degrees. This allows not only a longer and smoother power stroke but also an overlap between the power strokes of successively firing cylinders in a two stroke engine or a four cylinder four stroke engine.

The invention is not limited to internal combustion engines as external combustion engines and engines powered by a pressurised fluid also benefit from the invention.

While the invention can be applied to engines with multiple cylinders, it is however thought that the the invention might be particularly useful in single or two cylinder engines.

As the engine of the invention drives two cranks and flywheels, there is potential for two power outputs. The engine might thus be used to drive twin propeller shafts in a boat for example.

Further modifications will be apparent to those skilled in the art without departing from the scope of the present invention.

Claims

1. A piston engine comprising a cylinder, a piston which reciprocates within the cylinder, a pair of cranks supported for rotation in opposite directions as mirror images of each other, and a pair of con-rods each connecting a crank to the piston.

2. A piston engine as claimed in claim 1, in which the cranks form part of respective crankshafts and a flywheel is provided on each crankshaft, the two flywheels being interconnected to rotate in opposite directions in synchronism.

3. A piston engine as claimed in claim 2, in which the flywheels are interconnected by interengaging circumferential teeth.

4. A piston engine as claimed in any preceding claim, in which the con-rods are connected to a plate which pivots relative to the piston.

5. A piston engine substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

5. A piston engine as claimed in claim 4, in which the plate is generally an isosceles triangle in shape, with the apex of the triangle connected to the piston and the other corners connected to the con-rods.

6. A piston engine substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

Amendments to the claims have been filed as follows 1. A piston engine comprising a cylinder, a piston which reciprocates within the cylinder, a pair of cranks supported for rotation in opposite directions as mirror images of each other, and a pair of con-rods each connecting a crank to a plate which pivots relative to the piston.

4. A piston engine as claimed in any preceding claim, in which the plate is generally an isosceles triangle in shape, with the apex of the triangle connected to the piston and the other corners connected to the con-rods.