GB2332988A

GB2332988A - Opposed piston ic generator

Info

Publication number: GB2332988A
Application number: GB9727520A
Authority: GB
Inventors: Duncan Pinkerton
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-12-31
Filing date: 1997-12-31
Publication date: 1999-07-07
Also published as: GB9727520D0

Abstract

An electrical generator is formed of opposed piston and cylinder arrangements which are fixed together and operate to move an armature in an airgap in a magnetic circuit. The pistons and cylinders may be driven as internal combustion devices.

Description

Electrical Generator The present invention relates to the generation of electric current and in particular it relates to an electrical generator having a simple mechanical design.

More particularly, the present invention relates to the generation of electricity from a mechanical energy source in the form of an oscillation and in particular a linear oscillation.

It is known to provide self-contained electrical generators which use a fuel such as petrol of diesel to generate an electric output. Typically, the fuel is burnt in a conventional internal combustion engine in which the piston and cylinder arrangements firstly produce a linear oscillating output. This linear motion must be converted, by way of a crank shaft or the like, into a rotational movement so as to drive a conventional rotational electrical generation system.

It is also known to provide a self-contained source of electrical power in for instance a hybrid automobile, that is an automobile which is primarily driven electrically but is provided with a low power engine to keep the battery charged to increase the range of operation.

Electrical generators of the type outlined above are relatively complex in that they have a relatively high number of moving parts and in particular, as mentioned, there is the need for the energy conversion between linear and rotational motion which, in addition to increasing the complexity of the device, reduces its efficiency.

The present invention provides an electrical generator comprising a magnetic core defining a magnetic circuit having an airgap therein, at least one winding around the core, a magnetised armature positioned in said airgap and driving means having a pair of opposed piston and cylinder arrangements, the pistons being rigidly fixed together and to said armature and being alternately driven to cause said armature to oscillate in said airgap, whereby to induce an electric current in said at least one winding.

The present invention therefore uses a linear oscillating motion directly to generate electric current and preferably the driving means for the linear oscillation is an internal combustion engine comprising means to supply fuel to the cylinders and to cause combustion of the fuel in the cylinders to drive the oscillation.

In a generator device according to this invention there are many fewer moving parts than in the conventional arrangement outlined above and in the preferred embodiment, although the control and timing system may be different, the basic internal combustion arrangement is well known and relatively easy to implement.

It will be understood therefore that the preferred embodiment is essentially a boxer type engine, that is one where the pistons are horizontally opposed, having no crank and with the connecting rod between the cylinders being replaced by a shaft carrying a magnetisable armature moving through the coil to generate the automating current.

In this invention, the minimum of energy is wasted through heat and unnecessary movement (ie. rotation) and preferably the invention uses conventional two stroke design.

An implementation of this electrical generator further comprises control means arranged to compare the frequency of the induced electric current with a reference frequency, and to adjust the quantity of fuel supplied to the engine in response to the result of said comparison in order to reduce any difference between said frequencies.

The control means may be further arranged to operate a starting system in the event that the frequency of the induce current falls to zero indicating that the engine has stopped.

The preferred construction of the electrical generator provides the magnetic core in the form of two generally C-shaped portions, the ends of which are arranged in opposition to define two said airgaps. The armature preferably comprises ferro-magnetic material positioned in said airgaps, and there are further provided additional windings on said magnetic core which are driven to induce magnetic poles in said ferro-magnetic material.

In embodiments of the invention more than one pair of cylinders may be coupled together and driven in synchronism to increase the power output while reducing the vibration of the overall device.

There is of course provided the necessary control system which is preferably electronic control circuits controlling the fuel input according to the loading of the generator to keep the speed and power generation constant.

In order that this invention may be better understood a preferred embodiment will be described in the following by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic sectional view illustrating the engine of a preferred embodiment of the invention; Figure 2 is a series of diagrams illustrating the sequential combustion states of the engine; Figure 3 is a schematic diagram of the control system in the preferred embodiment; Figure 4 is a schematic diagram of the magnetic arrangement of the generator according to the preferred embodiment; Figure 5 is a schematic end on view of the armature view of the armature in the preferred embodiment; and Figure 6 is a schematic sectional view of the overall machine according to the preferred embodiment.

The Engine As shown in Figure 1, the engine consists conceptually oftwo piston units operating within a single cylinder with no rotating components.

The piston assembly in the preferred embodiment is a dumbbell shaped unit consisting of two pistons 1 rigidly connected by a connecting rod 2.

The whole unit travels back and forth along a cylinder 3 which has a central collar 4. In addition to conventional piston rings at the top of each cylinder a central piston ring is fitted to the collar (rather than to the connecting rod) to provide a seal at the centre point. The purpose of the central seal is to provide chambers beneath the pistons which emulate the crankcase in a conventional two stroke engine and which can be used to compress the mixture before the inlet port is exposed by the receding piston. Figure 2 illustrates the combustion status of the engine operating according to a standard 2-stroke cycle In order to generate a constant frequency of electricity the piston must move back and forth with a constant period and this period must be carefully controlled. Figure 3 shows a schematic of an example control circuitry and logic in which a series of sparks at a constant rate of repitition is generated by a multivibrator or flip-flop circuit 10. This is used to drive coils 12 which in turn provide the sparks at the spark plugs (not shown). The output of the vibrator is also input to one side of a frequency comparator 14, the other side being fed from the generated current.

The output of comparator 14 is used to control the generator via the starter system 16 and fuel servo system 18. In particular the comparator 14 compares the reference frequency (r) with the generated frequency (g) and performs the appropriate function: if g = 0 The engine is stopped so must be restarted if g > r The load has been reduced so reduce the fuel if g < r The load has been increase so increase the fuel if g = r Steady state - no adjustment required.

As mentioned above, a plurality of pairs of pistons as illustrated in Figure 1 may be implemented together and in this case the coils 12 may feed any number of spark plugs according to the number of multiple cylinders used.

The fuel servo system is preferably implemented using a fuel injection system as this is more precisely controllable than other systems.

The starter system 16 may be a further winding over the cylinder to push the piston left or right, with a set of small windings being provided if necessary to determine the exact position of the piston.

The Generator Figure 4 is a schematic illustration of the electrical and magnetic arrangement of the generator. In particular there are provided two magnetic core pieces 20 defining two airgaps between the ends thereof through which airgap moves the armature 30. As can be seen in Figure 4 the armature and magnetic core pieces are arranged such that a south pole on the armature moves in an airgap between two north poles and a north pole on the armature moves in an airgap between two south poles. While this may be achieved by permanent magnetisation of the various components, it is preferable that the desired magnetic arrangement be provided by way of DC windings 22 provided around the magnetic core pieces 20 and which will also induce the magnetic poles in armature 30. The DC windings 22 are preferably provided on one leg of the respective core pieces 20 but are illustrated elsewhere for convenience.

The movement of armature 30 in the airgaps induces an electrical current in the generator windings 24 which are also positioned around the core pieces 20.

The various windings are arranged so that they can be slid over the 'legs' of the laminated core; they must be wired so that there is a north pole on both sides of gap at one end and a south pole on both sides at the other end.

The size of the legs (a) is determined by the stroke of the engine, so that the oscillating rod moves completely through the poles of the laminated core.

Seen from end on the poles should be as close as possible (given a suitably strong crankcase) to the armature; they are shaped to concentrate the field onto the oscillating rod. In Figure 5 the armature is shown as circular to ease construction of the central seals in the engine.

Other Components In order to reduce costs the remainder ofthe engine preferably draws on conventional and available components, including an electrically powered pump for fuel, ignition coils, carburettor or fuel injection systems, exhaust systems and cooling. The exact nature ofthese components is not relevant to the invention as such.

Practical design In order that the windings and core may be sufficiently close to the armature the engine may be made in two halves with a longer connecting rod onto which a magnetic armature has been attached. Figure 6 shows a complete arrangement with both the engine and the generator connected together.

The connecting rod (a) passes through the base of the left hand cylinder at point (b) and carries a seal so that the space beneath the piston can be used to compress the mixture. (It is recognised that the seal at this point will be imperfect so a cover (c) collects the leakage from the two lower cylinder chambers).

Onto the connect rod is fixed a hollow soft iron rod (d) which is dumbbell shaped and a close fit within the poles of the magnetic core (e). In order to be able to assemble such an engine it may be that the connecting rods will be connected to the pistons using some form of gudgeon pin which will allow some movement, but it is necessary that the two halves of the engine, the right and left cylinders, are machined together and held rigidly in line along with the magnetic core. This may necessitate removable heads to the cylinders and long through bolts that will hold the whole assembly together.

Because of the risk of smoke, unburned fuel and oil entering the exhaust system with the simple port design described above, injection or inlet valves may be incorporated.

The risk of stalling or misfiring may be reduced by the use of electronic ignition and fuel injection but the control of the injection system and the way it reacts to additional load needs to be finely tuned in a practical arrangement to avoid the engine either stalling if response is too slow or hunting if the response is too fast.

There also needs to be a battery attached to enable the starter and ignition systems to operate.

If the engine is statically mounted, forced cooling may be required.

There will be a tendency for the whole piston assembly to rotate in the cylinder, indeed it may prove desirable to encourage it to do so to reduce wear.

Claims

Claims: 1. An electrical generator comprising a magnetic core defining a magnetic circuit having an airgap therein, at least one winding around the core, a magnetised armature positioned in said airgap and driving means having a pair of opposed piston and cylinder arrangements, the cylinders being rigidly fixed together and to said armature and being alternately driven to cause said armature to oscillate in said airgap, whereby to induce an electric current in said at least one winding.
2. An electrical generator according to claim 1 in which said driving. means is an internal combustion engine, further comprising means to supply fuel to said cylinders and to cause combustion of said fuel in said cylinders whereby to cause said oscillation.
3. An electrical generator according to claim 2 in which said internal combustion engine operates according to a two-stroke cycle.
4. An electrical generator according to claim 1, 2 or 3 in which said magnetic core comprises two generally C-shaped portions, the ends of which are arranged in opposition to define two said airgaps.
5. An electrical generator according to claim 4 in which said armature comprises ferro-magnetic material positioned in said airgaps, and there are further provided additional windings on said magnetic core which are driven to induce magnetic poles in said ferro-magnetic material.
6. An electrical generator according to claim 2 or 3 or according to claim 3 or 4 when dependent on claim 2 further comprising control means arranged to compare the frequency of said induced electric current with a reference frequency, and to adjust the quantity of fuel supplied to said engine in response to the result of said comparison in order to reduce any difference between said frequencies.
7. An electrical generator according to claim 6 in which said control means is further arranged to operate a starting system in the event that the frequency ofthe induce current falls to zero indicating that the engine has stopped.
8. An electrical generator according substantially as hereinbefore described with reference to the accompanying drawings.