GB2304151A

GB2304151A - Automotive i.c. engine with supplementary piston-and-cylinder energy accumulator

Info

Publication number: GB2304151A
Application number: GB9515223A
Authority: GB
Inventors: Guy Stewart Morton; Miles Leonard David Webb
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-25
Filing date: 1995-07-25
Publication date: 1997-03-12
Also published as: GB9515223D0

Abstract

A floating piston 11 is slidable in a cylinder bore 10 sealed at one end with automotive type piston rings. The piston 11 is preloaded against one closed end of the cylinder bore by a spring 12. The closed end against which the piston is preloaded is pierced so that a tube or airway 14 may communicate with the combustion chamber of an I.C. engine. The preload is made such that on the compression stroke of the engine the floating piston 11 will not move until the full compression pressure is reached. The subsequent pressure due to mixture burning moves the floating piston 11 against the spring 12 thus storing energy for use at a later portion of the engine stroke. The accumulator may be integral with the engine cylinder head or block or may be incorporated into the engine itself eg the working cylinder may contain two pistons spring loaded apart.

Description

AUTOMOTIVE ACCUMULATOR This invention relates to an automotive accumulator.

The internal combustion engine is well known as a means of providing motive power both as a gas or petrol engine or as a diesel engine.

In the gas or petrol engine, the burning or explosion takes place at constant volume with previous compression. The diesel engine on the other hand has a slower burning which is said to approximate to combustion at constant pressure with previous compression. As just described the gas or petrol engine particularly suffers a disadvantage. Following the compression stroke, a very short or near instantaneous burning period occurs at or near the commencement of the working stroke. The resulting burning gases are tightly confined by the combustion chamber and the piston.

During this period of time, they can do no useful work on the latter because the connecting rod and crank are at or near the vertical. Very high pressures and consequently high temperatures are attained, as a result of which a large amount of heat is lost largely by radiation through the surrounding metal with consequent loss of efficiency. The very high pressure means that a very high compressive load is applied to connecting rod, crankshaft, crankcase and bearings which have to be made strong enough and therefore heavy enough to withstand it. This also results in undesirable vibration.The following quotes on the subject of heat losses from a recognized text book may be found relevant : "The rate of heat-flow from the gas to any part of the walls at any instant depends on the then temperature density and motion of the gas, and also upon the temperature and condition of the wall surface. It will therefore differ widely at different points of the working stroke and by far the greater part of the heat-flow will occur in a very short time immediately after ignition and pass into the surface of the combustion chamber and piston and valves; comparatively little will pass into the barrel of the cylinder, since it is not uncovered by the piston until the density and temperature of the gas have fallen." "The very high temperature attained during the explosion results in a very rapid extraction of heat by the cylinder walls.The higher the temperature the more rapid is this loss to the water-jacket through the cylinder walls. Any suitable method, therefore, which has for its object the reduction of the maximum temperature reached in the engine cylinder, without decreasing the mean pressure during the cycle, should be beneficial in reducing this loss and raising efficiency." According to the present invention there is provided an automotive accumulator comprising a pressure reservoir which may take the form of a cylinder and a means of storing a quantity of the energy of the gases under pressure which may take the form of a slave piston and spring or springs. The storage chamber of the pressure reservoir is made to communicate with the combustion chamber of an internal combustion engine via a tubular passage or airway.The passage or airway may incorporate a restrictor or its bore may be made of such a diameter as to provide the rate of gas transfer most favourable to the burning of the mixture. A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 is a sectional view of the accumulator in use with a four stroke petrol engine, although it is applicable to any other type of internal combustion engine. The cylinder head, barrel and crankcase of the engine are also sectioned to show the position of the piston connecting rod and crank during the cycle. In this figure the latter are shown during burning of the mixture at or just after top dead centre.

Figure 2 is a specimen indicator diagram in which the continuous line shows pressure against volume for a typical four stroke car engine. The broken lines show the projected change in performance for the same engine modified to make use of the present invention.

Referring to the drawing, the accumulator comprises a cylinder barrel 10 closed at one end. The crown of a slave piston 11 , when at rest, is preloaded by a heavy coil spring 12 against the closed end. The space between the closed end and the slave piston 11 is made to communicate via a tube 14 with the engine combustion chamber 15. The closed end and the combustion chamber wall are pierced for this purpose.

Shown by lines AB and BC respectively in Fig 2. the induction and compression strokes ofthe engine occur in the normal manner, as the preload of the spring 12 is made sufficient to prevent movement of the slave piston 11 by the compression stroke pressure. Movement only occurs on build up of further pressure due to combustion.

The ignition spark occurs as usual followed by the burning of the mixture. Normally the burning gases would be totally confined by the combustion chamber and the piston crown causing the pressure to rise instantly to the very high level at D in Fig 2. As might be expected and as stated by the text books, by far the largest loss of heat to the cooling system would now occur. A portion of these hot gases now however flow through the tube 14 and expand, causing the slave piston 11 to move against the spring 12 in which a substantial portion of their energy now becomes stored within the line CPO in Fig 2. A large portion of the latter lies outside the normal expansion curve DF and shows around a 40% increase in mean effective pressure during the most torque productive part of the cycle.The elimination of the area in Fig 2. immediately under the point D in which large amounts of heat are normally lost appears to account for this increase.The very high pressure and temperature involved when this energy is stored totally in the gas with consequent loss of efficiency is avoided. By achieving a much cooler running engine, a further gain in efficiency should be achieved by the use of a higher than normal compression ratio without risk of pre-ignition.

As the engine piston descends, the spring 12 pushes the slave piston 11 back towards the closed end of the cylinder barrel 10. Its stored energy is thus progressively released along the line POF in Fig 2. and under the influence of the spring 12, pressure is applied to the crown of the engine piston throughout the torque productive part of the working stroke. At the end of the latter, the slave piston 11 again comes to rest against the closed end ofthe cylinder barrel 10, under the set preload ofthe spring 12.

Suitable cushioning may be provided against the resulting impact. Following the working stroke, the exhaust stroke occurs as usual along FBA in Fig 2. It may be noted that whilst the slave piston 11 will have a high acceleration and speed during the charging stroke, it operates only once every fourth stroke and the length of its stroke will be proportional to the amount of the charge admitted by the prevailing throttle opening.

If desired, the accumulator may be separately mounted on the engine as shown in any convenient attitude or apart from it or form an integral part of the cylinder head, block or any other component part of it. The accumulator may also be incorporated within the engine itself. For example, the engine cylinder bore or bores are made long enough to accept a two part piston. These two parts are sprung loaded apart and have some movement relative to each other but this is mechanically limited so that except during compression or extension of the spring, they move as one. Expanding gases due to combustion then store part of their energy as decribed above. Any suitable means for storing the energy of gases may be used in place of the cylinder barrel 10, the piston 11 and the coilspring 12. With multi-cylinder engines, two or more engine cylinders may be made to share the same accumulator using a system of pipes and valves.

Claims

1. An automotive accumulator including a floating automotive type piston fined with the usual rings in a bore with means for lubrication. The piston is preloaded against one closed end ofthe bore by a metal spring at the opposite end of the piston. Provision is made via a tube or airway to admit the burning gases from the combustion chamber of an I.C. engine. The spring preload is made such that the floating piston will not move until the full compression pressure ofthe I.C. engine is reached. The subsequent movement stores the energy of the combustion in the spring for use later in the stroke.

2. An automotive accumulator as in Claim 1 but the preloading metal spring is replaced by a gas spring such as Nitrogen preloaded as before inside a closed space or vessel. At this end ofthe piston the gas is sealed by a special sealing ring suitable for the purpose. Provision is made to regulate the gas pressure to compensate for the expansion caused by heat from the hot gases at the other end