WO2019012285A1

WO2019012285A1 - Improved piston arrangement

Info

Publication number: WO2019012285A1
Application number: PCT/GB2018/051984
Authority: WO
Inventors: Brian R KNIGHT
Original assignee: Knight Brian R
Priority date: 2017-07-13
Filing date: 2018-07-12
Publication date: 2019-01-17
Also published as: GB201711254D0

Abstract

An improved piston arrangement and method of operating an internal combustion engine. The piston arrangement has a piston (15) reciprocatively received within a cylinder (11), a crankshaft 17 and a cylinder bore assembly (12). The piston (15) has at least one piston ring configured to sealingly engage with a surface of the cylinder bore assembly (12). The cylinder bore assembly (12) comprises a lower bore portion (13) and an upper bore portion (14). At least a lower or upper bore portion (13, 14) is moveable within the cylinder (11) between a first position in which the lower bore portion (13) is in sealing abutment with the upper bore portion (14) and a second position in which the lower bore portion (13) is separated from the upper bore portion (14) so as to expose an air inlet port between said lower and upper bore portions (13, 14). Movement of the at least a lower or upper bore portion (13, 14) between said first and second position is controlled by a mechanism phased and timed in relation to the piston (15) and/or crankshaft (17) position. The relative movement of the piston (15) and cylinder bore assembly (12) is configured such that the at least one piston ring of the piston 15 transitions between the lower and upper bore portions (13, 14) when the cylinder bore assembly (12) is in the first position.

Description

IMPROVED PISTON ARRANGEMENT

TECHNICAL FIELD The present invention relates to an improved piston arrangement and method of operating an internal combustion engine. More specifically the present invention relates to a slidably movable and adjustable cylinder port and valve apparatus for a two stroke internal combustion engine. BACKGROUND

Despite the promise of various technologies such as Stirling engines or fuel cells or battery hybrid vehicles or full electric powered vehicles with electric motors that provide low-emission and high-efficiency drive arrangements for automobiles and light aircraft, these technologies will not be a completely viable alternatives to the internal combustion engines for motive power in all foreseeable future applications due to their inherent disadvantages in weight, space, drivability, energy density and cost or lack of electric charging infrastructure. The internal combustion piston engine will for many years continue to provide a powerplant for many automotive and vehicle applications.

The four-stroke internal combustion engine currently predominates in the automotive market, with three, four, six or V six or V eight configuration being common. The need for at least three or four cylinders to achieve a suitable rate of number of power strokes dictates the size, weight and shape of the engine, and therefore also greatly limits the designer's' options on how the engine is placed within the vehicle.

It has long been recognized by engine designers that two-stroke engines have a significant potential advantage over four-stroke engines in that each cylinder produces a power stroke every crankshaft rotation, which should allow for an engine with half the number of cylinders when compared to a four-stroke engine having the same rate of power stroke production. Inherently this will result in a more powerful engine with potentially lower weight. Two-stroke engines, however, have seen limited use because of several perceived drawbacks. Two-stroke engines have a disadvantage in mean effective pressure (i.e., poorer volumetric efficiency) over four-stroke engines because a significant portion of each stroke may be used for the removal of the combustion products of the preceding power stroke (scavenging) and the replenishment of the combustion air, and is therefore lost from the power stroke. Scavenging is also inherently problematic, particularly when the engine must operate over a wide range of speeds and load conditions.

Modern supercharging and fuel injection methods can overcome many of the limitations previously associated with two-stroke engines, making a two cylinder two-stroke engine a viable alternative to a four cylinder four-stroke engine. A two cylinder two-stroke engine has the same power stroke frequency as a four cylinder four-stroke engine.

However, as the four stroke engine has continued to be improved over recent years in terms of emissions and driveability due to such technologies such as variable inlet and exhaust valve timing and valve lift the two stroke engine has failed to be developed with such technologies and has therefore become less optimised for high power density applications with low or minimised fuel consumption and low exhaust emissions. For example it is known that the intake valve and/or port and exhaust valve and/or port of an engine should be opened and closed at accurate times to efficiently accomplish the induction and exhaust events in the cylinder of an internal combustion engine.

The optimal valve and/or port timing varies according to the engine speed, engine load, exhaust emissions requirements and the like, further it is known to use variable valve timing and or valve opening or lift mechanism which changes the phase of the intake or exhaust events in relation to the crankshaft position to optimise the operation of both two and four stroke internal combustion engines. In two stroke engines, which require the exhaust and inlet events to take place within a single crankshaft rotation, inlet and exhaust ports are often employed within the cylinder wall, alternatively a combination of inlet ports located within the cylinder wall and an exhaust poppet valve located within the engine cylinder head may be employed. Problematically a cylinder port is commonly a fixed orifice cut into the liner and therefore the opening or closing event is effected by the movement of the piston and piston skirt. Hence the timing of the inlet and or exhaust event is fixed relative to the piston and crankshaft position. As such it is difficult to optimise the piston geometry for efficient gas flow.

British published patent application GB191125204 discloses a reciprocating piston engine having ports within the cylinder wall where a mechanism g may slidably translocate the position of the port openings c in relation to the piston (not shown) see Figure 1.

Alternatively the mechanism may increase or decrease the available port area c, c' see Figure 2. GB191125204 does not disclose or suggest any means of operation where optimising port opening and or closing events may be achieved within a single crankshaft rotation or a single set of internal combustion engine events. SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a piston arrangement, a motor vehicle exhaust vibration damper, an internal combustion engine, and a means of operating an internal combustion engine as claimed in the appended claims.

According to an aspect of the invention, there is provided a piston arrangement comprising a piston reciprocativeiy received within a cylinder, a crankshaft and a cylinder bore assembly, the piston having at least one piston ring configured to sealingly engage with a surface of the cylinder bore assembly the cylinder bore assembly comprising a lower bore portion and an upper bore portion, wherein at least a lower or upper bore portion of the cylinder bore assembly is moveable within the cylinder between a first position in which the lower bore portion is in sealing abutment with the upper bore portion and a second position in which the lower bore portion is separated from the upper bore portion so as to expose an air inlet port between said lower and upper bore portions, and wherein movement of the at least a lower or upper bore portion between said first and second position is controlled by a mechanism phased and timed in relation to the piston and/or crankshaft position, and wherein the relative movement of the piston and cylinder bore assembly is configured such that the at least one piston ring of the piston transitions between the lower and upper bore portions when the cylinder bore assembly is in the first position. This arrangement provides an adjustable valve timing control apparatus, whereby the opening of the inlet port is controlled in relation to the piston and/or crankshaft position. By using the cylinder bore assembly to control the air inlet port, a smaller, lighter piston crown may be used. By ensuring that the cylinder bore assembly is in the first position when traversed by the piston ring, a more durable piston arrangement is provided. Furthermore, the downward stroke of the piston over the surface of the cylinder bore assembly in the first position allows any lubricant to be returned to the crankshaft region. This compares favourably to some known liner ports, whereby oil may be swept into the inlet ports, picked up by the incoming air and transferred into the combustion chamber.

The cylinder head may be fitted to an open end of the cylinder. At least one exhaust port may be provided in the cylinder head. This provides a uniflow scavenge arrangement.

As the downward stroke of the piston over the surface of the cylinder bore assembly in the first position returns any lubricant to the crankshaft region, the at least one exhaust port is maintained substantially free from lubricant which may otherwise be carried downstream.

The cylinder may have an inlet air plenum in fluid communication with the air inlet port when the cylinder bore assembly is in the second position.

The inlet air plenum may be located circumferentially to the cylinder bore assembly.

Thus a cylinder head is located to enclose one end of said cylinder and provide a combustion chamber, and at least an exhaust port. A cylinder bore is formed within the cylinder, at least one cylinder bore portion being operably movably received within said cylinder wherein at least one radially extending orifice is provided in the cylinder bore wall to connect the engine cylinder to the air inlet plenum to allow inlet air or inlet air fuel mixture to flow into the cylinder above the said piston. The lower bore portion may be moveable within the cylinder and the upper bore portion may be static within the cylinder.

This arrangement advantageously allows the relatively hotter portion of the cylinder assembly to be static whilst the relatively cooler portion of the cylinder assembly is moveable. This arrangement also allows for a more compact piston arrangement.

The lower bore portion may be moveable within the cylinder via a camshaft and finger follower mechanism.

The cylinder bore assembly may be returned to the first position by one of a return spring, a mechanical cam, an electronic solenoid, a hydraulic actuator or a pneumatic actuator. The lower bore portion may be in a fully retracted condition at piston bottom dead centre.

The piston arrangement may include camshaft variable valve lift or valve phasing mechanisms to allow variable motion of lower bore portion in relation to piston motion.

Movement of the lower bore portion may be restricted by a variable lift camshaft device.

Movement of the lower bore portion may be disabled during an inlet stroke. The air inlet port may be an annular gap.

The lower bore portion may be in sealing abutment with the upper bore portion in the first position with an interlocking finger abutment. Alternatively, the lower bore portion may be in sealing abutment with the upper bore portion in the first position with a butt joint abutment.

The lower and upper bore portions may be machined in matching pairs.

The piston may have three piston rings configured to sealingly engage with the surface of the cylinder bore assembly. According to another aspect of the invention, there is provided an internal combustion engine including at least one piston arrangement as hereinbefore described. The internal combustion engine may operate on a two stroke cycle.

The present invention provide a two stroke internal combustion engine having improved efficiency, higher power and advanced inlet port and emission control over the existing two stroke internal combustion engine.

According to yet another aspect of the invention, there is provided a method of operating an internal combustion engine wherein a piston is reciprocatively received within a fixed bore section during a first portion of an engine cycle and is reciprocatively received within an operable bore portion during a second portion of an engine cycle, between the first and second portion of the engine cycle said operable bore portion being moved in relation to the engine piston and or cylinder to form an inlet port after the transition of the at least one piston ring from a first fixed bore portion to an operable bore portion.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which :

Figure 1 (a), (b) shows a pictorial representation of a single cylinder two stroke engine of the present invention;

Figure 2 (a), (b), (c), (d) show possible examples of alternative cylinder liner valve abutment arrangements; and

Figure 3 (a), (b) show a typical symmetrical inlet event (a) versus an asymmetrical inlet event (b) of the piston arrangement of the present invention. DETAILED DESCRIPTION

A two stroke engine 1 is provided with a piston 15, reciprocatively received within a cylinder 11 and cylinder bore assembly 12, said piston being pivotably and rotationally mounted to a connecting rod 16 via a gudgeon pin 23 and big end crank pin 17', a crankshaft 17 is rotationally mounted within the crankcase 18.

A cylinder head 5 is fitted to the open end of the cylinder 11 and cylinder bore assembly 12 and forms the combustion chamber 5' and contains the exhaust valve 7, the spark plug 8 and the fuel injector 9, further an exhaust camshaft 2 valve rocker 3 and rocker post 4 are mounted on the cylinder head. Located circumferentially to the bore and within the cylinder 11 is an inlet air plenum or air chest or chamber 14, during operation of the engine inlet air or fuel air mixture 22 from a compressor, turbocharger or air pump (not shown) flows into the plenum or chamber. Operably slidably received within the cylinder 11 is a lower bore portion 13, said lower bore portion 13 may be associated with, for example, a camshaft and finger follower mechanism 19, 20 to enable the lower bore portion to be operably moved within the cylinder as shown in Figure lb. Springs, 21 may further be utilised to return the lower bore portion into a sealing abutment relationship with the upper stationary bore portion 12.

In operation the lower bore portion 13 is initially abutted against the upper stationary bore portion 12 and substantially prevents air flow from the air inlet port 14' and air plenum 14 into the cylinder, the piston is pulled down the cylinder bore by the action of the rotating crankshaft 17 and connecting rod 16. As the piston rings 15' transition from the upper bore portion to the lower bore portion the rotation of the cam shafts 19 driven by a chain or gears from the crankshaft (not shown) against the finger followers 20 moves the lower bore portion 13 away from the abutted sealing relationship with the fixed bore portion 12, compressing the return springs 21, and allowing inlet air to flow from the plenum or air chest 14 into the cylinder above the piston through the annular gap 14'. At this time the exhaust valve 7 is open to allow the incoming airflow to scavenge the cylinder with fresh air. Further rotation of the crankshaft causes the piston to reach bottom dead centre, (bdc) as shown in Figure lb. At this position the air inlet gap 14' is fully open and the lower cylinder bore portion 13 is in its fully retracted position. Further rotation of the crankshaft causes the piston to start to return up the bore, driven by the crank shaft continued rotation of the camshaft 19 allows the compressed springs to return the lower operable portion of the bore to return into sealing abutment with the upper fixed bore portion allowing the piston and piston rings to transition the now closed inlet air gap or port between the two bore portions 12 and 13. The exhaust valve is now closed. Further rotation of the crankshaft causes the piston to compress the inlet air / fuel mixture into the combustion chamber where fuel may be injected by the fuel injector and ignited by the spark plug. The expansion of the fuel air mixture causing the piston to descend on the power stroke, as the piston reaches the lower portion of the cylinder bore the exhaust valve will open and the piston and rings will transition the closed gap whereby the sequence of events will be repeated.

Importantly it is envisaged that the camshafts 19 may be of known variable valve lift or valve phasing (timing) mechanisms therefore allowing variable motion of the lower bore portion in relation to piston motion. For example should the engine be required to run at low power the maximum movement of the lower bore portion 13 may be restricted by any known variable lift camshaft device, this would limit the power and or emissions of the engine. It may also be further envisaged that the lower bore portion 13 may not be permitted to operate during a usual inlet stroke, the camshaft 19 for example may be disabled allowing the engine to skip cycle or for example 4 stroke or 6 stroke between firing pulses. Further, for example, the lower bore portion 13 may be operated between a maximum and a minimum position to limit the inlet airflow and therefore power and or assist in regulating the airflow and or emissions of the engine.

Further the phasing between the rotation of the crankshaft 17 and the camshafts 19 may be advanced or retarded to advance or retard the induction process.

It must be appreciated that the surface area of the annular port provided by the stroke of the lower bore portion away from the upper fixed bore portion is significantly greater than the surface area of standard two stroke ports or indeed standard 4 stroke poppet valves.

In operation it would be usual to ensure the lower bore portion and therefore the inlet port is closed or abutted prior to the piston rings traversing the joint between said bore portions preventing the piston rings from being damaged by the gap. It is also considered prudent that the upper and lower bore portions be machined in matching pairs to ensure accurate fit. It is appreciated that at all times the piston rings of the piston will not be allowed to transition between the upper and lower bore portions whilst the upper and lower bore portion are not abutted.

Although in the example description springs have been shown to return the lower bore portion to the closed or abutted position other mechanisms, for example mechanical cams, electronic solenoids or hydraulic or pneumatic actuators may be used. The abutment between the cylinder bore portions may be simple annular form or consist of interlocking fingers or of but joint form, for example see Figure 2 (a), (b), (c) or (d). Furthermore, whilst the abutment has been shown as approximately horizontal, across the piston arrangement, the abutment could be provided at an angle, so that the piston rings traverse circumferentially different portions of the abutment at different times.

Figure 3 (a) shows a timing diagram for a two stroke engine having a known piston arrangement, which includes inlet ports within the cylinder wall. The exhaust phase 100 commences at a piston rotation of 90° and finishes at a piston rotation of approximately 200°. The induction phase 200 commences at 130° and finishes at 230°. The induction phase is 200 is thus a symmetrical inlet event, as the downward stroke of the piston uncovers the inlet ports within the cylinder wall and the upward stroke of the piston covers the inlet ports. The inlet ports must be symmetrical about bottom dead centre - 180°, and hence there is a large overlap between the exhaust phase 100 and the induction phase 200.

Figure 3 (b) shows a timing diagram for a two stroke engine having the piston arrangement of the present invention. Like in Figure 3 (a), the exhaust phase 100 commences at a piston rotation of 90° and finishes at a piston rotation of approximately 200°. However, the induction phase 300 commences at 170° and finishes at 270°. This is possible as the uncovering and covering of the inlet ports is not governing solely by the position of the piston crown, but by the movement of the cylinder bore assembly. This allows for an asymmetrical inlet event.

Claims

1. A piston arrangement comprising :

a piston (15) reciprocatively received within a cylinder (11)

a crankshaft (17) and

a cylinder bore assembly (12),

the piston (15) having at least one piston ring configured to sealingly engage with a surface of the cylinder bore assembly (12)

the cylinder bore assembly (12) comprising a lower bore portion (13) and an upper bore portion (14),

wherein at least a lower or upper bore portion (13, 14) of the cylinder bore assembly (12) is moveable within the cylinder (11) between a first position in which the lower bore portion (13) is in sealing abutment with the upper bore portion (14) and a second position in which the lower bore portion (13) is separated from the upper bore portion (14) so as to expose an air inlet port between said lower and upper bore portions (13, 14),

and wherein movement of the at least a lower or upper bore portion (13, 14) between said first and second position is controlled by a mechanism phased and timed in relation to the piston (15) and/or crankshaft (17) position,

and wherein the relative movement of the piston (15) and cylinder bore assembly (12) is configured such that the at least one piston ring of the piston (15) transitions between the lower and upper bore portions (13, 14) when the cylinder bore assembly (12) is in the first position.

2. A piston arrangement according to claim 1 wherein a cylinder head (5) is fitted to an open end of the cylinder (11).

3. A piston arrangement according to claim 2 wherein at least one exhaust port is provided in the cylinder head (5).

4. A piston arrangement according to claim 1 wherein the cylinder (11) has an inlet air plenum (14) in fluid communication with the air inlet port (14) when the cylinder bore assembly (12) is in the second position.

5. A piston arrangement according to claim 4 wherein the inlet air plenum (14) is located circumferentially to the cylinder bore assembly (12).

6. A piston arrangement according to any preceding claim wherein the lower bore portion (13) is moveable within the cylinder (11) and the upper bore portion (14) is static within the cylinder (11).

7. A piston arrangement according to claim 6 wherein the lower bore portion (13) is moveable within the cylinder (11) via a camshaft and finger follower mechanism.

8. A piston arrangement according to any preceding claim wherein the cylinder bore assembly (12) is returned to the first position by one of a return spring, a mechanical cam, an electronic solenoid, a hydraulic actuator or a pneumatic actuator.

9. A piston arrangement according to any preceding claim wherein the lower bore portion (13) is in a fully retracted condition at piston (15) bottom dead centre.

10. A piston arrangement according to any of claims 7 to 9 including camshaft variable valve lift or valve phasing mechanisms to allow variable motion of lower bore portion (13) in relation to piston (15) motion.

11. A piston arrangement according to any of claims 7 to 10 wherein movement of the lower bore portion (13) is restricted by a variable lift camshaft device.

12. A piston arrangement according to any of claims 7 to 11 wherein movement of the lower bore portion (13) is disabled during an inlet stroke.

13. A piston arrangement according to any preceding claim wherein the air inlet port is an annular gap (14').

14. A piston arrangement according to any preceding claim wherein the lower bore portion (13) is in sealing abutment with the upper bore portion (14) in the first position with an interlocking finger abutment.

15. A piston arrangement according to any of claims 1 to 13 wherein the lower bore portion (13) is in sealing abutment with the upper bore portion (14) in the first position with a butt joint abutment.

16. A piston arrangement according to any preceding claim wherein lower and upper bore portions (13, 14) are machined in matching pairs.

17. A piston arrangement according to any preceding claim wherein the piston (15) has three piston rings configured to sealingly engage with the surface of the cylinder bore assembly (12).

18. An internal combustion engine including at least one piston arrangement according to any of claims 1 to 17.

19. An internal combustion engine according to claim 18, wherein the internal combustion engine is two stroke.

20. A method of operating an internal combustion engine wherein a piston is reciprocatively received within a fixed bore section during a first portion of an engine cycle and is reciprocatively received within an operable bore portion during a second portion of an engine cycle, between the first and second portion of the engine cycle said operable bore portion being moved in relation to the engine piston and or cylinder to form an inlet port after the transition of the at least one piston ring from a first fixed bore portion to an operable bore portion.