GB2271386A

GB2271386A - Uniflow scavenged two-stroke engine.

Info

Publication number: GB2271386A
Application number: GB9221001A
Authority: GB
Inventors: Alexander Coutts Brotherston
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-10-06
Filing date: 1992-10-06
Publication date: 1994-04-13
Also published as: GB9221001D0

Abstract

A piston valve 18 in a bore which slightly overlaps the cylinder controls the exhaust port 24. External and internal fins 30, 31 on the camshaft cover 49 provide for cooling of oil providing valve gear lubrication. Balance weights 6 are bolted to the crankshaft journals 3. Air or mixture is guided into the crankcase 1 by vanes 14 and passes through cooling passages 45, 46, 47 around the main bearings and the connecting rod 41. <IMAGE>

Description

UNIFLOW SCAVENGE TWO - STROKE ENGINE This invention relates to uniflow scavenge internal combustion engines.

The engine described herein is designed to take advantage of the well known benefits of uniflow scavenged two - stroke cycle engines. while retaining as much as possible of the simplicity and ease of manufacture of the cross flow and loop scavenged engines.

For purposes of simplicity and to separate adjacent crankcases the known tunnel type of crankshaft construction is adopted, but incorporating a special form of balance weight attachment.

Uniflow scavenging is achieved by means of a cam regulated piston valve, and bearing cooling is provided for by fluid flow arrangements.

The engine may be naturally aspirated or turbo charged. A single cylinder naturally aspirated embodiment of the engine will now be described with reference to the accompanying drawings in which Fig.1 shows a cross section A - A of the engine and Fig.2 shows a longitudinal section B - B.

Referring to the drawings the engine crankcase 1 houses the crankshaft 2 which is of the tunnel type where the main bearing journals 3 are directly connected to the crankpins.

The crankpins 4 are hollow being provided with a concentric lightening hole 5. Balance weights 6 are located in the holes 7 in the joumals by spigots 8 which are set at 1200 or 1800 to the crankpin depending on engine specification. The holes in the balance weights are the same diameter as the holes in the crankpins; and in multi cylinder units would constitute the end of the crankpin lightening hole of an adjacent cylinder. The centrally placed bolts 9 for securing the balance weights are provided with tapered heads which serve to expand the spigot when they are tightened, effectively locking the balance weights in position. The crankshaft joumal bearings 10 are one piece shell type provided with suitable low friction running surfaces, as are the gudgeon pin bushes 11.The crankpin bearing shells 12 are similar in nature but are split in normal fashion to provide for assembly and inspection.

The engine induction 13 leads to guide vanes 14 which are cast in the entry passage and direct the fluid flow into the crankcase. In the crankcase fluid is carried round in the direction of rotation and discharged via the scavenge belt 15 to the scavenge ports 16 which comprise an annular ring of holes cast at about mid length of the cylinder bore in a tangential form so as to impart a swirling motion to the entering charge. The timing of the fluid flow into the cylinder is governed by the movement of a normal piston 17 which uncovers the scavenge ports each time it approaches the bottom of it's stroke.

The exhaust gases are released by a piston valve 18 which is a running fit in a bored housing 19 in the cylinder head 20. The bored housing is offset from the cylinder head to accommodate a part spherical combustion chamber 21.

The piston valve is driven on its upward stroke by cylinder pressure; it's rate of movement being regulated by a cam 22. Exhaust gas release commences when the bottom of the piston valve has risen sufficiently to uncover the bottom of an annular recess 23 in the bored housing allowing the exhaust gases to pass to the outlet port 24. The piston valve is driven down by the cam, and shuts off the exhaust at the position in it's stroke as drawn. The piston valve is held against the face of the cam at the top of it's stroke.by springs; 25 preferably of the cantilevered type. The springs engage a pin 26 which is fitted in a hole 27 drilled through the piston valve and radially located by slots 28 milled in the bored housing of the cylinder head.

The camshaft is driven at engine speed by normal means, and the piston valve timing is arranged to suit the engine rating.

The cylinder head 29 forms a sump and is oil cooled: the temperature of the oil being maintained by intemal cooling fins 30 and extemal cooling fins 31 cast in the camshaft cover 49.

The engine cylinder jacket 32 is normally cooled by circulating water entering the engine at 33 and exiting at 34.

Bearing and cylinder lubricating oil is delivered by an engine driven reciprocating pump running at approximately 10% of engine speed. The lubricating oil supply is fed to the main bearing shells at 35 and passes round annular grooves 36 to drilled passages 37 crossing the crankshaft joumals. Drilling 38 leads from the crankshaft joumal to the crankpin and holes 39 and 40 take the oil to the crankpin bearings from where it passes up the centre of the connecting rods 41 to the gudgeon pin bushes and across a transverse hole 42 in the gudgeon pins to lubricate the cylinder liners.

The heat generated by fluid friction in the main bearings is cooled by a flow of cooling air or air and fuel which enters an annular groove 43 at the back of the bearing shells from openings 44 cast in the crankcase. The cooling flow results from displacement caused by the downward movement of the piston and exits from cast openings 45 at the bottom of the crankcase. The crankpin bearing shells receive a cooling flow in a similar manner through holes 46 drilled in the palms of the connecting rods which connect with annular grooves 47 machined around the connecting rod assemblies at the back of the bearing shells. The lateral movement of the connecting rods causes a cooling flow. The normal hollow and open ended gudgeon pins receive cooling as the pistons cross the scavenge ports each time.

Spark plugs and I or fuel injectors 48 are located in the cylinder head in the vicinity of the combustion chamber

Claims

CLAIMS 1. A two - stroke engine provided with a cam regulated piston valve timed to open and close the exhaust in such a manner as to achieve optimum fuel economy and optimum scavenge efficiency.
2. An engine is claimed in claim 1 where the exhaust piston valve is arranged so that it's outside diameter slightly overlaps the outside diameter of the engine cylinder in order to exhaust those products of combustion which lie close to the cylinder walls.
3. An engine as claimed in claims 1 and 2 arranged so that when the piston valve is at the top of it's stroke it is held against the face of the cam by means of a spring or springs.
4. An engine is claimed in claims 1,2 & 3 where the cylinder head is oil cooled ; the coolant also being used to lubricate the camshaft and valve gear.
5. An engine as claimed in claims 1 to 4 where the oscillating motion of the valve springs and valve gear assist the cylinder head cooling process by promoting turbulence in the oil sump.
6. An engine as claimed in claims 1 to 5 where heat in the cylinder cover cooling oil is dissipated by internal as well as external fins on the camshaft cover.
7. A two -stroke engine using balance weights located on a flat face of the main bearing journals by a spigot in a bored hole in the journal.
8. An engine as claimed in claim 7 where the balance weights are locked in position by taper headed bolts which act by expanding a spigot on the balance weight against the bored hole in which it fits.
9. An engine as claimed in claims 7 & 8 where the balance weights are arranged at 1200 or 1800 to the crankpin.
10. A crankcase induction two-stroke engine with guide vanes provided in the induction ports to direct the fluid flow entering the crankcase.
11. A crankcase induction two-stroke engine where the heat generated in the main bearing and crankpin bearing shells is dissipated by a fluid flow around annular grooves at the back of the bearing shells ; the flow being initiated by piston movement in the case of the main bearings, and by connecting rod movement in the case of the crankpin bearings.
12. A two-stroke engine substantially as described herein with reference to figures 1 & 2 in the accompanying drawings.

12. A two-stroke engine substantially as described herein with reference to figures 1 & 2 in the accompanying drawings.

Amendments to the claims have been filed as follows 1. A two - stroke engine provided with a cam regulated piston valve mounted in the cylinder head, and timed to open and close the exhaust in such a manner as to achieve optimum efficiency.

2. An engine as claimed in claim 1 where the exhaust piston valve is arranged so that it's outside diameter slightly overlaps the outside diameter of the engine cylinder in order to exhaust those products of combustion which lie close to the cylinder walls.

3. An engine as claimed in claims 1 and 2 arranged so that when the piston valve is at the top of it's stroke it is held against the face of the cam by means of a spring or springs.

4. An engine as claimed in claims 1,2 & 3 where the cylinder head is oil cooled ands incidentally7 also serves to lubricate the camshaft and valve gear.

5. An engine as claimed in claims 1 to 4 where the oscillating motion of the valve springs and valve gear assist the cylinder head cooling process by promoting turbulence in the oil sump.

6. An engine as claimed in claims 1 to 5 where heat in the cylinder cover cooling oil is dissipated by internal as well as external fins on the camshaft cover.

7. A two -stroke engine using balance weights located on a flat face of the main bearing journals by a spigot in a bored hole in the journal.

8. An engine as claimed in claim 7 where the balance weights are locked in position by taper headed bolts which act by expanding a spigot on the balance weight against the bored hole in which it fits.

9. An engine as claimed in claims 7 & 8 where the balance weights are arranged at 1200 or 1800 to the crankpin.

10. A crankcase induction two-stroke engine with guide vanes provided in the induction ports to direct the fluid flow entering the crankcase.

11. A crankcase induction two-stroke engine where the heat generated in the main bearing and crankpin bearing shells is dissipated by a fluid flow around annular grooves at the back of the bearing shells ; the flow being initiated by piston movement in the case of the main bearings, and by connecting rod movement in the case of the crankpin bearings.