US20120107165A1

US20120107165A1 - Engine cooling system

Info

Publication number: US20120107165A1
Application number: US13/262,523
Authority: US
Inventors: Paul Anthony McLachlan
Original assignee: Pivotal Engineering Ltd
Current assignee: MACE ENGINEERING Ltd; Pivotal Engineering Ltd
Priority date: 2009-03-30
Filing date: 2010-03-26
Publication date: 2012-05-03
Also published as: JP2012522177A; EP2414636A1; JP5662996B2; KR20120025449A; EP2414656A1; US20120097142A1; KR101640626B1; KR20120024546A; WO2010114394A1; EP2414656A4; WO2010114393A1; EP2414656B1; US8720391B2; JP2012522178A

Abstract

A piston cooling system for a pivoted piston (1) for an internal combustion engine, said piston (1) having a piston body (2), a pivot shaft (3) by which the piston body (2) may be pivoted about a pivot axis (4) within a combustion chamber of the internal combustion engine, a first arcuate sealing surface spaced from the pivot axis and transcribing a circumferential path about the pivot axis, and a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor (5) of the piston body (2), a portion of said floor (5) including a combustion chamber piston crown (6), characterised in that the cooling system includes a coolant path (10) formed in the piston, said coolant path having an entry point at a first end (11) of the pivot shaft (3) and an exit point at a second end (12) of the pivot shaft (3), wherein said coolant path (10) extends from the entry point, through a first portion (13) of the pivot shaft (3), into said piston body (2), beneath the piston floor (5), on through one or more passageways (16) adjacent the piston crown (6), back to a second portion of the pivot shaft (3), and out through the exit point, each said passageway (15/16/17) having a substantially constant cross section along its length.

Description

FIELD OF THE INVENTION

This invention relates to improvements in and to internal combustion engines. More particularly, but not exclusively, this invention comprises improvements in and to cooling systems for use in internal combustion engines which utilise one or more pivoting pistons.

BACKGROUND

In International Patent Specifications WO 95/08055 and WO 01/71160, the contents of which are incorporated herein by reference, there are described internal combustion engines which utilise a pivoted piston which rocks about a pivot point within a combustion chamber. The piston is connected adjacent the end of the piston remote from the pivot point to a connecting rod which drives a crankshaft. The piston has a first arcuate sealing surface to seal against a wall of the combustion chamber and a second sealing surface which is connected by a piston floor to the first arcuate sealing surface. Both sealing surfaces have a substantially constant radial dimension from the pivot point of the piston.
The first arcuate sealing surface forms a skirt so a portion of the wall of the arcuate sealing surface will make a gas seal with the wall of the combustion chamber. The skirt also assists in dissipating heat in the piston. The piston further includes an arrangement to allow liquid coolant to pass through the pivot shaft, through liquid cooling galleries in the piston and out of the pivot shaft.
One area of particular difficulty with the prior art engine configurations identified is in relation to managing the coolant flow and controlling the cooling of the piston during engine operation, particularly where multiple pistons are employed.

OBJECT OF THE INVENTION

It is an object of this invention to provide a solution to the above identified problem with the noted prior art engine configurations, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first broad aspect the invention may be said to comprise a piston cooling system for a pivoted piston for an internal combustion engine, said piston having a piston body, a pivot shaft by which the piston body may be pivoted about a pivot axis within a combustion chamber of the internal combustion engine, a first arcuate sealing surface spaced from the pivot axis and transcribing a circumferential path about the pivot axis, and a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor of the piston body, a portion of said floor including a combustion chamber piston crown, characterised in that the cooling system includes a coolant path formed in the piston, said coolant path having an entry point at a first end of the pivot shaft and an exit point at a second end of the pivot shaft, wherein said coolant path extends from the entry point, through a first portion of the pivot shaft, into said piston body, beneath the piston floor, on through one or more passageways adjacent the piston crown, back to a second portion of the pivot shaft, and out through the exit point, each said passageway having a substantially constant cross section along its length.
An advantage of this aspect of the present invention over the prior art is that the risk of any portion of the coolant medium getting caught in stagnation areas, or engaging in vortex motion, which can result in local “hot spot” areas, is much reduced.
A further advantage of utilising passageways of substantially constant cross section is that the structural integrity of the piston body is retained in the area of the piston crown, and that the piston/coolant interface surface area is increased and more effectively utilised.
Preferably the cross section of each passageway is circular.
Desirably each passageway runs across the piston body, parallel to the pivot axis.
Desirably there are two or more passageways, wherein each passageway is at a different radial offset from the pivot axis to every other passageway.
Optionally the diameter of passageways may be different as between one and another so as to provide even cooling across the piston floor.
In a second broad aspect the invention provides a piston cooling system for a pivoted piston for an internal combustion engine, said piston having a piston body, a pivot shaft by which the piston body may be pivoted about a pivot axis within a combustion chamber of the internal combustion engine, a first arcuate sealing surface spaced from the pivot axis and transcribing a circumferential path about the pivot axis, and a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor of the piston body, a portion of said floor including a combustion chamber piston crown, characterised in that the cooling system includes coolant medium flow control means whereby the flow pressure can be controlled independently of the cooling system for other components of the combustion engine.
Preferably the flow pressure of the piston cooling system can be controlled independently of the rotational speed of the combustion engine.
An important advantage of this aspect of the invention is that it provides the ability to preheat or speed up temperature gain of the piston at start up, for example, as well as to increase the flow when high load demands additional cooling of the piston relative to the demands on the engine cooling system.
Optionally the coolant flow control means can be located in the coolant path upstream of the piston. Alternatively the coolant flow control means can be located in the coolant path downstream of the piston.
Conveniently the coolant flow control means can further include a pre-heater means to preheat and circulate the preheated coolant medium around the coolant path prior to start up of the combustion engine.
In one form the coolant flow control means can be a coolant medium pump operated independently of the coolant medium pump pumping coolant medium for cooling of the other components of the combustion engine.
Alternatively the control means can comprise a valve on the main coolant medium line adapted to adjust the flow rate of coolant medium to and along the piston coolant path.
In a third broad aspect the invention provides a piston cooling system for a multi-chamber internal combustion engine utilising pivoted pistons, each said piston having a piston body, a pivot shaft by which the piston body may be pivoted about a pivot axis within a corresponding combustion chamber of the internal combustion engine, a first arcuate sealing surface spaced from the pivot axis and transcribing a circumferential path about the pivot axis, and a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor of the piston body, a portion of said floor including a combustion chamber piston crown, characterised in that the cooling system includes a coolant path formed in each piston, said coolant path having an entry point at a first end of the pivot shaft and an exit point at a second end of the pivot shaft, wherein said coolant path extends from the entry point, through a first portion of the pivot shaft, into said piston body, beneath the piston floor, on through one or more passageways adjacent the piston crown, back to a second portion of the pivot shaft, and out through the exit point, each said passageway having a substantially constant cross section along its length, the coolant paths of adjacent pistons being connected in series, with the coolant path exit point of one said piston in the series providing cooling medium flow to the coolant path entry point of the next piston in the series.
Preferably all cooling medium entering the entry point of the coolant path of the final piston in series must pass through the piston body before reaching the exit point of that said coolant path.
Desirably the pivot shaft of the penultimate piston includes a leak path along its length directly between the first portion and the second portion to, in use, allow a portion of the cooling medium entering the entry point of the coolant path to bypass the piston body and pass directly to the exit point.
Preferably when the multi-chamber engine includes three or more pistons the leak path of the preceding piston in the series allows a greater proportion of cooling medium to bypass its piston body than that of the piston that follows in the series.
An advantage of the present embodiment is that it aids management of the potential discrepancies in the cooling medium temperature as it flows from one piston to the next in an inline multi-chamber engine.. The stepped reduction in the size of the leak path in each pivot shaft as they progress toward the final outlet progressively accelerates the coolant flow speed through the piston crown gallery to counter the incremental increase in coolant temperature.
To enable the pivot shafts of adjacent pistons to operate in synchronise but at different phases of the combustion cycle while still allowing passage of cooling medium to flow along the coolant path through the full series of pistons of a multi-chamber combustion engine a tubular connector is required.
Accordingly, in a fourth broad aspect the invention provides a pivot shaft connector for use in connection with the cooling system of the third broad aspect, characterised in that the connector comprises a tubular section having a first end configured and arranged to sealingly rotatably engage with the second end of one pivot shaft and a second end adapted to sealingly rotatably engage with the first end of a second pivot shaft, the connector further including an outwardly projecting step midway along its length to prevent over insertion in to either the second end of the first pivot shaft or the first end of the second pivot shaft.
Preferably the step locates a further seal means to provide additional sealing between the opposing primary induction chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now briefly be described with the aid of the accompanying drawings, of which:

FIG. 1: is a side elevation view of a piston body according to one embodiment of the present invention illustrating a piston cooling system having multiple cross passageways beneath the piston crown;

FIG. 2: is a view from above of a piston body similar to that depicted in FIG. 1 but incorporating a single cross passageway for cooling medium beneath the piston crown;

FIG. 3: shows a semi-schematic view of the piston cooling system in a multi-chamber combustion engine. The coolant flow path is diagrammatically illustrated;

FIG. 4: is a side elevation of pivot shaft for use in a piston cooling system according to the invention;

FIG. 5 a: shows a sectional view of the pivot shaft of FIG. 4;

FIG. 5 b: shows a similar view to that of FIG. 5 a, but as an alternative with a partial leak path provided;

FIG. 5 c: shows a similar view to that of FIG. 5 b, but with a larger leak path opening;

FIG. 6 a: is a partial section view of the ends of two pivot shafts for adjacent pistons in a multi-chamber combustion engine joined by a connector according to the present invention;

FIG. 6 b: is a sectional view of the features illustrated in FIG. 6 a;

FIG. 7: is a perspective view of the connector partially illustrated in FIGS. 6 a and 6 b; and

FIG. 8: is a plan view of the connector of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The prior art engines disclosed in International Patent Specifications WO 95/08055 and WO 01/71160 incorporate pistons which are pivoted within a combustion chamber by a pivot pin and each have an arcuate first sealing surface which forms a skirt to the piston.
The prior art pistons also include a second arcuate sealing surface which is radially offset from the skirt with both the surface of the skirt and the second arcuate sealing surface describing a circumferential path about the pivot axis of the pivot pin. Each piston also includes a piston pin to receive an end of a connecting rod, by which the crankshaft of the engine is rotated.
Referring now to the drawings, and in particular to FIGS. 1 to 3, in one aspect the invention provides an improved cooling system for a pivoted piston 1 of the above described general prior art type for an internal combustion engine. In that regard, the piston 1 has a piston body 2 and a pivot shaft 3 by which the piston body 2 is pivoted about a pivot axis 4 within the combustion chamber of the internal combustion engine.
The piston body 2 includes a floor 5, a portion of which forms the combustion chamber piston crown 6.
The improved cooling system includes a coolant path 10 formed in the piston 1. The coolant path 10 enters the piston 1 at an entry point at one end 11 of the pivot shaft 3, exits the piston 1 at an exit point at the other end 12 of the shaft 3.
From the entry point the coolant path extends through a first tubular gallery 13 of the pivot shaft which gallery is centered on the pivot axis 4 of the shaft 3. The gallery 13 extends in to the shaft 3 for less than half the length of the shaft 3.
Part way along the length of the gallery 13 a substantially perpendicular passageway 14 runs radially outwardly into the body 2 of the piston 1, extending to a point substantially beneath the piston crown 6. At this point the coolant path runs across the width of the piston body 2 beneath the piston crown 6—as one or more substantially perpendicular passageways 15. Where two or more passageways 15 are provided, as illustrated in FIG. 1, each one is spaced radially outwardly from, but, parallel to, the next. Each passageway 15 is of substantially constant circular cross section along its length, but the cross sections of adjacent passageways 15 may be different to reflect different flow rates required to manage variations in heat generation location across the piston crown 6.
Multiple passageways 15, each of constant cross section, mitigates the risk of any portion of the coolant medium getting caught in stagnation areas, or engaging in vortex motion, which can result in local “hot spots”. A further advantage of utilising passageways 15 of substantially constant cross section is that the structural integrity of the piston body 2 is retained in the area of the piston crown 6, and that the piston/coolant interface surface area is increased and more effectively utilised.
Having passed under the piston crown 6 the coolant path then returns back towards the shaft 3 via a radially oriented passageway 16, re-entering the shaft 3 at a second tubular gallery 17 in the pivot shaft 3, again which gallery is centered on the pivot axis 4. Like the gallery 13, the gallery 17 extends in to the shaft 3 for less than half the length of the shaft 3. The coolant path then exits the shaft 3 at its end 12.
The flow rate of coolant medium through the coolant pathway, and thus the cooling effect that the coolant medium has, can be controlled via control of the flow pressure. This control can be achieved via control mechanisms independent of the cooling system for other components of the combustion engine, and in particular can potentially be controlled independently of the rotational speed of the engine. For example, if the coolant medium is water, then it can be supplied via a take-off from the main engine coolant circulation system, and flow rate control can be applied via use of a valve on the upstream or downstream side of the piston 1 so as, for example, to allow for increase in the flow when high load demands additional cooling of the piston relative to the demands on the engine cooling system.
Where an independent coolant medium supply is used it provides the ability to preheat or speed up temperature gain of the piston at start up, and the system can further include a pre-heater, for example an electric water heater, to preheat and circulate the preheated coolant medium around the coolant path prior to start up.
Turning now more specifically to FIGS. 3 to 8, where the combustion engine has multiple chambers the cooling system needs to include a coolant path for each piston 1. As illustrated in FIG. 3, this involves serially connecting the previously described coolant pathway of two or more adjacent pistons 2.
To ensure that potential discrepancies in the cooling medium temperature as it flows from one piston to the next in an inline multi-chamber engine the pivot shaft 3 of the penultimate piston 1 can include a leak path 20 directly between the gallery 13 and the gallery 17 to, in use, allow a portion of the cooling medium to bypass the piston body 2 of the penultimate piston 1 and pass directly on to the start of the coolant path for the final piston 1.
Where the multi-chamber engine includes three or more pistons the leak path of the preceding piston in the series allows a greater proportion of cooling medium to bypass its piston body than that of the piston that follows in the series, as shown in FIGS. 5 b and 5 c.
The stepped reduction in the size of the leak path in each pivot shaft as they progress toward the final outlet progressively accelerates the coolant flow speed through the piston crown gallery to counter the incremental increase in coolant temperature.
To enable the pivot shafts of adjacent pistons 1 to operate in synchronise but at different phases of the combustion cycle while still allowing passage of cooling medium to flow along the coolant path through the full series of pistons of a multi-chamber combustion engine a tubular connector, as generally indicated at 30 in FIGS. 6 a to 8, is required.
As shown in the drawings, the connector 30 preferably comprises a tubular section 31 having a first end 32 configured and arranged to sealingly rotatably engage with end 12 of one pivot shaft 3. It has a second end 33 adapted to sealingly rotatably engage with the end 11 of a second pivot shaft 3. Sealing can be achieved by using a bearing seal of known type, as the operating speed is not significant.
The connector 30 further includes an outwardly projecting step 34 midway along its length to prevent over insertion in to either the end 12 of the first pivot shaft 3 or the end 11 of the second pivot shaft 3.
Preferably the step locates an O-ring type seal 35 to provide additional sealing between the adjacent primary induction chambers.
Having read the specification, it will be apparent to those skilled in the art that various modifications and amendments can be made to the construction and yet still come within the general concept of the invention. All such modifications and changes are intended to be included within the scope of the claims.

Claims

1. A piston cooling system for a pivoted piston for an internal combustion engine, said piston comprising:

a piston body;

a pivot shaft by which the piston body may be pivoted about a pivot axis within a combustion chamber of the internal combustion engine;

a first arcuate sealing surface spaced from the pivot axis and transcribing a circumferential path about the pivot axis; and

a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor of the piston body, a portion of said floor including a combustion chamber piston crown,

wherein the piston cooling system comprises a coolant path formed in the piston, said coolant path having an entry point at a first end of the pivot shaft and an exit point at a second end of the pivot shaft, wherein said coolant path extends from the entry point, through a first portion of the pivot shaft, into said piston body, beneath the piston floor, on through one or more passageways adjacent the piston crown, back to a second portion of the pivot shaft, and out through the exit point, each said passageway having a substantially constant cross section along its length.

2. The piston cooling system of claim 1, wherein the cross section of each passageway is circular.

3. The piston cooling system of claim 2, wherein each passageway runs across the piston body, parallel to the pivot axis.

4. The piston cooling system of claim 3, wherein the one or more passageways comprise two or more passageways, wherein each passageway is at a different radial offset from the pivot axis to every other passageway.

5. The piston cooling system of claim 4, wherein the diameter of the two or more passageways may be different as between one and another of the two or more passageways so as to provide even cooling across the piston floor.

6. A piston cooling system for a pivoted piston for an internal combustion engine, said piston comprising:

a piston body;

wherein the piston cooling system comprises a coolant medium flow control whereby a flow pressure can be controlled independently of a second cooling system for other components of the internal combustion engine.

7. The piston cooling system of claim 6, further comprising a coolant flow control wherein the flow pressure of the piston cooling system can be controlled independently of a rotational speed of the combustion engine.

8. The piston cooling system of claim 7, wherein the coolant flow control is located in a coolant path upstream of the piston.

9. The piston cooling system of claim 7, wherein the coolant flow control is located in a coolant path downstream of the piston.

10. The piston cooling system of claim 7, wherein the coolant flow control further comprises a pre-heater to preheat and circulate a preheated coolant medium around the coolant path prior to start up of the internal combustion engine.

11. The piston cooling system of claim 7, wherein the coolant flow control comprises a first coolant medium pump operated independently of a second coolant medium pump pumping coolant medium for cooling of other components of the internal combustion engine.

12. The piston cooling system of claim 7, wherein the coolant flow control comprises a valve on a main coolant medium line adapted to adjust a flow rate of coolant medium to and along a piston coolant path.

13. A piston cooling system for a multi-chamber internal combustion engine utilising pivoted pistons, each said piston comprising:

a piston body;

a pivot shaft by which the piston body may be pivoted about a pivot axis within a corresponding combustion chamber of the multi-chamber internal combustion engine;

a second arcuate sealing surface radially offset from the first arcuate sealing surface and connected to the first arcuate sealing surface by a floor of the piston body, a portion of said floor comprising a combustion chamber piston crown,

wherein the cooling system comprises, a coolant path formed in each piston, said coolant path having an entry point at a first end of the pivot shaft and an exit point at a second end of the pivot shaft, and

wherein said coolant path extends from the entry point, through a first portion of the pivot shaft, into said piston body, beneath the piston floor, on through one or more passageways adjacent the piston crown, back to a second portion of the pivot shaft, and out through the exit point, each said passageway having a substantially constant cross section along its length, the coolant paths of adjacent pistons being connected in series, with the coolant path exit point of one said piston in the series providing cooling medium flow to the coolant path entry point of a next piston in the series.

14. The piston cooling system of claim 13, wherein all cooling medium entering the entry point of the coolant path of a final piston in series must pass through the piston body before reaching the exit point of that said coolant path.

15. The piston cooling system of claim 13, wherein the pivot shaft of a penultimate piston includes a leak path along its length directly between the first portion and the second portion to, in use, allow a portion of the cooling medium entering the entry point of the coolant path to bypass the piston body and pass directly to the exit point.

16. The piston cooling system of claim 13, such that where the multi-chamber internal combustion engine comprises three or more pistons the leak path of a preceding first piston in the series allows a greater proportion of cooling medium to bypass its piston body than that of a second piston that follows in the series.

17. The piston cooling system of claim 16, further comprising a tubular connector to enable the pivot shafts of adjacent pistons to operate in synchronise but at different phases of the combustion cycle while still allowing passage of cooling medium to flow along the coolant path through the full series of pistons.

18. A pivot shaft connector for use in connection with the cooling system of claim 17, wherein the connector comprises a tubular section having a first end configured and arranged to sealingly rotatably engage with the second end of one pivot shaft and a second end adapted to sealingly rotatably engage with the first end of a second pivot shaft, the connector further comprising an outwardly projecting step midway along its length to prevent over insertion in to either the second end of the first pivot shaft or the first end of the second pivot shaft.

19. The pivot shaft connector of claim 18, wherein a step locates a further seal to provide additional sealing between the opposing primary induction chambers.