GB1576926A

GB1576926A - Aircooled internal combustion engine having a spark plug well

Info

Publication number: GB1576926A
Application number: GB39623/77A
Authority: GB
Original assignee: Automobiles Peugeot SA; Automobiles Citroen SA
Current assignee: Automobiles Peugeot SA; Automobiles Citroen SA
Priority date: 1976-10-29
Filing date: 1977-09-22
Publication date: 1980-10-15
Also published as: ES462837A1; DE2745313C2; ATA713777A; DE2745313A1; SE424795B; IT1089480B; AT364200B; SE7712134L

Description

(54) AN AIR-COOLED INTERNAL COMBUSTION ENGINE HAVING A SPARK PLUG WELL (71) We, SOCIETE ANONYME AUTO MOBILES CITREON, a Company organised and existing under Articles 118 to 150 of the French Law concerning companies, of 117 to 167 Quai Andre Citroen, 75747 Paris, Cedex 15, France and AUTOMOBILES PEUGEOT, a French Body Corporate, of 75 Avenue de la Grande Armee, 75017 Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to an air-cooled internal combustion engine fitted to a vehicle, in which engine the cooling air is force-circulated through a duct adapted to direct the air on to and to cool the engine cylinder head, then to direct at least some of the heated air to the vehicle passenger compartment to heat the same, a spark plug well being disposed in such duct and serving to reduce the risk of pollution of the cooling air by a possible flow of gases from a leak between the spark p]ug and the cylinder head, the spark plug well being adapted to direct such polluting gases to atmosphere.

It is more particularly an object of the invention to improve the practical performance of spark plug wells in such engines, inter alia so that they are simple and cheap to construct and are readily adaDtable.

Accordingly the invention provides an aircooled internal combustion engine for a vehicle, in which engine the cooling air is force-circulated through a duct adapted to direct the air onto and to cool the engine cylinder head, then to direct at least some of the heated air to the vehicle passenger compartment to heat the same, a spark plug well being disposed in such duct and serving to reduce the risk of pollution of the cooling air by a possible flow of gases from a leak between the spark plug and the cylinder head, the spark plug well being adapted to direct such polluting gases to atmosphere, the spark plug well comprising a releasably fitted tubular element which is independent of the cylinder head and whose top part (as herein defined) is in free communication with atmosphere and whose bottom part (as herein defined) so co-operates with a mating surface rigidly secured to the cylinder head as to bound with the latter surface a passage narrow enough to ensure that, in the event of a leak between the spark plug and the cylinder head, the polluting gases escape mainly to atmosphere through the top part of the spark plug well, the tubular element extending through the cooling air duct and extending around the spark plug, the arrangement being such that, in the event of a leak between the spark plug and the cylinder head, for example because of the plug being loose or because of a fault in the gasket between the spark plug and the cylinder head, the gases escape to the inside of the tubular element and then to atmosphere.

In a first embodiment of the invention, a dished member is provided to co-operate with the said bottom part of the tubular element, the dished member being rigidly secured to the cylinder head by securing means independent of the spark plug, the tubular element being releasably connected by means of the dished member.

In this event, the outside surface of the dished member may form the mating surface co-operating with the inside surface of the tubular element to bound the narrow passage.

Preferably, the tubular element and the dished member are secured to one another by a bayonet fastening. The dished member is secured to the cylinder head by being force-fitted and stuck.

The top part of the tubular element is usually closed by a fitted cover providing free discharge of possible leaks to atmosphere.

The tubular element and the dished member may be made of sheet metal.

In a second embodiment of the invention resilient means are provided to apply the said bottom part of the tubular element to the mating surface of the cylinder head. the force which the resilient elements exert being sufficient to provide satisfactory sealing tight ness between the bottom part of the tubular element and the mating surface.

Advantageously, the resilient means take the form of a helical spring disposed inside the tubular element, the resilient means may bear at one end on an annular edge of the tubular element such edge bearing on a seat on the cylinder head, such seat forming the mating surface, the edge projecting radially inwards and bounding a central aperture of sufficient diameter for the spark plug to extend through it freely, the other end of the resilient means bearing on an abutment axially connected to the plug so that the reaction to the effort of the tubular element being applied to the cylinder head as exerted by the resilient means is transmitted to the securing, inter alia by screwthreading, of the spark plug to the cylinder head.

The abutment connected axially to the spark plug may be disposed on a sleeve connected thereto and may take the form inter alia of an outside shoulder of such sleeve.

The sleeve may have extending axially therethrough an electrical connection adapted to connect the spark plug to a supply cable, the connection having at the end near the spark plug a tapped recess adapted to be screwed to a screwthreaded terminal rigidly connected to the spark plug, the connection being rapidly secured to the sleeve.

Advantageously, the tubular element extends beyond an outside protuberance of the sleeve, and the end of the tubular element which is remote from the spark plug has zones which are so bent radially inwards as to engage the protuberance axially inside the tubular element.

The sleeve may be formed on its outside surface with at least one longitudinal groove as a means of communication between the inside and the outside of the tubular element and of thus forming a passage for the gases to the outside.

Co-operation between the bottom part of the tubular element and the mating surface rigidly secured to the cylinder head occurs in satisfactory conditions which help more particularly to simplify assembly and disassembly of the spark plug well while providing satisfactory sealing tightness.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectioned view of part of the cylinder head of an engine having a spark plug well in accordance with a first embodiment of the invention; Figure 2 is a section on the line Il-Il of the tubular element of the plug well; Figure 3 is a cross-section through the dished member which co-operates with the bottom part of the tubular element; and Figure 4 is a diagrammatic sectioned view showing a part of a cylinder head having a plug well according to a second embodiment of the invention.

Referring to Figure 1, there can be seen a part of a cylinder head 1 of an air-cooled internal combustion engine fitted to a vehicle. The cylinder head, which is usually a light alloy diecasting, has conventional cooling fins la. A sheet metal duct 2 extends around the engine cylinder and the cylinder head and is adapted to direct cooling air force-circulated by a blower (not shown) to the cylinder head 1 to cool the same.

Arrows F diagrammatically represent the flow of air in the duct 2 in Figure 1, The duct 2 has an extension 2a through which at least some of the cooling air which has been heated by the cylinder head can go the vehicle passenger compartment to heat the same. The duct 2 therefore separates the cooling air from the ambient air.

A spark plug 3 is engaged in the cylinder head 1 by its screwthread base 4 being screwed into a tapped aperture 5 in the cylinder head 1. The plug electrodes 3a, 3b are disposed in a combustion chamber C bounded by the cylinder head. The plug 3 extends through the duct 2 and must be accessible from the outside.

The plug is received in a spark plug well 6 which is disposed in the duct 2 and which protects the cooling air flowing therethrough from the risk of contamnation by gases coming from any leak between the spark plug base 4 and the cylinder head 1. The well 6 is adapted to direct contaminating gases to atmosphere -- i.e., to outside the duct 2. The well 6 comprises a releasably fitted tubular element 7 which is independent of the cylinder head 1 and which extends around the plug 3. The element 7 extends through an aperture 8 in the wall of duct 2; the gap between the edge of aperture 8 and the outer wall of the element 7 is so small that it is substantially impossible for the cooling air flowing through the duct 2 to escape through such gap.

As can be seen in Figure 1, the tubular element 7 in shape resembles a cylindrical surface of revolution whose diameter increases outside the duct 2. The widened top part of 7s of the element 7 - i.e., that part thereof which is remote from the cylinder head 1 - is in free communication with atmosphere by way of passages, as 9. The same are defined between a cover 10 placed on the open top end of the element 7 and the wall of the element 7. The cover 10, which is made for example of an electrically insulating material, comprises e.g. four strips or protuberances 11 which are angularly equidistant from one another, are engaged inside the element 7 and bear on the wall thereof. The strips 11 are separated by spaces defining the passages 9.The cover 10 can comprise a collar 12 which engages over the top edge of the element 7 far enough away therefrom radially to allow a free flow of the gases from inside the element 7 to the outside, as represented by arrows in Figure 1.

The cover 10 is formed at its centre with an aperture for a coaxial plug lead 13; a protective sheath 14 extends around the plug 3.

The bottom part 7b of the element 7 i.e., that part thereof which is near the cylinder head 1 - so co-operates with a mating surface 15 rigidly secrued to the cylinder head 1 as to bound with such surface a passage 16 narrow enough to ensure that, in the event of a leak between the plug 3 and the cylinder head 1, contaminating gases are removed substantially completely to atmosphere through the passages 9 at the top of the plug well.

The terms "top part 7a of the tubular element" and "bottom part 7b of the tubular element" must be understood broadly as denoting that the end of the tubular element which is remote from the cylinder head and that end of the tubular element which is near the cylinder head, respectively, for in some cases the so-called top part 7a might be below the part 7b, for instance, if the plug 3 and the element 7 were inclined to the horizontal oppositely to what is shown in the drawings.

To simplify the illustration, in Figure 1 the passage 16 is reduced to the contact between the surface 15 and the inside surface of the end 7b. In other words, leakages can discharge through the passages 9 with a much lower pressure drop than they can through the passage 16.

A dished member 17 is provided on the plug seat 18 to co-operate with the element bottom part 7b and is rigidly secured to the cvlinder head 1 by securing means independent of the plug 3; preferably, the dished member 17 is force-fitted in the seat 18 and is retained on the cylinder head 1 by sticking. Consequently, even if the plug 3 were to work loose because of vibrations, the dished member 17 would still remain rigidly secured to the cylinder head 1 and any gas leaks would occur inside the member 17 and not between the same and the cvlinder head wall. The dished member 17 is formed at its centre with an aperture 19 for the screwthreaded plug base screwable into the cvlinder head 1. Consequentlv, the member l7 is slqo clamped between the plug 3 and the cvlinder head 1.

Outside cvlindrical surface 20 of member 17 serves as the mating surface 15 and co-operates with the inside surface of the end 7b to bound the passage 16. Advantageously, the difference between the inside diameter of end 7b and the outside diameter of the member 17 is at most 0.1 mm for an average diameter which is usually of the order of from 20 to 30 mm.

The element 7 and member 17 are fastened together by a bayonet fastening.

For instance, the dished member 7 can have two outwardly projecting diammetrically opposite pins 21, as shown in Figure 3. The end 7b can be formed with two slots 22, as shown in Figure 2, which in shape are right-angled and have two parts 22a, 22b.

The part 22a is open at one end and extends in the direction of the generatrices of the tubular elements 7. The part 22b extends perpendicularly to the part 22a, so that the element 7 can be turned relative to the member 17 to engage the pins 21 in the slots 22.

The element 7 and the member 17 are made of sheet metal, and the cylinder-head fins or ribs la are arranged to present a passage for positioning the plug 3 and tubular element 7.

The foregoing description shows clearly how the element 7 is fitted to the dished member 17; the pins 21 are introduced into the slot portions 22a in the bottom of the element 7 until the pins 21 register with the parts 22b. The element 7 is then turned relative to the member 17 to engage the pins 21 in the slot parts 22b and to lock the element 7 to the dished member 17.

In the event of a leak between the plug 3 and the cylinder head 1, for instance, because of the plug working loose of because of a faulty seal between the plug and the cylinder head, the gases from the combustion chamber C discharge into the dished member 17 and into the element 7 and issue to atmosphere. Because of the narrowness of the passages 16 and of the pressure of the cooling air in the duct 2, the heated cooling air going to the passenger compartment experiences substantially no contamination by any gas leakage occurring between the cylinder head and the spark plug.

Figure 4 shows a second embodiment of the invention. Like or similar elements already described with reference to Figures 1 to 3 have the same numerical references and will not be described again.

Resilient means E are provided to apply the bottom part 7b of the element 7 to the mating surface 15. Advantazeously, the means E take the form of a helical spring 23 placed inside the element 7. The spring 23 bears at one end on an annular edge or shoulder 24 of the element 7. The shoulder 24 proiects radiallv inwards and is disposed in a plane perpendicular to the axis of the element 7. The edge 24 is rigidly connected to the bottom part 7b and bears axially on the mating or matching surface 15 embodied by a seat 25 on the cylinder head.

The edge 24 bounds a central aperture 26 of sufficient diameter for the plug 3 and its screwthreaded base 4 to pass through.

At its other end the spring 23 bears on an abutment 27 axially connected to the spark plug 3 and embodied by a shoulder on the outside surface of a sleeve 28 which is made e.g. of an electrically insulating plastics material and connected to the plug 3. Sleeve 28 can slide axially in the tubular element 7.

More particularly, the shoulder serving as abutment 27 is embodied by a transverse end surface of a protuberance 29 on the outside of the sleeve 28.

Extending axially therethrough is another electrical connector 30 formed at the end near the plug 3 with a tapped recess 31 adapted to be screwed to a screwthreaded terminal 32 rigidly connected to the plug 3.

The connection 30 comprises a proiecting outside cylindrical portion 33 which is roughened, e.g. knurled, to secure the connection 30 in the sleeve 28 so that the two latter elements are rigidly interconnected.

Consequently, screwing the connection 30 on to the plug 3 secures the connection 30 and sleeve 28 relatively to the plug 3.

Two flats or facets (not shown in the drawings) are formed on the outside surface of the'sleeve 28 so that the same can be rotated by a tool, such as a spanner, to tighten the stem or rod 32 in the aperture 31. The sleeve 28 has an extension 28a which engages inside the convolutions of the spring 23 and which extends around a part of the plug 3. The connection end 30a remote from the plug 3 is devised conventionally for the connection of a coaxial plug lead 13.

In the part remote from the plug 3 the tubular element 7 extends beyond the protuberance 29; the end forming the top part 7a has zones formed by strips 34 which are bent radially inwards so as to secure the protuberance 29 inside the element 7. Four strips 34 may be provided, for instance, and are distributed regularly around the circumference and separated from one another by gaps via which the inside of the element 7 can communicate with atmosphere.

To improve this communication between the inside of the element 7 and the outside so as to facilitate the escape of gases coming from a possible leak at the plug 3. the outside surface of the sleeve 28 is, formed with at least one longitudinal groove 35 long enough to extend from the inside of the element 7 to the outside so as to provide a passage for the gases even when the sleeve 28 is, as shown in, the drawing. in its position of maximum penetration in the element 7.

The strips 34 are bent after the protuberance 29 of the sleeve 28 has been introduced into the tubular element 7.

The assembly, operation and disassembly of the spark plug well acording to the second embodiment are as follows: When the well has been assembled -- i.e.

when the spring 23 has been introduced into the tubular element 7 and the protuberance 29 has been secured therein after the strips 34 have been bent - the well is ready to be placed on the spark plug 3. The same is screwed into the cylinder head 1 completely independently of the well; more particularly sealing tightness between the spark plug 3 and the cylinder head 1 requires the use of no part of the plug well, as is also the case in the first embodiment.

To position the plug well on the plug 3, the tubular element 7 is slid through the aperture 8 and the bottom part of the plug 3 is introduced into the central aperture 26 in element 7; part of the plug is surrounded by the convolutions of the spring 23. The sleeve 28 is then pushed so as to slide towards the plug 3 and compress the spring 23 and move the tapped hole 31 on to the screwthreaded end 32 of the plug 3. The sleeve 28 is then turned in the appropriate direction for screwing the hole 31 and rod screwthreaded end 32 together, the screwing being associated with further compression of the spring 23. The compressive force of the spring 23 engages the edge 24 with the cylinder-head surface 15. The compression is sufficient to provide satisfactory sealing tightness between the edge 24 and the surface 15.

The reaction to the latter compression is transmitted to the sleeve 28 and therefore to the connection 30 rigidly secured thereto.

The reaction is taken up by the plug 3 and transmitted to the screwthreaded connection between the plug base 4 and the cylinder head 1.

In the event of a gas leak occurring between the plug 3 and the head 1 in operation, the gases escape towards the inside of element 7 and then to atmosphere through the aperture in the top end 7a and by way of the or each groove 35. The sealing tights ness between the edge 24 and the surface 15 is sufficient to prevent contaminating gases from entering the duct 2.

The plug well can be disassembled readily.

All that is necessary is to disconnect the lead 13 from the end 30a, then to unscrew the sleeve. 28 from the end 32 by turning the sleeve 28 in the opposite direction to that required for assembly. The spring 23 gradually slackens and the system comprising the tubular element, sleeve 28, spring 23 and the connection 30 is withdrawn from the plug 3. A spanner can then be introduced to unscrew and remove the plug 3.-.

Should the plug 3 loosen accidentally, thus giving rise to a gas leak, the edge 24 remains in an adequately sealing-tight engagement with the surface 15 because of the spring 23.

The invention helps to seal off the inside of the tubular element 7 satisfactorily from the duct 2.

Assembly and disassembly of the spark plug well are simple. The external size is limited to the diameter of the. element 7.

WHAT WE CLAIM IS:- 1. An air-cooled internal combustion engine for a vehicle, in which engine the cooling air is force-circulated through a duct adapted to direct the air on to and to cool the engine cylinder head, then to direct at least some of the heated air to the vehicle passenger compartment to heat the same, a spark plug well being disposed in such duct and serving to reduce the risk of pollution of the cooling air by a possible flow of gases from a leak between the spark plug and the cylinder head, the spark plug well being adapted to direct such polluting gases to atmosphere, the spark plug well comprising a releasably fitted tubular element which is independent of the cylinder head and whose top part (as herein defined) is in free communication with atmosphere and whose bottom part (as herein defined) so co-operates with a mating surface rigidly secured to the cylinder head as to bound with the latter surface a passage narrow enough to ensure that, in the event of a leak between the spark plug and the cylinder head, the polluting gases escape mainly to atmosphere through the top part of the spark plug well, the tubular element extending through the cooling air duct and extending around the spark plug, the arrangement being such that, in the event of a leak between the spark plug and the cylinder head, for example because of the plug being loose of because of a fault in the gasket between the spark plug and the cylinder head, the gases escape to the inside of the tubular element and then to atmosphere.

2. An engine according to claim 1, comprising a dished member adapted to cooperate with the said bottom part of the tubular element, the dished member being rigidly secured to the cylinder head by securing means independent of the spark plug, the tubular element being releasably connected to the dished member.

3. An engine according to claim 2, in which the outside surface of the dished member forms the mating surface co-operating with the inside surface of the tubular element to bound the narrow passage.

4. An engine according to claim 2 or 3 in which the dished member is secured to the cylinder head by being force-fitted and stuck.

5. An engine according to any one. of claims 2 to 4, characterised in that a bayo net fastening is provided between the tubular element and the dished member.

6. An engine according to claim 3 or according to claim 4 of 5 when appendant to claim 3, in which the difference between the inside diameter of the tubular element and the outside diameter of the dished mem- ber is at most 0.1 mm.

7. An engine according to any preceding claim, in which the tubular element is provided at the top with a fitted cover allowing unrestricted . removal of possible leaks to atmosphere.

8. An engine according to claim 1, in which resilient means are provided to apply the said bottom.part of the tubular element to the mating surface of the cylinder head, the force which the resilient elements exert being sufficient to provide satisfactory sealing tightness between the bottom part of the tubular element and the mating surface 9. An engine according to claim 8, in which the resilient means take the form of a helical spring disposed inside the tubular element.

10. An engine according to claim 8 or 9, in which the resilient means bear at one end on an annular edge of the tubular element, such edge bearing on a seat on the cylinder head, such seat forming the mating surface, the edge projecting radially inwards and bounding a central aperture of sufficient diameter for the spark plug to extend through it freely, the other end of the resilient means bearing on an abutment axially connected to the plug so that the reaction to the effort of the tubular element being applied to the cylinder head as exerted by the resilient means is transmitted to the securing, for example by screwthreading, of the spark plug to the cylinder head.

11. An engine according to claim 10, in which the abutment connected axially to the spark plug is disposed on a sleeve connected thereto and takes the form, for example of an outside shoulder of such sleeve.

12. An engine acording to claim 11, in which the sleeve has extending axially therethrough an electrical connection adapted to connect the spark plug to a supply cable, the connection having at the end near the spark plug a tapped recess adapted to be screwed to a screwthreaded terminal rigidly connected to the spark plug, the connection being rigidly secured to the sleeve.

13. An engine according to claim 11 or 12, the tubular element extends beyond an outside protuberance of the sleeve, and the end of the tubular element which is remote from the spark plug has zones which are so bent radially inwards as to engage the protuberance axially inside the tubular element.

14. An engine according to any one of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. thus giving rise to a gas leak, the edge 24 remains in an adequately sealing-tight engagement with the surface 15 because of the spring 23. The invention helps to seal off the inside of the tubular element 7 satisfactorily from the duct 2. Assembly and disassembly of the spark plug well are simple. The external size is limited to the diameter of the. element 7. WHAT WE CLAIM IS:-

1. An air-cooled internal combustion engine for a vehicle, in which engine the cooling air is force-circulated through a duct adapted to direct the air on to and to cool the engine cylinder head, then to direct at least some of the heated air to the vehicle passenger compartment to heat the same, a spark plug well being disposed in such duct and serving to reduce the risk of pollution of the cooling air by a possible flow of gases from a leak between the spark plug and the cylinder head, the spark plug well being adapted to direct such polluting gases to atmosphere, the spark plug well comprising a releasably fitted tubular element which is independent of the cylinder head and whose top part (as herein defined) is in free communication with atmosphere and whose bottom part (as herein defined) so co-operates with a mating surface rigidly secured to the cylinder head as to bound with the latter surface a passage narrow enough to ensure that, in the event of a leak between the spark plug and the cylinder head, the polluting gases escape mainly to atmosphere through the top part of the spark plug well, the tubular element extending through the cooling air duct and extending around the spark plug, the arrangement being such that, in the event of a leak between the spark plug and the cylinder head, for example because of the plug being loose of because of a fault in the gasket between the spark plug and the cylinder head, the gases escape to the inside of the tubular element and then to atmosphere.

8. An engine according to claim 1, in which resilient means are provided to apply the said bottom.part of the tubular element to the mating surface of the cylinder head, the force which the resilient elements exert being sufficient to provide satisfactory sealing tightness between the bottom part of the tubular element and the mating surface

9. An engine according to claim 8, in which the resilient means take the form of a helical spring disposed inside the tubular element.

14. An engine according to any one of

claims 11 to 13, in which the sleeve. is for rued on its outside surface with at least one longitudinal groove as a means of communication between the inside and the outside of the.tubular element and thus as a passage for the gases to the outside.

15. - An engine according to claim 12 or according to claim 13 or 14 when appen claim to claim 12, in which the electrical con nection which extends through the sleeve comprises an putside projecting cylindrical part, Which anchors the connection inside the sleeve;

i6. An engine according to any one of claims 11 td 15, in which the sleeve is made of an insulating material, for example a plastics material.

17. An engine according to any preceding claim, in which the tubular element and/ or the dished member are made of sheet metal. -

18. An air-cooled internal combustion engine substantially - as hereinbefore described with reference to and as illustrated in Figures 1 to .3 of the accompanying drawings.

19. An air-cooled internal combustion engine substantially as hereinbefore described with reference to and as illustrated in Figure 4 of the accompanying drawings.