GB2350864A - Containment and support assembly, eg for an engine or gearbox, with a rigid framework and lower density outer casing - Google Patents

Abstract

The containment and support assembly consists of a rigid open structural framework, on which the components of a mechanical engineering apparatus are supported, and an outer casing fabricated from a lower density material to contain the apparatus to contain fluids or attenuate noise or thermal emissions. The mechanical engineering apparatus may be an engine cylinder block which cast without non-structural enclosures, enclosed cavities being formed instead by specific skin mouldings. For example, a coolant jacket 11 may be formed using pre-formed skins 12 produced by eg vacuum moulding ABS resin. A crankcase skin 22 may also be provided by sheet moulding. The structural unit complete with skin mouldings 12, 22 is then placed into a mould 30a, 30b and a low-density plastics encapsulant 31, eg a multi-component liquid foam, is poured or injected into the mould. The result is a composite metallic structural skeleton encapsulated in a low-density plastics body. The encapsulant may contain a reinforcing mesh 35. The invention may be applied to a gearbox (fig.4).

Description

2350864 Encapsulated Apparatus and Method of Manufacture The present

invention relates to a containment and support assembly for a mechanical engineering apparatus, in particular an assembly with a structural function and which is required to comprise an enclosure, for example to contain fluids or attenuate noise or thermal emissions.

The invention also relates to a method of containment of such an apparatus.

Many conventional engineering components and assemblies are structurally inefficient due to constraints imposed by manufacturing and other practical limitations. In a conventional engineering containment and support assembly such as an engine cylinder block or a gearbox casing, the same base material provides the structural and enclosure functions and this can lead to the disadvantages related below.

If the apparatus is a casting, the wall thickness is often determined by the technical limits of casting manufacturing processes, say 4 to 5 mm for sand castings. Highly stressed regions of the structure will need to be heavy sections and the adjacent walls will need to maintain a section size that will permit adequate metal flow.

2 If the apparatus is a fabrication, the welding of heavy frame sections to lighter panel sections creates a mismatch at the weld zone. Further, lighter welded sections may vibrate more than desired. Further still, the sealing efficiency of a fabricated apparatus between the frame and panels may not be adequate if the weld seam alone forms the seal.

Castings are often specified in place of fabrications due to the need to provide for flat-machined flanges which can be readily sealed. If the enclosure function could be removed, the structural load path through many apparatus could be reduced to a minimum and thus accommodated by a relatively simple fabricated frame made from beam sections or by a relatively simple casting.

A further consideration with many engineering structures is the level of noise emission. In many situations, environmental considerations create a pressure for reduction in noise emissions. Such considerations apply to, for example, the cylinder block of an internal combustion engine. A conventional cast metal engine cylinder block is relatively inefficient in attenuating the noise produced within the engine, and a cylinder block design which enhances noise attenuation is generally desirable.

3 A yet further problem in internal combustion engines is the need for thermal retention after coldstarting and in cold ambient conditions. A reduction in uncontrolled thermal losses from the engine cylinder block would assist a fast warm-up and thus would not only reduce the time for exhaust catalytic converters and in-vehicle air heating systems to commence operation but would also bring the engine up to its most fuel-efficient operating temperature in a shorter t ime.

There is further scope for improvements in mechanical engineering structural apparatus in reducing manufacturing costs and providing exterior profiles which are more aesthetically pleasing and more resistant to dirt entrapment.

Encapsulation of mechanical engineering structural apparatus, with the encapsulant providing the enclosure functions to a substantial extent, is proposed as an effective means to overcome each and all of the forementioned problems.

It is an object of the present invention to provide a containment and structural support assembly for a mechanical engineering apparatus with a relatively low mass encapsulation means to enclose fluids within the assembly, or to attenuate noise emissions or thermal emissions from the apparatus.

4 It is a further object to provide a method for containing and structurally supporting a mechanical engineering apparatus so as to provide a containment which is relatively rigid with a relatively low mass and which may efficiently enclose fluids and attenuate noise and thermal emissions.

Thus according to the present invention, a containment and support assembly for a mechanical engineering apparatus comprises a generally rigid open structural framework, provided with mounting means for engagement with components of a mechanical engineering apparatus such as to provide structural support for a mechanical engineering apparatus mounted thereon7 and an outer casing fabricated from a lower density material which co-operates with the framework to def ine and at least substantially enclose a volume in which the mechanical engineering apparatus is contained when mounted upon the framework.

In accordance with the invention, the structural framework provides substantially all of the mechanical strength required to support the mechanical engineering apparatus in use. The outer casing contributes little to the structural strength of the overall assembly, and instead performs the bulk of the enclosure and containment function, i.e. to contain, for example, a coolant or lubricant, to provide some form of noise or thermal insulation, or similar function.

In consequence, material selection for both the framework and the outer casing can concentrate on the specific requirements of these respective roles. In particular, the outer casing can be manufactured from a substantially lower density material than the framework, since it has little or no role in contributing to the overall strength of the assembly. The outer casing, and hence the overall assembly, can therefore be much lighter than would be the case for conventionally manufactured apparatus of this type. For example, the framework may of a relatively high density metallic material, and may be a casting. The casing may be a low density plastics or composite material, and may be a moulding. Significant potential weight advantages are offered compared with structures in which the casing is also a casting, and also compared with fabricated structures.

The outer casing may be a multi-component construction, comprising one or more relatively rigid inner wall elements which engage upon the framework to define internal volume(s) within the assembly for receipt of components of the mechanical engineering apparatus, over which a casing body of suitable light weight low density material is fitted.

6 The invention is particularly suited to embodiments where the apparatus is an internal combustion engine and the assembly comprises an engine cylinder block, or where the apparatus is a gear box and the assembly comprises a gear 5 box casing.

In accordance with a further aspect of the invention, a method for containing and structurally supporting a mechanical engineering apparatus comprises: providing a generally rigid open structural framework; engaging components of the mechanical engineering apparatus on mounting means provided upon the framework, such that the framework provides structural support for the mechanical engineering apparatus mounted thereon; applying an outer casing of lower density material to the framework which cooperates with the framework to define and at least substantially enclose a volume in which the mechanical engineering apparatus is mounted.

The outer casing is conveniently applied by a moulding process in which the outer casing is moulded around the assembled framework. Preferably, accessories, such as sensors and monitors with accompanying cables, fluid conduits, wiring harnesses etc may be mounted upon the 2S framework prior to the step in which the outer casing is applied.

7 In a preferred refinement of the process, cavities within the assembly are fabricated in a two stage process in which one or more relatively rigid preformed skin elements are first attached to the framework to define suitable volumes, and the body of casing is subsequently assembled therearound, for example by moulding.

The body of the casing preferably comprises a low density plastics material which is preferably poured or injected to a mould containing the framework and other elements as applicable, and fills the remaining mould cavity to complete the encapsulation.

In accordance with the apparatus and method of the present invention, the outer casing has no structural function during routine operation of the mechanical engineering apparatus. Nevertheless, it serves a containment function, which may place some material requirements in relation to strength and toughness on the material selection for the outer casing, and the invention is not intended to exclude this. In particular, where the outer casing of an engineering apparatus is required to provide a high degree of containment, for example to cope with the impact of components subsequent to failure of the apparatus, it may be necessary to incorporate a higher strength layer within or attached to a surface of the outer casing. This higher strength layer may comprise a mesh or netting such as a wire mesh. Equally, it may be desirable to incorporate 8 within or attach to a surface of the outer casing a layer of material with specifically tailored properties for other environmental or aesthetic considerations.

Further preferred features of the apparatus and method of the invention will readily understood from the description of specific embodiments thereof in relation to an engine cylinder block and a gear box casing, and to a specific method of manufacture, as set out hereinbelow. 10 By way of example, the invention will be described with reference to the accompanying drawings, of which:Figure 1 is a cross- sectional end view through a 15 structural part of an engine encapsulated prior to general engine assembly in accordance with first and second embodiments of the present invention; Figure 2 is a longitudinal cross- sectional view through the encapsulated structural part of the engine 20 of figure 1; Figure 3 is a cross-sectional end view through a partassembled engine encapsulated in accordance with a third embodiment of the invention; Figures 4a and 4b are respectively isometric and 25 cross-sectional views through a gearbox apparatus encapsulated subsequent to assembly in accordance with a fourth embodiment of the invention.

9 Referring to the drawings, f igures 1 and 2 show a structural unit, in the form of a cylinder block which will subsequently form part of an internal combustion engine (not shown), encapsulated in a plastic f oam matrix (encapsulant) in a manner to be described and in accordance with the present invention.

The cylinder block is cast to include one or more cylinder barrels 1, a top deck 2 to provide a mounting site for attaching a cylinder head (not shown), a coolant jacket flange 3, a crankshaft upper main bearing housing 4 and a crankcase 5. The crankcase 5 includes bearer facings 6 for attaching engine mountings (not shown) and a peripheral lower flange 7 for attaching a lubricating oil sump (not shown).

The cylinder block is cast as a structural unit devoid of any enclosures other than where these also have a structural function. For example, there are no cast external coolant jackets and the crankcase 5 is provided as an open casting unlike conventional crankcase castings which have a generally enclosing function. Thus, the crankcase casting provides the structural support function, and is equipped with mountings (eg. 6, 7) to this end, but excess cast material is not wasted on non-structural enclosures.

Enclosed cavities are rather formed by the placement or bonding of specific skin mouldings. In the present example, a coolant jacket 11 is formed by suitably locating pre-formed skins 12 to define volumes between the skins and the cylinder barrel 1. The skins may be produced by a sheet moulding process, such as vacuum moulding, from a suitable thermoplastic resin such as ABS.

At least one of the coolant gallery skins may include a blind coolant connection. Such a connection 13 is shown in Figure 1. The connection in this example is reinforced with a sleeve 14 and may be pierced following the subsequent encapsulation process (described below). If the encapsulant is subsequently introduced to cover an end of the coolant connection or other conduit, a hole can be bored through the encapsulant and skin to connect with the coolant jacket.

In the embodiment shown an oil pressure rail 16 is bonded into a groove 17 in a wall of the cylinder block and further components may similarly be positioned relative to the cylinder block before encapsulation. Examples are shown in Figure 1. A sensor unit 18 is bonded to the cylinder block with its connecting electrical cables 19 spaced apart from the cylinder block. A coolant conduit 21 is positioned adjacent to but spaced apart from the coolant jacket skin 12. Other components such as wiring harnesses, pipes, etc., may be included within the subsequent encapsulant both for a low cost and load distributing support and to provide an aesthetically clean-looking external appearance.

A crankcase skin 22 is provided which may be formed by a sheet moulding process in a similar manner to the coolant jacket skin 12. The crankcase skin 22 defines a crankcase volume 23 from which it is desired to exclude encapsulant and provides a harder skin surface than the encapsulant. The crankcase skin may include stub pipes. Such pipes 24 are provided in the embodiment of Figure 1 to which are attached a breather tube 25 and a dipstick tube 26. In the figure, the dipstick tube 26 has been fitted with a temporary plug 27 to prevent encapsulant intrusion during the encapsulation stage (described below).

The structural unit assembly complete with skin mouldings 12, 22 is placed into a mould which, in the given example, is split vertically into mould halves 30a, 30b and has a mould cavity shaped to the required external shape of the encapsulated assembly. In this example, the shape of the mould cavity will permit the encapsulant 31 to generally enclose the structural unit assembly but will exclude the encapsulant from the interior volume of the unit, the upper f ace of the top deck 2 and the engine bearer f acings 6.

12 The encapsulant 31, a low-density plastic material, is poured or injected into the mould 30a, 30b to fill the remaining mould cavity. The result is a composite of a metallic structural skeleton and its accessories encapsulated within a low-density plastic body. The plastic body provides an enclosure and sealing function.

The size and thermal inertia of the cast cylinder block will largely determine the selection of the low-density plastic material and the process specification. The selection will also depend upon the required function of the encapsulant, whether it be mainly an enclosure and interface seal or whether it will be required to possess specific noise and thermal attenuation properties.

Large components such as the cylinder block of the present example would be encapsulated within a multi-component liquid foam thermosetting plastic matrix. The thermal inertia and size of the component in this case prohibits conventional thermoplastic injection moulding. Multicomponent liquid foam plastic processing involves pouring or injecting a chemical mixture into a mould where it reacts and expands to fill the mould cavity with thermosetting cellular plastic. Foams are blown with a gas such as CO, generated by the chemical action or by volatile liquids which are vaporised by the heat of reaction. Moulding pressures are low, typically 2 bar, permitting light and low-cost mould construction.

13 Several resin systems can be employed, such as Polyurethane, Polyisocyanurate, Carbodiimide, Polyester and Silicone, but the Phenolic resin family is of most interest for automotive type components due to low cost and high temperature performance. Phenolic foams can have a specific gravity in excess of 1 down to 0, 13 and can be toughened as well as reinforced with glass and other fibres. It is possible to include elastomeric nodules within the foam matrix which improves noise attenuation.

As the foam expands within the mould cavity, it for-ms an intimate bond with the skeletal metal structure. Since some plastics utilise acidic catalysts, it may be necessary to pre-treat and protect the metal skeleton with a surface that promotes bonding with the foam. The differential expansion rates between the metal skeleton and the foam are accommodated by the relative flexibility of the foam.

In some cases, material performance improves during the curing process, which can be quite prolonged, perhaps up to 24 hours, and it may thus be important not to disturb the process. In order to produce a reasonable throughput, it may be necessary to have multiple moulding boxes, the expenditure on which will be relatively low due to the simple and lightweight nature of the moulding equipment.

14 Some foam encapsulations and processes can produce a closed cell skin forming surface which is preferable since the friable nature of open cell surfaces may lead to particle break-off and contamination. However, the robustness of skin surfaces may be inadequate for some critical surfaces, in which case it may be helpful to introduce pre-formed plastic skins (not shown) into the mould cavity, the skins being of a construction similar to the coolant jacket and crankcase skins described above. Due to the low processing pressures involved, it is possible to place the moulded skins between the skeleton structure and the mould walls, thus the outside form or shape of the finished moulding will be that of the skin f orm or shape. In this way, undercut features may be produced without the need for is complex moulds with loose pieces or moving walls.

The foam plastic encapsulant will reduce radiated noise.

Noise attenuation may be improved by special foam formulations employing elastomeric components. The encapsulant will also reduce thermal emissions, advantage of which can be taken in obtaining a f aster warm-up of the built engine (not shown) in operation, particularly with regard to early exhaust catalyst and vehicle internal heater operation. Thermal insulation of the structural unit of the engine may also be of benef it where users of the built engines in operation may be in close proximity.

The strength and impact resistance of the foam plastic encapsulant may not be sufficient where the walls of an engineering apparatus are required to provide a high degree of containment. For instance, in the engine of the present example, highly stressed dynamic or reciprocating components may break during operation and impact the encapsulant. The embodiment of Figure 1 includes an optional additional feature to mitigate this, in the form of provision within the encapsulant of a mesh 35 of preferably, but not restrictively, metal in either expanded or wire form. This provides a degree of containment. The mesh will be in some respects better than a solid cast metal in this regard since it will tend to dissipate energy by deformation / elongation and may retain the broken component, whereas a cast wall may fracture, permitting the broken component to escape and produce a hole for fluids to follow. The advantages of a deformable structure also apply to external impacts.

Nevertheless, the mesh 35 has no structural function in the sense of contributing to the structural strength of the cylinder block in its role as a support means for the engine component, and the mesh need not add unduly to the overall weight of the encapsulating part of the assembly.

The mesh may further provide support to the encapsulant 31 both during the mould filling process and against applied dynamic and pressure loads. For instance, it may indirectly 16 support the coolant jacket skin 12 against the load resulting from pressurisation of the overall coolant system (not shown).

In a further embodiment, with reference to figure 3, the engine is partly built-up before encapsulation to include, in this example, a crankshaft 40, pistons 41 and connecting rods 42. The required mechanical components and skins having been assembled to the structural unit, the unit is encapsulated in a similar manner to that described for the earlier embodiment by addition of encapsulation 48.

Engine covers may be partly or fully included within the encapsulation, an example being a sump 43 as shown. In this example, after placing the crankcase skin 44 in position with a flange of the crankcase skin 45 overlapping the crankcase lower flange 46, the sump flange 47 of the sump 43 is secured to the crankcase lower flange 46 by conventional means (not shown). The mould cavity may be shaped to permit the encapsulant 48 to generally enclose the sump to crankcase flanges 46, 47 as shown in the example figure. Alternatively (not shown) the encapsulant may enclose the whole of the sump. There may be no need to provide machined flanges since the encapsulant will provide a sealing function equivalent to, or better than, conventional flanged joints.

17 A cylinder head (not shown) may be attached to the top deck subsequent to the encapsulation process. It would be possible to attach the cylinder head before encapsulation but encapsulation of the cylinder head could lead to difficulties in carrying out routine servicing where this might include, for instance, checking and adjusting valve clearances. Difficulties could also arise in respect of the high temperatures that a cylinder head can reach and the effect these may have on the encapsulant.

The embodiment as described in which the engine is partly built up before encapsulation may be particularly relevant where the engine is configured to be non- serviceable; for example a low cost unit for which it would not be economical to extend the design life by remanufacture and which would not therefore require access to internal components subsequent to engine manufacture.

In a further embodiment, the foam encapsulation concept is adapted for application to power transmission assemblies, for example a gearbox as shown in figure 4. In this example, an open rigid structural frame 50 is provided with shafts 51 carrying gears 52. The open nature of the f rame 50 may significantly improve access for assembly of the gearbox when compared with conventional cast enclosures.

Following assembly of the gears 52 and shafts 51 into the gearbox, the frame is provided with enclosure by encapsulation 53, with a skin 54 defining an enclosed 18 cavity 55 from which the encapsulant is to be excluded, and the encapsulation 53 then being created by pouring or injecting into the cavity defined by a mould 56 in general accordance with the process and materials described in 5 respect of the foregoing embodiments.

Incorporation of complete assemblies within a plastic foam encapsulant, either self-skinning or with separate moulded skins, may allow the replacement of additional covers in machinery or vehicle installations with, if required, external surfaces custom designed to integrate with other parts of the machine or vehicle. The low cost of tooling would make this economic for low batch quantities.

The present invention has been described by example for engines and gearboxes but may be applied to other engineering structures.

19

Claims (20)

1. A containment and support assembly for a mechanical engineering apparatus comprises a generally rigid open structural framework, provided with means for engagement with components of a mechanical engineering apparatus such as to provide structural support for a mechanical engineering apparatus so engaged; and an outer casing fabricated from a lower density material which co- operates with the framework to define and at least substantially enclose a volume in which the mechanical engineering apparatus is contained when engaged with the framework.

2. An assembly in accordance with claim 1 wherein the framework comprises a relatively high density metallic material.

3. An assembly in accordance with claim 2 wherein the framework is a casting.

4. An assembly in accordance with any preceding claim wherein the casing comprises a low density plastics or composite material.

5. An assembly in accordance with claim 4 wherein the casing is a moulding.

6. An assembly in accordance with any preceding claim, wherein the outer casing comprises a multi-component construction, comprising one or more relatively rigid inner wall elements which engage upon the framework to define at least one internal volume within the assembly for receipt of components of the mechanical engineering apparatus, over which a casing body of light weight low density material is f itted.

7. An assembly in accordance with any preceding claim, wherein the apparatus comprises part of an internal combustion engine and the assembly comprises an engine cylinder block.

8. An assembly in accordance with any one of claims 1 to 6 wherein the apparatus comprises a gear train and the assembly comprises a gear box casing.

9. An assembly in accordance with any preceding claim wherein a higher strength layer is incorporated within or attached to a surface of the outer casing.

10. An assembly in accordance with claim 9 wherein the higher strength layer comprises a wire mesh.

11. A method for containing and structurally supporting a mechanical engineering apparatus comprises: providing a generally rigid open structural framework; engaging components of the mechanical engineering apparatus on means provided upon the framework, such that the framework 21 provides structural support for the mechanical engineering apparatus so engaged; applying an outer casing of lower density material to the framework which co-operates with the framework to define and at least substantially enclose a volume in which the mechanical engineering apparatus is contained.

12. A method in accordance with claim 11 wherein accessories, such as sensors and monitors with accompanying cables, fluid conduits, wiring harnesses etc are mounted upon the framework prior to the step in which the outer casing is applied.

13. A method in accordance with claims 11 or claim 12 is wherein cavities within the assembly are fabricated in a two stage process in which one or more relatively rigid preformed skin elements are first attached to the framework to define suitable volumes, and the body of casing is subsequently assembled therearound.

14. A method in accordance with any one of claims 11 to 13 wherein the outer casing is applied by a moulding process in which the outer casing is moulded around the assembled framework.

15. A method in accordance with any claim 9 to 14 wherein the body of the casing comprises a low density plastics material which is poured or injected into a mould 22 containing the framework and fills the remaining mould cavity to complete the encapsulation.

16. A method in accordance with any of claims 11 to 15 wherein the framework is cast from a relatively high density metallic material.

17. A method in accordance with any one of claims 11 to 16 further comprising the step of incorporating a higher strength layer within or attaching a higher strength layer to a surface of the outer casing.

18. A method in accordance with claim 17 wherein the higher strength layer comprises a wire mesh.

is

19. A containment and support assembly for a mechanical engineering apparatus substantially as hereinbefore described with reference to the accompanying drawings.

20. A method for containing and structurally supporting a mechanical engineering apparatus substantially as hereinbefore described with reference to the accompanying drawings.