GB2458600A

GB2458600A - Four-cylinder, four-stroke boxer configuration i.c. engine

Info

Publication number: GB2458600A
Application number: GB0912163A
Authority: GB
Inventors: Jean-Pierre Pirault
Original assignee: Southwest Research Institute SwRI
Current assignee: Southwest Research Institute SwRI
Priority date: 2005-05-25
Filing date: 2005-05-25
Publication date: 2009-09-30
Anticipated expiration: 2025-05-25
Also published as: GB2426550B; GB2426550A; GB0510624D0; GB0912163D0; GB2458600B

Abstract

A four-cylinder, four-stroke boxer configuration i.c. engine has a single-piece crankshaft supported on four main bearings and its two intermediate connecting rods are connected to crankpins 2d and 3d that share a common axis and are separated by a member to which a balance mass 23g is attached. The arrangement is intended to enable favourable compression ignition and spark ignition combustion system bore/strokes to be used, with compact cylinder spacing and simplified crankshaft configurations compared to state of art boxer configurations. The connecting rod big-end bearings on each crankpin may either be supplied with oil via drillings connected to the main bearing oil grooves, these drillings exiting on the main journal surfaces, or the connecting rod bearings on each crankpin and all main bearings may be supplied with oil via a series of drillings connected to an oil supply at one end of the crankshaft.

Description

Improvements to 4 Cylinder 4-stroke Boxer Configuration Engines

Field of the invention

The invention relates to the crankshaft proportions and cylinder spacing of 4 cylinder 4-stroke "boxer" configuration internal combustion engines, ie engines having 4 pistons and connecting rods attached to one crankshaft, the pistons and connecting rods being arranged in 2 cylinder banks that are disposed at 180 degrees to each other. Each cylinder bank has 2 pistons and connecting rods.

Background

State of art, spark ignited, gasoline combustion boxer engine configurations usually favour piston bore/stroke ratios which are greater than unity, ie greater than 1.0, so that there is adequate space to have reasonably proportioned crankshaft webs, crankpins and main bearings, whilst there is still adequate space for coolant between the cylinder bores. Even with bore/stroke ratios greater than 1.0, crankshaft proportions can be marginal.

Diesel engines usually operate at much higher cylinder pressures than gasoline engines, and the crank loadings become unacceptable with bore/stroke values greater than 1.0, this being particularly the case with boxer configurations. However, if more favourable diesel bore/strokes are used, ie less than 1.0, in order to limit the firing loads on the crankshaft structure and bearings by reducing the piston area, the axial space for the crankpins, crankwebs and main journals reduces almost as rapidly as the bore size reduction, or else the engine length becomes dominated by the required length of these crank elements, and the space between adjacent cylinder bores on each bank becomes too large.

This invention proposes an arrangement of the aforementioned boxer configuration that enables favourable diesel bore/strokes to be used, with compact cylinder spacing and simplified crankshaft configurations compared to the previously described state of art boxer configurations.

Prior Art

GB Patent number 897,648, Salzmann, 1958, discloses an air cooled four cylinder engine in which the cylinders are arranged in the form of a letter X when viewed along the axis of the crankshaft. The engine has, in effect, two banks of two cylinders in which the axes of adjacent cylinders in each bank are not parallel to each other. This provides a compact design with features appropriate to air cooling.

In one embodiment, the crankshaft design disclosed has three crankpins shared by four connecting rods. The centre two connecting rods share one crankpin and the two outer connecting rods run on individual crankpins.

The present invention combines the use of a similar crankshaft arrangement with a four cylinder, water cooled, Boxer type engine facilitating reduced cylinder spacing especially, but not exclusively, for use with diesel combustion systems.

Patent DE 3210088 Al, Klaue, 1982, discloses a four cylinder boxer configuration engine with a crankshaft that is assembled from several separate sections allowing the use of a combined balance weight and bearing arrangement. The crankshaft disclosed has the two intermediate connecting rods running on a substantially x1 common crankpin. The current invention uses a single piece crankshaft (one in which the main journals, the crankpins and connecting webs are manufactured from a single casting or forging) with the two intermediate connecting rods running on a common crankpin. A single piece crankshaft is appropnate for the types of engine which are the subject of this invention conferring benefits of reduced weight, ease of manufacture and reduced friction

Summary of the invention

The broadest aspect of the invention comprises a four cylinder, four stroke internal combustion engine of the boxer configuration containing a single piece crankshaft, supported on four main bearings, in which said crankshaft is connected to four connecting rods by means of crankpins characterised in that the two intermediate connecting rods share a single crankpin.

This invention is described, with various embodiments, in the following figures and text.

Brief Description of Figures

Fig.ia is a perspective diagram of a 4 cylinder state of art boxer crankshaft and piston layout Fig. lb is a plan view diagram of a 4 cylinder state of art boxer crankshaft and piston layout.

Fig.2a is a perspective diagram of a 4 cylinder according to the proposed invention, showing the crankshaft and piston layout.

Fig.2b is a plan view diagram of a 4 cylinder according to the proposed invention, showing the crankshaft and piston layout.

Fig.3 is a perspective diagram of a second embodiment to the proposed invention, showing the crankshaft and piston layout.

Fig.4 is a plan view of another embodiment of the invention, showing an alternative crankshaft lubrication system.

Detailed Description of the Preferred Embodiments

With reference to Figs. 1 a and 1 b, which show the elements and relative position of a state of art 4 cylinder 4-stroke boxer engine, 1, 2, 3 and 4 are the axes of piston oscillation, with pistons la and 3a forming the pistons of one cylinder bank, whilst 2a and 4a are the pistons of the other cylinder bank. Pistons 2 and 3 are referred to as the intermediate pistons. Similarly, the connecting rods connected to pistons 2 and 3 are referred to as the intermediate connecting rods. Piston 1 a is connected via the small end ig and big end ic of the connecting rod lb to the crankpin id, which is rigidly linked to crankwebs le and if, these crankwebs themselves being rigidly connected to main bearings lh and 2h respectively, the elements Id, le and If usually being referred to as a ucrank throw". The remaining pistons 2a, 3a and 4a are similarly joined to their respective crankpins 2d, 3d and 4d respectively through the connecting rods 2b, 3b and the connecting rod for the fourth cylinder; this being omitted from the Figures in order to make the crankpin 4d more visible, as the other crankpins are not visible. It will also be noted that there are main bearings either side of all crankpins, ie lh, 2h, 3h, 4h and 5h. As the engine length is governed by the individual lengths of the crank elements ih, if, Id, le, 2h, 2f, 2d etc, there is usually a great effort made to minimise these lengths by using high grade crankshaft materials or limiting the loadings on the crankpin from the gas firing pressures acting on the piston crown, and the inertia forces of the reciprocating and rotating masses of the pistons, connecting rods and crankshaft. On the other hand, it is not good practice to allow large spacing between the cylinder bores of adjacent pistons on one bank, eg pistons la and 3a, and therefore the piston diameter is usually increased until the distance between adjacent cylinder bores is adequate for the gas sealing of the cylinder head-to-block joint. This has the effect of increasing gas and inertia forces which is not desirable These considerations generally lead to 4-stroke spark ignited gasoline boxer engines having piston bore to engine stroke ratios (bore/stroke hereafter) which are larger than 1.

Modern pressure charged diesel engines have peak cylinder pressures that are typically 1.5-2.0 times greater than those of naturally aspirated gasoline engines, and this results in unacceptable loadings on the crank elements, when using the same bores and strokes as gasoline engines. It is therefore usual to achieve substantially similar engine displacements for the diesel, as the gasoline engine, by adopting smaller piston bores and longer crank strokes than the equivalent displacement gasoline engine. For a given crankshaft length, the piston bore of the diesel is reduced until the product of cylinder pressures and piston areas is substantially similar for both diesel and gasoline engine versions. But, as noted in the previous paragraph, smaller diameter pistons will result in large spaces between adjacent cylinder bores on each cylinder bank.

The unfavourable bore spacing of the boxer diesel configuration can be ameliorated by eliminating the intermediatemain bearings 2h and 4h and the associated webs, so that crankpins id and 2d are joined directly by a "flying" web, and this pair of crankpins and the associated crank elements are supported by main bearings lh and 3h. Likewise, crankpins 3d and 4d are joined directly by a "flying" web, and this pair of crankpins and its associated crank elements are supported by main bearings 3h and 5h. However, such 3 beanng crankshaft arrangements usually result in excessive loading of the main bearings, especially the centre main bearing, and the flying webs are also subject to excessive bending stresses because of the longer span between bearings.

With reference to Figs. 2a & 2b, the boxer engine still has cylinder axes 1 2, 3 and 4 which have substantially the same pistons and connecting rods as shown in Fig.la, but in the case of Fig.2a, there is no "centre" main bearing, ie bearing 3h of Fig.la has been removed, also webs 2f and 3e are removed, and the crankpins 2d and 3d of Fig.la are replaced by a single crankpin 23d, which is nominally the sum of the lengths of the crankpins 2d and 3d of Fig.la. (The connecting rod for the fourth cylinder is omitted from the Figures 2a and 2b in order to make the crankpin 4d more visible, as the other crankpins are not visible). This simplification of the crankshaft enables the distance between cylinders I and 3 to be reduced to a value where there is an acceptable distance between cylinder bores of each cylinder bank. On the other hand, the distance between adjacent main bearings 2h and 4h is acceptable and substantially lower than that of the 3 main bearing crank described above, and thus the bending loads on the supporting webs 2e and 3f are substantially lower than the bending loads of the crank webs of the 3 main bearing crankshaft described previously. In the arrangement of Figs 2a and 2b, the big ends of the connecting rods 2b and 3b are separated axially from each other by the designed axial clearance between the connecting rods, this clearance being specified to ensure 2)( 3 there is always some minimal clearance between the two adjacent connect rod big-end side faces for extreme tolerance stacks of the connecting rods, crank elements and axial movement of the crankshaft.

In one embodiment (Fig.2b), the connecting rod big-end bearings on each crankpin are supplied with oil via dnllings connected to the main bearing oil grooves, these driltings exiting on the main journal surfaces. Specifically, crankpin id may either be supplied by oil via drilling 65 from main bearing lh, or via a similar drilling from main bearing 2h, or by both dnllings. Crankpin 23d receives oil via drilling 67 from main 2h and via drilling 68 from main 4h. Crankpin 4d may either be supplied by oil via drilling 69 from main bearing 4h, or via a drilling from main bearing 5h, or by both dnllings from journals 4h and 5h.

With reference to Fig.3 this embodiment has the possibility of an additional balance mass 23g, attached to a crankweb located between the crankpins 2d and3d.

Fig.4 shows another embodiment of the invention in which the connecting rod bearings on each crankpin and all main bearings are supplied with oil via a series of dnltings connected to an oil supply at one end of the crankshaft. Specifically, crankpin id is supplied by oil via drilling 71, whch itself receives oil from end drilling 70. Crankpin 23d receives oil via drilling 74 & 76 from crankpin id. Crankpin 4d is supplied by drilling 77. Dnllings 73 and 78 connect with the drillings 74 and 77 respectively to provide oil to the main bearings that support main journals 2h and 4h, whilst journals 1 h and 5h receive oil from drilhings 71 and 79. Drilling 76 is a cross connection between drilhings 74 and 77.

With reference to Figs.2-4, the crankshafts may be made from various cast-iron materials, such as spheroidal graphite type cast iron, with local hardening of the bearing surfaces by induction hardening or tuftriding, which is a type of surface treatment, or may be of forged steel with local hardening of the bearing surfaces.

The forged steel crankshafts may also be nitrided.

With reference to Figs.2-4, the crankshafts may be used with additional detachable balance weights fitted to the front pulley and flywheel.

With reference to Figs.2-4, these crankshafts have 4 main bearings and axial thrust faces on two of the crankwebs connected to main bearings.

With reference to Figs.2-4, these crankshafts may be provided with pads for clamping, machining and balance adjustment, and have bosses for the flywheel attachment and front-end nose extensions to accommodate front-end drives.

With reference to Figs. 2-4, these crankshafts may also be used for either spark ignited or compression ignition engines. X4

Claims

Claims I A four cylinder, four stroke internal combustion engine of the boxer configuration containing a single piece crankshaft supported on four main bearings in which said crankshaft is connected to four connecting rods by means of crankpins charactensed in that the two intermediate connecting rods are connected to crankpins sharing a common axis and separated by a member to which a balance mass is attached.

2 A four cylinder, four stroke internal combustion engine of the boxer configuration containing a single piece crankshaft supported on four main bearings in which said crankshaft is connected to four connecting rods by means of crankpins charactensed in that the two intermediate connecting rods share a single crankpin.

3 An engine, as in Claim 1, in which the big ends, of the two intermediate connecting rods are axially separated from each other on the crankpin.

4 An engine, as in Claim 1, in which the connecting rod big ends, of the intermediate cylinders, are axially separated from each other by a crankweb and clearances between the big-ends and said crankweb.

An engine, as in any previous claim, in which oil reaches the crankshaft main journals via the main bearings.

6 An engine, as in any previous claim, in Which oil reaches the connecting rod bearings on each crankpin via crankshaft drillings connected to the main bearings.

7 An engine, as in any previous claim, in which oil reaches the connecting rod bearings on each crankpin and all main bearings via a series of dnllings connected to an oil supply at one end of the crankshaft.

8 An engine, as in any previous claim, in which the crankshaft is made of spheroidal graphite type cast iron material.

9 An engine, as in any previous claim, in which the crankshaft is tuftnded.

An engine, as in any previous claim, in which the crankshaft is made of forged steel material.

11 An engine, as in any previous claim, in which the crankshaft is nitrided.

12 An engine, as in any previous claim, in which the crankshaft has locally hardened bearing surfaces.

13 An engine, as in any previous claim, in which the crankshaft has 2 axial thrust faces on crankwebs that connect with main bearings.

14 An engine, as in any previous claim, in which the crankshaft has pads for clamping and machining purposes. s

An engine, as in any previous claim, in which the crankshaft has pads for balance adjustment purposes.

16 An engine, as in any previous claim, in which the crankshaft has a boss to accommodate the flywheel 17 An engine, as in any previous claim, in which the crankshaft has a front end nose extension to accommodate front-end drives.18 An engine, as in any previous claim, with additional detachable balance weights fitted to the front pulley and flywheel.