Arrangement for Insertion of Spark Plugs in Cylinder Head

The present invention relates to a cylinder head in an engine of the V type, or one which has horizontal opposing air intake valves, with the plug installed from the cam chain chamber side.

In a V type or horizontal opposition engine, in order to make effective use of space and to make the engine compact, cam shaft drive sprockets are normally placed at either of the two ends of the crank shaft, and the respective cam shafts are driven by means of the said sprockets and a cam chain.

Where the engine has a number of valves on the air intake side, in order to facilitate maintenance, if the spark plugs are to be installed from the cam chain side, they must of necessity be located on the exhaust valve side.

Accordingly, as shown in FIGS. 8 and 9 illustrating the prior art, in the case of a V type engine, for example, the cam chains 104, 105 which go around cam shaft drive sprockets 102, 103 at the two ends of crank shaft 101, etc., are respectively wound around secondary sprocket 107 of the front cylinder head 106 and secondary sprocket 109 of the rear cylinder head 108, so as to drive their respective cam shafts 111 and 112. With the front and rear cam shaft drive sprockets 102 and 103 fitted in reciprocally corresponding positions, with the respective cylinder heads 106 and 108 having their cam chain chamber 113 and 114 placed in mutually reversed positions, and with spark plugs 121 and 122 installed from the cam chain chamber side, in order to prevent interference involving the taut sides 104a and 105a and the slack sides 104b and 105b of the cam chains 104 and 105, respectively, the left to right angles of deviation from the central lines 106a and 108a for the respective cylinder heads 106 and 108 must be .theta.1 and .theta.2. Accordingly, the respective cylinder heads 106 and 108 must be manufactured separately, with a number of separate component parts, making it difficult to achieve cost reductions.

If the installation angles .theta.1 and .theta.2 are made equal for plugs 121 and 122, and if one attempts to use the two cylinder heads 106 and 108 together, plugs 121 and 122 will interfere with cam chains 104 and 105, respectively, so that it becomes necessary to enlarge the secondary sprockets 107 and 109. This in turn requires larger cylinder heads 106 and 108, precluding the possibility of making the engine more compact.

The present invention is intended to overcome these disadvantages, by means of a pair of cylinder heads, in a V type horizontal opposition engine, which have spark plugs installed from the cam chain chamber side, bringing about compactness as well as the ability to use the two heads together.

This objective is achieved, in the present invention, by installing the plug at an oblique angle (viewed axially from the cylinder), so that the inner end of the plug rests in the air exhaust hole, and the outer end of the plug is in a position approximately in the middle section of the cam chain chamber.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, wherein an embodiment of the invention is shown for purposes of illustration, and wherein:

FIG. 1 is a side view of a motorcycle having a V type engine;

FIG. 2 is a cross section view of the main parts of the engine;

FIG. 3 is a sectional view along line III--III in FIG. 2;

FIG. 4 is a detail view of the essential parts of FIG. 3;

FIG. 5 is a sectional view along line V--V in FIG. 2;

FIG. 6 is a sectional view of the cylinder head;

FIG. 7 is a sectional view along line VII--VII in FIG. 6;

FIG. 8 is an elevation showing a prior art arrangement of the cylinder heads;

FIG. 9 is a plan view thereof;

FIG. 10 is a view similar to FIG. 4, showing additional details; and

FIG. 11 is a section view along line III--III of FIG. 10.

As shown in FIG. 1, head tube 3 is located at the front end of the frame 2 of motorcycle 1. Front fork 5 is supported so it can operate freely by head tube 3, and it supports front wheel 4. The handle 7 is placed above top bridge 6.

The frame 2 comprises the main pipe 2a, extending rearwardly from the upper rear area of head tube 3; the down tube 2b, which extends downwardly from the lower part of head tube 3; the lower down tube 2e, which extends from the lower end of down tube 2b; center tube 2c, which slants up at an angle from the lower down tube 2e, and is connected to the rear of main pipe 2a; seat rail 2d, which extends rearwardly from main pipe 2a; and other parts.

As for the lower down tube 2e, below the down tube 2b, center tube 2c, and main pipe 2a, there are two of these, located to left and right. Fuel tank 8 is so located as to straddle the main pipes 2a of the frame 2; the seat 9 is placed on top of the seat rail 2d; the rear wheel 12 is supported by means of the rear fork 11 extending from the lower end of the center tube 2c; and the rear cushion unit 13 is placed between the rear fork 11 and the seat rail 2d.

Inside the space created among these parts of the frame 2, surrounded by main pipe 2a, down tube 2b, lower down tube 2e, and center tube 2c, there is placed the engine 14, shown here as a V type engine with the two cylinders at 45.degree. angles from each other.

Engine 14 comprises front and rear cylinders 15 and 16, and crank case 17. Front cylinder 15 contains a cam chain chamber 18a, on the left hand side of the vehicle body, while rear cylinder 16 contains a cam chain chamber 18b on the right-hand side of the vehicle body. The cylinder openings of front cylinder 15 and rear cylinder 16 are distributed in offset fashion to the left and the right respectively of a center line running through the vehicle body.

Cam shaft drive sprockets 22 and 23 are respectively attached at the two ends of the crank shaft 21 placed in crank case 17. The secondary sprocket 26 of the cam shaft located at the cylinder head 24 of the front cylinder 15, and the left side cam shaft drive sprocket 22, are connected by the cam chain 27, passing through the chain chamber 18a. The secondary drive sprocket 33 of the cam shaft located at the cylinder head 31 of the rear cylinder 16, and the right side cam shaft drive spocket 23, are connected by the cam chain 34, passing through the chain chamber 18b.

The cylinder head 24 of the front cylinder 15 and the cylinder head 31 of the rear cylinder 16 have the same shape and structure, and they are respectively rotated reciprocally in a 180.degree. plane, installed in the respective cylinder bodies 35 and 36.

As shown in FIG. 6, rear cylinder 16 has two air intake holes 41 and 42, and one exhaust hole 43, formed in cylinder head 31. So that spark plugs 44 and 45 may be respectively installed from the right-hand side of cylinder head 31, i.e., from the side of cam chamber 18b, and from the left-hand side of cylinder head 31, there are respectively fitted, on the cam chain chamber side 18b, in line with axis 46, guide hole 47, sleeve screw hole 48, and plug screw hole 49; and on the left-hand side of cylinder head 31 in line with axis 51, there are respectively fitted guide hole 52 and plug screw hole 53.

As shown in FIG. 6, relating to cylinder head 31, there is a crossing of a line extending from axis 46 and the axial line across the combustion chamber 54, at point 46a. This point 46a is slightly inclined in the direction of exhaust hole 43, away from the center point of the combustion chamber 54. The outer end 46b of axis 46 is slightly inclined towards exhaust hole 43, and away from line 57, which is the central axial line of the combustion chamber 54 (this central axial line of combustion chamber 54 is approximately parallel to the crank shaft 21). Further, portion 46c of axis 46 which faces the cam chain chamber 18b is located approximately in the middle of cam chain chamber 18, lengthwise, and the fitted plug 44 is arranged in such a way that it interferes with neither the taut side 34a nor the slack side 34b of the cam chain 34. In the illustrated embodiment, the axis line 46 is inclined at an approximately 3.degree. angle from axial line 57. In the horizontal view of cylinder head 31, shown in FIG. 7, the extension of axial line 46 approximately crosses the axis 56 of combustion chamber 54, and the outer end 46b of axis 46 is somewhat higher than the inner end.

The extension of axis 51, as shown in FIG. 6, if viewed vertically in terms of cylinder head 31, approximately crosses the center 56 of combustion chamber 54, and the outer end of axis 51 is inclined toward exhaust hole 43. In addition, viewed horizontally in terms of cylinder head 31, the extension of line 51 crosses 31a below the cylinder head at a position towards the outer end of axis 51, away from the center 56 of the combustion chamber 54. The outer end of axis 51 is located at a higher position than the inner end, and, taking into account the installation of the spark plug, axial lines 51 and 31a below the cylinder head extend at an angle to each other of less than 60.degree..

The sleeve is fitted in the above cited guide hole 47 and sleeve screw hole 48, while the plug 44 is fitted in the plug screw hole 49, with cap 62 fitted on the rear of plug 44, with the outer end of cap 62 held on the outer end of sleeve 61 by means of sealing element 63. In addition, plug 45 is fitted in the above cited guide hole 52 and plug screw hole 53.

In FIG. 1, 71 is the carburetor, 72 is the coolant tubing, and the portion of the coolant tubing 72 facing the cylinder body 35 is secured by means of rubber element 73, so as to prevent vibration of coolant tubing 72.

The plug 44 installed from cam chain chamber side 18b is so placed that it is located between the taut side 34a and the slack side 34b of the cam chain 34, and so that it appropriately inclines in the direction of the taut side 34a or the slack side 34b. Consequently, as shown in FIG. 5, when cylinder head 31 is placed in front cylinder 15, plug 44 does not interfere with the taut side 27a or the slack side 27b of the cam chain 27, and when cylinder head 31 is placed in rear cylinder 16, as shown by the hypothetical lines, plug 31 does not interfere with the taut side 34a or the slack side 34b of cam chain 34. As a result, it becomes possible to make cylinder head 31 more compact, and for it to be used with both front cylinder 15 and rear cylinder 16.

During insertion and removal of the two plugs 44 and 45, as shown in FIG. 4, the tools used do not interfere with main pipes 2a, and operations are carried out simply and quickly.

Although the foregoing discussion specifically mentions a V type engine, the invention is also suitable for a horizontal opposition engine having plugs fitted from the cam chain chamber side. In either case, the two cylinder heads can be made more compact, and commonly used, thereby reducing the total number of parts required and contributing toward a reduction of costs. In addition, simplicity, ease and speed of plug installation are enhanced.

An additional improvement provided by the present invention is shown in FIGS. 10 and 11.

While the insertion of spark plugs in the wall of the combustion chamber, passing through the cam chain chamber outside the said combustion chamber, is already known in the art, the use of a sleeve surrounding the spark plug and formed as a unit with the cylinder head, in order to prevent interference between the spark plug and the cam chain in the cam chain chamber, means that the cam chain must be arranged in joint linkage form, in a suspension and crossover movement, and such an arrangement is both complicated and inconvenient.

To overcome this problem, the present invention provides a structure in which the plug sleeve is removed from the cam chain chamber at will, and the fitting is such that during such removal the movement of the cam chain can continue. The spark plug is installed in such a fashion that it is inserted in the wall of the engine cylinder head combustion chamber, with its outer side passing through the cam chain chamber, and there is a fitting apparatus with a plug sleeve surrounding the spark plug passing through an aperture in the outer wall of the cam chain chamber, to permit insertion and removal at will.

As shown in FIG. 10, this improvement applies to a V-type engine 14 carried on a two-wheeled motor vehicle. On one side of the combustion chamber 54 of each cylinder head 24; 31, fitted on the top of each of the pair of cylinder blocks 35, 36 installed in such a fashion as to slope in the front and rear directions in the form of a V, as the first spark plug 44 is inserted through the outer cam chain chamber 18b, on the other side of combustion chamber 54 the second spark plug 45 is inserted so as to protrude directly out of cylinder head 24.

In FIG. 10, 21 identifies the cam shaft, located between the said head 31 and the head cover 31a above it, and the cam chain 34 moves through cam chain chamber 18b, between the sprocket 22 at the end of cam shaft 21 and sprocket 23 on top of the crank shaft (not shown).

61 identifies the sleeve surrounding the first spark plug 44, and this sleeve 61, in accordance with a special feature of the invention, passes through an opening 80 in the outer wall of cam chain chamber 18b, and is so made to fit in, and to be inserted and removed at will from the receiving opening 81 in the outer surface of the wall of combustion chamber 54. At the same time that sleeve 61 fits into opening 80 and receiving opening 81, in a liquid seal, its inner and outer ends, respectively, through O-rings 84, the tip of the inner end being screwed into the receiving opening 81, and the outer end having around it a fitting 82 for sleeve rotation, so that sleeve 61 can be inserted and removed.

The receiving opening 81 is formed so as to have a smaller diameter than opening 80, and the O-ring 84 around the inner end of sleeve 61 is correspondingly smaller in diameter; insertion and removal of sleeve 61 is facilitated by O-ring 84 freely placed around opening 80, so as to facilitate assembly. In addition, at the bottom area of receiving opening 81, as shown in FIG. 11, there is a water drain hole 83 protruding at the pitch of the slope of its respective cylinder block, so as to evacuate rain water and the like that might temporarily enter sleeve 61, draining out through the said water drain hole 83.

63 identifies a rubber cap placed over the outer part of sleeve 61; by means of a cap 63, plug cap 62 is placed so as to cover spark plug 44; in addition, fin area 63a on the outer surface of cap 63 is connected with the cylinder fins 85 to serve as a guide when cap 63 is mounted.

The operation of the improvement illustrated in FIGS. 10 and 11 is as follows. After movement of cam chain 34 has been phased in, spark plug 44 and sleeve 61 are placed through the opening 80 of the outer wall of cam chain chamber 18b. Since removal of sleeve 61 proceeds in a similar manner, it is possible to move along cam chain 34, operational characteristics are improved, and it is also possible to use an endless type of cam chain 34, which has greater durability than the joint linked type chain previously used.

In addition, while the engine is in operation, even when there is oscillation, e.g., due to slackness of cam chain 34 or other factors, spark plug 44 is protected by sleeve 61 from cam chain 34, there is no damage due to interference from chain 34, and, in addition, the entry of oil and other foreign matter is blocked.

Thus, according to the present invention, when a spark plug is fitted in the cam chain chamber side of the combustion chamber wall of the cylinder head, the plug sleeve required is a unit separate from the cylinder head, and may be removed as desired through the opening formed in the outer wall of the cam chain chamber. It is possible to move the cam chain along while the said sleeve is taken out; an endless type chain may be used as the cam chain; and the sleeve may be lighter and less thick than was necessary when it was unitary with the cylinder head, thus permitting size and weight reduction of the engine.