Stroke characteristic variable engine

A stroke characteristic variable engine comprising a primary link connected to a piston which is slidably fitted in a cylinder, a secondary link connecting the primary link with a crankshaft and a tertiary link connected to the primary link or the secondary link at one end and to an engine main body via a control shaft at the other end thereof. An oil level position of engine oil stored in an oil pan is set such that at least part of the control shaft is submerged in the engine oil, whereby since oil stored within the oil pan can be used as it is, the lubrication around the control shaft can be ensured in a simplified configuration.

The present invention claims foreign priority to Japanese patent application No. P. 2005-036137, filed on Feb. 14, 2005, the contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stroke characteristic variable engine, and more particularly to a stroke characteristic variable engine which can simplify the supply of lubricating oil to a piston stroke variation mechanism which includes a plurality of links.

2. Description of the Background Art

There is known a stroke characteristic variable engine in which a piston and a crankshaft are connected to each other by means of a plurality of links and a piston stroke is made to be varied by varying the position of a connecting end of one (a control link) of the links to an engine main body (refer to, for example, Japanese Patent Unexamined Publication No. JP-A-2004-116434).

In the event of the engine of this type, lubricating oil needs to be supplied to connecting portions where the respective links are connected to each other and a bearing for a control shaft which varies the position of the one of the links to the engine main body. Namely, the supply of lubricating oil needs to be increased compared to general engines.

However, since the configuration of the stroke characteristic variable engine disclosed in Patent Document No. 1 is such that the capacity of a lubricating oil pump is set for a needed volume when the engine is operated at a high compression ratio and the degree of communication of oil paths provided inside the control link and the control shaft is made to vary in accordance with a change in compression ratio in order to reduce the load to be borne by the pump when the engine is run at a low compression ratio, the number of manhours for manufacture tends to be increased due to an increase in capacity of the oil pump, as well as the complex configuration of the oil paths.

SUMMARY OF THE INVENTION

In view of the drawback inherent in the related art, a main object of the invention is to improve the stroke characteristic variable engine including the plurality of links in such a manner that the supply of lubricating oil can be implemented in a simply way.

With a view to solving the problem, according to a first aspect of the invention, there is provided a stroke characteristic variable engine comprising:

a primary link4connected to a piston3which is slidably fitted in a cylinder2;

a secondary link5connecting the primary link4with a crankshaft6; and

a tertiary link12comprising:a first end connected to the primary link4or the secondary link5; anda second end connected to an engine main body via a control shaft13,

wherein an oil level position of engine oil stored in an oil pan15is set such that at least part of the control shaft13is submerged in the engine oil.

In addition, according to a second aspect of the invention, there is provided a stroke characteristic variable engine comprising:

a primary link connected to a piston which is slidably fitted in a cylinder;

a secondary link connecting the primary link with a crankshaft; and

a tertiary link comprising:a first end connected to the primary link or the secondary link; anda second end connected to an engine main body via a control shaft,

wherein a connecting portion is defined between the control shaft and the tertiary link, and

an oil receiver (a plate-shaped semi-cylindrical portion20) for reserving engine oil is provided between the connecting portion and an oil level in an oil pan, so that at least part of the control shaft is made to be submerged in engine oil within the oil receiver.

According to a third aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the oil receiver is formed by a connecting member which connects together a plurality of support portions (bearing caps18) which pivotally support the control shaft on the engine main body.

According to a fourth aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that an outlet to a crankcase of an oil return passage22formed in a cylinder block opens above the oil receiver.

According to a fifth aspect of the present invention, as set forth in the second aspect of the present invention, it is preferable that the oil receiver includes an oil discharge hole21at a lower portion thereof.

According to a sixth aspect of the present invention, it is preferable that the stroke characteristic variable engine as set forth in the second aspect of the present invention, further comprising:

a housing33a,33bprovided with a discharge port40for engine oil which has flowed thereinto; and

a vibration alleviating device31disposed in the housing,

wherein a position of the discharge port of the housing is set such that oil discharged from the housing flows to fall into the oil receiver.

Furthermore, according to a seventh aspect of the invention, there is provided a stroke characteristic variable engine comprising:

a primary link connected to a piston which is slidably fitted in a cylinder;

a secondary link connecting the primary link with a crankshaft;

a tertiary link comprising:a first end connected to the primary link or the secondary link; anda second end connected to an engine main body via a control shaft; and

a vibration alleviating device housed in a housing provided with a discharge port41for engine oil which has flowed thereinto,

wherein the position of the discharge port is set such that oil discharged from the housing is brought into contact with the control shaft.

According to the configuration provided by the first aspect of the invention, since the oil stored in the oil pan can be used as it is, the implementation of lubrication around the control shaft can be ensured by the simple configuration. In addition, according to the second aspect of the invention, since oil that spreads within the crankcase can be used, the implementation of lubrication around the control shaft can be ensured by the simple configuration, and moreover, since the oil receiver is provided at a higher position than the oil level of the oil stored in the oil pan, no effect has to be caused which would otherwise result from a change in oil level within the oil pan during the running of the engine.

By adding the configuration provided by the third aspect to the configuration provided by the second aspect of the invention, an increase in the number of components does not have to be called for, and the support rigidity of the control shaft can be increased. By adding the configuration provided by the fourth aspect to the same, engine oil can be supplied to the oil receiver in an ensured fashion without calling for a complex construction, and moreover, since the time during which engine oil stays within the oil receiver can be shortened by increasing the supply amount of oil, a deterioration in quality of oil does not have to be triggered. In addition, by adding the configuration provided by the fifth aspect, the accumulation of metallic dust and sludge can be prevented. Then, by adding the configuration provided by the sixth aspect, the supply of engine oil to the oil receiver can be ensured without calling form a complex construction. Furthermore, according to the seventh aspect of the invention, since oil that has lubricated the vibration alleviating device can be used, the implementation of lubrication around the control shaft can be ensured by the simple configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in detail by reference to the accompanying drawings.

FIGS. 1 to 4are schematic views which show the configuration of a compression ratio variable engine as an example of a stroke characteristic variable engine to which the invention is applied with a cylinder head and an upper part of the engine than the cylinder head omitted from the illustration. For ease of understanding, the description will be made on one of pistons of the engine and associated components therewith. A piston3, which is slidably fitted in a cylinder2of the engine1, is connected to a crankshaft6via two links, a primary link4and a secondary link5.

The crankshaft6supports the secondary link5, which oscillates in a see-saw fashion, at a middle portion thereof by a crank pin9which is offset from a crank journal8(a rotational center of the crankshaft) which is supported within a crankcase7. Then, a big end portion4bof the primary link4, which is connected to a piston pin10at a small end thereof, is connected to one end5aof the secondary link5.

Note that the crankshaft6is configured basically similar to that of a normal fixed compression ratio engine in which a counterweight, which offsets a vibration component generated by the motion of the piston, is formed integrally on a crank arm which connects the crank journal8to the crank pin9.

A small end portion12aof a tertiary link12, which has the same configuration as that of a connecting rod which connects a piston to a crankshaft in a normal engine, is pin connected to the other end5bof the secondary link5. In addition, a bid end portion12bof the tertiary link12is connected by a bearing bore14which is divided into two halves to an eccentric portion13aof the control shaft13which is made up of an eccentric shaft which is rotatably supported within the crankcase7and is provided in such a manner as to extend in parallel with the crankshaft6.

The control shaft13supports the big end portion12bof the tertiary link12in such a manner that the big end portion12bcan move within a predetermined range within the crankcase7and is made such that the rotational angle of the control shaft13is changed continuously in accordance with the running state of the engine1and is held at an arbitrary angle by means of a stroke characteristic variation control actuator (not shown) which is provided at a shaft end of the control shaft13which protrudes outwardly of the crankcase7.

According to this engine1, the position of the big end portion12bof the tertiary link12varies between a position shown inFIGS. 1 and 2and a position shown inFIGS. 3 and 4by rotating the control shaft13, whereby the oscillating angle of the secondary link5varies in conjunction with the rotation of the crankshaft6. The range of a stroke of the piston3within the cylinder2, that is, a top dead center position and a bottom dead center position of the piston3vary continuously between a range indicated by reference character A inFIG. 2and a range indicated by reference character B inFIG. 4in accordance with the oscillating angle of the secondary link5. Namely, a piston stroke variation mechanism is made up of the primary to tertiary links4,5,12and the control shaft13, whereby a stroke characteristic varying function is provided which varies continuously at least either compression ratio or displacement.

In this engine1, a cylinder axis is inclined relative to a vertical line, and engine oil is stored by an oil pan15which is connected to a bottom of the crankcase7. In addition, the height of an oil level OL of engine oil is set such that a connecting portion where the big end portion12bof the tertiary link12and the control shaft13are connected to each other is partially submerged in engine oil so stored.

Thus, since engine oil stored within the oil pan15can be used, as it is, for lubrication of the connecting portion where the big end portion12bof the tertiary link12and the control shaft13are connected to each other and a pivotal securing portion where the control shaft13is pivotally supported to an engine main body by setting the height of the oil level OL of engine oil stored in the oil pan15such that at least part of the control shaft13is submerged in the engine oil so stored, oil paths for supplying lubricating oil to the tertiary link12and the control shaft13do not have to be formed, whereby the implementation of lubrication around the control shaft can be ensured by the simple configuration.

In addition, as to lubrication of the pivotal securing portion where the control shaft13is pivotally supported to the engine main body, a branch path16bfrom a oil path, which is provided inside the crankcase7to supply engine oil to, for example, the crank journal8or the like, may, needless to say, be provided inside both end walls of the crankcase7in a direction in which cylinders are aligned, as well as bulkheads17which are each formed inside the crankcase7to separate adjacent cylinders from each other.

FIG. 5is a schematic view, similar toFIG. 1, which shows the configuration of a second embodiment of the invention. In this embodiment, too, since the configuration of a piston stroke variation mechanism is not different at all from that of the first embodiment, the description thereof will be omitted.

A control shaft13is supported within a lower portion of a crankcase7by bearing bores19which are formed in such a manner as to be divided into two halves between lower surfaces of both end walls of the crankcase7in a direction in which cylinders are aligned and a plurality of bulkheads17formed within the crankcase7to separate adjacent cylinders2from each other and a plurality of bearing caps18which are joined, respectively, to the lower surfaces of the end walls and bulkheads17.

In this embodiment, the plurality of bearing caps18are integrally connected to each other by plate-shaped semi-cylindrical portions20which are each formed into a curved semi-cylindrical shape which protrudes downwardly. This plate-shaped semi-cylindrical portion20covers below a connecting portion where a big end portion12bof a tertiary link12is connected to the control shaft13and is disposed at a higher position than an oil level OL of engine oil stored within an oil pan15. In addition, in this plate-shaped semi-cylindrical portion20, an open surface thereof is oriented upwardly and a oil discharge hole21having an appropriate bore diameter is provided at an appropriate position in a lower portion thereof, whereby the plate-shaped semi-cylindrical portion20functions as an oil receiver which receives engine oil which spreads within the crankcase7.

On the other hand, an oil return passage22is formed outside the cylinder2within a cylinder block to return engine oil from a cylinder head to the oil pan15, and an outlet of this oil return passage22to the inside of the crankcase7is made to open at a position which faces the open surface of the plate-shaped semi-cylindrical portion20.

According to this configuration, engine oil falling from the oil return passage22flows downwards, for example, along the tertiary link12into the plate-shaped semi-cylindrical portion20(the oil receiver) and flows out through the oil discharge hole21. Here, the bore diameter of the oil discharge hole21is determined in consideration of a balance between a flow-in volume and a flow-out volume so that not only the accumulation of metallic dust and sludge can be prevented but also a sufficient amount of engine oil can be accumulated to allow the connecting portion between the big end portion12bof the tertiary link12and the control shaft13to be submerged in engine oil so accumulated.

Thus, since engine oil which spreads within the crankcase7can be received to thereby be used to lubricate around the control shaft by providing the plate-shaped semi-cylindrical portion20which functions as the oil receiver for temporarily reserving engine oil between the connecting portion where the big end portion12bof the tertiary link12is connected to the control shaft13and the oil level OL within the oil pan, so as to allow at least part of the control shaft13to be submerged in engine oil reserved within the plate-shaped semi-cylindrical portion20, a complex lubricating construction does not have to be called for.

In addition, engine oil within the plate-shaped semi-cylindrical portion20is replaced at all times, a deterioration in oil quality does not have to be triggered, and additionally, since the plate-shaped semi-cylindrical portion20is provided at the higher position than the oil level OL of engine oil within the oil pan15, no effect has to be caused which would otherwise result from a change in oil level within the oil pan during the running of the engine. Moreover, since the plurality of bearing caps18are configured as a single component in which the bearing caps18are connected to each other, an increase in the number of components does not have to be called for, and the configuration can contribute to an enhancement in the support rigidity of the control shaft13.

Since this stroke characteristic variable engine1generates rotational secondary vibration attributed to the motion of the piston stroke variation mechanism, a vibration alleviating device for offsetting the vibration may be provided below the crankshaft6.

FIG. 6shows an example of a vibration alleviating device31provided at a position adjacent to the control shaft13.

This vibration alleviating device31includes a pair of balancer shafts32a,32bwhich both extend in parallel with the crankshaft6and an upper housing33aand a lower housing33bwhich are divided halves and which support and receive the balancer shafts32a,32b. The balancer shafts33a,33bare connected to each other by virtue of mesh engagement between interlocking gears34a,34bhaving the same diameter which are provided integrally on the balancer shafts32a,32b, respectively, and a driven gear35provided on one of the balancer shafts, which is the balancer shaft32b(lying directly below the crankshaft6), meshes with a drive gear36provided on the crankshaft6, whereby the driving force of the crankshaft6is transmitted to the respective balancer shafts32a,32b, which are then caused to rotate in an opposite direction at a rotating speed which is twice the crankshaft speed.

Balancer weights37a,37bare provided on outer circumferential portions of the balancer shafts32a,32b, respectively, which each have a predetermined phase and a predetermined inertial mass which are necessary to balance an amount of unbalance generated by the motion of the piston stroke variation mechanism.

Side edges of side walls of the upper housing33aand the lower housing33bare offset from each other along a parting surface between the upper housing33aand the lower housing33bwith respect to a radial direction of the balancer shafts32a,32b. In addition, lateral protruding portions38are provided on side walls of the upper housing33ain such a manner as to extend in an axial direction of the housing, whereby upwardly open gaps39are formed on a plane on which centers of the balancer shafts32a,32bpass and open surfaces of the gaps39and the lateral protruding portions38are made to oppositely face each other, so that oil discharge ports40, which are opened sideways, are defined between the side edges of the side walls of the lower housing33band side edges of the lateral protruding portions38, respectively.

By this configuration, engine oil, which flows in from an oil inlet hole (not shown) formed in the upper housing33ato be accumulated in a bottom portion of the lower housing33b, is scooped up by both the balancer shafts32a,32bin conjunction with the rotation thereof (in directions indicated by arrows) to flow sideways out of the vibration alleviating device31from the discharge ports40via the gaps38.

In this embodiment, an open side edge of each plate-shaped semi-cylindrical portion20, which is similar to that described in the second embodiment, is disposed adjacent to the side edge of the right-hand side wall of the lower housing33b, and the discharge port40is positioned so as to open above the open side edge of the plate-shaped semi-cylindrical portion20, whereby engine oil flowing out of the vibration alleviating device31is designed to flow into the plate-shaped semi-cylindrical portion20. In addition, as with the second embodiment, a connecting portion where a big end portion12bof a tertiary link12is connected to a control shaft13is lubricated by engine oil accumulated within the plate-shaped semi-cylindrical portion20. Namely, the implementation of supply of engine oil to the surroundings of the control shaft can be ensured by the construction of the embodiment without calling for a complex lubricating construction.

As shown inFIG. 7, in the event that an oil discharge path42is made to extend from right-hand side walls of an upper housing33aand a lower housing33bof a vibration alleviating device31at a position which does not interfere with a big end portion12bof a tertiary link12in such a manner that a discharge port41thereof is made to open at a position which lies near a control shaft13, engine oil which has lubricated the vibration alleviating device31can be supplied directly to the control shaft13. According to this configuration, since the plate-shaped semi-cylindrical portions20which function as the oil receivers can be omitted, the lubricating construction for the surroundings of the control shaft can be simplified further. In addition, since the supply of engine oil to the surroundings of the control shaft can be ensured even in the vent that the control shaft13is spaced apart from the vibration alleviating device31, the degree of freedom in layout of the accessory components can be enhanced even in case the plate-shaped portions20are used. Note that a configuration may be adopted in which instead of the oil discharge path42, a pipe made up of a separate member is connected to the right-hand side walls of the upper housing32aand the lower housing32bof the vibration alleviating device31.

Thus, as has been described in detail heretofore, the invention can be applied equally to engines in which piston strokes are varied by varying the geometry of a plurality of links, whereby at least a compression ratio or displacement thereof can be varied, and can be applied to, for example, an engine of a type in which one end of a tertiary link is connected to the vicinity of a connecting portion where a primary link is connected to a secondary link.