Patent Description:
Usually, internal combustion engines have an oil pan in which oil is stored to lubricate moving parts of the internal combustion engine and which is disposed below a main body of the internal combustion engine.

There is known a typical oil pan which is of a box-shape designed to have an upper opening and has a bottom wall, a peripheral wall extending upward from a circumferential edge of the bottom wall with round corners, and a flange extending outward horizontally from an upper edge of the peripheral wall (see <CIT>).

The peripheral wall is waved in a planar view thereof along the circumferential edge of the bottom wall to have convex portions bulging inwardly and concave portions bulging outwardly which alternate with each other. The peripheral wall is capable of storing a given volume of lubricating oil equivalent to a total volume of the concave portions of the peripheral wall which bulge outwardly. The waved shape of the peripheral wall also serves to enhance the rigidity of the oil pan.

Too high the level of oil accumulated in the oil pan may result in a risk that the oil may be agitated by a counterweight of a crankshaft of the internal combustion engine. Conversely, too low the level of oil in the oil pan may cause air to be sucked into an oil pump.

It is, therefore, necessary to keep the level of oil stored in the oil pan at a required level. The level of oil stored in the oil pan, however, depends upon a stored amount of the oil. Increasing the stored amount of oil to increase the level of the oil in the oil pan will result in an increase in weight of the oil or may lead to a risk that the amount of oil which needs to be discarded upon oil change may be undesirably increased. <CIT> relates to an oil pan for an internal combustion engine.

The present invention was made in view of the above problem. It is an object of the invention to provide an oil pan which is capable of optimizing the volume or level of oil stored in a main body of the oil pan and minimizing the mechanical vibration of the oil pan.

According to one aspect of the invention, there is provided an oil pan for an internal combustion engine which comprises: an oil pan main body which includes a flange, a peripheral wall, and a bottom wall. The flange has a rectangular opening and is joined to a lower portion of a body of an internal combustion engine equipped with a crankshaft. The peripheral wall extends downward from an inner edge of the flange. The bottom wall is joined to a lower end of the peripheral wall. The bottom wall includes a deep bottom portion and a shallow bottom portion. The shallow bottom portion is arranged adjacent the deep bottom portion in a direction in which the crankshaft extends and located at a higher position than the deep bottom portion. The shallow bottom portion is joined to the shallow bottom portion through a stepped portion. The oil pan main body is configured to have the shallow bottom portion above which a level of a specified amount of oil stored in the oil pan main body lies. The shallow bottom portion includes a middle bottom section, a first raised bottom section, and a second raised bottom section. The middle bottom section occupies a central portion of the shallow bottom portion in a direction crossing the crankshaft. The first raised bottom section and the second raised bottom section are arranged on opposite sides of the middle bottom section in the direction crossing the crankshaft and located at a higher position than the middle bottom section.

The above structure in the invention serves to optimize the volume and level of oil stored in oil pan main body and reduce mechanical vibration of the oil pan main body.

An oil pan for an internal combustion engine according to an embodiment of the invention comprises an oil pan main body which includes a flange, a peripheral wall, and a bottom wall. The flange has a rectangular opening and is joined to a lower portion of a body of an internal combustion engine equipped with a crankshaft. The peripheral wall extends downward from an inner edge of the flange. The bottom wall is joined to a lower end of the peripheral wall. The bottom wall includes a deep bottom portion and a shallow bottom portion. The shallow bottom portion is arranged adjacent the deep bottom portion in a direction in which the crankshaft extends and located at a higher position than the deep bottom portion. The shallow bottom portion is joined to the shallow bottom portion through a stepped portion. The oil pan main body is configured to have the shallow bottom portion above which a level of a specified amount of oil stored in the oil pan main body lies. The shallow bottom portion includes a middle bottom section, a first raised bottom section, and a second raised bottom section. The middle bottom section occupies a central portion of the shallow bottom portion in a direction crossing the crankshaft. The first raised bottom section and the second raised bottom section are arranged on opposite sides of the middle bottom section in the direction crossing the crankshaft and located at a higher position than the middle bottom section.

The above structure in the embodiment of the invention is capable of optimizing the volume and level of oil stored in oil pan main body and reducing mechanical vibration of the oil pan main body.

An oil pan according to an embodiment of the invention will be described below with reference to the drawings.

<FIG> are views which illustrates the oil pan in the embodiment of the invention. In <FIG>, a vertical, longitudinal, and lateral directions will also be defined in the following way.

A direction which a crankshaft of an internal combustion engine extends will be defined as a lateral direction of the internal combustion engine. A region in which a left side wall of an oil pan exists along the crankshaft will be defined as a left side. A region in which a right side wall of the oil pan exist will be defined as a right side. A direction which horizontally extends perpendicular to the crankshaft will be referred to as a longitudinal direction of the internal combustion engine. A direction vertically extending perpendicular to the crankshaft will be referred to as a vertical direction.

The structure will be first described below.

Referring to <FIG>, the engine <NUM> which is mounted in a vehicle includes the engine body <NUM> and the oil pan <NUM>. The engine body <NUM> is equipped with the cylinder block 2A which retains the crankshaft <NUM> to be rotatable. The crankshaft <NUM> extends in a width-wise direction (i.e., the lateral direction) of the vehicle.

The cylinder block 2A has formed therein a plurality of cylinders, not shown, which are arrayed in the width-wise direction of the vehicle. Each of the cylinders has a piston, not shown, disposed therein. The pistons are connected to the crankshaft <NUM> through a connecting rod, not shown.

The pistons reciprocate in the cylinders to rotate the crankshaft <NUM> through the connecting rod. The engine body <NUM> includes a cylinder head, not shown, which is arranged on an upper portion of the cylinder block 2A and a cylinder head cover, not shown, which is disposed on an upper portion of the cylinder head. The engine <NUM> in this embodiment is implemented by an internal combustion engine. The engine body <NUM> constitutes a body of the internal combustion engine.

The oil pan <NUM>, as clearly illustrated in <FIG> and <FIG>, includes the oil pan main body <NUM>. The oil pan main body <NUM> is equipped with the flange <NUM>, the peripheral wall <NUM>, and the bottom wall <NUM>.

The flange <NUM>, as clearly illustrated in <FIG> and <FIG>, has the rectangular opening 12a. The flange <NUM> is fixed on the flange 2a (see <FIG> and <FIG>) disposed on a lower portion of the cylinder block 2A using bolts, not shown.

The peripheral wall <NUM>, as clearly illustrated in <FIG>, extends downward from the inner edge 12b of the flange <NUM> and is of a box-shape. The bottom wall <NUM> is joined to a lower end of the peripheral wall <NUM>. The peripheral wall <NUM> has an opened upper end and a lower end closed by the bottom wall <NUM>.

The bottom wall <NUM>, as can be seen in <FIG> and <FIG>, includes the deep bottom portion 14A and the shallow bottom portion 14B. The deep bottom portion 14A is located on the right side of the crankshaft <NUM>, as viewed in the direction in which the crankshaft <NUM> extends (which will also be referred to below as a crankshaft axial direction 4a). The shallow bottom portion 14B is arranged on the left side of the deep bottom portion 14A, that is, located adjacent the deep bottom portion 14A in the crankshaft axial direction 4a and at a higher position than the deep bottom portion 14A in the vertical direction. The shallow bottom portion 14B is joined to the deep bottom portion 14A through the stepped portion 14C. The stepped portion 14C, as referred to herein, is defined as a riser of a step. Specifically, the stepped portion 14C is formed by a portion of the bottom wall <NUM> which extends vertically between the deep bottom portion 14A and the shallow bottom portion 14B.

In brief, the bottom wall <NUM> in this embodiment is shaped stepwisely to have the deep bottom portion 14A and the shallow bottom portion 14B which are arranged adjacent each other in the width-wise direction of the vehicle and different in height in the vertical direction.

The stepped portion 14C is, as clearly illustrated in <FIG> and <FIG>, arranged on a middle portion of the bottom wall <NUM> in the crankshaft axial direction 4a. The deep bottom portion 14A occupies substantially a right half of the oil pan main body <NUM>, while the shallow bottom portion 14B occupies substantially a left half of the oil pan main body <NUM>.

The peripheral wall <NUM>, as can be seen in <FIG>, includes the front wall <NUM>, the rear wall <NUM>, the left side wall <NUM>, and the right side wall <NUM>.

The front wall <NUM> is, as shown in <FIG>, joined to a front edge (also called first edge) 14a of the deep bottom portion 14A which extends perpendicular to the crankshaft <NUM> and a rear edge (also called first edge) 14b of the shallow bottom portion 14B. The front wall <NUM> extends along the front edge 14a of the deep bottom portion 14A and the front edge 14b of the shallow bottom portion 14B in the crankshaft axial direction 4a. The front wall <NUM> has the flange <NUM> joined to an upper end thereof.

The crankshaft <NUM> is of a crank-shape. The direction perpendicular to or crossing the crankshaft <NUM>, as referred to herein, is defined as a direction which horizontally crosses the center axis of rotation of each straight section of the crankshaft <NUM>. The crankshaft axial direction 4a, as referred to herein, is defined to coincide with the center axis of rotation of the crankshaft <NUM>.

The rear wall <NUM> is joined to a rear edge (also called second edge) 14c of the deep bottom portion 14A (see <FIG>) which faces to cross the crankshaft <NUM> and a rear edge (also called second edge) 14d of the shallow bottom portion 14B which faces to cross the crankshaft <NUM>.

The rear wall <NUM> extends along the rear edge 14c of the deep bottom portion 14A and the rear edge 14d of the shallow bottom portion 14B in the crankshaft axial direction 4a and has the flange <NUM> joined to an upper end thereof. The front wall <NUM> and the rear wall <NUM> are oriented to face each other in a direction (i.e., the longitudinal direction) perpendicular to the length of the crankshaft <NUM>.

The left side wall <NUM> is located at the left end (also referred to as a first end) of the peripheral wall <NUM> and faces the right end of the peripheral wall <NUM> in the crankshaft axial direction 4a. The left side wall <NUM> connects the left end of the front wall <NUM>, the left end of the rear wall <NUM>, and the left end of the shallow bottom portion 14B together.

The right side wall <NUM> is located on the right end (also referred to as a second end) of the peripheral wall <NUM> and faces the right end (i.e., the left side wall <NUM>) in the crankshaft axial direction 4a. The right side wall <NUM> connects the right end of the front wall <NUM>, the right end of the rear wall <NUM>, and the right end of the deep bottom portion 14A together. The left side wall <NUM> faces the right side wall <NUM> in the crankshaft axial direction 4a.

In this embodiment, the left side wall <NUM> constitutes a first side wall. The right side wall <NUM> constitutes a second side wall. The front wall <NUM> constitutes a third side wall. The rear wall <NUM> constitutes a fourth side wall.

The shallow bottom portion 14B, as can be seen in <FIG> and <FIG>, includes the middle bottom section 14D, the front raised bottom section 14E (which will also be referred to below as a first raised bottom section), and the rear raised bottom section 14F (which will also be referred to below as a second raised bottom section).

The middle bottom section 14D occupies a central area of the shallow bottom portion 14B in the longitudinal direction (i.e., horizontal direction) crossing the crankshaft <NUM>.

The front raised bottom section 14E is arranged in front of the middle bottom section 14D in the longitudinal direction perpendicular to the crankshaft <NUM> and, as clearly illustrated in <FIG>, located at a higher position than the middle bottom section 14D.

The front raised bottom section 14E is joined at a front end thereof to the front wall <NUM> (see <FIG>). The front end of the front raised bottom section 14E coincides with the front edge 14b of the shallow bottom portion 14B.

The rear raised bottom section 14F is arranged in back of the middle bottom section 14D in the longitudinal direction crossing the crankshaft <NUM> and located at a higher position than the middle bottom section 14D (see <FIG>). The rear raised bottom section 14F is joined at a rear end thereof to the rear wall <NUM> (see <FIG>). The rear end of the rear raised bottom section 14F coincides with the rear edge 14d of the shallow bottom portion 14B.

The front raised bottom section 14E is, as can be seen in <FIG>, located at a higher position than the rear raised bottom section 14F. The middle bottom section 14D protrudes downward from the front raised bottom section 14E and the rear raised bottom section 14F.

The shallow bottom portion 14B, as apparent from the above discussion, includes the front raised bottom section 14E and the rear raised bottom section 14F which are arranged on opposite sides of the middle bottom section 14D and face each other in the longitudinal direction crossing the crankshaft <NUM>. The front raised bottom section 14E and the rear raised bottom section 14F are located at a higher position than the middle bottom section 14D in the vertical direction. Each of the front raised bottom section 14E and the rear raised bottom section 14F will also be referred to as a raised bottom section.

The front raised bottom section 14E and the rear raised bottom section 14F are, as can be seen in <FIG>, formed to occupy an entire area between the stepped portion 14C and the left side wall <NUM> which face each other in the crankshaft axial direction 4a. The left ends of the front raised bottom section 14E and the rear raised bottom section 14F are joined to the left side wall <NUM>.

The deep bottom portion 14A, as clearly illustrated in <FIG> and <FIG>, includes the central deepest bottom section <NUM>, the front raised bottom section <NUM>, and the rear raised bottom section 14I.

The central deepest bottom section <NUM> occupies a central area of the deep bottom portion 14A between the ends of the deep bottom portion 14A which face each other in the longitudinal direction crossing the crankshaft <NUM>. The central deepest bottom section <NUM> is the deepest in the bottom wall <NUM>.

The front raised bottom section <NUM> is, as can be seen in <FIG> and <FIG>, arranged in front of the central deepest bottom section <NUM> in the longitudinal direction crossing the length of the crankshaft <NUM> and located at a higher position than the central deepest bottom section <NUM> in the vertical direction (see <FIG> and <FIG>).

The front raised bottom section <NUM> has a front end joined to the front wall <NUM>. The front end of the front raised bottom section <NUM> coincides with the front edge 14a of the deep bottom portion 14A.

The rear raised bottom section 14I is arranged in back of the central deepest bottom section <NUM> in the longitudinal direction crossing the length of the crankshaft <NUM> and located at a higher position than the central deepest bottom section <NUM> in the vertical direction.

The rear raised bottom section 14I has a rear end joined to the rear wall <NUM>. The rear end of the rear raised bottom section 14I coincides with the rear edge 14c of the deep bottom portion 14A. The rear raised bottom section 14I is located at a higher position than the front raised bottom section <NUM> in the vertical direction.

As apparent from the above discussion, the deep bottom portion 14A includes the front raised bottom section <NUM> and the rear raised bottom section 14I which are arranged on opposite sides of the central deepest bottom section <NUM> in the longitudinal direction crossing the length of the crankshaft <NUM> and located at higher positions than the central deepest bottom section <NUM> in the vertical direction.

Each of the front raised bottom section <NUM> and the rear raised bottom section 14I, as can be seen in <FIG>, has a right end joined to the right side wall <NUM> and extends from the right side wall <NUM> toward the stepped portion 14C.

The front raised bottom section 14E and the rear raised bottom section 14F in this embodiment, as can be seen in <FIG>, have the upper surfaces 14e and 14f which are located below the lower level L that is a lower limit of the level of stored oil. The upper surfaces 14e and 14f are arranged in the vicinity of the lower level L.

The oil pan main body <NUM> in this embodiment is configured to store a specified amount of oil therein. The level of the stored oil lies above the shallow bottom portion 14B (i.e., the middle bottom section 14D, the front raised bottom section 14E, and the rear raised bottom section 14F).

The specified amount of oil, as referred to herein, is defined to have the level of oil which is stored in the oil pan main body <NUM> and located between the upper level H (i.e., an upper limit level) and the lower level L (i.e., a lower limit level).

The level of oil stored in the oil pan main body <NUM> can be measured by an oil level gauge, not shown, and is regulated to lie between marks of the oil level gauge indicating the lower level L and the upper level H.

The front wall <NUM>, as illustrated in <FIG> and <FIG>, has the filter mounting wall 14J and the bulging wall <NUM>.

The filter mounting wall 14J protrudes from an upper portion of the front wall <NUM> which is located near the flange <NUM> toward the rear wall <NUM> and is of a semicircular shape. The filter mounting wall 14J has a lower surface serving as the filter mounting surface <NUM> (see <FIG>) to which the oil filter <NUM> is secured.

The oil filter <NUM> is secured to the filter mounting surface <NUM> so that it hangs from the filter mounting wall 14J.

As viewed from above the oil pan <NUM> in <FIG>, the bulging wall <NUM> bulges from the front wall <NUM> toward the rear wall <NUM> in a semicircular shape to surround the oil filter <NUM> indicated by an imaginary line. The bulging wall <NUM> has an upper end joined to the top 14j of the filter mounting wall 14J, as viewed in a direction in which the filter mounting wall 14J protrudes.

The oil filter <NUM> in this embodiment is of a cylindrical shape. The semicircular bulging wall <NUM> is arranged to face the oil filter <NUM> through a given gap between itself and the oil filter <NUM> which is constant in a circumferential direction thereof.

As viewed from above the oil pan <NUM> in <FIG>, the oil filter <NUM> is arranged partially inside the oil pan main body <NUM> to have the rear end 21a which faces the rear wall <NUM> away from the front wall <NUM> and also have the front end 21b exposed frontward outside the front wall <NUM>.

With the above arrangements, the oil filter <NUM> does not protrude greatly outside the oil pan main body <NUM>, thereby reducing the volume of space occupied by installation of the oil filter <NUM> outside the oil pan main body <NUM>.

The right end of the front raised bottom section 14E and the left end of the front raised bottom section <NUM> are, as illustrated in <FIG> and <FIG>, joined to the bulging wall <NUM>. The oil is stored in a space above the front raised bottom section 14E surrounded by the bulging wall <NUM>, the front wall <NUM>, and the left side wall <NUM>.

The oil pan main body <NUM>, as illustrated in <FIG>, has the oil strainer <NUM> disposed thereon. The oil strainer <NUM> is arranged above the deep bottom portion 14A and has an oil inlet, not shown, formed in a lower surface thereof.

The oil strainer <NUM> has the oil outlet 22a which is connected to an oil pump, not shown, through an oil pathe formed in the cylinder block 2A.

When the oil pump is activated, the oil strainer <NUM> sucks oil and filters it. The oil is then sucked into the oil pump through an oil pipe, not shown.

The filter mounting wall 14J has the oil inlet hole <NUM> and the oil outlet hole 14i formed therein (see <FIG>). The oil inlet hole <NUM> and the oil outlet hole 14i communicate with the oil filter <NUM>.

The oil sucked from the oil pan main body <NUM> into the oil pump is discharged from the oil pump into the oil path, not shown, formed in the cylinder block 2A and then delivered into the oil filter <NUM> through the oil inlet hole <NUM>.

Afterward, the oil is filtered by the oil filter <NUM> and then discharged from the oil outlet hole 14i and supplied through a main gallery in the cylinder block 2A to parts of the engine <NUM> required to be lubricated.

The front raised bottom section 14E is, as illustrated in <FIG>, equipped with the rib 15A. The rib 15A protrudes upwardly from the front raised bottom section 14E and extends from the left side wall <NUM> toward the oil strainer <NUM>.

The above structure of the rib 15A serves to mechanically reinforce the front raised bottom section 14E, thereby enhancing the stiffness of the front raised bottom section 14E.

The rear raised bottom section 14F is equipped with the rib 15B. The rib 15B protrudes upward from the rear raised bottom section 14F and extends from the rear wall <NUM> toward the front wall <NUM>.

The above structure of the rib 15B serves to mechanically reinforce the rear raised bottom section 14F, thereby enhancing the stiffness of the rear raised bottom section 14F.

The central deepest bottom section <NUM> are equipped with the ribs 15C and 15D. The ribs 15C and 15D protrude upward from the central deepest bottom section <NUM> and extend from the right side wall <NUM> toward the stepped portion 14C.

The above structures of the ribs 15C and 15D serve to mechanically reinforce the central deepest bottom section <NUM>, thereby enhancing the stiffness of the central deepest bottom section <NUM>.

The deep bottom portion 14A, as illustrated in <FIG> and <FIG>, has the drain hole <NUM> formed therein. The drain hole <NUM> is closed by the plug <NUM> (see <FIG>). When it is required to exchange the oil stored in the oil pan <NUM>, it is discharged from the drain hole <NUM>.

The oil pan <NUM> in this embodiment, as apparent from the above discussion, includes the oil pan main body <NUM> and the plug <NUM>.

The operation of and beneficial advantages offered by the oil pan <NUM> in this embodiment will be described below.

The oil pan <NUM> includes the flange <NUM> and the oil pan main body <NUM>. The flange <NUM> has the rectangular opening 12a formed therein and is joined to the lower portion of the cylinder block 2A equipped with the crankshaft <NUM>. The oil pan main body <NUM> includes the peripheral wall <NUM> extending downward from the inner edge 12b of the flange <NUM> and the bottom wall <NUM> joined to the lower end of the peripheral wall <NUM>.

The bottom wall <NUM> includes the deep bottom portion 14A and the shallow bottom portion 14B. The shallow bottom portion 14B is located on an opposite side (i.e., the left side) of the crankshaft axial direction 4a to the deep bottom portion 14A and at a higher position than the deep bottom portion 14A. The shallow bottom portion 14B is also connected to the deep bottom portion 14A through the stepped portion 14C. The oil pan main body <NUM> is configured so that the level of stored oil is located above the shallow bottom portion 14B.

The shallow bottom portion 14B includes the middle bottom section 14D, the front raised bottom section 14E, and the rear raised bottom section 14F. The middle bottom section 14D occupies a central portion of the shallow bottom portion 14B in a direction crossing the crankshaft <NUM>. The front raised bottom section 14E and the rear raised bottom section 14F are located on opposite sides of the middle bottom section 14D and face each other in the direction crossing the crankshaft <NUM> and at higher positions than the middle bottom section 14D.

The front raised bottom section 14E and the rear raised bottom section 14F, therefore, serve to decrease the volume of oil stored on the shallow bottom portion 14B and also raise the level of oil totally stored in the oil pan main body <NUM>.

When the level of oil stored in the oil pan main body <NUM> is excessively high, it leads to a risk that the oil may be agitated by a counterweight, not shown, of the crankshaft <NUM>. Conversely, when the level of oil stored in the oil pan main body <NUM> is excessively low, it may result in a risk that an oil inlet of the oil strainer <NUM> may suck air which then enters the oil pump.

The oil pan <NUM> in this embodiment is capable of raising the level of oil stored in the oil pan main body <NUM> using the front raised bottom section 14E and the rear raised bottom section 14F, thereby keeping the level of oil stored in the oil pan main body <NUM> at a desired level even when the volume of coil stored in the shallow bottom portion 14B is decreased.

Since the oil strainer <NUM> is designed to suck the oil to be stored in the deep bottom portion 14A through the oil inlet, it is arranged on the deep bottom portion 14A. In contrast, there is no interferer, such as the oil strainer <NUM>, on the shallow bottom portion 14B, thereby facilitating increasing the size of the front raised bottom section 14E and the rear raised bottom section 14F.

It is, therefore, possible to eliminate the need for delivering the volume of oil into the oil pan main body <NUM> which is greater than that required to lubricate the engine <NUM> in order to raise the level of oil totally stored in the oil pan main body <NUM>. This alleviates a risk that the oil in the oil pan main body <NUM> may be agitated by the counterweight.

It is also possible to alleviate a risk that the level of oil stored in the oil pan main body <NUM> may be undesirably decreased due to a decrease in volume of oil needed to be delivered into the oil pan main body <NUM>, thereby avoiding suction of air into the oil pump.

The oil pan <NUM> in this embodiment is configured to have the middle bottom section 14D which protrudes downward in a convex shape relative to the front raised bottom section 14E and the rear raised bottom section 14F and is formed in the shallow bottom portion 14B. This enables the middle bottom section 14D which is of a curved convex shape in cross section to function as a rib joining the shallow bottom portion 14B to the stepped portion 14C, thereby enhancing the stiffness of the oil pan main body <NUM> to minimize mechanical vibration of the oil pan main body <NUM>.

The oil pan <NUM> in this embodiment is, as apparent from the above discussion, capable of optimizing the volume and the level of oil stored in the oil pan main body <NUM> and also minimizing the mechanical vibration of the oil pan main body <NUM>.

The oil pan <NUM> is also capable of reinforcing the mechanical strength of the front raised bottom section 14E, the rear raised bottom section 14F, and the central deepest bottom section <NUM> using the ribs 15A, 15B, 15C, and 15D to increase the stiffness of the front raised bottom section 14E, the rear raised bottom section 14F, and the central deepest bottom section <NUM>. This enhances the entire rigidity of the oil pan main body <NUM>, thereby greatly reducing the mechanical vibration of the oil pan main body <NUM>.

The oil pan <NUM> is, as described above, designed to include the front raised bottom section 14E and the rear raised bottom section 14F which have the upper surfaces 14e and 14f located below the lower level L defining a lower limit(s) of the level (i.e., surface) of oil stored in the oil pan <NUM>. The upper surfaces 14e and 14f are also located near the lower level L of oil.

The above structure serves to prevent the level of oil from being lowered suddenly below the upper surfaces 14e and 14f of the front raised bottom section 14E and the rear raised bottom section 14F when the oil is consumed by operation of the engine <NUM>, so that the level of the oil decreases from the upper level H to the lower level L. This minimizes a risk that air may be sucked into the oil pump.

The oil pan <NUM> is also equipped with the peripheral wall <NUM> which includes the left side wall <NUM> and the right side wall <NUM>. The left side wall <NUM> is located at the right side of the oil pan <NUM>. The right side wall <NUM> is located at the left side of the oil pan <NUM> which faces the left side (i.e., the left side wall <NUM>) thereof in the crankshaft axial direction 4a.

The front raised bottom section 14E and the rear raised bottom section 14F occupy an entire area between the stepped portion 14C and the left side wall <NUM> in the crankshaft axial direction 4a.

The above structure enables an area occupied by the front raised bottom section 14E and the rear raised bottom section 14F to be increased in the crankshaft axial direction 4a, thereby facilitating adjustment of the volume and level of oil stored in the oil pan main body <NUM>. This achieves effective optimization of the volume and level of oil stored in the oil pan main body <NUM>.

The oil pan <NUM> has the peripheral wall <NUM> which includes the front wall <NUM> and the rear wall <NUM>. The front wall <NUM> extends in the crankshaft axial direction 4a along the front edge 14a of the deep bottom portion 14A and the front edge 14b of the shallow bottom portion 14B which face in a direction crossing the crankshaft axial direction 4a. The rear wall <NUM> extends in the crankshaft axial direction 4a along the rear edge 14c of the deep bottom portion 14A and the rear edge 14d of the shallow bottom portion 14B which face in a direction crossing the crankshaft axial direction 4a. The front wall <NUM> and the rear wall <NUM> have upper ends joined to the flange <NUM>.

The front wall <NUM> is equipped with the filter mounting wall 14J which protrudes from the upper portion of the front wall <NUM> toward the rear wall <NUM> and has a lower surface serving as the filter mounting surface <NUM> to which the oil filter <NUM> is secured.

The front wall <NUM> also includes the bulging wall <NUM>. The bulging wall <NUM> is shaped to bulge from the front wall <NUM> toward the rear wall <NUM> and surround the oil filter <NUM>. The bulging wall <NUM> has the upper end connecting with the top 14j of the filter mounting wall 14J which faces in a direction in which the bulging wall <NUM> bulges. The bulging wall <NUM> also connects with the front raised bottom section 14E and the front raised bottom section <NUM>.

The above structure of the bulging wall <NUM> is capable of regulating the volume of the oil pan main body <NUM>, thereby achieving the optimization of the volume and level of oil stored in the oil pan main body <NUM>.

The bulging wall <NUM> also serves to mechanically reinforce the front raised bottom section 14E and the front raised bottom section <NUM> to increase the rigidity of the front raised bottom sections 14E and <NUM>. The bulging wall <NUM> also enhances the rigidity of the front wall <NUM>. This minimizes the mechanical vibration of the oil pan main body <NUM>.

Claim 1:
An oil pan for an internal combustion engine, comprising:
an oil pan main body (<NUM>) which includes a flange (<NUM>), a peripheral wall (<NUM>), and a bottom wall (<NUM>), the flange (<NUM>) having a rectangular opening (12a) and being joined to a lower portion of a body of an internal combustion engine (<NUM>) equipped with a crankshaft (<NUM>), the peripheral wall (<NUM>) extending downward from an inner edge (12b) of the flange (<NUM>), the bottom wall (<NUM>) being joined to a lower end of the peripheral wall (<NUM>), wherein:
the bottom wall (<NUM>) includes a deep bottom portion (14A) and a shallow bottom portion (14B), the shallow bottom portion (14B) being arranged adjacent the deep bottom portion (14A) in a direction in which the crankshaft (<NUM>) extends and located at a higher position than the deep bottom portion (14A), the shallow bottom portion (14B) being joined to the deep bottom portion (14A) through a stepped portion (14C),
the shallow bottom portion (14B) includes a middle bottom section (14D), a first raised bottom section (14E), and a second raised bottom section (14F), the middle bottom section (14D) occupying a central portion of the shallow bottom portion (14B) in a direction crossing the crankshaft, the first raised bottom section (14E) and the second raised bottom section (14F) being arranged on the opposite sides of the middle bottom section (14D) in the direction crossing the crankshaft (<NUM>) and located at a higher position than the middle bottom section (14D),
characterized in that:
the oil stored in the oil pan main body (<NUM>) lies above the shallow bottom portion (14B) as the oil pan main body (<NUM>) stores a specified amount of oil, and
the first and second raised bottom sections (14E, 14F) of the shallow bottom portion (14B) have their upper surfaces (14e, 14f) located below and in the vicinity of the lower level (L) of the oil stored in the oil pan main body (<NUM>), which is the lower limit of the level of the oil kept in the oil pan main body (<NUM>).