Oil cooler

1. An oil cooler comprising:

a plurality of flat tubes layered together with a clearance with respect to one another in a layering direction, and configured to be mounted in a case, the case being structured to allow cooling water to flow in the case through the clearance in a longitudinal direction of the flat tubes, and each tube of the plurality of flat tubes being structured to allow working oil to flow in each respective tube of the plurality of flat tubes; wherein

each tube of the plurality of flat tubes includes

a first plate;

a second plate including a periphery joined with a periphery of the first plate;

a fin plate held between the first plate and the second plate; and

an oil port having a cylindrical shape having a longitudinal axis extending in the layering direction, and provided at first longitudinal end portions of the first plate and the second plate, the first longitudinal end portions being configured to receive inflow of cooling water;

each tube of the plurality of flat tubes is connected to one another via the oil port;

wherein, in a respective flat tube of the plurality of flat tubes,

the first plate is recessed to form a fin plate accommodation portion accommodating the fin plate, wherein a first longitudinal end portion of the first plate is outside of the fin plate accommodation portion in the longitudinal direction of the respective tube of the plurality of flat tubes;

the second plate has a flat shape covering the fin plate accommodation portion of the first plate;

the first longitudinal end portion of the first plate and the first longitudinal end portion of the second plate are joined together to form a thin portion of the respective tube of the plurality of flat tubes; and

the oil port is provided at the thin portion of the respective tube of the plurality of flat tubes and located adjacent to the fin plate accommodation portion of the first plate;

each tube of the plurality of flat tubes includes a guide wall at a lateral periphery thereof, wherein the guide wall faces the oil port in a width direction of the plurality of flat tubes, and has a rectangular shape having a longitudinal axis extending in the longitudinal direction of the respective flat tube of the plurality of flat tubes, and projects in the layering direction, and has a projecting end facing an adjacent one of the plurality of flat tubes, wherein an entirety of the projecting end is out of contact with the adjacent flat tube; and

the guide wall, the thin portion, and a lateral wall of the oil port form a nozzle portion of the respective tube of the plurality of flat tubes to guide cooling water in the longitudinal direction of the respective tube of the plurality of flat tubes.

2. The oil cooler as claimed in claim 1 , wherein:

each tube of the plurality of flat tubes includes two of the oil ports arranged in the width direction of the plurality of flat tubes;

each tube of the plurality of flat tubes includes an inter-port passage formed between the oil ports, wherein the inter-port passage extends from the thin portion to an adjacent longitudinal end of the fin plate accommodation portion; and

the inter-port passage includes a slope connected between a level of the thin portion and a level of the fin plate accommodation portion.

3. The oil cooler as claimed in claim 1 , wherein the lateral wall of the oil port includes a base portion extending toward an adjacent longitudinal end of the fin plate accommodation portion and expanding in the width direction of the plurality of flat tubes.

4. The oil cooler as claimed in claim 3 , wherein:

the base portion of the lateral wall of the oil port includes a slope at a portion of the base portion expanding in the width direction of the plurality of flat tubes; and

the slope is connected between a level of the thin portion and a level of the fin plate accommodation portion.

5. The oil cooler as claimed in claim 1 , wherein the guide wall extends in a range covering an adjacent longitudinal end of the fin plate accommodation portion in the longitudinal direction of the respective tube of the plurality of flat tubes.

6. The oil cooler as claimed in claim 5 , wherein:

the oil cooler includes a plurality of embossed portions provided in each clearance for keeping each respective clearance; and

the guide wall extends between a central portion of the oil port and one of the embossed portions in the longitudinal direction of the respective tube of the plurality of flat tubes, wherein the one of the embossed portions is closer to the oil port in the longitudinal direction of the respective tube than at least another of the embossed portions.