Fluid expansion tank

A hydraulic drive device, comprising:

• a housing forming an internal sump for hydraulic fluid and having a variable first pressure;
• a transmission disposed in the sump;
• a tank body disposed in the sump and comprising a main body and a cover engaged thereto to define an internal expansion volume having a variable second pressure;
• a fluid inlet opening defined in the tank body, the fluid inlet opening in communication with the sump and the internal expansion volume;
• and
• a combination valve disposed on a lower end of the cover to control fluid flow between the sump and the internal expansion volume, the combination valve comprising a first valve that opens to permit fluid to enter the internal expansion volume from the sump when the first pressure in the sump exceeds the second pressure in the internal expansion volume by a first predetermined amount, and a second valve that opens to permit fluid to exit the internal expansion volume to the sump when the second pressure in the internal expansion volume exceeds the first pressure in the sump by a second predetermined amount.

An expansion tank for use with a drive device having a sump containing hydraulic fluid and having a variable first pressure, the expansion tank comprising:

• a tank body disposed in the sump and comprising a main body and a cover engaged thereto to define an internal expansion volume having a variable second pressure;
• a fluid inlet opening defined in the tank body, the fluid inlet opening in communication with the sump and the internal expansion volume;
• and
• a combination valve disposed on a lower end of the cover to control fluid flow between the sump and the internal expansion volume, the combination valve comprising an umbrella valve and a duckbill valve, wherein fluid enters the internal expansion volume from the fluid inlet opening through the umbrella valve when the first pressure in the sump exceeds the second pressure in the internal expansion volume by a first predetermined amount, and fluid exits the internal expansion volume through the duckbill valve and the fluid inlet opening to the sump when the second pressure in the internal expansion volume exceeds the first pressure in the sump by a second predetermined amount.