What is Power differential? on 2005 Honda CR-V

I was told that I need to have all my fluids replced on my 2005 Honda CRV. I was given a list Rear differential, power differential, Break Fluid, Coolant, and Manual Transmission. I have heard of all the fluids except for Power differential and cannot locate any information on it. What is Power Differential?

Asked by for the 2005 Honda CR-V

Document Type and Number:United States Patent 3653279

Abstract:A differential fluid coupling drive wherein a pair of fluid couplings in conjunction with an intermediate planetary type differential and lock-up clutch are employed to deliver power from a single engine to two separate dual power shift transmissions respectively driving opposite side wheels of a vehicle. The drive allows a normal differential action at small differences in wheel speeds, as in turning, but has high resistance to large wheel speed differentials, such as when one wheel loses traction.

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