2001 Honda HR-V 3dr 4x4 - Joy Machine

The dual pump system has a wet multi-plate clutch in the rear diff, which controls the connection between the driveshaft and the pinion - ie: it controls the power to the rear axle and is normally disengaged.

The dual pumps are literally two pumps, one driven by the driveshaft and one driven by the pinion, which feed the hydraulics for the wet clutch. When the driveshaft and pinion rotate at the same speed (no tyre slippage) then the pumps drive at the same speed and the pressures are in equilibrium, and the clutch does not engage. When there is a difference in speed (Driveshaft faster than rear axle during FWD skid), the pumps turn at different speeds, causing a pressure imbalance, and the difference in pump output causes hydraulic pressure to engage the wet clutch and drive the rear axle.

With the one I used to drive, the AWD cut in with an amusing, short moaning noise and the system worked quite well. You'd push it into sledge understeer (or handbrake into a drift) in the rain or offroad, pick up the throttle, after a very slight delay there'd be a moan from the driveline and the car would just straighten itself out with nice forward drive out of the slide in a 'hand of god' type feeling as the rear axle cut in.