Fluid coupling - hydraulic coupling

Japanese: 流体継手 - りゅうたいつぎて（英語表記）hydraulic coupling

A device in which the drive shaft and the passive shaft are aligned in a straight line, a pump impeller is attached to the end of the drive shaft and a water wheel impeller is attached to the end of the passive shaft, and the space between them is filled with liquid (usually oil), transmitting the rotation of the drive shaft to the passive shaft. Usually, the pump and water wheel impellers have the same shape, and the blades are radial. When the drive shaft is rotated, the liquid is rotated by the pump impeller and flows out, passing through the water wheel impeller to rotate the passive shaft, and the liquid flows between the two impellers. There is always some slippage, and the rotation of the passive shaft is smaller than that of the drive shaft, but the usual rotation speed ratio is about 0.95 to 0.98. When transmitting a certain amount of power, the greater the rotation speed and diameter, the less slippage and the higher the efficiency. A working fluid with good oiliness, a small viscosity coefficient, a high specific gravity, a low freezing point, a high boiling point, and a low deterioration resistance is suitable, and mineral oil is generally used. Under normal operating conditions, there is no need to extract oil for cooling (→ torque converter). Taking advantage of the smooth clutch action of the fluid coupling, hydromatic transmissions with four forward gears and one reverse gear are used in automobiles in combination with three planetary gears.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

駆動軸と受動軸とを一直線上に置き，駆動軸端にポンプ羽根車を受動軸端に水車羽根車をつけて向い合せ，両者の間に液体 (一般には油) を満たして，駆動軸の回転を受動軸に伝える装置。普通はポンプ，水車両羽根車の形状は等しく，羽根は半径方向である。駆動軸を回すと，ポンプ羽根車によって液が回されて流出し，水車羽根車を通って受動軸を回し，液は両羽根車間を回流する。常に若干の滑りがあり，受動軸の回転は駆動軸のそれより小さいが，常用の回転数比は 0.95～0.98程度である。一定の動力を伝達する場合，回転数，直径ともに大きくなるほど，滑りが少くなり効率がよくなる。作動液としては油性がよく，粘性係数が小さく，比重が大きく，低凝固点・高沸騰点で変質しにくいものが適し，一般に鉱物油が用いられる。普通の使用状況では油を外部に取出して冷却する必要はない (→トルクコンバータ ) 。流体継手のなめらかなクラッチ作用を利用して，3対の遊星歯車式変速装置と組合せて，前進4段，後進1段のハイドロマチック変速機が自動車用として用いられている。

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