Which device serves as a one-way clutch in some planetary gear trains?

Which device serves as a one-way clutch in some planetary gear trains?

• A. Sprag-type one-way clutches
• B. Hydraulic clutch
• C. Hydraulic piston
• D. Brake bands

Answer: (A)

Sprag-type one-way clutches provide directional engagement in planetary gear trains. They use wedge-shaped sprags that lock with the races when torque tries to drive the components in one direction, transmitting torque firmly. In the opposite direction, the sprags disengage and allow motion to continue without back-driving the source. This one-way behavior is exactly what some planetary gear configurations need to control which parts are driven or held during different operating modes. Hydraulic clutches, hydraulic pistons, and brake bands aren’t designed to provide this direction-specific torque transfer. A hydraulic clutch uses fluid pressure to engage or disengage, not inherently to block motion in one direction. A hydraulic piston is just an actuator component, and brake bands act as friction brakes to hold or slow rotation rather than enabling selective one-way drive.

Sprag-type one-way clutches provide directional engagement in planetary gear trains. They use wedge-shaped sprags that lock with the races when torque tries to drive the components in one direction, transmitting torque firmly. In the opposite direction, the sprags disengage and allow motion to continue without back-driving the source. This one-way behavior is exactly what some planetary gear configurations need to control which parts are driven or held during different operating modes.

Hydraulic clutches, hydraulic pistons, and brake bands aren’t designed to provide this direction-specific torque transfer. A hydraulic clutch uses fluid pressure to engage or disengage, not inherently to block motion in one direction. A hydraulic piston is just an actuator component, and brake bands act as friction brakes to hold or slow rotation rather than enabling selective one-way drive.