Abstract: A circular saw in which cutting speed of a saw blade is smoothly controlled. A speed change mechanism of a circular saw includes first and second rotating shafts disposed parallel to each other, and first and second gear trains having different gear ratios and each having a combination of a drive gear and a driven gear as one unit which are engaged with each other and transmit torque of the first rotating shaft to the second rotating shaft. A torque transmission path via the first gear train is defined as a first power transmission path and a torque transmission path via the second gear train is defined as a second power transmission path, and the transmission path is switched between the first power transmission path and the second power transmission path.

Abstract: A power tool includes a power source, a speed change mechanism and a tool bit. The speed change mechanism includes first and second rotating shafts disposed parallel to each other, a first power transmission path provided with a first gear train and a first clutch and a second power transmission path provided with a second gear train and a second clutch. The power transmission path is switched between the first power transmission path and the second power transmission path while the first and second gear trains are held engaged, by shifting of the first and second clutches between the power transmission state and the power transmission interrupted state according to a load applied to the tool bit. The speed change mechanism further includes a switching retaining mechanism, a switching preventing mechanism, a switching set value adjusting mechanism or a switching mechanism.

Abstract: A power tool includes a power source, a speed change mechanism and a tip tool wherein the speed change mechanism has first and second rotating shafts arranged in parallel, a first power transmission passage equipped with a first gear train and a first clutch, and a second power transmission passage equipped with a second gear train and a second clutch. The speed change mechanism is constituted to switch the transmission passage between the first power transmission passage and the second power transmission passage while keeping the first and second gear trains in meshed state by switching the first and second clutches between power transmission state and power interruption state depending on a load applied to the tip tool.

Abstract: One aspect of the invention includes a speed changing device which can be switched from a high-speed low-torque output state to a low-speed high-torque output state. In the high-speed low-torque state, a second stage internal gear rotates together with a first stage carrier. The low-speed high-torque output state is caused as the second stage internal gear is disconnected from the first stage carrier so as to be restricted from rotating. The timing of resetting the speed changing device is shifted relative to the timing of stopping the electric motor by an OFF operation of the switch lever with a delay mechanism, so that the second stage internal gear is engaged with the first stage carrier after the rotation through inertia is stopped, whereby its impact is reduced.

Abstract: One aspect of the invention can include an electric screw tightening machine in which a speed change to a low-speed high-torque output state is automatically achieved in conjunction with increase in an external torque of a spindle. This output state is locked by a speed change lock mechanism, and this lock state is reset by an OFF operation of a switch lever. A speed changing device can be switched from a high-speed low-torque output state to a low-speed high-torque output stage. In the high-speed low-torque state, the second stage internal gear rotates together with a first stage carrier. The low-speed high-torque output state is caused as the second stage internal gear is disconnected from the first stage carrier so as to be restricted from rotating.

Abstract: A circular saw in which cutting speed of a saw blade is smoothly controlled. A speed change mechanism of a circular saw includes first and second rotating shafts disposed parallel to each other, and first and second gear trains having different gear ratios and each having a combination of a drive gear and a driven gear as one unit which are engaged with each other and transmit torque of the first rotating shaft to the second rotating shaft. A torque transmission path via the first gear train is defined as a first power transmission path and a torque transmission path via the second gear train is defined as a second power transmission path, and the transmission path is switched between the first power transmission path and the second power transmission path.

Abstract: A power tool includes a power source, a speed change mechanism and a tip tool wherein the speed change mechanism has first and second rotating shafts arranged in parallel, a first power transmission passage equipped with a first gear train and a first clutch, and a second power transmission passage equipped with a second gear train and a second clutch. The speed change mechanism is constituted to switch the transmission passage between the first power transmission passage and the second power transmission passage while keeping the first and second gear trains in meshed state by switching the first and second clutches between power transmission state and power interruption state depending on a load applied to the tip tool.

Abstract: A power tool includes a power source, a speed change mechanism and a tool bit. The speed change mechanism includes first and second rotating shafts disposed parallel to each other, a first power transmission path provided with a first gear train and a first clutch and a second power transmission path provided with a second gear train and a second clutch. The power transmission path is switched between the first power transmission path and the second power transmission path while the first and second gear trains are held engaged, by shifting of the first and second clutches between the power transmission state and the power transmission interrupted state according to a load applied to the tool bit. The speed change mechanism further includes a switching retaining mechanism, a switching preventing mechanism, a switching set value adjusting mechanism or a switching mechanism.