Patent Description:
Exemplary impact power tools include a housing, a motor, a transmission, and an impact assembly including a cam shaft driven by the transmission, a hammer coupled to the cam shaft for rotational and axial movement relative to the cam shaft, and an anvil engageable by the hammer. At low torque levels, the cam shaft, the hammer, and the anvil rotate together to transmit torque to the anvil without impacts. At higher torque levels, the hammer moves axially and rotationally along the cam shaft and applies intermittent rotational impacts to the anvil. At very high torque levels, the hammer may travel a greater axial distance than desired along the cam shaft and strike the transmission, which can cause failure of transmission components. The impact power tool disclosed in <CIT> seeks to address the problem of avoiding contact with the transmission by the inclusion of a first stop member on the cylindrical flange of the cam shaft, and a second stop member on a rear portion of the hammer. While other disclosed impact power tools, such as that disclosed in <CIT>, fail to even recognize the problem of undesired contact of the hammer into the transmission.

The invention provides an impact power tool includes a housing, a motor received in the housing, a transmission with a transmission output shaft received in the housing and rotationally driven by the motor. A cam ring is removably rotationally coupled to the transmission output shaft by a decoupling mechanism. The cam ring includes a cam groove that receives a cam ball. An impact mechanism includes a hammer received over the cam ring and an anvil coupled to a tool output shaft. When a low amount of torque is applied to the tool output shaft, the cam ring remains rotationally coupled to the transmission output shaft by the decoupling mechanism transmits torque to the hammer, which remains engaged with the anvil and transmits rotational motion from the transmission output shaft to the tool output shaft without any impacts. When a higher amount of torque is applied to the tool output shaft, the cam ring remains rotationally coupled to the transmission output shaft by the decoupling mechanism and transmits torque to the hammer, while the hammer travels axially along the cam ring and transmits rotary impacts to the anvil and the tool output shaft. If the impactor has a high axial displacement (e.g., past a transverse line), the decoupling mechanism will decouple from the output shaft of the transmission.

Implementations of this aspect may include one or more of the following features. The decoupling mechanism may include retaining balls that are removably retained in grooves in the transmission output shaft. The hammer may include a bore having a first inner diameter portion and a second inner diameter portion having a greater diameter than the first inner diameter portion. At the low torque and higher torque levels, the first inner diameter portion may keep the retaining balls engaged with the recesses. At the very high torque levels, the second inner diameter portion may allow the balls to move radially out of the recesses to decouple the transmission output shaft from the cam ring.

The decoupling mechanism may include a coupling ring configured to releasably couple the transmission output shaft to the cam ring. The coupling ring may include splines configured to engage splines on the cam ring. The coupling ring may move between a first position in which the splines on the coupling ring engage the splines on the cam ring to transmit torque from the transmission output shaft to the cam ring and a second position in which the splines on the coupling ring are disengaged from the splines on the cam ring to interrupt torque transmission from the transmission output shaft to the cam ring. The coupling ring may be biased toward the first position by a spring or elastic member.

The decoupling mechanism may include a coupler coupled for rotation to the transmission to the output shaft and releasably coupled to the cam ring. The coupler may include a clutch ring coupled to the transmission output shaft and a plurality of clutch balls releasably engaging recesses in the cam ring. The coupler may move between a first position in which the coupler engages the cam ring to transmit torque from the transmission output shaft to the cam ring and a second position in which the coupler is disengaged from the cam ring to interrupt torque transmission from the transmission output shaft to the cam ring. The coupler may be biased toward the first position by a spring or elastic member.

An aspect not covered by the invention provides an impact power tool includes a housing, a motor disposed in the housing and including a motor output shaft, a transmission including a transmission output shaft and an input member rotatably drivable by rotation of the motor output shaft, a rotary impact assembly including a cam shaft extending along and rotatable about an axis, a hammer coupled to the cam shaft for axial and rotational movement relative to the cam shaft, an anvil rotatable about the axis, and a spring biasing the hammer toward the anvil, a tool output shaft at least partially received in the housing and rotatable by rotation of the anvil, and a coupler removably coupling the cam shaft to the transmission output shaft. When torque on the tool output shaft is less than or equal to a first threshold, the transmission output shaft, the cam shaft, the hammer, and the anvil rotate together to transmit torque to the tool output shaft. When torque on the tool output shaft is above the first threshold, the hammer moves along the cam shaft away from the anvil by at least a first distance and applies intermittent rotary impacts to the anvil and the tool output shaft. When the hammer moves along the cam shaft away from the anvil by at least a second distance greater than the first distance, the coupler decouples the transmission output shaft from the cam shaft, interrupting torque transmission to the tool output shaft.

Implementations of this aspect may include one or more of the following features. The cam shaft may comprise a cam ring received at least partially over the transmission output shaft. The hammer may include a portion that is configured to cause the coupler to move from a coupled position to a decoupled position when the hammer moves along the anvil by at least the second distance. The coupler may include a ball movable between the coupled position where the ball is received in a recess in at least one of the transmission output shaft or the cam shaft to non-rotatably couple the transmission output shaft to the cam shaft, and the decoupled position where the ball is movable out of the recess to decouple the transmission output shaft from the cam shaft. The hammer may include a bore having a first diameter portion that maintains the ball in the recess when the hammer moves along the cam shaft by less than the second distance, and a second larger diameter portion that allows the coupler ball to move out of the recess when the hammer moves along the cam shaft by at least the second distance. The coupler may comprise a coupler ring movable between the coupled position in which the coupler ring non-rotatably couples the transmission output shaft to the cam shaft, and the decoupled position in which the coupler ring disengages from at least one of the transmission output shaft or the cam shaft to decouple the transmission output shaft from the cam shaft. The hammer may include a rearward protrusion that pushes the coupler ring toward the decoupled position when the hammer moves along the cam shaft by at least the second distance. The coupler may comprise a clutch ring non-rotatably coupled to one of the transmission output shaft or the cam shaft and a clutch ball engaged by the clutch ring and receivable in a recess in the other of the transmission output shaft or the cam shaft, the clutch ring being movable between a first position where the clutch ball is engaged with the recess to non-rotatably coupled the transmission output shaft to the cam shaft, and a second position in which the clutch ball is disengagable from the recess to decouple the transmission output shaft from the cam shaft. The hammer may include a portion that is configured to push the clutch ring toward the second position when the hammer moves axially along the cam shaft by greater at least the second distance.

An aspect not covered by the invention provides an impact power tool includes a housing, a motor disposed in the housing and having a motor output shaft, a transmission having an input member rotatably drivable by rotation of the motor output shaft and a transmission output shaft, a rotary impact assembly including a cam shaft removably coupled to the transmission output shaft, a hammer coupled to the cam shaft and able to move axially and rotatably relative to the cam shaft, an anvil rotatable about the axis; and a spring biasing the hammer toward the anvil, a tool output shaft at least partially received in the housing and rotatable by rotation of the anvil, and a coupler removably coupling the cam shaft to the transmission output shaft, When torque on the tool output shaft is at or below a first threshold, the transmission output shaft, the cam shaft, the hammer, and the anvil rotate together to transmit torque to the tool output shaft without impacts. When torque on the tool output shaft is above the first threshold, and the hammer moves axially and rotationally along the cam shaft toward and away from the anvil to apply intermittent rotary impacts to the anvil and the tool output shaft. When torque on the tool output shaft is above a second threshold greater than the first threshold, the coupler decouples the transmission output shaft from the cam shaft, interrupting torque transmission to the tool output shaft.

Implementations of this aspect may include one or more of the following features. The cam shaft may comprise a cam ring received at least partially over the transmission output shaft. When torque above the first threshold is applied to the tool output shaft, the hammer may move along the cam shaft away from the anvil by at least a first distance, and when torque about the second threshold is applied to the tool output shaft, the hammer may move along the cam shaft away from the anvil by at least a second distance greater than the first distance to enable the coupler to decouple the transmission output shaft from the cam shaft. The coupler may include a coupler ball movable between a first position where the ball is received in a recess in at least one of the transmission output shaft or the cam shaft to non-rotatably couple the transmission output shaft to the cam shaft, and a second position where the ball moves out of the recess to decouple the transmission output shaft from the cam shaft. The hammer may include a first portion that maintains the coupler ball in the recess when torque applied to the output shaft is less than or equal to the second threshold, and a second portion that allows the coupler ball to move out of the recess when torque applied to the output shaft is greater than the second threshold. The coupler may comprise a coupler ring movable between a first position in which the coupler ring non-rotatably couples the transmission output shaft to the cam shaft, and a second position in which the coupler ring disengages from at least one of the transmission output shaft or the cam shaft to decouple the transmission output shaft from the cam shaft. The hammer may have a portion that moves the coupler ring toward the second position when torque applied to the output shaft is greater than the second threshold. The coupler may comprise a clutch ring non-rotatably coupled to one of the transmission output shaft or the cam shaft and a clutch ball receivable in a recess the other of the transmission output shaft or the cam shaft, the clutch ring being movable between a first position where the clutch ball is engaged with the recess to non-rotatably coupled the transmission output shaft to the cam shaft, and a second position in which the clutch ball is disengagable from the recess to decouple the transmission output shaft from the cam shaft. The hammer may have a portion that moves the clutch ring toward the second position when the torque applied to the output shaft is greater than the second threshold.

An aspect not covered by the invention provides an impact power tool includes a housing, a motor disposed in the housing and having a motor output shaft, a transmission having an input member rotatably drivable by rotation of the motor output shaft and a transmission output shaft, a rotary impact assembly including a cam shaft received at least partially over the transmission output shaft, a hammer coupled to the cam shaft and able to move axially and rotatably relative to the cam shaft, an anvil rotatable about the axis, and a spring biasing the hammer toward the anvil, a tool output shaft at least partially received in the housing and rotatable by rotation of the anvil, and a coupler removably coupling the cam shaft to the transmission output shaft. When torque on the tool output shaft is at or below a first threshold, the coupler non-rotatably couples the transmission output shaft to the cam shaft and the hammer continuously engages the anvil so that the transmission shaft, the cam shaft, the hammer and the anvil rotate together to transmit torque to the tool output shaft without impacts. When torque on the tool output shaft is above the first threshold, the coupler non-rotatably couples the transmission output shaft to the cam shaft and the hammer moves along the cam shaft away from the anvil at least a first distance and applies intermittent rotary impacts to the anvil and the tool output shaft. When torque above a second threshold greater than the first threshold is applied to the output shaft, the hammer moves along the cam shaft away from the anvil by at least a second distance that is greater than the first distance and causes the coupler to decouple the transmission output shaft from the cam shaft, interrupting torque transmission to the tool output shaft. In an implementation of this aspect, the coupler may be moveable between a coupled position where the coupler non-rotatably couples the transmission output shaft to the cam shaft, and a decoupled position where the coupler rotationally decouples the transmission output shaft from the cam shaft, and the hammer has a feature that forces the coupler toward the decoupled position when the hammer moves along the cam shaft by at least the second distance.

Advantages may include one or more of the following. The coupler may enable interrupting transmission of torque from the transmission output shaft to cam shaft and the tool output shaft when the hammer moves axially toward the transmission by greater than a threshold distance or when torque on the output shaft exceeds a threshold torque value. This may help inhibit the hammer from moving too far rearward, where it may strike and damage the transmission. These and other advantages and features will be apparent from the description, the drawings, and the claims.

Referring to <FIG>, in an implementation, an impact power tool <NUM> includes a housing <NUM> (including a motor housing portion <NUM> and an impact housing portion <NUM>) extending generally along a tool axis X, a motor <NUM> with a motor output shaft <NUM> received in the housing <NUM>, a transmission <NUM> received in the housing <NUM> and configured to be rotationally driven by the motor <NUM>, a rotary impact assembly <NUM> received in the housing and coupled to the transmission <NUM>, a tool output shaft <NUM> at least partially received in the housing <NUM> and extending from a front end <NUM> of the housing <NUM>, and a tool bit holder <NUM> coupled to a front end of the tool output shaft <NUM>. The impact power tool also includes a handle <NUM> with a top end portion <NUM> coupled to the housing <NUM> and a bottom end portion <NUM> coupled to a receptacle <NUM> for receiving a battery or other power supply (not shown), and a trigger switch <NUM> coupled to a control circuit <NUM> for controlling power delivery from the power supply to the motor <NUM>.

The transmission <NUM> includes a pinion or sun gear <NUM> rotated by a motor output shaft <NUM>, a plurality of planet gears <NUM> pivotally mounted to a rotatable carrier <NUM> and meshed with the pinion gear <NUM>, a stationary ring gear <NUM> that surrounds and is meshed with the planet gears <NUM>, and a transmission output shaft <NUM> extending along the tool. When the motor shaft <NUM> rotates about the axis X, the pinion gear <NUM> rotates, causing the planet gears <NUM> to rotate and revolve around the pinion gear <NUM>, in turn causing the carrier <NUM> and the transmission output shaft <NUM> to rotate about a tool output axis X.

The impact assembly <NUM> includes a cam shaft <NUM> extending along the axis X and selectively coupled for rotation to the transmission output shaft <NUM> by a coupler <NUM>, as described in more detail below. Received over the cam shaft <NUM> is a generally cylindrical hammer <NUM> that is configured to move rotationally and axially relative to the cam shaft <NUM>. The cam shaft <NUM> also has a front end <NUM> of smaller diameter that is rotatably received in an axial opening <NUM> in the tool output shaft <NUM>. Fixedly coupled to a rear end of the tool output shaft <NUM> is an anvil <NUM> having two radial projections <NUM>. The hammer <NUM> has two hammer projections <NUM> on its front end that lie in the same rotational plane as the radial projections <NUM> of the anvil <NUM> so that each hammer projection <NUM> may engage a corresponding anvil projection <NUM> in a rotating direction.

Formed on an outer wall of the cam shaft <NUM> is a pair of rear-facing V-shaped cam grooves <NUM> with their open ends facing toward the rear end portion <NUM> of the housing <NUM>. A corresponding pair of forward-facing V-shaped cam grooves (not shown) is formed on an interior wall of the hammer <NUM> with their open ends facing toward the front end portion <NUM> of the housing <NUM>. A cam ball <NUM> is received in and rides along each of the cam grooves <NUM>, <NUM> to couple the hammer <NUM> to the cam shaft <NUM>. A compression spring <NUM> is received in a cylindrical recess <NUM> in the hammer <NUM> and abuts a forward face of the planet carrier <NUM>. The spring <NUM> biases the hammer <NUM> toward the anvil <NUM> so that the so hammer projections <NUM> engage the corresponding anvil projections <NUM>.

At low torque levels (e.g., less than a first threshold), the impact mechanism <NUM> transmits torque to the output spindle <NUM> in a rotary mode. In the rotary mode, the compression spring <NUM> maintains the hammer <NUM> in its most forward position so that the hammer projections <NUM> engage the anvil projections <NUM>. This causes the cam shaft <NUM>, the hammer <NUM>, the anvil <NUM> and the output spindle to rotate together as a unit about the tool axis X so that the output spindle <NUM> has substantially the same rotational speed as the cam shaft <NUM>.

As the torque increases to exceed the first threshold (a torque transition threshold), the impact mechanism <NUM> transmits torque to the output spindle <NUM> in an impact mode. In the impact mode, the hammer <NUM> moves axially rearwardly against the force of the spring <NUM>. This decouples the hammer projections <NUM> from the anvil projections <NUM>. Thus, the anvil <NUM> continues to spin freely on its axis without being driven by the motor <NUM> and transmission <NUM>, so that it coasts to a slightly slower speed. Meanwhile, the hammer <NUM> continues to be driven at a higher speed by the motor <NUM> and transmission <NUM>. As this occurs, the hammer <NUM> moves axially rearwardly relative to the anvil <NUM> by the movement of the balls <NUM> rearwardly in the V-shaped cam grooves <NUM>. When the balls <NUM> reach their rearmost position in the V-shaped cam grooves <NUM>, <NUM> the spring <NUM> drives the hammer <NUM> axially forward with a rotational speed that exceeds the rotational speed of the anvil <NUM>. This causes the hammer projections <NUM> to rotationally strike the anvil projections <NUM>, imparting a rotational impact to the output spindle <NUM>. This impacting operation repeats as long as the torque on the output spindle <NUM> continues to exceed the torque transition threshold.

At very high torque (e.g., above a second threshold that is greater than the first threshold) the hammer <NUM> may move axially rearward further than desired, which if allowed may cause the rear end of the hammer <NUM> to strike the planet carrier <NUM> , causing damage to the planet carrier <NUM> and/or other transmission components. The coupler <NUM> alleviates this problem by decoupling the transmission output shaft from the cam ring at very high axial displacement of the hammer along the transmission output shaft, interrupting torque transmission from the transmission output shaft to the cam shaft, which also interrupts torque transmission to the hammer.

Referring also to <FIG>, the cam shaft <NUM> may be in the form of a cam ring <NUM> received over a portion of the transmission output shaft <NUM>. The cam ring <NUM> includes the V-shaped cam grooves <NUM> with the cam balls <NUM> traveling in the cam grooves <NUM> as the hammer <NUM> moves axially and rotationally relative to the cam shaft <NUM>. The cam shaft <NUM> is axially retained on the transmission output shaft <NUM> by a snap-ring <NUM> at the front end of the cam shaft <NUM>. The snap-ring <NUM> is received in an annular groove <NUM> in the transmission output shaft <NUM>. The cam shaft <NUM> is selectively able to rotate relative to the transmission output shaft <NUM>.

The coupler <NUM> includes a plurality of coupler balls <NUM> received in radial bores <NUM> in the cam shaft <NUM> and removably receivable in a plurality of radial recesses <NUM> in the transmission output shaft <NUM>. The coupler <NUM> further includes an axial bore <NUM> in the hammer <NUM> that receives the transmission output shaft <NUM> and the cam shaft <NUM>. The axial bore <NUM> is defined by an outer wall <NUM> having a rear portion 86A with a first diameter D1 and a front portion 86B with a second diameter D2 that is greater than the first diameter D1. When the rear portion 86A of the bore <NUM> is aligned with the coupler balls <NUM>, the outer wall <NUM> maintains the balls <NUM> radially in the radial recesses <NUM>, so that the transmission output shaft <NUM> is non-rotatably coupled to the cam shaft <NUM> to enable torque transmission between them. When the front portion 86B of the bore <NUM> is aligned with the coupler balls <NUM>, the outer wall <NUM> has a clearance that allows the balls <NUM> to move radially outward from the radial recesses <NUM>, rotationally decoupling the transmission output shaft <NUM> from the cam shaft <NUM> and interrupting torque transmission between them.

As shown in <FIG>, in operation, when torque on the tool output shaft <NUM> is less than the first threshold, the hammer <NUM> generally remains in a forward position (as shown in <FIG>) with the hammer projections <NUM> continuously engaged with the anvil projections <NUM>. At the same time, the rear portion 86A of the outer wall <NUM> of the axial bore <NUM> in the hammer axially are continuously aligned with the detent coupler balls <NUM>. The smaller diameter D1 of the rear portion 86A forces the detent coupler balls <NUM> radially inward so that they are continuously retained in the recesses <NUM> in the transmission output shaft <NUM> and the balls <NUM> non-rotatably couple the transmission output shaft <NUM> and the cam shaft <NUM>. This causes the transmission output shaft <NUM>, the cam shaft <NUM>, the hammer <NUM>, and the anvil <NUM> to rotate continuously together to transmit torque to the tool output shaft <NUM> without impacts.

As also shown in <FIG>, when torque on the tool output shaft <NUM> is above the first threshold, the hammer <NUM> moves radially and axially along the cam shaft <NUM> and transmission output shaft <NUM> away from the anvil by a first distance X1 up to at most line Y. Over the entirety of this travel distance X1, the smaller diameter D1 of the rear portion 86A forces the detent coupler balls <NUM> radially inward so that they are continuously retained in the recesses <NUM> in the transmission output shaft <NUM> and the balls <NUM> non-rotatably couple the transmission output shaft <NUM> and the cam shaft <NUM>. At the same time, the cam balls <NUM> travel in the cam groove <NUM> so that the hammer <NUM> applies intermittent rotary impacts to the anvil <NUM> and to the tool output shaft <NUM>.

As also shown in FIGS. 6A-6BB, when torque on the tool output shaft <NUM> is above the second threshold (which is greater than the first threshold), the hammer <NUM> moves radially and axially along the cam shaft <NUM> and the transmission output shaft <NUM> away from the anvil by a second distance X2 that is greater than the first distance X1, and that is past line Y. In this position, the front portion 86B of the outer wall <NUM> of the axial bore <NUM> in the hammer <NUM> is axially aligned with the detent coupler balls <NUM>. The larger diameter D2 of the front portion 86B of the outer wall <NUM> creates space that allows the detent coupler balls <NUM> to move radially outward from the recesses <NUM> in the transmission output shaft <NUM>. When the balls <NUM> move out of the recesses <NUM>, the transmission output shaft <NUM> and the cam shaft <NUM> are rotationally decoupled and torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM> is interrupted. This also interrupts torque transmission to the hammer <NUM>, the anvil <NUM> and the tool output shaft <NUM>. Interrupting torque transmission helps prevent the hammer <NUM> from moving further rearward and striking the planet carrier <NUM>.

<FIG> illustrate another implementation of a rotary impact power tool <NUM> including a housing, a motor, a transmission <NUM>, rotary impact assembly <NUM>, and tool output shaft substantially similar to the housing <NUM>, motor <NUM>, transmission <NUM>, impact assembly <NUM>, and a tool output shaft <NUM> of the rotary impact power tool <NUM> described above, except for the differences discussed below. The transmission <NUM> includes a planet carrier <NUM> that carries planet gears (not shown) and a transmission output shaft <NUM> fixed to the planet carrier <NUM> so that they rotate together about the axis X upon rotation of the motor. The rotary impact assembly <NUM> includes a cam shaft <NUM> in the form of a cam ring received at least partially over the transmission output shaft <NUM> and axially retained on the transmission output shaft <NUM> by a snap-ring <NUM> received in an annular groove in the front end of the cam shaft <NUM>. The impact assembly <NUM> further includes a generally cylindrical hammer <NUM> received over the cam shaft <NUM> and configured to move rotationally and axially relative to the cam shaft <NUM> to apply rotational impacts to the anvil (not shown). The impact assembly <NUM> also includes a pair of rear-facing V-shaped cam grooves <NUM> in the cam shaft <NUM>, a corresponding pair of forward-facing V-shaped cam grooves (not shown) formed on an interior wall of the hammer <NUM>, and a cam ball <NUM> received in and riding along the cam grooves <NUM>, <NUM> to couple the hammer <NUM> to the cam shaft <NUM>.

The transmission output shaft <NUM> and the cam shaft <NUM> are removably coupled to one another for common rotation by a coupler <NUM>. The coupler <NUM> includes a coupling ring <NUM> with at least one internal spline or projection <NUM> received in at least one corresponding external spline or recess <NUM> in the transmission output shaft <NUM> and in at least one corresponding external spline or recess <NUM> in the cam shaft <NUM>. The coupling ring <NUM> is movable axially between a forward position (shown in <FIG>) and a rearward position (shown in <FIG>) and is biased toward the forward position by a spring <NUM> that is disposed rearward of the coupling ring <NUM>. The hammer <NUM> includes a rearward projection <NUM> that is configured to push the coupling ring <NUM> toward the rearward position when the hammer <NUM> moves axially rearward along the cam shaft <NUM> (as shown in <FIG>).

In the forward position (<FIG> and <FIG>), the spline or projection <NUM> on the coupler ring <NUM> engages both the external spline or recess <NUM> in the transmission output shaft <NUM> and the external spline or recess <NUM> in the cam shaft <NUM> so that torque is transmitted from the transmission output shaft <NUM> to the cam shaft <NUM>. In the rearward position (<FIG>), the spline or projection <NUM> engages only the spline or recess <NUM> in the transmission output shaft <NUM> but not the spline or recess <NUM> in the cam shaft, <NUM>, which rotationally decouples the transmission output shaft <NUM> from the cam shaft <NUM> interrupts torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM>.

In operation, when torque on the tool output shaft is less than a first threshold, the hammer <NUM> generally remains in a forward position (as shown in <FIG>) with the hammer projections continuously engaged with the anvil projections. At the same time, the coupler ring <NUM> engages both the external spline or recess <NUM> in the transmission output shaft <NUM> and the external spline or recess <NUM> in the cam shaft <NUM> so that torque is transmitted from the transmission output shaft <NUM> to the cam shaft <NUM>. This causes the transmission output shaft <NUM>, the cam shaft <NUM>, the hammer <NUM>, and the anvil to rotate continuously together to transmit torque to the tool output shaft without impacts.

When torque on the tool output shaft is above the first threshold, the hammer <NUM> moves radially and axially along the cam shaft <NUM> and transmission output shaft <NUM> away from the anvil by a first distance X1 (e.g., between the positions shown in <FIG> and <FIG>). Over the entirety of this travel distance X1, the coupler ring <NUM> engages both the external spline or recess <NUM> in the transmission output shaft <NUM> and the external spline or recess <NUM> in the cam shaft <NUM> so that torque is transmitted from the transmission output shaft <NUM> to the cam shaft <NUM>. At the same time, the cam balls <NUM> travel in the cam groove <NUM> so that the hammer <NUM> applies intermittent rotary impacts to the anvil and to the tool output shaft.

When torque on the tool output shaft is above a second threshold (which is greater than the first threshold), the hammer <NUM> moves radially and axially along the cam shaft <NUM> and the transmission output shaft <NUM> away from the anvil by a second distance X2 that is greater than the first distance X1 (e.g., to the position shown in <FIG>). In this position, the rearward projection <NUM> on the hammer <NUM> pushes the coupler ring <NUM> axially rearward against the biasing force of spring <NUM>. In this position, the spline or projection <NUM> engages only the spline or recess <NUM> in the transmission output shaft <NUM> but not the spline or recess <NUM> in the cam shaft, <NUM>, which rotationally decouples the transmission output shaft <NUM> from the cam shaft <NUM>. This interrupts torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM>, to the hammer <NUM>, to the anvil and to the tool output shaft <NUM>. Interrupting torque transmission also helps prevent the hammer <NUM> from moving further rearward and striking the planet carrier <NUM>.

<FIG> illustrate another implementation of a rotary impact power tool <NUM> including a housing, a motor, a transmission <NUM>, rotary impact assembly <NUM>, and tool output shaft substantially similar to the housing <NUM>, motor <NUM>, transmission <NUM>, impact assembly <NUM>, and a tool output shaft <NUM> of the rotary impact power tool <NUM> described above, except for the differences discussed below. The transmission <NUM> includes a planet carrier <NUM> that carries planet gears (not shown) and a transmission output shaft <NUM> fixed to the planet carrier <NUM> so that they rotate together about the axis X upon rotation of the motor. The rotary impact assembly <NUM> includes a cam shaft <NUM> in the form of a cam ring received at least partially over the transmission output shaft <NUM> and axially retained on the transmission output shaft <NUM> by a flange <NUM> on the front end of the transmission output shaft <NUM>. The impact assembly <NUM> further includes a generally cylindrical hammer <NUM> received over the cam shaft <NUM> and configured to move rotationally and axially relative to the cam shaft <NUM> to apply rotational impacts to the anvil (not shown). The impact assembly <NUM> also includes a pair of rear-facing V-shaped cam grooves <NUM> in the cam shaft <NUM>, a corresponding pair of forward-facing V-shaped cam grooves (not shown) formed on an interior wall of the hammer <NUM>, and a cam ball (not shown) received in and riding along the cam grooves to couple the hammer <NUM> to the cam shaft <NUM>.

The transmission output shaft <NUM> and the cam shaft <NUM> are removably coupled to one another for common rotation by a coupler <NUM>. The coupler <NUM> includes a clutch ring <NUM> received over the transmission output shaft <NUM> and includes internal features (e.g., splines) engaged with external features (e.g., splines) on the transmission output shaft <NUM> so that the clutch ring <NUM> rotates together with the transmission output shaft <NUM>. The coupler <NUM> also includes clutch balls <NUM> received in recesses <NUM> in the rear end of the cam shaft <NUM> and in recesses <NUM> in the front end of the clutch ring <NUM>. The clutch ring <NUM> is biased axially toward the cam shaft <NUM> by one or more clutch springs <NUM>. In addition, the clutch ring <NUM> includes an annular rim <NUM> that is engageable by a rearward projection <NUM> on the hammer <NUM> when the hammer moves axially rearward along the cam shaft <NUM>.

When the clutch balls <NUM> are engaged with the recesses <NUM>, <NUM> in both the cam shaft <NUM> and the clutch ring <NUM>, torque is transmitted from the cam shaft to the cam ring via the clutch ring and the cam ring transmits torque to the hammer. When the clutch balls <NUM> become disengaged from either the recesses <NUM> or the recesses <NUM>, the transmission output shaft <NUM> is decoupled from the cam shaft <NUM>, interrupting torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM>.

In operation, when torque on the tool output shaft is less than a first threshold, the hammer <NUM> generally remains in a forward position (as shown in <FIG>) with the hammer projections continuously engaged with the anvil projections. At the same time, the clutch ring <NUM> is biased axially forward so that the clutch balls <NUM> engage the recesses <NUM> in the clutch ring <NUM> and the recesses in the cam shaft <NUM>, so that torque is transmitted from the transmission output shaft <NUM> to the cam shaft <NUM>. This causes the transmission output shaft <NUM>, the cam shaft <NUM>, the hammer <NUM>, and the anvil to rotate continuously together to transmit torque to the tool output shaft without impacts.

When torque on the tool output shaft is above the first threshold, the hammer <NUM> moves radially and axially along the cam shaft <NUM> and transmission output shaft <NUM> away from the anvil by a first distance X1 (e.g., between the positions shown in <FIG> and <FIG>). Over the entirety of this travel distance X1, the clutch ring <NUM> is biased axially forward so that the clutch balls <NUM> engage the recesses <NUM> in the clutch ring <NUM> and the recesses in the cam shaft <NUM>, and torque is transmitted from the transmission output shaft <NUM> to the cam shaft <NUM>. At the same time, the cam balls travel in the cam grooves <NUM> so that the hammer <NUM> applies intermittent rotary impacts to the anvil and to the tool output shaft.

When torque on the tool output shaft is above a second threshold (which is greater than the first threshold), the hammer <NUM> moves radially and axially along the cam shaft <NUM> and the transmission output shaft <NUM> away from the anvil by a second distance X2 that is greater than the first distance X1 (e.g., to the position shown in <FIG>). In this position, the rearward projection <NUM> on the hammer <NUM> pushes the annular rim <NUM> on the clutch ring <NUM> axially rearward against the biasing force of spring <NUM>. In this position, the clutch balls <NUM> engage only the recesses <NUM> in the clutch ring <NUM> but not the recesses <NUM> in the cam shaft <NUM>, which rotationally decouples the transmission output shaft <NUM> from the cam shaft <NUM>. This interrupts torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM>, to the hammer <NUM>, to the anvil, and to the tool output shaft. Interrupting torque transmission also helps prevent the hammer <NUM> from moving further rearward and striking the planet carrier <NUM>.

As shown in <FIG>, in an alternative implementation or under certain conditions of operation, the torque on the tool output shaft may cause the clutch ring <NUM> to move axially rearward against the force of the clutch springs <NUM> without the hammer projection <NUM> engaging the rim <NUM> on the clutch ring <NUM>. If this occurs, the clutch balls disengage from the recesses <NUM> in the cam shaft <NUM>, which rotationally decouples the transmission output shaft <NUM> from the cam shaft <NUM>. This interrupts torque transmission from the transmission output shaft <NUM> to the cam shaft <NUM>, to the hammer <NUM>, to the anvil, and to the tool output shaft. Interrupting torque transmission also helps prevent the hammer <NUM> from moving further rearward and striking the planet carrier <NUM>.

Claim 1:
An impact power tool (<NUM>) comprising:
a housing (<NUM>);
a motor (<NUM>) disposed in the housing (<NUM>) and including a motor output shaft (<NUM>);
a transmission (<NUM>) including a transmission output shaft (<NUM>) and an input member rotatably drivable by rotation of the motor output shaft (<NUM>);
a rotary impact assembly (<NUM>) including a cam shaft (<NUM>) extending along and rotatable about an axis, a hammer (<NUM>) coupled to the cam shaft (<NUM>) for axial and rotational movement relative to the cam shaft (<NUM>), an anvil (<NUM>) rotatable about the axis, and a spring (<NUM>) biasing the hammer (<NUM>) toward the anvil (<NUM>);
a tool output shaft (<NUM>) at least partially received in the housing (<NUM>) and rotatable by rotation of the anvil (<NUM>); and
characterized in that the impact power tool (<NUM>) further comprises a coupler (<NUM>) removably coupling the cam shaft (<NUM>) to the transmission output shaft (<NUM>),
wherein when torque on the tool output shaft (<NUM>) is less than or equal to a first threshold, the transmission output shaft (<NUM>), the cam shaft (<NUM>), the hammer (<NUM>), and the anvil (<NUM>) rotate together to transmit torque to the tool output shaft (<NUM>),
wherein when torque on the tool output shaft (<NUM>) is above the first threshold, the hammer (<NUM>) moves along the cam shaft (<NUM>) away from the anvil (<NUM>) by at least a first distance and applies intermittent rotary impacts to the anvil (<NUM>) and the tool output shaft (<NUM>), and
wherein when the hammer (<NUM>) moves along the cam shaft (<NUM>) away from the anvil (<NUM>) by at least a second distance greater than the first distance, the coupler (<NUM>) decouples the transmission output shaft (<NUM>) from the cam shaft (<NUM>), interrupting torque transmission to the tool output shaft (<NUM>).