Electric power tool

An electric power tool includes a motor; a speed reducer for transferring a rotational power of the motor at a reduced speed; and a reduction ratio changing unit for changing a reduction ratio of the speed reducer. The speed reduction mechanism includes an axially slidable changeover member and a gear member, the changeover member being engaged with or disengaged from the gear member depending on an axial slide position thereof. The reduction ratio changing unit includes a shift actuator for axially sliding the changeover member, a driving state detector for detecting a driving state of the motor, a slide position detector for detecting a slide position of the changeover member and a controller for driving the shift actuator and for temporarily decreasing or increasing a rotational power of the motor depending on detection results of the driving state detector and the slide position detector, respectively.

FIELD OF THE INVENTION

The present invention relates to an electric power tool capable of changing a reduction ratio.

BACKGROUND OF THE INVENTION

In an electric power tool of the type including a speed reduction mechanism, use is made of a structure for changing the reduction ratio of the speed reduction mechanism. In this structure, a changeover member such as a ring gear included in a planetary gear mechanism is axially slid to change the engagement state of the planetary gear mechanism.

For example, Japanese Patent Application Publication Nos. 2009-56590 and 2009-78349 disclose electric power tools in which the slide movement of a changeover member including a ring gear is automatically carried out by a solenoid. In such conventional electric power tools, when the solenoid is operated, the rotation of a motor is stopped or reduced in order to suppress a shock occurring when a changeover member is engaged with a counterpart gear member.

In the conventional electric power tool, when the current of the motor or the like is changed, the solenoid is started up and the rotation of the motor is stopped at a preset timing by a control unit that has detected such change.

However, there is somewhat of a difference between a timing at which the solenoid is started up and the changeover member is actually engaged with the counterpart gear member through a plurality of mechanisms and a timing at which the rotation of the motor is reduced and actually stopped.

For that reason, in the conventional electric power tool mentioned above, there has been employed a method for suppressing the engagement shock to the minimum by reliably performing the stopping of the motor or the like before driving the solenoid. However, it is difficult to complete the change of the reduction ratio in a short time by using the method.

In other words, the conventional electric power tool is not sufficient both to suppress the engagement shock when the reduction ratio is changed and to complete the change of the reduction ratio smoothly in a short time.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides an electric power tool capable of suppressing an engagement shock when a reduction ratio is changed and completing the change of the reduction ratio quickly and smoothly.

In order to accomplish the above object, the electric power tool of the present embodiment has a configuration summarized below.

An electric power tool in accordance with the present invention includes a motor as a drive power source, a speed reduction mechanism for transferring a rotational power of the motor at a reduced speed, and a reduction ratio changing unit for changing a reduction ratio of the speed reduction mechanism.

The speed reduction mechanism includes an axially slidable changeover member and a gear member, the changeover member being engaged with or disengaged from the gear member depending on an axial slide position thereof.

The reduction ratio changing unit includes a shift actuator for axially sliding the changeover member, a driving state detector unit for detecting a driving state of the motor, a slide position detector unit for detecting a slide position of the changeover member and a control unit for starting up the shift actuator depending on a detection result of the driving state detector unit and for temporarily decreasing or increasing a rotational power of the motor depending on a detection result of the slide position detector unit.

The control unit may be designed to change a drive control of the shift actuator depending on the detection result of the slide position detector unit.

The control unit may be designed to temporarily reverse the direction of slide movement of the changeover member caused by the shift actuator if the detection result of the slide position detector unit indicates that the changeover member fails to slide to a desired target position when the shift actuator is driven.

The control unit may be designed to change the sliding drive power of the changeover member applied by the shift actuator if the detection result of the slide position detector unit indicates that the changeover member fails to slide to a desired target position when the shift actuator is driven.

If the detection result of the slide position detector unit indicates that the changeover member fails to slide to a desired target position when the shift actuator is driven, the control unit may be designed to change a relative rotational position between the changeover member, and the gear member while keeping the driving of the shift actuator.

If the detection result of the slide position detector unit indicates that the changeover member fails to slide to a desired target position when the shift actuator is driven, the control unit may be designed to change relative rotational position between the changeover member and the gear member after stopping the driving of the shift actuator.

At this time, the control unit may be designed to change the relative rotational position by increasing the rotational power when it is determined by the detection result of the driving state detector unit that the rotational power of the motor is decreased or stopped.

Further, the control unit may be designed to change the rotational power of the motor such that the rotational acceleration of the rotational power becomes increased in the case that the changeover makes the slide movement compared with the case that the changeover member makes no slide movement.

The slide position detector unit may be designed to detect a position of the changeover member or a member interlocked with the changeover member.

The slide position detector unit may be designed to detect a driving state of the shift actuator and detect a position of the changeover member based on the detection result of the driving state.

At this time, the shift actuator may be of a rotary type, and the slide position detector unit may be designed to detect a rotational state of the shift actuator.

The shift actuator may be a linear actuator, and the slide position detector unit may be designed to detect a linear driving state of the shift actuator.

The present invention offers an advantageous effect in that it is capable of suppressing an engagement shock when a reduction ratio is changed and completing the change of the reduction ratio quickly and smoothly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described with reference to the accompanying drawings which form a part thereof.

First Embodiment

FIGS. 1 through 3show an electric power tool in accordance with a first embodiment of the present invention. The electric power tool of the present embodiment includes a motor (main motor)1as a drive power source, a speed reduction mechanism2for transferring the rotational power of the motor1at a reduced speed, a drive power delivery unit3for delivering the rotational power transferred from the speed reduction mechanism2to an output shaft4, and a trunk housing101for accommodating the motor1, the speed reduction mechanism2and the drive power delivery unit3. A grip housing102extends from the trunk housing101. A trigger switch103is retractably attached to the grip housing102. The trunk housing101and the grip housing102make up a body housing100of the electric power tool.

A shift actuator6is arranged within the trunk housing101in a parallel relationship with the motor1and the speed reduction mechanism2. The shift actuator6is of a rotary type and is designed to change a reduction ratio by slidingly moving a changeover member7of the speed reduction mechanism2through a shift cam plate8. Detailed description will be made later on this point.

InFIGS. 4 through 10, there are shown the structures of the speed reduction mechanism2and other components in more detail. The speed reduction mechanism2of the present embodiment includes a gear case9and three planetary gear mechanisms arranged within the gear case9. The reduction ratio of the speed reduction mechanism2as a whole is changed by changing over the reduction state and non-reduction state of the respective planetary gear mechanisms. In the following description, the planetary gear mechanisms will be referred to as first to third planetary gear mechanisms in the order of proximity to the motor1.

The first planetary gear mechanism includes a sun gear (not shown inFIG. 4) rotationally driven about its axis by the rotational power of the motor1, a plurality of planet gears11arranged to surround the sun gear10and meshed with the sun gear10, a ring gear12arranged to surround the planet gears11and meshed with the planet gears11, and a carrier14to which the planet gears11are rotatably connected through carrier pins13.

The second planetary gear mechanism includes a sun gear20(not shown inFIG. 4) coupled with the sun gear10of the first planetary gear mechanism, a plurality of planet gears21arranged to surround the sun gear20and meshed with the sun gear20, the ring gear12capable of meshing with the planet gears21, and a carrier24to which the planet gears21are rotatably connected through carrier pins23.

The ring gear12is configured to act as a member of the first planetary gear mechanism or as a member of the second planetary gear mechanism depending on the slide positions of the ring gear12. In other words, the ring gear12meshes with the planet gears11of the first planetary gear mechanism when being in the slide position near the motor1but meshes with the planet gears21of the second planetary gear mechanism when being in the slide position near the output shaft4.

In the description made below, the side near the motor1will be referred to as “input side” and the side near the output shaft4will be referred to as “output side.”

On the inner circumferential surface of the gear case9, there is provided a guide portion15with which the ring gear12engages in an axially slidable and non-rotatable manner. The ring gear12makes axial slide movement under the guidance of the guide portion15.

The third planetary gear mechanism includes a sun gear30coupled with the carrier24of the second planetary gear mechanism, a plurality of planet gears31arranged to surround the sun gear30and meshed with the sun gear30, a ring gear32meshed with the planet gears31, and a carrier34to which the planet gears31are rotatably connected through carrier pins33.

The ring gear32is axially slidably and rotatably arranged with respect to the gear case9. When being in the input side slide position, the ring gear32meshes with the outer peripheral edge of the carrier24of the second planetary gear mechanism. When being in the output side slide position, the ring gear32meshes with an engaging tooth portion40integrally formed with the gear case9. The ring gear32remains meshed with the planet gears31in either of the slide positions.

The first to third planetary gear mechanisms are axially connected to one another. Specifically, the sun gears10,20and30of the first to third planetary gear mechanisms are linearly arranged in the axial direction. Likewise, the ring gears12and32surrounding the sun gears10,20and30are linearly arranged in the axial direction.

The ring gears12and32are independently slidable in the axial direction. The reduction ratio is changed depending on the slide positions of the ring gears12and32, consequently changing the rotation output of the output shaft4to a first speed, a second speed or a third speed. In the present embodiment, each of the ring gears12and32serves as the axially movable changeover member7. In this regard, the first speed is available when the reduction ratio is smallest, the second speed is available when the reduction ratio is greater than that of the first speed, and the third speed is available when the reduction ratio is greater than those of the first and second speeds (when the reduction ratio is greatest).

FIGS. 6A and 6Bshow the speed reduction mechanism2kept in a first speed state.FIG. 7shows the speed reduction mechanism2in which the shift operation between the first speed and the second speed is underway.FIGS. 8A and 8Bshow the speed reduction mechanism2kept in a second speed state.FIG. 9shows the speed reduction mechanism2in which the shift operation between the second speed and the third speed is underway.FIGS. 10A and 10Bshow the speed reduction mechanism2kept in a third speed state.

In case of the speed reduction mechanism2being in the first speed state as shown inFIGS. 6A and 6B, the ring gear12serving as the changeover member7is held in the input side slide position and the ring gear32serving as the changeover member7is also held in the input side slide position. As a result, only the first planetary gear mechanism comes into a reduction state.

Specifically, the planet gears11meshing with the ring gear12make rotation on their own axes and revolution around the sun gear10by the rotation of the sun gear10. Thus, the torque of the sun gear10is transferred to the carrier14at a reduced speed. The carrier14rotates together with the carrier24of the second planetary gear mechanism. Likewise, the third planetary gear mechanism rotates together with the carrier24.

In case of the speed reduction mechanism2being in the second speed state as shown inFIGS. 8A and 8B, the ring gear12serving as the changeover member7is held in the output side slide position but the ring gear32serving as the changeover member7is held in the input side slide position. As a result, only the second planetary gear mechanism comes into a reduction state.

Specifically, the planet gears21of the second planetary gear mechanism meshing with the ring gear12make rotation on, their own axes and revolution around the sun gear10by the rotation of the sun gear20coupled with the sun gear10. Thus, the torque of the sun gear20is transferred to the carrier24at a reduced speed. The first and third planetary gear mechanisms rotate together with the carrier24.

In this regard, the dimensions of the respective members of the first and second planetary gear mechanisms are set differently so that the reduction ratio of the second planetary gear mechanism can be greater than the reduction ratio of the first planetary gear mechanism. Accordingly, the reduction ratio in the second speed is greater than that in the first speed, and the rotation speed of the output shaft4in the second speed becomes smaller than that in the first speed.

In case of the speed reduction mechanism2being in the third speed state as shown inFIGS. 10A and 10B, the ring gear12serving as the changeover member7is held in the output side slide position and the ring gear32serving as the changeover member7is also held in the output side slide position. As a result, the second and third planetary gear mechanisms come into a reduction state.

Specifically, the planet gears21of the second planetary gear mechanism meshing with the ring gear12make rotation on their own axes and revolution around the sun gear20by the rotation of the sun gear20coupled with the sun gear10. Thus, the torque of the sun gear20is transferred to the carrier24at a reduced speed. The first planetary gear mechanism rotates together with the carrier24of the second planetary gear mechanism. The torque of the carrier24is transferred to the sun gear30of the third planetary gear mechanism coupled with the carrier24. The planet gears31of the third planetary gear mechanism meshing with the ring gear32make rotation on their own axes and revolution around the sun gear30by the rotation of the sun gear30. Thus, the torque of the sun gear30is transferred to the carrier34at a further reduced speed.

The slide positions of the two ring gears12and32making up the changeover member7are determined by the rotational positions of the shift cam plate8. The shift cam plate8is a plate having an arc-like cross-sectional shape conforming to the outer circumferential surface of the cylindrical gear case9. The shift cam plate8is provided rotatably about the center axis of the gear case9.

The shift cam plate8has input side and output side cam slots41and42arranged side by side along the axial direction. The input side cam slot41is a through-groove curved in conformity with the slide movement of the ring gear12. The tip end portion of a shift pin45passing through the cam slot41is inserted into the gear case9through a guide hole48(seeFIG. 4) formed through the thickness of the gear case9. The tip end portion of the shift pin45engages with a depression formed on the outer circumferential surface of the ring gear12. The guide hole is formed to extend parallel to the axis of the speed reduction mechanism2.

The output side cam slot42is a through-hole curved in conformity with the slide movement of the ring gear32. The tip end portion of a shift pin46passing through the cam slot42is inserted into the gear case9through a guide hole49(seeFIG. 4) formed through the thickness of the gear case9. The tip end portion of the shift pin46engages with a depression formed on the outer circumferential surface of the ring gear32. The guide hole is formed to extend parallel to the axis of the speed reduction mechanism2and is arranged linearly with the guide hole48.

The shift cam plate8includes a gear portion47formed in one circumferential end portion thereof to mesh with the rotary shift actuator6. The shift actuator6includes a dedicated motor (sub-motor)50, a speed reducing mechanism51for transferring the rotational power of the motor50at a reduced speed, and an output unit52rotationally driven by the rotational power transferred through the speed reducing mechanism51.

In the electric power tool of the present embodiment, the speed reduction mechanism2includes the axially slidable changeover member7and a gear member5, the changeover member7being engaged with or disengaged from the gear member5depending on the axial slide position thereof.

As mentioned above, the changeover member7includes the ring gears12and32. Further, with respect to the ring gear12, the planet gears11of the first planetary gear mechanism and the planet gears21of the second planetary gear mechanism serve as the gear members5. In respect of the ring gear32, the carrier24of the second planetary gear mechanism and the engaging tooth portion40of the gear case9serve as the gear members5. The reduction ratio of the speed reduction mechanism2as a whole is changed depending on the engagement and disengagement states of the changeover member7and the gear member5.

As schematically shown inFIG. 5, the electric power tool of the present embodiment includes a driving state detector unit60for detecting the driving state of the motor1, a slide position detector unit61for detecting the slide positions of the changeover member7, and a control unit62for controlling the operations of the motors1and50.

The driving state detector unit60detects the driving state of the motor1by detecting at least one of the current flowing through the motor1and the rotational speed of the motor1. The detection result of the driving state detector unit60is inputted to the control unit62. The slide position detector unit61indirectly detects the positions of the changeover members7(i.e., the slide positions of the ring gears12and32) by detecting the rotational position of the shift cam plate8(interlocked with the changeover member7) with respect to the gear case9. The detection result of the slide position detector unit61is inputted to the control unit62. The slide position detector unit61may be either a contactless displacement detecting sensor or a contact type sensor making direct contact with the shift cam plate8.

Depending on the driving states of the motor1detected by the driving state detector unit60, the control unit62starts up the shift actuator6and slidingly moves the changeover member7, thereby changing the reduction ratio of the speed reduction mechanism2.

In the electric power tool of the present embodiment, a reduction ratio changing unit is made up of the shift actuator6for axially sliding the changeover member7, the driving state detector unit60for detecting the driving state of the motor1, the slide position detector unit61for detecting the slide positions of the changeover member7and the control unit62for operating the shift actuator6depending on the detection result of the driving state detector unit60.

When operating the shift actuator6(i.e., the motor50), the control unit62controls the motor1so that the rotational power thereof can be temporarily decreased or increased depending on the detection result of the slide position detector unit61. In this regard, the reason for decreasing or increasing the rotational power of the motor1is to reduce the relative rotation speed between the changeover member7and the sliding gear member5to a possible smallest value (preferably, to zero) when the changeover member7is engaged with the gear member5.

Next, the automatic shifts from the first speed to the second speed, from the second speed to the third speed, from the third speed to the second speed and from the second speed to the first speed will be described one after another.

The automatic shift from the first speed to the second speed is controlled in the following manner. The first speed is automatically shifted to the second speed if the driving state detector unit60detects that the load of the motor1has reached a specified level while the motor1is driven in the first speed state shown inFIGS. 6A and 6B.

Specifically, if the current flowing through the motor1becomes equal to or greater than a specified value, if the revolution number of the motor1becomes equal to or smaller than a specified value, or if the current and the revolution number satisfy a specified relationship, the driving state detector unit60detects that the load of the motor1has reached the specified level.

Upon receiving the detection result, the control unit62starts up the motor50of the shift actuator6to rotate the shift cam plate8. The shift pin45passing through the input side cam slot41of the shift cam plate8is slid toward the output side under the guidance of the guide hole48provided in the gear case9. The shift pin45slidingly moves the corresponding ring gear12as the changeover member7toward the output side.

The slidingly moved ring gear12is disengaged from the planet gears11of the first planetary gear mechanism and comes into the changeover progressing state shown inFIG. 7. At this time, the ring gear12is held against rotation with respect to the gear case9. In the meantime, the planet gears21of the second planetary gear mechanism, which are the gear member5to be engaged next time, are rotationally driven about the axis of the speed reduction mechanism2with respect to the gear case9by the rotational power of the motor1.

If the detection result indicating that the ring gear12has reached the changeover progressing state shown inFIG. 7is inputted from the slide position detector unit61, the control unit62temporarily reduces the rotational power of the motor1(to a value including zero) at that moment. As a result, engagement shocks can be suppressed by reducing the relative rotation speed between the ring gear12and the planet gears21(preferably, to zero) when the ring gear12is engaged with the planet gears21as shown inFIGS. 8A and 8B. This realizes a smooth and stable automatic shift operation and restrains wear or damage of the gears otherwise caused by collision.

Alternatively, the control unit62may control the motor1in such a manner that the rotational power of the motor1is reduced to a certain level from the startup time of the shift actuator6. In this case, the control unit62may gradually reduce the rotational power of the motor1in synchronism with the startup of the shift actuator6and may further reduce the rotational power of the motor1at the input time of the detection result indicating that the ring gear12has reached the changeover progressing state shown inFIG. 7.

The automatic shift from the second speed to the third speed is controlled in the following manner. The second speed is automatically shifted to the third speed if the driving state detector unit60detects that the load of the motor1has reached a specified level while the motor1is driven in the second speed state shown inFIGS. 8A and 8B. Specifically, if the current flowing through the motor1becomes equal to or greater than a specified value, if the revolution number of the motor1becomes equal to or smaller than a specified value, or if the current and the revolution number satisfy a specified relationship, the driving state detector unit60detects that the load of the motor1has reached the specified level.

Upon receiving the detection result, the control unit62starts up the motor50of the shift actuator6to rotate the shift cam plate8. The shift pin46passing through the output side cam slot42of the shift cam plate8is slid toward the output side under the guidance of the guide hole49provided in the gear case9. The shift pin46slidingly moves the corresponding ring gear32as the changeover member7toward the output side.

The slidingly moved ring gear32is disengaged from the carrier24of the second planetary gear mechanism and comes into the changeover progressing state shown inFIG. 9. At this time, the ring gear32engages with the planet gears of the third planetary gear mechanism and remains not fixed to the gear case9against rotation.

The ring gear32coming into the changeover progressing state shown inFIG. 9is continuously rotated by the rotary inertia generated when the ring gear32engages with the carrier24in the second speed state but, at the same time, is applied with the torque acting in the opposite direction to the rotary inertia due to the reaction force of the planet gears31of the third planetary gear mechanism driven by the motor1. In the meantime, the engaging tooth portion40, which is the gear member5to be engaged with the ring gear32next, is fixed with respect to the gear case9.

The control unit62reduces the relative rotation speed between the ring gear32and the engaging tooth portion40(preferably, to zero) by positively using the torque acting in the opposite direction to the rotary inertia. Therefore, if the slide position detector unit61detects that the ring gear32has reached the changeover progressing state shown inFIG. 9, the control unit62first stops the slide movement of the ring gear32at that moment. Then, the control unit62temporarily increases the rotational power of the motor1to rapidly reduce the rotation speed of the ring gear32with respect to the gear case9. Thereafter, the control unit62allows the ring gear32to make slide movement again and performs control so that the rotation speed of the ring gear32can become nearly zero when the ring gear32engages with the engaging tooth portion40.

This helps suppress engagement shocks when the ring gear32engages with the engaging tooth portion40, which makes it possible to realize a smooth and stable automatic shift operation and to restrains wear or damage of the gears otherwise caused by collision.

The relative rotation speed between the ring gear32and the engaging tooth portion40may be controlled only by temporarily increasing the rotational power of the motor1without having to first stop the slide movement of the ring gear32. The relative rotation speed may be controlled only by first stopping the ring gear32. The relative rotation speed may be controlled by gradually decreasing the rotational power of the motor1in synchronism with the startup of the shift actuator6and consequently reducing the rotational power of the ring gear32caused by the rotary inertia when the ring gear32engages with the carrier24in the second speed state.

The automatic shift from the third speed to the second speed is controlled in the following manner. The third speed is automatically shifted to the second speed if the driving state detector unit60detects that the load of the motor1has reached a specified level while the motor1is driven in the third speed state shown inFIGS. 10A and 10B.

Specifically, if the current flowing through the motor1becomes equal to or smaller than a specified value, if the revolution number of the motor1becomes equal to or greater than a specified value, or if the current and the revolution number satisfy a specified relationship, the driving state detector unit60detects that the load of the motor1has reached the specified level.

Upon receiving the detection result, the control unit62starts up the motor50of the shift actuator6to rotate the shift cam plate8. The shift pin46passing through the output side cam slot42of the shift cam plate8causes the corresponding ring gear32as the changeover member7to slide toward the input side.

The slidingly moved ring gear32is first disengaged from the engaging tooth portion40and comes into the changeover progressing state shown inFIG. 9. At this time, the ring gear32is engaged with the planet gears31of the third planetary gear mechanism and is not fixed to the gear case9against rotation.

The ring gear32coming into the changeover progressing state shown inFIG. 9is applied with the torque acting in the opposite direction to the rotating direction of the motor1due to the reaction force of the planet gears31of the third planetary gear mechanism driven by the motor1. In the meantime, the carrier24of the second planetary gear mechanism, which is the gear member5to be engaged with the ring gear32next, is rotated in the same direction as the rotating direction of the motor1.

If the detection result indicating that the ring gear32has reached the changeover progressing state shown inFIG. 9is inputted from the slide position detector unit61, the control unit62temporarily reduces the rotational power of the motor1(to a value including zero) at that moment. As a result, engagement shocks can be suppressed by reducing the relative rotation speed between the ring gear32and the carrier24(preferably, to zero) when the ring gear32engages with the carrier24as shown inFIGS. 8A and 8B. This realizes a smooth and stable automatic shift operation and restrains wear or damage of the gears otherwise caused by collision.

Alternatively, the control unit62may control the motor1in such a manner that the rotational power of the motor1is reduced to a certain level from the startup time of the shift actuator6. In this case, the control unit62may gradually reduce the rotational power of the motor1in synchronism with the startup of the shift actuator6and may further reduce the rotational power of the motor1at the input time of the detection result indicating that the ring gear32has reached the changeover progressing state shown inFIG. 9.

The automatic shift from the second speed to the first speed is controlled in the following manner. The second speed is automatically shifted to the first speed if the driving state detector unit60detects that the load of the motor1has reached a specified level while the motor1is driven in the second speed state shown inFIGS. 8A and 8B. Specifically, if the current flowing through the motor1becomes equal to or smaller than a specified value, if the revolution number of the motor1becomes equal to or greater than a specified value, or if the current and the revolution number satisfy a specified relationship, the driving state detector unit60detects that the load of the motor1has reached the specified level.

Upon receiving the detection result, the control unit62starts up the motor50of the shift actuator6to rotate the shift cam plate8. The shift pin45passing through the input side cam slot41of the shift cam plate8causes the corresponding ring gear12as the changeover member7to slide toward the input side.

The slidingly moved ring gear12is first disengaged from the planet gears21of the second planetary gear mechanism and comes into the changeover progressing state shown inFIG. 7. At this time, the ring gear12remains fixed to the gear case9against rotation. In the meantime, the planet gears11of the first planetary gear mechanism, which is the gear member5to be engaged next time, is rotationally driven about the axis of the speed reduction mechanism2with respect to the gear case9by the rotational power of the motor1.

If the detection result indicating that the ring gear12has reached the changeover progressing state shown inFIG. 7is inputted from the slide position detector unit61, the control unit62temporarily reduces the rotational power of the motor1at that moment. As a result, engagement shocks can be suppressed by reducing the relative rotation speed between the ring gear12and the planet gears11(preferably, to zero) when the ring gear12engages with the planet gears11as shown inFIGS. 6A and 6B. This realizes a smooth and stable automatic shift operation and restrains wear or damage of the gears otherwise caused by collision.

Alternatively, the control unit62may control the motor1in such a manner that the rotational power of the motor1is reduced to a certain level from the startup time of the shift actuator6. In this case, the control unit62may gradually reduce the rotational power of the motor1in synchronism with the startup of the shift actuator6and may further reduce the rotational power of the motor1at the input time of the detection result indicating that the ring gear12has reached the changeover progressing state shown inFIG. 7.

As described above, the control unit62of the electric power tool in accordance with the present embodiment starts up the shift actuator6depending on the driving state of the motor1and temporarily decrease or increase the rotational power of the motor1in conformity with the current positions of the changeover member7(the ring gears12and32) detected by the sensor. The reduction of the rotational power includes the stoppage of the motor1. This realizes a smooth and stable automatic shift operation and restrains wear or damage of gears otherwise caused by collision. The control unit62may be designed to gradually decrease or increase the rotational power of the motor1in synchronism with the startup of the shift actuator6.

The control unit62of the present embodiment changes the drive control of the shift actuator6in conformity with the positions of the changeover member7(the ring gears12and32) detected by the slide position detector unit61. This realizes a smooth and stable automatic shift operation and restrains wear or damage of gears otherwise caused by collision.

Next, detailed description will be made on how to control the shift actuator6.

By driving the shift actuator6, the control unit62causes the changeover member7(the ring gear12or the ring gear32) to engage with the target gear member5(the planet gears11, the planet gears21, the carrier24or the engaging tooth portion40). At this time, it is sometimes the case that the teeth of the changeover member7and the gear member5may not successfully engage with each other and the changeover member7may fail to slide to a desired target position. In this case, the shift operation is not performed successfully, thereby hindering the works. Moreover, heavy load is applied to the shift actuator6, which may be a cause of trouble.

In contrast, the control unit62of the present embodiment is designed to temporarily reverse the rotating direction of the motor50of the shift actuator6if the detection result inputted from the slide position detector unit61indicates that the changeover member7fails to slide to a desired target position. In other words, the direction in which the changeover member7is slid by the shift cam plate8is reversed for a specified time period, thereby causing the changeover member7to move away from the target gear member5.

The relative rotational positions of the changeover member7and the gear member5are changed by the motor1while the changeover member7and the gear member5are kept spaced apart from each other. Therefore, if the changeover member7is slid toward the gear member5by rotating the motor50of the shift actuator6in the forward direction, the changeover member7and the gear member5are made easy to successfully mesh with each other. When there occurs again such a situation that the changeover member7fails to slide to a desired target position, the control unit62repeats the same control as mentioned above. The control unit62may be designed to stop the motor1when the aforementioned situation occurs a specified number of times.

Next, other embodiments of the electric power tool in accordance with the present invention will be described one after another. The same configurations as those of the first embodiment will not be described in detail and description will be mainly focused on the characteristic configurations differing from the configurations of the first embodiment.

Second Embodiment

In the electric power tool of the present embodiment, the drive control of the shift actuator6is changed if the gears do not successfully engage with each other and the shift operation fails. This realizes a smooth and stable automatic shift operation and restrains wear or damage of gears otherwise caused by collision. The present embodiment differs from the first embodiment in the method of changing the drive control of the shift actuator6.

Specifically, if the detection result of the slide position detector unit61reveals that the changeover member7fails to slide to a desired target position, the control unit62changes the drive control of the shift actuator6so that the rotational power of the motor50of the shift actuator6can be increased. In other words, the changeover member7and the gear member5are made easy to mesh with each other by changing the sliding drive power with which the changeover member7is slid by the shift cam plate8.

The sliding drive power can be properly changed not only by increasing the rotational power of the motor50but also by first decreasing the rotational power and then increasing the same or by repeating the decrease and increase of the rotational power in a specified cycle. The control unit62may be designed to stop the motor1when the changeover member7fails to slide to the desired target position despite the change of the sliding drive power.

Third Embodiment

In the electric power tool of the present embodiment, the relative rotational position of the changeover member7and the gear member5is changed if the gears do not successfully engage with each other and the shift operation fails. This realizes a smooth and stable automatic shift operation and restrains wear or damage of gears otherwise caused by collision. The present embodiment differs from the first embodiment in the method of changing the control in the case of the failure of the shift operation.

Specifically, if it is determined that the changeover member7fails to slide to a desired target position and the motor is hardly driven, the control unit62changes the rotational power of the motor1while maintaining the operation of the shift actuator6. In other words, such control is carried out if the detection result of the slide position detector unit61reveals that the changeover member fails to slide to a desired target position while the shift actuator6is driven after the rotational power of the motor1is first changed.

More specifically, if it is determined from the detection result of the slide position detector unit61that the rotational power of the motor1is completely or substantially stopped and the motor is not driven, the control unit62increases the rotational power of the motor1while maintaining the operation of the shift actuator6.

When increasing the rotational power of the motor1, the control unit62changes the rotational power of the motor1such that the rotational acceleration of the rotational power becomes increased in the case where the changeover member7makes the slide movement compared with case where the changeover member7makes no slide movement.

Specifically, the control unit62controls the rotational power of the motor1such that the rotational acceleration of the rotational power becomes increased in the case that the gears engage with each other and the changeover member7makes the slice movement compared with the case where the gears do not successfully engage with each other and the changeover member7makes no slice movement.

The rotational power (sliding drive power) of the motor50may be maintained merely, but the sliding drive power may be properly changed by first decreasing the rotational power and then increasing the same or by repeating the decrease and increase of the rotational power in a specified cycle. The control unit62may be designed to stop the motor1when the changeover member7fails to slide to the desired target position despite the change of the sliding drive power.

Further, the state where the motor1is hardly driven includes the case of reducing the rotational power of the motor1in the shift operation and the case of stopping the driving of the motor1in accordance with the determination of work completion made by the control unit62. Specifically, the stopping of the motor1includes the state where the load of the motor1is substantially removed after reaching a predetermined level and the control unit62determinates that the work is completed and the state where the operation of the trigger switch103is released. In the automatic shift in such states, the control unit62controls the stopped motor1to be driven if the shift operation fails.

Fourth Embodiment

In the electric power tool of the present embodiment, the relative rotational position of the changeover member7and the gear member5is changed if the gears do not successfully engage with each other and the shift operation fails. This realizes a smooth and stable automatic shift operation and restrains wear or damage of the gears otherwise caused by collision.

The present embodiment differs from the first embodiment in the control method in case that the shift operation fails. In the meantime, the present embodiment is the same as the third embodiment in that the control is carried out when the changeover member7is not slid to a desired target position and it is determined that the motor1is hardly driven. However, the present embodiment differs from the third embodiment in the control method after the determination.

Specifically, if it is determined that the shift operation fails or the motor1is hardly driven, the control unit62first stops the driving of the shift actuator6and increase the rotational power of the motor1. Then, the control unit62controls the shift actuator6to be driven again. In other words, if the shift operation fails, the control unit62stops the driving of the shift actuator6and then controls the shift actuator6to be driven again after increasing the rotational power of the motor1.

When increasing the rotational power of the motor1, the control unit62changes the rotational power of the motor1such that the rotational acceleration of the rotational power becomes increased in the case that the changeover member makes the slide movement compared with the case that the changeover member7makes no slide movement.

Specifically, the control unit62controls the rotational power of the motor1such that the rotational acceleration of the rotational power becomes increased in the case that the gears successfully engage with each other and the changeover member7makes the slide movement compared with the case that the gears do not successfully engage with each other and the changeover member7makes no slide movement.

The rotational power of the motor1may be increased merely, but the rotational power may be properly changed by first decreasing the rotational power and then increasing the same or by repeating the decrease and increase of the rotational power in a specified cycle. The control unit62may be designed to stop the motor1when the changeover member7fails to slide to the desired target position despite the change of the sliding drive power.

Further, the state where the motor1is hardly driven includes the case of reducing the rotational power of the motor1in the shift operation and the case of stopping the driving of the motor1in accordance with the determination of work completion made by the control unit62. Specifically, the stopping of the motor1includes the state where the load of the motor1is substantially removed after reaching a predetermined level and the control unit62determinates that the work is completed and the state where the operation of the trigger switch103is released. In the automatic shift in such states, the control unit62controls the stopped motor1to be driven if the shift operation fails.

Fifth Embodiment

The electric power tool of the present embodiment differs from that of the first embodiment in terms of the slide position detector unit61. The slide position detector unit61employed in the present embodiment does not detect the position of other member (e.g., the shift cam plate8) interlocked with the changeover member7as in the first embodiment but directly detects the positions of the changeover member7.

FIGS. 11A,11B and11C schematically show the slide position detector unit61employed in the present embodiment. In case of the present embodiment, the shift actuator6is a linear actuator formed of a solenoid. The shift actuator6includes a plunger70whose axial protrusion amount is changeable. The ring gear32included in the changeover member7is connected to the plunger70through a connecting member71. The ring gear32is rotatable about the axis of the speed reduction mechanism2with respect to the connecting member71and is axially slidable together with the connecting member71.

The slide position detector unit61is a displacement detecting sensor installed in the gear case9so that it can be positioned radially outwards of the ring gear32. While this sensor is of a contact type making direct contact with the ring gear32, a contactless sensor may be used in place thereof.

Sixth Embodiment

The electric power tool of the present embodiment differs from that of the first embodiment in terms of the slide position detector unit61. The slide position detector unit61employed in the present embodiment does not detect the position of other member (e.g., the shift cam plate8) interlocked with the changeover member7but detects the driving state of the shift actuator6to indirectly detect the positions of the changeover member7based on the detection result.

FIG. 12schematically shows the slide position detector unit61employed in the present embodiment. The slide position detector unit61of the present embodiment is a displacement sensor for detecting the rotational position of an output unit52of the rotary shift actuator6. This displacement sensor may be either a contact type sensor making direct contact with the output unit52or a contactless sensor.

Seventh Embodiment

The electric power tool of the present embodiment differs from that of the first embodiment in terms of the slide position detector unit61. The slide position detector unit61employed in the present embodiment indirectly detects the positions of the changeover member7by detecting the driving state of the shift actuator6. In this respect, the slide position detector unit61of the present embodiment is the same as that of the sixth embodiment. However, the slide position detector unit61of the present embodiment differs from that of the sixth embodiment in the following aspects.

FIGS. 13A,13B and13C schematically show the slide position detector unit61employed in the present embodiment. In case of the present embodiment, the shift actuator6is a linear actuator formed of a solenoid. The shift actuator6includes a plunger70whose axial protrusion amount is changeable. The ring gear32included in the changeover member7is connected to the plunger70through a connecting member71. The ring gear32is rotatable about the axis of the speed reduction mechanism2with respect to the connecting member71and is axially slidable together with the connecting member71.

The slide position detector unit61is a displacement sensor for detecting the protruding position of the plunger70of the linear shift actuator6. While this displacement sensor is of a contact type making direct contact with the plunger70, a contactless sensor may be used in place thereof.

The detailed configurations of the electric power tools in accordance with the first through seventh embodiments have been described hereinabove.

As described above, each of the electric power tools of the first through seventh embodiments includes the motor1as a drive power source, the speed reduction mechanism2for transferring the rotational power of the motor1at a reduced speed and the reduction ratio changing unit for changing the reduction ratio of the speed reduction mechanism2. The speed reduction mechanism2is designed to change the reduction ratio by using the axially slidable changeover member7and the gear member5whose engagement and disengagement with the changeover member7are changed depending on the axial slide positions of the changeover member7.

The reduction ratio changing unit includes the shift actuator6for axially sliding the changeover member7, the driving state detector unit60for detecting the driving state of the motor1, the slide position detector unit61for detecting the slide positions of the changeover member7, and the control unit62for starting up the shift actuator6depending on the detection result of the driving state detector unit60and for changing the drive control of the shift actuator6depending on the detection result of the slide position detector unit61.

In the electric power tool having the configurations described above, when the changeover member7makes the slide movement to a certain degree by driving the shift actuator6, it is possible to control the rotational power of the motor1to be changed depending on the actually detected slide position of the changeover member7to significantly reduce the relative rotational speed between the changeover member7and the gear member5. For that reason, it is possible to smoothly complete the automatic change of the reduction ratio in a short time while maintaining the rotation of the motor1. As a result, in the electric power tool of the present embodiment, it is possible to suppress the engagement shock when the reduction ratio is changed and quickly and smoothly complete the change of the reduction ratio.

Further, in the first to seventh embodiments, the control unit62is designed to change the drive control of the shift actuator6depending on the detection result of the slide position detector unit61. In other words, depending on the actually detected slide position of the changeover member7, the control can be carried out to change the rotational power of the motor1and the drive control of the shift actuator6. Accordingly, it is possible to more smoothly complete the automatic change of the reduction ratio while maintaining the rotation of the motor1.

Especially, in the electric power tools of the first, fifth to seventh embodiments, the control unit62is designed to temporarily reverse the direction of slide movement of the changeover member7caused by the shift actuator6if the detection result of the slide position detector unit61indicates that the changeover member7fails to slide to a desired target position when the shift actuator6is driven. Accordingly, if the changeover member7fails to successfully engage with the gear member5, the changeover member7is temporarily spaced apart from the gear member5. After changing the relative rotational position of the changeover member7and the gear member5, an attempt can be made to cause the changeover member7and the gear member5to mesh with each other.

Further, in the electric power tool of the second embodiment, the control unit62is designed to change the sliding drive power of the changeover member7applied by the shift actuator6if the detection result of the slide position detector unit61indicates that the changeover member7fails to slide to the desired target position when the shift actuator6is driven. Accordingly, if the changeover member7fails to successfully engage with the gear member5, the changeover member7and the gear member5can be made easy to mesh with each other by, e.g., increasing the drive power of the shift actuator6.

Further, in the electric power tool of the third embodiment, if the detection result of the slide position detector unit61indicates that the changeover member7fails to slide to the desired target position when the shift actuator6is driven, the control unit62is designed to change the relative rotational position between the changeover member7and the gear member5while maintaining the driving of the shift actuator6. Accordingly, the changeover member7and the gear member5becomes easy to mesh with each other and, furthermore, it is possible to slide the changeover member7by quickly dealing with the case when the changeover member7slide to such a position that it can easily mesh with the gear member5. Therefore, it is possible to smoothly change the reduction ratio in a short time.

In the electric power tool of the fourth embodiment, if the detection result of the slide position detector unit61indicates that the changeover member7fails to slide to the desired target position when the shift actuator6is driven, the control unit62is designed to change the relative rotational position between the changeover member7and the gear member5after stopping the driving of the shift actuator6. Accordingly, if the changeover member7fails to engage with the gear member5, the slide movement of the changeover member7is stopped to easily change the relative rotational position between the changeover member7and the gear member5. After the relative rotational position between the changeover member7and the gear member5is changed, an attempt can be made to cause the changeover member7and the gear member5to mesh with each other.

In the electric power tool of the third and the fourth embodiment, when changing the relative rotational position between the changeover member7and the gear member5by increasing the rotational power of the motor1, the control unit62changes the rotational power of the motor1such that the rotational acceleration of the rotational power becomes increased in the cases that the changeover member7makes the slide movement compared with the case that the changeover member7makes no slide movement. This makes it easy to re-put the rotational power of the motor1the work this process and, thus, it is possible to shorten a changeover time required for changing the reduction ratio.

In the electric power tool of the first to the fifth embodiment, the slide position detector unit61is designed to detect a position of the changeover member7or a member interlocked with the changeover member7. Accordingly, it is possible to more directly the actual slide position of the changeover member7.

In the electric power tool of the sixth and the seventh embodiment, the slide position detector unit61is designed to detect the driving state of the shift actuator6and indirectly detect the position of the changeover member based on the detection result of the driving state. Accordingly, the degree of freedom in installation and type of a sensor of the slide position detector unit61is increased.

In the electric power tool of the sixth embodiment, the shift actuator6is of a rotary type and the slide position detector unit61is designed to detect the rotational state of the shift actuator6. Accordingly, it is possible to configure the sensor of the slide position detector unit61to contact with or to be close to the shift actuator6in a compact manner.

Further, in the electric power tool of the seventh embodiment, the shift actuator6is a linear actuator and the slide position detector unit61is designed to direct the linear driving state of the shift actuator6. This also makes it possible to configure the sensor of the slide position detector unit61to contact with or to be close to the shift actuator6in a compact manner.

While the present invention has been described above based on the embodiments shown in the accompanying drawings, the present invention is not limited to these embodiments. The respective embodiments may be properly modified in design and may be appropriately combined without departing from the scope of the invention.

Although the relative rotational position between the changeover member7and the gear member5is changed by decreasing or increasing the rotational power of the motor1in the electric power tool of the third and the fourth embodiment, the present invention is not limited to the adjustment of the relative rotational position by changing the rotational power of the motor1. For example, the relative rotational position may be changed by providing a separate driving unit other than the motor1and controlling the driving unit to reduce the relative rotation speed between the changeover member7and the gear member5. Moreover, the motor50as the driving unit of the shift actuator6may be also used to reduce the relative rotation speed between the changeover member7and the gear member5.

The state where the rotational power of the motor is stopped when the shift operation fails includes the case of the operation for initializing the reduction ratio, e.g., the shift operation from the third speed to the first speed, for the next operation by stopping the motor in advance, for example, when the work using the electric power tool is finished. In other words, in case that the operation for initializing the reduction ratio is executed when the driving of the motor1is stopped after the work is finished, if the shift operation fails, the control unit62drives the motor1and increases its rotational power. This makes it possible to quickly initialize the reduction ratio and improve the operation efficiency of the electric power tool.