JPS5848305B2 - Automatic transmission for power tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic transmission for a power tool.

Conventionally, methods for obtaining high torque in power tools such as nutrunners have been made by increasing the output of the prime mover or using a reduction gear.

However, the former has drawbacks such as the tool body becoming larger.
The latter has the disadvantage that the rotation speed of the driven shaft at the tip of the tool becomes low due to the large reduction ratio, resulting in poor workability.

Therefore, a power tool with an automatic transmission is required, which rotates at high speed when torque is low and rotates at low speed when torque is high.

A method in which a one-way clutch is provided in a planetary gear system as an automatic transmission, and the driven shaft and the driving shaft are connected and disconnected using a torque-sensitive clutch to convert speed.
This has been done traditionally.

However, in the air drive system, there are the following difficulties in the method of holding a disengaged clutch for a necessary period of time without reconnecting it.

That is, a method has been adopted in which mediate energy such as compressed fluid is used as a holding device to hold the disengaged clutch by compressive force, but this method cannot be used unless mediate energy is provided by a compressor, hydraulic device, etc. However, it has drawbacks that cannot be used with electric power tools.

There is also a method of operating the planetary gear system without providing mediated energy, but after the speed is changed to low speed, the tool is rotated while constantly applying a large load that causes the clutch to slip, resulting in large mechanical losses. It has the disadvantage of decreasing efficiency.

An object of the present invention is to provide a method for automatically shifting gears using a planetary gear system, in which a clutch is disengaged in response to torque.
It is an object of the present invention to provide a power tool that can be held and changed speed without using mediating energy such as compressed fluid and with less mechanical loss.

The present invention provides a clutch section that controls switching torque and disengages the clutch using two cams each having a cam surface and a clutch spring, and provides rotational resistance to the disengaged clutch. A mechanism is provided to keep the clutch from re-engaging during low-speed operation, and this is equipped with a one-way clutch that idles at high speeds when the clutch is engaged and is fixed at low speeds when the clutch is disengaged. By linking it to a speed reduction mechanism such as a planetary gear system, it becomes a power tool that automatically changes speed.

Embodiments of the present invention will be described below with reference to the drawings.

In the housing 1 of the power tool, 2 is a motor such as an electric motor or an air motor.

A drive shaft 3 is directly connected to the moke 2.

On the other hand, a driven shaft 4 is rotatably supported at the front portion of the housing 1 .

A planetary gear device 5 is provided between the drive shaft 3 and the driven shaft 4 as a reduction mechanism.

The planetary gear device 5 includes a planetary gear 6 supported by the driven shaft 4 as an arm, and a one-way clutch 7 on the inner periphery of the housing 1.
This planetary gear 6 meshes with a pinion 9 formed at the tip of the drive shaft 3.

On the other hand, a sleeve-shaped dog clutch 11 having an engaging portion 10 at its front end is attached to the outer periphery of the drive shaft 3, and is always urged forward by a clutch spring 12 to form a clutch device.

An engaging portion 13 that engages with a dog clutch 11 is provided at the rear end of the driven shaft 4 .

The outer periphery of the dog clutch 11 is formed into two stages, a thin lower part and a thicker upper part, with gradually increasing steps, and a clutch holding device 19 consisting of a metal screw 16, a spring 17, and a lining 18 slides on this outer periphery. It is press-fitted so that it can move freely.

Next, the cam device will be described. Reference numeral 20 is a driving cam fixed to the drive shaft 3 by a pin 21 and a stop ring 22 at the rear of the pinion 9 at the front of the drive shaft 3.

Further, a driven force arm 23 facing the motive force arm 20 is press-fitted into the inner periphery of the dog clutch 11.
A steel hole 24 is inserted between 0 and the driven arm 23.

The motive force arm 20 and the driven force arm 23 have the same cam surface, that is, an inclined surface 25, a gently inclined surface 26, and a locking portion 27 as shown in FIG.

The relationship between the amount of axial displacement during cam operation, that is, the amount of engagement between the dog clutch 11, the driven shaft 4, and the engagement portions 10 and 13 at the rear end, and changes is as shown in FIG.

When the steel pole 24 reaches the inflection point where it moves from the slope 25 to the gently sloped surface 26, the clutch is disengaged and the steel ball 24 moves on the gently sloped surface 26 with a slight rotational force and is engaged. The stop portion 27 is reached.

The steel balls 24 are used here to replace the sliding resistance on the cam surface with rolling resistance and to enable smooth movement of the cams 20, 23 in the thrust direction and radial direction.

The operation of the above configuration will be explained below.

When the motor 2 is first rotated, the torque is transmitted through the drive shaft 3, the pin 21, the driving force 20, the steel ball 24, the driven force 23, the dog clutch 11, the engaging parts 10 and 13, and the driven shaft 4, that is, Transmitted through a high-speed rotation, low-torque transmission path.

The transmitted torque at this time is set by the clutch spring 12.

Further, since the one-way clutch 7 is provided so as to be rotatable in the clockwise direction, it does not affect the rotation of the driven shaft 4.

Next, when the transmitted torque becomes larger than the set torque, the driving force 20 starts rotating relative to the driven force 23, and displaces the driven force 23 and dog clutch 11 in the thrust direction via the steel balls 24. let

After the engagement part 10 of the dog clutch 11 is separated as shown in FIG.
3 also tries to rotate at the same time as the motive force 20.

However, at this time, since rotational resistance is applied to the dog clutch 11 by the clutch holding device 19, it does not rotate together with the drive shaft 3, and therefore the cam is attached to the locking portion 27 by the steel ball as shown in FIG. 5d. 24 and continues rotation.

On the other hand, the planetary gear device 5 starts operating from the time when the dog clutch 11 is disengaged.

That is, the torque transmitted from the pinion 9 to the planetary gear 6 tries to rotate the fixed gear 8, or since the one-way clutch 7 is provided so as to be fixed in the counterclockwise direction, the fixed gear 8 also rotates in the housing 1. Fixed.

Therefore, the revolution of the planetary gear 6 is transmitted to the driven shaft 4, forming a so-called low-speed, high-torque transmission path, and bolt tightening is performed at low speed and with high torque.

When the motor 2 is stopped after completion of tightening, the pressing force in the rotational direction from the driving force arm 20 to the driven force arm 23 disappears, so the clutch spring 12 causes the driving force arm 20 to stop.
Then, the driven arm 23 and the steel ball 24 automatically return to the state shown in FIG. 5a.

On the cam surface, the inclined surface 25 is set to control the tightening torque, and the gently inclined surface 26 is provided to reduce the resistance in the rotational direction from the driven arm 23 to the driving arm 20 generated by the clutch spring 12. It is being

In other words, in the case of only the inclined surface 25, the component force in the rotational direction that acts to return the driven arm 23 is large, and the driving arm 20
must overcome this and rotate, resulting in a large torque transmission loss.

On the other hand, if the gently inclined surface 26 is further made into a plane perpendicular to the axis, the component force in the rotational direction becomes O, but when the tool is stopped, the cam automatically returns to its initial state. power is lost.

Therefore, in this case, a separate reset device for returning the cam is required.

When the dog clutch 11 is engaged with the driven shaft 4, the clutch holding device 19 engages with the thin outer diameter portion 14 of the dog clutch 11, and the suppressing force of the spring 17 hardly acts.

Then, when the engagement is disengaged, the clutch holding portion 19 engages with the thick portion 15 of the outer diameter of the dog clutch 11 for the first time, and provides rotational resistance thereto.

In this way, a decrease in torque transmission efficiency during high-speed, low-torque transmission is prevented.

The present invention provides a rotary power tool having a speed reduction mechanism as described above, including: a cam device that separates a driving shaft and a driven shaft according to a transmitted torque;
A clutch device that disconnects a drive shaft and a driven shaft and reconnects the drive shaft and driven shaft via a speed reduction mechanism, and a clutch that maintains the disconnected state of the clutch device by applying rotational resistance to the clutch device. Since the present invention is equipped with a holding device and is configured to automatically change the torque transmission path in response to fluctuations in the transmission torque as appropriate, it is possible to automatically shift gears in accordance with the tightening torque without using any other mediating energy.

Further, when the motor is stopped after tightening, the cam and clutch device automatically return to their initial states, so that continuous tightening of bolts, etc. can be carried out efficiently and without fear of malfunction.

Further, since the cam device and the clutch device are provided separately and held by the clutch holding device, power transmission can be reliably and smoothly switched from high speed, low torque to low speed, high torque.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of an automatic transmission according to the present invention, Fig. 2 is a sectional view of one person A in Fig. 1, Fig. 3 is a sectional view taken along line B-B, and Fig. 4 is the same <C -C sectional view. Figure 5 is a diagram showing the relationship between the claw eye and the rolling motion of the rotating body on the cam surface. FIG. 6 is a front view of the clutch cam 20, and FIG. 7 is its D-
It is a D sectional view. FIG. 8 is a developed view of the cam surfaces of the clutch cam 20 and spindle cam 17. 1...Housing, 2...Motor, 3
... Drive shaft, 4 ... Driven shaft, 5 ...
...Deceleration mechanism, 10, IL12, 13...
Clutch device, 19...Clutch holding device, 2
0, 23, 24...cam device.

Claims (1)

[Claims] 1. An automatic transmission device disposed between the drive shaft and the driven shaft of a power tool, which has a housing, a drive shaft that outputs the driving force of a motor within the housing, and a driven shaft driven by the drive shaft. a planetary gear device comprising a planetary gear meshing with the drive shaft and mounted on the driven shaft; and a fixed gear mounted on the inner wall of the housing via a one-way clutch; a clutch device that is installed via a cam device that disconnects the drive shaft and the driven shaft when the transmitted torque reaches a certain value, and that engages with the rear end of the driven shaft and forms a power transmission path during low torque; At high torque, when the clutch device is disengaged due to the operation of the cam device, the clutch device engages with the large outer diameter portion of the clutch device, and its rotational resistance maintains the clutch device at zero disengagement, thereby driving the planetary gear. a clutch holding device that forms a high torque transmission path through the clutch device, and normally contacts a thin portion formed via a step that gradually changes from the thick portion of the outer diameter to form a low torque transmission path through the clutch device; What is claimed is: 1. An automatic transmission device comprising: an automatic transmission device that changes a torque transmission path as appropriate in accordance with fluctuations in transmission torque;