Ratchet wrench

The powered ratchet wrench 10 is constructed of several components. A throttle lever 20 controls the air flow to a rotary air motor 30. The rotary output of the motor is transmitted to the hammer assembly 40 of an impact clutch mechanism. A spring 50 biases an anvil shaft 60 into association with the hammer assembly 40. The anvil can be directly driven by the motor through the hammer assembly or can be driven intermittently by a series of rotational impacts from the hammer assembly. The rotation of the anvil shaft causes the reversible ratchet mechanism 70 to rotate in the desired direction, thus tightening or removing a threaded fastener. Only a small reaction force is transmitted by the tool to the operator once the fastener is tightened.

FIELD OF THE INVENTION 
This invention pertains to a powered ratchet wrench for tightening or 
removing threaded parts. An impact clutch mechanism connects the ratchet 
mechanism with a rotary power source. 
BACKGROUND OF THE INVENTION 
Conventional powered ratchet wrenches, such as that disclosed in Japanese 
utility model gazette No. 1976-16,555, have a motor operated by compressed 
air in the base of the housing. When a throttle lever is pressed, 
compressed air flows to the motor, and the output shaft of the motor turns 
a transmission shaft by way of speed reducing gears. Slow speed and high 
torque are transmitted to the transmission shaft. The eccentric rotation 
of a crankshaft at the front end of the transmission shaft oscillates a 
ratchet yoke. The movement of the ratchet yoke causes the ratchet spindle 
or tool head of a ratchet mechanism to rotate so that a bolt, nut, or 
other threaded part is tightened or removed. 
In a conventional ratchet wrench, the gear drive continues to transmit 
motor torque directly to the operator even after the fastener has been 
tightened to a specified tightening torque. That is, if the throttle lever 
is held open after the fastener has been firmly tightened, compressed air 
continues to drive the motor and the gears, which in turn drive the 
transmission shaft and ratchet mechanism. Thus, a considerable reaction 
force is transmitted to the operator as the tool tries to rotate around 
the tightened, stationary fastener. The operator's hand can be jerked 
forward by the wrench, or the operator may lose his grip. Even if the 
operator quickly releases the lever as soon as tightening is finished, a 
reaction force is still transmitted to the hand. It is difficult to 
prevent the hand from being pulled along or from losing its grip. Hence, 
the operator usually releases the lever before tightening is finished. The 
operator then turns the tool manually to finish tightening. The tightening 
force applied by these prior art tools can therefore be inconsistent. 
In some situations, conventional powered ratchet wrenches are unsuitable 
for use in tight places where there is room for only one hand. Because the 
ratchet wrench cannot be gripped tightly in such cramped places, and since 
it is difficult to release the throttle lever at exactly the right time, 
the hand is often jerked or loses its grip. The operator's hand can be 
forcefully thrown against an obstruction and injured, or the ratchet 
wrench can forcefully strike a projecting part and be damaged. 
There is therefore a need for a powered ratchet wrench which minimizes the 
motor torque reaction force transmitted to the operator. It is desirable 
to provide a powered ratchet wrench which minimizes the torque reaction 
force transmitted to the operator's hand so that the hand is not pulled 
along with the tool while the motor is still operating and torque is still 
acting on the fastener. 
SUMMARY OF THE INVENTION 
This invention provides a powered ratchet wrench such that, when used to 
tighten or remove a part or fastener, an impact clutch mechanism provides 
the connection between the tool motor and the ratchet mechanism. To 
tighten a fastener, the impact clutch mechanism provides an initial direct 
connection between the motor and the ratchet mechanism to set or snug-up 
the fastener during "run down". The ratchet mechanism is thereafter 
rotated by a series of rotational impacts delivered by the impact clutch. 
To remove a fastener, the impacts break the fastener loose, while the 
direct drive "runs up" the fastener. If the throttle lever is not released 
when fastener tightening is completed, only minimal torque reaction force 
is transmitted to the operator due to the impact clutch. Thus, the tool 
can preform consistent tightening quickly and reliably, without manual 
assistance. 
More particularly, the ratchet wrench according to this invention is 
constructed so that the motor and ratchet mechanism are connected with an 
impact clutch rather than a speed reducing gear device, as in the 
conventional wrench. The impact clutch allows the ratchet mechanism to 
rotate either under direct motor power or by rotational impacts. An impact 
can be produced rapidly and extremely smoothly during each motor rotation, 
so that the threaded part can be firmly tightened by the ratchet. Thus, 
while the ratchet is tightening the part, and after the part is fully 
tightened, the connection between the motor and the ratchet is 
intermittently broken, so that the ratchet is rotating with minimum 
reaction to the operator. 
Thus, if the throttle lever is not released when tightening is completed, 
only a minimal reaction force is transmitted to the operator. This allows 
complete tightening to be carried out consistently and reliably. 
This wrench is also suitable for use in tight places with room for only one 
hand on the tool. The hand won't be thrown against the work piece and 
injured, as could happen previously. Also, the danger of the ratchet 
wrench striking an obstruction and being damaged is avoided.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a longitudinal cross section through a preferred embodiment of 
the ratchet wrench. The ratchet wrench 10 is constructed of several 
components which will first be described generally. A throttle lever 20 
controls the air flow to a rotary air motor 30. The rotary output of the 
motor is transmitted to the hammer assembly 40 of an impact clutch 
mechanism. A spring 50 biases an anvil shaft 60 into association with the 
hammer assembly 40. The anvil shaft can be directly driven by the motor 
through the hammer assembly or can be driven intermittently by a series of 
rotational impacts from the hammer assembly. The rotation of a crank on 
the anvil shaft causes the reversible ratchet mechanism 70 to rotate in 
the desired direction, thus tightening or removing a threaded part or 
fastener. Only a small reaction force is transmitted by the tool to the 
operator once the fastener is tight. 
More specifically the tool 10 includes a motor housing 11 and a ratchet 
housing 12, secured together in fixed relation such as by a threaded 
coupling ring 13 and coupling nuts 14. 
A throttle lever 20 opens and closes a throttle valve 22. When throttle 
valve 22 is in the open position, compressed air enters the tool at air 
inlet 24 which is connected to a suitable compressed air source. The 
compressed air flows into the rotary air motor 30 and transfers its energy 
to the rotor. The spent air is exhausted from exhaust 26. 
The rotary motor 30 is located in the motor housing 11. In the preferred 
embodiment, an air motor is shown, but any rotary power source such as a 
hydraulic or electric motor could also be used. 
Air motor 30 has a rotor 34 and an extending output shaft 31. The two ends 
of rotor 34 are supported by bearings 33 which in turn are supported by 
end plates 32. The rotor is mounted for rotation in the cylinder 35, the 
open ends of which are covered by the end plates 32. The cylinder has an 
eccentric bore, as is typical of conventional air motors. A plurality of 
vanes 36 are slidably mounted in radial slots in the rotor. The vanes 
slide radially back and forth in the slots as the rotor turns due to 
centrifugal force and the eccentric inner surface of cylinder 35. As the 
inlet air pushes against vanes 36, it causes rotor 34 to rotate, thus 
causing output shaft 31 to rotate therewith. 
Numeral 41 designates the hammer cage. It is cup shaped, having a 
cylindrical wall portion and a base portion which together form an inner 
surface designated by numeral 44. Within the hammer cage on the inner 
surface 44 are two diametrically opposed axial grooves. The axial grooves 
extend only part way down the cylindrical wall portion, forming 
semi-circular shoulders at a specified distance above the base portion. 
The hammer cage 41 in this preferred embodiment is directly driven by the 
output shaft 31, as for example by a splined connection. Alternatively, 
however, the hammer cage could be gear driven. 
Formed in the base portion of the hammer cage is a circular raceway 47, 
which is concentric about the axis of rotation. Coinciding with the 
raceway, but extending for only a limited number of degrees, is a 
larger-dimensioned cam ball pocket 46. The cam ball pocket typically 
describes an arc in the range of 45 to 180 degrees. A cam ball 43 is held 
in the pocket and rolls freely through the arc. 
The anvil shaft 60 carries an axially extending cam 62. The cam 62 is 
preferably a one-sided cam and projects axially from the end of the anvil 
shaft. The cam forms a cam peak with preferably one gradually rising 
inclined surface adjacent the cam peak and one sharply falling surface 
adjacent the other side of the peak. The inclined surface occupies about a 
90 degree arc on the anvil shaft. The sharp surface facilitates escape of 
the cam. The cam 62 and the raceway 47 are dimensioned so that when the 
hammer cage rotates with the cam extending into the raceway, the hammer 
cage rotates freely without interference from the cam. In other words, as 
the raceway rotates relative to the cam, the raceway permits the cam to 
extend into it without interference. 
The anvil shaft carries at least one, and preferably two anvil jaws 63. The 
anvil jaws are diametrically opposed and radially extending. The outer 
radial surfaces of the anvil jaws are dimensioned so that the inner 
chamber 44 of the hammer cage can rotate freely about the anvil jaws. 
The anvil shaft also carries an eccentric crank 61 at the shaft end 
opposite the cam 62. The anvil shaft 60 is supported by needle bearing 54 
so that it slides freely in the axial direction as well as freely rotates. 
The anvil shaft is also journaled for rotation and axial movement by a 
bore in hammer cage top 42. 
Numeral 50 designates a helical coil biasing spring of a size to fit around 
a reduced diameter portion of the anvil shaft 60 and abut against a 
shoulder on the shaft. This biasing spring normally urges the anvil shaft 
60 toward the base portion of the hammer cage 41, such that the extending 
cam 62 normally projects into the raceway 47. 
At least one, and preferably two hammer jaws 45 are received in the axial 
grooves of the hammer cage 41. The hammer jaws are harden pins and when in 
place are half embedded in the cylindrical wall portion and half exposed 
in the inner chamber 44. The hammer jaws rest on the shoulders of the 
axial grooves so as not to extend to the base portion of the hammer cage. 
An uninterrupted cylindrical surface is provided below the shoulders at 
the base of the inner chamber 44. This surface allows the hammer cage 41 
to rotate relative to the anvil jaws 63 when the biasing spring urges the 
anvil shaft toward the base portion of the hammer cage without impacting 
on the anvil jaws. 
The hammer cage top 42 has a short, snug-fitting, reduced diameter portion 
that is inserted into the inner chamber 44 of the hammer cage. The cage 
top also has two diametrically opposite pilot bores that axially align 
with the axial grooves of the hammer cage. The hammer jaws 45 are also 
received into these pilot bores to fix the hammer jaws in an axial 
position and to lock the hammer cage and hammer cage top together against 
relative rotation. 
FIG. 1 illustrates the ratchet wrench in a position when the biasing spring 
50 is extended and the cam 62 is positioned in the raceway 47. The anvil 
jaws 63 are biased by the spring toward the base of the hammer cage such 
that during rotation of the hammer cage, the hammer jaws 45 do not 
intercept the anvil jaws 63. The uninterrupted cylindrical portion of the 
hammer cage 41, that portion located below the hammer jaws, rotates 
radially adjacent to the anvil jaws. 
When the anvil jaws 63 move axially forward, due to the cam 62 riding up on 
cam ball 43 and compressing the biasing spring 50, the orbit of the 
rotating hammer jaws 45 intercepts the new position of the anvil jaws. 
When the cam 62 moves the anvil shaft axially forward during each rotation 
of the hammer cage, the hammer jaws 45 produce a series of rotational 
impact against the anvil jaws 63. 
Eccentric crank 61 is positioned at the end of the anvil shaft 60 opposite 
the cam 62. The crank slides axially in the bore of a drive bushing 52 so 
as to allow for the axial movement of the anvil shaft. 
Drive bushing 52 slides vertically in a bushing pocket 72 of ratchet yoke 
71 so as to accommodate the up and down movement of the crank 61 as it 
rotates. The oscillating movement of the ratchet yoke is transferred to 
the ratchet mechanism 70. The ratchet mechanism rotates a ratchet spindle 
or tool head 73 in a conventional manner as is well known in the prior 
art. 
By turning the ratchet reverse knob 74 to the appropriate setting, the 
direction of rotation of the ratchet spindle can be determined. The tool 
can be operated to tighten or remove a fastener by setting the ratchet 
reverse knob 74. 
OPERATION 
To set a threaded fastener, the ratchet mechanism is first simply directly 
driven by the motor through the impact clutch to rotate or "run down" the 
fastener to a snug position. Next, to fully tighten the fastener, impacts 
are applied by the impact clutch mechanism to further rotate the ratchet 
mechanism and further torque the fastener. 
FIG. 1 illustrates the "run down" position of the tool. The anvil shaft 60 
is in its normal axial position, that is biased toward the base portion of 
the hammer cage with the one-sided cam 62 extending into the raceway 47. 
The cam ball 43 is contained in the limited arc cam ball pocket 46. When 
the air motor rotates, output shaft 31 causes hammer cage 41 to rotate 
with it due to the splined connection. The trailing shoulder of the 
rotating cam ball pocket engages and drives the cam ball in the direction 
of rotation directly of the hammer cage. The cam ball next engages but 
does not roll up the inclined surface of the one-sided cam 62. The 
rotating cam ball imparts rotation to the anvil shaft 60. The rotation of 
the crank 61 at the end of the anvil shaft causes the ratchet mechanism to 
"run down" the fastener. Until the ratchet mechanism and the anvil shaft 
60 encounter sufficient resistance from the fastener as it becomes snug, 
the motor is directly driving the ratchet mechanism through the cam ball 
of the impact clutch mechanism. 
When the ratchet mechanism and the anvil shaft 60 encounter sufficient 
resistance, the gradual inclined surface of the cam 62 begins to ride up 
on the cam ball 43 due to the continued rotation of the cam ball with the 
hammer cage. The anvil shaft and the attached anvil jaws 63 are moved 
axially forward away from the base portion of the hammer cage. In other 
words, the cam ball cooperates with the cam to move the cam and attached 
anvil shaft axially forward as the cam rides up on the cam ball as it 
revolves within the cam ball pocket and rotates with the hammer cage. 
When the cam peak overrides the top of the cam ball, the cam momentarily 
maintains its axial momentum and clears the cam ball, which continues to 
rotate beneath the cam. The cam is momentarily in "free flight" before an 
impact occurs. There are a few degrees of clearance between the trailing 
shoulder of the cam ball pocket and the hammer jaws. The anvil jaws 63 
have been moved axially away from the hammer base portion and are now in 
an axial position which intercepts the orbit of the rotating hammer jaws 
45. The exposed portions of the hammer jaws 45 intercept the new position 
of the anvil jaws and an impact is delivered to the anvil jaws. 
This impact drives the anvil shaft 60 in the direction of rotation of the 
hammer cage until sufficient resistance is met. This resistance is the 
resistance the fastener encounters as it tightens and is transferred from 
the fastener through the ratchet mechanism to the anvil shaft 60. When 
sufficient resistance is met, the anvil shaft stops rotating and the 
hammer jaws and anvil jaws will begin to disengage. 
At that time, the force in the compressed biasing spring 50 overcomes the 
axial momentum of the anvil shaft and begins to push the cam back towards 
the hammer cage base. As the cam peak moves toward the base, the steep 
escape surface adjacent the cam peak kicks the cam ball in the direction 
of the leading edge of the cam ball pocket. The cam peak then again enters 
the raceway 47. 
As the hammer cage continues to rotate, the cam 62 once again encounters 
the cam ball 43. The cam ball rotates in the cam ball pocket with the cam 
until the ball reaches the trailing edge of the pocket. If there still is 
sufficient resistance due to fastener tension, the cam ball will again 
force the cam to ride up on the cam ball and the impact sequence will be 
repeated until the fastener can not be further tightened. The cam ball 
thus times the impacts. At ultimate tighening torque, the impact clutch 
mechanism will continue to cause the hammer to impact on the anvil. The 
ratchet mechanism will not provide any more tightening torque to the 
fastener. However, the tool operator will not experience any torque 
reaction due to the tool turning on the tightened fastener. Rather the 
operator will experience only the minimal reactions due to the impact 
clutch. 
Other embodiments are considered to be within the scope of this invention. 
For example, anvil shaft 60 can be constructed of two pieces to facilitate 
the manufacture and assembly of the tool. A separate cam portion having 
the cam peak and anvil jaws can be positioned inside the inner chamber 44 
of the hammer cage and splined to a shaft portion extending through the 
bore of the hammer cage top. Furthermore, biasing spring 50 can be 
positioned anywhere along the shaft portion of the anvil shaft 60. For 
example, in the embodiment with a two piece anvil shaft, the biasing 
spring can be positioned on the splined connection between the cam portion 
and the shaft portion. 
The purpose of the impact clutch mechanism is to translate rotary motion to 
interrupted rotary motion having less torque reaction. The impact clutch 
mechanism described in connection with the preferred embodiment can be 
broadly categorized as a unique embodiment of a cam engage, spring 
disengage impact clutch. Other embodiments of the cam engage, spring 
disengage type impact clutch are also considered to be within the scope of 
this invention. For example, in the preferred embodiment, the anvil shaft 
moves axially. An alternate embodiment can provide for the hammer jaws to 
move axially rather than the anvil shaft. 
Additionally, other types of impact clutch mechanisms, such as the cam 
engage, cam disengage impact clutch of Mauer (U.S. Pat. No. 3,661,217 
issued May 9, 1972), and the spring engage, spring disengage impact clutch 
of Pott (U.S. Pat. No. 3,369,615 issued Feb. 20, 1968), are considered to 
be within the scope of this invention. The Pott impact clutch is 
particularly suitable for electric driven ratchet wrenches. 
One advantage of this invention over the prior art includes minimizing the 
torque reaction to the tool operator when a fastener is tight and the tool 
continues to run. This allows the tool to be safely operated with one hand 
and also in confined and awkward situations. The tool will also produce a 
consistent tightening torque. The operator will not have to stop the tool 
before the fastener is tight and manually tighten the fastener out of 
concern for his own safety and well-being. Additionally, the tool allows a 
faster "run-down" of the fasteners than prior art powered ratchets. 
From the foregoing, those skilled in the art will recognize the 
improvements over prior art tools and the considerable advantages. 
Changes and modifications in the specifically described embodiments can be 
carried out without departing from the scope of the invention which is 
intended to be limited only by the scope of the appended claims.