Pressure-operated power wrench

The power wrench has a substantially T-shaped configuration and comprises a transversely extending housing (10) and a headpiece (11) extending centrally therefrom. The housing (10) comprises a working cylinder (17) and an additional cylinder (21). Both cylinders guide a unit (60) having at the one end a working piston (25) and at the other end an additional piston (29). The lever (41) of the headpiece (11) engages in a coupling member (27). The additional cylinder (21) drives the return stroke. Its area is substantially smaller than that of the working cylinder (17), so that the return movement does not require much hydraulic fluid. The headpiece (11) can easily be exchanged. Its lever (41) loosely engages in the coupling member (27) of the unit (60).

The invention is directed to a pressure-operated power wrench for turning 
screws and the like, wherein the rotational force is produced by a working 
piston movable in a working cylinder. 
From European Patent 0,153,711, a power wrench is known in which the 
housing forming the working cylinder is integrally formed with a headpiece 
containing a rotatable annular member. A lever acting on the annular 
member via a ratchet engages in a recess of the working piston to be 
pivoted thereby in a reciprocating manner. The center of attack of the 
lever at the piston thereby moves on a tangent to the annular member. The 
working piston is only pressurized from one side. The return movement is 
effected by a spring acting on the piston. Such a power wrench is only 
applicable for a single wrench width or a strongly restricted range of 
wrench widths. Another drawback is the relatively slow working motion 
caused by the return spring. If the return spring is strong and produces a 
great return force, its force has to be overcome by the hydraulic pressure 
in the working cylinder so that the working stroke begins relatively late 
and much energy gets lost. If, however, the return spring is relatively 
soft, the return movement of the working piston and the pressing of the 
hydraulic fluid out of the working cylinder takes a long time so that the 
next working stroke starts late. 
A similar power wrench is known from European Patent 0,240,931 A1, wherein 
the working piston moves the lever driving the annular member in the one 
direction whereas a return spring effects the return movement of the 
lever. In the case of this power wrench, the speed of the return movement 
is also limited by the low force of the return spring. The return spring 
presses the end of the lever against the end of the working piston. The 
headpiece is a part of the housing containing the working cylinder and 
cannot be exchanged by the user therein. 
Furthermore, power wrenches are known comprising a double-acting working 
piston, wherein the pressure chamber and the counterpressure chamber of 
the working piston are alternately pressurized. In this case, the return 
movement of the working piston is hydraulically effected, the fluid amount 
required for the return movement of the working piston is not essentially 
smaller than the fluid amount required for the working stroke. 
A power wrench known from British Patent Application 2,182,592 comprises in 
the driving housing one piston at each of the two sides of a lever, one of 
which pistons is provided for the working stroke and the other one for the 
return stroke. Both pistons and the cylinders in which they move have the 
same dimensions. 
From the book "Olhydraulik", 7th edition, VEB Verlag Technik Berlin, 1961, 
page 97, a hydro-pneumatic installation of a machine tool is known in 
which a hydraulic piston and a pneumatic piston are connected with each 
other. The cylinder of the hydraulic piston has a smaller diameter than 
that of the pneumatic cylinder in order to produce a greater force in the 
hydraulic cylinder. Such an installation functions as pressure amplifier. 
It is the object of the invention to provide a pressure-operated power 
wrench being capable of producing great forces with small structural 
dimensions and permitting a fast operation mode. 
In the power wrench according to the invention, the cross-sectional area of 
an additional cylinder, which acts as return unit, is essentially smaller 
than that of the working cylinder. Thereby, it is achieved that 
substantially less pressure fluid is necessary for the return stroke of 
the lever than for the working stroke, so that the return stroke takes 
only a very short period of time. It has to be considered that the feeding 
pipes, valves and the like leading to the power wrench form flow 
resistances limiting the flow rate of the pressure medium. 
Even in case of high pressures of several hundred bars, it takes a certain 
time until the required fluid amount enters the respective cylinder. The 
smaller the volume of this cylinder is, the shorter is the filling 
duration. Due to the required working force, the working piston must have 
a relatively large pressure area and thus also a relatively large cylinder 
diameter. The additional piston, however, which only has to produce the 
return force, has a smaller diameter, so that the additional cylinder also 
has a smaller diameter. Thereby, short periods of time for the return 
movement are possible. The cross sectional area of the additional cylinder 
is half of the cross-sectional area of the working cylinder at maximum, 
preferably one third of this cross-sectional area at maximum, and in 
particular a quarter of this cross sectional area at maximum. Thus, the 
return time can be reduced to at least a corresponding fraction of the 
advance stroke time. 
The pressurizations of the working cylinder and the additional cylinder are 
effected in an opposite direction with respect to each other. This means 
that when the working cylinder is pressurized, the additional cylinder 
becomes pressureless, and that when the working cylinder becomes 
pressureless, the additional cylinder is pressurized. 
The working cylinder and the additional cylinder, which both have 
substantially the same length, are preferably arranged in projections of 
the housing protruding symmetrically to both sides of the plane of 
symmetry of the headpiece. The plane of symmetry of the headpiece is the 
plane in which the pivotable lever takes its mid position. Thereby, the 
power wrench has a substantially T-shaped structure, with the headpiece 
forming the central member and the two cylinders forming the relatively 
short side members. Such a power wrench with small dimensions is also 
applicable at places with difficult access. 
The working piston and the additional piston form, together with a coupling 
member arranged between them, if necessary, preferably an altogether rigid 
member which is slidingly guided with both ends at the respective 
cylinder. Thus, a jam-free and secure guidance of the piston is permitted 
and wear and tear are reduced. 
The power wrench according to the invention is preferably a hydraulic power 
wrench. Basically, however, the principle can also be used with pneumatic 
pressure media.

In the drawing, a longitudinal section of the power wrench is schematically 
illustrated. 
The power wrench comprises an elongated housing 10. A headpiece 11 with two 
mounting members 12,13 is exchangeably mounted to the central region of 
the length of the housing. The entity of the housing 10 and the headpiece 
11 results in an about T-shaped form of the power wrench. 
The elongated housing 10 includes a channel 14 provided with different 
steps and extending over the entire length. In the one end of the channel 
14, a first bush 15 is inserted which is open at one end and comprises a 
bottom 16 at the other end which is directed to the outside. The interior 
of the bush 15 forms the working cylinder 17. 
A second bush 18 is arranged in the opposite end of the housing 10. This 
bush 18 comprises a bottom 19 at its end directed toward the housing 
interior and it is sealingly closed by a cover 20 at its outwardly 
directed end. The interior of the bush 18 forms the additional cylinder 
21. 
The channel 14 extending over the entire length of the housing 10 comprises 
several steps, so that its width reduces more and more in a step-like 
manner from the left end of the housing to the right end. From the left 
end, the bush 15 can be introduced into the housing 10 and it is screwed 
with a thread 22, so that it is non-displaceably fixed in the housing. 
Seals 23 seal the periphery of the bush 15 against the housing. The bush 
18, with its right end, abuts a step 24 of the channel 14 and it is 
secured against displacements from the opposite end by the cover 20 
screwed into the housing. 
The working piston 25 is displaceable within the working cylinder 17. The 
working piston 25 is rigidly connected with a piston rod 26 which 
comprises a coupling member 27. From the coupling member 27, a piston rod 
28 extends to the additional piston 29 displaceable within the additional 
cylinder 21. The pistons 25 and 29 form together with the piston rods 26 
and 28 as well as the coupling member 27 an altogether rigid member 60. 
The piston rod 28 extends through a sealed bore in the bottom 19 of the 
bush 18. The two pistons 25 and 29 are arranged along a common axis. The 
diameter of the working cyliner 17 and the working piston 25 is at least 
twice as much as the diameter of the additional piston 29 and the 
additional cylinder 21. The dimensions of the pressure attack areas of 
these two pistons are thus at least in a ratio 4:1. 
While the piston rod 26 of the working piston 25 leads out of the bush 15 
without being sealed, the passage of the piston rod 28 through the bottom 
19 of the bush 18 is sealed by a seal 30. Thereby, a counterpressure 
chamber 21a is created behind the additional piston 29 in the space 
surrounding the piston rod 28. 
About in the middle of its length, the housing 10 comprises two pressure 
connectors 33,34 facing away from the headpiece 11 and arranged one after 
the other in the drawing. The connector 33 is connected via bores 35,36 to 
the working cylinder 17 and also via bores 37 to the counterpressure 
chamber 21a of the additional cylinder 21. The connector 34 is connected 
via bores 38 and 39 to the pressure chamber of the additional cylinder 21. 
The two connectors 33 and 34 are alternately pressurized and made 
pressureless, one of the connections being pressurized and the other being 
made pressureless. 
About in the middle of its length, the housing 10 comprises a lateral 
passage opening 40 at the two sides of which the mounting members 12,13 
are arranged. The lever 41 of the headpiece 11 protrudes through this 
passage opening 40. The lever 41 is connected to a bearing ring 42 in 
which an annular member 43 is pivotably supported. The annular member 43 
comprises a polygonal through opening 44 which can be set on a screw head 
or serves for inserting a socket. The annular member 43 is provided with 
an outer toothing 45 in which a ratchet element of the bearing ring 42 
engages for taking along the annular member 43 only in the one rotational 
direction of the bearing ring 42. On its part, the bearing ring 42 is 
supported in the headpiece housing 50. The headpiece housing 50 is 
substantially U-shaped, the ends of the legs 50a and 50b extending between 
fork-shaped projections 51,52 of the housing 10 and being locked there 
with the two bolt shaped mounting members 12 and 13. These mounting 
members 12 and 13 can be drawn out to remove the headpiece 11 from the 
housing 10. The headpiece 11 contains the bearing ring 42 with the 
protruding lever 41 and the ratchet element 46 as well as the annular 
member 43. The headpiece 11 can be replaced by another headpiece having a 
differently shaped or dimensioned opening 44. 
The lever 41 protrudes out of a passage opening 55 between the two legs 50a 
and 50b of the headpiece housing 50. This lever comprises two bolts 56 
extending into two opposite directions and engaging with the coupling 
member 27. The coupling member 27 is hollow, so that the end of the lever 
41 can enter the coupling member 27. In the two opposing side walls 57 of 
the coupling member 27, slots 58 are provided into which the bolts 56 
enter when the headpiece 11 is set to the housing 10 and the lever 41 is 
guided through the passage opening 40 to engage the coupling member 27. 
The user of the power wrench can easily detach the headpiece 11 from the 
housing and exchange it, since the member 60 is not deformed or displaced 
when detaching the headpiece. 
When operating the power wrench, the connector 33 is pressurized, whereas 
the connector 34 is pressureless and connected to a tank. The pressure in 
the working cylinder 17 advances the working piston 25, the coupling 
member 27 taking along the lever 41 and rotating the bearing ring 42 with 
the annular member 43. The pressure prevailing in the working cylinder 17 
is supported by the pressure acting in the counterpressure chamber 21a of 
the additional cylinder 21 so that a force also acts upon the additional 
piston 29 which force acts in the same direction than that acting upon the 
working piston 25. During the working stroke, pressure medium is pressed 
out of the additional cylinder 21 through the bores 39 and 38. After the 
working stroke has finished, the reversal is effected, the connector 34 
being pressurized while the connector 33 is connected with the tank. 
Thereby, pressure enters the additional cylinder 21, whereby the 
additional piston 29 is driven to the right. Since the volume of the 
additional cylinder 21 is essentially smaller than that of the working 
cylinder 17, only a relatively small amount of hydraulic fluid is required 
to drive the entire member 60 consisting of the pistons 25,29, the piston 
rod 26,28 and the coupling member 27, into the retracting position. 
In order to prevent that the member 60 is deformed in case of a large load 
moment, the coupling member 27 is slidably supported at a guide path 61 of 
the housing 10. This guide path 61 is opposite to the passage opening 40 
of the housing 10. 
The bushes 15 and 19 wherein high pressure forces prevail and which serve 
for guiding the pistons are subject to high stresses. They can be easily 
exchanged. Preferably, these bushes are made of high-quality steel. The 
housing 10 can be made of a simpler material, for example of pressure 
diecasting or fiber-reinforced plastic. Due to the fact that the bushes 15 
and 18 are enclosed by the housing 10, a burst protection is achieved, as 
in case of tearing of one bush, this bush is held together by the housing.