A torque wrench having a shaft with a tool head at one end a handle at the other end. The handle is supported on a lever system having a first and a second two-armed lever. One arm of the first lever engages one arm of the second lever. The handle is supported at two points on the other arm of the first lever and the other arm of the second lever. The other arm of the first lever engages a force sensor, which is attached to the shaft. The levers are dimensioned such that the measuring force acting upon the force sensor, when an applied force acts on the handle, is independent of the point of application of the applied force and is always proportional to the torque exerted about the axis of rotation of a tool.

The invention relates to a one-armed torque wrench, comprising 
(a) a shaft, which at one end has a tool head for a tool, 
(b) a force sensor at the other end of the shaft, and 
(c) a handle, which is mounted at the other end of the shaft at two points 
on a lever system having two levers mounted pivotably on the shaft, which 
lever system is arranged to exert a force on the force sensor, which force 
is only dependent of the torque exerted about the point of rotation of the 
tool, but not of the point of attack at the handle. 
A bolt or another threaded element shall be tightened with a predetermined 
torque by means of a torque wrench. This ensures, on one hand, that the 
screw is sufficiently tightened in a well-defined way. On the other hand 
it prevents the thread from ripping off as a result of too strong 
tightening of the bolt. 
With prior art torque wrenches measurement of the exerted torque is 
effected by means of the most different measuring systems. 
In on known torque wrench for example a bending bar serves as torque 
sensor, on which the handle is provided through which the torque is 
transmitted to a tool engaging the screw. The bending bar is deflected as 
a function of the transmitted torque. A mark is provided on a housing 
portion, which is not loaded by the torque transmission and which extends 
along the bending bar. When the bending bar is deflected, this mark moves 
over a dial provided on the bending bar. The applied torque can be read 
from this dial. 
Other torque wrenches based on a similar principle are known, with which a 
signal is given for example in form of a noticeable jerk or a click when a 
certain preset torque is attained (catalogue D 89 of Eduard Wille GmbH & 
Co., 5600 Wuppertal-Cronenberg). 
In the prior art torque wrenches an auxiliary torque is indicative of the 
torque exerted about the axis of rotation of the bolt, which auxiliary 
torque is effective about an axis outside this axis of rotation. Thus the 
torque indication or rather the torque, at which the signal is given, 
depends on the point, at which the user engages the torque wrench. 
FR-A-2,242,202 discloses a torque wrench of the above defined type, which 
avoids these problems. In this prior art torque wrench a projection is 
provided on the shaft at its end remote from the tool head, which 
projection extends into the tubular handle. An elongated movable element 
is arranged parallel to this projection in the handle and engages the 
inner wall of the handle through rollers. The movable element is connected 
to the projection through two links of different lengths, which 
accordingly form different angles with the longitudinal direction of the 
projection. An adjustable compression spring extends between the 
projection and the movable element and urges the movable element in the 
direction toward the shaft, the handle, being kept in engagement with a 
stop means on the projection through the links and the rollers. The links 
are two levers which are mounted pivotably on the shaft and form a lever 
system together with the elongated movable element. The handle is mounted 
on this lever system at two points, namely on the two rollers. In the 
prior art torque wrench the links or levers together with the compression 
spring form a toggle lever mechanism. At a certain torque the toggle lever 
mechanism yields, overcoming the bias of the spring. The elongated element 
engages the projection. The user feels this at a corresponding yielding of 
the handle, which, in turn, is supported on this element through the 
rollers. By appropriate choice of the angle between the links and the 
longitudinal direction of the projection, it is possible to make this snap 
point of the toggle lever mechanism independent of the point, at which the 
force is applied to the handle and a well-defined torque is exerted about 
the axis of rotation of the tool. In this prior art torque wrench the 
toggle lever mechanism serving as dynamometer and the lever transmission 
for compensation of the lengths of the lever arms are integrated. Levers 
or links are arranged, which extend at an angle relative to the 
longitudinal direction of the shaft. The angles between these links and 
the longitudinal direction of the shaft have to be chosen in a certain 
well-defined way to compensate for the lengths of the lever arms. 
Therefore relatively long levers are required. Thus the toggle lever 
mechanism and thus the handle enclosing the toogle lever mechanism become 
quite unwieldy. 
DE-A-3,139,374 discloses a mechanical torque wrench, with which likewise an 
indication is obtained independent of the point of engagement. In one 
embodiment of DE-A-3,139,374 the deflection of the shaft at a mechanically 
weakened first point is converted into a stroke through a first lever 
arranged on the shaft on the tool side of this point. The stroke is 
measured by means of a dial gauge, which is arranged on the shaft and 
engages the first lever. A second mechanically weakened point of the shaft 
is provided in order to eliminate the dependency on the point of 
engagement, which results from the distance between said first point and 
the point of rotation of the tool. On the handle side of this second point 
a second lever carrying the dial gauge is attached to the shaft. When a 
torque is exerted on the torque wrench, the shaft is slightly bent also at 
the second point and causes a pivotal movement of the second lever with 
the dial gauge. Appropriate selection of the lengths of the lever arms 
permits the indication of the dial gauge to be indicative of the torque 
exerted about the point of rotation of the tool. In another embodiment of 
DE-A-3,139,374 based on a similar principle, a toggle lever mechanism is 
provided instead of a dial gauge, which toggle lever mechanism snaps at a 
snap point unambiguously depending on the exerted torque. 
In this torque wrench the measuring elements and the levers for 
compensation for the lengths of the lever arms are located on the shaft, 
whereby handling of the torque wrench is made more difficult. 
It is the object of the invention to obtain a simple and compact 
construction of the toggle lever mechanism in a tension wrench of the 
above defined type, with which a force sensor and a lever mechanism for 
the above described compensation of the lever arm ratios are arranged in a 
handle, such that this toggle lever mechanism can be placed in a slender 
handy handle. 
According to the invention this object is achieved in that 
(d) the two levers of the lever system are two-armed levers, engaging each 
other with a first arm each, 
(e) the handle is supported at its ends on the second arm of the two 
levers, and 
(f) the force sensor responds to the force exerted between the second arm 
of a lever and the shaft. 
The lever system consists of two levers, which extend in the longitudinal 
direction of the shaft, such that the lever system is simple and 
elongated. Thus it can by placed in a slender handle in a space-saving 
way. The proportion of the lengths of the lever arms of the lever system 
for obtaining a measurement independent of the point of engagement can be 
provided reproducibly and with high precision. The function of the lever 
system is completely separated from the function of the force sensor, such 
that any type of force sensor can be used. 
Further modifications of the invention are subject matter of the sub-claims 
.

The torque wrench according to FIG. 1 comprises a shaft 10, which has a 
tool head 12 at one end. The tool head 12 has a square 14, on which a 
socket wrench insert can be placed. A handle 16 is located at the other 
end of the shaft 10. A torque sensor is formed by a force sensor 18 
arranged between the handle 16 and the shaft 10. In the embodiment of FIG. 
1, the force sensor 18 consists of a bending body 20, which is inserted 
into an end face of the shaft 10, and of a dial gauge 22 held in the shaft 
10 and engaging the bending body 20. The force exerted on the torque 
wrench by the user is transmitted from the handle 16 through an edge 24 in 
a way to be described hereinbelow. The force-proportional deflection of 
the bending body 20 is measured by the dial gauge 22 and indicated as a 
measure of the force and thus of the exerted torque. 
The force exerted on the shaft 10 through the handle 16 for providing a 
torque is applied to the force sensor 18 through a lever system 26, such 
that the force acting on the force sensor 18 is proportional to the 
exerted torque independently of the point of attack of the force exerted 
on the handle 16. For this purpose an arm 28 is provided on the shaft 10, 
which arm 28 extends into the interior of the hollow handle. The arm 28 
carries spaced from each other a joint 30 and an edge 32, which defines 
the pivot axes 34 and 36, respectively, for a first two-armed lever 38 and 
for a second two-armed lever 40. Thus the two levers 38 and 40 are mounted 
on the shaft 10 in the area of the handle 16. The two levers 38 and 40 
engage each other with a first arm each 42 and 44, respectively, through 
an edge 46 provided on the lever 40. In fact the arm 44 engages, with its 
edge 46, the arm 42 of the lever 38 from below in FIG. 1. The handle 16 is 
supported at its two ends on the second arms 48 and 50, respectively, from 
above in FIG. 1. This is done through edges 52 and 54, respectively, in 
the schematically illustrated embodiment of FIG. 1. The force sensor 18 
responds to the force exerted between the second arm 48 of the lever 38 
and the shaft 10. For this purpose the edge 24 of the bending body 20 
engages the arm 48 of the lever 38 on the bottom side in FIG. 1. The 
handle 16 engages, with its edge 52, the arm 48 of the lever 38 on the 
opposite side, that is the upper side in FIG. 1, which edge 52 is aligned 
with the edge 24. The first arm 48 of the first lever 38 has the same 
length H3 of the lever arm between a point of support of the handle 16 on 
the first lever 38 defined by the edge 52 and the pivot axis 34 defined by 
the joint 30 as the lever arm between the pivot axis 34 and the point of 
engagement of the second lever 40 defined by the edge 46. The length H1 of 
the lever arm of the arm 50 of the second lever 40 between the point of 
support of the handle 16 on the second lever 40 defined by the edge 54 and 
the pivot axis 36 of the second lever 40 defined by the edge 32 has the 
same proportion relative to the length H2 of the lever arm of the first 
arm 44 of the second lever 40 between the pivot axis 36 and the point of 
engagement of the first lever 38 defined by the edge 46 as the distance 
LH+LG of the point of suport of the handle 16 on the second lever 40 from 
the point of rotation 56 of the torque wrench to the distance LH of the 
point of support of the handle 16 on the first lever 38. 
The described arrangement operates as follows: 
An actuating force P.sub.B acts on the handle 16 at the distance LH+LB 
(FIG. 1) from the point of rotation 56. The point of attack of the 
actuating force P.sub.B can be anywhere along the length LG of the handle 
16. LH designates the length of the shaft 10 measured from the point of 
rotation 56 to the point of support of the handle 16 on the lever 38. The 
tightening torque is therefore 
EQU M=P.sub.B (LH+LB) (1) 
This tightening torque is to be measured. The measuring force P.sub.M 
acting on the force sensor 18 is composed of two components, namely a 
first component, which is transmitted directly from the handle 16 to the 
bending body 20 through the edge 52. This component is 
##EQU1## 
The second component is effective through the edge 54 of the handle 16 and 
the lever system 26. The edge 54 transmits to the second lever 40 a force 
##EQU2## 
This force seeks to rotate the lever 40 clockwise. The arm 44 of the lever 
40 transmits a force directed upwards to the arm 42 of the lever 38 
through the edge 46, which force is 
##EQU3## 
due to the different lengths H1 and H2 of the lever arms. The lever 38 
having equal lengths H3 of the lever arms only serves to reverse the force 
direction. It exerts with the arm 48 an additional force directed 
downwards on the force sensor 18, which force has the above mentioned 
amount. Thus a force 
##EQU4## 
acts on the force sensor 18. 
As mentioned above, H1 and H2 are selected such that 
##EQU5## 
Introducing this relation into equation (2), yields 
EQU M=P.sub.M .multidot.LH=P.sub.B (LH+LB). (4) 
Thus the measuring force P.sub.M with the constant and known coefficient of 
proportionality LH is always proportional to the tightening torque, 
regardless of the point (or the distance LB), at which the user exerts a 
force on the handle 16. Thus the tightening torque M is always measured 
without systematic errors. The shaft 10 can be a simple rigid element, 
whereby the torque wrench can be made more slender and lighter. 
FIG. 2 shows a constructional embodiment of a torque wrench. 
A shaft 60 carries, at one end, a tool head 62 similar to the tool head 12 
in FIG. 1 and, at the other end a handle 64. For application of the torque 
a force is exerted on the handle 64 from above in FIG. 2. The shaft 60 has 
a projection 66 extending into the handle 64, which projection 66 
corresponds to the arm 28 of FIG. 1 with regard to its function. Bearing 
pins 68 and 70 are located in the projection 66, which bearing pins 
correspond to the joint 30 and the edge 32, respectively, of FIG. 1. Two 
armed levers 72 and 74, respectively, are mounted on the bearing pins 68 
and 70. the two levers 72 and 74 engage each other with stop faces at 76. 
A pin 78 is located in the handle 64 and engages a stop face at the outer 
end of the lever 74. The pin 78 corresponds to the edge 54 of FIG. 1 with 
regard to its function. A further pin 80 corresponding to the edge 52 of 
FIG. 1 is provided on the handle 64. This pin 80 extends with sufficient 
clearance through an aperture 82 in the projection 66. Furthermore the 
handle 64 is pivotably mounted with the pin 80 at the end of the lever 72. 
Furthermore a tilting body 84 having a lug 86 is mounted on the pin 80. 
The lug is supported with a plane surface on a L-shaped recess of a slide 
88, which is longitudinally movably guided in the projection 66. The slide 
88 is exposed to the action of a biased spring 90, which is supported on 
an abutment 92 and which urges the slide 88 towards the left in FIG. 2. 
This abutment 92 is straightly guided by a guide 94 and guided as a nut on 
a threaded spindle 96. The threaded spindle 96 is adjustable through an 
aperture 98 in the handle 64 by means of a screw driver. Thereby the 
abutment 92 can be displaced in longitudinal direction and the bias of the 
spring 90 can be varied. The guide 94 is provided with a graduation 100, 
along which an indicator connected to the abutment 92 is movable. 
The described arrangement operates as follows: 
Because of the levers 72 and 74, the lengths of the lever arms of which 
correspond to those in FIG. 1, the measuring force P.sub.M acting on the 
pin 80 downwards in FIG. 2 is proportional, as in the embodiment of FIG. 
1, to the exerted tightening torque independently of the point, at which 
the user engages the handle 64. The tilting body 84 in combination with 
the spring-loaded slide 88 serves as "force sensor" 102. In the state of 
rest the tilting body 84 is kept in the illustrated position by the spring 
90. When the measuring force P.sub.M exceeds a predetermined value, the 
force component effective in the longitudinal direction overcomes the bias 
of the spring 90 just like in a toggle lever. The slide 88 snaps to the 
right in FIG. 2, the pin 80 moves downwards and the tilting body 84 is 
pivoted counterclockwise. Due to the lever arrangement also the pin 78 
moves downwards at the same time as the pin 80. Thereby the handle 64 
makes a sudden movement clearly perceptible to the user, which movement 
suddenly stops when the upper inner surface of the handle abuts against 
the top edge of the projection 66. Thereby the tilting body 84 is pivoted 
so far, that the effective force component does not quite reach the 
dead-center position of the toggle lever and therefore all the movable 
elements automatically return to their initial positions after the handle 
has been released. The sudden movement of the handle in combination with 
the impact sound gives a signal, which indicates that a certain tightening 
torque is attained. The magnitude of the torque, at which the signal is 
given, is adjustable by means of the adjusting spindle 96 with the aid of 
the graduation 100.