US3869941A

US3869941A - Torque wrench

Info

Publication number: US3869941A
Application number: US472369A
Authority: US
Inventors: Hiroshi Tsuji
Original assignee: Tohnichi Mfg Co Ltd
Current assignee: Tohnichi Mfg Co Ltd
Priority date: 1973-08-29
Filing date: 1974-05-22
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11
Also published as: JPS5136520B2; FR2242202B1; FR2242202A1; SE416277B; JPS5045397A; DE2441064A1; GB1446379A; DE2441064B2; SE7409077L

Abstract

Preset type torque wrench capable of tightening a screw at a predetermined torque set therein. The wrench has a head rod secured to the torque applying head and a slide rod arranged in parallel to the head rod. A pair of toggle links are provided adjacent to the opposite ends of the slide rod and each pivotally connected to the head rod and the slide rod. A compression spring is interposed between the head rod and the slide rod so as to urge the head rod and the slide rod in the opposite directions lengthwise thereof.

Description

United States Patent [191 Tsu'i [111 3,869,941 Mar. 11,1975

TORQUE WRENCH [75] Inventor: Hiroshi Tsuji, Tokyo, Japan [73] Assignee: Tonichi Manufacturing Co., Ltd.,

Tokyo, Japan [22] Filed: May 22, 1974 [21] Appl. No.: 472,369

[30] Foreign Application Priority Data Aug. 29, 1973 Japan 48-97029 [52] US. Cl. 81/52.5 [51] Int. Cl. B25b [58] Field of Search 8l/52.4 R, 52.5

[56] References Cited UNITED STATES PATENTS 2,268,081 12/1941 Pagnard 8l/52.5

Primary Examiner-James L. Jones, Jr. Attorney, Agent, or Firm-Totem, McGeady and Stanger [57] ABSTRACT Preset type torque wrench capable of tightening a screw at a predetermined torque set therein. The wrench has a head rod secured to the torque applying head and a slide rod arranged in parallel to the head rod. A pair of toggle links are provided adjacent to the opposite ends of the slide rod and each pivotally connected to the head rod and the slide rod. A compression spring is interposed between the head rod and the slide rod so as to urge the head rod and the slide rod in the opposite directions lengthwise thereof.

3 Claims, 6 Drawing Figures Keen 81/524 R minimum I ma 3. 869,941

SHEET 1 95 2 F/G.2 F/G.3

BACKGROUND OF THE INVENTION The present invention relates to improvements in a preset type torque wrench capable of tightening a screw at a predetermined torque manually or by a driving motor.

A preset type torque wrench as described above is provided therein a mechanism generating a sound or a tactile impression when the tightening reaches a predetermined torque so that the operator is aware of the completion oftightening by the sound or the tactile impression. Various types have been utilized for this mechanism. One of the most conventional types of this mechanism is that in which a toggle link mechanism is used.

However, in the prior art torque wrench using the toggle link mechanism has a disadvantage in that the actual torque for tightening the screw varies from the set torque when the point at which the force is applied to the torque wrench varies. In effect, it is difficult to maintain the point at which the force is applied to the wrench at a fixed position, thereby rendering the accuracy in the torque for tightening the screw to be deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a preset type torque wrench using a toggle link mechanism in which the actual torque for tightening the screw is kept constant regardless of the fact that the point at which the force is applied to the torque wrench varies.

The other object is to provide a preset type torque wrench of the type described above in which the mechanism for presetting the torque is arranged within the handle of the torque wrench to which the force is applied.

The above objects are achieved in accordance with the present invention by the provision of a torque wrench having a head rod secured to the torque applying head of the wrench, a slide rod arranged in parallel to the head rod, a pair of toggle links arranged adjacent to the opposite ends of the slide rod and each pivotally connected to the head rod and the slide rod, and a spring interposed between the head rod and the slide rod so as to urge the head rod and the slide rod in the opposite directions lengthwise thereof.

In accordance with a further feature of the present invention, the length of one of the toggle links is made different from that of the other toggle link while the toggle setting angle between one of the toggle links and the head rod is made correspondingly different from that between the other toggle link and the head rod.

By the above arrangement, the actual torque of the torque wrench for tightening the screw is made constant regardless of the position at which the force is applied to the torque wrench.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view, partly in cross-section, showing the internal construction of an example of the prior art torque wrench;

FIGS. 2 and 3 are side views showing the general configurations of some examples of the prior art torque wrench;

FIG, 4 is a fragmentary sectional view, with the torque applying head being omitted, showing the main portions of an embodiment of the torque wrench constructed in accordance with the present invention;

FIG. 5 is a fragmentary sectional view similar to FIG. 4 but showing the manner of operation of the torque wrench shown in FIG. 4; and

FIG. 6 is a schematic diagram showing the relationship between various components of the forces applied to the torque wrench shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Prior to the description of the present invention, a brief description of the prior art torque wrench is given below with reference to FIGS. 1 to 3.

In FIG. 1, the torque applying head 1 of the torque wrench is pivotally supported by a head pin 3 to the tube 2 serving as the handle of the torque wrench. The inner end of the head 1 is pivotally connected to one end of the toggle line 5, the opposite end of which is pivotally connected to one end of the slide rod 6 having a roller adapted to slidably contact with the inner wall of the tube 2.

The opposite end of the slide rod 6 is attached to a member slidable in the tube 2 and contacting with one end of a compression spring 4 housed in the tube with the opposite end secured by an adjustable member adjustably secured to the tube 2 so as to urge the slide rod 6 toward the head 1 with a force F.

As shown, the toggle link 5 is positioned at an angle a with respect to the vertical line, so that the roller of the slide rod 6 is slidably urged against theinner wall of the tube 2 by the force F.

When a force P applied to the tube 2 at a position remote from the'head l is increased, a torque T applied to a screw engaging with the head 1 increases, and, when the torque T reaches a limit, the head 1 is swung anticlockwise relative to the tube 2 so that the toggle link 5 is actuated so as to urge the slide rod 6 apart from the head 1 against the force F applied by the spring 4, thereby giving indication that the torque T reaches the predetermined value set by the force F of the spring 4.

Assuming that the distance between the center of the screw to which the torque T is to be applied and the head pin 3 is lh and the distance between the head pin 3 and the pivot point of the toggle link 5 to the slide rod 6 is r, while the distance between the center of the screw and the point at which the force P is applied is l, the torque T is expressed by the following equations:

T= P lh r.F.cot 01 plied, i.e., the value I, varies, thereby making it difficult to maintain the torque to be applied to the screw at a desired constant value exactly, because it is difficult in the actual practice to keep the value of l constant.

Although it is possible to lessen the influence by the portion lto which the force P is given by shortening the length lh from the center of the bolt to the head pin, the length lh will be considerably large in case when the top end of the head is bent as shown in FIG. 2, or in case when the head portion includes a power device as shown in FIG. 3, so that only small change of the portion I to which the force is given will cause a large change of the working torque T.

The present invention avoids the above described disadvantage of the prior art torque wrench and provides a torque wrench in which the torque to be applied to the screw is always kept accurately at a desired predetermined value regardless of the point at which the force is applied to the torque wrench and the torque limiting mechanism is housed in the handle of the torque wrench to which the force is applied.

Referring now to FIGS. 4 6 showing the preferred embodiment of the torque wrench of the present invention, a head member 10 for applying a torque to a screw is fixedly secured to a head rod 11. A slide rod 12 is arranged in parallel to the head rod 11 as shown.

A pair of

toggle links

13, 14 are provided adjacent to the opposite ends of the slide rod 12 and each pivotally connected at its opposite ends to the head rod 11 and slide rod 12, respectively, the links l3, 14 being oriented obliquely with respect to the length of the head rod 11 as shown.

A compression spring 15 is interposed between the head rod 11 and the slide rod 12 with its one end secured to a portion of the slide rod 12 adjacent to the pivot point of the link 13 while the other end of the spring 15 is held by a member, which is mounted on an adjusting screw threadedly engaged with a portion of the head rod 11 adjacent to the pivot point of the link 14, so that the compressive force of the spring 15 is made adjustable by rotating the adjusting screw 20.

A stopper 16 is secured to the head rod 11 as shown, while rollers 19 are provided adjacent to the opposite ends of the slide rod 12.

A tube-like cover 17 is swingably connected to a portion of the head rod 11 exterior of the cover 17 through a connecting link 18 as shown, and the remaining portion of the head rod 11, the slide rod 12 and the spring 15 as well as'the

links

13, 14 are housed in the cover 17. Thus, the stopper 16 of the head rod 11 abuts against the inner wall of the cover 17 at one side thereof while the rollers 19 are urged to slidably contact with the inner wall of the cover 17 at its opposite side along the generating line of the inner wall of the cover 17 by virtue of the action of the spring 15 and the oblique orientation of the

links

13, 14.

Considering the actuation of the torque wrench described above, when a force P is applied to a point on the cover 17, the head rod 11 is moved relative to the cover 17 against the action of spring 15 in the direction opposite to the direction in which the force P is applied. Thus, the slide rod 12 swingably connected to the head rod 11 through the

toggle links

13, 14 is moved along the inner wall of the cover 17 to the right in FIG. 5 relative to the head rod 11 so that the head rod 11 abuts against the slide rod 12 as shown in FIG. 5, thereby giving indication that a predetermined value of the torque is reached.

In other words, the force P is applied to the slide rod 12 during the operation and, when the torque T reaches a predetermined value, the

toggle links

13, 14 are actuated so as to engage the head rod 11 with the slide rod 12 against the force F of the spring 15 the value of which is adjustable.

It is now assumed that:

P, Vertical component of the force applied to the toggle link 13.

P Vertical component of the force applied to the toggle link 14.

F, Horizontal reaction force of the toggle link 13.

F Horizontal reaction force of the toggle link 14.

L Distance between the center of the screw to be tightened and the pivot point of the toggle link 13 to the slide rod 12.

l= Distance between the pivot point of the toggle link 13 to the slide rod 12 and the pivot point of the toggle link 14 to the slide rod 12.

l, Distance between the pivot point of the toggle link 13 to the slide rod 12 and the point at which the force P is applied.

1 Distance between the point at which the force P is applied and the pivot point of the toggle link 14 to the slide rod 12.

a, Angle formed between the toggle link 13 and the longitudinal axis of the head rod 11.

a Angle formed between the toggle link 14 and extension of the longitudinal axis of the head rod 11. Then, the torque T is expressed as follows:

T= P-(L 1,)

P, P-l /l P P-l,/l

F, P, cot a,

F2 P2 a F F, F PH (1 cot a, +1, cot a From equation (4) l(L+l,)F

l cot a +l cot 12 cot a Cot 01 Then, the equation (10) is rewritten as follows:

T L-F/cot 01,

Therefore, it is apparent that, when the angles a 01 are selected to satisfy the equation (1 l then the torque T applied to the screw will not vary even though the position at which the force P is applied, i.e., the values l l varies.

Further, as seen from FIGS. 4 and 5, when the lengths of the toggle links 13, 14 are selected to be different from each other, the angle or is generally greater than the angle :1 with the length a of the toggle lever 13 being smaller than the length a of the toggle link 14, and the head rod 11 is moved substantially in the translational movement parallel to the slide rod 12 (FIG. 5), thereby affording convenient tactile impression while the spring is conveniently arranged between the

rods

11, 12.

Referring to FIG. 6, deviation in the torque T might occur, when the force P is applied obliquely as the force P with an angle 0 formed between the perpendicular to the cover 17 and the direction of the force P, because a horizontal component P-sin 6 of the force P directly affects the force F of the spring 15.

In order to avoid the above error, the slide rod 12 is provided with rollers 19 freely slidable along the inner wall of the cover 17. Thus, when the force P is applied to the cover 17, the head rod 11 is moved to urge the slide rod 12 along the inner wall of the cover 17 by the free rolling of the rollers 19 of the slide rod 12 thereby permitting only the vertical component of the force P to be transmitted to the torque wrench even though the force P is applied in the direction obliquely of the perpendicular to the cover 17 without causing any deviation in the torque T.

As described above, the position at which the force is applied to the torque wrench for tightening the screw can be selected at any position in the wide range of the handle cover without causing any errors in the torque to be applied to the screw, thereby permitting accurate tightening effect to the obtained.

1 claim:

1. Preset type torque wrench having a toggle mechanism therein, wherein the improvement comprises a head rod secured to the torque applying head of said wrench, a slide rod arranged in parallel to said head rod, two pairs of toggle links arranged in spaced relationship from each other lengthwise of said head rod and said slide rod adjacent to the opposite ends of said slide rod and each pivotally connected to said head rod and said slide rod, and a spring interposed between said head rod and said slide rod and connected thereto.

2. Torque wrench according to claim 1, wherein the length of one of said toggle links forming said pair is set to be different from that of the other of said toggle links while the toggle setting angle formed between said one of said toggle links and said head rod as well as said slide rod is set to be correspondingly different from that formed between said other of said toggle links and said head rod as well as said slide rod.

3. Torque wrench according to claim 1, wherein said slide rod is arranged within a tubular handle slidably along the generating line of said handle.