The invention relates to a power wrench of the impulse type which comprises a housing, a rotation motor with a stator and a rotor, an impulse unit with an output shaft, a power control unit connected to the motor, and a trigger means supported on the housing and connected to the power control unit and arranged to selectively deliver signals to

activate the power control unit.

The problem being solved by the invention is to provide an impulse wrench with a so called push start function by which the operation efficiency of the tool is substantially increased. Instead of having to manually operate one or more triggers at each tightening object to control the power supply to the motor, the invention makes it possible for the operator just to press the tool against a threaded fastener to start the motor. This will speed up the

assembly process in many applications.

The push start feature per se is well known in prior art and has been previously used in continuous torque

delivering power nutrunners and screw drivers. This feature means that the operator does not have to press a trigger to initiate power supply to the motor when starting a screw joint tightening process but could accomplish the same function just by pressing the wrench axially against the screw joint to be tightened. Thereby, the output shaft and associated parts are displaced axially in relation to the wrench housing and initiate power supply to the motor. It also means that when a tightening process is completed the power supply to the motor is shut off as the axial force on the wrench housing is discontinued and the output shaft and associated parts are allowed to return to their initial positions .

It is an object of the invention is to implement a push start feature on an impulse type power wrench to thereby facilitate handling of this type of power tools.

Further objects and advantages of the invention will appear from the following specification and claims.

A preferred embodiment of the invention is below described in detail with reference to the accompanying drawings.

In the drawings

Fig. 1 shows a longitudinal section through an impulse wrench according to the invention with the drive unit occupying its forward most position.

Fig. 2 shows the same view as Fig. 1 but with the drive unit in its rear position.

The impulse wrench illustrated in the drawings is a hand held tool comprising a housing 10 with a handle 11, an electric motor 12, a hydraulic pulse unit 13 with an output shaft 14. The motor 12 comprises a stator 17 with motor windings 16, and a rotor 18, wherein the stator 17 is surrounded by the rotor 18 and rigidly connected to the housing 10. The rotor 18 and the pulse unit 13 are

rotatively supported in the housing 10 by two bearings 20, 21 which are axially displaceable relative to the housing 10.

The rotor 18, the pulse unit 13 and the output shaft 14 are rigidly connected to each other and form together a rotary unit. Due to the axial movability of the two bearings 20, 21 the entire rotary unit is axially displaceable relative to the housing 10 between a forward rest position (Fig. 1) and a rear activated work position (Fig. 2) . A spring 23 is arranged between the rear bearing 21 and a shoulder 25 in the housing 10 to exert a forward directed bias force on the pulse unit 13 and thereby on the entire the rotary unit. Another weaker spring 26 is located between the forward bearing 20 and a shoulder 29 for accomplishing together with the spring 23 an axial bias force on the bearings 20, 21 to thereby eliminate axial play in the bearings. Both springs 23 and 26 comprise Belleville springs, i.e. a stack of two or more conical spring

washers .

At the rear part of the housing 10 there is mounted a sensor 28 which is arranged to indicate the axial position of the rotary unit by identifying the rear end portion of the rotor 12. The sensor 28 has the function of a trigger to initiate power supply to the motor 12 as the rotary unit is displaced to its rear active position. The sensor 28 is of the inductive type and reacts on the rotor 12 being displaced into a coinciding position. See Fig. 2. A CPU 27 is connected to the sensor 28 and arranged to initiate power supply to the motor 12 as a signal is received from the sensor 28. To that end the CPU 27 is connected to a drive unit 30 which communicates both with a power source and the motor windings 16. The latters are fed with a three phase voltage for energizing the motor 12. The CPU 27 and the drive unit 30 form together a power control unit 32. In operation of the wrench the drive unit initially

occupies its forward rest position due to the action of spring 23, (Fig. 1), wherein the rotor 12 is out of reach for the sensor 28. This means that no power supply

initiating signal is sent to the CPU 27 and that the motor 12 will remain inactive. When the wrench is put to work on a threaded fastener to be tightened the operator applies an axial push force on the housing handle 11 which, whereby a reaction force from the fastener on the output shaft 14 will dominate the bias force of the spring 23 and result in a rearward displacement not only of the output shaft 14 but of the entire rotary unit relative to the housing 10. This means that the motor rotor 18 will be moved into a sensor 28 activation position, (Fig. 2), and that a power supply signal is sent from the sensor 28 to the CPU 27 to activate the drive unit 30 to deliver power to the motor 12. Now, the motor 12 starts delivering a torque to the fastener via the pulse unit 13 and the output shaft 14. This will continue until a set target torque level is reached in the fastener, whereat the CPU 27 will initiate discontinuation of the power supply from the drive unit 30 to the motor 12. As the tightening process is completed the operator lifts the wrench off the fastener which means that the axial force on the housing 10 is discontinued and that the spring 23 will be able to return the rotary unit 24 to the forward inactive position, (Fig. 1), wherein the rotor 18 no longer can activate the sensor 28. This results in a

discontinuation of the power supply signal to the CPU 27 and a power shut-off to the motor 12 is accomplished. A push started power wrench operation is completed. In the drawings there is indicated an alternative location of the sensor 28, namely in the front part of the housing 10 close to the pulse unit 13, such that axial

displacements of the latter including the output shaft 14 will make the sensor 28 generate power control signals to the CPU 27.

It is to be noted that the invention also includes

embodiments other than the one described above. One such alternative embodiment comprises an arrangement of the rotary parts wherein the pulse unit 13 including the output shaft 14 is axially displaceable whereas the motor rotor 18 is not. This is due to a splines connection arranged between the motor rotor 18 and the pulse unit 13. This means that the rotary unit is divided into two parts, whereof one is axially displaceable and the other is not. In this case the displacement sensor 28 is located in the front part of the housing 10, as described above, so as to be activated by the pulse unit 13 at axial displacements of the latter and the output shaft 14.

Although not illustrated in the drawings the power source to be used for energizing the power wrench may be a mains connection or a battery as preferred or suitable for the actual wrench design.