Automatic Shut-Off Valve for Power Tools

This invention relates to power tools and more particularly to an improved fluid-actuated shut-off valve for a fluid-powered tool such as a wrench.

U.S. Pat. No. 4,243,111, issued Jan. 6, 1981, to R. A. Willoughby, et al, discloses a prior art fluid-actuated shut-off valve for a fluid-powered tool. The prior art tool works well for wide variations in inlet pressure. However, high pressure motive fluid is directly vented to the atmosphere during motor shutdown and stall. This is undesirable because the vented fluid strikes the tool operator. Also the motive fluid contains lubricant which is directly discharged into the work place. Finally it is economically desirable to conserve air pressure.

A principal object of this invention is to provide a novel fluid-actuated valve mechanism of the foregoing type which substantially eliminates or minimizes the undesirable venting of high pressure motive fluid to the atmosphere.

Other important objects of this invention are: to provide a fluid actuated shut-off valve responsive to the torque load on a tool without a restriction in the fluid inlet passage of the tool; and to provide a tool shut-off valve of a simplified and economical construction which incorporates means for regulating control pressure during operation and means for reliable shutoff without venting high pressure fluid to the atmosphere upon achieving stall torque.

In general, the foregoing objects are attained in a tool construction including a fluid motor, a fluid inlet passageway and a fluid exhaust passageway, a fluid-operated valve located in the inlet passageway and movable between alternate positions including an open position allowing motive fluid to flow to the motor and a closed position preventing motive fluid from flowing to the motor, spring means urging the valve to its open position, first valve-operating means subject to a regulated pressure and time rise rate of pressure and urging the valve to its closed position, second valve-operating means subject to pressure in the exhaust passageway and urging the valve to its open position with the spring means, the first and second valve-operating means being arranged so that the valve will move to its closed position in response to the drop in fluid pressure in the exhaust passageway when the motor slows down and stalls under a load, and means associated with the first valve-operating means for preventing high pressure motive fluid from venting to atmosphere during motor shutdown.

The invention is described in connection with the accompanying drawing wherein:

FIG. 1 is an elevational view with portions shown in section of a power tool containing the shut-off valve of this invention and showing the valve in its open position; and

FIG. 2 a fragmentary view of FIG. 1 showing the valve spool in elevation and in the closed position.

FIG.1 shows the rear portion of a power wrench casing 1. The casing 1 includes a hose fitting 2 at its rear end adapted to connect to an air hose (not shown) and opening into a supply or inlet passageway 4. The inlet passageway 4 contains a conventional lever-type throttle valve 5 operated by a throttle lever 6. The throttle valve 5 is urged shut by a spring 8.

The casing 1 contains a conventional vane-type rotary motor 10 including a rotor 11 mounted in a rear bearing 12 and rotating in a fixed cylinder 13. The rotor 11 also engages a rear end plate 14. The motor includes an inlet 15 connected to the inlet passageway 4 and an exhaust passageway 16.

A novel shut-off valve mechanism is mounted in the casing 1 in the inlet passageway 4 intermediate the throttle valve 5 and the motor 10. This valve mechanism includes a closed-end housing or sleeve 18 mounted in a corresponding opening provided in the casing 1 and extending across the inlet passageway 4. The valve sleeve 18 is locked in place in the casing 1 by conventional means. The sleeve 18 contains a cylindrical bore 20 slidably containing a spool valve 21 and having respective inlet and outlet ports 22 and 23 communicating with the passageway 4.

The spool valve 21 is shaped and arranged so that it opens the passageway 4 when in the down position as shown in FIG. 1 and blocks the passageway 4 when in the up position shown in FIG. 2. The bottom end 24 of the valve 21 contains a cavity which cooperates with the bottom end 25 of the valve sleeve 18 to form a chamber 26. A short passage 27 extends from the passageway 4 on the supply of the valve 21 to a port opening into the cylindrical bore 20 a short distance from the sleeve end 25 where it is covered by the spool valve 21 in its open position as shown in FIG. 1. A clearance is provided between the valve 21 and the cylindrical bore 20 sufficient for fluid pressure to flow into the chamber 26 from the inlet passageway 4 in a restricted manner. Fluid pressure in the chamber 26 urges the valve 21 towards its closed position, as shown in FIG. 2.

The sleeve end 25 is provided with two passageways leading to atmosphere. A pressure regulating device is installed in pressure regulating passageway 42. The pressure regulating means provided in the passageway consists of a ball regulator 43 which is held against a first regulator valve seat 44 by means of a spring 45. A second regulator valve seat 41 is positioned in passageway 42 downstream from seat 44. An adjustable end cap 46 is threadingly engaged in pressure regulating passageway 42 to bias spring 45 against ball 43. The adjustable end cap is provided with a vent hole 47 to allow the pressure fluid bypassing valve seat 44 to escape to atmosphere. Adjustable vent passageway 48 is also provided in the sleeve end 25, and flow through the connecting passageway 49 to vent hole 47 is controlled by means of a threaded meter valve 50.

It may be appreciated by one skilled in the art, therefore, that the pressure in chamber 26 may be controlled by the spring force setting on ball regulator 43. A higher pressure in chamber 26 may be obtained by rotating adjustable end cap 46 to further compress spring 45. A lower pressure in chamber 26 may be obtained by screwing adjustable end cap 46 out so as to relieve the spring force on ball regulator 43. In general, the function of the pressure regulating device is to control the pressure in chamber 26.

For the shut-off valve to function properly, it should be understood that the rate of rise of pressure in chamber 26 must be controlled. Manufacturing tolerances without greater expense do not allow for the degree of control of radial clearance between the spool valve 21 and its bore 20 to adequately control the rate of pressure rise over a wide range of inlet pressures. The adjustable vent passageway 48 has been provided in the present novel combination to accommodate the valve so as to control the pressure rate of rise in chamber 26. This is an especially important consideration in the prevention of premature shut-off which can occur during starting of the motor and until the time the motor has achieved running speed. If the pressure is allowed to build up in chamber 26 too rapidly, the balancing force in chamber 31 may be insufficient to prevent the spool valve 21 from shifting to its closed position. The pressure in chamber 31 is dependent on the exhaust pressure which is "0" at the start of the tool, but builds up quite rapidly as the tool accelerates.

The top end 29 of the valve 21 contains a cavity which cooperates with the casing 1 to form a chamber 31, and a spring 32 is disposed in the chamber 31 between the casing and the valve 21 to urge the valve 21 toward its open position. Exhaust passageway 16 interconnects the chamber 31 with the motor whereby exhaust fluid pressure from the motor urges the valve 21 toward its open position. Conduit 33 leads the exhaust from chamber 31 to a muffler 35 and eventually to atmosphere.

In describing the operation of the shut-off valve, we assume that, at the start, the throttle valve is closed, typical line pressure is available at the hose fitting 2, the shut-off valve 21 is in its open position as shown in FIG. 1 and the motor 10 is not operating.

The opening of the throttle valve 5 will allow air pressure to quickly start the motor 10. We will assume that the tool is a power wrench, such as an angle wrench, driving a nut as the motor starts. The pressure will rise in the exhaust passageway 16 and in the chamber 31 to urge the valve 21 toward the open position. Also, pressure will flow into the chamber 26 from the inlet passageway 4 through the clearance provided to urge the valve 21 toward its closed position. As previously explained, the function of the pressure regulating device and the adjustable vent serve to control the maximum pressure in chamber 26 and its rate of rise during motor operation. By controlling the maximum pressure achieved in chamber 26 by means of the ball regulator 43, wider ranges of inlet pressure may be tolerated by the shut-off valve mechanism. The exhaust pressure at shut-off is relatively unaffected by the inlet pressure for a normal air motor. By venting a portion of the air reaching chamber 26 through adjustable vent passage 48 and connecting passageway 49, it may be appreciated that the rate of rise of pressure may thereby be controlled. A slower rate of rise is achieved by venting a greater portion of the pressure fluid through meter valve 50. Utilizing the combination of the pressure regulation and chamber venting, it is possible to have a reliable shut-off over a wide range of inlet pressures. The problem of premature shut-off may be eliminated by this combination without undue tolerances control between the valve 21 and its bore 20. While the motor operates, the pressure in the inlet passagewy 4 is substantially less than supply pressure due to the motor 10 using a large volume of air. Also, the exhaust pressure in the exhaust passageway 16 is relatively high due to the flow of large air volumes through the motor 10.

As the nut driven by the wrench is tightened, the torque load on the motor rises and eventually the motor stalls. As the motor slows down, its consumption of air is reduced. The air pressure in the valve operating chamber 26 remains relatively constant due to the pressure regulator. However, as the air flow through the motor is reduced, the exhaust pressure in the valve-operating chamber 31 is reduced.

Eventually, the differential forces on the valve spool 21 are shifted to move the valve toward its closed position. As the valve 21 approaches its closed position, as shown in FIG. 2, it uncovers the short passage 27 to allow the air to flow freely from the inlet passageway 4 directly into the chamber 26. There is a rapid pressure rise in chamber 26 which kicks the valve 21 to its closed position. The pressure rise in chamber 26 also causes the regulator ball 43 to move outward against spring 45 to seal against the second regulator valve seat 41 and thereby seal both pressure regulating passageway 42 and vent passageway 48 from atmosphere. Thus high pressure motive fluid can not escape from chamber 26 through veht hole 47 after the motor stalls and the spool valve 21 closes.

The valve 21 will remain in its closed position as shown in FIG. 2, stopping the motor 10 so long as the throttle valve 5 remains open. Also high pressure fluid can not leak from vent hole 47 since regulator ball 43 will continue to seal second regulator valve seat 41 and thus passageways 42 and 48 as long as the throttle valve remains open.

When throttle lever 6 is released and throttle valve 5 is returned to its closed position, the pressure in the chamber 26 is reduced due to leakage past the motor. As the pressure in the chamber 26 falls, the force of the spring 45 overcomes the pressure in chamber 26 and moves the ball regulator 43 off the second valve seat 41. This further reduces the pressure in chamber 26 until the ball returns to the first valve seat 44. At the same time valve 21 is returned to its open position by its spring 32 where it is ready for another operating cycle.

This novel fluid-actuated valve eliminates the constant stream of high pressure motive fluid vented to the work place during motor shut down and stall in prior art tools. As a result, the tool operator is no longer struck by an uncomfortable blast of high pressure air. Also less lubricant is discharged into the workplace and line air pressure is conserved.

While only a single embodiment of the invention is illustrated and described in detail, this invention is not limited merely to this embodiment, but contemplates other embodiments and variations which utilize the concepts and teachings of this invention.