TECHNICAL FIELD OF THE INVENTION

The present invention relates to a rotation unit for drilling comprising a motor, reduction gear and an output shaft arranged in sequence with a common center axis in a cylindrical housing dimensioned for insertion into the borehole.

BACKGROUND AND PRIOR ART

More particularly, the invention relates to a rotation unit for drilling adapted to the type of open hydraulic system which utilizes water, or other environmentally friendly liquid, both as a driving liquid and as a flushing medium for transporting drilling dust out of the borehole. A rotation unit according to the invention can, for example, be utilized in connection with drilling or percussion drilling in soil and rock.

It is a known problem of water powered systems that the lack of lubricant typically has to be compensated for by greater play between contact surfaces in motion, which in turn usually results in leakage and an associated reduced efficiency.

SUMMARY OF THE INVENTION

The object of the present invention is to design a rotation unit for drilling powered by water or other environmentally friendly liquid in such a way that it delivers both low leakage and high efficiency.

The object is achieved by a rotation unit of the kind mentioned in the introduction, wherein the motor is a liquid-driven gear motor comprising a central wheel and one or more planetary wheels which are in displacing gear engagement with the central wheel, and wherein the central wheel of the motor is non-rotatably connected via a shaft portion to the sun wheel of a planetary gear connected in sequence, whose planetary carrier is in rotationally transmitting engagement, directly or indirectly, with the output shaft. The central wheel and planetary wheels of the motor are rotatably mounted, partly in an upstream motor compartment end wall and partly in a downstream motor compartment end wall seen in the flow direction of the liquid. The upstream located motor compartment end wall comprises inlets for driving liquid for each of the planetary wheels of the motor and the downstream located motor compartment end wall comprises driving liquid outlets for each of the planetary wheels of the motor. The outlets mouth to an annular cavity which is open towards said shaft portion, wherein an inlet for driving liquid is arranged to mouth in the outside of said shaft portion to extend therefrom in radial direction into a centrally located drainage channel running axially from the shaft portion through the sun wheel and the output shaft.

A technical effect and advantage provided by the proposed combination of gear motor and planetary gear is that the speed of the output shaft can be significantly reduced despite the minimum axial length of the assembly.

As an example of this, an embodiment of the rotation unit may comprise a gear motor in which the speed ratio between the planetary wheel and central wheel is 2.5:1 , or in other words in which the central wheel has 2.5 times the number of teeth of the planetary wheel. This ratio can result in a downshift from a speed of the planetary wheels of 4000 rpm to 1600 rpm of the central wheel, e.g. If in the planetary gear connected in sequence, the sun wheel and planets have a mutually equal number of teeth a speed ratio of 4:1 is obtained. The speed of the output shaft in this embodiment is thus reduced to 400 rpm.

It should be added that by connecting a second planetary gear in series with the first one, the speed of the output shaft can be correspondingly reduced to 100 rpm, e.g.

Another technical effect and advantage provided by the proposed combination is that the assembly can be accommodated in an enclosing cylindrical housing of reduced axial length. A contributing factor to the short length of the assembly is the design of the gear motor in which the central wheel is driven by planetary wheels of significantly smaller radius, and which can therefore be distributed around the central wheel in a compact unit of minimized length with a maintained efficient and working gear engagement, and with an efficiency corresponding to the efficiency of a much longer, conventionally designed gear motor.

A drain for driving liquid is arranged to mouth in the outside of said shaft portion, to lead from there into a centrally located outlet channel which runs axially from the shaft portion, through the sun wheel and the output shaft. The shaft portion between the central wheel of the gear motor and the sun wheel of the planetary gear connected in sequence therefore acts as a swivel which brings together the drive flows of the gear motor and introduces the waste water into the central outlet channel.

Through the above-mentioned annular cavity, the outlet mouth of the shaft portion is in constant communication with the driving liquid so that an uninterrupted flow can be maintained through the central outlet channel.

In one embodiment, the reduction gear has two or more planetary gears arranged in tandem in such a way that the planetary carrier of a forward planetary gear is non-rotatably connected to the sun wheel of a rear planetary gear, and wherein said drainage channel runs through all planetary carriers and sun wheels to the output shaft. In another embodiment, the inlets to the motor are in communication with a common cavity for driving liquid under pressure located upstream of the motor compartment.

In another embodiment, the shaft portion comprises a screw connection between the central wheel of the motor and the sun wheel of the planetary gear connected in sequence.

In another embodiment, the rotation unit comprises a pressure equalization channel which connects end surfaces of the central wheel of the motor.

In another embodiment, one or more grooves are formed by the teeth in the circumferential direction of the sun wheels, planetary wheels and an outer gear ring included in the planetary gears.

In another embodiment, the corresponding grooves are formed in corresponding positions, partly in the sun wheels and partly in the gear ring, surrounding the planetary wheels, which is supported on the inside of the housing.

In another embodiment, the output shaft supports a circular flange with an axially extending cylindrical wall which during operation forms a rotating part of the outside of the rotation unit.

Other details, advantages and technical effects as well as features of the invention will become apparent from the following detailed description and the appended dependent patent claims.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are explained in more detail below with reference to the accompanying schematic drawings, in which

Fig. 1 is a longitudinal section of the sectional plane l-l of Fig. 3, passing through the center of a rotation unit for drilling according to the present invention,

Fig. 2 is a cross-section of the sectional plane ll-ll of Fig. 1 , seen in the flow direction of the liquid through the rotation unit from left to right in Fig. 1 ,

Fig. 3 is a cross-section in the sectional plane Ill-Ill of Fig. 1 seen in the opposite direction to the flow direction of the liquid through the rotation unit, and

Fig. 4 is an broken-away portion of the longitudinal section of Fig. 1 shown on a larger scale and with an alternative embodiment of a planetary gear included in the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Initially, it should be noted that the drawing figures are schematic and primarily suitable for supplementing the description. For simplicity, engagements between teeth in the motor and planetary gears are illustrated by cross-sectional markings, with the exception of Fig. 2 in which gear rings on sun wheel and planetary wheels are indicated by two concentric circles in the peripheries of the wheels.

Fig. 1 is an axial section through the center axis CL of a rotation unit 1 intended for drilling. The rotation unit 1 consists of a cylindrical housing 2 the outer diameter of which corresponds to the diameter of a drill pipe (not shown) which can be connected in the left end of the rotation unit 1 according to the drawing. At said end there is a collecting chamber 3 to which driving liquid, preferably water, is fed at high pressure. The pressure of the water in the chamber 3 can amount to the order of about 180 bar. In the flow direction of the water, from left to right in Fig. 1 , a first motor compartment end wall 4 is arranged downstream of the collecting chamber 3, which together with a second motor compartment end wall 5 arranged downstream thereof form a cylindrical motor compartment, with an enclosing cylindrical wall consisting of a part length of the surrounding housing 2.

In the motor compartment, a gear motor is arranged to be driven in rotation by the pressurized water in the collecting chamber 3. The axial extent of the motor in the rotation unit is illustrated by the double arrow M. The gear motor comprises a central wheel 6 which is in gear engagement with a number of planetary wheels 7, all mounted for rotation in the first and second motor compartment end walls 4 and 5. The teeth of the central wheel and the planetary wheels are designed in a manner known per se for a liquid-displacing engagement.

It should here be noted that Fig. 1 shows an embodiment of the gear motor which in fact comprises four planetary wheels 7 arranged with a mutual angular distance of 90°, of which, however, only two can be illustrated in a longitudinal section through the center axis CL.

Inlet ducts 8 for continuous feeding of pressurized water to the motor, during operation, are arranged through the first motor compartment end wall 4, while outlet ducts 9 for continuous discharge of water from the motor are arranged through the second motor compartment end wall 5. All gear engagements between the central wheel and the surrounding planetary wheels are assigned separate inlet and outlet channels for through-flowing water, wherein these inlet and outlet channels 8 and 9, respectively, are mutually angularly offset about the center axis. The nature of the angular displacement is schematically illustrated by dashed lines in Fig. 3.

For the sake of clarity, it should be explained that the inlet to the upper inlet duct 8 in Fig. 1 is located in the broken-away portion of the sectional view and is therefore not shown in Fig. 1 , while the inlet to the lower inlet duct 8 in Fig. 1 is located in the casting of the motor compartment end wall 4 and is therefore obscured and illustrated by dashed lines.

The outlet channels 9 mouth in an annular cavity 10 in which the individual outlet flows are combined in a continuous liquid-filled space. The cavity 10 can be designed as a turned cavity in the downstream side of the second motor compartment end wall 5. The cavity 10 can alternatively consist of an unused empty section of the rotation unit.

From the downstream end of the central wheel 6 a shaft portion 11 extends through the second motor compartment end wall 5 and past the cavity 10. Via the shaft portion 11 , the central wheel 6 of the gear motor is non-rotatably connected to a sun wheel 12 of a first planetary gear 13 connected in sequence (see double arrow 13). The sun wheel 12 and the central wheel 6 can be connected to each other by means of a threaded connection in a dividing 14 through the shaft portion 11.

In the outside of the shaft portion 11 , an inlet 15 extending in the radial direction mouths into a central drainage channel 16 running through the shaft portion 11 and the sun wheel 12.

The drainage channel 16 continues through an output shaft 17 driven in rotation, to mouth into the downstream located end 18 of the output shaft. Said end suitably has coupling means, for example in the form of a thread 19, for mounting a drill bit or other tool at the end of the output shaft 17. The drainage channel 16 leads the water to the drill bit for flushing the borehole. The drainage channel 16 can thus also be considered to constitute a flush water channel.

To equalize the axial pressure which the water exerts against the central wheel 6, a pressure equalizing channel 20 is suitably arranged through the central wheel to pressure-connect the two end planes 21 and 22 of the central wheel.

In one embodiment, the planetary wheels 23 of the first planetary gear 13 are rotatably mounted in a planetary carrier 24, which in turn is non-rotatably connected to the sun wheel 25 of a second planetary gear 26 connected in sequence (see double arrow 26). The planetary carrier 24 and the sun wheel 25 can, as shown in Fig. 1 , be made with shaft pivots 27 and 28, respectively, which are rotatably received in seats of corresponding shape, arranged in the sun wheel 12 and in a planetary carrier 29 belonging to the second planetary gear. The planet wheels 30 of the second planetary gear are rotatably mounted in said planetary carrier 29, which in turn is non-rotatably connected to the output shaft 17.

In this context it should be noted that Figs. 1 and 2 show an embodiment of the planetary gears which comprises four planetary wheels 23 or 30 arranged with a mutual angular distance of 90°, of which, however, only two can be illustrated in a longitudinal section through the center axis CL. However, the invention is not limited to the embodiment shown, but generally comprises the utilization of two or more planetary wheels in one or more planetary gears operatively coupled to a liquid-powered gear motor comprising a central wheel assigned to two or more planetary wheels.

The output shaft 17 is guided and mounted in a bushing 31 which is mounted by being inserted into the downstream located end of the housing 2. A flange 32 mounted on the output shaft 17 has an axially extended cylindrical wall 33 which encloses the bushing 31 and meets the housing 2 at the same outer diameter, whereby the rotating unit has an unbroken periphery along its entire length. In other words, the output shaft supports a circular flange with an axially extending cylindrical wall which during operation forms a rotating part of the outside of the rotation unit.

It should be noted that the outer gear ring 34 of the planetary gears may be mounted by being inserted in the housing 2, but that it may also alternatively be integrally formed in the inside of the housing 2. The gear ring 34 may, as shown in Fig. 1 , extend in unbroken length through the first and the second planetary gear. In embodiments with more than two planetary gears, all of them can be assigned a common gear ring.

The above-described solution for a rotation unit for drilling, which is submersible or insertable into a borehole, results in a short assembly with short toothed segments, smaller displacements and short flow paths for the water. By downshifting the speed in two or more steps, the motor can be dimensioned to operate at a higher speed and at the same time deliver effective torque to the output shaft. The compact structure of the motor and gears results in an acceptable internal leakage that enables the use of a hydraulic water-driven gear motor in an application in which the drive water is also used for flushing the borehole.

From the above description it is understood that the drainage channel 16 extends through three components, namely the sun wheel 12, the sun wheel 25 and the output shaft 17, which rotate at mutually different rotational speeds. Without seals between sliding surfaces, a smaller leakage can still be accepted between the components, especially as the compact structure with short flow paths overall also provides fewer leakage paths.

In an alternative embodiment, however, drainages may, if necessary, be made in the form of circumferential grooves 35 through the teeth in the circumferential direction of the sun wheel, planetary wheels and the outer gear ring. The grooves 35 are, if appropriate, mutually placed such that they form a free passage for water and thereby prevent the rotation of the wheels from being slowed down by leaking water.

Embodiment alternatives include the possibility of forming the motor's central wheel 6 and the sun wheel 12 of the planetary gear connected in sequence in one piece. In this embodiment, the downstream located motor compartment end wall 5 can be made in two parts with the dividing plane in the center line to facilitate assembly.

Other alternatives include the possibility of forming the sun wheel 25 of the second planetary gear in one piece with the planetary carrier 23 of the first planetary gear, as well as the possibility of integrating the output shaft 17 with the planetary carrier 29 of the second planetary gear.

Yet another embodiment alternative is shown in Fig. 4. The embodiment of Fig. 4 differs from the embodiment described above in that the planetary wheels of the first planetary gear are designed as rings or gear rings 36, which are rotatably mounted externally about a shaft journal 37 projecting from the planet carrier 24. Of course, if appropriate, several or all of the planetary gears included in a rotation unit can have planetary wheels designed as the planetary wheel 36.

Although the exemplary embodiment shows a single motor unit 6, 7, it should be emphasized that alternative embodiments may comprise two or more motor units connected in sequence with mutually non-rotatably connected central wheels. Similarly, more than two planetary gears can also be connected in series.

The person skilled in the art will appreciate that for manufacturing and mounting the rotation unit, internal machining of the housing may be required, as well as welding, crimping or screw mounting to fix the motor compartment end walls and the guide bushing for the output shaft. Without being specifically shown in this description, it will also be appreciated by the person skilled in the art that plain or ball bearings can be utilized in the mounting of the motor's central wheel and planetary wheels in the motor compartment end walls, as well as in the mounting of the planetary wheels of the planetary gears in associated planetary carriers.

From the above it is also understood that the solution presented is not limited to the exemplary embodiment shown in the drawings but is to be interpreted in a broader sense such as the solution is defined in the appended patent claims.