FIELD OF INVENTION

This invention relates to hydraulic motors which derive their output power from the flow of fluid under pressure to the rotating parts.

The invention will be described in relation to a hydraulic motor of the kind that may be installed as a down-hole drill motor at the lower end of a long drill string and be driven by the pressurised slurry normally used for drill bit lubrication and cooling. However, it is to be understood that the invention is not limited thereto as the motor (albeit with or without minor modifications) may be used with general purpose hydrostatic transmission systems as a high torque/slow speed motor.

BACKGROUND ART

Down-hole drill motors are known in various forms, the most familiar and widely known of which, is the turbo¬ drill. As the name implies, the turbo-drill is based on the multi-stage turbine principle with drilling mud as the working fluid.

Other positive displacement hydraulic motors used commercially, or which may still be at the experimental

stage, include eccentric lobed rotor (as in the mono pump) and flexible vane types. Most down-hole turbo-drills or positive displacement motors derive their high torque/slow speed characteristic from a gradual pressure drop of the motive fluid over a relatively large axial length.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a hydraulic motor having high torque/slow speed characteristics within a relatively short axial dimension, making it particularly suitable for directional drilling, together with simplicity and ruggedness of design as will be suitable for bore or well applications.

According to the invention there is provided a hydraulic motor comprising a body defining a chamber that has a plurality of cylinders formed therein, a drive element within the chamber adapted to be coupled to an output shaft, a multi-lobed rotor mounted on the drive element with the lobes adapted to co-operate sequentially with the cylinders, a passageway in each lobe through which fluid applied to the interior of the rotor is directed to the cylinder during pre-deter ined locations of each lobe whereby the lobe is forced from the cylinder and the force so produced is transferred as torque to the drive element. Preferably, there are three rotors each with three lobes and ten cylinders but the prinicple can equally be

applied to a three rotor/three lobe, six, eight or nine cylinder configuration.

The motor is capable of staged assembly whereby each individual power module or motor may be connected in line with one or more further modules to increase the final output shaft power.

In a preferred form of the invention, the working fluid is the pressurized mud slurry used for flushing of drilling debris and lubrication and cooling of the drill bit at the end of a drill string. The working fluid passes through each stage in turn and a portion of the total flow is extracted at each intermediate stage to provide motive power for the module of that stage. The motor modules are, in effect, operating hydraulically in parallel and mechanically in series.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings in which: Fig. 1 is a cross-sectional view of a single stage hydraulic motor according to one embodiment of the invention. Fig. 2 is a cross-sectional view of a second stage or module hydraulic motor adapted to be connected to the first stage shown in

Fig. 1, Fig. 3 is a diagrammatic representation of the porting arrangement by which fluid is transmitted to and discharged from the cylinders of the hydraulic motor shown in

Fig. 1, Fig. 4 is a diagrammatic representation of the porting arrangement by which fluid is transmitted to and discharged from the cylinders of the motor shown in Fig. 2,

Fig. 5 is an exploded view of the central portion of the motor shown in Fig. 1, and. Fig. 6 is a schematic view of a down-hole drill string, motor and drill bit arrangement. The hydraulic motors shown in Figs 1 and 2 each include a hollow body 10 that is closed by a non-drive end housing 12 and a drive end housing 13 all of which are held in position by bolts 11. A plurality of radial slots or recesses 14 formed in the inner face of the body 10 constitute the working cylinders of the motor (see Fig. 3). The first and second stages are substantially similar and will, when appropriate, be described together.

The end housings 12 and 13 have taper roller bearings 16, 17 which support a drive element 15 in the chamber defined by the body 10. Oil or grease is sealed within the bearings 16, 17 by polymer seal plates 18 which act against mating faces of the drive element or rotor 15 and by plates

18a sealing against locking rings 20 attached to the non- drive end stub shafts 24 (Fig. 2) and 24a (Fig. 1) and to the drive-end stub shafts 26 (Fig 2) and 26a (Fig. 1). As shown in Fig. 2, sealing pressure is provided by compression springs 40, 41 which act against seal plates 18 and 18a respectively.

The drive element 15 (see Fig. 2) consists of two flanged components 19, 19a that are connected together by three equally spaced circular, hollow pins 21. Each pin 21 carries a rotor 22 having three lobes 23 free to rotate on the pin 21. The drive element for the second stage motors also has three transfer tubes 50 between the flange components 19, 19a (see Fig. 4) and the drive element for the first stage has three rotor torsion pins 51 between the flange components 19, 19a (see Fig. 3).

As can be see in Figs. 3 and 4, the rotor lobes 23 engage each cylinder 14 in turn as the drive element 15 and rotors 22 turn (in opposite directions) thereby forming a sealed chamber to which the pressurised fluid is admitted. The porting arrangement and method of transfer by which fluid is transmitted to and discharged from the cylinders 14 is shown diagramatically in Fig. 3 for the first stage motor of Fig. 1 and in Fig. 4 for the second stage motor of Fig. 2. High pressure (i.e. inlet) fluid is indicated by solid lines and low pressure (i.e. discharge) fluid by broken lines. The non-drive end flange component 19 has a hollow stub shaft 24 (Fig 2), 24a (Fig. 1) and a

- b

pressurised fluid passageway 25 (Fig. 2), 25a (Fig. 1) through which the driving fluid is introduced into the motors of Figs. 1 and 2 in the direction of arrows A.

The drive end flange component 19a has a hollow stub shaft 26 (Fig. 2) having a passageway 27 (Fig. 2) through which a portion of the pressurised driving fluid is discharged in the case of the Fig. 2 motor in the direction of arrows B to the motor of Fig. 1. An annular connector flange 28 is used to join the first and second stages and the drive end stub shaft 26 of one unit receives the non-drive end shaft 24a of the next unit with a seal 29 therebetween.

Each rotor pin 21 has a port slot 31 which overlaps, in turn, with three corresponding ports 32 in the rotor • 22. The rotor ports 32 provide a passageway for fluid under pressure through each lobe 23 into the cylinder chambers 14 to provide the power stroke by forcing the lobe from the cylinder.

The rotor ports 32 open at the top dead centre of each lobe 23 in a cylinder 14 and close at the point of departure of the lobe from the cylinder. The force produced on the rotor 21 is transferred as torque to the drive element 15 and to the final output shaft (not shown) of the motor. During operation, the body of the motor is full of fluid at discharge pressure. When a lobe 23 is entering a cylinder 14, the fluid is displaced by an axial rectangular

groove 33 on the periphery of each lobe 23 which breaks the seal over that segment of the working cycle. In a multi¬ stage motor, discharge fluid is then released from the first stage by passageway 34 in the non-drive end plate 12 and passageway 35 in the drive end plate 13, in the direction of arrows D. If the motor is the final or only stage as is the case with the Fig. 1 motor, all pressure fluid is translated into rotational energy through the drive element 15. Spent fluid is discharged into the body 10 and thence through the passageway 27a to the drill bit (arrows C in Figs 1 and 3).

The use of an hydraulic motor of the invention as a down-hole drill motor is shown in Fig. 5 where the first motor unit 60 is bolted direct to- the lower flange of the drill string of pipes 61 which provide the inlet supply fluid from supply line 62. The outward shaft of the final motor unit is connected direct to the drill bit 64 or through an intermediate coupling.

Thus, it can be seen that the hydraulic motor derives its output power from a flow of fluid supplied under pressure to the rotating parts.

Although the motor is designed principally as a down the hole drill motor for deep wells it may also be applied (with suitable modifications) to general purpose hydrostatic transmission systems as a high torque/slow speed motor.

The motor can be readily adapted for 'staged' assembly

whereby each individual motor as described above may be connected in line with one or more further motors to increase the final output shaft power.

When used as a drill motor, the working fluid is pressurised mud slurry as used conventionally for flushing, lubrication and cooling a drill bit, which passes through each stage in turn. A portion of the total flow is extracted at each motor stage to provide motive power for that drive element. After discharge from the working stroke the fluid is released from the motor body to provide flushing, lubrication and cooling for the drill bit attached to the motor output shaft.

Various modifications may be made in details of design and construction without departing from the scope and ambit of the invention. For example, when adapted for general use, the hydraulic motor is not subjected to the stringent diametral constraints of a down the hole drill motor and thus the inlet and outlet connections for the working fluid (such as hydraulic oil) could be located in one plate or casting at the non-drive end of the motor.