The earlier French patent specification FR 383273 describes a milling tool that is connected to a barge and where there is a connection between the barge and the excavation equipment in the form of the milling tool. Mud that is milled away from the seabed can be sucked up and brought to the surface. In an alternative embodiment, a mill of this kind can be connected to a shaft that extends down from the barge. The British patent specification GB 2065751 teaches a pipeline for bringing milled, excavated materials up to the surface from a seabed.

The British patent specification GB 2176153 relates to somewhat more traditional digging equipment, the object of which is to enable excavated material to be brought to the surface. However, a platform anchored to the seabed by means of legs is used in this case, and the digging equipment is either connected to said legs or pivotally secured to the platform itself.

US Patent 3629963 relates to a crawler-mounted bulldozer that can be operated from the surface of the sea. An oil pressure pump in the bulldozer is driven from the surface via a power cable.

US Patent 3683521 describes a crawler-mounted vehicle that is controlled by an operator who is on board in a pressure chamber 32. In this case the intention is to use the solution to bring sediments milled out of the seabed up to the surface.

US Patent 3857250 relates to a subsea vehicle for laying cables and pipelines in the seabed. The vehicle has milling tools for forming a trench for the said cables and pipelines, but the use of powerful water jets instead of such milling tools is also envisaged.

US Patent 3978679 relates to a form of milling tool for use in the excavation of trenches and the like, but also for other purposes. In this case too, there are means for sucking up the spoil.

US Patent 3990377 relates to a typical plough attachment where the attachment is remote-controlled via an electric cable. The equipment carries out both ploughing and the subsequent laying of cables in the seabed.

US Patent 4409747 relates to equipment for digging trenches in the seabed, where two mutually-inclined, almost paternoster-like digging means are provided.

The object of the present invention is to provide, unlike that possible with the known devices, a device on a subsea vehicle for carrying out work on the seabed, preferably at great ocean depths of more than 200 metres.

According to the invention, the device is characterised in that the subsea vehicle is a hydraulically operated vehicle of an excavator type that is known per se equipped with tools, for example, a shovel, and a unit for generating hydraulic driving pressure for the propulsion of the subsea vehicle and movement of the arms and links that control the tool, that on the subsea vehicle there is provided an automatic pressure regulating device for compensation of the pressure that the water pressure at the seabed exerts on the hydraulic system of the subsea vehicle, and a hydraulic tank for compensation of changes in volume in the hydraulic system due to variations in the amount of oil in the working cylinders of the system, that the device consists of a piston/cylinder structure, where the surrounding water pressure acts against the underside of the piston and the hydraulic oil flow in the system is adapted to pass through the chamber volume found between the upper side of the piston and the top end wall of the cylinder and that is variable due to the water pressure and changes in oil volume, that there is provided a hydraulic tank which is pressurised by the water pressure at the seabed in order to oil- pressurise mechanically moveable parts of the subsea vehicle, e. g. , the crawler drive, turning gear and the like, and that the hydraulic system pump is electrically driven by power supply from control equipment located above the surface of the sea.

According to one embodiment of the device, the subsea vehicle is equipped with electrically operated control valves for controlling via an umbilical from said control equipment at least one of the following functional devices on the vehicle: driving gear for operating the propulsion machinery of the vehicle, as for example, driving belts, lifting jacks for movement of arms to which the tool is articulated, driving means for turning a turret to which one of the arms is articulated.

According to a further embodiment of the device, where the tool is a shovel, there is provided a suction device designed to cover the shovel opening when, after the excavation operation, the shovel, filled with excavated material, is turned into a backward-facing position.

The tool of the subsea vehicle can be designed in different ways, depending upon the function to be performed. According to the invention, the tool is intended to be capable of performing at least one of the following functions: formation of trenches or channels in the seabed and optional filling in of the same ; general excavation in the seabed or in an article on or that extends up from the seabed, dredging, cleaning, cutting, inspecting, gathering minerals or plants on the seabed.

The invention will now be described in more detail with reference to the attached drawings.

Fig. 1 shows an illustrative use of the device according to the invention in a seabed environment.

Fig. 2 shows a typical embodiment of the subsea vehicle.

Fig. 3 shows in more detail the interdependence between the subsea vehicle and equipment located above the surface of the sea.

Fig. 4 shows in more detail the principle of pressure equalisation in the hydraulic system of the device.

Fig. 5 shows a detail of the drive mechanism in connection with the belt-driven vehicle.

Fig. 6 shows an embodiment of the device with a suction device fitted to the shovel.

Fig. 1 shows a subsea vehicle 20 fitted with driving belts 21. The vehicle is equipped with a rigid first arm 22 which at its free end is articulated to a second arm 23, wherein this arm 23 is in turn connected via an articulation to a shovel 24. Jack 25 is provided to adjust the angularity between the two arms 22,23, whilst jack 26 is provided to adjust the angle of the shovel 24 relative to the arm 23. The reference numeral 5

indicates an umbilical containing power supply to the hydraulic pump motor 8 which via the umbilical is supplied with electric power from equipment above the surface of the sea. A termination device and transformer 6 are advantageously provided on the subsea vehicle to provide sufficient drive voltage to the motor 8. A light projector 14 and a video camera 13 are advantageously provided, so that the operations carried out by the subsea vehicle on the seabed can be adequately illuminated by the light projector 14 and monitored via the camera 13 which delivers signals via the umbilical to a control cabinet 1 located above the surface of the sea. The reference numeral 2 in Fig. 3 indicates a main power supply unit for supplying regulated power supply to the motor 8, and possibly other operative equipment on the subsea vehicle via the unit 6.

An electronics unit 7 is provided for transmitting operation signals to valves (known per se) that control the operation of components such as the lifting jack 25,26, and makes it possible to control the turning of the turret 27 that is pivotally secured to the chassis of the subsea vehicle in order to turn the arms 24,25 with attached excavating tool to one side or the other, as in commonly known for excavators and similar machines. The reference numeral 3 indicates a winch for storing the umbilical. The power supply to the unit 2 comes from, for example, an external supply mains via cable 2'. The signals that are to control, inter alia, control valves on the subsea vehicle are indicated by means of the reference numeral 4 in Fig. 3. The umbilical 5 running from the control equipment above the surface of the sea down to the subsea vehicle is indicated by the reference numeral 5 in Figs. 1-3. The reference numeral 9 in Fig. 3 indicates in general a valve assembly for controlling jacks, belt drive and turning gears.

It will be seen that the valve assembly 9 controls, inter alia, the jack 10 that regulates the position of the arm 22 relative to the chassis of the subsea vehicle and the turret 27.

A hydraulic oil tank for the hydraulic system is also provided on the subsea vehicle.

This tank is pressurised by external, static seawater pressure.

There is also an oil tank that is pressurised by external static seawater pressure in order to oil-pressurise mechanically moveable parts of the structure such as belt gears and turning gears.

It will be understood immediately that the umbilical may optionally be designed so as to contain a wire for lifting or lowering the subsea vehicle. The vehicle will be capable of being remote-controlled from the surface by means of electronically transmitted signals from an operator to the control valves 9 of the machine. The operator will easily be able

to control the subsea tool with the aid of screen images, for example shown on a display 1', that are transmitted from the video camera 13.

The reference numeral 4'in Fig. 3 indicates signal cables for transmitting control signals from the electronics unit 7 to/from the valve assembly 9 and to the camera 13 and the light projectorl4.

The said hydraulic oil tank for the vehicle's hydraulic system is explained in more detail in connection with Fig. 4. It will be seen from this figure that the system has a unit 11 which may consist of a piston/cylinder structure, where the piston is indicated by means of the reference numeral 11'. The components of the hydraulic system, such as the jacks 10,25, 26, the turning gear 28 and belt drive 20, are shown in more detail in Fig. 4. A flow of hydraulic oil 30 is passed via a chamber indicated by the reference numeral 11" that is variable by means of the surrounding water pressure 32 and is located between the upper side of the piston 11'and the top 11"'and wall of the cylinder 11. As indicated, an external water pressure will prevail against the rear side of the piston, and the piston 11'may optionally be provided with a pushing spring 31. The unit 11 thus represents a first pre-pressurising unit for giving the drive oil in the hydraulic system an increased pressure equivalent to the external water pressure so as to create relatively normal working conditions for the hydraulic system that is to operate the tool. The hydraulic tank or the unit 11 will, with the aid of, inter alia, the spring load 31, compensate for variations in the amount of oil in the cylinders. However, the system is pressurised with the aid of the static water pressure which in Fig. 4 is schematically indicated by the reference numeral 32. The pump 8 is a hydraulic pump that provides a pressure increase equivalent to normal working pressure for the cylinders and other hydraulically powered components, such as those indicated by the reference numerals 10,25, 26,28 and 29. The valve assembly 9 effects control of these components. As shown in more detail in Fig. 5, a belt gear and a turning gear, generally indicated by the reference numeral 33, can be provided to turn the turret or top part 27 and provide power for the drive belts 21. In relation to that shown in Fig. 2, the belt gear is also symbolically indicated by the reference numeral 29 in Fig. 5, whilst the turning gear is indicated by the reference numeral 28. In this case, the oil tank, which functions as a second pre-pressurising unit and which, as indicated earlier by the reference numeral 12, is also pressurised by external static seawater pressure that oil-pressurises mechanically moveable parts of the structure, such as the belt gear 29 and the turning gear 28. The engine/hydraulic system side of the belt drive and turning of the turret or top part are thus also protected from water penetration.

This tank 12 thus protects the gear mechanism, in that the gear housings are filled with oil that is pressurised by external water pressure. This is a very important feature of the present invention, in addition to that illustrated and described in connection with Fig. 5.

It will also be understood that the system shown in position 11 prevents the penetration of water into the hydraulic system because the whole tank is put under static water pressure.

Fig. 6 shows an embodiment of the device where the tool is a shovel. There is provided a suction device 34 having a suction hood 34', a suction canal 34'and a suction pump 35 which causes the material sucked up to passed out of and behind the excavator 36. The suction hood is designed to cover the shovel opening when, after the excavation operation, the shovel 24, filled with excavated material, is turned into a backward facing position. It may be particularly important to suck up from the shovel mud or the like which otherwise would cause substantial pollution of the water if the shovel was emptied, e. g. , at the side of a trench.