The invention relates to a device for controlling a level of oil in a main tank of a supply circuit.

In particular, the invention relates to the field of operator vehicles provided with one or more hydraulic actuators for performing various operations, for example activation of a digger blade, a turret, a lift arm or other.

In operator vehicles such as earth-moving machines or agricultural machines, there is normally a hydraulic fluid supply circuit, the fluid being hydraulic oil, comprised in a main tank. The main tank is typically constituted by the motor casing and/or the gear box. A first constant-flow pump takes oil from the main tank. A second variable-flow pump is connected in aspiration with the delivery of the first pump. The second pump is predisposed to supply the oil to one or more hydraulic distributors which are connected in outlet to one or more actuators.

The first pump also supplies a lubrication circuit, predisposed to send oil to various zones of the operator vehicle with the aim of lubricating various organs of the operator vehicle. The lubrication circuit is connected in inlet to an intermediate point between the first pump and the second pump, while it is connected in discharge to the main tank. An auxiliary conduit, provided with a check valve, is arranged in parallel with the lubrication circuit.

The supply circuit functions as follows. The first pump continuously develops a constant flow of oil which is divided between the lubrication circuit and the second pump, which second pump supplies the oil to the distributors. During the working stages of the vehicle, in which the activation of the actuator is not required, all the oil flow developed by the first pump is directed towards the lubrication system. This flow, which considerably exceeds the flow required by the lubrication circuit, flows in part back through the auxiliary conduit, and the relative check valve, to the main tank. During the working stages, in which the activation of the actuators is required, a part of the oil flow developed by the first pump is directed, by means of the second pump, to the hydraulic distributors.

The quantity of oil present overall in the vehicle supply circuit must be sufficient to enable both lubrication of the vehicle and all the parts requiring lubrication, as well as activation of the actuators on board the vehicle. This is therefore a not insignificant amount of oil, which occupies a certain volume of the main tank. As already mentioned herein above, the main tank of the supply circuit is constituted generally by the engine casing and/or the gear box. The drive shaft and the vehicle gear box are therefore immersed in an abundant quantity of oil, rotation of shafts and gears represents a significant element for energy dissipation.

The aim of the present invention is to provide a control device of an oil level in a main tank of a supply circuit which limits the quantity of oil present internally of the main tank to what is strictly necessary for the operations which have to be performed at any given time, such that the energy dissipation produced by the agitating of the oil is proportionally reduced.

An advantage of the device of the present invention is that it does not lead to an increase in the space taken up on board the vehicle.

A further advantage of the device is that it can be installed on board vehicles which have not been originally predisposed for the device.

Further characteristics and advantages of the present invention will better emerge from the indicative and therefore non-limiting description, with reference to the accompanying figures of the drawings, in which:

□ figure 1 is a schematic diagram of a first embodiment of the present invention;

□ figure 2 is a schematic diagram of a second embodiment of the present invention;

□ figures 3 and 4 are schematic diagram of a third embodiment of the present invention, in two distinct functional configurations;

□ figure 5 is a schematic diagram of a main hydraulic circuit which can be managed by means of the present invention;

□ figures 6a, 6b, 7 are schematic drawings of discharge valves which can be employed with the present invention. With reference to the figures the control device of the present invention is illustrated in combination with a supply circuit of an operating fluid in an operator vehicle. The supply circuit comprises a main tank 4 which is normally constituted by the engine casing, which supplies a first, charge pump 1 . The charge pump 1 , which is generally a constant-flow pump, develops an oil flow which is sent to a main hydraulic circuit 100 comprising some hydraulic circuits of the operator vehicle. The main hydraulic circuit 100 is connected in inlet to the delivery of said charge pump 1 and at least one outlet is connected to the main tank 4.

For example, as illustrated in figure 5, the main hydraulic system 100 can comprise a lubricating circuit 10 of the vehicle. One or more fluid distributors 3 are interposed between the first pump 1 and the hydraulic actuators 30, which distributors 3 are controllable by the vehicle operator who commands them to send the oil to the hydraulic actuators 30 required to be activated for a specific task.

The oil is sent to the distributors 3 by means of a second, main pump 2, being a variable-flow pump, which is interposed between the charge pump 1 and the hydraulic distributors 3. During the functioning stages of the vehicle in which no activation of any actuator is required, the main pump 2 does not deliver oil to the distributors 3, and the whole oil flow developed by the first pump 1 is sent to the vehicle lubrication circuit 10. There exist also small operator vehicles, such as small tractors, in which only the pump 1 is present. In this case the hydraulic distributors 3 are fed by the pump 1 together with the lubricating circuit.

The lubrication circuit 10 of the vehicle receives the oil from a connection located in an intermediate position between the charge pump 1 and the main pump 2. The lubricating load has been generically denoted by a valve 101 . The lubricating circuit

10 is connected in discharge to the main tank 4.

The oil supply circuit further comprises a first auxiliary conduit 1 1 which is arranged in parallel with the lubricating circuit 10. The first auxiliary conduit 1 1 may be provided with a check valve 12. The first auxiliary conduit 1 1 is operable to return the

011 to the main tank 4, by-passing at least a tract of the main hydraulic circuit 100. The function of the check valve 12 is to enable passage of oil through the first auxiliary conduit 1 1 only in a case in which the fluid pressure in the main hydraulic circuit 100 is greater than the calibration of the valve 12 itself. This guarantees the necessary fluid supply to the lubricating circuit 10.

The oil level control device of the present invention comprises an auxiliary tank 5. The auxiliary tank 5, in discharge, is placed in communication with the main tank 4. A first auxiliary conduit 1 1 connects at least a section of said main hydraulic circuit 3 with said auxiliary tank 5.

The auxiliary tank 5 is interposed between the auxiliary conduit 1 1 and the main tank 4. At least a control valve 8 is operable to control the oil passage from the first auxiliary conduit 1 1 to the main tank 4 through the auxiliary tank 5. At least a relief valve 7 is arranged on the auxiliary tank 5 such as to enable discharge of the operating fluid towards the main tank 4 should a predetermined level be exceeded.

In a first embodiment of the control device, illustrated in figure 1 , the control valve 8 is interposed between auxiliary tank 5 and the main tank 4. The control valve 8, which is preferably electromechanically activated, can be normally closed or normally open. In the first case the auxiliary tank 5 may optionally be provided with a discharge valve 6 which enables discharge of at least a minimum oil flow from the auxiliary tank to the main tank 4 in a case of malfunctioning of the control valve 8. In any case, discharge valve 6 may further represent leakages between the tanks.

The functioning of the device, in this first embodiment, is the following. In conditions of low oil demand, for example while the vehicle is moving and no activation of the hydraulic actuators 30 is required and or the main pump 2 does not send oil to the distributors 3, the whole oil flow developed by the charge pump 1 exceeds the flow rate required by main hydraulic circuit 100, and the excess flow is sent via the first auxiliary conduit 1 1 to the auxiliary tank 5. The pressure along the auxiliary conduit 1 1 is, in this case, sufficient to bring the check valve 12 into an open configuration. The control valve 8 is activated into a closed configuration such that the auxiliary tank 5 fills up to a predetermined level, thus freeing the main tank 4 of the oil which is not required for the main hydraulic circuit 100.

If the demand for operating oil increases, for example in a case of activation of the hydraulic actuators 30, the control valve 8 is activated into an open configuration, in which it enables passage of the oil from the auxiliary tank 5 to the main tank 4. The auxiliary tank 5 progressively empties, while the fluid level in the main tank 4 increases.

In a second embodiment of the control device, illustrated in figure 2, the control valve 8 is interposed between the first auxiliary conduit 1 1 and the auxiliary tank 5. In this case too the control valve 8, which is preferably electromechanically activated, can be normally closed or normally open. In this second embodiment of the control device the auxiliary tank 5 is provided not only with a relief valve 7 but also with a discharge valve 6 which enables constant passage of a predetermined flow of oil from the auxiliary tank 5 to the main tank 4. As described with regard to the first embodiment of the device, where there is a low demand for oil, the control valve 8 is activated into an open configuration, while when there is a high demand for oil the control valve 8 is activated into a closed configuration.

In a third embodiment of the control device, the control valve 8 is interposed between the first auxiliary conduit 1 1 and the auxiliary tank 5. The auxiliary tank 5 is further provided with a discharge valve 6 which enables constant passage of a predetermined oil flow from the auxiliary tank 5 to the main tank 4.

In the third embodiment, the control valve 8 is a four-way two-position valve. In inlet the valve 8 is connected to the first auxiliary conduit 1 1. Two outlets of the control valve 8 are connected respectively to the auxiliary tank 5 and to a second auxiliary conduit 13 which in turn is connected to the main tank 4.

In a first operating configuration, the control valve 8 sets the first auxiliary conduit 1 1 in communication with the auxiliary tank 5. The first operating configuration of the control valve 8 is indicated during the working stages of the vehicle, when there is a low demand for oil. As described for the two preceding embodiments, the oil flow developed by the first pump 1 considerably exceeds the flow demanded by the main hydraulic circuit 100 in condition of low demand, and the excess flow is sent through the first auxiliary conduit 1 1 to the auxiliary tank 5. The pressure along the auxiliary conduit 1 1 moves the check valve 12 into an open configuration. The auxiliary tank 5 thus fills up to a predetermined level, freeing the main tank 4 of the oil which is not required for the main hydraulic circuit 100. A predetermined oil flow passes, however, from the auxiliary tank 5 to the main tank 4 through the discharge valve 6 and through the relief valve 7. When there is an increase in the demand for oil in the main hydraulic circuit 100, for example by the hydraulic actuators 30, the oil flow which, via the auxiliary conduit 1 1 supplies the auxiliary tank 5, falls and the auxiliary tank progressively empties through the discharge valve 6. In this way the oil level in the main tank 4 increases.

If the oil demand grows further, for example during operations in which a considerable use of the hydraulic actuators 30 is required, the control valve 8 is activated into a second operating configuration, in which it sets the first auxiliary conduit 1 1 in communication with the second auxiliary conduit 13, by-passing the auxiliary tank 5 which, consequently, progressively empties through the discharge valve 6. In this way, substantially all the oil is conveyed and collected by the main tank 4.

In all the described embodiments, the auxiliary tank 5 can be provided with a level sensor 14 operable to detect the level of oil internally of the auxiliary tank 5 and to send a signal to a control unit which is operable to command the opening or the closing of the control valve 8 on the basis of the signal received. In the embodiment illustrated in figure 1 , in the case of exceeding a predetermined oil level the control valve 8 is activated to open, while in the embodiments illustrated in the other figures it is activated to close. The above-mentioned control unit is typically an electronic control panel which presides over numerous operations of the vehicle.

In all the described embodiments, the control device can further be provided with a temperature sensor 9 predisposed to detect the temperature of the operating fluid internally of the main tank 4 and to send a corresponding signal to the control unit, which is predisposed to command the opening or closing of the control valve 8 on the basis of the signal received. In the embodiment illustrated in figure 1 , in a case of exceeding a predetermined temperature value, the control valve 8 is activated to open, while in the embodiments illustrated in the other figures it is activated to close. Alternatively, the auxiliary tank 5 can be provided with a heat-sensitive valve which, in a case of exceeding a determined oil temperature value, automatically opens and thus frees up a passage towards the main tank 4.

In all embodiments, the auxiliary tank 5 can advantageously be provided with one or more further discharge openings towards the main tank 4, which openings are positioned such as to enable a transfer of oil from the auxiliary tank 5 to the main tank 4 in a case in which the vehicle assumes an inclination which exceeds a determined angle with respect to a horizontal plane. This is particularly useful as if the fluid level in the main tank 4 is not sufficiently high, a particularly accentuated inclination of the vehicle might cause some parts to emerge from the oil and thus compromise lubrication. Said further discharge openings FO are controlled by means of valve which may be of a passive kind or of an active kind. In the case of a passive valve, a closure element is mobile between a closing position and an open position under effect of gravity, following the tilting of the vehicle. The closure element V could be, for example, in the form of a sphere which can roll between the open and closing position, as illustrated in figure 6. An alternative form of the closure element could be a swinging lid which moves in the open position if the vehicle tilts over a predetermined angle. In the case of an active valve, a closure element V is still mobile between a closing position and an open position following the tilting of the vehicle, but the closure element is electrically operated according to a signal sent by a sensor which detects the tilting angle of the vehicle. The opening of the closure element V may be operated by means of a bowden cable BC.

At least one of the above cited further discharge openings may be provided with a temperature sensitive device, such as shape memory alloys, that mechanically opens a discharge path between the auxiliary tank and the main tank when the oil temperature in the main tank is too high.

In all the described embodiments, the auxiliary tank 5 can be located internally 9 of the engine casing or the gear box, in particular the auxiliary tank 5 can be conformed in such a way as to occupy the free spaces internally of the engine casing or the gear box. This arrangement is advantageous as it avoids additional space occupied on board the vehicle. The auxiliary tank 5 located internally of the engine casing or the gear box might further be made in the form of two half-shells which can be coupled without any particular constructional attention, as any fluid leakage would deposit internally of the main tank.

The control device of the present invention provides important advantages.

It enables precise and reliable control of the quantity of oil present internally of the main tank 4, such that there is always an amount of oil available that is strictly necessary for correct performing of the operations the vehicle is required to carry out. This enables energy dissipation due to continual mixing of the oil, which occurs in known-type devices, to be very considerably limited.

The control device is also simple and easily integrated into vehicles which were not originally predisposed for it.