WO2018203798A1

WO2018203798A1 - A lubrication system for a gearbox arranged in a vehicle

Info

Publication number: WO2018203798A1
Application number: PCT/SE2018/050411
Authority: WO
Inventors: Oskar LINDSTRÖM; Mattias Ingesson; Mikael Bergquist
Original assignee: Scania Cv Ab
Priority date: 2017-05-05
Filing date: 2018-04-23
Publication date: 2018-11-08
Also published as: SE1750550A1; SE541602C2; DE112018001936T5

Abstract

The present invention relates to a lubrication system (8) for a gearbox (3) which is arranged in a motor vehicle (1). The lubrication system comprises a first lubrication circuit (9) with a mechanical pump (12) delivering lubricant to the gearbox (3) and a second lubrication circuit (20) with an electric pump delivering lubricant to the gearbox (3). The mechanical pump (12) is driven by a component in a powertrain of the vehicle via a mechanical transmission (13). The mechanical transmission (13) comprises a coupling member (15) movably arranged between a connected state in which it transfers a driving force from said component (14) to the mechanical pump (12) and a disconnected state in which it breaks the transfer of driving force from the component (14) to the mechanical pump (12). A control unit (26) is configured to move the coupling member (15) to the disconnected state when the electric pump (21) has capacity to deliver a required lubricant flow to the gearbox (3).

Description

A lubrication system for a gearbox arranged in a vehicle

BACKGROUND TO THE INVENTION AND PRIOR ART

The present invention relates to a lubrication system for a gearbox arranged in a vehicle according to the preamble of claim 1.

A powertrain of a hybrid vehicle may comprise a combustion engine, an electric machine and a gearbox. A lubrication system with a mechanical pump is usually used for supplying lubricant in the form of an oil to the gearbox. The mechanical pump may be a fixed displacement pump delivering a constant volume of oil during each pumping cycle. The pump may be driven by a component in the powertrain such as the counter shaft of the gearbox. In this case, the mechanical pump circulates an oil flow in the lubrication system related to the speed of the counter shaft. Especially during operating conditions when the mechanical pump operates at a high speed and the required driving torque of the vehicle is low, the mechanical pump supplies an excessive lubricant flow to the gearbox. During such operating condition, the mechanical pump consumes an unnecessary amount of energy.

The electric machine may drive the hybrid vehicle independently or together with the combustion engine. During other operating conditions, the electric machine operates as a generator where it supplies electrical energy to an energy storage. In any event, the electric machine gets hot during operation. Conventional cooling of an electric machine may be performed by air or water led past an external surface of a housing enclosing the electric machine. A more effective cooling method is to spray oil on the stator windings of the electric machine. An electric pump can be arranged in a cooling circuit supplying oil to the electric machine. US 2016/0123457 shows a dual circuit lubrication method for lubrication of a main power transmission gearbox of an aircraft. Each circuit comprises a pump which serves to draw lubrication liquid via suction points arranged at different depths of a lubrication liquid tank. The flows in the circuits can be individually started and stopped in order to avoid emptying out of the lubrication liquid in the tank. SUMMARY OF THE INVENTION

The object of the invention is to provide a lubrication system providing lubrication of a gearbox arranged in a vehicle in a reliable and energy efficient way.

This object is achieved by the lubrication system defined in the characterizing part of claim 1. The lubrication system comprises a first circuit with a mechanical pump by which it is possible to direct lubricant to the gearbox. A mechanical pump provides a lubricant flow to the gearbox in view of its speed. However, the speed of the mechanical pump is not always related to the required lubricant flow to the gearbox. Especially during operating conditions when the driving torque of the vehicle is low, a mechanical pump supplies an excessive lubricant flow to the gearbox. During such operating conditions, the mechanical pump consumes an unnecessary amount of energy. The lubrication system comprises a second cooling circuit with an electric pump powered by an electric motor. An electrical pump is easy to control within a large speed range such that it delivers a lubricant flow to the gearbox with a high accuracy. In view of this fact, it is more energy economic to use the electric pump instead of the mechanical pump during most operating conditions. The existence of the coupling member in the mechanical transmission, which transfers a driving force from a component in the powertrain of the vehicle to the mechanical pump, makes it possible to disconnect the operation of the mechanical pump in a simple manner. This possibility can, for example, be used during operating conditions when the mechanical pump supplies an excessive lubricant flow to the gearbox. During such operating condition, it is possible to use the electric pump and supply a lubricant flow to the gearbox which corresponds to the required lubricant flow with a high accuracy. The design of the lubrication system makes it possible to use the pump which is best suited to deliver lubricant to the gearbox at the actual operating condition.

According to an embodiment of the present invention, the lubrication system comprises a control unit configured to control said coupling member, to control the operation of the electric pump, to receive information about at least one operating parameter and to control the operation of the pumps in view of said information. The control unit may have access to stored data indicating which of the pumps to be used during different operating conditions. According to an embodiment of the present invention, the control unit is configured to receive information about an operating parameter related to the viscosity of the lubricant in the lubricant storage, and to initiate operation of the mechanical pump and no operation of the electric pump during operating conditions when the viscosity of the lubricant is higher than a specific value. The operating parameter may be the temperature of the lubricant. The viscosity of a lubricant such as an oil is significantly higher at low temperatures than at high temperatures. A mechanical pump which is driven by a component in the powertrain of the vehicle has capacity to pump oil with a very high viscosity. An electric pump, which is not oversized, has not this capacity.

According to an embodiment of the present invention, the control unit may be configured to estimate if the electric pump has capacity to deliver the required lubricant flow to the gearbox during operating conditions when the viscosity of the lubricant in the lubricant storage is lower than said specific value. In view of the fact that it is possible to deliver a requested lubricant flow to the gearbox with a higher accuracy by the electric pump than by the mechanical pump during substantially all operating conditions, it is desired to use the electric pump as much as possible when the lubricant has reached a regular operating temperature. The control unit may be configured to receive information about the driving torque of the vehicle and to estimate if the electric pump has capacity to deliver the required lubricant flow to the gearbox in view of this information. The required lubricant flow to the gearbox is related to the driving torque of the vehicle. The control unit may have access to data or be able to calculate the requested lubricant flow to the gearbox in view of information about the actual driving torque of the vehicle. In case the driving torque is low, it is likely that the electric pump is able to deliver the requested lubricant flow to the gearbox.

According to an embodiment of the present invention, the control unit may be configured to move the coupling member to the disconnected state when the electric pump is estimated to be able to deliver the requested lubricant flow to the gearbox and to control the electric pump such that it delivers the requested lubricant flow to the gearbox. On the other hand, the control unit may be configured to move the coupling member to the connected state when the electric pump is estimated not to be able to deliver the requested lubricant flow to the gearbox and to control the operation of the electric pump so that the electric pump and the mechanical pump together deliver the requested lubricant flow to the gearbox. In the latter case, the control unit may estimate the lubricant flow provided by the mechanical pump by means of information about its speed and control the operation of the electric pump such that it provides the difference between the requested lubricant flow and the lubricant flow delivered by the mechanical pump.

According to an embodiment of the present invention, the second lubrication circuit also has an extension between the lubricant source and a further object to be lubricated or cooled during operation of the vehicle. In this case, the second lubrication circuit and the electric pump has two tasks namely to lubricate the gearbox and to cool and/or lubricate the further object. The further object may be an electric machine. In this case, the vehicle may be a hybrid vehicle driven by the electric machine and a combustion engine. The cooling demand of the electric machine may change quickly and it may be high during certain operating conditions. In view of these facts, it is suitable to use an electric pump for supplying lubricant to the electric machine since it is easy to control within a large speed range with a high accuracy. Furthermore, an electric pump is a good complement to a mechanical pump since they have difficult properties.

According to an embodiment of the present invention, the second lubrication circuit comprises a valve arrangement by which it possible to direct the lubricant flow to the gearbox and/or the further object. The valve members may be two way valves which are movably arranged between an open position and a closed position. The control unit may set one of the valve members in the open position and the other valve member in the closed position when the lubricant flow in the second lubrication circuit is to be delivered to the gearbox or the further object. In case both valve members are set in the open position, a part of the lubricant flow in the second lubrication circuit is delivered to the gearbox and a remaining part of the flow in the second lubrication circuit is delivered to the further object.

According to an embodiment of the present invention, the first lubrication circuit and the second lubrication circuit receive lubricant from a common lubricant source. The use of a common lubricant which is pumped from a common lubricant source makes it possible to give the lubrication system a design which is compact and comprises fewer components than two separate lubrication systems. Since a common lubricant is used in the two lubrication circuits and it can be enough to arrange a lubricant filter in one of the two lubrication circuits. According to an embodiment of the present invention, the first lubrication circuit and the second lubrication circuit comprise a common initial part in which lubricant is sucked from the lubricant sump. The initial part may comprise a common suction strainer.Furthermore, such a common initial part reduces the total pipe length of the first lubrication circuit and the second lubrication circuit. It is of course possible to use separate initil parts in the lubrication systems. The first lubrication circuit may comprise a part comprising the mechanical pump and a first check valve, the second lubrication circuit may comprise a part comprising the electric pump and a second check valve, and that said parts of the first lubrication circuit and the second lubrication circuit are arranged in parallel. The task of the check valves is to prevent a lubricant flow in an incorrect direction during operating condition when the respective pumps are not in operation. The first lubrication circuit and the second lubrication circuit may comprise a common final part delivering lubricant to the gearbox. Such a common final part reduces further the total pipe of the first lubrication circuit and the second lubrication circuit.

The present invention is also related to a vehicle comprising a lubrication system according to claims 1-14. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described below by way of an example with reference to the attached drawings, on which: Fig. 1 shows a vehicle comprising a lubrication system according to the

invention and

Fig. 2a-2c shows the lubrication system more in detail during three different

operating conditions. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig 1 shows a powertrain of a hybrid vehicle 1. The powertrain comprises a combustion engine 2, a gear box 3, a number of drive shafts 4 and drive wheels 5. An electric machine 6 is arranged in a housing between the combustion engine 2 and the gear box 3. During certain operating conditions, the electric machine 6 supplies power to the powertrain. During other operating conditions, the electric machine 6 works as a generator where it supplies electrical energy to a not visible energy storage in the vehicle 1. The combustion engine 2 may drive the vehicle independently or together with the electric machine 6. The gearbox 3 transmits power from the combustion engine 2 and the electric machine 6 to the drive shafts 4 and the drive wheels 5. The gearbox 3 comprises components 7 in the form of bearings, shafts and gears which need to be lubricated and cooled during operation of the vehicle. The electric machine 6 is heated during operation and it needs to be cooled. A lubrication system 8 is schematically indicated in Fig. 1 which lubricates and cools said components 7 in the gearbox 3 and the electric machine 6.

Fig. 2a-2c shows the lubrication system 8 more in detail. The lubrication system 8 comprises a first lubrication circuit 9 having an extension from an oil sump 10 to the gearbox 3. An initial part 9a of the first lubrication circuit 9 comprises a suction strainer 11. An intermittent part 9b of the first lubrication circuit 9 comprises a mechanical pump 12. The mechanical pump 12 may be a fixed positive-displacement pump. Thus, the mechanical pump 12 delivers a constant volume of oil through the lubrication circuit 9 during each pump cycle and at a given speed. The mechanical pump 12 is driven, via a mechanical transmission 13, by a component in the powertrain of the vehicle 1. In this case, the component is a countershaft 14 in the gearbox 3. The mechanical pump 12 pumps an oil flow in the lubrication circuit 9 which varies with the speed of the countershaft 14. The oil flow pumped in the lubrication circuit 9 by the mechanical pump 12 may vary within a relatively large range during different operating conditions of the vehicle 1. The mechanical transmission 13 comprises a coupling member 15 by which it is possible to disconnect the counter shaft 14 from the mechanical pump 12. Furthermore, the intermediate part of the first lubrication circuit 9b comprises an oil filter 16 arranged in a downstream position of the mechanical pump 12. A bypass valve 17 is arranged in a bypass line 18 to the oil filter 16. Only in case the oil filter 16 is clogged, the bypass valve 17 is to be open. A check valve 19 is arranged in a position downstream of the oil filter 16. The task of the check valve 19 is to allow oil flow in one direction but prevent oil flow in the opposite direction. Finally, the first lubrication circuit 9 comprises a final part 9c directing oil to the gearbox 3. The lubrication system 8 comprises a second lubrication circuit 20 having an extension from the oil sump 10 to the gearbox 3. The second lubrication circuit 20 comprises an initial part 20a which corresponds to the initial part 9a of the first lubrication circuit 9. Thus, the first lubrication system 9 and the second lubrication system 20 comprises a common suction strainer 11. The second lubrication circuit 20 comprises an intermediate part 20b comprising an electrical pump 21. The electrical pump 21 is driven by an electric motor 22. The oil flow pumped through the second lubrication circuit 20 varies with the speed of the electric pump 21. The intermediate part 20b of the second lubrication circuit 20 further comprises a valve member 23. The valve member 23 is settable in an open position in which it allows an oil flow to the gearbox 3 and in a closed position in which it prevents an oil flow to the gearbox 3.

Furthermore, the intermediate part of the second lubrication circuit 20b comprises a check valve 24 which allows oil flow in one direction but prevents oil flow in the opposite direction. The second lubrication circuit 20 comprises a final part 20c corresponding to the final part 9c of the first lubrication circuit 9, directing oil to the gearbox 3. The second lubrication circuit 20 comprises a fourth part 20d via which it is possible to direct oil to the electric machine 6. The fourth part 20d of the second lubrication circuit 20 comprises an inlet arranged in a position between the electrical pump 21 and the valve member 23 in the intermediate part 20b of the second lubrication circuit 20. The fourth part 20d of the second lubrication circuit 20 comprises a valve member 25. The valve member 25 is settable in an open position in which it allows oil flow, via the fourth part 20d, to the electric machine 6 and in a closed position in which it prevents oil flow to the electric machine 6.

The lubrication system comprises a control unit 26 receiving information about a number of operating parameters. In this case, the control unit 26 receives information 27a about the temperature of the oil in the oil sump 10, information 27b about the temperature of the electric machine 6, information 27c about the required driving torque of the vehicle and information 27d about the speed of the counter shaft 14 in the gearbox 3. In view of these information 27a-d, the control unit 26 controls the operation of the mechanical pump 12, the electric pump 21 and the positioning of the valve members 23, 25. The control unit 26 controls the mechanical pump 12 by means of the coupling member 15. The control unit 26 initiates a movement of the coupling member 15 to a connected state and a disconnected state by means of an actuator 28. The control unit 26 controls the electric pump 12 by means of the electric motor 22. The valve members 23, 25 may be solenoid valves. During an initial operating period after cold start of the vehicle 1, the oil in the oil sump 10 has a low temperature and a high viscosity. During such an operating condition, it requires a relatively high pumping capacity to pump oil from the oil sump 10 to the gearbox 3. Only the mechanical pump 21 has such a high pump capacity. Consequently, when the control unit 26 receives information 27a indicating that the oil has a lower temperature than a specific temperature, it moves the coupling member 15 to the connected state by means of the actuator 28 such that the mechanical pump 12 is driven by the counter shaft 14 of the gearbox 3. Consequently, the mechanical pump 12 pumps oil from the oil sump 10, via the first lubrication circuit 9, to the gearbox 3. During an initial operating period after cold start of the vehicle 1, there is no demand to cool the electric machine 6.

After a certain period of operation, the control unit 26 receives information 27a indicating that the temperature of the oil has increased to a higher temperature than said specific temperature. The viscosity of the oil has now been reduced to a value at which it is possible for the electric pump 21 to pump oil from the oil sump 10. Since it is not possible to control the oil flow pumped by the mechanical pump 12 with a high accuracy, the losses of the mechanical pump 12 is higher than the losses of the electrical pump 21. Especially at operating condition when the counter shaft 14 is driven with a high speed at the same time as the driving torque of the vehicle 1 is low, the mechanical pump 12 usually pumps an excessive oil flow to the gearbox 3. In order to reduce the above mentioned pump losses, the control unit 26 is configured to use the electric pump 21 as much as possible and the mechanical pump 12 only during a start process when the oil has a high viscosity and during operating conditions when the electric pump 21 is not able to provide a required oil flow to the gearbox 3 and the electric machine 6.

Fig 2a shows an operating condition in which the control unit 26 has received information 27a indicating that the oil in the oil sump 10 has a higher temperature than said specific temperature and information 27b indicating that the electric machine 6 has a higher temperature than a threshold temperature at which the electric machine 6 has to be cooled. Consequently, it is possible to use the electric pump 21 but it must primarily be used to cool the electric machine 6. Further, the control unit 26 receives information 27c about the speed of the counter shaft 14 and thus the oil flow capacity of the mechanical pump 12. Finally, the control unit 26 receives information 27d about the driving torque of the vehicle 1 and thus the requested oil flow to the gearbox 3. In view of these information, the control unit 26 estimates, during this operating condition, that the mechanical pump 12 is able to supply the requested oil flow to the gearbox 3 and that the electric pump 21 is not able supply the requested oil flow to the gearbox 3 in addition to the oil flow to the electric machine 6. Consequently, the control unit 26 sets the valve member 23 in a closed position and the valve member 25 in an open position. Thereafter, the control unit 26 activates the electric pump 21 such that it supplies the requested oil flow to the electric machine 6. Furthermore, the control unit 26 activates the actuator 28 such that it moves the coupling member 15 to the connected state if it is not already in this state. This measure results in that mechanical pump 12 starts to pump an oil flow to the gearbox 3 which at least corresponds to the required oil flow.

Fig 2b shows an operating condition in which the control unit 26 has received information 27a indicating that the oil in the oil sump 10 has a higher temperature than said specific temperature and information 27b indicating that the electric machine 6 has a higher temperature than a threshold temperature at which the electric machine 6 has to be cooled. Consequently, it is possible to use the electric pump 21 but it must primarily be used to cool the electric machine 6. Further, the control unit 26 receives information 27c about the speed of the counter shaft 14 and thus the oil flow capacity of the mechanical pump. Furthermore, the control unit 26 receives information 27d about the driving torque of the vehicle 1 and thus the requested oil flow to the gearbox 3. In view of these information, the control unit 26 estimates, during this operating condition, that the mechanical pump 12 is not able to supply the requested oil flow to the gearbox 3 but that the mechanical pump 12 and the electric pump 21 together are able to supply the required oil flow to the gearbox 3. Consequently, the control unit 26 sets the valve member 23 in an open position and the valve member 25 in an open position. Thereafter, the control unit 26 activates the electric pump 21 such that it supplies the requested oil flow to the gearbox 3 and the electric machine 6.

Furthermore, the control unit 26 activates the actuator 28 such that it moves the coupling member 15 to the connected state if it is not already in this position. This measure results in that mechanical pump 12 starts to pump an oil flow to the gearbox 3 which together with the oil flow from the electric pump 21 corresponds to the required oil flow to the gearbox 3. Fig 2c shows an operating condition in which the control unit 26 has received information 27a indicating that the oil in the oil sump 10 has a higher temperature than said specific temperature and information 27b indicating that the electric machine 6 has a lower temperature than a threshold temperature at which the electric machine 6 has to be cooled. Thus, it is possible to use the electric pump 21 and it does not need to be used to cool the electric machine 6. Further, the control unit 26 receives information 27c about the speed of the counter shaft 14 and thus the oil flow capacity of the mechanical pump. Furthermore, the control unit 26 receives information 27d about the driving torque of the vehicle 1 and thus the requested oil flow to the gearbox 3. In view of these information, the control unit 26 estimates, during this operating condition, that the electric pump 21 are able to supply the required oil flow to the gearbox 3.

Consequently, the control unit 26 sets the valve member 23 in an open position and the valve member 25 in a closed position. Thereafter, the control unit 26 activates the electric pump 21 such that it supplies the requested oil flow to the gearbox 3.

Furthermore, the control unit 26 activates the actuator 28 such that it moves the coupling member 15 to the disconnected state. This measure results in that the driving force to the mechanical pump 12 via the mechanical transmission is ceased.

During the operating conditions shown in Fig. 2 and 3, the oil flow to the gearbox 3 is at least partly supplied by the electric pump 21. During these operating conditions, it possible to control the electric pump 21 such that the oil flow to the gearbox 3 corresponds to the requested oil flow with a high accuracy. During these operating conditions, it is possible to avoid an excessive oil flow to the gearbox 3 and avoid unnecessary energy losses.

The invention is in no way limited to the embodiment to which the drawing refers but may be varied freely within the scopes of the claims. The lubricant system can, for example, be used to supply lubricant to only a gearbox. Furthermore, the motor vehicle does not need to be a hybrid vehicle, it can be a vehicle driven by a single motor such as an electric machine or a combustion engine.

Claims

1. A lubrication system (8) for a gearbox (3) which is arranged in a motor vehicle (1), a first lubrication circuit (9) having an extension between a lubricant source (10) and the gearbox (3), a mechanical pump (12) configured to provide a lubricant flow through the first lubrication circuit (9) from the lubricant source (10) to the gearbox (3), and a mechanical transmission (13) configured to transfer a driving force from a component (14) in a powertrain of the vehicle (1) to the mechanical pump (12), characterized in that the lubrication system comprises a second lubrication circuit (20) having an extension between a lubricant source (10) and the gearbox (3), an electric pump (21) configured to provide a lubricant flow in the second lubrication circuit (20) from the lubricant source (10) to the gearbox (3), and a coupling member (15) of the mechanical transmission (13) which is movably arranged between a connected state in which it transfers a driving force from said component (14) to the mechanical pump (12) and a disconnected state in which it breaks the transfer of driving force from the said component (14) to the mechanical pump (12).

2. A lubrication system according to claim 1, characterized in that the lubrication system comprises a control unit (26) configured to control the activation of the mechanical pump (12) by means of said coupling member (15), to control the operation of the electric pump (21) by means of an electric motor (22), to receive information (27a-d) about at least one operating parameter and to control the operation of the mechanical (12) and the electric pump (21) in view of said information (27a- 27d).

3. A lubrication system according to claim 2, characterized in that the control unit (26) is configured to receive information (27a) about an operating parameter related to the viscosity of the lubricant in the lubricant storage (10), and to initiate operation of the mechanical pump (12) and no operation of the electric pump (21) during operating conditions when the viscosity of the lubricant is higher than a specific value.

4. A lubrication system according to claim 3, characterized in that the control unit (26) is configured to estimate if the electric pump (21) has capacity to deliver the required lubricant flow to the gearbox (3) during operation conditions when the viscosity of the lubricant is lower than said specific value.

5. A lubrication system according to claim 4, characterized in that the control unit (26) is configured to receive information (27d) about the driving torque of the vehicle and to estimate if the electric pump (21) has capacity to deliver the required lubricant flow to the gearbox (3) in view of this information (27d).

6. A lubrication system according to claim 4 or 5, characterized in that the control unit (26) is configured to initiate a movement of the coupling member (15) to the disconnected state when the electric pump (21) is estimated to be able to deliver the requested lubricant flow to the gearbox (3) and to control the electric pump (21) such that it delivers the requested lubricant flow to the gearbox (3).

7. A lubrication system according to claim 4 or 5, characterized in that the control unit (26) is configured to initiate a movement of the coupling member (15) to the connected state when the electric pump (21) is estimated not to be able to deliver the requested lubricant flow to the gearbox (3) and to control the operation of the electric pump (21) such that it only or together with the mechanical pump (12) deliver the requested lubricant flow to the gearbox (3).

8. A lubrication system according to any one of the preceding claims, characterized in that the second lubrication circuit also has an extension between the lubricant source

(10) and a further object (6) to be lubricated or cooled during operation of the vehicle (1).

9. A lubrication system according to claim 8, characterized in that the further object is an electric machine (6).

10. A lubrication system according to claim 8 or 9, characterized in that the second lubrication circuit (20) comprises a valve arrangement (23, 25) by which it possible to direct the lubricant flow to the gearbox (3) and/or the further object (6).

11. A lubrication system according to any one of the preceding claims, characterized in that the first lubrication circuit (9) and the second lubrication circuit (20) receive lubricant from a common lubricant source (10).

12. A lubrication system according to any one of the preceding claims, characterized in that the first lubrication circuit (9) and the second lubrication circuit (20) comprises a common initial part (9a, 20a) in which lubricant is sucked from the lubricant sump (10).

13. A lubrication system according to any one of the preceding claims, characterized in that the first lubrication circuit (9) comprises a part (9b) comprising the mechanical pump (12) and a first check valve (19), that the second lubrication circuit (20) comprises a part (20b) comprising the electric pump (21) and a second check valve (24), and that said parts (9b, 20b) of the first lubrication circuit and the second lubrication circuit (20) are arranged in parallel.

14. A lubrication system according to any one of the preceding claims, characterized in that the first lubrication circuit (9) and the second lubrication circuit (20) comprises a common final part (9a, 20a) delivering lubricant to the gearbox (3).

15. A vehicle comprising a lubrication system according to any of the preceding claims