One example of such a machine assembly is a turbo assembly in a vehicle driven by a combustion engine. The cooling of such a turbo assembly is provided by an oil pump driven by the combustion engine and conveying oil to the turbo assembly. This means that when the engine is shut off also the oil transported by the oil pump stops circulating in the cooling circuit. Thereby, the sensitive parts of the turbo assembly, in the form of bearings and sealings, are not any longer cooled and lubricated. Problems arise in the first place when the engine is shut off after having been loaded. A turbo assembly may thereby have a number of revolution of 75 000 to 120 000 rpm. A turbo assembly includes normally a compressor, which compresses an inlet gas to the engine, and a turbine, which is driven by the exhaust gases from the engine, wherein the compressor and the turbine have a common axis of rotation with bearings and sealings, which are extremely sensitive to high temperatures. The compressor and the turbine may during operation be subjected to very high temperatures. For instance, the exhaust gases of the combustion engine, which drives the turbine, may have a temperature of above 700°. When the engine is shut off, the cooling and the lubrication of the turbine assembly shaft with the bearings and sealings thus disappear, and the turbine shaft continues to rotate during a period of time, which may be 15-20 seconds without any supply of oil. The heat, which is stored and which arises in the turbine and the compressor, is thereby conducted to said bearings and sealings inter alia, which rapidly

may be heated to unallowably high temperatures. The oii is usually conveyed through 3 to 4 mm thick channels to the bearings of the turbo assembly and in case of overheating of said bearings, stagnant oil in the channels may cokify or oxidise, and thereby clog said channels. In case of such clogged oil channels the turbo will break down.

Trials have been made to solve said problem by using water-cooled bearing housings. The purpose of the water is here to stabilise the temperature in the turbo assembly. A disadvantage of such bearing housings is that the water may boil at extremely high loads.

Another method is to use a timer of a motor vehicle. Thereby, the engine continues to run from 15 seconds to 2 minutes after the driver has shut off the engine. This is not suitable in any circumstances, inter alia when a motor vehicle with a turbo assembly is parked in a garage.

Also within other fields, there is a problem of overheating of bearings and sealings of machine assemblies. Such machine assemblies may be compressor assemblies or hydraulic units, which are used inter alia within the air and marine sector. Turbo assemblies are also used to a large extent in racing vehicles of different types.

FR 2 584 778 discloses a device for cooling the bearings of a turbo compressor, which is associated with a combustion engine. The device includes an additional container, which is arranged to be filled with oit during the operation of the combustion engine and to build up a pressure in the container by means of which the oil, which is collecte in the container, may be discharged to the bearings after the interruption of the turbo compressor and the combustion engine. Possibly, the air cushion which is present in the container, is separated from the oil by means of a membrane.

Nothing is mentioned in this document about a completely emptying of the container when the oil has been discharged after the interruption of the turbo compressor.

CH 652 453 discloses a device, which ensures lubrication of the bearings and the sealings of a turbo assembly after interruption of the combustion engine associated with the turbo assembly. This lubrication afterwards is obtained by means of an electric pump, which is provided in an additional oil conduit connected to an additional oil container. This known device thus has a complicated construction.

SUMMARY OF THE INVENTION The object of the present invention is to provide a device of the initially defined type, which prevents sensitive parts of a machine assembly from being subjected to powerful heating after interruption of the engine.

This object is obtained by a device of the initially defined type, which includes the features in the characterising portion of claim 1.

By such second means, a continued cooling of said sensitive parts may take place during a suitable period of time after the interruption of the engine so that overheating of said parts is avoided.

According to a preferred embodiment of the present invention, the device includes a cooling circuit, which has such an extension that a cooling medium flowing in the cooling circuit is arranged to be in cooling contact with said parts of the machine assembly. Thereby, it is possible for the cooling medium to flow via said sensitive parts of the machine assembly also after the engine is shut off.

Advantageously, said second means includes a container, which is arranged to receive and store said cooling medium during the state of operation of the engine. By such a container, a suitable quantity of cooling medium may be stored at a suitable location in the vehicle and be used to cool sensitive parts of the machine assembly during a period of time when the engine is shut off. The container must not be mounted to the engine since the cooling medium in this case may form foam due to vibrations of the engine. Such a period

time may be about 5 minutes. For cooling of said sensitive parts, said second means may include a first connection, which is arranged to permit the cooling medium to flow from the container to the machine assembly during said period of time. Bu such a connection, the cooling medium may, when the engine is shut off, be conveyed to the cooling circuit, whereafter it may flow via said sensitive parts of the machine assembly, and thereby cool the latter.

According to a further embodiment of the invention, the container and the first connection are designed in such a way that they permit the container to be substantially completely emptied during said period of time. In such a way, breaking down of the cooling medium may be prevented. Thereby, the cooling medium in the container may be arranged to have a higher pressure than the pressure of the cooling medium in the cooling circuit during said period of time. By means of this raised pressure, the cooling medium may be fed to be components in question of the machine assembly, and the emptying of the container is ensured.

According to a further embodiment of the invention, the container is located at a higher level than the machine assembly. In such a way, emptying of the container by means of the gravitation force is facilitated, i. e. no oil residuals remain in the container when the machine assembly is not used.

According to a further embodiment of the invention, a pump is arranged to force the cooling medium to the container during the active state of operation of the engine. The pump may be arranged to build up a pressure, which is higher than the atmospheric pressure, in the container. Advantageously, the container is arranged in such a way that it permits the formation of a gas cushion in the container above the cooling medium collecte in the container, which gas cushion ensures a successive discharge of the cooling medium out of the container so that it is substantially completely emptied.

According to another preferred embodiment of the invention, a collecting member is arranged to collect the cooling medium after it has passed the machine assembly. Such a collecting member may be a storing container for the cooling medium, which stores the cooling medium when the machine assembly is not in use. The pump may be arranged to force the cooling medium from said collecting member, via a second connection, to the container during the active state of operation of the engine. When the engine is started, the cooling medium may thereby by means of said pump be brought to flow to the container from the collecting member until it is filled or has received a cooling medium quantity which is suitable for the successive cooling of the machine assembly when the engine is shut off. Advantageously, said second connection includes a control unit, which is arranged to prevent a return flow of cooling medium in said second connection. Thereby, all cooling medium, which has been stored in the container, is conveyed via the machine assembly when the engine is shut off. Such a contol unit may be a one-way valve. Advantageously, said second connection includes a first portion, which extends between the pump and the control unit, wherein said first connection includes a second portion, which extends between the control unit and the machine assembly, and said first and second connections include a common third connection, which extends between the control unit and the container. Thereby, the container gets a connection to the ordinary cooling circuit by the third portion and the control unit. The cooling medium in said third portion may thus flow both to and from the container.

According to another preferred embodiment of the invention, a control unit is arranged to guide the cooling medium flow from the pump to both the container and the machine assembly during an initial period of the active state of operation of the engine. During this period, the cooling medium is thus conveyed both to the machine assembly for cooling and lubricating its sensitive parts and to the container. This guiding of the cooling medium continues until the container is filled or has received a pre-determined quantity of cooling medium corresponding to a determined pressure in the

container. Thereafter, the control unit conveys the cooling medium merely to the machine assembly and the cooling of the machine assembly thus continues during the remaining part of the active state of operation of the engine in a conventional manner. When the engine then is shut off, the control unit is arranged to guide the cooling medium stored in the container to the machine assembly during said period of time. That is to say, substantially immediately after the interruption of the active state of operation of the engine, the control unit guides the cooling medium stored in the container to the machine assembly in order to enable the cooling of its sensitive parts. Such a cooling medium may include oil, which has the advantage that it may both cool and lubricate the machine assembly.

According to an advantageous embodiment, the engine includes a combustion engine for driving the machine assembly. The machine assembly may include a compressor assembly, which is a machine assembly frequently subjected to large temperature loads. Such a compressor assembly may include a compressor, which is arranged to compress an inlet gas to a combustion engine, and a turbine, which by means of the exhaust gases of the combustion engine drives the compressor. Such a compressor assembly may be a turbo assembly in a motor vehicle.

According to another preferred embodiment of the invention, said sensitive parts of the machine assembly include portions, which are necessary for permitting rotation of the machine assembly, such as bearings and/or sealings. In the first place, it is bearings and sealings which are sensitive to heating and thus necessary to be cooled in a machine assembly immediately after the interruption of the active state of operation of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS In the following a preferred embodiment of the invention is described as an example and with reference to the drawings attached, in which: Fig 1 discloses schematically a device according to the present invention for a turbo assembly of a vehicle, Fig 2 discloses an alternative embodiment of a control unit according to the present invention, and Fig 3 discloses schematically how the temperature may vary for a shaft bearing of a turbo assembly with and without the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig 1 discloses schematically a device according to the present invention applied to a motor vehicle, which is driven by a combustion engine 1 and a turbo assembly 2, which is connected when additional power is required. The turbo assembly 2 includes a turbine 3, which is driven by means of the exhaust gases of the combustion engine 1, and a compressor 4, which is arranged to compress an inlet gas to the combustion engine 1. The turbine 3 and the compressor 4 include a common rotatable shaft 5. During operation of the vehicle, sensitive parts, such as bearings and sealings, of the turbo assembly 2 are cooled by conveying oil from the oil pan 6 of the engine by means of an oil pump 7 in a cooling circuit 8. The oil flows thereby through channels to the shaft 5 for cooling and lubricating its bearings and sealings. After the oil has passed the turbo assembly 2, it is conveyed back to the oil pan 6 of the engine 1. Such a cooling circuit 8 is used in a conventional cooling of a turbo assembly 2 of a motor vehicle.

A disadvantage of such a conventional cooling of the turbo assembly 2 is that the operation of the oil pump 7 and thereby the

cooling of the turbo assembly 2 ceases when the combustion engine 1 is shut off. In the cases when the turbo assembly 2 is subjected to high loads, the turbine 2 may have a very high number of revolutions and a high temperature. The exhaust gases, which drives the turbine, may have a temperature above 700°C. The turbine thus has a significantly higher temperature than the bearings and sealings of the cooled shaft 5 of the turbo assembly 2 during operation of the combustion engine 1. When the combustion engine 1 is shut off, the heat energy stored in the turbine 3 is distributed to the shaft 5, which now is not cooled and thus quickly heated. Also the compressor 4 has normally a higher temperature than the bearings of the shaft 5 when the combustion engine 1 is shut off. Also this stored heat energy is distributed to the shaft 5.

The bearings and the sealings of the shaft 5 are thus heated powerfully and in addition remaining oil in the oil channels may thereby be heated to such an extent that it is cokified so that the channels, which has a thickness of 3 to 4 mm, in a worse case may be clogged. Clogged oil channels means that the turbo assembly during the following operation will break down due to lack of lubrication.

The present invention according to the first embodiment in Fig 1 includes the provision of a control unit 9, here in the form of a one- way valve 10, in the conventional cooling circuit 8. The oil in the cooling circuit 8 may thereby be conveyed to a container 11 which is arranged to receive and store oil during the state of operation of the combustion engine 1. When the combustion engine 1 is started, it drives the oil pump 7, which pumps oil from the oil pan 6. The oil is conveyed in a first portion 12 of the cooling circuit 8 to the control unit 9. The control unit 9, which here includes the one-way valve 10, let the oil through. Thereafter, the oil is conveyed partly via a second portion 13 of the cooling circuit 8 to the turbo assembly 2 for cooling and lubrication thereof and partly via a third portion 14 of the cooling circuit 8 to the container 11. Said distribution of the oil in control unit 9 continues until the container 11 is substantially filled with oil. This takes place when the oil in the container 8 has substantially the same pressure as the oil in the second portion 13

of the cooling circuit 8. The pressure in the container 11, will then exceed the atmospheric pressure. The gas, which is present in the container 11 will form a compressed gas cushion 11 a above the oil which is collecte in the container 11. Thus, the container 11 may not receive more oil and the oil is then in the following only conveyed via the second portion 13 to the turbo assembly 2. After the turbo assembly 2 the oil is conveyed back to the oil pan 6 through a forth portion 15 of the cooling circuit 8. This circulation of the cooling medium in the cooling circuit 8 for cooling and lubricating the turbo assembly 2 continues until the combustion engine 1 is shut off. When the combustion engine 1 has been shut off, also the pump 7 stops, which then ceases to circulate oil through the cooling circuit 8 and the oil pressure in the cooling circuit 8 decreases. The container 11 is here mounted at a higher level than the turbo assembly 2 and it has now a higher oil pressure than the second portion 13 of the cooling circuit 8. Due to the pressure, the oil in the container 11 will flow down through the third portion 14 to the control unit 9. Since the control unit 9 includes a one-way valve 10, the oil may thus only be conveyed further via the second portion 13 of the cooling circuit 8 to the turbo assembly 2.

The oil collected in the container 11 is thus forced by means of the gravitation force and the overpressure in the container 11 down via the third portion and the second portion 13 of the cooling circuit 8 to the turbo assembly 2, where it during a period of time of for instance 3-5 minutes after the combustion engine 1 has been shut off flows via and cools the bearings and the sealings of the turbo assembly 2. Thereby, these parts are efficiently prevented from being overheated and the risk of stagnant oil forming coke in the oil channels in the proximity of the shaft 5 is substantially reduced.

The oil flows after the turbo assembly 2 via the fourth portion 15 of the cooling circuit 8 to the oil pan 6 of the combustion engine 1.

When the container 11 has been emptied oil has been collecte in the conduit portion 14a immediately above the one-way valve 10, i. e. between the one-way valve 10 and the branching to the second portion 13. This oil quantity will be supplie to the turbo assembly 2 immediately after the combustion engine and the pump 7 have been

started. Thereby, sufficient cooling and lubricating of the turbo assembly 2 are ensured in an initial period of operation.

Fig 2 discloses another embodiment of the control unit 9. The control unit 9 here includes a control valve 10 with a ball 16 which by means of a spring 17 may abut a valve seat 18. In the position of the ball 16 disclosed in Fig 2, the combustion engine 1, and thus also the pump 7, are closed and possible remaining oil in the container 11 may flow via the third portion 14 and the second portion 13 to the turbo assembly 2. In the state of operation of the combustion engine 1, oil is conveyed through the first portion 12, wherein the ball 16 is pressed back and oil may flow to the second portion 13 and the third portion 14. When the container 11 is filled with oil, the oil flows only from the first portion 12 to the second portion 13.

Fig 3 disclosed schematically, as an example, how the temperature in the shaft bearing of the turbo assembly 2 may vary with and without the present invention. At point A in the diagram, the combustion engine is started and the temperature of the bearing increases to a level immediately above 100°C. In the state of operation of the combustion engine, oil is conveyed through the turbo assembly 2 and cools the bearing of the shaft 5, which thereby will have a relatively constant temperature. After 20 minutes of operation, at point B, the combustion engine 1 is shut off. By the present invention the cooling of the shaft 5 continues during a period of time by conveying the oil stored in the container 11 through channels to the bearing of the shaft 5 for lubricating and cooling thereof. Since the oil flow here normally is somewhat less that during a normal state of operation, a slight increase of the temperature of the bearing may take place, which is disclosed by the curve C. On the other hand, if the turbo assembly 2 is not equipped with a cooling according to the present invention and if the turbo assembly is subjected to a large load before the combustion engine 1 is shut off, the turbine 3 and the compressor 4 of the turbo assembly have very high temperatures when the combustion engine 1 is shut off. Since the cooling of the bearing of

the shaft 5 ceases when the combustion engine 1 is shut off, the heat energy stored in the turbine 3 and the compressor 4 is distributed to said bearing so that these are heated powerfully. One example of how the temperature development of the bearing of the shaft 5 may be is disclosed by the curve D. How much the shaft 5 is heated thus depends on the load of the turbo assembly 2 before the combustion engine 1 has been shut off. When the bearing of the shaft 5 is overheated, there is a risk that stagnant oil in the channels at the bearings is cokified, wherein the channels may be clogged. At a successive operation the bearings of the shaft 5 will thus not be lubricated and the turbo assembly 2 will thus break down.

The present invention is however not in any way limited to the embodiments described above but may be modified and varied freely within the scope of the claims. The control unit 9 does not need to be a one-way valve. It may for instance include sensors, which detect when the container has received a sufficient oil level, and switch members for controlling and distributing the oil between the machine assembly 2 and the container 11. The invention may be applied to most machine assemblies which are dependent on cooling. Such machine assemblies may be associated with different form of motor vehicles, such as for instance cars, boats, aircrafts, crawler type vehicles and different types of construction machineries, but also be provided in stationary units and machines.