Patent Application
20150345365
The present invention relates to an arrangement and procedure for pressurizing a cooling system to cool an internal combustion engine in a vehicle according to the preamble of patent claims 1 and 11.
The coolant circulating in a cooling system for cooling an internal combustion engine generally has an operating temperature of some 80-100° C. When cold-started, the coolant in the internal combustion engine is at a considerably lower temperature. However, the coolant occupies a greater volume in the cooling system when warm than when cold. In order to allow the volume of the coolant to change in an operational state, the cooling system includes an expansion tank. The expansion tank is made up of an enclosed space containing air and coolant. The expansion tank is fitted with a filler cap and a pressure relief valve which limits the pressure in the latter as well as a non-return valve which prevents underpressure occurring in the tank. As the coolant expands during heating, the pressure in the tank rises. However, the pressure cannot exceed a maximum permitted value defined by the opening temperature of the pressure relief valve.
The expansion tank is normally connected to other parts of the cooling system via a vertical pipe called a static line. The height of the expansion tank is thus positioned at a certain level above the coolant pump circulating the coolant in the cooling system. By virtue of such a design a column of coolant is thus formed, extending from the coolant pump up to an expansion tank, thereby creating overpressure at the point of the coolant pump intake, preventing the occurrence of cavitation whenever the coolant pump is started.
However, the coolant pump's tendency to cavitate increases with the temperature of the coolant. When the coolant has reached operating temperature, the overpressure generated by the static line column is not normally sufficient to eliminate the risk of cavitation in the coolant pump. The coolant expands when heated up, however, resulting in the creation of overpressure in the cooling system. The volume of the expansion tank occupied by air and coolant is dimensioned such that suitable overpressure arises when the coolant expands. Together, this overpressure and the static line create overpressure at the coolant pump intake, ensuring that the coolant pump does not cavitate when the coolant is hot.
However, a cooling system is not altogether tight; rather, there will invariably be minor leakage of both air and coolant from the cooling system when the internal combustion engine is running The fluid leakage occurs principally in the gland packing on the coolant pump and the air leakage principally in the non-return valve of the expansion tank. The leakage lowers the pressure level in the cooling system when the internal combustion engine is running. The leakage is so slight, however, that the pressure level around the vehicle is lowered only negligibly when the vehicle is operating normally with intervening periods when the coolant has a chance to cool down to the ambient temperature.
Once the coolant cools down after a period of operation, it resumes its original volume, thereby creating underpressure in the cooling system equivalent to the leakage in the cooling system during the period of operation. The non-return valve opens and subsequently adjusts this leakage. A transport vehicle can essentially run around the clock without intervening periods during which the coolant cools down. Even if the air and coolant leakage is very slight, the leakage during a long period of non-stop operation can lower the overpressure to such a low level as to create a risk of cavitation damage to the coolant pump.
DE 10 2007 058 575 shows a cooling system for an internal combustion engine in which the pressure in the cooling system can be regulated while the internal combustion engine is running In this case a sophisticated pressure regulation system is used to regulate the pressure in the cooling system to a desired level, knowing the coolant's temperature and the operating state of the internal combustion engine. Among other things, the pressure can be raised to an extra-high level by quickly turning off a hot internal combustion engine in order to avoid steam forming in the internal combustion engine block. As a result, the expansion tank can be made smaller, as it requires no extra volume to receive the copious amount of steam otherwise formed when a hot internal combustion engine is turned off quickly.
The aim of the present invention is to provide an arrangement that prevents cavitation damage to a coolant pump even if the cooling system is primarily operated continuously for long periods. Another aim is to provide an arrangement with a simple design incorporating components that can be applied to an existing cooling system with relative ease.
These aims are achieved with the type of cooling system mentioned by way of introduction, characterized by the distinctive features set out in the characterizing clause of patent claim 1. When operational, a slight amount of air and fluid leakage thus occurs in the cooling system. Such leakage results in a gradual reduction in the overpressure in the cooling system as the cooling system operates continuously with the hot coolant. It is possible to estimate this leakage with a relatively high degree of accuracy, however. In accordance with the invention an air flow is continuously supplied to the cooling system whenever the internal combustion engine is running The volume of air supplied is such as always to be at least equal to the estimated leakage from the cooling system. In this respect a designated overpressure can be maintained in the cooling system, irrespective of how long the internal combustion engine continues running for. The size of the designated overpressure in the cooling system is such that, together with the static line, it prevents cavitation arising in the coolant pump. Thus, in order to create this arrangement, components only need be added that continuously supply compressed air to the cooling system in a suitable quantity. Such components can be relatively simple in design and can also be beneficially applied to an existing cooling system. The amount of compressed air that needs to be supplied is so small as to be negligible compared to the amount of compressed air consumed by other components in, say, a heavy goods vehicle (HGV).
According to an embodiment of the invention, said compressed air-entraining agent is geared to supplying a continuous air flow of a size that exceeds the air flow estimated to escape from the cooling system. Rather more air should preferably be supplied to the cooling system than escapes. Essentially, all conventional expansion tanks contain a pressure relief valve. In this case the pressure in the cooling system will rise until it reaches the overpressure defined by the pressure relief valve. When the opening pressure on the pressure relief valve is reached, it opens and air escapes, reducing the pressure in the cooling system. The pressure relief valve thus ensures that the pressure level does not exceed a maximum permitted level. In the process the pressure in the cooling system is maintained at a basically constantly high level, which is defined by the pressure relief valve's opening pressure as long as the internal combustion engine is activated. Thus, the pressure relief valve releases the difference here between the amount of air supplied in the cooling system and the leakage from the cooling system.
The compressed air supply should preferably exceed the estimated leakage by a relatively small margin. Too great a flow of compressed air to the cooling system results in very frequent opening of the pressure relief valve and unduly great consumption of compressed air. Although the leakage can be estimated with relatively great accuracy, there still needs to be a certain margin for error so that the influx of compressed air to the cooling system is certain to equal the actual leakage. The leakage in the cooling system is not constant but related to the size of the overpressure in the cooling system. Maximum leakage occurs at the maximum permitted overpressure thus prevalent in the cooling system immediately prior to the pressure relief valve opening. It is an advantage if the flow of compressed air supplied is basically constant and equal to the maximum leakage. Thus the pressure rises relatively quickly in the cooling system when there is low overpressure and hence little leakage, whereas the pressure increases considerably more slowly when there is greater overpressure and hence greater leakage.
According to an embodiment of the invention, said pressurizing agent includes a compressed air source and a compressed air line, which conveys compressed air from the compressed air source to the cooling system. Heavy vehicles generally have access to compressed air at all times, which can beneficially be exploited to this end. Said compressed air source can be made up of an accumulator tank that stores compressed air for an existing in-vehicle compressed air system. When a vehicle is in operation, predetermined, relatively high air pressure is usually maintained in an accumulator tank by a compressor that runs off the internal combustion engine. Such accumulator tanks are relatively tight so that compressed air can be stored at relatively great overpressure for long periods of time even when the vehicle is not operational. The accumulator tank, for example, can store compressed air for an existing compressed air system for the vehicle's brakes.
According to an embodiment of the invention, said compressed air line contains a throttle device with regular throttling that defines the air flow to the cooling system.
Most compressed air sources in a vehicle store compressed air at considerably higher pressure than the pressure required to pressurize the cooling system. Knowing the pressure in the compressed air source and in the cooling system, the throttle device can be dimensioned so as to convey the compressed air from the accumulator tank to the cooling system in the quantity desired. If the compressed air source is at a constant high pressure in relation to the pressure in the cooling system, the air flow to the cooling system obtained will basically be constant, since the pressure changes in the cooling system are relatively slight.
According to an embodiment of the invention, the compressed air line includes a valve arranged in said line which is set to the open position when the internal combustion engine is started and to the closed position when the internal combustion engine is switched off. Thus the compressed air supply to the cooling system will start as soon as the internal combustion engine starts and will stop as soon as the internal combustion engine is switched off. Said valve can include the throttle device. Such a valve can be designed so as to reduce the compressed air pressure when in the open position and hence reduce the air flow to the cooling system to a desired level. In this case, when in the open position, the valve has a relatively narrow flow duct for the compressed air. Alternatively, the throttle device and the valve can comprise separate components in the compressed air line.
According to an embodiment of the invention, said pressurizing agent can include a control unit geared to receiving information that indicates when the internal combustion engine is turned on and switched off, and to controlling said valve with the aid of this information. Such a control unit can constitute part of an engine control unit or a separate control unit receiving information from, say, a motor control unit. The valve can beneficially be an electrically controlled valve such as a solenoid valve. With the aid of such a valve the control unit can simply and quickly open and shut off the supply of compressed air to the cooling system.
In accordance with another embodiment of the invention, the compressed air line conveys compressed air to the expansion tank in the cooling system. Since an expansion tank already contains air in an upper area, it is expedient to supply the compressed air to this area of the expansion tank. The compressed air supplied raises the air pressure in the area above the coolant in the expansion tank. The air pressure thus acts with compressive force on the coolant in the expansion tank so that it takes on corresponding pressure. The pressure of the coolant in the expansion tank is transferred to the coolant in other parts of the cooling system. Alternatively, the air can be supplied to a static line or some other suitable point in the cooling system. It is an advantage if the expansion tank contains the pressure relief valve. The expansion tank can also contain a safety valve. A safety valve is normally arranged in the expansion tank cover. It can open and help lower the pressure in the tank if the pressure relief valve does not have the capacity to lower the pressure in a particular way desired.
In accordance with another preferred embodiment of the invention the expansion tank contains a non-return valve which ensures that the pressure in the expansion tank does not fall below the pressure of the ambient air. Such a non-return valve is generally an existing component of an expansion tank. The non-return valve opens if the pressure in the expansion tank falls below the pressure of the surroundings. The presence of such a non-return valve guarantees that the pressure in the expansion tank presents at least the air pressure of the surroundings after the coolant in the cooling system has cooled down after operation.
The aim stated by way of introduction is also achieved with the procedure in accordance with patent claim 11.
By way of example, a preferred embodiment of the invention is described below, with reference to the drawing attached, in which:
The volume of the coolant in the cooling system varies with the temperature of the coolant. For that reason the cooling system contains an expansion tank 12 with an internal space that accommodates the varying volume of the coolant. In this case the expansion tank 12 is connected via a line 13 to the line 7 in a position on the suction side of the coolant pump 3. In a top section the expansion tank 12 contains a removable cover 14 to allow the cooling system to be replenished with coolant. The cover 14 contains a schematically displayed pressure relief valve 15. The pressure relief valve 15 opens when the pressure in the expansion tank 12 exceeds a maximum acceptable pressure in the cooling system. The pressure relief valve 15, for example, can open at an overpressure of 0.9 bar. The expansion tank 12 also contains a non-return valve 16. The non-return valve 16 ensures that the pressure in the expansion tank 12 is at least equal to the pressure of the ambient air. It thus opens and lets in air if underpressure arises in the expansion tank 12 in relation to the surroundings.
In this case the vehicle 1 is provided with a compressed air source in the form of an accumulator tank 17. The accumulator tank 17 contains compressed air, which is used in a compressed air system to activate the vehicle's compressed air brakes. When the internal combustion engine 2 is in operation, a brake compressor maintains predetermined, relatively high air pressure in the accumulator tank 17. Given that an accumulator tank 17 has a very tight structure, the air pressure in the accumulator tank can be kept relatively constant for a long time after the vehicle's internal combustion engine 2 is switched off. As a result, the compressed air brakes can be utilized as soon as the vehicle 1 is to be used. The accumulator tank 17 is connected with the expansion tank 12 via a compressed air line 18. The compressed air line 18 contains an electronically controlled valve 19 such as a solenoid valve, which can be adjusted to a closed position, in which it prevents compressed air being conveyed from the accumulator tank 17 to the expansion tank 12, and to an open position, in which it allows compressed air to be conveyed from the accumulator tank 17 to the expansion tank 12.
The compressed air line 18 also contains a throttle device 20 which provides regular throttling of the compressed air conveyed from the accumulator tank 17 to the expansion tank 12. The air ducted into the expansion tank 12 thus presents considerably lower pressure than the air in the accumulator tank 17. In order to throttle the air, the throttle device 20 contains a flow duct having a small cross-sectional area, thereby also providing a relatively small air flow from the accumulator tank 17 to the expansion tank 12. Knowing the pressure in the accumulator tank and the pressure in the expansion tank 12, the regular throttle device 20 can be dimensioned so as to receive the desired air flow from the accumulator tank 17 to the expansion tank 12 with great precision. The valve 19 and the throttle device 20 make up separate units in this case. Alternatively, the valve 19 and the throttle device 20 can be designed as one component in the form of a throttle valve, which in the open position provides a flow duct to give suitable throttling of the air conveyed from the accumulator tank 17 to the expansion tank 12.
The cooling system contains a control unit 21. The control unit 21 is set to receive information indicating when the internal combustion engine 2 starts and when it is switched off. In this case the control unit 21 receives information from a motor control unit 22. The control unit 21 puts the valve body 19 into the open position when the internal combustion engine 2 starts and into the closed position when the internal combustion engine 2 is switched off. The valve body 19 is always in the open position when the internal combustion engine is activated and in the closed position when not activated. When the control unit 21 receives information indicating that the internal combustion engine 2 has been activated, the valve body 19 then opens. In so doing, a continuous flow of compressed air is conveyed from the accumulator tank 17 to the expansion tank 12 whenever the internal combustion engine 2 is activated.
The coolant receives overpressure in the line 7 on the suction side of the coolant pump 3, which is defined by the height of the static line column and the overpressure in the expansion tank 17. When the coolant is cold, the static line column generates adequate overpressure on the suction side of the coolant pump 3 to prevent cavitation. When the internal combustion engine is in operation, the coolant circulating in the cooling system is heated up. Since the coolant has been heated, the coolant pump 3 has an increased tendency to cavitate. However, hot coolant absorbs a greater volume than cold coolant, creating overpressure in the cooling system when the coolant is heated up. Together, this overpressure and the static line create sufficiently high pressure to prevent cavitation in the coolant pump 3 when the coolant is hot. A cooling system is not completely tight. A certain amount of fluid leakage occurs, for instance, at a gland packing on the coolant pump 3 and some air leakage occurs, for instance, at the non-return valve 16. The leakage is reduced by the overpressure in the cooling system when the internal combustion engine is in operation. Particularly if the vehicle is operated non-stop for a very long period, there is a risk that the overpressure will be substantially reduced owing to said leakage. There is also a risk that the overpressure in the cooling system will be reduced by the cover on the cooling system being opened when the coolant is hot.
The air and coolant leakage experienced in a cooling system can be estimated with relatively good accuracy. For example, the non-return valve 16 contains particulars of maximum leakage. The control unit 21 thus receives information from the engine unit 22 when the internal combustion engine 2 starts up. The control unit thereby places the valve 19 in the open position. In as much as the pressure in the accumulator tank 17 is higher than the pressure in the expansion tank 12, an air flow is obtained from the accumulator tank 17, via the compressed air line 18, to the expansion tank 12. The throttle device 20 and the pressure differential between the accumulator tank 17 and the expansion tank define the size of the air flow. The throttle device 20 has been dimensioned so that the size of the air flow supplied is such as to always be at least equal to the leakage occurring from the cooling system. As such, a designated overpressure in the cooling system can be maintained regardless of how long the internal combustion engine 2 continues to operate. This overpressure, with the static line, guarantees that pressure is received at the intake to the coolant pump, preventing cavitation.
The dimensions of the throttle device 20 are advantageous in that it supplies a continuous flow of air to the expansion tank 17 of a size that exceeds the estimated leakage from the cooling system. The pressure in the cooling system will thus increase until it reaches the maximum permitted overpressure defined by the pressure relief valve 15. When the opening pressure on the pressure relief valve 15 is reached, it will open and release air, reducing the pressure in the expansion tank 12. The pressure relief valve 15 thus ensures that the pressure level does not exceed a maximum permitted level in the cooling system. The pressure in the cooling system is thereby maintained at a basically constantly high level as long as the internal combustion engine is activated. This overpressure, together with the static line, guarantees that sufficiently great pressure is obtained at the coolant pump intake so as to avoid cavitation.
The compressed air supply should preferably exceed the estimated leakage by a relatively small margin. Too great a flow of compressed air to the cooling system will result in very frequent opening of the pressure relief valve 15 and unduly great compressed air consumption. Although the leakage at the gland packing on the coolant pump and the non-return valve 16 can be estimated with relatively high accuracy, there must nevertheless be a certain margin for error so that the inflow of compressed air to the cooling system is certain to be at least equal to the actual leakage. The leakage in the cooling system is not constant but related to the size of the overpressure in the cooling system. Maximum leakage occurs at the maximum permitted overpressure thus prevalent in the cooling system immediately prior to the pressure relief valve 15 opening. It is an advantage if the flow of compressed air supplied is basically constant and equal to the maximum leakage. The pressure in the cooling system will thus increase relatively quickly, as there is low overpressure and little leakage, whereas the pressure rises considerably more slowly when there is higher pressure and greater leakage.
A pressure relief valve 16 is found in essentially all conventional expansion tanks. A compressed air source 17 is generally found in at least a heavy vehicles 1. In order to supply compressed air to the expansion tank 12, therefore, only a compressed air line 18, a valve 19, a throttle device 20 and a control unit 21 are needed. These components can also be beneficially applied to an existing vehicle without any major problems. The quantity of compressed air that needs to be supplied is so small as to be negligible compared with the quantity of compressed air consumed by other components in an heavy vehicle 1.
The invention is in no way confined to the embodiment described in the drawing but can be varied at will within the parameters of the patent claim.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1251396-6 | Dec 2012 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2013/051357 | 11/19/2013 | WO | 00 |
