SE535167C2 - Arrangement for supply of a medium in an exhaust gas flow - Google Patents

Abstract

An arrangement for supplying an agent in an exhaust gas flow from an internal combustion engine comprises, inter alia, a pump (15) intended to generate a pressurized flow of medium from a tank (12) through the line (13) to the dosing module (14). Non-injection medium is led back to the tank via a return line (16). The medium is also used to arrange the dosing module (14) in the exhaust gas outlet. To ensure cooling even after the pump (15) has been stopped, the line comprises an accumulator tank (17), which medium is led during the operation of the pump and which medium is led back to the line (13) after the pump is switched off in order to maintain a cooling fl deserted dosing module (14). To enable the flow to be maintained for a relatively long time after the pump has been switched off, the line to the accumulator tank comprises a valve which makes it possible to vary the cross-sectional area of the connecting line (18). (Fig. 1)

Description

535 'E57 2 However, a problem arises when the engine is switched off because the temperature in the exhaust system will remain high for a considerable time after the engine has been switched off. The supply of reducing agent to the dosing module is terminated when the motor is switched off, which means that fl the fate and thereby the cooling of the dosing module ceases. The lack of cooling of the dosing module can then result in damage to the dosing module. The high temperature in the dosing module also means that the stationary reducing agent in the dosing module evaporates, which can give precipitates which clog the dosing module and which reduce the function on restart.

To prevent these damages to the dosing module, there are currently several different solutions, each with different shortcomings. A solution to the problems is obtained by allowing the pump to continue circulating the reducing agent through the dosing module so that the necessary cooling effect is maintained even for a certain time after the motor has been switched off. This means, in addition to the pump giving rise to a lot of noise, that power from a battery will be consumed, which can be a problem as the power supply in batteries is limited. Another complicating factor is that this solution is not applicable to certain engines, such as engines in vehicles in certain areas of use. One such example is vehicles used for the transport of flammable materials. For these vehicles, the main current must be cut off when the vehicle is parked during, for example, loading and unloading of the flammable material in order to reduce the risk of accidental ignition. This means that the necessary fl fate to obtain the cooling of the dosing module is not possible even if sufficient battery capacity is available.

Furthermore, some vehicle operators wish to disconnect the power from the battery when the vehicle is switched off to ensure that it does not consume the limited electrical energy stored in the vehicle's batteries, which also results in the cooling fate being stopped.

Another solution to the problem is to provide the dosing module with a separate cooling by means of, for example, a coolant which is passed through the module so that the temperature in the dosing module is limited. However, this solution is complicated, which makes it expensive to manufacture and maintain.

A further known solution is described in WO 2010/034401. In this case, the line to the dosing module is equipped with an accumulator which is charged with l5 535 1G during operation? 3 reducing agents. When the operation of the pump ceases, reducing agents continue to be led from the accumulator to the dosing module, whereby cooling thereof can be maintained for a further time. A problem with this solution is that the accumulator has a limited volume and that the agent contained therein has been recirculated back to the tank relatively quickly. The cooling obtained is thus limited to a relatively short time after the shutdown.

Corresponding problems and conditions also exist in other contexts where a heat-exposed component needs to be cooled by a supplied medium.

There is thus a need for an arrangement which solves the problems described above.

Among other things, there is a need for the cooling to continue long enough after switching off the pump to ensure sufficient cooling of the dosing module.

SUMMARY OF THE INVENTION The object of the present invention is to meet the above-mentioned needs. The object is achieved by an arrangement according to claim 1.

The arrangement according to the invention meets the needs described above in that the pump, when it is in operation, in addition to generating the pressurized flow of means, also quickly successively fills the accumulator tank with means. When the motor, and thereby also the pump, is switched off, the agent in the accumulator tank will maintain the cooling flow of agent to the dosing module until the accumulator tank is empty without the action of the pump. The necessary fl fate of coolant is thereby maintained e fi is that the engine is turned off without any power having to be consumed or the pump having to be activated. This arrangement is thus also useful in applications where no power is available after the motor has been switched off. This is advantageous as the risk of accidents due to overheated dosing module is significantly reduced. The arrangement also maintains the cooling fl fate without interference or active selection by the operator. Because the supply line to the accumulator tank comprises a valve, the flow to and from the accumulator tank can be regulated depending on whether the pump is operated or not. 535 18? By means of a valve device it is possible to vary the cross-sectional area of the connecting line.

This allows the accumulator tank to be filled quickly even if the motor and pump are switched off relatively shortly after starting. The cross-sectional area in the connection line is reduced with duty when the motor is switched off so that the limited volume of means in the accumulator tank is sufficient to give increased duration in the cooling flow through the dosing module for a relatively long time after the pump is switched off. It is usually required in a vehicle, such as a truck, that fl the fate can continue for up to 30 minutes and hide for over 40 minutes after the engine and pump have been switched off in order for the temperature in the exhaust system to drop to a level harmless to the dosing module before the vehicle in the accumulator tank is exhausted. The valve device still enables the accumulator tank to be filled quickly after start-up.

Furthermore, the valve device makes it possible to vary the cross-sectional area in the connecting line between a larger area and a smaller area, the larger area being occupied during operation of the pump (13) and the smaller cross-sectional area being occupied automatically when the pump is not operated. This type of valve has the advantage that it does not require any energy to obtain the desired function of the valve device.

The valve can in an advantageous discharge form consist of an electrically controlled solenoid valve.

The valve can then be activated simultaneously with the activation of the purge, which means that the control of the valve can be arranged in a simple manner.

In another advantageous embodiment, the valve can be a pressure-controlled valve, which is controlled by the pressure in the line between the pump and the dosing module. An advantage of this solution is that the pressure can build up quickly at start-up and ensures that the dosing module receives a sufficient amount of agent. Admittedly, the supply of funds to the accumulator is somewhat delayed, but in most cases it is of secondary importance. Incidentally, this type of valve becomes completely self-regulating and no external is needed.

In one form of exhaust, the dosing module comprises a nozzle connected to the line for injecting agents into the exhaust gas. Does the nozzle make it possible to distribute the supplied 535 1G? the agent which is advantageous as it facilitates its reaction with the residues in the exhaust gas.

In one embodiment, a restriction is provided in the dosing module or the return line, which means that the fate returned via the return line must pass a reduced cross-sectional area. This throttling makes it easier for the pump to generate the desired pressure in the system. Furthermore, the throttling means that the genom fate through the system after the engine has been switched off is reduced, which in turn means that the cooling fl fate can be maintained for a longer period of time without the need to increase the volume of the accumulator tank.

In one embodiment, the arrangement comprises a valve, preferably a non-return valve, which ensures the direction of fate in the system which further increases the reliability as no reducing agent can flow in the opposite direction through the pump.

In one embodiment, the accumulator tank is tight and at its bottom it is connected to the connection line. This design of the accumulator tank has the advantage that the trapped lid in the tank will be compressed as the accumulator tank is filled with means. The compressed lu fl in the tank will thereby help to equalize the pressure in the arrangement when pressure variations occur by the dosing module injecting the agent in pulses of varying length. This is a great advantage as the pressure from the pump to the dosing module otherwise varies considerably in that the pressure drops when the agent is injected, whereupon this pressure drop there is to be compensated by the pump.

These variations increase the load on the pump and can eventually result in breakdowns.

Secondly, the overpressure in the accumulator tank facilitates the emptying of the tank when the pump is switched off.

The invention also relates to a vehicle comprising an internal combustion engine from which the exhaust gases are led via an exhaust system and an arrangement according to one of the embodiments described above for supplying an agent in the exhaust gas flow in the exhaust system. 535 'IST Brief Description The invention is described in more detail below with reference to the accompanying schematic drawings of arrangements according to the invention, of which Fig. 1 shows a first embodiment, and Fig. 2 shows a second embodiment.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows an arrangement 10 for reducing NOx emissions in an exhaust gas pass which passes through an exhaust pipe 11 arranged to direct the exhaust gases from an internal combustion engine 1. This can be arranged as a drive engine for a heavier vehicle such as a truck or bus, but can alternatively be an engine for marine or industrial use. For example, the engine can be a diesel engine. The exhaust pipe ll is part of an exhaust system designed to direct the exhaust gases to an exhaust outlet located in a suitable place. The exhaust system may include various components and systems to reduce emissions from the internal combustion engine. Such a component may be any type of catalyst 2, for example an SCR catalyst, through which the exhaust gas passes.

The arrangement 10 comprises a tank 12 intended to contain a liquid reducing agent. In this example, the reducing agent is an aqueous solution of urea, which is often marketed under the name AdBlue. The volume of the tank is dimensioned based on the expected need for reducing agents, the desired length between the filling intervals and the available space.

From the tank 12 a line 13 extends to a dosing module 14 for transferring reducing agent from the tank 12 to the dosing module 14. The transfer takes place by means of a pump 15 which during operation generates the desired flow of reducing agent and generates a desired pressure in the system. The pump 15 is arranged in a suitable place along the line 13. 535 TE? The dosing module 14 comprises a nozzle (not shown) for injecting finely divided reducing agent into the exhaust gas. The dosing module is part of a system for dosing reducing agents and may in addition include, for example, sensors for temperature, as well as control unit and control devices to actively control when and how much reducing agent is to be supplied exhaust gas via the nozzle based on the actual amount of NOx in exhaust gas.

In the dosing module, the line 13 is connected to a return line 16 which returns uninjected reducing agent to the tank.

The pump 15 preferably generates a greater fl fate through the system than the maximum consumption of reducing agent injected into the exhaust fl fate. The flow of reducing agent to the dosing module, ie both the fl fate that is injected and the fl fate that is not injected but that is recirculated in the system, continuously cools the dosing module and prevents overheating of the dosing module and the sensors and controls contained in the dosing module.

The arrangement further comprises an accumulator tank 17 which is connected to the line 13 via a connection line 18 which extends between the line 13 and the accumulator tank 17 and is connected to the line 13 somewhere between the pump and the dosing module. When the motor 1 is in operation, the pump 15 is also in operation and pumps reducing agent to the dosing module 14. However, part of the flow passes through the connection line 18 and further into the accumulator tank 17 which is successively filled with reducing agent. The supply of reducing agent to the accumulator tank stops automatically when the pressure in the accumulator tank is the same as the pressure emitted by the pump. When the arrangement is switched off and the pump 15 stops pumping, the reducing agent flows due to the overpressure in the accumulator tank in the opposite direction through the connection line 18 and further in the line 13 to the dosing module 14 which no longer injects any reducing agent into the exhaust gas. continued fl fate of reducing agent through the dosing module 14 thereby acts as a cooling fl fate as long as there is reducing agent in the accumulator tank. 535 15? 8 The size of the accumulator tank is chosen so that the volume of reducing agent in the accumulator tank is sufficient to maintain the desired cooling rate for the desired time or when the pump is switched off. In case the engine is arranged in a vehicle, such as for example a truck, the accumulator tank preferably has as small a volume as possible so as not to increase the total weight of the vehicle more than necessary. However, the volume must be large enough to maintain a sufficient length of the required cooling flow through the dosing module after the engine has been switched off, which is the same as switching off the pump.

The connection line 18 comprises a valve 19 which makes it possible to adjust the cross-sectional area of the connection line 18. An advantageous design of the valve 19 is a valve which is adjustable in two different positions, which corresponds to two different throttling positions being introduced for the connecting line. A first position of the valve where the cross-sectional area in the connecting line has a larger area and a second position where the cross-sectional area has a smaller cross-sectional area. As long as the pump is in operation, the valve 19 is placed in the first position so that the accumulator tank 17 is filled with reducing agent as quickly as possible to be ready for use if the pump is switched off. As soon as the pump is switched off, the valve is switched to the second position, which means that the flow out of the accumulator tank 17 is somewhat limited and the total time that the cooling flow can be maintained increases.

Another advantage of having a large cross-sectional area in the valve 19 when the pump is in operation is that the damping effect on pressure variations in the line 13 is improved.

The valve 19 in the shaft 1 is designed as a conventional electric solenoid valve which assumes an active position if a voltage is applied to its solenoid, and under the action of a spring automatically assumes an inactive position. The active position is taken while the pump 15 is active and the inactive position is taken when the pump is switched off. This adjustment of the valve to the inactive position thus does not result in any current consumption or active input from an operator. The valve is maintained in this position without consuming any energy. For controlling the valve to these active positions, it is connected to the previously mentioned control system (not shown). The active position of the valve 19 thus corresponds to the above-mentioned first position and the inactive position of the second position. 535 'H57 9 In alternative embodiments it is possible to have a certain delay of the changeover of the valve to the active position at the start of the pump in order to ensure a sufficient flow of medium to the dosing module before medium is supplied to the accumulator tank. Such a solution also has the advantage that a sufficiently high pressure builds up quickly in the line to the dosing module. This delay can be achieved by the adjustment of the valve in dependence on a control unit which senses the pressure in the line, so that the change takes place only after a sufficiently high pressure has been reached in the line.

Alternatively, the changeover can take place a certain predetermined time after the pump has been started. In an alternative embodiment, the valve 19 may be a valve which not only has two specific positions but it may have a number of different positions with different degrees of throttling.

A valve can also be continuously adjustable between different degrees of throttling depending on different operating conditions of the pump and / or motor.

The connection line 18 is advantageously arranged in the bottom of the accumulator tank 17, which is not provided with any discharge. When driving and wherever the accumulator tank is filled with reducing agent, the enclosed air increases the pressure in the tank. The compressed lug in the tank acts when the pump is in operation as a pressure equalizer by effectively reducing the pressure variations in the line 13, so that when the pump is switched off actively influencing the expulsion of the reducing agent from the accumulator tank 17. In alternative embodiments the accumulator tank may be conventional. type, for example in the form of a cylinder where a spring-loaded piston is used to squeeze out the medium when the pump is switched off. Although this embodiment is somewhat more complicated than the former, on the other hand it allows a freer placement.

Built into the dosing module 14 or in the return line 16 is a throttle 20, in order to make it easier for the pump 15 to generate the desired system pressure. The choke 20 may be either a fixed choke or a choke in which the cross-sectional area is adjustable. This throttle 20 is also used to reduce the fate and thereby increase the total time that the fate can be maintained through the dosing module when the pump is switched off. 535 1G? To ensure the direction of fate so that no flow of reducing agent is returned to the tank via the pump when it is switched off, the arrangement comprises a valve with a non-return valve function. This refers not only to a physical non-return valve (not shown) which is arranged in the pump 13 or after it but before the connection of the connecting line 18 to the line 13, but also the case where the pump itself is of such a construction that fate is prevented in the reverse direction of the pump. Likewise, this valve can consist of a shut-off valve that completely blocks the flow through the pump. This ensures that the flow of medium from the accumulator tank 17 is led back to the tank 12 via the dosing module 14 and cools it.

At the pump 13 of the pump 13, after at least a certain time, the accumulator tank 17 will be filled with medium of a pressure corresponding to the normal working pressure of the pump and no further supply can then take place. After the motor 1 has been switched off and also the operation of the pump 15 has ceased, reducing agent will be led from the accumulator tank 17 via the dosing module 14 and the return line 16 back to the tank and thereby cause a cooling of the dosing module 14, until the accumulator tank is completely emptied. When restarting the motor and pump, refill the accumulator tank in the manner specified above.

Fig. 2 shows an alternative embodiment of the invention. This embodiment is substantially the same as that described with reference to Fig. 1 and the constituent components are therefore shown with the same reference numerals. What distinguishes the two embodiments is the design of the valve 19. In the embodiment according to Fig. 2, the valve consists of a pressure-controlled valve where the pressure in the line 13 controls which position the valve is to assume. For this purpose, a control pressure line 21 is arranged between the line 13 and the valve 19. When the pump 15 is in normal operation, the pressure in the line 13 is high enough to set the valve 19 in the first active position and so that medium can be introduced relatively easily into the accumulator tank. When the operation of the pump ceases, the pressure in the line 13 decreases and the valve then assumes the inactive position during the spring valve, which inactive position corresponds to the above-mentioned second position. Thereby, the throttling in the valve 19 will limit the fate of the means which is led back from the accumulator tank to the line 13. This valve can in alternative embodiments be designed with corresponding properties as described above with the embodiment according to Fig. 1. 535 15? ll The invention has been described above on the basis of exemplary embodiments which can of course be combined in different ways. The invention is thus not only applicable to an SCR system for an internal combustion engine where reducing agents in conjunction with an SCR catalyst are used to reduce the NOx emissions from an internal combustion engine. The invention can be used to advantage in other applications where analogous problems and conditions exist, for example when it comes to injecting some other means into an exhaust line. One such case may be the injection of a hydrocarbon (HC) into an exhaust line upstream of an oxidizing catalyst (DOC) in order to improve the exhaust gas purification in a subsequent SCR catalyst. Likewise, injection of hydrocarbon may occur in connection with the desire to raise the exhaust gas temperature prior to purification of a subsequent particle filter. The invention is thus limited only to what is stated in the claims.

Claims (9)

10 15 20 25 30 535 15? 12 PATENT REQUIREMENTS An arrangement for supplying an agent in an exhaust gas port to an exhaust system for an internal combustion engine, comprising a tank (12) intended to contain the agent, a dosing module (14) from which agent can be injected into the exhaust gas, a line (13) for supplying means from the tank (12) to the dosing module (14), a pump (15) intended to generate a pressurized flow through the line (13) for supplying means from the tank (12) to the dosing module (14), a return line (16) connected to the line (13) for supplying means in the dosing module (14) and intended to lead uninjected means from the dosing module (14) back to the tank (12), and an accumulator tank (17) connected via a connecting line (18) to the line (13) for supply of agents to the dosing module. characterized in that the connecting line (18) comprises a valve (19), which makes it possible to vary the cross-sectional area of the connecting line (18), and that the valve (19) makes it possible to vary the cross-sectional area in the connecting line (18) between a larger area and a smaller one. area and that the larger area is taken up when the pump (13) is driven and the smaller cross-sectional area is taken up when the pump (13) is not driven, whereby a waste of means to the dosing module (14) is led from the accumulator tank (17) after switching off the pump ( 15) and provides cooling of the dosing module (14). Arrangement according to Claim 1, characterized in that the valve (19) consists of an electrically controlled solenoid valve. Arrangement according to Claim 1, characterized in that the valve (19) consists of a pressure valve which is controlled under the influence of the pressure in the line (13) between the pump (15) and the dosing module (14). Arrangement according to one of the preceding claims, characterized in that the dosing module (14) comprises a nozzle connected to the line (13) for injecting agents into the exhaust gas stream. 10 15 535 15? 13 Arrangement according to one of the preceding claims, characterized by a choke (20) arranged in the return line (16) or in the dosing module (14), which means that the flow returned via the return line (16) must pass a reduced cross-sectional area. Arrangement according to one of the preceding claims, characterized by a valve, preferably a non-return valve, which, when the pump (15) is switched off, ensures a direction of destruction of the medium from the accumulator tar (17) via the dosing module (14) to the tank (12). Arrangement according to one of the preceding claims, characterized in that the accumulator tank (17) is a tight tank and is connected at its bottom to the connecting line (18). Arrangement according to one of the preceding claims, characterized in that the agent consists of a reducing agent, for example an aqueous solution of urea. Vehicle comprising an internal combustion engine from which the exhaust gases are led via an exhaust system and an arrangement (10) according to any one of claims 1 to 8 for supplying an agent in the exhaust gas port of the exhaust system.