US20110011066A1

US20110011066A1 - Exhaust Gas After-Treatment System

Info

Publication number: US20110011066A1
Application number: US12/783,976
Authority: US
Inventors: Peter Back; Beatrice Hodel
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 2009-06-08
Filing date: 2010-05-20
Publication date: 2011-01-20
Also published as: EP2261476A2; EP2261476A3; DE102009026818A1

Abstract

An exhaust gas after-treatment system includes an oxidation catalytic converter, a carbon-particulate filter, a device for burning off carbon-particulate matter within the carbon-particulate filter, and an exhaust gas cooling unit downstream of the filter for reducing the exhaust gas temperature in the exhaust gas flow. In order to reduce the fuel consumption overall, the device cooling unit can be deactivated.

Description

FIELD OF THE INVENTION

The present invention relates to an exhaust gas after-treatment system with an exhaust gas flow, an oxidation catalytic converter, a carbon-particulate filter, a device for burning off carbon-particulate matter in the carbon-particulate filter, as well as a downstream exhaust gas cooling unit.

BACKGROUND OF THE INVENTION

In motor vehicles, in order to meet newer exhaust gas standards, exhaust gas after-treatment systems are provided that cause a reduction in the pollutants in the exhaust gas due to the after-treatment of the exhaust gas generated by the internal combustion engine and discharged to the surroundings. Such exhaust gas after-treatment systems are required, because the guideline values demanded by legislative bodies can be achieved not at all or only with very high expense just through measures reducing pollutants in the combustion system. For example, exhaust gas after-treatment systems are known that comprise a carbon-particulate or diesel-particulate filter with upstream oxidation catalytic converters. Carbon-particulate matter produced during combustion is captured or filtered out in the diesel-particulate filter. The diesel-particulate filter is dimensioned such that the maximum permissible carbon-particulate load is achieved after a defined operating time, which is to be avoided by burning off carbon-particulate matter, because this would otherwise lead to undesirably high carbon-particulate loads in the diesel-particulate filter and thus to disadvantageously high exhaust gas back pressures in the exhaust gas flow.
Burning off carbon-particulate matter can be realized based on so-called passive or active regeneration in the exhaust gas flow. If a combustion engine is operated at a high load, as a rule, the exhaust gas temperatures are high enough that continuous burn-off of the carbon-particulate matter takes place in the diesel-particulate filter. This so-called passive regeneration occurs approximately at the exhaust gas temperatures above 320° C. However, in order to also guarantee burning off of carbon-particulate matter at lower engine loads, so-called active regeneration systems are used in exhaust gas after-treatment systems. Here, the carbon-particulate load in the diesel-particulate filter is determined (or calculated by means of a mathematical model in connection with a measurement of the differential pressure across the diesel-particulate filter) and the exhaust gas temperature increases artificially when a threshold is exceeded, in that, for example, fuel is injected into the exhaust gas flow and this fuel is then oxidized under release of heat in the oxidation catalytic converter. In this process that is performed at intervals for a certain operating time of approx. 20-25 min, higher exhaust gas temperatures can be generated than are typical in regular operation without an active regeneration system (above 630° C.). In order to reduce these high exhaust gas temperatures, typically an exhaust gas diffuser downstream in the exhaust gas flow is used. Therefore, ambient air is mixed in with the exhaust gas in the diffuser and the exhaust gas temperature is reduced.
A disadvantage in such exhaust gas after-treatment systems with exhaust gas diffusers is that, through the use of an exhaust gas diffuser in the exhaust gas flow, an increased exhaust gas back pressure is generated, so that a higher exhaust gas back pressure continuously predominates, although a reduction of the exhaust gas temperature by means of the exhaust gas diffuser is required only during the active regeneration phase for the burn-off of the carbon-particulate matter that takes place for approx. 20-25 min on average only for every 6 operating hours. Through the increased exhaust gas back pressure, the work to be performed in the exhaust gas flow increases for pushing out the exhaust gas, by means of which, in turn, increased fuel consumption is to be noted. Overall, the use of an exhaust gas diffuser leads to increased fuel consumption.

SUMMARY

Accordingly, an object of this invention is to provide an exhaust gas after-treatment system of the type named above through which the above problems are eliminated.
These and other objects are achieved by the present invention, wherein an exhaust gas after-treatment system of the type named above is constructed such that the exhaust gas cooling unit can be deactivated. The exhaust gas after-treatment system is suitable, in particular, for combustion engines that operate with diesel fuel and that have, in their exhaust gas flow, dvantageously, a diesel oxidation catalytic converter and a diesel-particulate filter or also a carbon-particulate filter. The exhaust gas after-treatment system according to the invention is not limited, however, to diesel fuels, but is also likewise suitable for biodiesel fuels or fuels based on rapeseed oil or the like. Therefore, because the exhaust gas cooling unit can be deactivated, this can be deactivated or bypassed or turned off or varied; according to the effect, the exhaust gas temperature is no longer reduced outside of the active regeneration times, that is, for operation of a combustion engine under normal or high load in which a passive regeneration of the carbon-particulate filter or diesel-particulate filter can take place by burning off carbon-particulate matter due to a regular exhaust gas temperature. Only when falling below a temperature value measured in the exhaust gas flow and/or when exceeding a certain carbon-particulate load in the diesel-particulate filter and/or another sensitive state in the exhaust gas after-treatment system or in the exhaust gas flow, the device for reducing the exhaust gas temperature is reactivated or turned on. Thus an advantageous exhaust gas after-treatment system with a device controlled according to demands for reducing the exhaust gas temperature is created with which an increase in the average fuel consumption can be avoided.
The exhaust gas cooling unit is constructed such that a medium cooling the exhaust gas is fed into the exhaust gas flow. This cooling medium is advantageously fed by means of an opening in the exhaust gas flow directly to the exhaust gas or mixed with this exhaust gas or brought into active connection with the exhaust gas in a heat exchanger or the like. The cooling medium can be constructed here as a fluid or gaseous medium.
The medium, advantageously in the form of ambient air or fresh air obtained from the surroundings of the exhaust gas flow, is advantageously mixed directly with this exhaust gas. If the ambient air has a lower temperature than the exhaust gas, which is generally the case, this results in cooling of the exhaust gas.
The exhaust gas cooling unit can comprise a diffuser that is arranged in the exhaust gas flow and that is deactivated or bypassed or activated or turned on according to demand. Through the use of the diffuser, a medium may be drawn in from the surroundings of the exhaust gas flow and used for cooling the exhaust gas.
The diffuser may be constructed such that its geometry is variable and a passage cross section of the diffuser can be adjusted by means of an adjustment mechanism. Here, the diffuser can be adjusted, for example, such that its actual diffuser effect in an adjustable, variable geometric construction (of a first geometric extreme position) is equal to zero or minimal and in another adjustable, variable geometric construction (of a second geometric extreme position), a maximum diffuser effect can be achieved. Furthermore, intermediate values lying between a minimum and maximum diffuser effect can also be achieved through corresponding adjustment of the diffuser.
The diffuser may be equipped, for example, with diffuser flaps that close an opening cross section to the surroundings of the exhaust gas flow, for example, to the ambient air, or that even open up this opening cross section and draw in ambient air through the action of the diffuser. At the same time, the passage cross section of the diffuser changes for the exhaust gas flowing through the diffuser. Through corresponding adjustment of the diffuser flaps and thus the passage cross section of the diffuser or the opening cross section for ambient air, the cooling of the exhaust gas can be varied to different degrees. If the diffuser flaps are held closed, no cooling is realized by the ambient air. The diffuser flaps can be adjusted by means of the adjustment mechanism and by means of a remote-controllable actuator connected to this mechanism. As an actuator, among other things, for example, pneumatic, hydraulic, or also electric servomotors are suitable (pneumatic cylinders, hydraulic cylinders, stepper motors).
In one alternative embodiment, the exhaust gas cooling unit may comprise, instead of an adjustable diffuser, a bypass line that may be turned on in the exhaust gas flow and in which a diffuser with constant passage cross section is arranged and through which the exhaust gas can be guided. A corresponding controllable adjustment device or valve device may be provided for this purpose, through which the exhaust gas is guided through the bypass line for cooling according to demand. If no cooling is performed, the exhaust gas is guided through the regular exhaust gas line without a diffuser. Thus, here a variable, controllable device is also created that can be deactivated or activated or turned on or off like a variable, adjustable diffuser as a function of different state parameters that can be derived from the exhaust gas system or as a function of sensitive, determinable state parameters.
The device for burning off the carbon-particulate matter in the diesel-particulate or carbon-particulate filter comprises a supply of fuel for combustion in the exhaust gas flow. In this way, advantageously in the provided oxidation catalytic converter, a specified quantity of fuel is combusted and by means of the combustion heat, a corresponding increase in temperature of the exhaust gas in the exhaust gas flow or in the carbon-particulate filter is achieved, by means of which, in turn, active burn-off of the carbon-particulate matter is generated at low engine loads, when the provided passive burn-off of the carbon-particulate matter cannot take place due to exhaust gas temperatures that are too low.
Such systems for exhaust gas after-treatment are suitable, in particular, for agricultural machines, for example, tractors or self-propelled harvesting machines that can be subjected to a large number of operating hours for alternating engine loads and that should feature the lowest possible fuel consumption while fulfilling all legally prescribed exhaust gas standards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an agricultural machine with an exhaust gas after-treatment system according to the invention;

FIG. 2 is a schematic block diagram of an exhaust gas after-treatment system according to the invention with adjustable diffuser in its activated position;

FIG. 3 is a schematic block diagram of the exhaust gas after-treatment system according to the invention of FIG. 2 with an adjustable diffuser in its deactivated position; and

FIG. 4 is a schematic block diagram of an alternative embodiment of an exhaust gas after-treatment system according to the invention with a static diffuser in a bypass line.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an agricultural vehicle 10 in the form of a tractor or hauler is driven by a combustion engine 12 and that has available an exhaust gas after-treatment system 16 and an exhaust pipe 14 through which flows exhaust gas from the engine 12. The vehicle 10 is shown here only as an example as a tractor or hauler. Other agricultural machines that are operated by means of a combustion engine 12, for example, self-propelled, agricultural sprayers, combine harvesters, field choppers, or other self-propelled harvesting machines, may also be constructed with an exhaust gas after-treatment system 16 according to the invention.
As becomes clear especially in FIGS. 2 to 4, the exhaust gas after-treatment system 16 includes an oxidation catalytic converter 18 arranged in the flow of exhaust, a carbon-particulate filter 20, or also a diesel-particulate filter, a device 22 for burning off the carbon-particulate matter in the carbon-particulate filter, and also a downstream cooling unit 24 for reducing the temperature of the exhaust gas.
The device 22 for burning off the carbon-particulate matter in the carbon-particulate filter 20 comprises a fuel injection device 26 which injects fuel into the exhaust gas, wherein this fuel then contributes, through its combustion, to increasing the exhaust gas temperature for burning off the carbon-particulate matter in the carbon-particulate filter 20.
The cooling unit 24 for reducing the exhaust gas temperature comprises, in a first embodiment according to FIGS. 2 and 3, an adjustable diffuser 28 that can be adjusted by an adjustable motor or actuator 30. The geometry of the diffuser 28 and a passage opening therein and through which the exhaust gas is guided is adjusted from a minimum passage opening 32′ (activated state of the device for reducing the exhaust gas temperature, see FIG. 2) to a maximum passage opening 32″ (deactivated state of the device for reducing the exhaust gas temperature, see FIG. 3). The passage opening 32′, 32″ is adjusted by adjustable diffuser flaps (34) or wall elements that are formed on the diffuser walls and that are variable, for example, in their position by a hinge connection 36. The adjustment takes place by means of an adjustment mechanism 38 formed between the actuator 30 and the diffuser flaps 34. Thus, in an active position (FIG. 2), the diffuser flaps 34 are moved into the interior of the exhaust gas flow 14, wherein the minimum passage opening 32′ is formed and simultaneously an intake opening 40 to the ambient air is formed or opened. In the opposite way, the diffuser flaps 34 can be moved or adjusted outward back toward the walls of the diffuser 28 starting from this active position, wherein the maximum passage opening 32″ for the exhaust gas is created and simultaneously the intake opening 40 is closed again (deactivated position, FIG. 3). Alternatively, the diffuser flaps 34 may also be constructed as slide elements (not shown) that can move in the axial direction or relative to the periphery of the exhaust gas flow and that, in a first position, open the intake opening 40 to the surroundings (activated position) and, in another (shifted) position, close the intake opening 40 to the surroundings (deactivated position). The slide elements (not shown) can be adjusted or shifted into a correspondingly adapted shape by a similar actuator 30.
An electronic control unit 42 signals the various state data 44 of the vehicle 10 and/or the engine 12 and/or the exhaust gas after-treatment system 16 or the exhaust gas flow 14 or that receives corresponding control signals. Such control signals can be supplied from corresponding sensors, for example, as a function, in general, of time, of the traveling speed of the vehicle 10, of the rotational speed of the engine 12, or of temperatures in the oxidation catalytic converter 18, in the diesel-particulate filter 20, in the rest of the exhaust gas flow, in the surroundings of the exhaust gas flow, etc. A control algorithm stored in the control unit 42 generates a control signal for activating/deactivating the device 22 for burning off the carbon-particulate matter (or for the control of the fuel injection device 26) and/or for activating/deactivating the cooling unit 24 or driving the actuator 30).
The switchable diffuser 28 is advantageously activated only when regeneration of the diesel-particulate filter 20, that is, burning off the carbon-particulate matter, is required. During regular operation of the vehicle 10 or the engine 12, i.e., for normal-load and high-load operation, burning off of carbon-particulate matter in the diesel-particulate filter 20 takes place automatically due to the high exhaust gas temperatures. In these load ranges, the diffuser 28 is advantageously in its maximum passage opening position 32″ and thus the device for increasing the exhaust gas temperature is, to some degree, deactivated, wherein the intake opening 40 is closed. In the low-load or idle range, the state can appear that regeneration of the diesel-particulate filter 20 does not take place automatically, even though it should take place due to an increased carbon-particulate load on the diesel-particulate filter 20. This state is detected by the sensors discussed above and a control signal that activates the device 22 for burning off the carbon-particulate matter or that starts the fuel injection device 26 is generated according to the control algorithm. The fuel injection into the exhaust gas leads to an increase in the temperature of the exhaust gas that, in turn, promotes or supports or starts the burn-off of the carbon-particulate matter. Consequently, it is necessary to cool the exhaust gas again due to the increased temperature after leaving the diesel-particulate filter 20, which is realized by the described cooling unit 24. The actuator 30 is driven so that the diffuser flaps 34 are moved inward and an intake opening 40 to the surroundings is opened (analogously, slide elements may also be shifted accordingly, such that an intake opening 40 is opened). Through the diffuser effect activated in this way, ambient air or fresh air is drawn into the exhaust gas flow and the exhaust gas is cooled. After successful cooling of the exhaust gas or as soon as the state named above is eliminated (which is determined and signaled using sensors according to the state parameters 44), the device 22 for burning off the carbon-particulate matter and also the cooling unit 24 for reducing the temperature are deactivated again by means of the electronic control unit 42, wherein the diffuser 28 is brought by the actuator 30 from its position with a minimal passage opening 32′ back into its deactivated position, i.e., into its position with maximum passage opening 32″ in which the intake opening 40 will be or is closed.
The advantages of the exhaust gas after-treatment system 16 described above relative to known systems for exhaust gas after-treatment lie in that, due to the arrangement of a static diffuser in the exhaust gas flow or in a device for reducing the temperature in the exhaust gas, a higher exhaust gas back pressure also predominates simultaneously. This is associated, in turn, with higher fuel consumption. In contrast, a variable cooling unit 24 for reducing the exhaust gas allows this increase of the exhaust gas back pressure or the increase of the fuel consumption is taken into account only at some times, that is, only during the active regeneration phase for the diesel-particulate filter 20, that is, only when there is no normal operation or high-load operation. Because the diffuser 28 constructed with a variable geometry is activated by the control unit 42 only according to demand, that is, only during a fraction of the entire operating time of the vehicle 10, this may also be designed so that an essentially more effective cooling of the exhaust gas takes place, because here, in the design of a static diffuser, no compromise must be made between a general exhaust gas back pressure increase and effective cooling of the exhaust gas. Another advantage consists in that an intake opening 40 is automatically closed as soon as the cooling unit 24 for reducing the exhaust gas temperature (or the diffuser 28) is deactivated. In this way it is guaranteed that exhaust gas can flow back via the diffuser 28, when, for example, the vehicle 10 is connected at the factory to an exhaust gas hose for discharging the exhaust gases.
According to FIG. 4, an alternative embodiment of the exhaust gas after-treatment system 16 includes a cooling unit 46 for reducing the exhaust gas temperature that differs from the embodiment shown in FIGS. 2 and 3. It differs in that a diffuser 48 with a constant geometry, that is, a static diffuser, is provided in a bypass line 50 that is arranged parallel to the exhaust gas flow 14 instead of the diffuser 28 with a variable geometry. This is driven analogously by means of an adjustment device 52 or by means of a valve device of the electronic control unit 42, so that, in a state of active regeneration for the diesel-particulate filter 20, the cooling unit 46 for reducing the exhaust gas temperature is activated in that the exhaust gas is guided via the adjustment device 52 through the bypass line 50 and thus through the diffuser 48. As soon as this state of active regeneration for the diesel-particulate filter is completed, the adjustment device 50 is driven as a function of the state parameters 44 by the control unit 42, such that the exhaust gas is led back through the regular exhaust flow without the diffuser 48. The functioning for the rest and also the effect of the exhaust gas after-treatment system 16 in the alternative embodiment in FIG. 4 corresponds to the functioning and effect as were already described with respect to the above embodiment according to FIGS. 2 and 3.
While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.

Claims

1. An exhaust gas after-treatment system through which flows exhaust gas from an internal combustion engine, the system having an oxidation catalytic converter, a carbon-particulate filter, a device for burning off carbon-particulate matter within the filter, and a cooler unit for cooling the exhaust gas, characterized in that:

the cooler unit can be deactivated.

2. The exhaust gas after-treatment system of claim 1, wherein:

a cooling medium is fed through the cooler unit for reducing the exhaust gas temperature.

3. The exhaust gas after-treatment system of claim 2, wherein:

the cooling medium is ambient air.

4. The exhaust gas after-treatment system of claim 1, wherein:

the cooling unit comprises a diffuser through which the exhaust gas flows.

5. The exhaust gas after-treatment system of claim 4, wherein:

the diffuser has a variable geometry and a passage cross section of the diffuser can be adjusted by an adjustment mechanism.

6. The exhaust gas after-treatment system of claim 5, wherein:

the diffuser includes diffuser flaps for adjusting the passage cross section of the diffuser, wherein the diffuser flaps can be adjusted by the adjustment mechanism and by a remote-controllable actuator that is connected to the adjustment mechanism.

7. The exhaust gas after-treatment system of claim 4, further comprising:

a exhaust gas bypass line and a switch for directing exhaust gasses through the bypass line, the cooling unit being arranged in the bypass line.

8. The exhaust gas after-treatment system of claim 1, wherein:

the device for burning off the carbon-particulate matter within the carbon-particulate filter comprises a supply of fuel for combustion in the exhaust gas flow.