WO2013058683A1

WO2013058683A1 - Vehicle exhaust gas diluting device

Info

Publication number: WO2013058683A1
Application number: PCT/SE2011/000183
Authority: WO
Inventors: Sassan Etemad; Torbjörn WIKLUND; Jesper AXELSSON
Original assignee: Volvo Lastvagnar Ab
Priority date: 2011-10-20
Filing date: 2011-10-20
Publication date: 2013-04-25

Abstract

An exhaust gas control device, comprising an exhaust tail pipe and an exhaust outlet cover, where the exhaust tail pipe comprises a plurality of radial openings near the exhaust outlet, where the exhaust outlet cover is in a closed state when the exhaust mass flow is below a first mass flow level such that the exhaust gas is distributed through the radial openings, and where the exhaust outlet cover opens when the exhaust mass flow rises above the first mass flow level. The advantage of the invention is that hot exhaust gas generated during the regeneration of a diesel particulate filter is diluted and mixed with cool ambient air when the vehicle is standing still with the engine running with low load, and that the pressure loss during high engine load is minimized.

Description

Vehicle exhaust gas diluting device

TECHNICAL FIELD

The present invention relates to an exhaust gas control device for a vehicle. BACKGROUND ART

Most modern diesel engines are provided with a filter for cleaning the exhaust gas. Such a filter is often referred to as a diesel particulate filter and is designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. There are different kinds of suitable filters available, both disposable filters and filters that can be cleaned and reused. A common method for cleaning a filter is to temporarily rise the temperature of the exhaust gas which in turn rises the temperature of the filter surface such that the accumulated particles burn off.

This is referred to as filter regeneration and can be done either passively by using a catalyst or through an active technology, such as a fuel burner which heats the filter to soot combustion temperatures, by altering the combustion of the engine in order to heat the exhaust gases or to produce high amounts of NO_x, or through other methods. The regeneration of a diesel particulate filter occurs when one or more predefined conditions are fulfilled. Such a condition may be e.g. a specific driving distance, a specific time interval or an estimated contamination of the filter. This means that the regeneration may occur either when the vehicle travels on a road or when the vehicle is stationary with the engine running at load conditions slightly over or at idle speed. One problem with the regeneration of a diesel particulate filter at a high exhaust gas temperature is that exhaust gas at a high temperature, flows out of the exhaust pipe. In normal running conditions, the hot exhaust gas is mixed with the surrounding air and is thus diluted to a low temperature which will not cause any problems. If the regeneration occurs when the vehicle is standing still, problems may arise due to the high exhaust gas temperature. For a vehicle provided with an exhaust pipe pointing upwards, the problem may occur when the vehicle is standing e.g. in a garage or in a ferry, where a roof is situated above the vehicle. When the regeneration of the diesel particulate filter starts, hot exhaust gas will blow upwards from the roof which may heat up with a possible damage as a result.

A similar problem may occur for a vehicle having a low exhaust pipe pointing sideward, when the vehicle is parked next to a wall or another vehicle. When hot exhaust gas blows out of the exhaust pipe, the wall or vehicle may also be damaged. A pedestrian or a cyclist standing next to the vehicle e.g. at a traffic light may catch a burn injury if hot exhaust gas suddenly blows out of the exhaust pipe. Different solutions have been presented to solve this problem. In one solution, a diffusion device is positioned at the end of the exhaust pipe. WO 2008/018821 , WO 2009/078845, EP 1767753 and US 4069668 show different diffusion devices which will aid the dispersion of hot exhaust gases from the exhaust pipe. These diffusion devices will however give a higher back-pressure which results in a pressure loss in the exhaust system with increased fuel consumption as consequence.

Another way is to let the vehicle control system delay the regeneration of the diesel particulate filter until the vehicle is moving. This solution will only work well for vehicles that do not stand still for longer periods. Should a vehicle run at stand still for too long without regenerating the diesel particulate filter, there is a risk that the filter cannot be regenerated completely if too many particles are allowed to deposit in the filter.

There is thus room for an improved exhaust gas control device.

DISCLOSURE OF INVENTION An object of the invention is therefore to provide an improved exhaust gas control device which will dilute the exhaust gas when the exhaust mass flow is below a predefined value. A further object of the invention is to provide an improved exhaust gas control device which will allow the exhaust gas to escape the exhaust pipe without additional pressure loss when the exhaust mass flow is above a predefined value.

The solution to the problem according to the invention is described in the characterizing part of claim 1. The other claims contain advantageous further developments of the inventive exhaust gas control device. In an exhaust gas control device, comprising an exhaust tail pipe and an exhaust outlet cover, where the exhaust tail pipe comprises a plurality of radial openings near the exhaust outlet, the object of the invention is achieved in that the exhaust outlet cover is in a closed state when the exhaust mass flow is below a first mass flow value such that the exhaust gas is distributed through the radial openings, and that the exhaust outlet cover opens when the exhaust mass flow rises above the first mass flow value.

By this first embodiment of the exhaust gas control device according to the invention, an exhaust gas control device which will dilute the exhaust gas at low exhaust mass flow is provided, and that at the same time will not provide an additional pressure loss at higher exhaust mass flow. This is achieved in that the exhaust gas will flow out of a plurality of radial openings near the exhaust outlet of the exhaust pipe at a low exhaust gas mass flow. A low exhaust gas flow will occur when the vehicle is standing still or running very slowly with the engine running with no or little load. The engine speed will in this case be close to the idling speed. The exhaust gas is thus diluted with cool ambient air which lowers the temperature of the exhaust gas near the vehicle. At a higher exhaust gas flow, the exhaust gas does not need to pass through the radial openings but flows directly out of the axial exhaust outlet opening of the exhaust gas pipe. In this way, there is no additional pressure loss at higher exhaust gas flow, which will help to minimize the pressure loss of the exhaust gas system. The exhaust gas control device comprises an exhaust outlet cover that closes the axial exhaust gas opening at lower exhaust gas mass flow and that opens the axial exhaust gas opening at higher exhaust gas mass flow. In this way, a dilution of hot exhaust gas for a vehicle standing still can be provided without affecting the performance when driving. The exhaust outlet cover may comprise a single cover or may comprise two or more cover parts. The exhaust outlet cover is thus in a closed state when the exhaust mass flow is below a first mass flow value such that the exhaust gas is distributed through the radial openings of the exhaust pipe. The first mass flow value is selected such that the exhaust mass flow corresponds to a low engine load and speed, preferably at idle speed or higher. When the exhaust mass flow rises above the first mass flow value, the exhaust cover opens. The exhaust outlet cover is completely open when the exhaust mass flow is larger than a second exhaust mass flow value. The second exhaust flow value may be selected such that it corresponds to an engine load and speed of around half the maximum engine load, or such that the second exhaust flow value is approximately twice the first mass flow value.

It is also possible to open the cover depending on the vehicle speed or the wind speed at the vehicle. In these cases, the cover will be closed when the vehicle speed is below a predefined speed value or when the actual wind blowing at the vehicle is below a predefined wind speed value. The exhaust gas will in these cases exit through the radial openings of the exhaust tail pipe such that the exhaust gas is diluted with the ambient air. When the vehicle speed or the actual wind speed exceeds the predefined value, the cover is opened. When the vehicle speed or the actual wind speed is above the predefined value, the exhaust gas will be mixed with enough ambient air when the exhaust gas exits through the axial opening. With the cover opened, there is no additional pressure loss which helps to minimize the pressure loss of the exhaust gas system.

The exhaust outlet cover can be held in the closed state in different ways. In one example, the exhaust outlet cover is held in the closed state by a weight. The weight may be the weight of the cover itself or may include an additional weight attached to the cover. The weight is selected such that the cover is closed when the exhaust mass flow is below the selected first exhaust mass flow value. The size and position of the weight will depend on the design and position of the exhaust pipe. The exhaust outlet cover can also be held in the closed state by a resilient element, such as a spring of some sort. In one example, the resilient element is provided at the hinge that holds the cover to the exhaust pipe.

The exhaust outlet cover may also be held in the closed state by a temperature sensitive element. The temperature sensitive element may be bi-metal controlled valve that opens and closes the cover at a predefined temperature. The temperature sensitive element may also comprise a temperature sensor and an electrical actuator, e.g. a motor or an electromagnet.

The first mass flow value is preferably larger than the exhaust mass flow of the engine when the vehicle engine is regenerating a particle filter and the vehicle is standing still. By selecting the first mass flow value in this way, the exhaust outlet cover will be closed when the diesel particulate filter is regenerated when the vehicle is standing still. The risk of overheating an object close to the exhaust output is thus reduced significantly. The first mass flow value may also be twice the exhaust mass flow of the engine when the vehicle engine is regenerating a particle filter and the vehicle is standing still. In this way, the exhaust outlet cover will also be closed at a somewhat higher engine load. By making the first mass flow value equal to the second mass flow value, the cover will open directly when the mass flow value exceeds the first mass flow value. BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in greater detail in the following, with reference to the attached drawing, where

Fig. 1 shows a cut view of an exhaust gas control device according to the invention with the exhaust outlet cover closed,

Fig. 2 shows a cut view of an exhaust gas control device according to the invention with the exhaust outlet cover opened,

Fig. 3 shows a cut view of an exhaust gas control device according to the invention with the exhaust outlet cover closed by an actuator, and

Fig. 4 shows a cut view of an exhaust gas control device according to Fig. 3 with the exhaust outlet cover opened.

MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims.

Figs. 1 and 2 show an exhaust gas control device 1 according to the invention for the use in an exhaust gas system of a vehicle. Although the exhaust gas control device may be used on any vehicle having a diesel particulate filter, the main use will be on heavy vehicles such as trucks, busses and construction vehicles. The exhaust gas control device is provided upstream or at the end of the exhaust pipe of the vehicle and comprises the end region of the exhaust tail pipe 2 and an exhaust outlet cover 3. The exhaust tail pipe is provided with a plurality of radial openings 4 which are arranged in the vicinity of the exhaust outlet 5. The radial openings may be arranged symmetrically or asymmetrically around the exhaust tail pipe or may be arranged only at a part of the exhaust tail pipe, preferably distributed at least over half of the circumference of the exhaust pipe.

The exhaust outlet cover 3 is adapted to close the exhaust outlet 5 when the exhaust mass flow is below a predefined mass flow value. This mass flow value is selected such that the exhaust outlet cover closes the exhaust outlet when the engine is running at low engine load. The exhaust outlet will thus be closed when the engine is shut off and also when the engine is running at low engine load, which generates a low exhaust mass flow. The term low engine load is understood as an engine condition at which the engine runs with an engine speed which is close to or equal to the set idle speed of the vehicle and where the engine is subjected to no or little load. A low engine load is preferably less than 1.2 times an idle condition. This condition mostly occurs when the vehicle is standing still but may also occur when the vehicle is travelling with a low speed. At higher engine loads, such that the exhaust mass flow is greater than the predefined mass flow value, the exhaust outlet cover will open. When the exhaust outlet cover opens up, the exhaust gas will be able to flow out of the exhaust pipe in the axial direction with almost no additional pressure loss compared to the conventional exhaust pipes. At higher engine loads, the exhaust pipe will thus resemble a conventional exhaust pipe. The main exhaust gas flow is indicated with arrows 9 and the diluted exhaust gas flow is indicated with arrows 10.

The radial openings 4 are adapted to blow out exhaust gas when the engine is running at a low engine load. The size and number of the openings, i.e. the total opening area, is selected such that the exhaust gas at low mass flow conditions can blow out of the openings at a predefined pressure level, as indicated with arrows 10. When the load of the engine is low, the additional pressure loss from the radial openings will not affect the fuel consumption of the vehicle to any substantial degree because the pressure loss is proportional to the mass flow in square. Further, since the exhaust gas flow has to exit through the radial openings only during regeneration or other low load situations such as idle, the effect of the pressure drop over the openings is restricted to very short periods of time. The purpose of the radial openings is to distribute the exhaust gas over a larger area. The exhaust gas will thus be able to mix with the cooler ambient air which will lower the temperature of the exhaust gas close to the exhaust gas outlet.

The position of the radial openings may be chosen depending on the position of the exhaust gas outlet and the position of the exhaust pipe. If the exhaust pipe is directed upwards, positioned at the back of the cab, the radial openings are preferably directed backwards, away from the cab. If the exhaust pipe extends above the roof of the cab, the radial openings may be positioned around the complete exhaust pipe. For an exhaust pipe mounted low, the radial openings may be positioned such that no opening is facing in the direction of another component of the vehicle.

The mixing of the exhaust gas with ambient air is especially important when the vehicle control system regenerates the diesel particulate filter. During the regeneration, the temperature of the exhaust gas is raised to a much higher temperature level than for normal operation. The exhaust gas temperature may during regeneration be 500 °C or more, compared with 100 - 200 °C during normal operation.

At higher engine loads, the exhaust outlet cover is open. The exhaust gas can thus blow out of the exhaust outlet with almost the same pressure loss as in the conventional case. If the regeneration of the diesel particulate filter starts when the engine is running at a high engine load, the hot exhaust gas will blow out of the exhaust pipe in a conventional manner. However, in this case, the vehicle will in most situations be moving and the risk of overheating the surrounding is avoided. It is also possible to let the cover open completely depending on the vehicle speed. In this way, the cover will be closed when the vehicle is travelling with a speed that is below a predefined speed. The predefined speed is preferably a low speed, in the range below 20 km/h. In this way, the cover will be closed when the vehicle is moving slowly, such as when the vehicle is marshalling. The exhaust gas will exit through the radial openings when the vehicle is moving slowly and will thus be diluted with cool ambient air which lowers the temperature of the exhaust gas near the vehicle. At a higher vehicle speed, the exhaust gas does not need to pass through the radial openings but flows directly out of the axial exhaust outlet opening of the exhaust gas pipe. In this way, there is no additional pressure loss at higher vehicle speed. This helps to minimize the pressure loss of the exhaust gas system. The speed of the vehicle is obtained from the speedometer of the vehicle. The cover is opened by an actuator which is controlled by a control unit, either a stand alone control unit or by an existing control unit of the vehicle.

The cover may also be opened in dependency of the actual wind speed at the vehicle. In this way, the cover will be closed when the actual wind speed is lower than a predefined wind speed. The predefined wind speed is preferably a relatively low wind speed, in the range below 20 km/h. In this way, the cover will be closed if the vehicle is standing still or is moving slowly and the wind blows with a low wind speed. In this way, the exhaust gas will exit through the radial openings when a wind with a low wind speed is blowing and will thus be diluted with cool ambient air which lowers the temperature of the exhaust gas near the vehicle. At a higher wind speed, the exhaust gas does not need to pass through the radial openings but flows directly out of the axial exhaust outlet opening of the exhaust gas pipe, since the higher wind speed will help to dilute the exhaust gas even if the vehicle is standing still. The actual wind speed at the vehicle can be measured by a wind speed sensor positioned e.g. on the roof of the vehicle. The wind speed is preferably measured when the vehicle is standing still or possibly when the vehicle is travelling with a low speed in order to obtain a proper wind speed value. The cover is opened by an actuator which is controlled by a control unit, either a stand alone control unit or by an existing control unit of the vehicle. The cover can also be opened by a lever connected to a wind catching means, e.g. formed as a blade. The wind catching means is preferably arranged perpendicular to the travelling direction of the vehicle. In this way, the air flow created when the vehicle travels puts a load on the wind catching means which is mechanically connected to the cover. The cover will thus open when the vehicle travels faster than a predefined speed. The cover and the wind catching means may be arranged on the same axis.

The exhaust outlet cover may comprise a single cover or may be divided in two or more parts. In a first example, the exhaust outlet cover is closed by the weight of the exhaust outlet cover 3. The exhaust outlet cover may provide the required weight to close the exhaust outlet cover by itself, or an additional weight 8 may be positioned on the exhaust outlet cover 3 in order to close the exhaust outlet 5 when the exhaust mass flow is below the first predefined mass flow value. The exhaust outlet cover may be mounted to the exhaust pipe by a hinge mechanism 6. The weight may be placed on either side of the hinge, depending on the exhaust pipe position. In such a solution, the cover starts to open when the actual mass flow exceeds the first predefined mass flow value. When the mass flow increases, the cover will open up more and more. The cover is preferably completely open when the actual mass flow exceeds a second predefined mass flow value. The relation between the first mass flow value and the second mass flow value is preferably selected such that the cover is more or less completely open at an actual mass flow which is in the region of two to four times the first mass flow value. In this way, the pressure loss of the exhaust system is minimized when the engine is working under load. In one example, the exhaust outlet cover is closed by a resilient member 7. The resilient member may be a steel spring of some kind. It is possible to place a spring in the hinge 6 that attaches the exhaust outlet cover to the exhaust tail pipe. This spring may be combined with a weight 8, depending on the design of the exhaust gas control device. The spring may also be placed at another location and may act directly on the exhaust outlet cover or on a lever extending from the cover.

By closing the exhaust outlet cover with a weight and/or a spring, an easy, reliable and cheap solution is obtained, which requires no or little maintenance. The opening of the exhaust outlet cover is governed by the exhaust mass flow of the engine. In this way, the properties of the exhaust gas control device can be preselected and do not have to be adjusted at a later stage.

It is also possible to use a temperature sensitive member to control the opening of the exhaust outlet cover. In one example, a bi-metal member is connected to the exhaust outlet cover. The bi-metal member is preferably positioned inside the exhaust gas pipe such that it is affected directly by the exhaust gas temperature. When the exhaust gas temperature is below a predefined temperature value, the exhaust outlet cover will be opened. When the temperature rises above this predefined temperature value, the exhaust outlet cover is closed by the bi-metal member. The bi-metal member may also be used together with a spring such that the exhaust outlet cover also can open at higher exhaust mass flow, even if the exhaust temperature is high. In another example, as shown in Figs. 3 and 4, the temperature sensitive member is a temperature sensor 11 which will actuate an electrical actuator 12 depending on the measured temperature. In this way, the exhaust outlet cover 3 is open when the exhaust gas temperature is below a predefined temperature. When the temperature rises above this level, the actuator closes the exhaust outlet cover. The actuator 12 may be e.g. a motor or an electromagnet. The temperature sensor 11 and the actuator 12 are preferably connected to an electronic control unit (not shown) of the vehicle, which controls the actuator depending on the temperature signal. When an electronic control unit is used, it is also possible to use other vehicle parameters in order to control the exhaust outlet cover. It is e.g. possible to open the exhaust outlet cover also when the exhaust mass flow is above a predefined value and/or when the speed of the vehicle is above a predefined speed. In this way, the pressure loss of the system can be reduced as much as possible. By the inventive exhaust gas control device, it is possible to obtain a solution that can dilute the hot exhaust gas created when the diesel particulate filter of a vehicle is regenerated and the vehicle is standing still, and which at the same time reduces the pressure loss of the exhaust system when the engine runs in higher load conditions. In conventional exhaust gas systems that use known exhaust gas outlet diffusers, the pressure loss will increase with engine load, i.e. with exhaust gas mass flow. This will in turn increase the fuel consumption of the vehicle. A further problem with the known solutions is that they are adapted for exhaust dilution at low engine load. When the engine is running at full load, the exhaust gas will also spread in a radial direction, which may lead to exhaust gas entering the cab of the vehicle or blowing on sensitive vehicle components. A further problem with the known solutions adapted for exhaust dilution at low mass flow is the noise level, which may increase above legislative levels at higher gas mass flows due to the fixed dilution arrangement.

One purpose of the invention is to reduce the temperature of the exhaust gas created when the diesel particulate filter is regenerated. If the regeneration of the particulate filter occurs when the vehicle is travelling on a road, there will not be a problem with hot exhaust gases since the exhaust gases are diluted by continuously approaching fresh and colder ambient air when the vehicle travels. On the other hand, a problem may arise if the vehicle is standing still and is idling, and the regeneration of the diesel particulate filter starts. In this case, hot exhaust gas will blow out of the exhaust pipe in the direction of the outlet opening. If the vehicle is standing in an enclosed area, or if the wind is still, there may be a temperature build up in the region around the exhaust pipe outlet opening. This temperature may rise to a level that may damage components close to the outlet opening or that may hurt a pedestrian passing by. By the inventive solution, the temperature in the close vicinity of the exhaust pipe outlet opening is reduced to a level lower than the exhaust gas flowing in the exhaust pipe.

The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.

REFERENCE SIGNS

1 : Exhaust gas control device

2: Exhaust tail pipe

3: Exhaust outlet cover 4: Radial openings

5: Exhaust outlet

6: Hinge

7: Resilient member

8: Weight

9: Main exhaust gas flow

10: Diluted exhaust gas flow

1 1 : Temperature sensor

12: Actuator

Claims

1. Exhaust gas control device (1), comprising an exhaust tail pipe (2) and an exhaust outlet cover (3), where the exhaust tail pipe (2) comprises a plurality of radial openings (4) near the exhaust outlet (5), characterized in that the exhaust outlet cover (3) is in a closed state when the exhaust mass flow is below a first mass flow value such that the exhaust gas is distributed through the radial openings (4), and that the exhaust outlet cover (3) opens when the exhaust mass flow rises above the first mass flow value.

2. Exhaust gas control device according to claim 1, characterized in that the exhaust outlet cover (3) is completely open when the exhaust mass flow is larger than a second exhaust mass flow value.

3. Exhaust gas control device according to claim 1, characterized in that the exhaust outlet cover (3) is completely open when the vehicle speed is above a predefined level.

4. Exhaust gas control device according to claim 1, characterized in that the exhaust outlet cover (3) is completely open when the actual wind speed at the vehicle is above a predefined level.

5. Exhaust gas control device according to any of claims 1 to 4, characterized in that the exhaust outlet cover (3) is held in the closed state by a weight (8).

6. Exhaust gas control device according to any of claims 1 to 4, characterized in that the exhaust outlet cover (3) is held in the closed state by a resilient element (7).

7. Exhaust gas control device according to any of claims 1 to 4, characterized in that the exhaust outlet cover (3) is held in the closed state by a temperature sensitive member.

8. Exhaust gas control device according to claim 7, characterized in that the temperature sensitive member is a bi-metal controlled valve.

9. Exhaust gas control device according to claim 7, characterized in that the temperature sensitive member comprises a temperature sensor (11) and an electrical actuator (12).

10. Exhaust gas control device according to any of claims 1 to 9, characterized in that the exhaust outlet cover (3) comprises two cover halves.

11. Exhaust gas control device according to any of claims 1 to 10, characterized in that the first mass flow value is larger than the exhaust mass flow of the engine when the vehicle engine is regenerating a particulate filter and the vehicle is standing still and the engine load is low.

12. Exhaust gas control device according to claim 11, characterized in that the first mass flow level is twice the exhaust mass flow of the engine when the vehicle engine is regenerating a particulate filter and the vehicle is standing still and the engine load is low.

13. Exhaust gas control device according to any of claims 1 to 12, characterized in that the exhaust outlet cover (3) is held in the closed position when the vehicle engine is regenerating a particulate filter and the vehicle is standing still and the engine load is low.

14. Exhaust gas control device according to any of claims 1 to 13, characterized in that the first mass flow value is equal to the second mass flow value.

15. Vehicle comprising an exhaust gas control device according to any of claims 1 to 14.