WO2006032913A1

WO2006032913A1 - Exhaust pressure governor

Info

Publication number: WO2006032913A1
Application number: PCT/GB2005/003682
Authority: WO
Inventors: Clive Henry Buckberry; Alan Melvyn Bhimani
Original assignee: Imi Vision Limited
Priority date: 2004-09-25
Filing date: 2005-09-23
Publication date: 2006-03-30
Also published as: WO2006032913A8; GB0421381D0

Abstract

The exhaust conduit (34) of an internal combustion engine, for example a diesel engine, includes an exhaust pressure governor valve (14, 33) that serves to create and control, especially for engine braking purposes, a back pressure in the conduit (34). The valve (14, 33) is characterised in that it comprises a pressure control element (20) defining a plurality of flow passageways (23) for the exhaust gas which are configured to cause the gas to expand as it flows through them, and a restriction member (19) operatively associated with the pressure control element (20) for selectively varying the number of the passageways (23) exposed to the gas flow whereby the back pressure generated in the conduit (34) upstream of the valve (14, 33) may be selectively varied.

Description

EXHAUST PRESSURE GOVERNOR

This invention relates to exhaust gas management, more particularly to Exhaust Pressure Governor (EPG) valves used for engine braking and engine management especially on diesel vehicles.

The use of an EPG valve in the exhaust conduit of an internal combustion engine (ICE) to create and to some degree control a back pressure in the exhaust conduit between the valve and the cylinder is well known and documented in the art. There are two main functions of EPG valves. The first is to create a back pressure on the exhaust side of the cylinders which acts as a brake, and the other is to create a back pressure on the cylinders when the vehicle is stationary and at idle to control the temperature at which the engine idles. By managing this temperature the engine can be made to operate more efficiently and idle at a lower rpm.

The most common type of EPG valve, as exemplified in United States patent number 6,152,853, is a butterfly valve which is located in the exhaust conduit, and this or a similar system is currently used on the majority of commercial vehicles to provide up to around 90 % of their braking. However, although a simple butterfly valve provides a practical solution there are a number of problems associated with using it as the back pressure control element. One problem associated with butterfly valves is that as they are centrally pivoted there is a danger that they can fail closed - i.e. there is a possibility that if there is a failure then the valve could fail in a closed position and the exhaust pressures acting on the valve would hold it closed resulting in a build up of pressure within the exhaust conduit above those required for braking. This could lead to the unwanted phenomenon of forced opening of the combustion chamber exhaust valves. Several solutions are known in the art for overcoming these problems such as providing bleed holes in the butterfly valve or a bypass with a burst valve which opens should the pressure upstream of the butterfly valve increase above a specific pressure. Such remedies increase the complexity and ultimately the cost of a solution. Another problem associated with butterfly valves is that while they are effective for controlling fluid flow rates they are not effective for controlling back pressure. To enable the maximum flow rate needed through the exhaust conduit, all the control in the region required by such applications in vehicle breaking occurs when the valve is very close to its seat. Thus over an operational rotation of 90 degrees all the control occurs within approximately the first 10 degrees opening of movement. When trying to control the pressure in a linear way then this, combined with the rotational to linear relationship, makes the necessary control hard to achieve.

Another EPG valve used on vehicles is basically a large poppet valve with a proportional actuator. This solution has a number of problems associated with it and although used commercially does not provide a satisfactory solution. One of the main problems is similar to that which occurs with butterfly valves in that due to the orifice size required to provide the required maximum flow, for a simple poppet valve, the area of control of the back pressure is substantially within the first 10% of the lift of the actuator. Because of the nature of poppet valves there is no linear relationship between valve opening and back pressure thus giving a non linear (approximating exponential) control over a very short travel resulting in inaccurate and difficult control. Effectively the entire control of the back pressure occurs within the first 3mm of valve lift.

Another problem associated with the poppet valve is that of valve chatter. Due to the small travel of the closure from the valve seat during back pressure control and to the pulsile nature of an internal combustion engine, the valve has a tendency to chatter and hit the valve seat as the proportional control attempts to maintain a steady back pressure. This valve chattering creates a large amount of noise and is highly undesirable. As there is pneumatically-operated proportional positioning of the poppet valve closure, a compressible fluid is being used to attempt to position the valve accurately to a high resolution against a pulsile flow and this results in irregular pressure control.

While the existing solutions work reasonably as a brake, due to the total control being only over a few millimetres of the actuator travel, and to the pulsile nature of the exhaust gas, the valves can only give a few discrete braking positions. This means that, using current technology, it is not possible to have a proportional EPG valve which gives proportional braking dependant on the input from the driver, i.e. there is not the finesse of control to enable the braking back pressure created on the engine to be proportional to the movement of the brake pedal.

In addition it is not possible to modulate the EPG valve to use the back pressure to act as a speed modulator, for example when the vehicle is going downhill.

The present invention attempts to mitigate these problems by providing an exhaust pressure governor valve that gives an enlarged control zone resulting in increased proportional back pressure control.

According to one aspect of the present invention, there is provided an internal combustion engine having an exhaust gas pressure governor valve located in the exhaust conduit thereof, the valve comprising a valve body having an inlet and an outlet defining a flow path therebetween, a pressure control element located in the flowpath and comprising a plurality of flow passageways for the exhaust gas and configured to cause the gas to expand as it flows therethrough, and a restriction member operatively associated with the pressure control element for selectively varying the number of passageways exposed to gas flow and, therefore, the back pressure generated, in use, in the exhaust gas conduit upstream of the valve.

Preferably, when the valve is in the fully restricted position there is maintained a minimal flowpath through the valve, the restriction caused by said restriction member resulting in a maximum allowable back pressure upstream of the valve. Preferably this maximum back pressure is in the region of 6 to 10 bar.

In a preferred arrangement the restriction caused by the restriction member in the fully restricted position causes a maximum back pressure, equivalent to maximum braking, when the engine is running under its minimum load conditions. Preferably the passageways, each of which has an inlet, through which the flow enters, and an outlet, through which the flow exits, increase in cross sectional area from inlet to outlet thereby aiding the expansion of the gas as it passes therethrough.

In one preferred arrangement the passageways comprise a number of substantially 90 degree turns round which the flow must pass. Preferably these flow paths may subdivide to aid expansion of the gas.

In an alternative preferred arrangement the passageways comprise a number of vortex chambers with the flow entering tangentially to the outer edge of the chamber and spiralling to an outlet in the centre of the chamber.

In a further preferred arrangement, the passageways are circular in cross section and the diameter of the passageway increases from inlet to outlet.

In one preferred arrangement, the pressure control element containing the expansion passageways comprises a plurality of individual profiled disc shaped elements which together form a toroidal cylinder, and a plurality of passageways leading from the internal surface of the cylinder wall to the external surface of the cylinder wall.

In an alternative preferred arrangement, the pressure control element is manufactured as one solid piece of material. For example, the pressure control element may be manufactured from a piece of metal tube with the passageways being drilled or bored into it. In an alternative preferred arrangement the pressure control element is cast as one piece with the passageways formed in it as part of the casting process.

Preferably, the restriction member comprises a closure which fits concentrically within the central bore of the pressure control element and is movable along the central axis of the pressure control element to cover and expose a variable number of entrances to the passageways. Preferably, the tolerance of fit between the external surface of the closure and the internal surface of the cylinder bore is such that the exhaust gas leaking through this gap and then out of the passageways is not sufficient to reduce the back pressure created below the maximum required back pressure. Alternatively, the restriction member may be stationary and the pressure control element movable relative thereto by means of an actuator.

Preferably, the number and location of the passageways is such that a variable control of the back pressure created can be tailored to suit a specific engine design and /or control system. For example, by varying the position and number of passageways a substantially linear relationship between restriction member displacement and back pressure may be achieved. Alternatively, if greater control is required close to maximum pressure then the position and number of passageways can be modified to increase the displacement of the restriction member in which it controls these pressures.

According to another aspect of the present invention, there is provided an exhaust gas conduit, or a part thereof, incorporating an exhaust gas pressure governor valve as defined above.

According to yet another aspect of the present invention, there is provided a method of governing the back pressure in an exhaust gas conduit of an internal combustion engine which comprises using an exhaust gas pressure governor valve as defined above.

According to a still further aspect of the present invention, there is provided the use, for governing the back pressure in an exhaust conduit of an internal combustion engine, of an exhaust gas pressure governor valve as defined above.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagram of an ICE exhaust conduit incorporating an EPG valve for use with the invention;

Figure 2 is a diagram of a flowpath of a pressure control element for an EPG valve for use in the invention;

Figure 3 is a diagram of an alternative pressure control element of a valve for use in the invention;

Figure 4 is a diagram of an alternative valve design for use in the invention;

Figure 5 is a diagram of an alternative pressure control element of a valve for use in the invention;

Figure 6 is a diagram of an alternative passageway arrangement of a valve for use in the invention;

Figure 7 is a diagram of a control system for controlling the EPG valve for use in the invention; and

Figure 8 is a diagram of an alternative pressure control element of a valve for use in the invention

Referring to Figures 1 to 3 an EPG valve 1 is shown which comprises a valve body 2, which may be a cast metal body, with an inlet 3 into which exhaust gas from the engine flows, and an outlet 4 from which the exhaust gas exits with a flowpath therebetween. In the flowpath there is a valve restriction member 5, which is positionable by a linear actuator 6 via an actuator arm 7 to move the restriction member 5 axially within the bore of a pressure control element 8. Axial movement of restriction member 5 within the pressure control element 8 selectively covers and uncovers a number of flowpaths 9 (only one shown for clarity), leading from the inner surface 10 to the outer surface 11 of the pressure control element 8. The flowpath 9 increases in cross sectional area as it passes from the inner surface 10 to the outer surface 11 enabling the exhaust gas to expand. The pressure control element 8 consists of a thick walled cylinder with a plurality of passageways 9 selectively uncovered to effectively increase the number of passageway inlets 12 through which the exhaust gas can flow. The distribution of the passageways 9 throughout the element 8 can be varied to give the finesse of control required, for example they may be distributed in such a manner as to give a linear relationship between displacement of the restriction member 5 and the back pressure created, or alternatively may be positioned to give a bias towards more control in a specific back pressure range, hi addition the sizing and number of the passageways may be varied to accommodate a number of engine sizes, enabling the rest of the structure to remain common. The pressure control element 8 is preferably manufactured as a single element, ideally as either a pressure die casting or an investment casting

The axial movement of the restriction member 5 is limited by a lip 13 placed on its upper edge, but this may be similarly achieved by internal restrictions within the actuator 6. When restriction member 5 moves such that its lip 13 abuts the pressure control element 8, the valve is in its fully restricted position creating its maximum back pressure on the engine. However, in that position, the valve is not fully closed as a through flow of exhaust is required at all times. In this embodiment the through flow of exhaust is enabled by the clearance of the outer surface of the restriction member 5 and the inner surface 10 of the pressure control element 8. By maintaining a minimum clearance between these parts there is a constant flowpath between the two components and out through the passageways.

Referring to Figures 4 and 5 an alternative arrangement of an EPG valve is shown in which a valve 14 comprises a body 15 with an inlet 16 and an outlet 17 and a valve cavity 18. Extending into the valve cavity 18 is an inlet extension 19 which is substantially cylindrical in shape. A pressure control element 20 with a central bore extending partway into it is placed about the inlet extension 19 and can move along the direction of the central axis of the bore such that it surrounds greater or lesser part of the inlet extension 19. The axial movement of the pressure control element 20 is controlled by a proportionally acting linear actuator 21, to which the pressure control element 20 is connected by means of an actuator rod 22. The pressure control element 20 has a number of passageways 23 passing from its interior 24 to its exterior 25. As the actuator 21 moves the pressure control element 20 away from the inlet extension 19 a progressively increasing number of the passageways 23 are exposed allowing exhaust gas to pass therethrough. As shown in this embodiment the passageways 23 can simply be a plurality of holes extending between the interior 24 and the exterior 25 of the pressure control element 20. The amount of flow restriction caused by the passageways can be controlled by changing their length, effectively controlling the outer diameter of the pressure control element 20. hi addition to reduce noise by creating a more controlled pressure let down across the valve the passageways may expand in cross sectional area as the gas passes through them - i.e. the diameter of the holes may increase from interior to exterior such that the passageway forms the shape of a truncated cone, hi operation the actuator 21 moves the control element 20 proportionally between two extreme positions, one where there is a maximum back pressure and one where there is a minimum back pressure. These two positions may be controlled by the physical constraints of the valve or internally within the actuator 21. Either way, in the minimum back pressure position there is a maximum number of passageways exposed, and to ensure minimum back pressure in this position the passageways may increase in size as they are progressively exposed. When in the fully retracted position the pressure control element 20 is not moved completely clear of the inlet extension 19 such that the exhaust gas must still pass through the pressure control element 20, effectively enabling the inlet extension 19 to act as a guide for the pressure control element 20 as it closes. As described in the previous embodiment it is important that there is no complete shut off of the valve and that there is always a bleed path for the exhaust. This may be achieved as in the previous embodiment but as shown in this embodiment, to enable the valve geometry to act as the restriction of the travel of the pressure control element 20 in the fully closed position the end 26 of the inlet extension 19 abuts the end of the bore in the pressure control element 20, preventing it moving further. As this effectively creates an annular seal, leakage holes 27 are provided in the end face of the pressure control element 20 to prevent total blockage of the flow.

Referring to Figure 6 an alternative arrangement of the passageways of Figure 5 is shown. In Figure 5 as there are discrete rows of passageways, a fairly stepped increase in back pressure would occur as the pressure control member restricts the flow of exhaust gas. The arrangement in Figure 6 overcomes this stepped effect by overlapping the passageways such that the second row of passageways is starting to be exposed before the first row of passageways is fully exposed thus smoothing the relationship between actuator displacement and back pressure.

Referring to Figure 7, in operation a controller 28 receives signals from the engine 29, the brake pedal 30, a selectable speed limiter/cruise control 31 and a pressure sensor 32 located upstream side of the valve restriction either in the EPG valve 33 or in the exhaust conduit 34. hi response to these signals the controller 28 sends a signal to the EPG valve 33 actuator causing it to function to provide a specific back pressure on the engine 29.

The controller 28 may be a stand alone controller for the EPG system or may alternatively be connected to, or be a subsystem of, the whole vehicle control system and have access to the data contained on the vehicle control system.

For the purpose of the braking mode of operation, the brake pedal 30 has a sensor associated with it which provides a proportional signal dependant on the displacement of the pedal. The controller 28 receives the braking signal, and using signal inputs from the engine 29, and where the controller 28 is linked to or a part of the whole vehicle control system other signals, for example speed, calculates the required back pressure to apply the required braking. A signal is then sent to the EPG actuator 35 which operates in a proportional manner and displaces the valve closure member to provide the required back pressure. The pressure sensor 32 located upstream of the EPG valve 33 senses the back pressure created and the actuator 35 is modulated via the controller 28 to ensure the required back pressure is applied and maintained. As the driver increases or decreases the displacement of the brake pedal 30 the EPG valve 33 will receive signals via the controller 28 to respond to increase or decrease the applied back pressure accordingly.

In speed regulation mode, a required speed may be requested by the driver via a selectable speed limiter/cruise control 31, and a signal related to this speed requirement is sent to the vehicle control system. The vehicle control system receives this speed requirement signal and other signals from various sensors on board, e.g. the speed of the vehicle, engine and other parameters and calculates the required braking back pressure set up by the EPG valve 33. The EPG controller 28 then actuates the EPG valve actuator 35 to create the required braking and hence speed modulation, hi this manner, for example on long downhill roads, the EPG valve 33 can be used to control the speed of the vehicle. Further, by controlling all aspects of the engine 29, including controlling the back pressure via the EPG valve 33, the vehicle can maintain a speed whilst having a greater element of control over all engine parameters, thus improving fuel efficiency by operating the engine at optimal conditions.

Referring to Figure 8 an alternative arrangement for passageways of a valve of the invention is shown wherein a plurality of passageways 36, 37, 38 are shown and which are arranged on a control element of the invention as an alternative to the holes shown in Figure 5 or the torturous path shown in Figure 3. The passageways are shaped such that, as the control element is progressively exposed, an increasing area of flow path is available for the exhaust gas ranging from a minimum at 39 to a maximum at 40 and whereby, in use, a variable amount of back pressure may be achieved by exposing a greater or lesser amount of the flow passages 36, 37, 38.

The dimensions of the flow passages, e.g. its width at the minimum flow area and its rate of change of gradient, may be altered to characterise the amount of back pressure created by a certain amount of actuation of the valve. To achieve finer control at higher back pressures then the flowpaths may have different geometry, with only one or a few of the flowpaths being exposed initially, i.e. flow passage 36 will be exposed first and then with continued actuation of the valve flow passages 37and 38 will be exposed. Alternatively all the flow passages may have the same dimensions. The area of the flow passages at their maximum exposure, i.e. when the full flow path is exposed, is equal or larger to the inlet flow area and therefore creates negligible back pressure on the system.

Claims

1. An internal combustion engine having an exhaust gas pressure governor valve located in the exhaust conduit thereof, characterised in that the valve (1, 14, 33) comprises a valve body (2, 15) having an inlet (3, 16) and an outlet (4, 17) defining a flowpath therebetween, a pressure control element (8, 20) located in the flowpath and comprising a plurality of flow passageways (9, 23) for the exhaust gas and configured to cause the gas to expand as it flows therethrough from the inlet to the outlet, and a restriction member (5, 19) operatively associated with the pressure control element (8, 20) for selectively varying the number of passageways (9, 23) exposed to the gas flow and, therefore, the back pressure generated, in use, in the exhaust gas conduit (34) upstream of the valve (1, 14, 33).

2. An internal combustion engine according to claim 1 wherein the flow passageways (9, 23) have a cross-sectional area which increases in the direction of flow of the exhaust gas thereby aiding expansion of the gas as it flows therethrough.

3. An internal combustion engine according to claim 1 or claim 2 wherein the flow passageways (9, 23) are of substantially circular cross-section.

4. An internal combustion engine according to any of claims 1 to 3 wherein the flow passageways (9, 23) comprise a plurality of substantially 90° turns.

5. An internal combustion engine according to any one of claims 1 to 4 wherein the flow passageways (9, 23) define a plurality of vortex chambers which the exhaust gas enters substantially tangentially at an outer region of the chamber and flows in vortex fashion to an outlet located substantially on a centreline of the chamber.

6. An internal combustion engine according to any one of claims 1 to 5 wherein the pressure control element (8, 20) comprises a plurality of annular disc¬ shaped elements each having channels formed in its surfaces, the disc-shaped elements being stacked together to form an annular cylinder whereby the channels of adjacent elements define flow passageways (9, 23) extending from the inner surface (10) of the cylinder to the outer surface (11) of the cylinder.

7. An internal combustion engine according to any one of claims 1 to 5 wherein the pressure control element (8, 20) comprises a unitary member having the flow passageways (9, 23) drilled or cast therein.

8. An internal combustion engine according to any one of claims 1 to 7 wherein the pressure control element (8) is static and the restriction member (5) is in the form of a plug axially moveable, by an actuator (6), in a bore of the element (8) so as to selectively vary the number of passageways (9, 23) through which the gas can flow.

9. An internal combustion engine as claimed in any one of claims 1 to 7 wherein the restriction member (19) is static and the pressure control element (20) is axially moveable relative thereto by an actuator (21, 35) so as to selectively vary the number of passageways (9, 23) through which the gas can flow.

10. An internal combustion engine as claimed in any one of the preceding claims wherein, when the valve (1, 14, 33) is in a fully restricted position, a minimal flowpath is maintained through the valve (1, 14, 33).

11. An internal combustion engine as claimed in claim 10 wherein, the restriction caused by the restriction member (5, 19) in the fully restricted position causes a maximum back pressure upstream of the valve (1, 14, 33).

12. An internal combustion engine as claimed in claim 11 wherein the maximum back pressure is equivalent to maximum braking when the engine is running under its minimum load conditions.

13. An internal combustion engine as claimed in any one of the preceding claims wherein, the number and location of the passageways (9, 23) is configured such that a substantially linear relationship between relative displacement of the restriction member (5, 19) and control element (8, 20) and back pressure can be achieved.

14. An internal combustion engine as claimed in any one of claims 1 to 12 wherein, the position and number of passageways (9, 23) is configured to increase the relative displacement of the restriction member (5, 19) and control element (8, 20) for controlling pressures close to the maximum back pressure.

15. An exhaust gas conduit, or a part thereof, for an internal combustion engine, incorporating an exhaust gas pressure governor valve as characterised in any one of claims 1 to 14.

16. A method of governing the back pressure in an exhaust gas conduit of an internal combustion engine which comprises using a valve as characterised in any one of claims 1 to 14.

17. The use, for governing the back pressure in an exhaust conduit of an internal combustion engine, of a valve as characterised in any one of claims 1 to 14.