Turbogenerator

Field of the Invention

The present invention relates to a method and apparatus for controlling the flow of exhaust fluid to a turbogenerator, and more particularly, to a method and apparatus for controlling the flow of exhaust fluid to a turbogenerator using a regulator valve.

Background of the Invention

Turbochargers and turbogenerators can be fitted to the exhaust systems of combustion engines to improve the overall energy efficiency of the system by recovering energy from the waste exhaust gases emitted from the combustion engine. Where both a turbocharger and a turbogenerator are used together, they may work in tandem to increase the energy efficiency of the system still further. In systems of this kind, the turbocharger uses the flow of waste gases from the engine to increase the pressure inside the engine such that the fuel efficiency is improved, whilst the turbogenerator simultaneously generates electrical power from the waste exhaust gases.

Both the turbocharger and the turbogenerator increase the gas pressure in the exhaust system and in the combustion engine. This pressure build-up can sometimes reach undesirable levels where the efficiency of the engine can be greatly reduced, or the combustion engine is damaged. As such, it is desirable to control the pressure inside the energy recovery system to maximise electricity produced by the turbogenerator without negatively impacting the combustion engine.

In energy recovery systems comprising both a turbocharger and a turbogenerator, it is important to regulate and control exhaust fluid flow to each of the components. Additionally, it is important to control the pressure within each section and component of the system. Whilst current methods of controlling these pressures attempt to address this issue, present solutions are unsatisfactory in at least their relatively slow response to pressure changes within the energy recovery system

Objects and aspects of the present claimed invention seek to alleviate at least this problem of the prior art. Summary of the Invention

According to an aspect of the present invention, there is provided a method for controlling the flow of exhaust fluid to a turbogenerator, the method comprising the steps of:

driving a turbogenerator turbine with a flow of exhaust fluid;

providing a waste-gate valve within the flow of exhaust fluid, the waste-gate valve able to move between a waste-gate open position and a waste-gate closed position;

providing a regulator valve within the flow of exhaust fluid, the regulator valve able to move between a regulator open position and a regulator closed position;

monitoring the position of the waste-gate valve between the waste-gate open position and the waste-gate closed position;

wherein the method further comprises the steps of measuring a rate of change in the position of the waste-gate valve, and

controlling the position of the regulator valve between the regulator open position and the regulator closed position in response to the rate of change in the position of the waste-gate valve.

Preferably, the method further comprises determining if the rate of change is smaller than, equal to or greater than a predetermined or calculated maximum value. Preferably, the method further comprises determining if the rate of change is smaller than a predetermined or calculated maximum value. Preferably, the method further comprises determining if the rate of change is equal to a predetermined or calculated maximum value. Preferably, the method further comprises determining if the rate of change is greater than a predetermined or calculated maximum value.

Preferably, the step of controlling the position of the regulator valve comprises moving the regulator valve towards the regulator open position if the rate of change is greater than or equal to the predetermined or calculated maximum value.

Preferably, the step of controlling the position of the regulator valve comprises maintaining the position of the regulator valve if the rate of change is smaller than the predetermined or calculated maximum value.

Preferably, the step of controlling the position of the regulator valve comprises the step of proceeding to a subsequent method step if the rate of change is smaller than the predetermined or calculated maximum value. Preferably, the step of controlling the position of the regulator valve comprises moving the regulator valve towards the open position of the regulator valve or towards the closed position of the regulator valve by a predetermined distance. Preferably, the predetermined distance is fixed. Preferably, the predetermined distance is dynamic and varies with the regulator position. Preferably, the predetermined distance is found using a calibration curve.

Preferably, the step of controlling the position of the regulator valve comprises calculating a distance to move the regulator valve towards the open position of the regulator valve or towards the closed position of the regulator valve. Preferably, the step of calculating the distance to move the regulator valve comprises interrogating or using the rate of change. Preferably, the step of calculating step to move the regulator valve comprises comparing the difference between the rate of change and the maximum rate of change.

Preferably, the subsequent optional method step comprises determining if the position of the waste-gate valve lies within a range of optimal waste-gate positions.

Preferably, the method further comprises moving the regulator valve towards the regulator open position when the position of the waste-gate valve lies between the waste-gate open position and the range of optimal waste-gate positions.

Preferably, the method comprises moving the regulator valve towards the regulator closed position when the position of the waste-gate valve lies between the waste-gate closed position and the range of optimal waste-gate positions.

Preferably, the method comprises maintaining the position of the regulator valve when the position of the waste-gate valve lies within the range of optimised positions. This is beneficial as it stops over-control or control jitter of the regulator valve with respect to the waste-gate valve as the regulator valve is not moved by this method when the waste-gate valve is within the optimal range of waste-gate positions.

Preferably, the optimal range of waste-gate positions is a range. Preferably, the optimal range of waste-gate positions is a static range. Preferably, the optimal range of waste-gate positions is a dynamic range. Preferably, the optimal range of waste-gate positions is centred on an optimal value. Preferably, the optimal value is predetermined. Preferably, the optimal value is dynamic. Preferably, the optimal range of waste-gate positions is a single value.

Preferably, the method further comprises the step of repeating the method. Preferably, the method is continually looped.

Preferably, the step of repeating the method comprises pausing for a predetermined or calculated period of time before repeating the method. Preferably, the method comprises pausing for a predetermined or calculated period of time if the regulator valve has been moved by the method. Preferably, the time period is predetermined and fixed.

Preferably, the step of providing a regulator valve within the flow of exhaust fluid comprises placing the regulator valve in a position where the flow of exhaust fluid through the regulator valve bypasses the turbogenerator.

Preferably, the method further comprises the step of providing a turbocharger within the flow of exhaust fluid.

Preferably, the step of providing a turbocharger within the flow of exhaust fluid comprises providing the turbocharger in parallel with the turbogenerator. Preferably, the step of providing a turbocharger within the flow of exhaust fluid comprises splitting the flow of exhaust fluid between the turbocharger and the turbogenerator.

Preferably, the step of providing a waste-gate valve within the flow of exhaust fluid comprises providing the waste-gate valve in parallel with the turbocharger and in series with the turbogenerator.

Preferably, the step of providing a waste-gate valve within the flow of exhaust fluid comprises providing the waste-gate valve in series with the turbocharger and in parallel with the turbogenerator.

Preferably, the method further comprises controlling the flow of exhaust fluid to the turbocharger with the waste-gate valve.

Preferably the method comprises driving a plurality of turbogenerator turbines with a flow of exhaust fluid. According to a second aspect of the invention, there is provided a turbogenerator system configured to operate the method and any of its optional features described herein.

Detailed Description

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a schematic drawing of a turbogenerator system in accordance with the present invention; and

Figure 2 is a flowchart depicting a method of controlling fluid flow to a turbogenerator in accordance with the present invention.

Referring to Figure 1 there is depicted a schematic drawing of exhaust energy recovery system 10 in accordance with the present invention. The exhaust energy recovery system 10 comprises an engine 12 which, during operation, is supplied with air by a compressor 14. Whilst the engine 12 is operational, the airflow into the engine 12 from the compressor 14 is cooled by the engine charge air cooler 16 to improve the efficiency of the system.

In the illustrated system the compressor 14 forms part of a turbocharger 18. In use, the engine 12 produces waste exhaust gases, also known as exhaust fluid, that exit the engine 12 and enter the engine exhaust conduit 20. The turbine 19 of the turbocharger 18 is rotated by waste gas flow, which is also known as the exhaust fluid flow, from the engine 12 through the engine exhaust conduit 20 towards the exhaust outlet 21 . The exhaust outlet 21 vents the waste exhaust gases to the external environment. Due to this rotation of the turbine 19 of the turbocharger 18, the compressor 14 draws in air through an air inlet 15 to supply air to the engine 12.

The actions of the compressor 14 and turbine 19 of the turbocharger 18 serve to increase the pressure inside the engine 12 and engine exhaust conduit 20. The engine exhaust conduit 20 comprises a waste-gate valve 22 to control, limit and prevent the build-up of pressure inside the engine 12 and engine exhaust conduit 20.

The waste-gate valve 22 is located on a branch of the engine exhaust conduit 20 parallel to the turbocharger 18 and the exhaust outlet 21 . As such, the waste-gate valve 22 vents waste exhaust fluid flow gases away from the turbocharger 18 and towards a turbogenerator 24.

Within the engine exhaust conduit 20, the position of the waste-gate valve 22 can be varied between a closed position and an open position by the engine controller 26. The engine controller 26 communicates with the waste-gate valve 22 via the communication link 27. In the open position, the waste-gate valve 22 does not impede the flow of waste exhaust gases through the engine exhaust conduit 20 towards the turbogenerator 24, and in the closed position, the waste-gate valve 22 completely occludes the engine exhaust conduit 20, and no waste exhaust gases can flow towards the turbogenerator 24. Instead, in the closed position, the waste-gate valve 22 directs the flow of waste exhaust gases towards the turbocharger 18.

The position of the waste-gate valve 22 is continuous and can be set and held at any position in between the open position and the closed position. When the waste-gate valve 22 is in any position other than the closed position, a portion of the waste exhaust gases is directed through the waste-gate valve 22 and a second portion of the waste exhaust gases is directed towards the turbocharger 18. An actuator is used to move the waste-gate valve 22 between positions, the actuator itself controlled by the engine controller 26 via the communication link 27.

In operation, the engine controller 26 changes the position of the waste-gate valve 22 to vary the flow of waste exhaust gases to the turbocharger 18 such that the engine 12 consistently operates at optimum boost pressure. The engine controller 26 can reduce the pressure inside the engine 12 by moving the waste-gate valve 22 towards its open position such that more waste exhaust gases are diverted away from the turbocharger 18. Alternatively, the engine controller 26 can increase the pressure inside the engine 12 by moving the waste- gate valve 22 towards its closed position such that less waste exhaust gases are diverted away from the turbocharger 18. As such, the position of the waste-gate valve 22 is configured to control the pressure inside the engine 12. In this way, the waste-gate valve 22 can be controlled by the engine controller 26 to prevent performance reducing pressure build-up inside of the engine 12.

Waste exhaust gases which are diverted away from the turbocharger 18 through the waste- gate valve 22 flow along a turbogenerator conduit 25 towards the turbogenerator 24. In the turbogenerator 24, the flow of exhaust gases is used to generate electricity. In the turbogenerator 24, the turbine 28 is rotated by the flow of the waste exhaust gases, concomitantly rotating a generator 30 to produce electrical power. The waste exhaust gases that flow through the turbine 28 are emitted into the environment through a second exhaust conduit 31 .

Further to the waste-gate valve 22, the flow of waste gases along the turbogenerator conduit 25 to the turbogenerator 24 is controlled by two additional valves: an isolator valve 32 and a regulator valve 34. The isolator valve 32 is located within the turbogenerator conduit 25 in series with the inlet to the turbine 28, such that the isolator valve 32 and can be used to isolate the turbine 28. To isolate the turbine the position of the isolator valve 28 is moved to completely occlude the turbogenerator conduit 25 and prevent all fluid flow to the turbine 26.

The regulator valve 34 is located on a branch of the turbogenerator conduit 25 parallel to the inlet of the turbine 28. In this embodiment of the invention, the regulator valve 34 links the turbogenerator conduit 25 to the second exhaust conduit 31 . The regulator valve 34 provides a bypass to the turbogenerator 24 and turbine 28. As such, the regulator valve 34 can be used to regulate fluid flow to the turbogenerator 24 and turbine 28. Bypassing the turbine 28 reduces the pressure inside the turbogenerator conduit 25, which concomitantly reduces exhaust fluid flow to the turbocharger 18.

The regulator valve 34 regulates flow by changing position. The position of the regulator valve 34 can be varied from a closed position to an open position. In the open position, the regulator valve 34 does not impede the flow of waste exhaust gases, and fluid flow is therefore directed towards the second exhaust outlet 31 . In the closed position, the regulator valve 34 is completely occluded, and the flow of waste exhaust gases is directed towards the turbine 28.

The position of the regulator valve 34 is continuous and can be set and held at any position in between its open position and its closed position. In this case, a portion of the exhaust fluid is directed through the regulator valve 34 and a second portion of the exhaust fluid is directed towards the turbogenerator 24. The regulator valve 34 comprises an actuator to change its position. The actuator of the regulator valve 34 is in communication with a power electronics unit 36 via communication link 37 of the energy recovery system 10. The power electronics unit 36 is connected to generator 30 and provides the electrical output 38 of the turbogenerator system 10. The position of the waste-gate valve 22 is communicated to the power electronics unit 36 by the engine controller 26 via communication link 39. There is depicted in Figure 2 a flow chart of the method 100 for controlling the flow of exhaust fluid to a turbogenerator 24 in an energy recovery system 10 in accordance with an embodiment of the present invention.

The method 100 comprises providing the apparatus as described in Figure 1 and operating the apparatus. As such, the engine 12 is running and producing exhaust fluid which is flowing through the engine exhaust conduit 20 and powering the turbine 19 of the turbocharger 18. Additionally, the waste-gate valve 22 is also partially open such that exhaust fluid flows through the turbogenerator conduit 25 and powers the turbine 28 of the turbogenerator 24. The amount of fluid flow to the turbogenerator 24 is controlled by the position of the waste-gate valve 22 and the regulator valve 34, where the position of the regulator valve 34 is controlled by the power electronics 36.

The method 100 further comprises step 102, which involves monitoring the position of waste-gate valve 22 using the engine controller 26. The position of the waste-gate valve 22 is measured over time. From this continuous monitoring, the rate of change in the position of waste-gate valve 22 can be determined, and this measurement is hereinafter described as the rate of change value (ROC).

The subsequent method step 104 is then performed. In this step, the engine controller 26 then compares the rate of change value ROC to a maximum rate of change value MAX. The maximum rate of change value MAX is predetermined for the system and stored in a memory of the engine controller 26.

If the rate of change value is greater than or equal to the maximum rate of change value MAX, then the method 100 resets a waste-gate valve timer WGT in method step 106. If the comparison of method step 104 instead finds that the rate of change ROC value is less than the maximum rate of change value MAX, then the method proceeds to step 108. Method step 108 comprises incrementing the waste-gate timer WGT and proceeding to step 1 10.

The waste-gate timer WGT only reset when the rate of change ROC is greater than or equal to the maximum rate of change value MAX. Thus, the waste-gate timer WGT measures the time between this event reoccurring.

After the waste-gate timer, WGT has been reset in method step 106 the method 100 proceeds to perform method step 118. Method step 1 18 comprises moving the regulator valve 34 towards its open position by an amount D and then pausing the method for a period of time T before proceeding to start method step 102 again.

Subsequent to incrementation of the timer in step 108, the position of the waste-gate valve WG is compared against a range of optimal waste-gate positions OPT, where OPT-X is the lower limit, and OPT+X is the upper limit of the range of optimal waste-gate positions OPT, respectively.

Method step 1 10, which succeeds step 108, determines if the position of the waste-gate valve WG lies between the waste-gate closed position and the range of optimal waste-gate positions OPT. In particular, if the position of the waste-gate valve WG is less than the lower limit of the range of optimal waste-gate positions OPT-X, then the method 100 proceeds to step 1 14. Or, if the position of the waste-gate valve WG is greater than or equal to the lower limit of the range of optimal waste-gate positions, then the method 100 instead proceeds to step 1 12.

The method step 1 12 compares the position of the waste-gate valve WG against the range of optimal waste-gate positions OPT and determines if the position of the waste-gate valve WG lies between the waste-gate open position and the range of optimal waste-gate positions OPT. In particular, method step 1 12 comprises determining if the position of the waste-gate valve WG greater than the upper limit of the range of optimal waste-gate positions OPT+X. If true then the method 100 proceeds to step method 1 18, where method step 1 18 is the same as described above. Or, if the position of the waste-gate valve WG is less than or equal to the upper limit of the range of optimal waste-gate positions OPT+X, then the method 100 proceeds to step 102 and begins the method 100 again.

The method step 1 14, which may proceed step 1 10, comprises comparing the waste-gate timer WGT against a waste-gate check time WGCT. In particular, if waste-gate timer WGT is less than or equal to the waste-gate check time WGCT then the method 100 proceeds to method step 102, or if the waste-gate timer WGT is greater than the waste-gate check time WGCT then the method 100 proceeds to method step 116.

In essence, method 1 14 checks that enough time, the waste-gate check time WGCT, has passed since the last time than the rate of change ROC exceeded the maximum rate of change MAX before proceeding with method step 1 16, as method step 116 comprises closing the regulator valve 34, which may cause a sudden change in the position of the waste-gate valve WG. Method step 116 comprises moving the regulator valve 34 towards its closed position by an amount D’ and then pausing the method for a period of time T' before proceeding to start method step 102 again.

The distances D, D’ which the regulator valve 34 is moved towards its open or closed position can be provided in several ways. In this embodiment, the distances D, D’ are both predetermined and fixed to be a certain percentage of the distance between the open position and the closed position of the regulator valve 34. In other embodiments it is envisaged, the distances D, D’ would vary in the distance in relation to the difference between the rate of change value ROC and the maximum rate of change value MAX.

Likewise, in this embodiment, the periods of time T, T are set to be predefined values. However, other embodiments are envisaged where the periods of time T, T would vary in length with the difference between the rate of change value ROC and the maximum rate of change value MAX.

The method steps 1 12, 114, 1 16 and 1 18 all proceed to step 102. All routes through the method 100 loops back to step 102. In this way, method 100 is a looped continuous method 100 of monitoring the position of the waste-gate valve 22, WG and actuating the position of the regulator valve 34.

The method 100 controls the regulator valve 34 in reference to the rate of change ROC in the position of the waste-gate valve 22. As such, the method 100 enables the regulator valve 34 to respond quickly to changes in the position of the waste-gate WG, as method 100 does not wait for the position of the waste-gate WG to be beyond acceptable limits but instead responds to quicker movements of the waste-gate valve 22. It has been found that quicker movements of the waste-gate valve 22 are indicative that the position of the regulator valve 34 needs to be controlled to maintain the correct pressure within the engine 12