Patent Description:
Variable geometry turbines (VGT) can be employed in various applications, such as in commercial vehicles, e.g. to improve the energy efficiency of an internal combustion engine driving such a vehicle. The VGT can extract residual energy from the exhaust gas produced by the engine, which can in turn e.g. be used for powering other components in the vehicle, such as a compressor By improving the energy efficiency, the internal combustion engine and corresponding power train can be downsized without a net reduction in output power. As such, proper implementation of a variable geometry turbine can also lead to improved fuel efficiency and reduced emission of harmful exhaust gases, such as NOx and CO<NUM>.

VGTs typically comprise an adjustable nozzle to regulate the mass flow of exhaust gas to the rotor. At low exhaust mass flows, the adjustable nozzle may for example be narrowed, to adjust the aspect ratio of the turbine by accelerating the mass flow to the rotor. However, by narrowing the adjustable nozzle it forms a venturi, reducing the pressure in the exhaust gas as it passes through the adjustable nozzle. As a result, a suction force is applied between the walls of the thus formed venturi, which may cause the adjustable nozzle to narrow further, thereby effectively closing the VGT and restricting the mass flow significantly. This would, in turn, result in a sharp increase in pre-turbine pressure, which can significantly affect the pumping losses of the engine. To avoid the influence of pressure effects in the low mass flow region, the configuration of a VGT can be adjusted to the properties of the internal combustion engine and exhaust system. Due to part-to-part variations between individual VGTs, however, this means that
a significant margin may be used to reduce the sensitivity of VGTs to these pressure effects during use, e.g. due to changing operating conditions or wear of the VGT, engine, or exhaust system. As a consequence of the margin, it may not be possible to utilize the full working range of the VGT, and as such the internal combustion engine may not achieve optimal performance and emissions.

<CIT>, <CIT>, <CIT>, and <CIT> describe known methods for calibrating a VGT.

An object of the present invention is to improve the effectiveness of variable geometry turbines, by adjusting their working range based on operating conditions.

In summary, the invention provides a variable geometry turbine (VGT), comprising an intake channel, a rotor, an adjustable nozzle, a nozzle actuator and a controller. The intake channel is arranged for receiving a mass flow of exhaust gas from an internal combustion engine. The rotor is arranged downstream the intake channel for extracting energy from the mass flow of exhaust gas. The adjustable nozzle comprises a nozzle orifice having an adjustable cross sectional area and arranged for adjusting the mass flow of exhaust gas from the intake channel to the rotor. The adjustable nozzle is adjustable between an open position, in which the nozzle orifice has a maximum cross sectional area, and a closed position, in which the nozzle orifice has a minimum cross sectional area. The nozzle actuator is arranged for actuating the adjustable nozzle between the open position and the closed position, and the controller is arranged for controlling the nozzle actuator based on a nozzle position demand. The controller comprises a calibration routine, arranged for calibrating the VGT during normal operation thereof. In the calibration routine, the controller is arranged for performing the steps of: adjusting the adjustable nozzle from an initial position towards the closed position, while monitoring a pre-turbine pressure measured in the mass flow of exhaust gas upstream the VGT; detecting a deflection point position of the adjustable nozzle at which a sharp difference in the pre-turbine pressure occurs; and adjusting a working range of the nozzle actuator , wherein the minimum cross sectional area in the closed position excludes the detected deflection point position.

Accordingly, the working range of the VGT can be maximized during use, regardless of varying operating conditions, to utilize low exhaust mass flow regions while being less sensitive to the influence of pressure effects in these regions, thereby creating a more predictable exhaust mass flow. By detecting and excluding the deflection point position from the working range, any margin between the deflection point position and the working range of the VGT can be minimized. In this way, performance of the engine can be increased and the emission of harmful exhaust gases, such as NOx, can be reduced.

In some embodiments, the controller is arranged for comparing the detected deflection point position to a stored deflection point position of a pre-calibrated VGT, to determine a deflection point position offset, as a difference between the detected deflection point position and the stored deflection point position. The controller can be arranged for applying the deflection point position offset to the nozzle position demand, so that the difference is applied as a trim to the VGT position demand. This distinguishes from a conventional generic, or average safety margin that can be implemented to cover a large distribution of errors and tolerances between individual VGTs, engines, exhaust systems, and other system components. In contrast, by the applied offset the working range of individual VGTs can be increased, because the safety margin accounting for these variations can be reduced. By determining a deflection point position offset, the working range of an individual VGT can be adjusted with respect to its own respective deflection point position, to avoid the occurrence of the sharp difference in the pre-turbine pressure, without having to implement an average safety margin. In statistical terms this means that the standard deviation between VGTs can be reduced, making it possible to calibrate the mean closer to the optimal deflection point position.

To reduce the effect of measurement errors and dynamic behaviour of components on the detected deflection point position, the controller can be arranged for detecting the deflection point position by monitoring a second derivative of a filtered pre-turbine pressure sensor signal. The second derivative reaches its maximum precisely when there is a strong deviation from a smooth characteristic, which can be used to detect the deflection point position.

The present invention is applicable to various types of actuators, such as hydraulic, pneumatic or electric actuators. As such the VGT is compatible with the most common designs of actuators. Preferably, the controller is arranged for controlling the nozzle actuator to adjust the adjustable nozzle based on the measured pre-turbine pressure, to counteract external forces on the VGT.

In some embodiments, the intake channel is arranged for providing the mass flow of exhaust gas to the rotor in a direction substantially perpendicular to an axis of rotation of the rotor. As such, a radial variant of the rotor is provided, which receives the mass flow of exhaust gas from a radial direction and discharges the mass flow of exhaust gas in an axial direction. The present invention may however also be suitable for other variants of rotor designs, such as axial variants, in which the intake channel is arranged for providing the flow of exhaust gas to the rotor along the axis of rotation of the rotor.

To increase the efficiency of the VGT and accelerate the mass flow of exhaust gas, the intake channel can be formed as a volute that is coaxially aligned with the rotor.

In one embodiment, the adjustable nozzle comprises a slidable element. The element is slidable by the nozzle actuator to close the intake channel. Alternatively, the VGT may also be compatible with adjustable nozzle designs that comprise rotatable or pivotable vanes.

Another aspect of the invention relates to a commercial vehicle, comprising a variable geometry turbine as described herein.

Yet other aspects pertain to a method for calibrating a variable geometry turbine (VGT). The VGT comprises an intake channel, a rotor, and an adjustable nozzle. The intake channel is arranged for receiving a mass flow of exhaust gas from an internal combustion engine. The rotor is arranged downstream the intake channel for extracting energy from the mass flow of exhaust gas. The adjustable nozzle comprises a nozzle throat having an adjustable cross sectional area arranged for adjusting the mass flow of exhaust gas from the intake channel to the rotor, wherein the adjustable nozzle is adjustable between an open position, in which the nozzle throat has a maximum cross sectional area, and a closed position, in which the nozzle throat has a minimum cross sectional area. The method comprises the steps of: (i) adjusting the adjustable nozzle from an initial position towards the closed position, while monitoring a pre-turbine pressure measured upstream the VGT; (ii) detecting a deflection point position of the adjustable nozzle at which a sharp difference in the pre-turbine pressure occurs; and (iii) adjusting a working range of the nozzle actuator, having an adjusted minimum cross sectional area in the closed position that excludes the detected deflection point position.

<FIG> illustrates an embodiment of a variable geometry turbine, VGT <NUM>, e.g. suitable for automotive applications wherein the VGT is arranged in the exhaust system of an internal combustion engine, such as a diesel or spark ignition engine. The VGT <NUM> can for example be part of a mechanical turbocharger, to convert energy recovered from exhaust gases into boost pressure. Alternatively, the VGT <NUM> can for example be used for driving an electric compressor or for driving an electric generator, to convert energy recovered from exhaust gases into electric power, which can e.g. be stored in an electric power source or can be applied directly, to power other components.

The VGT <NUM> comprises an intake channel <NUM>, arranged for receiving a mass flow of exhaust gas from an internal combustion engine. The VGT <NUM> may comprise multiple intake channels <NUM>, each arranged for receiving a mass flow of exhaust gas from the internal combustion engine. For example, the intake channel <NUM> can comprise one or more exhaust gas entry ports, each of which is fluidly connected to one or more exhaust manifolds, which, in turn, are arranged for collecting exhaust gas discharged through exhaust ports on the cylinders of the internal combustion engine.

The VGT <NUM> further comprises a rotor <NUM>, arranged downstream the intake channel <NUM> for extracting energy from the mass flow of exhaust gas received from the intake channel <NUM>. The rotor for example comprises blades for converting kinetic and potential energy in the mass flow of exhaust gas into torque to propel a rotor shaft of the VGT, e.g. to power a compressor or an electric generator. The rotor <NUM> can e.g. be a radial variant, arranged for receiving a mass flow of exhaust gas from a radial direction and discharging the mass flow in an axial direction. Alternatively, the rotor <NUM> can e.g. be an axial variant, arranged for receiving a mass flow of exhaust gas from an axial direction and discharging the mass flow in a radial direction.

As illustrated in <FIG>, the VGT <NUM> comprises an adjustable nozzle <NUM>, comprising a nozzle orifice <NUM> having an adjustable cross sectional area. The adjustable nozzle <NUM> is arranged for adjusting the mass flow of exhaust gas from the intake channel <NUM> to the rotor <NUM>. The adjustable nozzle <NUM> can e.g. comprise sliding or pivoting vane elements, arranged for narrowing or widening the cross sectional area, in dependence of operating conditions of the VGT. The adjustable nozzle <NUM> is adjustable between an open position, in which the nozzle orifice <NUM> has a maximum cross sectional area, and a closed position, in which the nozzle orifice <NUM> has a minimum cross sectional area.

The VGT <NUM> further comprises a nozzle actuator <NUM>, arranged for actuating the adjustable nozzle <NUM> between the open position and the closed position. For example, the VGT <NUM> may additionally comprise a transmission mechanism arranged for providing a mechanical transmission, e.g. comprising a linkage or a drive train, between the nozzle actuator <NUM> and the adjustable nozzle <NUM>. Alternatively, the nozzle actuator <NUM> can be coupled directly to the adjustable nozzle <NUM>. The nozzle actuator <NUM> can e.g. be a pneumatic actuator, arranged for using a gas, such as air, to actuate the adjustable nozzle <NUM>, e.g. via a transmission mechanism. Alternatively, the nozzle actuator <NUM> can e.g. be an hydraulic actuator, arranged for using a fluid, such as water or an oil, for actuating the adjustable nozzle <NUM>. Alternatively, the nozzle actuator <NUM> can e.g. be an electric actuator. Any combinations of the above described types of nozzle actuator <NUM> may also be suitable for actuating the adjustable nozzle <NUM>, e.g. by using a transmission mechanism.

The VGT <NUM> further comprises a controller <NUM>. The controller <NUM> can for example be a processor on board of the VGT. Alternatively, the controller <NUM> can e.g. be part of a central processing unit or an engine control unit, and communicatively coupled with elements of the VGT. The controller <NUM> is arranged for controlling the nozzle actuator <NUM> based on a nozzle position demand, e.g. a nozzle position between the open and closed position, for example based on operating conditions of the VGT such as the pressure upstream and/or downstream the turbine, rotor speed, or power output.

There may be small variations in hardware between individual VGT's, e.g. due to manufacturing and assembly tolerances, deviations in mechanical parts and sensors, and/or wear and degradation of components. Accordingly, the position of the adjustable nozzle <NUM> at which a VGT is most sensitive to pressure effects in the exhaust system, e.g. a deflection point position of the adjustable nozzle at which a sharp difference in pre-turbine pressure upstream the VGT occurs, may vary between individual VGTs. As a result, a mean deflection point position can be considered, and a safety margin can be implemented to account for variations between VGTs. However, this implies that the working range of some VGTs may be unnecessarily limited, thereby reducing the effectiveness of these VGTs, especially in the low exhaust mass flow region, where the benefits of improved fuel efficiency and reduced emission of harmful exhaust gases are most likely to be obtained.

Instead, according to the invention, to reduce the part-to-part spread between VGTs, and increase the working range of individual VGTs to improve their effectiveness, e.g. in the low exhaust mass flow region, the controller <NUM> is provided with a calibration routine <NUM>, arranged for calibrating the VGT <NUM> during normal operation thereof, e.g. during an online calibration procedure. For example, while the VGT <NUM> is in use, such as in a driven commercial vehicle, the controller <NUM> runs the calibration routine <NUM> to calibrate the VGT <NUM>, e.g. in dependence of operating conditions of an internal combustion engine powering the commercial vehicle. Because of varying operating conditions the mass flow of exhaust gas supplied to the intake channel <NUM> of the VGT <NUM> may change, e.g. in quantity or in pressure. As such, the VGT <NUM> may need to be calibrated accordingly, by the calibration routine <NUM>, to keep the VGT <NUM> in an optimal working range. The calibration routine <NUM> can e.g. be run during stationary operating condition, e.g. when the commercial vehicle is in idle condition. In this case, an internal combustion engine powering the vehicle may be run at a constant speed and/or load to calibrate the VGT across a broad spectrum of operating conditions. The calibration routine <NUM> can e.g. be arranged to determine the deflection point position during idle condition comprising specific engine modes and/or sensor values, such as a condition in which an exhaust gas recirculation (EGR) valve is closed and a brake pressure valve is opened. Under such conditions, the pre-turbine pressure P upstream the turbine can be maximized while the pressure downstream the turbine is minimalized. Accordingly, the force reversal effect, which causes the sharp difference in the pre-turbine pressure P, can be induced by adjusting the adjustable nozzle <NUM> towards the deflection point position <NUM>.

In the calibration routine <NUM>, the controller <NUM> is arranged for controlling the nozzle actuator <NUM> to adjust the adjustable nozzle <NUM> from an initial position towards the closed position. The initial position can be set to preference, e.g. to detect a deflection point position <NUM> over a larger range or to speed up the calibration routine <NUM>. For example, in the initial position the cross sectional area can be between <NUM>% and <NUM>% of the maximum cross sectional area in the open position, e.g. <NUM>% of the maximum cross sectional area. Additionally, the adjustment speed at which the adjustable nozzle is adjusted from the initial position towards the closed position can be set to preference. In this way, the sensitivity of the calibration routine <NUM> can e.g. be increased or the time to perform the calibration routine <NUM> can be decreased. For example, the adjustment speed can be between <NUM>% and <NUM>% of the maximum cross sectional area per second, e.g. <NUM>% of the maximum cross sectional area per second. For example, the initial position and the adjustment speed can be set, such that the expected time to perform the calibration routine <NUM>, e.g. from the start of the calibration routine <NUM> until the detection of the deflection point position <NUM>, is approximately <NUM> seconds. The calibration routine <NUM> can for example be performed after (re)assembling or replacing a turbine, or after a predefined time period since completing a previous calibration routine <NUM>.

While adjusting the adjustable nozzle <NUM>, the controller <NUM> monitors a pre-turbine pressure measured in the mass flow of exhaust gas upstream the VGT <NUM>, e.g. in an exhaust manifold of an internal combustion engine supplying exhaust gas to the intake channel <NUM> of the VGT <NUM>.

As illustrated in <FIG>, the controller <NUM> can for example be arranged for logging the position X of the adjustable nozzle <NUM>, e.g. by receiving position data from a sensor or encoder that measures the nozzle position X, such as a capacitive sensor, a hall sensor, an LVDT, an optical encoder, etc. Alternatively, the position X of the adjustable nozzle <NUM> can be derived from a status of the nozzle actuator <NUM>.

The position data obtained can for example be used for determining a zero reference value, e.g. a zero-position, to define the closed position of the adjustable nozzle <NUM>. As such, a change in position of the adjustable nozzle <NUM> from the zero reference value toward the open position can for example be logged in absolute distance units, such as in millimetres, measured from the closed position. Alternatively, by additionally assigning a reference value to the open position, e.g. when the cross sectional area of the nozzle orifice is at a maximum, the position of the adjustable nozzle <NUM> can for example be logged in relative units, such as a percentage between the closed and open position, e.g. measured from the closed position, with <NUM>% being fully closed and <NUM>% being fully opened.

The controller <NUM> may e.g. be arranged for logging the position X of the adjustable nozzle <NUM> as a function of a first time t1. The controller <NUM> may e.g. further be arranged for logging the pre-turbine pressure P as a function of a second time t2, wherein the second time t2 is synchronized with the first time t1. Alternatively, or additionally, the controller <NUM> can e.g. be arranged for logging the pre-turbine pressure P as a function of the position X of the adjustable nozzle <NUM>.

The controller <NUM> is further arranged, in the calibration routine <NUM>, for performing a step of detecting a deflection point position <NUM> of the adjustable nozzle at which a sharp difference in the pre-turbine pressure P occurs, as can be seen in <FIG>. For example, when monitoring the pre-turbine pressure P while adjusting the adjustable nozzle <NUM> between the open and closed position, the controller <NUM> may detect a sharp, sudden difference in pre-turbine pressure P. The deflection point position <NUM> can for example be defined as the position of the adjustable nozzle <NUM> at which the sharp difference in pre-turbine pressure P starts, when moving the adjustable nozzle <NUM> from the open position to the closed position.

In the calibration routine <NUM>, the controller <NUM> is further arranged for adjusting the minimum cross sectional area in the closed position. In this way the controller <NUM> can adjust a working range of the VGT <NUM>, e.g. a range between the open position and the closed position, in dependence of varying operating conditions, such as pre-turbine pressure, rotor speed, power output, etc. The working range excludes the above described detected deflection point position <NUM>, e.g. by (re)defining the closed position of the adjustable nozzle <NUM>, such that the sharp difference in pre-turbine pressure does not occur when moving the adjustable nozzle <NUM> between the open position and the (re)defined closed position and yet the cross sectional area is minimized respective to the detected deflection point position, so that the minimal cross sectional area can be updated to a smaller value, which is yet sufficiently away from the deflection point position.

<FIG> illustrates another or further embodiment of the VGT <NUM>. Here, the controller <NUM> is arranged for comparing the detected deflection point position <NUM> to a stored deflection point position <NUM> of a pre-calibrated VGT, to determine a deflection point position offset <NUM>. The deflection point position offset can e.g. be determined by performing the calibration routine <NUM> during idle conditions of the vehicle. In general, the stored deflection point position <NUM> comprises one entry, associated with a position of the adjustable nozzle at which a sharp difference in the pre-turbine pressure P occurs. In some cases, however, the stored deflection point can comprise more than one entry, wherein each entry is associated with a specific operating condition of the VGT and/or of the internal combustion engine, e.g. to represent different nozzle positions at which a sharp difference in pre-turbine pressure P can occur, depending on the respective operating condition. The entries can for example be stored in a memory accessible by the controller <NUM>, such as from a lookup table.

The controller <NUM> can be arranged for applying the deflection point position offset <NUM> to the nozzle position demand. In this way the working range of the VGT <NUM> can virtually be shifted away from the detected deflection point position <NUM>. This can be used to effectively align the deflection points of individual VGTs, reducing the need for a safety margin in the calibration process.

Preferably, the controller <NUM> is arranged for detecting the deflection point position <NUM> by monitoring a second derivative of a filtered pre-turbine pressure sensor signal. Filtering and/or determining the second derivative of the sensor signal can e.g. be performed by the controller <NUM>, or can be performed by another processing unit, such as an engine control unit or sensor processor. By using the second derivative of a filtered signal, the calibration routine <NUM> can be made less sensitive to high frequency effects e.g. caused by dynamic behaviour of components and/or measurement errors.

<FIG> illustrates another or further embodiment of the VGT <NUM>, e.g. as part of a turbocharger, wherein the VGT <NUM> is arranged for driving a compressor <NUM>. In some embodiments of the VGT <NUM>, e.g. as can be seen in <FIG>, the adjustable nozzle <NUM> comprises vanes <NUM> disposed around a circumference of the rotor <NUM>. The vanes may have a flow guiding surface that is arranged for guiding the mass flow of exhaust gas from the intake channel <NUM> to the rotor <NUM>, e.g. in a tangential direction. The vanes <NUM> can e.g. form a ring around the rotor <NUM>, and each vane can have a flow guiding surface that is oriented at an angle for guiding the mass flow of exhaust gas. A slidable tube <NUM> may be coaxially aligned with the rotor <NUM>. The slidable tube <NUM> may be slidable around the vanes <NUM>, e.g. along a direction parallel to the axis of rotation of the rotor <NUM>, to adjust the flow guiding surface of the vanes <NUM>. For example, the slidable tube <NUM> may comprise an edge <NUM> which is slidable towards an opposing wall of the intake channel <NUM>, thereby adjusting the cross sectional area of the nozzle orifice <NUM>, e.g. to open or close the intake channel <NUM>.

The nozzle orifice <NUM> for example is formed by a gap between the slidable tube <NUM> and an opposing wall of the intake channel <NUM>. The nozzle actuator <NUM> can for example be arranged for actuating the slidable tube <NUM>, e.g. by translating the slidable element <NUM> against the opposing wall. The slidable tube <NUM> can for example be a cylindrical tube that is coaxially aligned with the rotor <NUM>, with a tube wall that is arranged perpendicular to a direction of the mass flow of exhaust gas from the intake channel. Accordingly, when the nozzle actuator <NUM> e.g. translates the cylindrical tube to close the intake channel <NUM>, the tube wall reduces the cross sectional area of the nozzle orifice <NUM>.

Around the deflection point position described herein, the edge <NUM> is near the opposing wall of the intake channel <NUM>. Accordingly, a venturi is formed and the pressure in the mass flow of exhaust gas flowing through the adjustable nozzle is decreased. As a result, the slidable tube <NUM> is sucked towards the opposing wall of the intake channel and the cross sectional area of the nozzle orifice is further reduced, which may cause a significant decrease in mass flow and a build up of pressure in the exhaust line upstream the VGT <NUM>. By performing the calibration routine as described herein to detect the deflection point position, the working range of the VGT <NUM> can be adjusted to avoid the above described situation.

Similar effects may occur in alternative embodiments, wherein the vanes are rotatable to adjust the cross sectional area of the nozzle orifice. For example, the adjustable nozzle may comprise pivotable vanes, that are pivotable around an axis which is parallel to the axis of rotation of the rotor. By pivoting, e.g. opening and closing, the vanes, the mass flow of exhaust gas to the rotor can be adjusted. The nozzle actuator can be arranged for actuating, e.g. rotating, the vanes. When the vanes are rotated such that the gaps between the vanes are relatively narrow, a venturi is formed and the pressure in the mass flow of exhaust gas flowing through the gaps is reduced. As a result, a suction-effect is created between the vanes, which may cause the vanes to rotate further towards a more closed position, thereby decreasing the mass flow and increasing the pre-turbine pressure. By performing the calibration routine, the deflection point position at which this phenomenon occurs can be detected, and the above described effect can be avoided.

The nozzle actuator <NUM> shown here is a pneumatic actuator, comprising a piston <NUM>, movable inside a piston chamber <NUM> and arranged for actuating the adjustable nozzle <NUM>, via an actuation mechanism <NUM> comprising linkages. The piston chamber <NUM> can e.g. comprise a pressure inlet <NUM>, e.g. arranged for receiving gas, such as air at a controlled pressure. The pneumatic actuator may further comprise a biasing element <NUM>, such as a spring or diaphragm, mounted between the piston <NUM> and the piston chamber <NUM> and arranged for biasing the adjustable nozzle <NUM>, e.g. towards the open or closed position. The actuator may further comprise a pressure generator <NUM>, fluidly connected to the pressure inlet <NUM> and arranged for generating a pressure inside the piston chamber <NUM> to move the piston <NUM> by counteracting against the biasing element <NUM>. The pressure generator can e.g. be a vacuum pump controlled by the controller <NUM> to generate a vacuum inside the piston chamber <NUM>. Alternatively, the nozzle actuator <NUM> can be an hydraulic actuator, arranged for actuating the adjustable nozzle <NUM> using a pressurized fluid, such as water or oil. Alternatively, the nozzle actuator <NUM> can be an electric actuator, e.g. comprising an electric motor, e.g. a DC motor or a solenoid, optionally coupled to a transmission, to actuate the adjustable nozzle <NUM>.

Preferably, the controller <NUM> is arranged for controlling the pneumatic actuator to adjust an actuation pressure based on the measured pre-turbine pressure P. For example, when the pre-turbine pressure is relatively high, the controller <NUM> may be arranged for controlling the pressure generator <NUM>, such as a vacuum pump, to provide a stronger vacuum to actuate the adjustable nozzle <NUM>.

In some embodiments of the VGT <NUM>, e.g. as shown in <FIG>, the intake channel <NUM> is arranged for providing the mass flow of exhaust gas to the rotor <NUM> in a direction substantially perpendicular to an axis of rotation of the rotor <NUM>. As such, the rotor <NUM> can be used as a radial variant. Alternatively, when the rotor <NUM> is an axial variant, the intake channel <NUM> may be arranged for providing the mass flow of exhaust gas in a direction substantially parallel to the axis of rotation of the rotor <NUM>.

The intake channel <NUM> may be formed as a volute that is coaxially aligned with the rotor <NUM>. For example, the rotor <NUM> can be a radial variant and the intake channel can be formed as a volute, e.g. a curved funnel, with a center of curvature that is coaxially aligned with the axis of rotation of the rotor <NUM>. The radius of curvature of the volute may e.g. decrease tangentially towards the rotor <NUM> to narrow the cross sectional area of the intake channel <NUM> along the direction of the flow, thereby accelerating the mass flow of exhaust gas fed to the rotor <NUM>.

In <FIG> is illustrated a commercial vehicle <NUM>, e.g. a truck or a bus, comprising a VGT <NUM> as described herein. The VGT <NUM> can for example be arranged in the exhaust system of the internal combustion engine <NUM> powering the commercial vehicle, such as a diesel or spark ignition engine. The VGT <NUM> can for example be part of a turbocharger, wherein the VGT <NUM> e.g. mechanically powers a compressor <NUM>, to convert energy recovered from exhaust gases into boost pressure.

<FIG> provides a schematic representation of a method <NUM> for calibrating a VGT <NUM>, e.g. arranged in an exhaust system of an internal combustion engine. The VGT <NUM> comprises an intake channel <NUM>, a rotor <NUM>, and an adjustable nozzle <NUM>. The intake channel <NUM> is arranged for receiving a mass flow of exhaust gas from the internal combustion engine. The rotor <NUM> is arranged downstream the intake channel <NUM> for extracting energy from the mass flow of exhaust gas. The adjustable nozzle <NUM> comprises a nozzle throat <NUM> having an adjustable cross sectional area <NUM> arranged for adjusting the mass flow of exhaust gas from the intake channel <NUM> to the rotor <NUM>, wherein the adjustable nozzle <NUM> is adjustable between an open position, in which the nozzle throat <NUM> has a maximum cross sectional area <NUM>-<NUM>, and a closed position, in which the nozzle throat <NUM> has a minimum cross sectional area <NUM>-<NUM>.

As illustrated in <FIG>, the method <NUM> comprises step <NUM> of adjusting the adjustable nozzle <NUM> from an initial position towards the closed position, while monitoring a pre-turbine pressure P measured upstream the VGT <NUM>. The adjustable nozzle <NUM> can for example be adjusted manually or by an actuator, while the position of the adjustable nozzle is logged, e.g. as a function of time. The pre-turbine pressure P can for example be measured by a pressure sensor, e.g. arranged in an exhaust manifold or in an exhaust line between the internal combustion engine and the VGT <NUM>. The measured pre-turbine pressure P can e.g. be logged as a function of time.

The method <NUM> further comprises step <NUM> of detecting a deflection point position <NUM> of the adjustable nozzle <NUM> at which a sharp difference in the pre-turbine pressure P occurs. The deflection point position <NUM> can for example be detected visually, by comparing the time-logged nozzle position and pre-turbine pressure, or can be detected computationally, e.g. by comparing a derivative of the pre-turbine pressure against a threshold value. For example, the deflection point position <NUM> can be defined when a first or second derivative of the pre-turbine pressure exceeds a threshold value.

Step <NUM> of the method <NUM> comprises adjusting the minimum cross sectional area <NUM>-<NUM> in the closed position, to adjust a working range of the VGT <NUM> in dependence of varying operating conditions, wherein the working range excludes the detected deflection point position <NUM>.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description and drawings appended thereto. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

The invention applies not only to automotive applications where the variable geometry turbine is used for improved energy efficiency, but also to other technical, agricultural or industrial applications where a variable geometry turbine is used. It will be clear to the skilled person that the invention is not limited to any embodiment herein described and that modifications are possible which may be considered within the scope of the appended claims. In the claims, any reference signs shall not be construed as limiting the claim.

The terms 'comprising' and 'including' when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus expression as 'including' or 'comprising' as used herein does not exclude the presence of other elements, additional structure or additional acts or steps in addition to those listed. Furthermore, the words 'a' and 'an' shall not be construed as limited to `only one', but instead are used to mean `at least one', and do not exclude a plurality.

Claim 1:
A variable geometry turbine (VGT), comprising:
- an intake channel (<NUM>), arranged for receiving a mass flow of exhaust gas from an internal combustion engine;
- a rotor (<NUM>), arranged downstream the intake channel (<NUM>) for extracting energy from the mass flow of exhaust gas;
- an adjustable nozzle (<NUM>), comprising a nozzle orifice (<NUM>) having an adjustable cross sectional area (<NUM>) and arranged for adjusting the mass flow of exhaust gas from the intake channel (<NUM>) to the rotor (<NUM>), wherein the adjustable nozzle (<NUM>) is adjustable between an open position, in which the nozzle orifice (<NUM>) has a maximum cross sectional area (<NUM>-<NUM>), and a closed position, in which the nozzle orifice (<NUM>) has a minimum cross sectional area (<NUM>-<NUM>);
- a nozzle actuator (<NUM>), arranged for actuating the adjustable nozzle (<NUM>) between the open position and the closed position; and
- a controller (<NUM>), arranged for controlling the nozzle actuator (<NUM>) based on a nozzle position demand;
wherein the controller (<NUM>) comprises a calibration routine (<NUM>), arranged for calibrating the VGT during normal operation thereof; characterized in that, in the calibration routine (<NUM>), the controller (<NUM>) is arranged for performing the steps of:
- adjusting the adjustable nozzle (<NUM>) from an initial position towards the closed position, while monitoring a pre-turbine pressure (P) measured in the mass flow of exhaust gas upstream the VGT;
- detecting a deflection point position (<NUM>) of the adjustable nozzle at which a sharp difference in the pre-turbine pressure (P) occurs; and
- adjusting a working range of the nozzle actuator (<NUM>), having an adjusted minimum cross sectional area in the closed position that excludes the detected deflection point position (<NUM>).