DE102008014681A1 - Charge pressure drop preventing method for turbocharger, involves determining values based on pressure drop to increase performance of turbine, and supplying air mass flow, and adjusting turbine performance adjusted based on values - Google Patents

Abstract

The method involves determining whether pumping of a compressor is performed or not, and determining air mass flow supplied to the compressor for producing pre-rotation of the compressor to reduce or prevent pumping of the compressor. Drop of charge pressure (P2) is determined when supplying the air mass flow, and values are determined based on the pressure drop to increase performance of a turbine and/or the compressor connected with the turbine for reducing or preventing the pressure drop. The air mass flow is supplied, and the turbine performance is adjusted based on the values. An independent claim is also included for a turbocharger comprising a valve arrangement.

Description

The The invention relates to a method for counteracting the waste a boost pressure when, for example, a pre-swirl in a turbocharger is generated to prevent a pump of the compressor. Furthermore The invention relates to a turbocharger with a control device to perform of the procedure.

Of the Compressor of an exhaust gas turbocharger is characterized by a map in which, at certain turbocharger speeds and mass flows, a produce uniquely assigned pressure. This map is included in huge mass flows limited by the so-called Stopfgrenze. At low mass flows is the map is limited by the surge limit. This so-called surge limit occurs due to a stall at the compressor wheel inlet or at the compressor wheel outlet or at both up.

Out The prior art is known that by means of the pre-swirl the surge line in the compressor map to smaller mass flows out can be moved. However, there may be a drop in boost pressure, if the Vordrall by an added Bleed air is generated, which branches off from the pressure side of the compressor becomes.

Therefore it is the object of the present invention to provide a method with which prevents the drop of the boost pressure or at least can be reduced.

These The object is achieved by a method having the features of the patent claim 1 solved.

• a) Bestimmen, ob im Betrieb ein Pumpen des Verdichters auftritt bzw. bevorsteht,
• b) Wird festgestellt, dass ein Pumpen auftritt bzw. bevorsteht:
• c) Bestimmen eines dem Verdichter zuzuführenden Luftmassenstroms, der ausreichend ist um einen Vordrall vor dem Verdichter zu erzeugen, um ein Pumpen des Verdichters zumindest zu reduzieren oder im Wesentlichen zu verhindern, und
• d) Bestimmen des sich ergebenden Abfalls des Ladedrucks beim Zuführen des Luftmassenstroms und Bestimmen eines Werts basierend auf dem Ladedruckabfall, um den die Leistung der Turbine bzw. des damit verbundenen Verdichters erhöht werden muss, um den Ladedruckabfall zumindest zu reduzieren oder im Wesentlichen zu verhindern und
• e) Zuführen des Luftmassenstroms und Einstellen der Turbinenleistung auf Basis dieses Werts.

Accordingly, according to the present invention there is provided a method for preventing a drop in boost pressure in a turbocharger, comprising the steps of:

• a) determining whether a pumping of the compressor occurs or is imminent in operation,
• b) If it is determined that pumping is occurring or is imminent:
• c) determining an air mass flow to be supplied to the compressor sufficient to produce a pre-whirl prior to the compressor to at least reduce or substantially prevent pumping of the compressor, and
• d) determining the resulting drop in boost pressure upon delivery of the mass air flow and determining a value based on the boost pressure drop by which the power of the turbine or associated compressor must be increased to at least reduce or substantially prevent the boost pressure drop;
• e) supplying the air mass flow and adjusting the turbine power based on this value.

The Method has the advantage that on the one hand the occurrence of a pump in which the compressor can be counteracted by an air mass flow supplied to the compressor which produces a suitable pre-whirl. On the other hand can prevents a drop in the boost pressure due to the blowing off of the air or at least reduced by determining the boost pressure drop which results from the blow-off of the air and accordingly increases the turbine power become.

advantageous Refinements and developments of the invention will become apparent the dependent claims and the description with reference to the drawings.

In an embodiment of the invention a valve arrangement is provided, via which the air mass flow via a outflow can be fed to the compressor is to generate a pre-whirl in a compressor of the turbocharger. The valve arrangement can in this case, for example, a bleed air valve have, with a variable cross-section. Such a valve has the advantage that a predetermined air mass flow easy lets set, fed to the compressor is to produce a sufficient pre-twist. It can do that For example, bleed valve have a conical valve seat, wherein over the Slope of the cone valve seat and the feed of the cross section the bleed air valve can be suitably adjusted and thus the bleed air mass flow. Instead of a cone valve seat can However, a differently shaped valve seat can be provided to to blow off a predetermined mass air flow.

In a further embodiment according to the invention, the power of the turbine is adapted, for example, via a device for varying the power of the turbine. The device for varying the power of the turbine may, for example, have a wastegate, a variable turbine geometry with movable guide vanes and / or a sliding sleeve. By way of a corresponding actuator, in this case, for example, a wastegate flap of the wastegate is correspondingly activated or an actuator for the verse Position of the vanes or the sliding sleeve. As an actuator, in this case, for example, an electrical or electromechanical and / or electromagnetic actuator can be used. For example, a stepper motor. This has the advantage that it can be controlled very accurately.

The Invention will be described below with reference to the schematic figures the drawings specified embodiments explained in more detail. It demonstrate:

1 2 shows a partial sectional view of a turbocharger with a control device for compensating a drop in a boost pressure P2 according to an embodiment of the invention,

2 a schematic, sectional front view of a compressor housing, wherein the compressor housing is provided with a groove for introducing air for generating a Vordralls;

3 a further schematic, cut front view of a compressor housing, wherein the compressor housing has a bore for introducing air for generating a pre-whirl.

In all figures are the same or functionally identical elements and devices - if nothing else is stated - with the same reference numerals have been provided.

In 1 is a simplified partial sectional view of a turbocharger 10 shown. There is a wave 12 of the turbocharger 10 in its housing 14 arranged, being on the shaft 12 a turbine wheel 16 and a compressor wheel 18 is arranged. For the sake of clarity, some details have been omitted, such as the bearing of the shaft 12 , the diverter valve, water and oil channels, besides, the rotor has been greatly simplified as a part.

In the present case, as in 1 is shown, the turbine housing 20 of the turbocharger 10 for example, a wastegate channel 22 up, over a wastegate flap 24 can be opened and closed, to blow off the pressure on the turbine. In principle, however, the present invention can also be applied, for example, to a turbocharger with a variable turbine geometry VTG, in which movable guide vanes are provided in order to adjust the flow cross-section of the turbine appropriately. Furthermore, the invention can also be applied, for example, to a turbocharger with an adjustable sliding sleeve VST.

The comments on the turbocharger 10 with a Wastgate therefore also apply accordingly for such turbochargers, in which instead of the wastegate or in addition to this, for example, movable guide vanes (VTG) or an adjustable sliding sleeve (VST) are used to change the flow cross-section of the turbine suitable. In the latter two embodiments, instead of a wastegate actuator as actuating device, the corresponding actuating device of the movable guide vanes or of the sliding sleeve is actuated by an associated control device STG. As an actuating device in this case, for example, an electric actuator can be used. In principle, however, any other type of actuator can also be used as actuating device which can be controlled via a control device in order to suitably change the flow cross-section of the turbine by actuating, for example, the movable guide vanes or the sliding sleeve.

As in the example in 1 shown is the wastegate flap 24 via the assigned wastegate actuator 26 operated as an actuator. This can for example be an electrical actuator. As in 1 is shown, the wastegate actuator 26 from the controller 28 driven.

In the compressor housing 30 of the turbocharger 10 is a supply or an outflow channel 32 provided for blowing off air to produce a predetermined pre-whirl in front of the compressor inlet, so that the occurrence of a "pumping" on the compressor wheel 18 essentially prevented or at least reduced.

So that there is now a pressure build-up on the compressor, the wastegate is through the wastegate actuator 26 or the associated wastegate flap 24 closed. The wastegate does not have to be fully closed automatically. Depending on the desired boost pressure and the current mass flow at the turbine, the wastegate is usually slightly open. The wastegate actuator 26 is determined by the aforementioned control device STG 28 controlled or controlled. The control device STG 28 Here, for example, an extra controller for the turbocharger 10 be or by a motor control be taken over. Furthermore, the control device STG 28 , as in 1 is shown, also a bleed air actuator 34 control, which will be described in more detail below.

For "pumping" it can be on the compressor wheel 18 come when the boost pressure P2, ie the pressure at the compressor outlet, is very high or when the pressure P1, ie the pressure at the compressor inlet, is very low. As in 1 is shown, the boost pressure P2, for example via a pressure sensor 36 be determined which z. In the volute 38 of the compressor is arranged. Accordingly, the pressure P1 in front of the compressor via a corresponding pressure sensor (not shown) can be determined.

It follows that the pressure ratio or the quotient PQ = P2 / P1 can become very large. If the pressure conditions are too high and the mass flow is too low, so-called pumping can occur. This means that there are stalls on the compressor blades 40 , for example, on the leading edge of the compressor blade. This in turn leads to pressure fluctuations, which can lead to damage to the compressor or bearing damage after a short time.

The control device STG 28 For example, it is possible to determine from the measured air volume and the boost pressure P2 that the compressor is operating in a region close to the pumping limit or recognizes via pressure fluctuations that a pump is impending on the compressor. Two examples of methods for determining when pumping occurs in a compressor and for generating a pre-poppet advance to counteract pumping will be discussed in more detail below. However, these methods are here purely exemplary Lich to determine a pump on the compressor and to generate a corresponding Vordrall. The invention is not limited to these methods.

If it is determined that a pumping occurs at the compressor, the control device STG 28 the bleed air actuator 34 so control that an actuator, here a stamp 42 a bleed valve 35 , is pulled backwards and the associated outflow channel 32 partially or completely release so that air from the compressor side via the outflow channel 32 can be blown off. As a result, on the one hand the working range of the compressor can be shifted to a higher volume flow. On the other hand, the blown air, here the bleed air, so on the compressor in the intake passage 44 be blown, so that in the inflowing air, a swirl or pre-whirl is generated, which is suitable for the stall on the compressor blades 40 or to counteract the pumping on the compressor.

Examples of the design of the discharge channel 32 or the feeder will be described below with reference to 2 and 3 explained.

When opening the bleed air valve 35 the boost pressure P2, ie, the pressure at the compressor outlet, in this case go back because the outflow of compressed air this is conveyed in a circle around the compressor. In other words, it will u. U. give away a part of the energy that is transmitted from the exhaust gas to the turbine, since the boost pressure P2 is reduced at first moment. This energy must also be provided by the turbine. For this purpose, the pressure in front of the turbine must be increased.

A boost pressure control, for example, the wastegate on the turbine or the wastegate flap 24 controls noticed the drop of the boost pressure P2. The boost pressure control provided by the controller 28 is carried out, the wastegate will therefore for example close a little further and thereby increase the pressure on the turbine and thus their performance. Thus, a drop in the boost pressure P2 is counteracted by blowing off the bleed air.

A normal common Boost pressure control, for example, a PID control device with a proportional (P), integral (I) and diffenrential (D) Proportion that is part of the controller may account for this pressure drop compensate for the boost pressure P2.

It However, it requires a certain deviation, so that the proportional (P) portion of the PID control device is active or a certain Time until the integral (I) portion of the PID controller the Control deviation has completely compensated. However, it can - depending on Goodness of Regulation - anyway come to a more or less severe collapse of the boost pressure P2.

The invention now provides that a possible drop in boost pressure due to the blowing off of air at the compressor can be counteracted early on, so that a strong drop in the boost pressure, for example, can be prevented in advance. At the same time, however, it is ensured that By blowing off the air, a suitable pre-whirl can be generated at the compressor, which preferably substantially prevents pumping of the compressor.

For this purpose, according to the invention by the control device 28 and their control device, a suitable pilot control instead or in the previously described case support the boost pressure control by a feedforward control.

According to the invention, the - by the controller STG 28 self-induced disturbance, ie the drop of the boost pressure P2 by the blowing off of air to produce a pre-whirl, included in a pilot control to assist the controller 28 next to the bleed air actuator 34 the wastegate actuator 26 actuated.

In this case, the known disturbance variable, ie the boost pressure P2 or its drop, can be used for a precontrol in support of the control device 28 whose control device has, for example, a PID control device. This can be done in different ways.

According to parameters, such as the boost pressure P2 behind the compressor or the Verdichterradaustritt and the pressure P1 upstream of the compressor or the Verdichterradeintritt, the intake temperature of the flow through the compressor and / or the amount of air blown, a value or a corrective Input control quantity determined and to the corresponding, associated control device 28 or their control device handed over. For example, an addititve turbine or compressor power or an additive control value or control value for the wastegate actuator can be determined as corrective pilot control variable and transferred to the control device of the wastegate.

The additive turbine or compressor capacity is the additional turbine or compressor power that must be applied to reduce or substantially prevent a drop in the boost pressure P2, which, when air is blown off via the discharge channel, increases by a pre-whirl generate, which counteracts a pumping of the compressor. According to the additionally required turbine or compressor power then the wastegate or the wastegate channel 22 additionally closed a little more to increase the turbine power and thus the compressor power by the corresponding additive turbine or compressor performance. The same applies to turbochargers, for example with variable turbine geometry VTG or sliding sleeve VST. Here, the moving blades are correspondingly closed a bit stronger to increase the turbine power suitable.

Corresponding is also the sliding sleeve shifted to increase the turbine power suitable.

In addition to the additive turbine or compressor capacity, the amount of bleed bleed air can furthermore be determined directly and sent to the control device 28 the Wastegate be handed over or their control device. On the basis of pressures such as the pressure at the compressor inlet P1 and the boost pressure P2, and / or one or more other suitable parameters, which are already known for example from other contexts or the control device 28 can exist, the control device 28 or the control device itself calculate the required feedforward control or a suitable corrective pilot control variable and thus calculate or determine the preventive intervention for the control of the turbine.

In other words, according to the invention, the expected drop in pressure P2 caused by the blowing off of air to prevent the pumping can be determined or estimated. On the basis of the previously calculated or estimated pressure drop, a corresponding corrective pilot control variable is determined, for example, an additional turbine power or compressor power that must be provided in order to substantially prevent or at least reduce the drop in the boost pressure P2. As Vorsteuergröße can also, for example, directly a control variable for the wastegate flap 24 or their wastegate actuator 26 be determined to close the wastegate by an appropriate level, so that thereby the performance of the turbine and thus the performance of the compressor can be increased appropriately, so that the pressure drop of the pressure P2 can be counteracted.

The Determining the amount of bleed air that is supplied to a suitable For example, to create pre-twist and thus prevent pumping by a suitable measurement (s) or by calculation for example, according to the St. Venant equation or by another appropriate modeling, such as a map.

bei einer kritischen Strömung (wenn der Luftfluss in der Drossel Schallgeschwindigkeit erreicht, engl. choked flow):

The St. Venant equations are as follows:

at a critical flow (when the air flow in the throttle reaches the speed of sound, choked flow):

C_D:

Durchflusskoefizient

A_T:

die Fläche der Drosselstelle

P₀:

Druck vor der Drosselstelle

P_T:

Druck nach der Drosselstelle

T₀:

Temperatur vor der Drosselstelle

R:

ideale Gaskonstante

γ:

Isentropenkoeffizient

ṁ_real:

Massenstrom über die Drossel

Where:

C _D :

Durchflusskoefizient

A _T :

the area of the throttle point

P ₀ :

Pressure in front of the throttle point

P _T :

Pressure after the throttle point

T ₀ :

Temperature in front of the throttle point

R:

ideal gas constant

γ:

Isentropenkoeffizient

_real :

Mass flow through the throttle

Of the Mass flow is diverted from the compressor side and as Bleed air tangentially into the flow of the compressor can be introduced orders of magnitude of 0% to 50% assume (where all intermediate values are included) and Preferably, for example, a value of about 25% of the compressor mass flow at the surge limit.

Of the innovative step lies in the concatenation of the two control interventions, Blow off the bleed air and change the control of the turbine. According to the invention the regulation of the turbine is not left to itself and to the breaking in maintained the charge pressure. Instead, the regulation of the turbine supports with the information that is available anyway, such as the one to be supplied Bleed air flow and thus the associated pressure drop of the pressure P2.

in the The following two methods are briefly explained, by means of which a pump the compressor can be determined and wherein a corresponding Air mass flow over the discharge channel is blown off to counteract the pumping of the compressor.

In a first step, for example, the pressure P2 behind the compressor outlet is determined. Alternatively, however, a pressure of the air mass flow before and / or behind the compressor or behind the diffuser outlet and / or before the diffuser inlet can be measured. In a next step, it is determined whether the course of the pressure P2 reaches the surge limit. In this case, there are essentially periodic fluctuations in the pressure P2, ie a rotating stall occurs. This rotating stall is a harbinger of pumping, with this it comes to a demolition of the flow and thus to a collapse of the air flow in a channel of the compressor wheel. This effect moves from one channel to the next in the compressor wheel and causes pressure fluctuations with high frequency but small amplitude. Exceeds the pressure fluctuation of the pressure P2 or its amplitude, for example in a frequency range adapted a predetermined limit, from which a rotating stall of the compressor is detected and thus it is clear that a pump is imminent, so in a next step, air via a bleed valve 35 blown in front of the compressor to produce a suitable Vordrall counteracts the pumping of the compressor.

In the second method, at least one map is used with the operating range of a turbocharger 10 and its surge limit, for example, depending on parameters such as the air mass flow and the pressure ratio of pressure at the outlet of the compressor / pressure at the inlet of the compressor.

On the basis of the map can be determined whether a turbocharger reaches the pumping limit during operation or a pumping occurs. When a pumping occurs again a bleed valve 35 are actuated, is blown over the air so that a suitable Vordrall can be generated in front of the compressor, which counteracts the pumping.

The bleed valve 35 can open one of the pressure ratio of pressure at the outlet of the compressor / pressure at the inlet of the compressor dependent valve cross-section A (N) to dissipate, for example, a dependent of the pressure P2 air mass flow. The valve cross-section A (N) can from a corresponding z. B. 3-dimensional map are taken that z. B. indicates the valve cross section A (N) in dependence on the air mass flow, the aforementioned pressure ratio and the turbocharger speed.

In a further embodiment Can the valve opening via a converted St. Venant equation can be determined.

The bleed valve 35 can be formed with a variable cross section A, wherein it has, for example, a conical valve seat, wherein on the slope of the conical seat 42 and the feed of the cross section A of the bleed air valve 35 can be suitably adjusted to allow a predetermined air mass flow to flow through the outflow channel.

The discharge channel 32 as he is in 1 can be shown in one embodiment of the invention, for example, with a groove 46 be connected. This groove 46 is in 2 in a schematic front view of a compressor housing 30 shown. The groove 46 In this case, it can be substantially circumferential and can optionally taper towards its end, as in FIG 2 is shown. The distance of the groove 46 from the compressor wheel 18 can z. B. be chosen so that the distance of the groove 46 at least 1/4 of the diameter at the compressor impeller inlet and at most five times the diameter at the compressor impeller inlet. Preferably, the distance of the groove 46 of the compressor wheel is 1.5 times the diameter at the compressor wheel inlet.

In a further embodiment, as in 3 is shown, the outflow channel 32 be oriented or arranged so that the air substantially or at least almost tangentially into the compressor housing 30 or the compressor feed introduces. In this case, the outflow channel 32 also with a groove 46 as previously stated by 2 has been described.

In principle, however, the invention is not based on these embodiments of the outflow channel 32 or its connection to the interior of the compressor housing, as in the 2 and 3 shown is limited. The embodiments in the 2 and 3 are only examples. The invention can be applied to all types of inflow channels 32 and their connection to the interior of the compressor housing 30 be used to effectively counteract in addition to a suitable Vordrall to prevent pumping and an undesirable pressure drop of the pressure P2.

Even though the present invention above based on the preferred embodiments It is not limited to this, but in many ways and modifiable. The embodiments described above are combined with each other, in particular individual features thereof.

Claims (13)

Method for preventing a drop in charge pressure in a turbocharger ( 10 ) comprising the steps of: a) determining whether pumping of the compressor is occurring or imminent in operation, b) determining that pumping is occurring or imminent: c) determining an air mass flow rate to be supplied to the compressor that is sufficient to produce a pre-swirl d) determining the resulting drop in boost pressure when feeding the mass air flow and determining a value based on the boost pressure drop by which the power of the turbine or turbine is increased; the associated compressor must be increased to at least reduce or substantially prevent the boost pressure drop; and e) supplying the air mass flow and adjusting the turbine power based on this value. Method according to claim 1, characterized in that a valve arrangement ( 35 ) is provided, via which the air mass flow via an outflow channel ( 32 ) is fed to the compressor, for generating a pre-whirl in a compressor of the turbocharger ( 10 ). Method according to Claim 2, characterized in that the valve arrangement ( 35 ), for example, at least one bleed valve ( 35 ), for example, a bleed air valve with a variable cross section, wherein such a bleed valve z. B. a cone valve seat ( 42 ), wherein on the slope of the conical valve seat and the feed of the cross section of the bleed air valve can be suitably adjusted to allow a predetermined air mass flow to flow through the outflow channel. Method according to at least one of claims 1 to 3, characterized in that for adjusting the turbine power a device for changing the power of the turbine ( 22 . 24 ) of the turbocharger ( 10 ), wherein the means for varying the power of the turbine ( 22 . 24 ), For example, a wastegate, a variable turbine geometry with movable vanes and / or a sliding sleeve. A method according to claim 4, characterized in that the means for varying the power of the turbine via an actuator ( 26 ) is driven, for example, an electrical or electromechanical and / or electromagnetic actuator, wherein the actuator z. B. is a stepper motor. Method according to claim 4, characterized in that that means to change the power of the turbine over a pressure cell is controlled, which acts on a control pressure becomes. Method according to at least one of claims 1 to 6 characterized, that step a) for determining whether pumping of the compressor is imminent further comprising the steps: a1) Determining a pressure curve of a pressure of the mass air flow, which a conclusion allows, whether a pump is imminent or not in the compressor, a2) Determine if the pressure trace of the pressure reaches a surge line or not, a3) If the surge limit is reached or exceeded, determine whether an amplitude of the pressure curve of the pressure a predetermined Limit for exceeds recognizing Rotating Stable, if the limit is exceeded, thus, it is determined that pumping of the compressor is imminent. Method according to at least one of claims 1 to 7, characterized, that step a) for determining whether a pumping of the compressor is present or is still pending Steps: a1) providing at least one characteristic map in which the surge limit of the compressor is specified, a2) determining whether the compressor exceeds the surge limit, wherein when exceeded the pumping limit is determined that a pumping of the compressor is present. Method according to at least one of claims 1 to 8, characterized in that the value, based on the expected boost pressure drop, for example, determined by a map or by a control device ( 28 ) is calculable. Turbocharger, comprising: - a valve arrangement ( 35 ) via which an air mass flow can be supplied to a compressor, - a device for changing a flow cross section of the turbine ( 22 . 24 ), and - a control device ( 28 ), which controls the valve arrangement and the device for changing a flow cross-section according to the method of one of claims 1 to 9. Turbocharger according to claim 10, characterized in that the control device ( 28 ) has, for example, a PID control device. Turbocharger according to at least one of claims 10 or 11, characterized in that the means for varying the power of the turbine ( 22 . 24 ), For example, a wastegate, a variable turbine geometry with movable vanes and / or a sliding sleeve. Turbocharger according to at least one of claims 10 to 12, characterized in that the turbocharger ( 10 ) an outflow channel ( 32 ) is blown through the air, for generating a suitable pre-whirl, wherein the outflow channel ( 32 ) is arranged such that the air is substantially tangentially into the compressor housing ( 30 ) is blown off and / or the outflow channel ( 32 ) with a groove ( 46 ) is connected to the circumference of the compressor housing, wherein the groove, for example, is formed substantially circumferentially and, for example, tapers towards its end.