DE102012223421A1 - Method for operating pressure wave supercharger for compaction of gas in motor system with combustion engine, involves determining desired speed of cell wheel based on predetermined target boost pressure - Google Patents

Abstract

The method involves determining desired boost pressure for operating an internal combustion engine (2) based on a motor operating point. A pressure wave supercharger (7) and a feeder are fixed with channels by rotation of a cell wheel to perform fresh air compression. Desired speed of the cell wheel is determined based on the predetermined target boost pressure. The speed of the cell wheel is set for adjusting the preset boost pressure based on sound speed of the internal combustion engine. Characteristic of fuel ratio and an engine load is determined. Independent claims are also included for the following: (1) a device for operating a pressure wave supercharger in a motor system (2) a motor system (3) a computer program has a set of instruction for operating a supercharger (4) an electronic memory medium has a set of instruction for operating a supercharger (5) an electronic control device.

Description

Technical area

The present invention relates to a method and an apparatus for operating pressure wave superchargers, in particular pressure wave superchargers for compressing a gas for an internal combustion engine.

State of the art

With pressure wave chargers, pressure waves generated by the opening and closing of exhaust valves of an internal combustion engine in the exhaust tract can be used to suck in and compress fresh air.

So you can provide a pressure wave supercharger having a rotatable feeder in a cylindrical housing. The cell wheel is driven by the internal combustion engine and is fixedly coupled to the crankshaft of the internal combustion engine. By the rotation of the cellular wheel cells are alternately connected to an engine side portion of the exhaust tract and an output side portion of the exhaust tract, so that combustion exhaust gases first flow from the engine side portion into the cell and flow out after a corresponding further rotation of the bucket in the output side portion of the exhaust tract. By flowing the combustion exhaust gases, fresh air in the cell is discharged into an engine-side portion of an air supply portion, the fresh air having previously been sucked into the relevant cell upon discharge of combustion exhaust gas into the exit-side portion of the exhaust gas.

Disclosure of the invention

According to the invention, a method for operating a pressure wave charger according to claim 1 as well as the device, the motor system and the computer program product according to the independent claims are provided.

Further advantageous embodiments of the present invention are specified in the dependent claims.

According to a first aspect, a method for operating a pressure wave supercharger in an engine system with an internal combustion engine is provided, wherein for operating the internal combustion engine, a target supercharging pressure is predetermined as a function of an engine operating point. The blast loader has a cellular wheel with a number of channels, wherein by rotation of the cellular wheel, ends of the channels are alternately connectable to openings on a first end side and a second end side of the cell wheel to effect a compression of fresh air. A rotational speed of the cell wheel is set depending on the predetermined target boost pressure.

One idea of the above method of operating a blast loader is to vary the speed of the impeller depending on the desired setpoint boost pressure. This approach is based in particular on the recognition that for a given engine operating state of the internal combustion engine there is an optimum rotational speed for the pressure wave loader's cellular wheel, at which a desired charge can be achieved.

By specifying the target boost pressure, a setpoint speed of the cell wheel can then be determined. Depending on the required target boost pressure, the desired charge may be less than the maximum charge at the current engine operating point. A corresponding desired speed can be adjusted by adjusting a calculated base speed. The base speed can be determined from an optimal speed for a maximum achievable at the relevant operating point of the engine supercharging and determined by the target boost pressure adjustment factor. In other words, adjusting the engine operating point can therefore be accomplished by adjusting the rotational speed of the feeder based on the calculated target speed.

Furthermore, the optimum rotational speed of the star feeder for setting a maximum charge or a maximum boost pressure achievable at the engine operating point can be determined depending on a sonic velocity and an exhaust gas temperature of the combustion exhaust gas expelled from the engine, wherein the target rotational speed of the feeder is adjusted depending on the determined optimum rotational speed ,

According to one embodiment, the desired rotational speed of the star feeder can be determined as a function of a dynamic component of the rotational speed, the dynamic component being determined as a function of an indication of a rapid change in load, in particular a rapid reduction in the load on the internal combustion engine.

It can be provided that the rotational speed of the feeder is set by specifying the corresponding desired speed in accordance with a speed control.

The setpoint speed can furthermore be determined as a function of a desired operating point of the internal combustion engine in accordance with a setpoint charging pressure to be set.

Furthermore, a low-frequency modulation can be applied to the set speed to be set, wherein an adaptation value is structurally adapted depending on a change in the adjusting boost pressure, which is used to determine the target speed.

It can be provided that the setpoint speed is set to zero for switching off the internal combustion engine.

According to a further aspect, an apparatus for operating a pressure wave supercharger in an engine system with an internal combustion engine is provided, wherein for operating the internal combustion engine, a target supercharging pressure is predetermined as a function of an engine operating point. The pressure wave supercharger has a cellular wheel with a number of channels, wherein by a rotation of the cellular wheel ends of the channels are alternately connectable to an opening on a first end side and a second end face of the cellular wheel, wherein the device is adapted to a rotational speed of the cell wheel dependent set by the predetermined target boost pressure.

In another aspect, an engine system is provided, including an internal combustion engine, a pressure wave supercharger, and the above apparatus.

According to another aspect, there is provided a computer program product including program code which, when executed on a data processing device, performs the above method.

Brief description of the drawings

Preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 a schematic representation of an engine system with an internal combustion engine and a pressure wave supercharger; and

2a and 2 B a schematic cross-sectional view of a pressure wave supercharger for operating according to the inventive method.

Description of embodiments

In the figures, elements having the same or similar functions are given the same reference numerals.

In 1 is an engine system 1 with an internal combustion engine 2 shown. The internal combustion engine 2 may be formed for example in the form of a diesel or gasoline engine and a plurality, in the illustrated embodiment four, cylinder 3 exhibit.

The cylinders 3 Fresh air is supplied via an air supply system 5 supplied and combustion exhaust gases are via an exhaust gas discharge tract 6 from the cylinders 3 dissipated. In the air supply system 5 and in the exhaust discharge tract 6 is a charging device 7 provided, which is constructed in the form of a pressure wave supercharger. The pressure wave loader 7 has a bucket wheel that uses an electric motor 8th is driven.

The pressure wave loader 7 is via an input side feed section 51 of the air supply system 5 Air supplied and via an engine-side feed section 52 of the air supply system 5 compressed air is provided. In the engine side feed section 52 of the air supply system 5 is still a throttle 9 provided in the internal combustion engine 2 flowing mass air flow depends on their position.

Combustion exhaust gas becomes when cylinders (not shown) exhaust valves 3 of the internal combustion engine 2 in a motor-side discharge section 61 the exhaust discharge tract 6 ejected and from there the pressure wave loader 7 fed. At an exhaust outlet of the pressure wave supercharger 7 the combustion exhaust gas becomes an exit-side exhaust section 62 the exhaust discharge tract 6 pushed out.

It is a control unit 10 provided the operation of the engine system 1 controls. Depending on a default variable, such as a driver's desired torque, the throttle valve, the compression behavior of the charging device can via appropriate adjuster, such as injectors 7 , in gasoline engines, the specification of a firing angle, the operation of the internal combustion engine 2 be influenced to operate this according to the default size.

The construction of a pressure wave loader 7 is in the 2a and 2 B explained in more detail. 2a shows a sectional view of the pressure wave supercharger 7 along the axial direction and 2 B shows a cross-sectional view of the pressure wave supercharger 7 along the section line AA. The pressure wave loader 7 has a cell wheel in the core 71 up, that on an axis 72 is rotatably mounted. Between the cell wheel 71 and the axis 72 are storage arrangements 73 arranged to a possible frictionless rotation of the bucket 71 to ensure.

The cell wheel 71 is from a housing 75 surrounded, which is formed substantially cylindrical and at the first end side 76 of the input side feed section 51 of the air supply system 5 and the engine side feed section 52 of the air supply system 5 are connected so that these have openings with the interior of the housing 75 keep in touch. A second front side 77 of the housing 75 has openings over which the engine-side discharge section 61 the exhaust discharge tract 6 and the exit-side discharge section 62 the exhaust discharge tract 6 with the cell wheel 71 keep in touch. For example, in each case the openings on the first end face 76 for the input side feed section 51 and the engine side supply section 52 of the air supply system 5 and the openings on the second end face 77 for the connections of the engine-side discharge section 61 and the exit-side discharge section 62 the exhaust discharge tract 6 with respect to the axis 72 have an angular offset from one another, in particular an angular offset of 90 °.

In the case 75 is a the cellular wheel 71 integrated electric motor, wherein the electric motor is designed as an external rotor motor. This is on the axis 72 a stator 78 arranged, which may comprise (not shown) stator coils, which by means of a suitable motor drive 80 , which is part of the control unit 10 can be driven to the cell wheel 71 drive. The cell wheel 71 is further provided with rotor poles, each with a permanent magnet 79 are provided to form the exciting magnetic field.

For the design of the electric motor various topologies are possible, which are known for the realization of brushless electric motors. The engine control 80 can by default of Kommutierungsmustern the speed of the feeder 71 adjust or regulate in any way, to a target speed of the feeder 71 to reach. In addition, it is also possible to design the electric motor as a brush-commutated electric motor.

The cell wheel 71 is in the present embodiment cylindrical with axially parallel channels 82 provided that penetrate the cylinder body. The cell wheel 71 is like that with the rotor 79 connected to it, when driving the rotor 79 is taken. As in the cross section of the 2 B represented are the channels 82 adjacent to each other at the same radial distance from the axis 72 arranged as equidistantly as possible.

To ensure a reliable low-leakage connection of the individual feed sections 51 . 52 of the air supply system 5 and the discharge sections 61 . 62 the exhaust discharge tract 6 with the respective ends of the channels 82 to achieve labyrinth seals 83 be provided, extending radially outward and radially inward through the channels 82 formed annular region extend fully, so that an exit of the compressed fresh air between the cellular wheel 71 and the front ends 76 . 77 is avoided.

During operation of the pressure wave charger 7 enter the channels 82 by their rotation about the axis 72 each with one of its open ends in registration with a corresponding opening in the first or second end face 76 . 77 so that each of the channels 82 depending on the position of the bucket wheel 71 with a first end having one of the feed sections 51 . 52 and a second end having one of the discharge sections 61 . 62 can get in touch. Furthermore, intermediate positions are possible in which some channels are closed at both ends, in particular so that the pressure waves have a possibility for direction reversal after expelling the fresh air or after their suction.

The compression of fresh air takes place using the energy of the engine 2 flowing pulsating combustion exhaust gas. The following is the operation of the pressure wave charger 7 considering a single one of the channels 82 explained in more detail. Once the considered channel 82 with its second end via the corresponding opening with the engine-side discharge section 61 the exhaust discharge tract 6 Combustion exhaust gas flows from the internal combustion engine 2 in the channel 82 , Because the first end of this channel 82 is closed, pressure builds up in the channel. Upon further rotation of the bucket wheel 71 leaves the second end of the channel 82 the opening to the engine-side discharge section 61 the exhaust discharge tract 6 and is thereby closed, so that a pressure built therein is conserved. In the considered channel 82 finds only a small mixing of the incoming combustion exhaust gas with previously in the channel 82 introduced fresh air.

The pressure in the channel 82 is maintained until the first end of the considered channel 82 through the corresponding opening on the first front side 76 with the motor-side feed section 52 of the air supply system 5 comes into contact. Then it flows in the considered channel 82 located under pressure fresh air in the engine side feed section 52 and is there under an increased pressure, the boost pressure ready. The outflow of air into the engine side feed section 52 of the air supply system 5 causes a first pressure drop in the channel 82 to the level of the boost pressure provided.

Another pressure drop occurs after further rotation of the bucket 71 on, in the channel 82 located gas over the second end of the considered channel 82 and over at the second end 77 associated opening in the output-side discharge section 62 the exhaust discharge tract 6 flows. The second pressure drop causes due to the kinetic energy of the outflowing gas, a reduction of the pressure in the interior of the considered channel 82 under the ambient pressure, so that upon further rotation of the bucket wheel 71 the second end is closed again and then the first end of the channel 82 in contact with the input side feeding section 51 associated with the opening, so that through the channel 82 prevailing negative pressure fresh air is sucked in. The so sucked fresh air is by connecting the second end of the channel 82 with the engine-side discharge section 61 the exhaust discharge tract 6 compressed again and the process described is repeated.

To a mixing of the sucked fresh air and the combustion exhaust gas from the engine side section 61 the exhaust discharge tract 6 to avoid, can in the channels 82 (Not shown) separating body may be provided which are arranged displaceably and divide the channel sections into two separate chambers. In this way, mixing of the fresh air with combustion exhaust gas can be avoided. By appropriate stops in the channels 82 can push out the separator from the channels 82 be avoided.

In contrast to conventional pressure wave loaders, the described pressure wave loader allows 7 an additional degree of freedom in the control of the compaction performance. While in conventional systems the cellular wheel 71 firmly with the crankshaft of the internal combustion engine 2 coupled and thus no control of the speed of the bucket 71 is possible, can in the previously described blast loader 7 the speed of the bucket 71 be chosen freely.

The target speed N _{ROT of} the rotor to be determined 79 is determined as the sum of a pilot-controlled basic rotational speed N _BAS , a control component N _REG , an adaptive component N _AD , a dynamic component N _DYN . The following applies: N _RED = N _BAS + N _REG + N _AD + N _DYN <N _Lim wherein N _{Lim represents} a predetermined maximum allowable rotor speed, which results from the mechanical load capacity of the pressure wave supercharger.

By means of a suitable speed control, the thus determined setpoint speed N _{ROT of} the rotor 79 the cellular wheel 71 in a known manner by the engine control 80 set.

The base speed N _BAS results from geometric factors of the pressure wave loader 7 , in particular from the length of the channels 82 and from the speed of sound of pressure waves in the in the channels 82 incoming combustion exhaust gas. With regard to the speed of sound a, the following applies: a = (cp / cv x R x T) ^0.5 , where cp / cv corresponds to the isotropic exponent, R the gas constant and T the exhaust gas temperature. The exhaust gas temperature varies in an exhaust system of a motor vehicle to a considerable extent and is substantially load, speed and location dependent. The relevant exhaust gas temperature at the rotor inlet can be measured or - as usual - suitably modeled.

The isotropic exponent cp / cv and the gas constant are dependent on the composition of the exhaust gas and can essentially be determined by means of an indication of the air / fuel ratio λ. This results in the following simplified relationship for the speed of sound a: a = T x F (λ, load) ^0.5 , where F (λ, load) corresponds to a size determined by a map, dependent on the exhaust gas composition. The base speed N _BAS is thus calculated as a function of the speed of sound a, in particular by means of a suitable basic speed map F _NBAS (a), the base speed map being the length of the channels 82 and further the geometry of the arrangements of the openings for the feed sections 51 . 52 and the discharge sections 61 . 62 of the air supply system 5 or the exhaust gas removal tract 6 considered. The following applies: N _BAS = F _NBAS (a) × F _PL ;

The use of an adaptation factor F _PL (<= 1.0) represents the fact that in the partial load range of the engine no maximum energy transfer from the exhaust to the fresh air side of the engine is desired, ie the target boost pressure PL is lower than the maximum achievable. Thus, N _BAS includes all pilot portions of the rotor speed control.

The control _component N _REG serves to cover the physical influences that are not adequately detected at the base speed N _BAS . The control component N _REG is determined in quasi-stationary engine operating states as a superimposed proportionately limited low-frequency speed modulation. With their change, the change in the actual target size of the engine control system is at the same time 80 observed (namely, the boost pressure) and thus the direction and size of the control component N _{REG are} evaluated, so that the value that causes only minimal deviation from the optimal compressor behavior in the current engine operating condition, as to be considered adaptive component N _AD , is stored.

The adaptive component N _{AD of} the rotational speed is structurally stored. For this purpose, an appropriate subdivision into a grid of load / speed ranges is made according to the entire engine operating range, for the permanent (based on neutral default assignments with '0') each determined an optimized adaptation value and stored and rewritten again with further improvements , In order to restrict the effect of any incorrect adaptation, a permissible value interval can be defined as the limit. According to the currently existing engine operating range, the stored memory value to date is read out and as adaptive component N _AD for the above calculation of the setpoint rotational speed of the rotor 79 considered.

Furthermore, the setpoint speed N _ROT can be acted upon by a dynamic portion N _DYN, which is to be determined so that the dynamic control deviation between the setpoint and actual boost pressure can be minimized when the operating point is changed quickly. In general, with rising or falling, but only slowly varying target boost pressure, it can be assumed that the previously determined basic rotational speed N _BAS and the adaptive component N _{AD are} sufficient to determine the optimum target rotational speed. At higher, in particular negative load dynamics, however, the system must be detuned, so that should be caused by rapid and possibly strong rotor speed changes that only minimal or no pressure waves from the combustion exhaust gas to be fed into the intake system.

Claims (11)

Method for operating a pressure wave loader ( 7 ) in an engine system ( 1 ) with an internal combustion engine ( 2 ), wherein for operating the internal combustion engine ( 2 ) a setpoint boost pressure (PL) is specified as a function of an engine operating point, wherein the pressure wave supercharger ( 7 ) a cellular wheel ( 71 ) with a number of channels ( 82 ), wherein by a rotation of the cellular wheel ( 71 ) Ends of the channels ( 82 ) alternately with openings on a first end face and a second end face of the cellular wheel ( 71 ) are connectable to effect a compression of fresh air; wherein a setpoint speed (N _ROT ) of the cell wheel ( 71 ) is set depending on the preset target boost pressure (PL). Method according to claim 1, wherein the nominal rotational speed (N _ROT ) of the cellular wheel ( 71 ) for setting the predetermined target supercharging pressure (PL) as a function of a speed of sound (a) which is determined from an exhaust gas temperature (T) of the engine ( 2 ) and its exhaust gas composition, which results in particular from a characteristic map, which is spanned by the fuel air ratio (λ) and the engine load, is determined. Method according to claim 2, wherein the nominal rotational speed (N _ROT ) of the cellular wheel ( 71 ) is determined as a function of a dynamic component of the rotational speed (N _DYN ), the dynamic component (N _DYN ) being dependent on an indication of a change in the nominal charging pressure of the internal combustion engine ( 2 ) is determined. Method according to one of claims 1 to 3, wherein the actual rotational speed of the cellular wheel ( 71 ) is set by specifying a corresponding desired speed (N _ROT ) according to a speed control. The method of claim 4, wherein a low-frequency modulation is applied to the set target speed (N _ROT ), wherein an adaptation value is structurally adapted depending on a change in the adjusting boost pressure, which is used to determine the target speed (N _ROT ). Method according to one of claims 1 to 5, wherein for stopping the internal combustion engine ( 2 ) the target speed (N _ROT ) is set to zero. Device for operating a pressure wave loader ( 7 ) in an engine system ( 1 ) with an internal combustion engine ( 2 ), wherein for operating the internal combustion engine ( 2 ) a setpoint boost pressure is specified as a function of an engine operating point, the pressure wave loader ( 7 ) a cellular wheel ( 71 ) with a number of channels ( 82 ), wherein by a rotation of the cellular wheel ( 71 ) Ends of the channels ( 82 ) alternately with openings on a first end face and a second end face of the cellular wheel ( 71 ) are connectable to effect a compression of fresh air; wherein a setpoint speed (N _ROT ) of the cell wheel ( 71 ) is set depending on the predetermined target boost pressure. Engine system ( 1 ) comprising: - an internal combustion engine ( 2 ); - a pressure wave loader ( 7 ); and - an apparatus according to claim 7. Computer program adapted to carry out all the steps of a method according to one of Claims 1 to 6. An electronic storage medium on which a computer program according to claim 9 is stored. Electronic control unit, which has an electronic storage medium according to claim 10

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