Exhaust gas turbocharger for an internal combustion engine of a motor vehicle

This is a Continuation-In-Part Application of pending international patent application PCT/EP2009/005349 filed Jul. 23, 2009 and claiming the priority of German patent application 10 2008 039 086.0 filed Aug. 21, 2008.

The invention relates to an exhaust gas turbocharger for an internal combustion engine with a turbine housing having first and second spiral inlet channels for directing exhaust gas onto a turbine which is disposed in the turbine housing. The invention further relates to a motor vehicle with an internal combustion engine and such an exhaust gas turbocharger.

Due to the continuous tightening of the emission limit values, for example the NO x and soot emission values of motor vehicles, the demands of exhaust gas turbochargers or charged internal combustion engines also increase. Thus, there are increasing demands regarding the charge pressure provision with high exhaust gas recirculation rates (AGR rate) over medium to high load demand ranges of the internal combustion engine whereby the turbines of exhaust gas turbochargers are increasingly scaled down geometrically. In other words, the required high turbine performances of exhaust gas turbochargers are realized by an increase of the retention ability and a corresponding reduction of the intake ability of the turbines in cooperation with the respective internal combustion engine.

The performance of exhaust gas turbochargers is further affected by exhaust gas treatment systems arranged in the exhaust gas tract downstream of the turbine as for example soot filters, catalysts or SCR systems. These exhaust gas treatment systems lead to a pressure increase at an exhaust gas outlet of the exhaust gas turbocharger. This again causes a reduction of a turbine pressure gradient defining the performance of the exhaust gas turbocharger, wherein the turbine pressure gradient can be determined as the quotient of a gas pressure before the turbine wheel or an exhaust gas inlet of the turbine wheel housing and a gas pressure behind the turbine wheel or an exhaust gas outlet of the turbine housing. Also, due to this reason, the turbine size again has to be designed for lower values and thus lower efficiencies in order to be able to satisfy the performance demand of the compressor of the exhaust gas turbocharger.

A certain improvement is provided by exhaust gas turbochargers known in the state of the art, whose turbine housings comprise two spiral channels through which exhaust gas can be separately admitted to the turbine and which are respectively coupled to different exhaust gas lines of an exhaust gas tract of the internal combustion engine via annular inlet vane structures. The exhaust gas lines themselves are associated with different cylinders or cylinder groups of the internal combustion engine. One of the spiral channels thereby usually serves as a so-called lambda spiral which provides for the necessary air-fuel ratio via its exhaust gas retention ability. The other spiral channel serves in contrast as a so-called exhaust gas recirculation spiral (AGR spiral) and is responsible for the exhaust gas recirculation ability of the exhaust gas turbocharger.

With the design limit conditions of exhaust gas turbochargers, which are usually defined by a nominal operating point, a charge change aspect and a fuel consumption aspect of the internal combustion engine, particularly the lower load and speed range of internal combustion engines can often not be attended to in an optimum manner even with exhaust gas turbochargers with two spiral inlet channels. The flow cross-sectional areas of the spiral channels are in principle chosen to be as small as possible for this purpose, in order to be able to generate the necessary exhaust gas flow speeds.

It is a disadvantage of the known exhaust gas turbochargers that they have comparatively low efficiencies, so that also the requirement of an internal combustion engine provided with the exhaust gas turbocharger relatively high. This necessitates additional measures for an efficiency increase, whereby the manufacturing costs however also increase considerably.

It is thus the object of the present invention to which provides for an efficiency improvement with manufacturing costs as low as possible even with the highly transient requirements of internal combustion engine or motor vehicles.

In an exhaust gas turbocharger for an internal combustion engine of a motor vehicle with a turbine comprising a turbine housing with at least a first and a second spiral channel, each being coupled to an exhaust gas line of an exhaust gas tract of the internal combustion engine for conducting exhaust gas to a turbine wheel arranged within the turbine housing and driving a compressor wheel of a compressor of the exhaust gas turbocharger, an area ratio Q g of the turbine corresponds to the formula Q g =(A λ +A AGR )/A R >0.40, wherein A λ refers to a narrowest flow cross-section of the first spiral channel, A AGR to a narrowest flow cross-section of the second spiral channel ( 52 b ) and A R to a wheel exit flow cross-section of the turbine exhaust channel. The invention further relates to a motor vehicle with a combustion engine and such an exhaust gas turbocharger.

In other words, the spiral channels of the turbine of the exhaust gas turbocharger according to the invention have a significantly increased narrowest flow cross-sectional area sum A λ +A AGR compared to the state of the art in relation to the narrowest cross-sectional area downstream of the spiral channels, namely the wheel exit flow cross-sectional area A R . The exhaust gas turbochargers or turbines known from the state of the art are designed in such a manner that the major exergy amount of the total pressure gradient of the turbine is converted to speed in front of the turbine wheel in the spiral channels and not in the turbine wheel channels. In the turbines known from the state of the art the reaction degree of the turbine, which is defined by the quotient of the speed conversion in the turbine wheel channel and the speed conversion in the spiral channels, is thus below the value 0.4. Compared to this, a deviating gradient division of the total gradient of the turbine can be achieved with the exhaust gas turbocharger according to the invention during operation, wherein reaction degrees are achieved that are above 0.5. As the sum of the flow cross-sectional areas A λ A AGR is larger in comparison with the state of the art, additionally only low demands are made with regard to the manufacturing limits, so that cost-efficient sand casting methods or the like can be used for the manufacture of the turbine housing without any problems.

In an advantageous embodiment of the invention the area ratio Q g of the turbine is at least 0.45 and preferably at least 0.5. Increased efficiencies are achieved hereby for larger mass exhaust gas flows, whereby the total behavior of the exhaust gas turbocharger becomes very advantageous with regard to the air delivery in large operating ranges. The multi-flow turbine thereby has a reaction degree, which is above the value of 0.45 or 0.5 of the design operating point which is unusual.

Further advantages are obtained with an area ratio Q λ between the narrowest flow cross-sectional area A λ of the first spiral channel and the wheel exit cross-sectional area A R of the turbine wheel channel which is at least 0.35. Particularly when the first spiral channel is arranged as a so-called lambda spiral in the exhaust gas tract, a correspondingly improved efficiency can be achieved, as no exhaust gas recirculation volume losses occur.

In a further advantageous embodiment of the invention, the area ratio Q x between the narrowest flow cross-sectional area A λ of the first spiral channel and the exit cross-sectional area A R of the turbine wheel channel is at least 0.4, preferably at least 0.5 and particularly at least 0.6. In this manner, the first spiral channel can be operated with correspondingly high reaction degrees according to an optimal reaction turbine, whereby particularly high turbine efficiencies can be achieved and the total behavior of the exhaust gas turbocharger is particularly advantageous in wide operating ranges with regard to its air delivery.

In a further arrangement of the invention, it is provided that an area ratio Q AGR of the second spiral channel and the wheel exit cross-sectional area A R of the turbine wheel channel is at most 0.3. Particularly when the second spiral channel is in the form of a so-called AGR spiral, the second spiral channel can operate with reaction degrees below 0.3 according to an impulse turbine. The respective area ratio Q AGR is preferably chosen in dependence on the AGR, (Exhaust Gas Recirculation) requirement of the internal combustion engine.

Further advantages result in that the area ratio Q AGR of the narrowest flow cross-sectional area A AGR of the second spiral channel and the wheel exit cross-sectional area A R of the turbine wheel channel is at most 0.28, preferably at most 0.25 and particularly not more than 0.1. Particularly strict emission limit determinations can hereby also be accounted for and the emission behavior of the associated internal combustion engine can be improved correspondingly.

In a further advantageous embodiment of the invention, the narrowest flow cross-sectional area A λ of the first spiral channel and/or the narrowest flow cross-sectional area A AGR of the second spiral channel are provided in the exit area of the first and second spiral channels to the turbine wheel channels. The narrowest flow cross-sectional area A λ or A AGR is advantageously in the form of an annular nozzle for generating high exhaust gas flow speeds.

In a further advantageous arrangement of the invention, the first and/or the second spiral channel comprises at least two spiral segment channels which are separated in a fluidic manner, and which can be coupled to different exhaust gas lines of the internal combustion engine. An exhaust gas turbocharger with a turbine formed with at least three flows is created in this manner, wherein the spiral segment channels enable an impact charging operating with a more effective use of the expansion energy of individual cylinders or cylinder groups. Lower load and speed regions of the internal combustion engine can hereby also be provided in an optimal manner, so that a considerable efficiency improvement is ensured over a wider operating range of the internal combustion engine. The flow cross-sectional area A λ designates in this case the sum of the flow cross-sectional areas of the at least two spiral segment channels. The number of the spiral segment channels can thereby be adapted to the number of the cylinders or cylinder groups. It can also be provided that both spiral channels have two or more spiral segment channels. It can alternatively or additionally be provided that the turbine of the exhaust gas turbocharger comprises three or more spiral channels.

In order to be able to better adapt the operation of the turbine to the operation of the internal combustion engine, it has been shown to be advantageous in a further arrangement that the turbine comprises an inlet vane structure. A flow control depending on the geometric arrangement of the vane structure is facilitated hereby. The vane structure is adjustable whereby the inflow of the exhaust gas can advantageously be controlled depending on a load or flow rate. The vane structure can for example be mounted in the turbine housing so as to be translationally movable or the vanes are pivotally adjustable.

Particular advantages are obtained if the narrowest flow cross-sectional area A λ of the first spiral channel and/or the narrowest flow cross-sectional area A AGR of the second spiral channel are formed by the vane structure and/or can be adjusted by the vane structure. A particularly high geometric variability of the turbine and a corresponding adjustability of the flow guidance is given in this manner. A further increase of the efficiency can be achieved hereby, as the corresponding spiral channel upstream of the vane structure can be provided with an enlarged cross-sectional area.

A further aspect of the invention relates to a motor vehicle with an internal combustion engine which comprises at least two cylinders or cylinder groups, which are connected to at least two exhaust gas lines of an exhaust gas tract, and with an exhaust gas turbocharger, which comprises a compressor arranged in an intake tract of the internal combustion engine and a turbine arranged in the exhaust gas tract of the internal combustion engine. The turbine comprises on its part a turbine housing with at least a first spiral channel coupled to a first exhaust gas line, a second spiral channel coupled to a second exhaust gas line, and a turbine wheel arranged within a turbine wheel channel of the turbine housing. The turbine wheel is thereby driven by the exhaust gas of the internal combustion engine which is guided through the at least two spiral channels for driving the compressor wheel of the compressor, the compressor wheel being rigidly coupled to the turbine wheel by a common shaft. According to the invention, an efficiency improvement is thereby obtained with highly transient requirements of the internal combustion engine or of the motor vehicle with relatively low manufacturing costs in that the exhaust gas is formed according to one of the preceding embodiments. The advantages resulting from this can be taken from the corresponding descriptions.

The invention will become more readily apparent from the following description of an exemplary embodiment with reference to the accompanying drawings.

FIG. 1 shows schematically an internal combustion engine of a motor vehicle which is provided with an exhaust gas turbocharger according to one embodiment of the invention,

FIG. 2 shows an axial cross-sectional view of a turbine of the exhaust gas turbocharger shown in FIG. 1 , and

FIG. 3 shows a turbine performance graph of the exhaust gas turbocharger according to the invention.

FIG. 1 shows schematically an internal combustion engine 10 of a motor vehicle (not shown), which is provided with an exhaust gas turbocharger 12 . The internal combustion engine 10 comprises an intake tract 14 with an air filter 16 . A compressor 18 of the exhaust gas 12 is arranged downstream of the air filter 16 . The compressor 18 has a compressor wheel 20 , which is connected rigidly to a turbine wheel 24 by means of a common shaft 22 of a turbine 26 of the exhaust gas turbocharger 12 . The intake tract 14 includes a charge-air cooler 28 downstream of the compressor wheel 20 . The internal combustion engine 10 is a Diesel engine in the present embodiment and comprises six cylinders 30 a - f which are divided into two cylinder groups 32 a , 32 b , so that the individual cylinders 30 a - f do not influence each other during a charge change. The cylinder groups are connected to the turbine 26 of the exhaust gas turbocharger via two separate exhaust gas lines 34 a , 34 b of an exhaust gas tract 36 of the internal combustion engine 10 . An exhaust gas recirculation device 38 with a valve 40 and an exhaust gas cooler 42 is arranged between the cylinders 30 d - f and the intake tract 14 so that exhaust gas can be directed from the exhaust gas line 34 b into the intake tract 14 . Also, a bypass line 44 with a relief valve 46 is arranged upstream of the turbine, whereby exhaust gas can bypass the turbine 26 when necessary. The bypass line 44 and the relief valve 46 are integrated into a turbine housing 50 of the turbine 26 . An exhaust gas treatment system 48 is finally arranged in the exhaust gas tract 36 downstream of the turbine 26 , by means of which treatment system an exhaust gas treatment is carried out.

The turbine 26 of the exhaust gas turbocharger 12 will be explained in the following in connection with FIG. 2 , which shows an axial cross-sectional view of the turbine 26 . The turbine housing 50 of the turbine 26 which is formed as a cost-efficient sand casting part, comprises a first spiral channel 52 a coupled to the first exhaust gas line 34 a , a second spiral channel 52 b coupled to the second exhaust gas line 34 b and the turbine wheel 24 arranged within a turbine wheel channel 54 . The spiral channel 52 a is arranged at the exit side and formed as a full spiral with a looping angle of approximately 360°, whereas the spiral channel 52 b is arranged on the bearing side and is formed as a partial spiral with a looping angle of less than 360°. In principle, both spiral channels 52 a , 52 b can however be formed as a full and/or partial spiral. It can also be provided that at least one spiral channel 52 a or 52 b is formed as a segment spiral with two or more segment channels distributed over the circumference of the turbine housing 50 , which are coupled to a correspondingly adapted number of exhaust gas lines 34 . The spiral channel 52 a is thereby formed as a so-called lambda spiral which affects the necessary air-fuel ratio via its exhaust gas retention ability. The other spiral channel 52 b serves, in contrast, as a so-called exhaust gas recirculation spiral (AGR spiral) and is responsible for the exhaust gas recirculation capability of the exhaust gas turbocharger 12 or of the turbine 26 .

In order to provide for an efficiency improvement with manufacturing costs as low as possible even with the highly transient requirements of the internal combustion engine 10 , an area ratio Q g of the turbine corresponds to the formula

Q g =( A λ +A AGR )/ A R ≧0.50

wherein A λ refers to a narrowest flow cross-section of the first spiral channel 52 a , A AGR to a narrowest flow cross-section area of the second spiral channel 52 b , and A R to an outlet cross-section of the turbine wheel channel 54 in the exit region of the turbine wheel 24 . Additionally, an area ratio Q λ between the narrowest flow cross-section A λ of the first spiral channel 52 a and the wheel exit cross-section area A R of the turbine wheel channel 54 is at least Q A =A 80 /A R =0.4 and an area ratio Q AGR between the narrowest flow cross-section A AGR of the second spiral channel 52 b and the wheel exit cross-section A R of the turbine wheel channel 54 is at most Q AGR =A AGR /A R =0.25. It can alternatively be provided that the area ratio Q AGR is chosen in dependence on the AGR requirement of the internal combustion engine 10 and thus can also be chosen to be lower than 0.25, possibly lower than 0.1. It can alternatively be provided that the flow cross-sectional areas A λ , A AGR are formed by a vane structure (not shown), whereby a further increase of the turbine efficiency can be achieved, as the spiral channels 52 a , 52 b can in this case be formed with enlarged cross-sectional areas upstream the corresponding vane structure.

FIG. 3 shows a performance graph of the turbine 26 of the exhaust gas turbocharger 12 . A flow rate parameter D[kg*√K/s*bar] is thereby provided on the ordinate over a turbine pressure ratio T=p 3t /p 4 of the pressure p 3t at the flange entry of the spiral channels 52 a , 52 b and the pressure p 4 at the turbine wheel 24 outlet. The flow rate characteristic lines K 1-3 are thereby depicted for different pressures. The flow rate line K 1 shows the flow rate behavior with opened spiral channel 52 a , 52 b . The flow rate K 2 shows the flow rate behavior with opened spiral channel 52 a and closed spiral channel 52 b , the flow rate line K 3 finally shows the flow rate behavior with an opened spiral channel 52 b and closed spiral channel 52 a.