Patent Description:
A compressor of a turbo charger increases the power of a combustion engine by supplying charge to the combustion engine. The operation of a compressor can be defined in a compressor map plotting mass flow as a function of pressure ratio. The boundary of a stable operating region in such a map is defined by a surge limit. Operation of the compressor in a region outside the stable operating region may result in what is known as surge. Surge is defined by an irregular and probably reversed air flow through a compressor wheel. The operating point of a compressor risks to be moved into the surge region during operating conditions when the air flow rate to the combustion engine or energy to the turbine of the turbo charger is drastically reduced.

<CIT>, <CIT> and <CIT> show examples of compressors provided with an inlet portion having a structure that has become known as a MWE structure "map width enhanced". The MWE structures comprises a tubular insert or the like arranged in an air intake passage of the compressor. The tubular insert provides an additional air passage located radially outside of the air intake passage to the compressor wheel. At high air flow rates and at high speeds of the compressor wheel, the additional air passage usually supplies an additional air flow rate to the compressor as an addition to the air flow rate in the air intake passage. At low air flow rates, a part of the air flow in the air intake passage recirculates, via the additional air passage, to an upstream position of the air intake passage. The recirculation of a part of the air flow in the air intake passage of the compressor moves the surge limit to a lower flow in the map which increases the stable operating region of the compressor.

<CIT> describes a compressor comprising an annular gas flow passage defined between the inner and outer tubular walls of a gas inlet pipe. The upstream end of the annular passage communicates with the intake or inducer portions of the inlet through at least one upstream aperture and at least one downstream aperture communicates between a downstream portion of the annular flow passage and the impeller. The inner tubular wall has a length L2 extending upstream from the downstream aperture(s).

The object of the present invention is to provide a compressor arrangement providing a stable operation in a larger operating region than a conventional compressor arrangement.

This object is achieved by the compressor of the initially mentioned kind which is characterized by the features defined in the characterizing part of claim <NUM>. Inevitably, recirculating of air in an air intake passage disturbs the ordinary air flow in the air intake passage. It takes some time and a certain flow distance for the disturbed air flow to again become relatively uniform. In order to provide a stable operation of a compressor, it is important to supply a relatively uniform air flow to the compressor wheel both in axial and radial direction. A conventional compressor comprises a short additional air passage for recirculation of air. Thus, the air flow is recirculated from the compressor wheel in the air intake passage to an upstream position located close to the compressor wheel. In this case, the recirculated flow will disturb the air flow in a position close to the compressor. As a consequence, the air flow to the compressor is far from uniform. According to the present invention, an additional air passage is provided allowing recirculation of air from the compressor to an air line supplying air to the compressor. In this case, it is possible to recirculate the air to an upstream position located at a relatively long distance from the compressor wheel. Thereby, the air flow has a lot of time to become more uniform before it enters the compressor wheel. Such a recirculation of a part of the air flow in the air intake passage results in a more stable operation of the compressor within a larger operating region than a corresponding region of a conventional compressor according to the above. Furthermore, the recirculating air obtains a higher temperature by the compressor wheel before it is recirculated. As a consequence, the temperature of the air flow directed to the compressor wheel will increase during recirculation of air. Since the air is recirculated to a position at a longer distance from the compressor wheel than in the conventional case, the heating of the air entering the compressor wheel will be lower than in the conventional case. An increased temperature of the air reduces the efficiency of the compressor.

According to the invention, the additional air passage is configured to return air to the air conduit in a position located at a flow distance from the compressor wheel corresponding to at least <NUM>,<NUM> times the inlet diameter to the compressor wheel, preferably within the range of <NUM>-<NUM> times the inlet diameter to the compressor wheel. In this case, the disturbed air flow in the air conduit has time to become more uniform before it enters the compressor wheel.

According to an embodiment of the invention, the additional air passage is defined by at least one return conduit having an extension between a downstream end connected to an opening in the housing and an upstream end connected to an opening in the air conduit. To attach the upstream ends of one or several return conduits to the compressor housing and the air line supplying air to the compressor is a relatively simple measure.

According to an embodiment of the invention, a part of the additional air passage is defined by an annular air gap extending around the compressor wheel in the air intake passage. Such an annular air gap makes it possible to provide a symmetrical output of a part of the air flow in the air intake passage to the additional air passage during certain operating conditions and a symmetrical input of air from the additional air passage to the air flow in the intake passage during other operating conditions. A part of the additional air passage may be defined by an annular space receiving air from the annular air gap. It is relatively easy to connect an end of a return conduit to such an annular space arranged radially outside of the air intake passage via a radial opening in the compressor housing. The air flow to the compressor is most non-uniform at the outer periphery of the intake passage. As a consequence, it is favorable to recirculate this part of the air flow.

According to an embodiment of the invention, the housing comprises a tubular portion defining a wall between the air intake passage and the annular space. The tubular portion may be made in one piece with the housing. Alternatively, the tubular member may be a separate component which is attached in the air intake passage of the housing. The tubular portion may comprise a downstream located end portion defining a side surface of the annular air gap. The housing may define the opposite side surface of the annular air gap. The tubular portion may comprise an upstream located end portion forming a closed wall section between the air intake passage and the annular space. This closed wall section prevents the additional air passage to recirculate air to an upstream position in the air intake passage of the housing.

According to an embodiment of the invention, the housing comprises a inlet portion defining at least a part of the air intake passage, wherein the inlet portion comprises a connection surface connected to an end portion of the air conduit delivering air to the compressor. Such a connection surface allows a releasable or fixed connection between an end of the air conduit and the inlet portion of the housing.

According to an embodiment of the invention, the air conduit has a curved portion closed to the air intake passage of the compressor, wherein the additional air passage is configured to recirculate air to a position of the air line located upstream of said curved portion. Many times, air conduits delivering air to a compressor has to have a curved portion closed to the compressor. The supply of recirculating air to a curved portion of the air conduit may disturb the air flow more than a corresponding supply to a straight portion of the air conduit. There is usually no difficulties to recirculate the air to a straight portion of the air line located in an upstream position of the curved portion.

According to an embodiment of the invention, the housing comprises a hollow portion configured to receive a shaft connecting the compressor wheel and a turbine wheel. In this case, the compressor is a part of a turbo charger. The compressor wheel is driven by the turbine wheel and the exhaust gases of the combustion engine. The problem with surge may arise in a compressors of a turbo charger when the air flow rate to the combustion engine is drastically reduced at the same time as the turbine is still spinning with a high speed generating power to the compressor wheel. In diesel engines, this problem will arise when the fuel supply to the engine ends. Since the exhaust manifold has a smaller volume of exhaust gases than the volume of charged air in the charged air line, parts of the accumulated charge air risks to leak through the compressor in a backward direction. However, the above mentioned recirculation of air to an upstream position located at a relatively large distance from the compressor wheel significantly reduces the problem of surge.

According to an embodiment of the invention, the additional air passage comprises flow restricting means. The flow restricting means may be a throttle valve with a constant throttle area or an adjustable throttle area. A throttle valve with a constant throttle area may be dimensioned to provide an air flow through the additional air passage such that it allows optimal operating properties of the compressor in a large operating region. A throttle valve with an adjustable throttle area may provide an adjustable air flow through the additional air passage during different operating conditions. In this case, it is possible to further provide the ability of the compressor to operate in an optimally manner in a large operating region.

According to further embodiments a turbo charger comprises such an air line and a vehicle driven by a combustion engine comprises such a turbo charger.

In the following a preferred embodiments of the invention is described, as an example, with reference to the attached drawings, in which:.

<FIG> shows a compressor for a combustion engine <NUM> powering a schematically indicated vehicle <NUM>. The vehicle <NUM> may be a heavy vehicle and the combustion engine <NUM> may be an internal combustion engine such as a diesel engine. The exhaust gases from the cylinders of the combustion engine <NUM> are led via an exhaust manifold <NUM> to an exhaust line <NUM>. The combustion engine <NUM> is provided with a turbo charger <NUM> comprising a turbine wheel <NUM> and a compressor wheel <NUM>. The exhaust gases are initially led, via the exhaust line <NUM>, to the turbine wheel <NUM>. The pressure of the exhaust gases provide a driving power of the turbine wheel <NUM> which is transmitted, via a shaft <NUM>, to the compressor wheel <NUM>. As a consequence, the exhaust gases leaving the turbine wheel <NUM> have a reduced pressure. The compressor wheel <NUM> is arranged in a charge air line <NUM> directing charge air to the combustion engine <NUM>. During operation of the compressor wheel <NUM>, air is drawn from the surrounding, via a first air conduit 9a of the charge air line <NUM>, to the compressor wheel <NUM>. The air leaves the compressor wheel <NUM> with an increased pressure and an increased temperature. The charge air line <NUM> comprises a second air line 9b directing the charge air from the compressor <NUM> to at least one charge air cooler <NUM>. In this case, the charged air cooler is exemplified as an air cooled charge air cooler <NUM> arranged in a front position of the vehicle together with a radiator <NUM>. The charge air is cooled in the charge air cooler <NUM> by air of ambient temperature which is forced through the charged air cooler <NUM> and the radiator <NUM> by a radiator fan <NUM> and the ram air of the vehicle <NUM>. The cooled charged air is directed from the charged air cooler <NUM>, via a third air line 9c of the charge air line <NUM> and an inlet manifold <NUM>, to the cylinders of the combustion engine <NUM>.

The turbo charger <NUM> comprises a compressor unit <NUM> which is shown in <FIG>. The compressor unit <NUM> comprises a housing <NUM> enclosing the compressor wheel <NUM>. The housing <NUM> comprises further an inlet portion <NUM> receiving air from the first air conduit 9a.

The inlet portion <NUM> forming a first part of an air intake passage <NUM> directing air to the compressor wheel <NUM>. The inlet portion <NUM> comprises a connecting surface 16a configured to receive an end of the first air conduit 9a. Furthermore, the housing <NUM> comprises an outlet volute <NUM> delivering charged air to the second air line 9b. The compressor unit <NUM> comprises a tubular portion <NUM> having a radially inner surface <NUM> defining a second part of the air intake passage <NUM> directing air the compressor wheel <NUM>. The tubular portion <NUM> has in an upstream position a closed wall section <NUM> fixedly connected to the inlet portion <NUM> and in a downstream position a free end portion <NUM> located at an axial distance from a radial surface <NUM> of the housing <NUM>.

The distance between the free end portion <NUM> of the tubular portion <NUM> and the radial surface <NUM> of the housing <NUM> forms an annular axial gap <NUM>. The annular axial gap <NUM> is located in a radially outer position of a part compressor wheel <NUM>. The housing <NUM> has a curved inner surface <NUM> defining a third part of the air intake passage <NUM>. The annular axial gap <NUM> is connected to an annular space <NUM> defined by a surface of the housing <NUM> and a radially outer surface <NUM> of the tubular portion <NUM>. The housing <NUM> comprises at least one radial opening <NUM> to the annular space <NUM>. The radial opening <NUM> is configured to receive a first end 29a of a return conduit <NUM>. A second end 29b of the return conduit <NUM> is arranged in an opening <NUM> in the first air conduit 9a. The second end 29b of the return conduit <NUM> is located in an upstream position in relation to the inlet portion <NUM> of the housing <NUM> and the compressor wheel <NUM>. In this case, the first air conduit 9a comprises a curved portion 9a<NUM> in the vicinity of the compressor unit <NUM>. The second end 29b of the return conduit <NUM> is connected to an opening <NUM> in the first air conduit 9a located upstream of the curved portion 9a<NUM> of the first air conduit 9a. The housing <NUM> comprises a hollow portion <NUM> configured to receive the shaft <NUM> connecting the compressor wheel <NUM> and the turbine wheel <NUM>.

During operation of the compression engine <NUM>, the exhaust gases in the exhaust line <NUM> drives the turbine wheel <NUM>. The turbine wheel <NUM> in turn drives, via the shaft <NUM>, the compressor wheel <NUM>. The compressor wheel <NUM> drawn air from the surrounding, via the first air conduit 9a, to the compressor unit <NUM>. During operating conditions when the compressor wheel <NUM> works close to choke with a high speed and supplies a large quantity of charge air to the combustion engine <NUM>, the static pressure in the air intake passage in a position radially inside the air gap <NUM> will be lower than the static pressure in the first air conduit 9a at the opening <NUM>. In this case, an air flow is entering the opening <NUM>, via the return conduit <NUM>, the radial opening <NUM>, the annular space <NUM> and the air gap <NUM>, to the flow passage. Thus, during such operating conditions, the return conduit <NUM> provides an additional air flow to the compressor wheel <NUM>.

During operating conditions when the compressor wheel <NUM> runs close to surge and provides a low air flow at a relatively high pressure through the air intake passage <NUM>, the static pressure in a position radially inside the air gap <NUM> increases to a higher value than the static pressure in the first air conduit 9a at the opening <NUM>. In this case, a part of the air flow in the air intake passage <NUM> is led into the air gap <NUM>, whereupon it is directed, via the annular space <NUM>, the radial opening <NUM> and the return conduit <NUM>, to the opening <NUM>. Consequently, a part of the air flow entering the inlet portion <NUM> is recirculated to the first air conduit 9a at a distance from the compressor unit <NUM>. This recirculating part of the air flow is mixed with the ordinary air flow in the first air conduit 9a and again directed to the compressor unit <NUM>. The opening <NUM> in the first air conduit 9a is arranged in a first transverse plane A<NUM> through first air conduit 9a. The compression of the air starts in the air intake passage <NUM> in a second transverse plane A<NUM> extending through a front surface of the compression wheel <NUM>.

The average flow distance D of the air along a center axis in the first air line 9a from the first plane A<NUM> to the second plane A<NUM> is indicated in <FIG>. It is important to supply a relatively uniform air flow to the compressor wheel <NUM> in order to provide a stable operation of the compressor. A relatively uniform supply of air to the compressor wheel <NUM> may provide a large stable operating region in a compressor map plotting mass flow as a function of pressure ratio. The supply of the air flow from the returning line <NUM> to the first air conduit 9a disturbs the relatively uniform air flow in the first plane A<NUM>.

However, after a certain flow distance from the first plane A<NUM>, the air flow will again become relatively uniform. The flow distance D between the first plane A<NUM> and the second plane A<NUM> is chosen such the air flow has become sufficiently uniform when it reaches the compressor wheel <NUM>. The value of the distance D depends on a number of factors such as the dimension of the first air conduit 9a, the air flow rate in the first air conduit 9a, the air flow rate in the air intake passage <NUM>, the air flow rate in the return conduit <NUM> etc. The distance D is at least <NUM>,<NUM> times the inlet diameter d to the compressor wheel <NUM> but preferably longer and within the range of <NUM>-<NUM> times the inlet diameter d to the compressor wheel <NUM>.

<FIG> shows a second embodiment of the invention. In this case, the return conduit <NUM> has been equipped with a throttle valve <NUM>. Furthermore, the air gap <NUM> has been increased. As a consequent, the air flow through the return conduit <NUM> is mainly restricted by the throttle valve <NUM>. The throttle valve <NUM> may have an adjustable throttle area. In this case, the throttle vale <NUM> is controlled by a control unit <NUM>. The control unit <NUM> receives information about suitable operating parameters and controls the throttle valve <NUM> by means of this information. In this case, it is possible to adjust the air flow through the return conduit <NUM> during different operating conditions in order to optimize the operating properties of the compressor wheel <NUM> in a large operating region. Alternatively, the throttle valve have a constant throttle area. In this case, the throttle area is dimensioned to allow an air flow through the return conduit <NUM> such that it allows substantially optimal operating properties of the compressor wheel <NUM> in a large operating region.

Claim 1:
An air line (<NUM>) supplying charged air to a combustion engine (<NUM>) comprising a compressor arrangement, wherein the compressor arrangement comprises:
- a compressor unit (<NUM>) comprising a housing (<NUM>) including an air intake passage (<NUM>), a compressor wheel (<NUM>) arranged in said air intake passage (<NUM>), and an additional air passage (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) allowing recirculation of air from the air intake passage (<NUM>) in a position radially outwardly of a part of the compressor wheel (<NUM>) to an air conduit (9a) delivering an air flow to the air intake passage (<NUM>) of the compressor unit (<NUM>) in a position located at an average flow distance (D) from the compressor wheel (<NUM>),
- a part of the additional air passage is defined by a return conduit (<NUM>) having an extension between a downstream end (29a) connected to an opening <NUM> in the housing (<NUM>) and an upstream end (29b),
the air conduit (9a) has a curved portion (9a<NUM>) closed to the intake passage (<NUM>) of the compressor unit (<NUM>), wherein the return conduit (<NUM>) is configured to return air to an upstream position of said curved portion of the air conduit (9a), characterized in that
the upstream end (29b) of the return conduit (<NUM>) is connected to an opening (<NUM>) through the air conduit (9a) and
- the average flow distance (D) is defined as a distance along a center axis in the air conduit (9a), from a first plane (A1) transverse through the air conduit (9a) where the air opening (<NUM>) is arranged, to a second transverse plane (A2) extending through a front surface of the compressor wheel (<NUM>), the average flow distance (D) corresponding to at least <NUM>,<NUM> times the inlet diameter (d) of the compressor wheel (<NUM>).