Patent Application
20140241866
The present invention relates to a wheel for a turbocharger, and more particularly, to an automotive turbocharger wheel having blades spaced at angles that limit the generation of noise in the audible range.
Radial automotive turbines are generally configured with an inlet volute in which a stream of exhaust gas spirals in to drive the blades of a turbine wheel. At the location around the volute where the exhaust stream first opens up to the turbine wheel, there is a structural feature where the blades pass from being in close proximity to the surrounding volute wall to being distant from the volute wall. Because of the appearance of this feature in cross section, it is sometimes referred to as the tongue.
Automotive turbochargers often have on the order of seven to eighteen turbine blades. Within the lower range of numbers of blades, and at typical turbine rotational rates, the blades may pass the tongue at a frequency that is within the human audible range. This creates a humming noise that is not desirable.
One solution to this problem is to increase the number of blades, such as from eleven to thirteen blades for a smaller automotive turbocharger. This causes the blades to pass the tongue at a frequency that is above the human audible range at typical operating speeds. Unfortunately, the increase in the number of blades can lead to several undesirable consequences. For example, the increase in blades can lead to a wheel that is more expensive to make (both because of an increase in materials and because of an increase in tooling costs). Also, because there is less room for fillets at the base of each blade, the blade support is weakened, leading to a less durable turbine wheel. Moreover, because the wheel will likely have a greater rotational inertia, it will be less responsive to changes in the exhaust pressure, such as during engine transient operating conditions.
There exists a need for durable and cost-efficient turbine wheels that minimize undesirable noise. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.
In various embodiments, the present invention solves some or all of the needs mentioned above, providing a durable and cost-efficient turbine wheel that minimizes undesirable noise.
The turbocharger wheel, e.g., a turbine wheel, which is for use as part of a rotor group, includes a hub and a plurality of blades. The turbine wheel is characterized by a line defining an axis of rotation. Both the center of mass (“CM”) of the hub and the CM of the plurality of blades are on the axis of rotation. The plurality of blades is circumferentially spaced around the hub such that the blades are rotationally asymmetric around the axis of rotation. Advantageously, this asymmetry spreads the acoustic energy generated by the blades passing the volute tongue over a range of different frequencies, thereby reducing the acoustic energy at any one frequency. This, in turn, provides for automotive turbine wheels to be made with fewer blades than might otherwise be desirable for rotationally symmetric blades that concentrate acoustic energy in frequencies that are audible to humans.
Each consecutive pair of blades is characterized by a spacing angle between the consecutive pair of blades. A set of spacing angles that meet all the requirements can be iteratively calculated. In a further feature, the turbocharger wheel, e.g., a turbine wheel is characterized by a second line that intersects with and is normal to the line defining the axis of rotation. The line defining the axis of rotation and the second line define a plane of symmetry by extending along and being contained within the plane, and the spacing angles of the plurality of blades are symmetric across the plane of symmetry. Advantageously, this planar symmetry provides for the angles to be iteratively calculated using a significantly reduced number of variables, and therefore a reduced number of calculations.
Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The detailed description of particular preferred embodiments, as set out below to enable one to build and use an embodiment of the invention, are not intended to limit the enumerated claims, but rather, they are intended to serve as particular examples of the claimed invention.
The invention summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read with the accompanying drawings. This detailed description of particular preferred embodiments of the invention, set out below to enable one to build and use particular implementations of the invention, is not intended to limit the enumerated claims, but rather, it is intended to provide particular examples of them.
Typical embodiments of the present invention reside in a motor vehicle equipped with an internal combustion engine (“ICE”) and a turbocharger. The turbocharger is equipped with a turbine wheel characterized by a unique blade configuration that provides for durability, a low rotational moment of inertia, and quiet operation within the human range of hearing.
With reference to
The turbine housing 105 and turbine wheel 111 form a turbine configured to circumferentially receive a high-pressure and high-temperature exhaust gas stream 121 from an engine, e.g., from an exhaust manifold 123 of an internal combustion engine 125. The turbine wheel (and thus the rotor group) is driven in rotation around the axis of rotation 103 by the high-pressure and high-temperature exhaust gas stream, which becomes a lower-pressure and lower-temperature exhaust gas stream 127 and is axially released into an exhaust system (not shown).
The compressor housing 107 and compressor wheel 113 form a compressor stage. The compressor wheel, being driven in rotation by the exhaust-gas driven turbine wheel 111, is configured to compress axially received input air (e.g., ambient air 131, or already-pressurized air from a previous-stage in a multi-stage compressor) into a pressurized air stream 133 that is ejected circumferentially from the compressor. Due to the compression process, the pressurized air stream is characterized by an increased temperature over that of the input air.
Optionally, the pressurized air stream may be channeled through a convectively cooled charge air cooler 135 configured to dissipate heat from the pressurized air stream, increasing its density. The resulting cooled and pressurized output air stream 137 is channeled into an intake manifold 139 on the internal combustion engine, or alternatively, into a subsequent-stage, in-series compressor. The operation of the system is controlled by an ECU 151 (engine control unit) that connects to the remainder of the system via communication connections.
Turbine
With reference to
At the location where the exhaust gas entrance passageway 217 leads into the primary-scroll passageway 219, there is a structure that is characterized by a tongue-like shape when viewed in the cross-section of
It is desirable for typical automotive turbochargers to have on the order of eleven turbine blades 231, and often have a radius between 12 mm and 75 mm. Within the typical eleven-blade automotive turbine, and at typical automotive turbine rotational rates, the blades pass the tongue 235 at a frequency that is within the human audible range. This creates a humming noise that is not desirable.
Under a first embodiment of the invention, the turbine wheel 111, which is part of the rotor group, is characterized by a line defining the axis of rotation 103 (i.e., the axis is collinear with the line). The turbine wheel may include a rotationally symmetric hub 241 (possibly being characterized by spherical symmetry around the axis of rotor rotation). The turbine hub supports the plurality of blades. The center of mass (“CM”) of the hub is on the axis of rotation, and the CM of the plurality of blades is also on the axis of rotation.
Unlike prior art turbine wheels, the plurality of blades 231 are circumferentially spaced around the hub at varying angles such that the blades are rotationally asymmetric around the axis of rotation 103. For the purposes of this application, it should be understood that the term rotationally asymmetric is defined to mean that the wheel cannot be rotated around the axis of rotation (by any amount other than an integer multiple of 360 degrees) to a position in which the structure is substantially identical (i.e., identical to within a functionally reasonable measurement tolerance level).
In this particular embodiment, the turbine wheel 111 consists only of the hub 241 and the plurality of blades 231, and the hub is rotationally symmetric around the rotor group axis of rotation. It should be understood that the blades include a fillet that distributes blade root stresses to the hub.
With reference to
The calculation of the set of spacing angles 301 that avoids rotational symmetry of the wheel 111 (and more particularly of the blades 231), and yet that has the CM on the rotor group axis of rotation 103, is a complex mathematical problem. The problem can be substantially simplified by allowing for the spacing of the blades to have a plane of symmetry. More particularly, the turbine wheel (and more particularly the plurality of turbine blades) is characterized by a second line 303 that is normal to and intersecting with the line defining the axis of rotor rotation 103. The axis of rotation and the second line define a plane of symmetry by extending along and being contained within the plane, and the spacing angles of the plurality of blades are symmetric across the plane of symmetry (i.e., they are mirrored, as indicated in
As was previously noted, a prior art solution to this problem was to increase the number of blades to a point at which the hum frequency is out of the human range of hearing (e.g., greater than 20,000 Hz). One of the downsides of this solution is that the blade crowding limited the size of the fillets, and therefore limited the spreading of blade root stresses. Therefore, the blade spacing angles 301 Sn are preferably limited to at least the minimum size of the blade spacing between evenly spaced blades for the fewest number of blades necessary to take the hum out of the range of human hearing (e.g., 13), and possibly larger number (e.g., 18) as long as the blade root stresses are within acceptable level. As was hinted at above, the problem of finding good series of blade spacing angles 301 is a difficult optimization problem. This problem may be solved by using an iterative computerized software system. The system will be programmed to implement a method of designing and creating turbine wheel tooling for creating a turbine wheel having n asymmetrically spaced blades and an axis of rotation.
With reference to
Next, an iterative optimization computer program is run 403 on a computer. The program is configured to solve a constrained optimization problem using the steps of (1) calculating 405 a CM 501 of either the complete set of blades 231 or of the entire wheel 111 (i.e., a CM indicative of the CM of the blades with respect to the axis of rotor rotation); (2) iteratively adjusting 407 the spacing angles such that the distance between the calculated center of mass and the wheel axis of rotation is decreased and the spacing angles vary according to a set of one or more constraints and an objective variable in order to limit the acoustic energy generated at any one frequency audible to humans; and (3) continuing the iterations 409 until the calculated CM is effectively on the axis of rotation and the variation of consecutive spacing angles is optimized to establish a set of final spacing angles SF in consecutive order. Greater detail of the optimization computer program is not necessary, as the field of programming computers to iteratively optimize variables is known.
The distance between the calculated center of mass and the wheel axis of rotation is a relatively straight forward calculation. Nevertheless, a variety of different constraints and/or objective variables might be used to limit the acoustic energy generated at any one frequency. Each set of one or more constraints and an objective variable will have strengths and weaknesses, such as required computation time and/or accuracy in representing an optimal acoustic solution. Such constraints and objective variables might include comparisons of consecutive blade angles, and comparisons of all blade angles to one another, among other options.
As an example of the first type of constraint and objective variable described above, an objective variable that might be used is to maximize the variation of each consecutive blade angle, while the blade angles are constrained to be within a minimum and a maximum angle. As an example of the second type of constraint and objective variable described above, the standard deviation of the set of all blade angles could be maximized, while the blade angles are constrained between a minimum and a maximum angle.
For the purposes of this application, the variation of consecutive spacing angles is considered to be optimized when the optimization computer program iteratively reaches an optimum level on the objective variable (e.g., the variation of each consecutive pair of blade angles is maximized). It should be noted that optimized spacing angles may be different when different constraints and/or objective angles are used. Other objective variables that might be used include: target standard deviation level (rather than maximum), target angle variation (rather than maximum), angle variations within a certain range, and the like.
The step of iteratively adjusting 407 the spacing angles is preferably done by increasing the variation of consecutive spacing angles. It should be noted that a variety of techniques may be used to establish a level of the variation of consecutive spacing angles. For example, the sum of the absolute value of the difference between each consecutive pair of spacing angles may be calculated. The larger this number is, the greater variation there is considered to be between all such consecutive spacing angles.
It should be noted that during the iterations of the solution, the CM will not be restricted to the plane of symmetry unless the spacing angle is considered to be the spacing between the CM of each blade.
Once the optimization program has established a set of final spacing angles SF in consecutive order, tooling is formed 411. The tooling is configured to create a void usable for creating turbine wheels characterized by having the set of final spacing angles SF angles in consecutive order.
As was discussed above, the optimization problem is simplified when the blade spacing angles are symmetric across a plane of symmetry. To implement that, in the step of establishing 401 initial spacing angles, the initial spacing angles SIN are selected to be symmetric 421 across a plane of symmetry that contains and is defined in part the line defining the axis of rotation. Additionally, in the step of running 403 an iterative optimization computer program, the iterative adjustment of the spacing angles maintains 423 the symmetry of the spacing angles across the plane of symmetry. Advantageously, this reduces the number of variables.
As was previously discussed, it is preferable to set a minimum spacing angle that allows for good mechanical and aerodynamic characteristics. Thus, in the step of iteratively adjusting the spacing angles, each spacing angle is constrained to be greater than a minimum spacing angle SMIN, such as 20.0 or 27.7 degrees (corresponding to the spacing of 18 or 13 blade evenly spaced blades).
With reference to
It is to be understood that the invention comprises apparatus and methods for designing and for producing a turbine blade, as well as the apparatus of the turbine blade itself. Alternate variations of these embodiments could comprise other types of blade configurations. Moreover, while this invention is described for a turbine wheel, compressor wheels may also be within the scope of the invention, although there might be greater risk of flow instability issues. In short, the above disclosed features can be combined in a wide variety of configurations within the anticipated scope of the invention.
While particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Thus, although the invention has been described in detail with reference only to the preferred embodiments, those having ordinary skill in the art will appreciate that various modifications can be made without departing from the scope of the invention. Accordingly, the invention is not intended to be limited by the above discussion, and is defined with reference to the following claims.
