Turbine Nozzle Ring with Thermal Management Slots
This application claims the benefit of US Provisional Patent Application No. 61/847,105, filed July 17, 2013.
Field of the Invention The invention is directed to nozzle rings for variable geometry turbochargers used with internal combustion engines.
Background and Summary
Turbochargers are used to supply air under pressure to the intake of an internal combustion engine. A turbocharger typically includes a turbine rotor and a compressor rotor mounted on a common rotatable shaft. Engine exhaust gas is directed to the turbine rotor through an inlet passageway in a turbine housing to drive the turbine rotor. The turning turbine rotor imparts rotary motion by way of the shaft to the compressor, which draws atmospheric air into a compressor housing, compresses it, and delivers compressed air to the engine intake.
Variable geometry turbines are a form of turbine that allows the size of the inlet passageway to be varied to optimize gas flow velocities over a range of mass flow rates. Setting the size of the inlet passageway allows the power output of the turbine to be varied to suit varying engine demands. For example, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the annular inlet passageway. Turbochargers provided with a variable geometry turbine are referred to as variable geometry turbochargers.
In one type of variable geometry turbine, an axially moveable wall member, generally referred to as a "nozzle ring", defines one wall of the inlet passageway. The position of the nozzle ring relative to a facing wall of the inlet passageway is adjustable to control the axial width of the inlet passageway.
Thus, for example, as gas flow through the turbine decreases, the inlet passageway width may be decreased to maintain gas velocity and optimize turbine output.
The nozzle ring may be provided with vanes which extend into the inlet to guide the gas flow. A shroud covers a recess in the opposing wall of the inlet passageway and includes slots to accept the vanes to accommodate movement of the nozzle ring. Alternatively, vanes may extend from the fixed facing wall and through slots provided in the nozzle ring.
Typically the nozzle ring may comprise an annular disk defining a radially extending wall (which forms one wall of the inlet passageway) and radially inner and outer axially extending walls. The radially inner and outer walls or flanges extend into an annular cavity formed in the turbine housing behind the radial face of the nozzle ring. Radial and annular are used to indicate position and directions relative to the axis of rotation of the turbine shaft. The cavity is formed in a part of the turbocharger housing (usually either the turbine housing or the turbocharger bearing housing) and accommodates axial movement of the nozzle ring. The flanges may be sealed with respect to the cavity walls to reduce or prevent leakage flow of exhaust gas around the back of the nozzle ring. In one common arrangement the nozzle ring is supported on rods extending parallel to the axis of rotation of the turbine wheel and is moved by an actuator which axially displaces the rods.
A variable geometry turbocharger can be operated in a so-called "heat mode" in which the inlet passageway is closed to a minimum width less than the smallest width that would be appropriate under normal engine operating conditions. In heat mode, the amount of airflow through the engine is reduced for a given fuel supply level (while maintaining sufficient airflow for combustion) to increase the exhaust gas temperature. This is useful for engine apparatuses in which a catalytic exhaust after-treatment system is present and regeneration of the catalyst is periodically performed by operating in heat mode.
One problem with operating a turbine in heat mode is that closing the nozzle to a small width or gap increases boost pressure to the engine, which can increase the air flow. The cooling effect of the increased airflow counteracts the heating effect.
US Patent No. 6,931,849 to Parker and US Patent No. 7,810,327 to Parker disclose a bypass gas path around the nozzle ring arranged to open at inlet passageway widths smaller than those appropriate for normal fired mode operation conditions but which are appropriate to operation in an exhaust gas heating mode. The bypass path is formed by slots in the inner and outer nozzle ring flanges that open when aligned with recesses in the turbine housing. The bypass gas flow reduces turbine efficiency thus avoiding high boost pressures which might otherwise counter the heating effect. In addition to the bypass gas path, the '327 patent and '849 patent show pressure balancing holes provided on the radially-extending nozzle ring plate to aid control of the nozzle ring position in an exhaust gas heating mode. The pressure balancing holes are shown in combination with the bypass slots on the inner and outer flanges. The '327 patent shows in Figure 13b a nozzle ring having pressure balancing holes on the radial plate in combination with two bypass slots on the inner flange of the nozzle ring.
A problem with the solution shown in the '327 and '849 patents is the control of the nozzle ring position is not reliable. Control of the nozzle ring position at small inlet gaps is difficult because there can be a rapid increase in the load on the nozzle ring as it approaches the closed position. The nozzle ring cannot be reliably positioned at a small gap to produce the heat mode. As a result the system fails to increase exhaust temperature sufficient to perform regeneration of the exhaust gas filter.
Control of the nozzle ring position at a small inlet gap is also a problem when the engine is operating at Low NOx idle. Low NOx idle is a regulated engine operating condition in which the engine NOx emissions are limited to not more than 30 grams/hour.
The invention solves the problems in the art by providing a nozzle ring having a radially-extending plate, an outer axial flange and an inner axial flange with four equally circumferentially distributed bypass slots formed on the inner axial flange.
According to a preferred embodiment, the bypass slots are formed in an edge of the inner axial flange and are each about 8 mm deep and 8 mm wide.
According to another aspect of the invention, the radial plate includes a plurality of balance holes.
The invention will be better understood by reference to the following detailed description read in conjunction with the attached drawings.
Brief Description of the Drawings Figure 1 is a perspective view of a nozzle ring according to an embodiment of the invention;
Figure 2 is a schematic section view of a turbine showing a nozzle ring of the invention positioned for normal engine operation; and,
Figure 3 is a schematic section view of a turbine showing a nozzle ring of the invention positioned at a narrow gap for heat mode operation. Detailed Disclosure
Figure 1 shows in perspective view a preferred embodiment of a nozzle ring according to the invention.
The nozzle ring includes a ring shaped plate or disk 20 having a radially inner edge 22 defining a hole 24 and a radially outer edge 26. An inner flange 30 extends axially from the inner edge 22. An outer flange 32 extends axially from the outer edge 22. The flanges 30, 32 are formed as cylindrical sections.
The nozzle ring as shown also includes a plurality of nozzle vanes 40 mounted on the disk 20 on a side opposite to the flanges 30, 32. The disk 20 has formed in it a plurality of balance holes 42.
According to the invention, the inner flange 30 includes four slots 34 cut into the inner flange.
The slots 34 extend axially from a free edge of the inner flange 30 and are preferably 8 mm deep (in the axial direction) and 8 mm wide (in the circumferential direction). The depth relates to the position of the nozzle ring in the turbine housing when the margin of the slot passes the sealing arrangement and the bypass path opens as will be described below in connection with Figure 3.
According to one aspect of the invention, the slots are equally spaced about the circumference of the inner flange 30, that is, at 90° intervals. Figure 2 shows schematically a section of a turbine having a nozzle ring according to the invention. The turbine includes a turbine inlet chamber 50. An inlet passage 52 directs exhaust gas from the inlet chamber 50 to a rotor blade 54 of a rotor wheel. The nozzle ring 10 forms one wall of the inlet passage 52. A shroud 56 forms the opposite wall of the inlet passage. The shroud 56 includes slots through which the nozzle vanes 40 extend. A cavity 60 is formed in the turbine housing to receive the nozzle vanes 40.
The nozzle ring 10 is movable in an axial direction (relative to the turbine shaft, which is right to left in the figure) to adjust the opening width or gap of the inlet passage 52. The flanges 30, 32 extend into a nozzle cavity 70 formed in the turbine housing and an actuator mechanism (not shown, but examples are known in the art) is connected to move the nozzle ring to a desired position. Seals 72, 74 mounted in the housing contact the outer flange 32 and inner flange 30, respectively, to restrict the flow of exhaust gas under normal operating conditions.
Figure 3 shows the same view as Figure 2, but with the nozzle ring 10 in a position forming a narrow inlet passage 52 gap. In this position, an exhaust gas bypass is formed. The inner flange 30 has
moved to where the slots 34 pass the seals 74, which allows exhaust gas to flow through the balance holes 42 into the nozzle ring cavity 70 and out through the slots 34.
Not intending to be bound by theory, the inventors believe that the total flow area of the slots is important to the reliability of the bypass for inducing heat mode. Alternative arrangements under this theory would include other numbers of slots presenting the same or equivalent flow area.
Another factor considered by theory to be important is the spacing of multiple slots about the circumference. It is believed that a single slot or two slots do not provide the same reliable effect as the embodiment of four slots.
Low NOx Idle mode of the engine is improved by the invention as well. In an older design of the nozzle having no slots on the flanges, there were "pads" that were 1 mm tall disposed on the vane- carrying face of the nozzle ring. The pads allowed the ring to slam against the housing to a closed position with a 1 mm gap (known as "zero gap" operation) but still allowed enough exhaust gas to pass through to not drive engine back pressures too high. There were no flange slots in this design. A later design, having one slot or two slots did not include the pads (or had pads of lower height) and with this later design, "zero gap" is closer to an actual "zero gap"
position. Unfortunately, positioning of the nozzle ring as was done with the older design including 1 mm pads (i.e., slamming the ring against the housing), could not be done with a ring having lower- height or no pads because a true "zero gap" did not allow enough gas flow and resulted in excessive engine back pressures. For Low NOx idle operating mode with the nozzle ring having a single slot in the inner flange, another, less stable operating point for the nozzle ring is required.
The four slot nozzle according to the invention allows use of "zero gap" Low NOx Idle mode. It relieves the excessive pressures that resulted from the reduced pad heights (or absent pads) and the single slot. Emissions targets for Low NOx idle mode can be met without exceeding pressure, temperature and engine loads requirements.
A nozzle ring according to the invention may include pads 36 on the disk projecting 0.3 mm in height on the vane mounting side. Note that the drawings are not to scale.
The inventors realized that bypass arrangement in the art was not allowing sufficient flow past the nozzle ring. They realized the slot arrangement could be modeled as a sharp edge orifice. Using this as a starting point, a flow coefficient "C" was calculated for this theoretical "Orifice" for Low NOx Idle and Parked Regeneration for 3 conditions:
Condition 1: current design (not zero gap) - nozzle ring with one slot 5mm x 8mm, pad height = 0.3 mm
Condition 2: Old Zero Gap design - nozzle ring with no slots, pad height = 0.6 mm - 1.0 mm Condition 3: Zero Gap design - nozzle ring with four slots according to the invention, pad height
= 0.3 mm
C was calculated using the following equation:
Where, Q is the volumetric flow rate (at a cross-section) in m3
rh is the mass flow rate (at any cross-section) in m3/s,
C is the orifice flow coefficient,
A2 is the cross-sectional area of the orifice hole in m2,
Pi is the fluid pressure upstream of the orifice, in kg/ (m*s2),
P2 is the fluid pressure downstream of the orifice hole, in kg/(m*s2), and
p is the fluid density.
The data for Q, m, Pi, P2, and p were derived from measurements taken during stable operation of a turbine at the three conditions.
Calculations for C under Condition 1: current design (not zero gap) - nozzle ring with one slot 5mm x 8mm, pad height = 0.3 mm were,
For Parked Regeneration, "C" = 4.43
For Low NOx Idle, "C" = 6.62 Calculations for C under Condition 2: Old Zero Gap design (US2007) - no slots, pad height = 0.6 mm - 1.0 mm were,
For Parked Regeneration, "C" = 6.20
For Low NOx Idle, "C" = 9.17
Calculations for C under Condition 3: Zero Gap design - Optimized slots, pad height = 0.3 mm, with x4 slots at 8mm x 8mm each, were,
For Parked Regeneration, "C" = 6.34
For Low NOx Idle, "C" = 9.37
From these calculated values for C, the inventors returned to the orifice equation to calculate values for the "orifice" flow area. In testing the invention, a turbocharger having a prior art, single slot nozzle ring, was compared to the same turbocharger with a nozzle ring according to the invention substituted for the single slot nozzle ring for a parked vehicle regeneration cycle.
In a first trial, the prior art turbocharger failed to maintain exhaust gas temperature sufficient for regeneration of a diesel particulate filter, and further, the engine ECU was unable to properly set the nozzle gap to and maintain a position which allows an acceptable exhaust flow while reaching the target exhaust gas temperature. In addition, indicated torque exceeded the threshold of 700 NM, which is set as a limit to avoid excessive vibration.
By contrast, when the same turbocharger was tested with a nozzle ring according to the invention installed, the problems of exhaust gas temperature and nozzle ring position control were solved. Exhaust temperature reached and maintained a target temp of 320° C, and regeneration was completed. The engine control unit (ECU) was able to set the nozzle ring at the optimal position on its own at 6% VGT position. Further, torque stayed below 500 N through the regeneration cycle, well below the 700 NM limit.
The same turbocharger with the nozzle ring according to the invention was tested for a Zero Gap regeneration, with the result that exhaust temperature reached its target temperature of 320° C, and the nozzle ring was set and maintained at a gap of 2.1%, which is 0.08 mm from an actual zero gap. Engine torque stayed below 500 Nm, well below the 700 Nm limit.
In the present application, the use of terms such as "including" is open-ended and is intended to have the same meaning as terms such as "comprising" and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as "can" or "may" is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.
While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.