Motor-assisted variable geometry turbocharging system

The motor-assisted variable geometry turbocharging system has a motor to add power to the turbocharging shaft, especially at low exhaust gas volume. Additionally, the turbocharger has control over compressor air inlet direction and/or control of exhaust gas to a two-volute expander. These are individually controlled directly or indirectly from an engine controller to enhance turbocharger performance. In a preferred embodiment, the motor is an electric motor, mounted directly on the turbocharger shaft intermediate the turbo expander and turbo compressor and within the main housing.

FIELD OF THE INVENTION 
The present invention relates generally to variable geometry components 
used in turbochargers applied to internal combustion engines that operate 
over a broad range of speed and load. 
BACKGROUND OF THE INVENTION 
Fixed geometry turbochargers can be designed to operate efficiently at a 
particular engine load and speed. However, when operated over a broad 
range of engine speed and load, the compressor and turbine components are 
forced to function off their design points and consequently suffer losses 
in efficiency that affects engine performance adversely. If the 
turbocharger is matched to an engine at the engine's rated speed, it will 
run considerably off its maximum efficiency where the engine is "torqued 
down" to low engine operating speeds. Conversely, if the turbocharger is 
matched to an engine's low speed range, the turbocharger will have a 
tendency to "overspeed" when the engine is operated at maximum speed and 
load. 
To prevent overspeeding in turbochargers that have been matched to the low 
engine speed range, a waste gate is frequently used to bypass exhaust gas 
around the turbine to limit turbine speed over the high engine speed 
range. The waste gate, however, allows the escape of exhaust gas energy, 
which could be better utilized by the turbocharger turbine and results in 
a substantial loss in system efficiency. 
A more efficient system generally known in the trade is one comprising 
variable geometry components in the turbocharger compressor, the 
turbocharger turbine, or both. The most common types are variable nozzle 
vanes ahead of the turbine wheel and/or variable diffuser vanes in the 
compressor component. 
Variable nozzle vanes ahead of the turbine wheel are connected together so 
that the throat area of each nozzle passage can be reduced over the low 
engine speed range and increased as the engine speed approaches its 
maximum, so that the turbocharger speed is kept within a safe operating 
range. The positioning of the vanes must be precisely controlled by engine 
speed and load, and they must be freely movable in the hot exhaust gas 
environment with minimal leakage through clearance spaces. 
The various movable devices that have been employed in the turbocharger 
turbine have been complicated, expensive, and subject to questionable 
durability. Consequently, they have met with limited commercial success. 
A more practical approach to a variable device in the engine exhaust system 
was disclosed in U.S. Pat. No. 3,557,549 to Webster, assigned to 
Caterpillar Tractor Co., 1971. This system employs a flapper valve so 
positioned in a divided manifold system that it resides in a neutral 
position at high engine speed and load, but can be moved to a second 
position where it diverts all engine exhaust gas flow into one passage of 
a divided turbine casing at low engine speeds. This essentially doubles 
the flow of exhaust gas through the single turbine casing passage and 
maintains the turbocharger speed at higher levels than otherwise could be 
reached at low engine speeds. This device is much simpler than the 
complicated variable nozzle vane systems and does not require a precise 
control system for positioning. 
The use of the flapper valve to divert exhaust gas allows the turbocharger 
to be matched efficiently to the higher engine speeds where the flapper is 
in a neutral position. When the engine is operated at low engine speeds, 
the diversion of full exhaust flow to the single turbine casing passage 
ahead of the turbine increases the turbocharger rotor speed to provide 
higher boost pressure to the engine cylinders, allowing the engine to 
produce more power and torque than otherwise could be obtained. 
The increase in boost at low engine speeds produced by the diverted flapper 
valve might be great enough to cause the turbocharger compressor to 
operate in its surge or unstable area. In this case, the compressor must 
be rematched to move its surge line to lower air flow so that the engine 
operating points fall within its stable operating regime. However, this 
causes a movement of the compressor efficiency islands and choke area to 
lower flow and can result in lowering the compressor efficiency when the 
engine is operating at high speed and load. 
A variable geometry compressor that can shift the performance map of the 
compressor to a lower or higher flow range is one solution to the problem 
of keeping the compressor out of surge at low engine speeds and still 
maintain high efficiency at high engine speeds. Variable diffuser vanes is 
one type of variable geometry compressor that could be employed, but the 
movable vanes cause significant mechanical complication internally in the 
construction of the turbocharger and must be precisely positioned by a 
rather elaborate control system. 
A more practical type of variable geometry device is to employ movable 
pre-whirl vanes upstream of the compressor wheel to provide positive and 
negative pre-whirl to the air entering the inducer of the compressor 
wheel. Negative pre-whirl moves the compressor operating range to higher 
flow and usually improves compressor efficiency. Positive pre-whirl moves 
the compressor operating vane to lower flow and usually lowers compressor 
efficiency somewhat. However, since the maximum island of compressor 
efficiency is also moved to lower flow, the net effect of positive 
pre-whirl is to raise the level of efficiency available to the operating 
area of the engine. 
It is thus advantageous to connect the movable flapper valve in the exhaust 
stream to the movable prewhirl vanes in the air stream by a mechanical 
linkage causing them to move in synchronization. With the flapper in 
neutral, the pre-whirl vanes are positioned to provide negative pre-whirl 
to the compressor, moving its flow range so that maximum efficiency is 
available in the high engine speed range. When the flapper is in the 
diverted position, the pre-whirl vanes are moved to the positive pre-whirl 
position, thereby moving the maximum compressor efficiency to the low 
engine speed range. A simple, hydraulic cylinder can be employed as a 
control means to move the mechanical linkage to either the high flow or 
low flow position by sensing the engine speed at which the transition is 
required to be made. 
Both the flapper valve and the pre-whirl vanes are external from the 
turbocharger construction, resulting in much lower overall cost than other 
devices that must be built into the internal construction of the 
turbocharger. 
The movement of the compressor flow range by utilizing positive and 
negative pre-whirl is more fully described in a paper published in the 
Proceedings of the Institute of Mechanical Engineers, Vol. 18943/75, 
titled "Experimental and Theoretical Performance of a Radial Flow 
Turbocharger Compressor with Inlet Pre-whirl," by Wallace, Whitfield and 
Atkey. It is also described in U.S. Pat. No. 5,025,629 to Woollenweber, 
June 1991. 
At very low engine speed, for example, at low idle, there is insufficient 
exhaust gas energy to drive the turbocharger fast enough to produce 
significant levels of boost. Consequently, there is an appreciable lag 
time between opening of the engine throttle and when the turbocharger is 
running fast enough to produce enough boost pressure to eliminate smoke on 
acceleration, for example. Fuel control devices, such as rack limiters or 
aneroid controls, are employed to limit the amount of fuel delivered to 
the engine cylinders until the turbocharger is capable of delivering 
sufficient air to produce smoke-free combustion. These fuel limiting 
devices cause slower response to throttle opening and a sluggishness in 
engine and vehicle response. 
SUMMARY OF THE INVENTION 
In order to aid in the understanding of this invention, it can be stated in 
essentially summary form that it is directed to a motor-assisted variable 
geometry turbocharging system. The variable geometry is provided by the 
exhaust gas flow configuration into the exhaust gas turbine and/or the air 
inlet flow into the air compressor, together with a motor drive for both 
the turbine and compressor to enhance performance of a variable geometry 
turbocharging system. 
It is thus a purpose and advantage of this invention to provide a motor 
drive for the turbo expander shaft to supply power into the turbocharger 
system in addition to that which can be achieved by extraction from the 
exhaust gas, even with a two-volute turbo expander to enhance performance, 
especially at low exhaust gas flow rates. 
It is a further purpose and advantage of this invention to provide a motor 
for adding power to a turbocharger which also includes control of the air 
inlet to the turbo compressor, to enhance performance of the turbocharger 
even when it is equipped with pre-whirl vanes upstream of the compressor 
wheel which controls the rotation of the air as it enters the inducer of 
the compressor wheel, to enhance performance of such systems by providing 
the power necessary to provide adequate pre-whirl even at low exhaust gas 
flow rates. 
It is a further purpose and advantage of this invention to supply power to 
a turbocharger which is driven by exhaust gas expansion by including a 
motor to supply torque to aid in rotating the shaft in the same direction 
as exhaust gas expansion, and to include such a turbocharging motor 
together with control of air flow into the turbo compressor to enhance 
vehicle performance. 
It is a further purpose and advantage of this invention to provide a motor 
connected to a turbo compressor shaft and control the motor in addition to 
controlling exhaust gas flow to the turbine and/or air flow into the turbo 
compressor to enhance engine performance. 
It is a further purpose and advantage of this invention to provide an 
electric motor, mounted directly on the turbocharger shaft intermediate 
the turbo expander and turbo compressor and within the main housing, so 
that the above-described purposes and advantages can be attained with 
minimum space utilization and as an item of original equipment for the 
vehicle manufacturer. 
The features of the present invention which are believed to be novel are 
set forth with particularity in the appended claims. The present 
invention, both as to its organization and manner of operation, together 
with further objects and advantages thereof, may be best understood by 
reference to the following description, taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
To improve engine and vehicle response to opening of the throttle, an 
external power source is needed to operate the turbocharger at higher 
speed at engine idle in order to provide increased boost levels in the 
engine intake system in preparation for quick acceleration. This external 
power source can be any convenient rotating power source, such as an 
electric motor, a hydraulic motor, a pneumatic motor, or the like, and 
particularly a motor which can have its power output controlled. A 
preferred example and the example given below of an external power source 
is an electric motor that engages the turbocharger rotor at engine idle 
and increases the idle speed of rotation of the rotating assembly. 
Having higher boost pressure available at engine idle speed than the boost 
pressure the turbocharger can provide from exhaust gas energy alone, 
allows fuel to be injected into the engine cylinders sooner during 
acceleration and reduces smoke and emissions during the transient period. 
The engine is able to produce more output torque during transients, and 
the higher boost pressure during acceleration should eliminate the need 
for fuel limiting devices, such as the aneroid control referred to 
previously. 
The electric motor, coupled to the turbocharger rotor, can be energized 
before the engine is started. Then, during cranking of the engine, a 
positive differential pressure will exist across the engine from intake 
manifold to exhaust manifold. In the case of a two-cycle engine, a 
positive differential is necessary for scavenging the cylinder during 
cranking. Therefore, if a two-cycle engine is turbocharged with an 
electric motor assist, the need for a gear-driven blower to provide the 
scavenge differential pressure needed for starting is eliminated. 
The motor-assisted variable geometry turbocharging system of this invention 
is generally indicated at 10 in FIG. 1. Diesel engine 12 has two exhaust 
manifolds 14 and 16 which are separately ducted to the two volutes 18 and 
20 of exhaust gas turbine 22. Valve 24 controls whether or not exhaust gas 
is delivered to one or both volutes. When exhaust gas volume is low, 
delivery to one volute provides a higher exhaust gas pressure, which 
delivers more power to the exhaust gas turbine rotor 26. Valve 24 is 
controlled by valve controller 28, which responds to signals from the 
engine controller 30. Various signals are fed into the engine controller, 
such as engine demand and current engine operating conditions, so that the 
valve 24 can be appropriately set. The output of the engine controlled 
includes fuel inlet control in addition to the air inlet control in 
accordance with this invention. 
The exhaust gas turbine rotor 26 is mounted on turbocharger shaft 32 which, 
in turn, drives turbo compressor 34. The turbo compressor has a compressor 
rotor 36 therein so that, when rotated, air is drawn into inlet 38 and is 
delivered to outlet 40 to the engine intake system. 
This structure is generally seen in Woollenweber U.S. Pat. No. 5,025,629, 
the entire disclosure of which is incorporated herein by this reference, 
see FIG. 9 thereof. For the reasons discussed above and in addition to the 
variable geometry discussed in that patent, there are problems in 
delivering enough combustion air to the engine 12, particularly at low 
exhaust gas rates. For this reason, motor 42 is attached to rotate 
turbocharger shaft 32 in the turbocharging direction. The motor 42 may be 
an electric motor, a pneumatic motor, a hydraulic motor or other type of 
motor, providing it can be controlled. Preferably, however, motor 42 is an 
electric motor, with its rotor mounted on shaft 32 and its stator mounted 
on the interior of the turbocharger housing, with electric control line 45 
supplying the appropriate motor control signals. Motor controller 44 is 
connected to be managed by engine controller 30. The engine controller 30 
preferably is part of the vehicle engine management system and manages the 
valve control and motor control for optimum operation of the system to 
deliver the optimum amount of combustion air to the engine in accordance 
with engine demand and current engine operating conditions. When the 
engine is operating at low speed and there is an engine demand for more 
power and more speed, the valve 24 is in the single-volute position and 
the motor 42 is energized to add power to the turbocharger. As the exhaust 
gas volume goes up, the valve can be switched to the double-volute 
position and, when exhaust gas is fully adequate to supply the entire 
power demand of the turbo compressor, no power need be supplied to the 
motor 42. If the motor 42 is configured so that it cannot be rotated as 
fast as the top speeds of the shaft 42, the motor 42 can be disconnected 
via control line 45. Thus, power is supplied to the motor 42 and the valve 
24 is appropriately controlled for optimum turbocharger operating 
conditions under the engine speed and demand requirements. 
FIG. 2 illustrates a similar turbocharging system 46 for a diesel engine. 
Turbocharging system 48 has an exhaust gas turbo expander rotor 50 mounted 
on turbocharger shaft 52. Compressor rotor 54 is driven by the shaft 52 
and is mounted in compressor housing 56. Air is delivered from outlet 58 
to the air inlet of the engine. Electric motor 60, as described with 
respect to motor 42, is controlled by a motor controller 62 via line 63 
which, in turn, is managed by engine controller 64. The engine controller 
receives engine demand signals as well as current engine operating 
condition signals. From those signals, motor control 62 receives 
appropriate signals to supply power to motor 60 to drive the shaft 52 in 
the compressor rotation direction. Additionally, the inlet 66 of the 
turbocharger has adjustable vanes such as at 67 therein which provide 
pre-whirl to the inlet stream. As discussed in the references above, this 
pre-whirl enhances the compressor performance. The pre-whirl can be 
adjusted by appropriate adjustment of the vanes which cause the pre-whirl 
to adjust compressor performance. The vane control 68 thus provides 
variable geometry in the turbo compressor. Both the vane control 68 and 
the motor control 62 are managed from the engine controller 64. Each is 
individually adjusted to provide optimum turbocharging performance under 
the particular engine operating parameters and performance demands. The 
adjustment of turbo compressor conditions by control of input pre-whirl is 
discussed in the above-referenced publication. 
FIG. 3 shows a turbocharging system 70 similar to the system shown in FIGS. 
1 and 2. The turbocharging system 70 has a dual volute exhaust gas 
expander with the diverter valve 71, which diverts all exhaust gas flow 
from the split manifold of the engine to one volute for higher performance 
at low exhaust gas flow rates, as previously described. Furthermore, the 
compressor 72 has a pre-whirl control 74 at the air inlet to the 
compressor 72. Additionally, motor 76 is directly connected to the 
turbocharging system main shaft 77 to drive it in the compressor 
direction. The pre-whirl vane control 78 and the motor control 80 
respectively control the pre-whirl vanes and the motor 76 but, as FIG. 3 
illustrates, they are coordinated with each other to optimize cooperative 
turbocharger air outlet under the existing conditions. This coordination 
is also present in the valve control 28 with respect to motor control 44 
in FIG. 1 and is also present with respect to the vane control 68 and 
motor control 62 in FIG. 2. The vane control 78 and motor control 80 of 
FIG. 3 are both energized by signals from the engine controller 82, which 
includes demand as well as operating parameters. Contrasted to this, the 
valve control 83 is operated directly from the signals available in the 
engine controller 82. Thus, the motor and the pre-whirl control are 
synchronized and coordinated, while the diverter valve 71 is independently 
controlled from the valve controller 83. 
FIG. 4 shows a system 84 which is structurally much like the system of FIG. 
3. In the controlling of the turbocharging system 84, the engine 
controller 86 provides signals to the motor control 88 which controls 
motor 90 via line 89. Coordinated therewith and cooperating therewith, 
controller 92 controls through line 93 both the vanes 94 which control the 
pre-whirl and, through line 96, controls diverter valve 97. Since the 
pre-whirl control also controls the diverter valve, the two functions are 
coordinated. Since the motor control is related to the valve control 92, 
all of the functions are coordinated and are adjusted in accordance with 
signals received from the engine controller 86. 
FIG. 5 shows a system 98 which is similar to the system 84 of FIG. 4 
because it has all three of the turbocharging system variables. The 
pre-whirl vanes 100 and the diverter valve 102 are both controlled by 
controller 104, which receives its signals from the engine controller 106. 
It is seen that these two variables are cooperative and coordinated 
because their signal comes from the same controller 104. In this case, 
however, motor 108 is controlled by motor controller 110, which receives 
its signal directly from the engine controller 106. Thus, the pre-whirl 
vanes and exhaust diverter valve are coordinated and are cooperatively 
adjusted. The motor 108 is controlled separately from engine control 
signals. 
The motor is sized so that it can contribute torque over a broad operating 
range of the turbocharging system. When the engine starts from idle, the 
motor is the first and largest contribution to an increase in turbocharger 
output. The motor remains contributing torque until the exhaust gas, in 
combination with the turbo compressor inlet control, can provide adequate 
air to prevent the engine from running too rich. However, in order to 
prevent too much boost, as the boost pressure goes up, the motor is turned 
off before the compressor inlet is controlled to reduce or limit increase 
in boost. 
This invention has been described in its presently contemplated best modes, 
and it is clear that it is susceptible to numerous modifications, modes 
and embodiments within the ability of those skilled in the art and without 
the exercise of the inventive faculty. Accordingly, the scope of this 
invention is defined by the scope of the following claims.