Charge air systems for four-cycle internal combustion engines

Charge air systems may include a small electric motor-driven compressor for supplying charge air to four-cycle internal combustion engines, including systems with turbocharger charge air compressors in series and parallel connection. The disclosed charge air systems can provide an effective charge air flow path to the internal combustion engine and avoids air flow restrictions at high engine operating speeds.

TECHNICAL FIELD 
This invention is directed to methods and apparatus for delivering charge 
air to a four-cycle internal combustion engine. 
BACKGROUND ART 
The use of turbochargers to increase power output and decrease fuel 
consumption in four-cycle internal combustion engines is common practice 
today. Both spark ignition and diesel engines use turbochargers to 
advantage and, in the case of diesel engines, the power output of an 
engine of a given cylinder displacement can easily be doubled by the 
addition of turbocharging with aftercooling. The turbocharger has gone 
through decades of development, and modern turbochargers used on 
high-speed diesel and gasoline engines are relatively low in cost and high 
in efficiency, and are durable commercial products. 
Although the turbocharger utilizes exhaust gas energy that would otherwise 
be wasted, the imposition of an exhaust gas turbine in the engine exhaust 
system necessitates raising the average back pressure on the engine 
cylinders in order to generate sufficient pressure drop across the turbine 
to generate the power necessary to drive the turbocharger's compressor. 
This back pressure acts against the upstroke of the piston as it forces 
residual products of combustion out of the cylinder through the exhaust 
valves and increases the pumping loss of the engine. The level of back 
pressure caused by high pressure turbocharging of four-cycle engines is 
very high, even with the use of turbochargers that have relatively high 
overall efficiency. Any means that may be employed to lower the back 
pressure caused by the turbocharger turbine can result in significant 
improvement in engine performance. For example, if a diesel engine 
requires a pressure ratio of 2.5 times atmospheric pressure to reach the 
desired rated engine power output, a single turbocharger would impose a 
back pressure in the exhaust system of approximately two times atmospheric 
pressure. 
The use of series turbochargers is common today on engines that are rated 
in high power output. If the two compressors are placed in series 
combination, the pressure ratios of the compressors are multiplied so high 
supercharge pressure can be supplied to the engine beyond that which a 
single turbocharger could produce by itself. If, for instance, a highly 
rated engine requires 4.5 pressure ratio, which is beyond the capability 
of a single commercial turbocharger, series turbochargers can provide a 
low pressure stage of 2.1 pressure ratio and a high pressure stage of 2.15 
pressure ratio, the product of which is 4.51 pressure ratio overall. This, 
however, significantly raises the exhaust gas back pressure. 
DISCLOSURE OF THE INVENTION 
The invention is directed to charge air systems that may include a small 
electric motor-driven compressor for supplying charge air to four-cycle 
internal combustion engines, including systems with turbocharger charge 
air compressors in series and parallel connection. Charge air systems of 
the invention can provide an effective charge air flow path to the 
internal combustion engine that avoids the air flow restriction of a small 
charge air compressor and a need for its continuous operation to avoid the 
restriction effect of a small charge air compressor. 
The invention permits the use of a small motor-driven compressor to provide 
charge air at engine speeds from idle to about 2000 to 2500 rpm without 
restricting charge air flow to the engine at high engine speeds, and 
permits such uses with a small motor-driven compressor in series and in 
parallel with a turbocharger compressor. The small motor-driven 
compressors used in this invention are compressors having an air output 
capacity that is incapable of supplying the charge air requirements of an 
internal combustion engine operating at high engine speeds, for example, 
in excess of about 2500 rpm, and would present an unacceptable restriction 
to charge air flow at such engine speeds in the absence of their 
operation. The invention permits the use of charge air compressors capable 
of supplying only a third, or less, of the charge air requirements of a 
four-cycle internal combustion engine operating at full rated speed. 
A charge air system of the invention includes a small charge air compressor 
having an inlet and an outlet, an electric motor connected to drive the 
charge air compressor, a first charge air conduit connected with the 
outlet of the charge air compressor, a second charge air conduit and 
junction for the first and second charge air conduits, with the junction 
being connected with the intake manifold of a four-cycle internal 
combustion engine, and a charge air check valve located at, or upstream 
of, the junction for one of said first and second charge air conduits. In 
one preferred charge air system of the invention, the inlet of the small 
charge air compressor and the second conduit are connected with ambient 
atmosphere, preferably through an air cleaner, and the charge air check 
valve operates to close the second charge air conduit upon operation of 
the charge air compressor. 
Another such charge air system of the invention provides two-stage 
compression with a turbocharger, having an exhaust gas driven turbine and 
a turbocharger compressor, driven by the exhaust gas driven turbine, with 
its air inlet connected with the junction and its compressed air outlet 
connected with the intake manifold of the internal combustion engine. In 
such preferred two-stage charge air systems, the turbocharger may be 
provided with an electric motor assisting the exhaust driven turbocharger 
turbine in driving the turbocharger compressor. 
Another parallel operating charge air system of the invention includes a 
charge air compressor having an inlet and an outlet, an electric motor 
connected to drive the charge air compressor, a first charge air conduit 
connected with the outlet of the charge air compressor, a turbocharger 
having an exhaust gas driven turbine connected with the exhaust gas from a 
four-cycle engine and a turbocharger compressor having an air inlet and a 
compressed air outlet, a second charge air conduit connected with the 
compressed air outlet of the turbocharger compressor, a junction for said 
first and second charge air conduits, with the junction being connected 
with the air intake manifold of the four-cycle internal combustion engine, 
and a charge air check valve located at, or upstream of, the junction for 
one of said first and second charge air conduits. In preferred embodiments 
of such parallel operating charge air systems, the charge air check valve 
can close the second charge air conduit upon operation of the charge air 
compressor at low internal combustion engine speeds and close the first 
charge air conduit at high internal combustion engine speeds. Further, in 
such preferred charge air systems the turbocharger can include an electric 
motor assisting the exhaust gas driven turbocharger turbine in driving the 
turbocharger compressor. 
Still another charge air system of the invention includes a charge air 
compressor having an inlet and an outlet, an electric motor connected to 
drive the charge air compressor, a turbocharger having an exhaust gas 
driven turbine connected with the exhaust gas from the four-cycle internal 
combustion engine and a turbocharger compressor having an air inlet and a 
compressed charge air outlet, a charge air cooler having its inlet 
connected with the compressed charge air outlet of said turbocharger 
compressor, a first charge air conduit connected with an outlet of the 
charge air cooler, a second charge air conduit connected with ambient 
atmosphere, a junction for the first and second charge air conduits, a 
third charge air conduit connecting the junction of the first and second 
charge air conduits with the air inlet of the charge air compressor, and a 
charge air check valve operable to open said second charge air conduit 
upon operation of said charge air compressor and to close the second 
charge air conduit upon operation of said turbocharger at high engine 
speeds. In such systems, the turbocharger may be provided with an electric 
motor assisting the exhaust gas turbine in driving the turbocharger 
compressor. 
In charge air systems of the invention, an electric control can operate the 
motor driving the small charge air compressor in various modes for an 
improved supply of charge air to the internal combustion engine. The small 
motor-driven compressor may be energized by the control when acceleration 
from low engine speeds is desired and/or may be energized at a 
predetermined minimum speed to provide boost pressure with minimal delay 
at the engine intake manifold, reducing the response time of the internal 
combustion engine and the generation of harmful pollutants. The control 
can also operate any assisting electric motor that may be connected to 
assist the exhaust gas energy in driving a turbocharger compressor, and 
such controls generally energize, and super-energize, the motor assist of 
such turbochargers at low engine speeds. 
The invention also provides a method of improving the performance of 
four-cycle engines by the use of a small motor-driven compressor. By 
utilizing an external power source to drive the small charge air 
compressor, the engine can be supercharged without imposing back pressure 
on the exhaust system as does a turbocharger, and an increase in charge 
air density can be achieved more rapidly, allowing fuel to be burned more 
efficiently, with the desirable result of less harmful pollutants emitted 
into the atmosphere in the engine exhaust. 
The invention also provides a method of improving the performance of a 
turbocharger equipped engines by eliminating the time lag of the 
turbocharger compressor upon sudden throttle opening, by providing a small 
electrically powered charge air compressor which is connected supply 
charge air to the engine intake manifold. 
Further features and advantages of the invention will be apparent from the 
drawings and more detailed description of currently best known modes and 
embodiments of the invention that follow.

BEST MODES FOR CARRYING OUT THE INVENTION 
A conventional internal combustion engine is shown in schematic 
cross-section and is generally indicated at 10 in FIG. 1. The engine 10 
has a cylinder block 12 in which is located cylinder 14. In this case, the 
cylinder has an upright axis. Piston 16 reciprocates up and down within 
the cylinder under control of crank 18. The crank rotates around the 
cranks axis and is connected to the piston by means of connecting rod 20. 
The crankshaft and connecting rod are housed in crankcase 22, which may 
contain oil for lubricating the lower part of the engine. There is usually 
a plurality of cylinders along the crankshaft axis. 
The cylinders in the cylinder block are covered by cylinder head 24. The 
cylinder head has an intake manifold 26 forming a charge air inlet and 
carries intake valve 28, which controls flow of air or air plus fuel mix 
to the cylinder. The cylinder head 24 also has an exhaust gas outlet 30 
for each cylinder. The exhaust gas outlet 30 is controlled by exhaust 
valve 32. The opening and closing of the intake valve and exhaust valve 
for each cylinder is coordinated with the movement of the piston by 
mechanical interconnection of the crankshaft with the cam shafts which 
control the valves. Fuel is introduced into the cylinder at the 
appropriate times through fuel injection nozzle 34. In some cases, the 
fuel may be delivered to the cylinder as a fuel-air mixture through the 
intake valve. By increasing the amount of air delivered to the cylinder 
and by a corresponding increase of fuel, the power output of the engine 10 
can be appreciably increased; in addition, the engine efficiency can be 
increased to yield more work per unit of fuel. 
FIG. 1 illustrates a charging system 40 of the invention for the four-cycle 
internal combustion engine 10. Charge air system 40 includes a small 
charge air compressor 42 having an inlet 43 and an outlet 44. An electric 
motor 45 is connected to drive the charge air compressor 42. A first 
charge air conduit 46 is connected with the outlet 44 of the charge air 
compressor 42. Charge air system 40 also includes a second charge air 
conduit 47 and a junction 48 for the first and second charge air conduits 
46, 47. As shown in FIG. 1, junction 48 is connected with the intake 
manifold 26 of the internal combustion engine 10. The charge air system 
also includes a charge air check valve 50 located at (or possibly upstream 
of) the junction 48. The charge air check valve operates to close one of 
first charge air conduit 46 or second charge air conduit 47. As shown in 
FIG. 1, the charge air check valve 50 is operated by the air pressure 
created by charge air compressor 42 upon its operation to close the second 
charge air conduit 47, preventing back flow of charge air from junction 48 
into air cleaner 52, and at high engine speeds charge air drawn through 
the second charge air conduit 47 by the internal combustion engine 10 
operates the charge air check valve 50 to close the first charge air 
conduit 46, as indicated by the dashed lines of FIG. 1. Preferably, as 
shown in FIG. 1, the inlet 43 of the charge air compressor and the second 
conduit 47 are connected with an air cleaner 52. 
A control 54 controls the application of electrical energy from an 
electrical power source 55 in response to signals 56 received from an 
engine speed sensor and/or from the internal combustion engine operator's 
acceleration control. In preferred control systems of the invention, the 
small motor-driven compressor 42 is energized by control 54 at engine 
speeds up to about 2000-2500 rpm. In the charge air system 40 of FIG. 1, 
the motor-driven compressor 42 can be maintained by control 54 at a 
predetermined minimum speed to provide boost pressure to the intake 
manifold 26 of the engine 10 in preparation for acceleration so that the 
desirable amount of air can be present in the engine cylinder 14 before 
additional fuel is injected when engine acceleration is called for. In 
addition, the electric motor 45 may be energized or super-energized upon 
receiving a signal from the engine acceleration control so that charge air 
and boost pressure can be rapidly increased when engine acceleration is 
called for. Because system 40 includes a small compressor, its transient 
time to reach high operating speeds and high boost pressures is 
significantly reduced and fuel can be burned more completely and the 
amount of harmful pollutants in the engine exhaust can be substantially 
lessened. 
In the charge air system 40 of FIG. 1, the combination of the first charge 
air conduit 46 with a second charge air conduit 47 leading to ambient 
atmosphere through a check valve 50 avoids the restriction that may be 
otherwise imposed on the flow of charge air to the internal combustion 
engine 10 at high engine speeds, for example, speeds in excess of about 
2000-2500 rpm because of the small size of compressor 42. In the charge 
air system 40, the small compressor 42 can be de-energized and the engine 
can draw its charge air requirements from ambient atmosphere, for example, 
through air cleaner 52, by means of the second conduit 47 and past the 
charge air check valve 50 which will be urged into a position (shown in 
dashed lines) opening the second conduit means 47 by the pressure of the 
charge air generated by the internal combustion engine. 
The charge air system 40 of the invention thus permits an effective flow of 
charge air to the internal combustion engine 10 throughout its entire 
speed range and permits the use of a small motor-driven centrifugal 
compressor 42 that would impose an unacceptable restriction to engine air 
flow at higher internal combustion engine speeds. 
The charge air system 40 allows the charge air compressor 42 to be made 
much smaller in size to match engine charge air requirements at only low 
speeds below about 2000 to 2500 rpm, and charge air systems of the 
invention can be more economical than prior art systems because of the 
smaller size of the centrifugal charge air compressor. 
FIG. 2 illustrates a second preferred embodiment of charge air systems of 
the invention used with a four-cycle internal combustion engine 10. This 
four-cycle internal combustion engine 10 is as illustrated in FIG. 1 and 
described above. The charge air system 60 in FIG. 2 differs from that of 
FIG. 1 primarily by the inclusion of a turbocharger 62, including an 
exhaust gas driven turbine 63 connected with an exhaust outlet 30 of the 
internal combustion engine 10 and a turbocharger compressor 64 having an 
air inlet 65 and a compressed air outlet 66. In the preferred charge air 
system of FIG. 2, the turbocharger 62 also includes an electric motor 67 
for assisting the exhaust gas driven turbine 63 in driving the 
turbocharger compressor 64. The charge air system of FIG. 2 further 
comprises a charge air compressor 42 having an inlet 43 and an outlet 44, 
and an electric motor 45 connected to drive the charge air compressor 42. 
A first charge air conduit 46 is connected with the outlet 44 of the 
charge air compressor 42. A second charge air conduit 47 extends from 
ambient atmosphere to a junction 48 for the first charge air conduit 46 
and second charge air conduit 47. In the system of FIG. 2, the junction 48 
is connected with the air inlet 65 of the turbocharger compressor 64. Like 
the charge air system 40 of FIG. 1, charge air system 60 of FIG. 2 
includes a charge air check valve 50 located at, or located upstream of, 
the junction 48 for closing one of the first and second charge air 
conduits 46, 47. 
The charge air system 60 of FIG. 2 is further provided with an electric 
control 54 which is operated by signals 56 from the internal combustion 
engine, such as from an engine speed sensor and/or the engine operator's 
acceleration control to energize the electric motor 45 and the electric 
motor 67 from the electric power source 55. 
The charge air system of FIG. 2 can provide two-stage compression of the 
charge air for the internal combustion engine 10, particularly at low 
engine speeds when the electric motor 45 for charge air compressor 42 and 
the electric motor 67 of turbocharger 62 are both energized by the control 
54. In such operation, ambient air is drawn to the inlet 43 of the charge 
air compressor 42 compressed by operation of the compressor 42 by the 
electric motor 45 and delivered through the first charge air conduit 46 to 
junction 48 where the pressure of the compressed air closes charge air 
check valve 50 and second charge air passageway 47, as shown in FIG. 2. 
The compressed charge air from charge air compressor 42 is conducted to 
the inlet 65 of the turbocharger compressor 64 where it is further 
compressed and delivered from the turbocharger compressor outlet 66 to the 
air inlet 26 of the internal combustion engine 10. Operation of the 
assisting electric motor 67 of the turbocharger 62 at low engine speeds, 
where the exhaust gas energy of the internal combustion engine is low, and 
the contemporaneous operation of the small charge air compressor 42 
provides two-stage compression of the charge air to the internal 
combustion engine. 
As known in the art, the pressure boost from the two-stage operation of 
charge air system 60 permits a pressure boost which is the product of the 
pressure ratio of charge air compressor 42 and the pressure ratio of 
turbocharger compressor 64. In the charge air system of FIG. 2, 
centrifugal compressor 42 has its compressed air outlet 44 connected with 
the air inlet 65 of the turbocharger compressor 64 to form a series 
connected compression system. The first stage centrifugal compressor 42 
can be driven by the electric motor 45 at low engine speeds in response to 
input signals 56 such as from a boost pressure sensor and/or throttle 
sensor, but since first stage compressor 42 is not driven by an exhaust 
gas turbine, it does not raise the exhaust gas back pressure. In addition, 
first stage compressor 42 is a small compressor which can respond quickly 
in raising the boost pressure in response to signals 56 through the 
operation of electric motor 45. The result is a relatively uncomplicated 
two-stage charge air system providing enhanced boost pressures with 
reduced back pressure on the engine. For example, if a diesel engine 
requires a pressure ratio of 2.5 times atmospheric pressure to reach the 
desired rated engine power output, a single turbocharger would impose some 
back pressure on the exhaust system of approximately 2 times atmospheric 
pressure. However, in a charge air system 60 with the motor-driven 
compressor 42 in series with the turbocharger compressor 64, the required 
pressure ratio of 2.5 can be achieved by producing a 1.3 pressure ratio 
from the motor-driven compressor 42 and a 1.92 pressure ratio from the 
turbocharger compressor 64, and the charging pressure ratio of 
turbocharger compressor 64 can be reduced from 2.5 to 1.92 resulting in a 
reduction of exhaust back pressure to approximately 1.5 times atmospheric 
pressure. This significantly reduces the pumping loss of the internal 
combustion engine 10 resulting in lower fuel consumption, higher power 
output or both, and decreased exhaust gas pollution. 
Furthermore, the operation of the charge air system shown in FIG. 2 can be 
enhanced by the addition and use of an assisting electric motor 67 and a 
turbocharger 62. The assisting electric motor 67 for turbocharger 62 can 
be energized by the control means 54 in response to appropriate input 
signals from the internal combustion engine. For example, a boost pressure 
sensor can be used to send a signal to the electric control 54 when the 
engine is operating at low speed and load; and when the engine is called 
upon to accelerate, the boost pressure sensor, and/or a throttle sensor, 
can generate an input signal 56 to control 54, and the motor 45 for charge 
air compressor 42 and the motor 67 assisting rotation of the turbocharger 
compressor 64 can both be energized to provide increased air supply during 
the acceleration period. When the internal combustion engine 10 provides 
exhaust gas with sufficient energy to operate the turbocharger fast enough 
to provide an adequate charge air supply to the engine, an engine speed 
signal from the internal combustion engine can de-energize both the charge 
air compressor 42 and the assisting electric motor 67 of the turbocharger. 
Alternatively, at high engine speed and load when maximum power output is 
required, the assisting electric motor 67 for turbocharger 62 can be 
energized by control 54 and motor-driven compressor 42 can remain 
energized to provide high boost pressure. 
When control 54 de-energizes both motor 45 for the charge air compressor 42 
and the assisting electric motor 67 of turbocharger 62 in the high speed 
range of the engine (where the exhaust gas energy is sufficient to drive 
the turbocharger compressor to arrive at charge air and boost pressure 
needed by the engine,) the charge air check valve 50 opens conduit 47 by 
the flow of charge air from ambient atmosphere through the second charge 
air conduit 47 to the inlet 65 of the turbocharger compressor 64. As in 
charge air system 40 of FIG. 1, charge air system 60 of FIG. 2 avoids the 
restrictive effect of the small turbocharger compressor 42 by allowing 
ambient air to flow in an unrestricted fashion through check valve 50 to 
the inlet 65 of the turbocharger compressor 64. In addition, as shown in 
the charge air system 40 of FIG. 1, the second charge air conduit and air 
inlet of the charge air compressor 42 preferably obtain their air input 
through a charge air filter 52. 
The assisting electric motor 67 and its connection with the electric 
control 54 are shown in dashed lines in FIG. 2 to indicate that while they 
represent part of a preferred embodiment, they are not necessary to the 
invention of charge air system 60. 
A third preferred embodiment of charge air systems of the invention is 
shown in FIG. 3. The charge air system 70 of FIG. 3 uses a motor-driven 
compressor 42 and turbocharger 62 in a parallel arrangement for charging 
the four-cycle internal combustion engine 10 through a charge air check 
valve 50 connected in swing valve fashion. 
The charge air system 70 of FIG. 3 includes a charge air compressor 42 
having an inlet 43 and an outlet 44, an electric motor 45 connected to 
drive the charge air compressor 42 and a first charge air conduit 46 
connected with the outlet of the charge air outlet 44 of charge air 
compressor 42. The turbocharger 62 includes an exhaust gas driven turbine 
63 connected with the exhaust gas outlet 30 of the internal combustion 
engine 10, and a turbocharger compressor 64 having an air inlet 65 and a 
compressed air outlet 66 connected with the second charge air conduit 68. 
The charge air system 70 further includes a junction 48 connected with the 
first charge air conduit 46 and the second charge air conduit 68. The 
junction 48 is connected with the air inlet 26 of the intake manifold 24 
of the internal combustion engine and a charge air check valve 50 is 
located at the junction for closing one of the first and second charge air 
conduits 46, 68. In operation of the charge air system 70, charge air 
check valve 50 operates as a swing valve and closes the second charge air 
conduit 68 upon operation of the charge air compressor 42 at low engine 
speeds of the four-cycle internal combustion engine (as shown in dashed 
lines) and closes the first charge air conduit 46 upon operation of the 
turbocharger 62 at high engine speeds of the four-cycle internal 
combustion engine. 
In preferred operation of the charge air system 70, at engine idle and 
during acceleration the motor-driven compressor 42 is energized by the 
electric control 54 and electric motor 45, and the compressed charge air 
from charge air compressor outlet 44 swings the charge air check valve 50 
to the position shown in dashed lines in FIG. 3 closing the second charge 
air conduit 68, and is conducted from the junction 48 to the charge air 
inlet 26 of the internal combustion engine 10. Once sufficient exhaust gas 
energy is supplied from the internal combustion engine to the 
turbocharger, for example, at engine speeds of about 2000 rpm to about 
2500 rpm, the motor-driven compressor 42 can be de-energized and the 
turbocharger compressor 64 supplies charge air and boost pressure moving 
the charge air check valve 50 to the position shown in solid lines in FIG. 
3 to close the first charge air conduit 46 and supply compressed charge 
air from the junction 48 to the air inlet 26 of the internal combustion 
engine 10. As with the charge air systems described earlier, control 54 
can energize the electric motor 45 driving the charge air compressor 42 at 
low engine speeds and in response to demands for acceleration from low 
engine speed by a signal 56 which can be taken from an engine speed sensor 
and/or an acceleration demand sensor (not shown). As shown in FIG. 3, 
preferably the air inlet 43 for the charge air compressor 42 and the air 
inlet 65 for the turbocharger compressor 64 are connected with an air 
cleaner 52. 
The parallel connection of the small electric motor-driven compressor and 
turbocompressor as shown in FIG. 3 can improve the performance of a 
turbocharged four-cycle engine by compensating for the time lag of the 
turbocharger compression 64 upon sudden throttle opening by providing the 
charge air output of the small charge air compressor 42, which is 
connected directly to the air intake 26 of the internal combustion engine 
10 through the swing valve 50. Back flow of compressed air from a junction 
48 into second conduit 68 is prevented by the pressure-activated charge 
air check valve 50. When sufficient speed is obtained by the 
turbocompressor 64 its pressure output will overcome the check valve 50 
allowing its compressed air to enter the junction 48 and the air inlet 26 
of the internal combustion engine, and back flow of air from the junction 
48 through the first charge air conduit 46 and the small charge air 
compressor 42 is prevented by the closure of this passage by swing valve 
50. 
FIG. 4 shows a fourth preferred charge air embodiment of the invention 80 
in which the compressed charge air output of a turbocharger compressor 64 
is conveyed through an aftercooler 82, such as the air-to-air intercoolers 
used in turbocharged internal combustion engine systems, and hence to the 
air input 43 of charge air compressor 92 to provide a series arrangement 
and two-stage compression of charge air for the internal combustion engine 
10. The charge air system 80 of FIG. 4 includes, in addition to air 
cleaner 52, an auxiliary air cleaner 84 and a charge air check valve 50 
that allows the motor-driven compressor 92 to supply charge air to 
internal combustion engine 10 from ambient atmosphere immediately upon 
being energized without the restrictions that may be imposed by air 
cleaner 52, turbocharger compressor 64, aftercooler 82 and the associated 
conduits. 
The charge air system 80 of FIG. 4 comprises a charge air compressor 92 
having an air inlet 93 and an outlet 94, an electric motor 95 connected to 
drive the charge air compressor 92 and a turbocharger 62 having an exhaust 
gas driven turbine 63 connected with the exhaust gas outlet 30 of the 
internal combustion engine 10, and a turbocharger compressor 64 having air 
inlet 65 and a compressed charge air outlet 66 which is connected to the 
inlet of charge air cooler 82. A further charge air conduit 84 is 
connected with the outlet of the cooler 82, and a second charge air 
conduit 86 is connected with ambient atmosphere, and the further charge 
air conduit 84 and the second charge air conduit 86 are connected at 
junction 48 which is connected by a third charge air conduit 88 with the 
inlet 93 of the charge air compressor 92. A charge air check valve 50 
operates upon operation of the charge air compressor 92 to open the second 
charge air conduit 86 so charge air can be supplied from ambient 
atmosphere through the auxiliary air cleaner 84 to the inlet 93 of charge 
air compressor 92 for compression and delivery to the air inlet 26 of the 
internal combustion engine 10. Charge air check valve 50 operates to close 
the second charge air conduit 86 when the turbocharger 62 is operated by 
the internal combustion engine at high engine speeds. 
Unlike the charge air systems of FIGS. 1-3, however, the charge air 
compressor 92 must be operated by the control at high engine speeds to 
avoid restricting the flow of charge air from the turbocharger compressor 
64 to the air inlet 26 of the internal combustion engine. However, the use 
of a motor-driven compressor 92 in combination with the check valve 50 and 
ambient air conduit 86 permits the internal combustion engine to be 
supplied with a more rapid increase in boost pressure for acceleration. 
As suggested by FIG. 4, the charge air compressor 92 can be mounted closely 
adjacent the intake manifold 26 of the internal combustion engine and can 
eliminate the restrictive impact of air cleaner 52, turbocharger 
compressor 64, after cooler 82 and conduits 84 and 85. In operation of the 
charge air system 80, centrifugal compressor 92 can be driven by electric 
motor 45 in response to control 54 at predetermined minimum speed to 
provide boost pressure to the engine intake manifold at engine idle and at 
low load and speed conditions. Thus, in such operation a significant 
amount of charge air and boost pressure can be present at the air inlet 26 
of the internal combustion engine before additional fuel is injected as 
engine acceleration is demanded by the engine operator. In addition, the 
charge air compressor 92 can be super-energized by control 54 and electric 
motor 45 upon receipt of an acceleration demand signal 56, and the charge 
air compressor 92 can respond rapidly in response to such 
super-energization to provide rapid increases in charge air and boost 
pressure at the intake manifold 24 when acceleration of the engine is 
demanded. 
Due to the higher charge air provided by charge air systems of the 
invention when engine acceleration is called for, engine acceleration can 
be increased, fuel burned more completely, and harmful pollutants in the 
engine and exhaust substantially reduced. As it will be apparent to those 
skilled in the art, the signal 56 for operation of charge air systems of 
the invention may be taken from any one or more of intake manifold 
pressure, engine speed, acceleration demand sensors and other appropriate 
sensors of engine load and operation. 
While FIGS. 3 and 4 does not indicate that the turbocharger compressor 62 
includes an assisting electric motor, an assisting electric motor 
controlled from control 54 can be provided in the charge air system 70 if 
desired. 
Thus, the charge air systems of the invention permit the charge air 
requirements of the internal combustion engine to be provided rapidly in 
response to demands for engine acceleration through the use of small 
electric motor-driven compressors and without imposing restrictions on 
charge air flow that may otherwise may be imposed upon the charge air 
system by such small charge air compressors, and the invention permits 
such systems to utilize two-stage charge air compression through the 
additional use of a turbocharger compressor, or a larger electric 
motor-driven compressor, and permit a supply of charge air from parallel 
operation of small motor-driven compressor and a turbocharger compressor, 
or a larger motor-driven compressor. 
While this invention has been described in several currently best known 
modes, it will be clear to those skilled in the art that the invention may 
embodied in other modes and embodiments. Accordingly, the scope of the 
invention is defined by the following claims.