Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2000-11-14
2001-11-06
Nguyen, Hoang (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C060S602000, C060S612000
Reexamination Certificate
active
06311493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a turbo charging system for a diesel engine, and more particularly to such a turbo charging system that can improve both engine performance and fuel consumption rate with a simple construction and control.
2. Description of the Related Art
Diesel engines are suited for a turbo charger since unlike gasoline engines there is no need to adjust an amount of intake air for engine performance (output) control. A typical structure of a turbo charger system for a diesel engine is illustrated in
FIG. 5
of the accompanying drawings. This is a one-stage turbo charger.
As illustrated, this turbo charger system
38
includes a compressor
44
provided on an intake air passage
42
of a diesel engine
40
, a turbine
48
provided on an exhaust gas passage
46
, and a rotating shaft
50
connecting the compressor
44
with the turbine
48
. As the turbine
48
is rotated by an exhaust gas flowing in the exhaust gas line
46
, its rotation is transmitted to the compressor
44
via the shaft
50
. The compressor
44
then pressurizes the intake air and feeds it to the engine
40
. An after cooler
52
is optionally provided between the compressor
44
and engine
40
.
If engine revolution speed rises and exhaust gas flow rate (mass flow) correspondingly increases, a rotational speed of the turbine
48
rises and simultaneously the compressor
44
rotates at an increased speed. As a result, a supercharging pressure to the engine
40
may become excessively high. In order to avoid it, a bypass line
54
is provided on the exhaust gas line
46
over the turbine
48
, and a bypass valve
56
is provided on the bypass line
54
for causing part of the exhaust gas to bypass the turbine
48
when the supercharging pressure exceeds a predetermined value. By opening the bypass valve
56
, the rotational speed of the turbine
48
can be suppressed, i.e., the rotational speed of the compressor
44
can be suppressed. Consequently, the supercharging pressure is controlled.
Referring now to
FIG. 6
of the accompanying drawings, illustrated is a performance map of the compressor
44
of the turbo charger system
38
shown in
FIG. 5
, together with an engine performance curve (operation curve) when running under a full load condition. The curve
60
indicates a surge limitation, the curve
62
a maximum rotation limit, the point
64
a maximum torque of the engine
40
, the point
66
a maximum output of the engine
40
, the point
68
a maximum efficiency of the compressor
44
, and the multi-circle
70
iso-efficiency curves of the compressor
44
. As understood from this diagram, when the engine
40
is running under the full load condition, the bypass valve
56
is closed until the engine demonstrates the maximum torque
64
(i.e., until the engine revolution speed reaches a corresponding value), and if the engine revolution speed exceeds that value, the bypass valve
56
is gradually opened to control the supercharging pressure.
The vertical axis of the graph shown in
FIG. 6
indicates a pressure ratio, and the horizontal axis indicates a corrected mass flow, which are given by the following equations respectively:
Pressure ratio=total pressure at compressor outlet/total pressure at compressor inlet
Corrected mass flow=(measured mass flow×(inlet temperature/reference temperature)
0.5
)/(inlet pressure/reference pressure)
where the reference temperature=20° C.
(reference value for correction), and
the reference pressure=atmospheric pressure
(reference value for correction).
When the engine output and torque should be raised in the above described turbo charger system
38
, the turbine
48
may be tuned so that the turbine rotational speed is raised relative to the same exhaust gas flow rate (i.e., same engine revolution speed) and the compressor rotational speed is raised as well. This shifts the operation curve upwards in the graph of
FIG. 6
so that it passes a high pressure ratio area. However, as the pressure ratio is raised, the efficiency drops, i.e., the high pressure ratio area is a low efficiency area. Thus, raising the operation curve into the high pressure ratio area results in deterioration of fuel consumption ratio.
Specifically, if the pressure ratio is raised and a low compressor efficiency area is used as mentioned above, the turbine
48
must perform more work (torque of the rotating shaft
50
) in order to raise the intake air pressure (supercharging pressure). This brings about exit clogging of the exhaust gas, which raises the exhaust gas pressure. As a result, as shown in
FIG. 8
, the intake air pressure does not exceed the exhaust gas pressure, and pumping loss occurs as indicated by the shaded area. This deteriorates the fuel consumption rate. Here, the intake air pressure is an air pressure downstream of the compressor
44
, and the exhaust gas pressure is an air pressure upstream of the turbine
48
.
Even if the engine output and torque are suppressed and a low compressor pressure ratio area is used, the operation curve inevitably passes the low efficiency area because the centrifugal compressor
44
has a high efficiency area in a narrow flow rate range due to its structure whereas the automobile engine
40
is operated in a wide rotation speed range and the exhaust gas has a wide flow rate range. Thus, for the reason mentioned earlier, there is only a limited range of good fuel consumption rate, and it is difficult to improve the fuel consumption rate as a whole.
There is also known a variable displacement turbo charger system which aims to improve the fuel consumption rate. By changing a turbine displacement (capacity) in accordance with change of the exhaust gas flow rate, this turbo charger system intends to adjust the turbine rotational speed such that the compressor is used in a high efficiency area as much as possible. However, since the turbine displacement is variable, throttle loss occurs and exhaust gas pressure increases. Further, the variable range itself is limited. Accordingly, great improvement cannot be expected on the fuel consumption rate. In addition, a variable displacement turbine requires a complicated mechanism. This raises a manufacturing cost.
Another type of conventional turbo charger system includes two turbo chargers having different characteristics. In this system, two compressors are provided in series on intake air line of an engine and two turbines are provided on an exhaust gas line. This is a two-stage turbo charger system.) Each of the compressors and turbines has a bypass line with a bypass valve, and these bypass valves are closed and opened according to the engine running condition such that the two turbo chargers are selectively operated. In this arrangement, when one of the turbo chargers is driven, the other turbo charger is fundamentally deactivated (full switching type). Accordingly, timing control for switching is difficult, i.e., it requires complicated control.
SUMMARY OF THE INVENTION
One of the objects of the present invention is to a turbo charger system for a diesel engine that has a simple structure and operates under less complicated control, but can raise output and torque and improve fuel consumption rate.
According to one aspect of the present invention, there is provided a turbo charger system for a diesel engine including high- and low-stage turbines provided in series on an exhaust gas line of the engine, high- and low-stage compressors provided in series on an intake air of the engine such that the high-stage compressor is operatively coupled to the high-stage turbine and the low-stage compressor is operatively coupled to the low-stage turbine, a bypass line with a valve provided on the exhaust gas line such that the bypass line bypasses the high-stage turbine, and a controller for controlling an opening degree of the bypass valve such that the bypass valve is completely or substantially completely closed until the diesel engine reaches its maximum torque point at least when the engi
Adachi Toshiaki
Fujisaki Takao
Inoue Takao
Kodaira Takao
Kurihara Hirokazu
Isuzu Motors Limited
McCormick Paulding & Huber LLP
Nguyen Hoang
LandOfFree
Turbo charging system of diesel engine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Turbo charging system of diesel engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Turbo charging system of diesel engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2603384