JPH0519012B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a variable displacement turbocharger, and particularly to an improvement of a variable displacement turbocharger for an automobile engine having an exhaust bypass mechanism.

[Prior art] Automotive turbocharged engines generally use exhaust energy to supercharge intake air to improve engine torque. In this case, supercharging pressure (positive pressure) is specified to prevent engine damage. An exhaust bypass mechanism is provided to prevent the pressure from rising above the specified value, and the actuator to which the supercharging pressure is guided opens the bypass valve (swing type wastegate valve) to bypass the exhaust gas.

On the other hand, a turbocharger equipped with a variable displacement mechanism has been proposed in order to improve performance over a wide range.
Flap valve type nozzle installed at the turbine inlet,
Alternatively, the opening degree of the ring-shaped nozzle is changed to improve the boost pressure at all engine speeds (see Japanese Utility Model Application No. 53-50310).

In other words, the variable displacement turbocharger closes the nozzle when the capacity is low (low engine speed range) and, conversely, opens the nozzle when the capacity is high (high engine speed range).
The purpose is to exhibit performance that is appropriate for each engine rotational speed, thereby obtaining a predetermined supercharging pressure.

However, with such conventional variable displacement turbochargers, when the nozzle is closed in an attempt to increase boost pressure in the low engine speed range, the exhaust pressure at the turbine inlet rises in the initial stage, causing the predetermined boost pressure to rise. The bypass valve opens before the pressure is reached,
There is a problem in that the engine torque decreases because the boost pressure does not rise to the specified value.

The reason for this is as follows.

In other words, in order to increase the engine boost pressure, an appropriate pressure difference is required before and after the turbine nozzle.The turbine obtains its velocity energy from this pressure difference, and the compressor coaxial with it is rotated at high speed to increase the boost pressure. You can get it. In this way, since the engine exhaust pressure at the turbine inlet has increased and then the opening is adjusted to the next nozzle opening, the bypass valve upstream of the nozzle is affected by this exhaust pressure.

Therefore, in the conventional bypass valve, the balance between the supercharging pressure of the actuator that operates the bypass valve and the built-in spring is disrupted by the above-mentioned increase in exhaust pressure, and the valve opens.
This will bypass the exhaust.

As a result, the supercharging pressure drops below the specified value, ie, a so-called slump occurs, resulting in a problem that the torque also decreases.

[Object of the Invention] The present invention has been made by focusing on such conventional problems, and an object thereof is to prevent the supercharging pressure of a variable capacity turbocharger from sagging, and thereby improve engine torque. With the goal.

[Structure of the Invention] In order to achieve the above object, the present invention includes a variable capacity mechanism that changes the flow rate characteristics of a turbine by operating a nozzle, an exhaust bypass mechanism that bypasses the turbine by a bypass valve and allows exhaust gas to flow, a diaphragm and a driving means for driving the bypass valve, including a spring that presses a diaphragm and a pressure chamber that opposes the spring; and a drive means that applies a pressure lower than the supercharging pressure to the pressure chamber through a supercharging pressure passage that applies supercharging pressure to the pressure chamber. A control valve that can be introduced into the chamber and a control valve that supplies boost pressure to the pressure chamber in the operating region of the exhaust bypass mechanism to open the bypass valve, while supplying boost pressure to the pressure chamber in the operating region of the variable displacement mechanism. and control means for controlling the control valve to supply a lower pressure and close the bypass valve.

[Operation] When the nozzle of the variable displacement mechanism is open, the control means controls the control valve to supply atmospheric pressure in addition to supercharging pressure to the pressure chamber of the drive means, and the bypass valve of the exhaust bypass mechanism The bypass valve maintains its closed operation even if the exhaust pressure upstream of the nozzle increases. Therefore, all of the exhaust gas flows to the turbine, which rotates at high speed and raises the intake air to a specified boost pressure by the coaxial compressor. This prevents a drop in supercharging pressure and, in turn, a drop in torque. When the engine speed eventually rises and the boost pressure exceeds the specified value, the control means controls the control valve to supply only boost pressure to the pressure chamber of the drive means, thereby opening the bypass valve as usual. This prevents damage to engine equipment due to overcharging, etc.

[Example] The present invention will be described below based on the drawings. 1 to 4 are diagrams showing an embodiment of the present invention.

First, the overall configuration will be explained with reference to FIG. The engine 1 obtains intake air through an intake pipe 2 and releases exhaust gas after operation to the atmosphere through an exhaust pipe 3.

The turbocharger 4 includes a turbine 5 and a compressor 6 coaxially, and also includes a variable displacement mechanism 7 and an exhaust bypass mechanism 8 at the exhaust inlet of the turbine 5, which are controlled by a control mechanism 9.

FIG. 2 shows a specific example, in which intake air is measured by an air flow meter 11, pressurized by a compressor 6, becomes supercharging pressure Pb at the outlet, controlled by a throttle valve 12, and sucked into the engine 1.

Exhaust passes from engine 1 through exhaust pipe 3, and on the way,
Turbine 5 via nozzle 13 of variable displacement mechanism 7
gives energy to and then discharges it.

As shown in FIG. 3, the nozzle 13 rotates about a shaft 14, and the area of the throat 15 is variable to correspond to the amount of exhaust gas entering the spiral scroll 16.

Referring again to FIG. 2, the shaft 14 of the nozzle 13 is connected via a lever 17 and a rod 18 to a diaphragm 20 of an actuator 19.

The actuator 19 is provided with a conduit 2 that guides the outlet pressure of the compressor 6 of the intake pipe 2, that is, the supercharging pressure Pb.
1 is provided, and a diaphragm 22 is provided in the middle,
A relief conduit 23 is branched downstream of this throttle 22, and the other end is connected to the inlet side of the compressor 6. In addition, a spring 24 is installed in the atmospheric chamber 27 of the actuator 19.
is provided so that it faces the boost pressure Pb.

The relief conduit 23 is provided with a solenoid valve 25 as a control valve, which is duty-controlled by a control unit 26 as a control means.

In the exhaust bypass mechanism 8, a bypass valve 31 is swing-mounted at the entrance of a bypass passage 30, and is connected to a diaphragm 35 of an actuator 34 as a driving means by a bell crank 32 and a rod 33. The diaphragm 35 is urged in the opposite direction of the rod 33 by a spring 36 provided in the atmospheric chamber 28. Also, the actuator 34 has a supercharging pressure Pb
A conduit 37 is connected as a boost pressure passage for introducing the pressure, but the pressure outlet is upstream of the solenoid valve 25,
Preferably, as shown in FIG. 2, the position is located upstream of the throttle 22 and exhibits a predetermined line resistance (described later) from the intake port 38 of the intake pipe 2.

The actuators 19, 34, solenoid valve 25, conduits 21, 37, etc. described above are the control mechanism 9 of FIG.
Configure.

The intake pipe 2 is equipped with a boost pressure sensor 41 that detects the boost pressure (intake pipe pressure at the compressor outlet) Pb.
An emergency relief valve 42 is installed.

The control unit 26 is mainly composed of a microcomputer consisting of a microprocessor, a memory, and an interface. It receives the engine rotation speed Ne from the crank angle sensor 43 and the throttle valve opening from the throttle valve opening sensor 44 as input signals. Among these signals, analog signals are input as digital signals via an A/D converter. The memory stores programs that control the microprocessor and various data necessary for operations executed by the microprocessor, and also temporarily stores data imported from outside. The microprocessor calculates the fuel injection amount, injection timing, ignition signal, etc. according to the program and outputs the injection signal Si and ignition signal Sp appropriate for the operating condition, and also calculates the duty value of the solenoid valve 25. Outputs control signal _DM .

Next, the operation of the above embodiment will be explained.

First, according to the flowchart in Figure 4, the solenoid valve 2
The duty value D _M of 5 is determined. In the figure, P ₁ to _{P 7} indicate each step of the flowchart.

A/D of engine speed Ne and intake flow rate Qa at P ₁
The converted value is input, and the air flow rate Tp per engine revolution is calculated at _P2 . _P3 looks up the predetermined duty value for the engine speed and air flow rate per revolution Tp.
In this table, the division points of Ne and Tp are finite, and the basic duty value D _M is determined by performing proportional interpolation calculation on the numerical values between the division points.

Furthermore, in P ₄ , the basic duty value D _M that has been looked up is set to an upper limit value Du and a lower limit value to prevent the operation delay time of the solenoid valve and the malfunction of the calculation software section.
Determine whether it is between D _L , and if it is greater than Du, fix D _M to the upper limit with P ₅ ,
When D is smaller than _U , fix D _M to the lower limit value with _P6 . Then, the basic duty value D _M looked up in _P7 is stored, and a timer measuring section (not shown) calculates the duty to the solenoid valve according to the value in this memory, and the result is sent to the solenoid valve via the I/O interface. Determine valve operation.

Next, the actual operation will be explained with reference to FIGS. 5, 6, and 7.

In FIG. 5, the horizontal axis represents the engine rotational speed Ne, and the vertical axis represents the air flow rate Tp per engine rotation. As shown in the figure, the operating line with the throttle valve fully open is line E, and the point where the boost pressure Pb reaches the specified value, for example 375 m/m of mercury, when the nozzle is fully closed is B _L , and the point where it also reaches the specified value with the nozzle fully open is B L . The region C between these regions is a region where the nozzle opening degree changes, and the nozzle opens as it goes in the direction of the arrow.

Further, the exhaust bypass valve operates in a region D between A and a fully open operating line E, which are determined before and after the point Bu.

In the above figure, write the duty value of the solenoid valve in terms of Ne and Tp and provide this as a table.
This table is predetermined to provide control duty values for each engine speed and air flow rate so as to achieve the maximum boost pressure allowed by the characteristics and durability of the engine.

FIG. 6 shows the relationship between the solenoid valve duty value, the actuator positive pressure, and the opening degrees of the nozzle and bypass valve.

The opening degree of the above-mentioned C area is C line, and the duty value at this time is in the range of F line (100 to 50), and the opening degree of D area is D line, and the duty value at this time is in the range of G line (50 to 50). 0) range.

That is, in FIG. 2, when the duty value to the solenoid valve 25 is increased, the opening time of the solenoid valve 25 increases, the positive pressure of the actuator 19 decreases, and the force of the spring 24 overcomes and the nozzle 13 is fully closed. shall be. Conversely, when the duty value is decreased, the positive pressure increases and the nozzle 13 is fully opened via the rod 18.

During the nozzle operating range F (FIG. 6), the bypass valve is fully closed as indicated by _d1 . and,
The bypass valve gradually opens like d ₂ and d ₃ .

Figure 7 is a graph showing how the pressure in the conduit to the actuator decreases (R) depending on the distance of the conduit and each element when the duty value is 0%, 50% and 100%. When the duty value is close to 0, there is no flow and the positive pressure to the actuator does not escape, so there is almost no drop.

Therefore, in the operating range (C) of the nozzle 13,
Due to the on/off operation of the solenoid valve 25, the pressure in the conduit 21 decreases and is applied to the actuator 34 of the bypass valve 31, so by appropriately selecting the tension of the spring 28, the force of the spring 28 is applied to the actuator 34 of the bypass valve 31. As a result, the bypass valve 31 can be closed, and a premature start of opening of the bypass valve 31 due to an increase in exhaust pressure can be easily delayed.

In this way, since the control pressure of the bypass valve 31 is reduced by i with respect to the starting pressure P ₀ , it is kept fully closed during this period, and when P ₀ is reached, it opens as shown in d ₂ . become.

In addition, in region H, although the actuator positive pressure does not change, the opening operation continues as shown in d ₃ , but this is due to the increase in the differential pressure before and after the valve due to the increase in bypass flow rate. Since the nozzle control is now outside the opening/closing operation range where the nozzle remains fully open, no inconvenience occurs.

FIG. 8 shows the change in exhaust pressure with respect to the engine speed, where A is when the nozzle is fully closed, B is when the nozzle is fully open, and the exhaust pressure is in a transient state as shown in C when the nozzle is opened and closed. Since outside the K range is the operating range of the bypass valve, when the exhaust pressure rises at the X portion of the transient line C, this pressure builds up in the bypass valve, and conventionally the boost pressure increases as shown by the dotted line Y in Figure 9. This caused a so-called slump.

However, in the embodiment of the present invention, the bypass valve 31 is closed by the control mechanism 9 such as the electromagnetic valve 25 and the actuator 34 during the nozzle opening/closing operation, so that the supercharging pressure is increased as shown by the solid line Z in FIG. It rises sharply and eliminates the sagging that occurs in the past. As a result, the engine torque is improved, and the nozzle opening/closing operation enables better performance.

Furthermore, in the embodiment described above, the supercharging pressure to be controlled is used as the operating pressure of the actuator, so when the supercharging pressure increases, the nozzle or bypass valve opens to try to lower it, causing feedback. It takes a while and is convenient.

FIG. 10 shows another embodiment.

This embodiment differs from FIG. 2 in that a three-way solenoid valve 45 is provided in the conduit 37 of the bypass valve 31 to the actuator 34, and this is controlled by the control unit 26.

When the three-way solenoid valve 45 is energized, the actuator 34
A conduit 47 communicates with the atmosphere port 46, and when the current is not energized, the conduit 47 communicates with the conduit 21 of the nozzle-side actuator 19.
I understand.

In this embodiment, even if the duty value of the solenoid valve 25 is set close to 100% with respect to the operation start pressure P ₀ of the bypass valve, a sufficient margin pressure i until the nozzle opens is not secured. It is necessary to lower the positive pressure of the bypass valve actuator 34 to close it, and this is effective in that case. According to this embodiment, the bypass valve 31 can be reliably closed by issuing a command from the control unit 26 at the same time as the nozzle is activated, energizing the three-way solenoid valve 45, and lowering the pressure of the actuator 34 to atmospheric pressure. .

This kind of thing happens when the nozzle actuator 1
In order to improve the transient characteristics of the diaphragm 9, it is often necessary to increase the area of the diaphragm 22. especially,
When the nozzle opening is narrowed, the turbine inlet exhaust pressure increases, and the inlet exhaust pressure also increases before the turbocharger rotation increases, such as during engine acceleration, which makes it easier to open the bypass valve.
Therefore, it is necessary to securely close the valve with a large pressure difference as in the above embodiment.

[Effects of the Invention] As explained above, according to the present invention, when the supercharging pressure is controlled by the variable displacement means of the variable displacement turbocharger, the pressure chamber of the drive means for driving the exhaust bypass valve The structure is such that the exhaust bypass valve is closed by introducing a pressure lower than the boost pressure into the engine, so even if the turbine inlet pressure increases, the bypass valve does not open, allowing the boost pressure to rise to the predetermined level. , the effect of increasing engine torque can be obtained.

Further, in other embodiments, since the bypass valve is reliably closed, there is no need to worry about the supercharging pressure sagging.

It should be noted that the present invention is applicable even when a vacuum is used as the control pressure for the actuator, and is also applicable when duty-controlled the bypass valve.

[Brief explanation of drawings]

FIG. 1 is an overall view of an embodiment of the present invention, FIG. 2 is a specific configuration diagram of FIG. 1, FIG. 3 is a sectional view showing a variable capacitance mechanism, and FIG. 4 is a control signal program of FIG. 2. Flow chart, Figure 5 is a table explanatory diagram, Figure 6 is an opening degree and pressure diagram against duty value, Figure 7 is an explanatory diagram showing the pressure gradient of the conduit, and Figure 8 is the engine exhaust pressure when the nozzle is activated. Performance chart, No. 9
The figure is a boost pressure performance diagram, and FIG. 10 is a specific configuration diagram of another embodiment. Explanation of symbols representing main parts of the drawings: 1...Engine, 2...Intake pipe, 3...Exhaust pipe, 4...Turbocharger, 5...Turbine, 6...Compressor, 7...Variable displacement mechanism, 8...Exhaust bypass mechanism, 9 ...control mechanism, 13...nozzle, 19...actuator, 25
...Solenoid valve, 26...Control unit, 30...
Bypass passage, 31... Bypass valve, 34... Actuator, 45... Three-way solenoid valve.

Claims (1)

[Claims] 1. A variable capacity mechanism that varies the flow rate characteristics of the turbine by operating a nozzle, an exhaust bypass mechanism that bypasses the turbine and allows exhaust gas to flow through a bypass valve, a diaphragm, a spring that presses the diaphragm, and a pressure chamber that opposes the spring. a drive means for driving the bypass valve, a control valve capable of introducing a pressure lower than the boost pressure into the pressure chamber via a boost pressure passage that applies boost pressure to the pressure chamber, and the exhaust bypass mechanism. In the operating region, supercharging pressure is supplied to the pressure chamber to open the bypass valve, while in the operating region of the variable displacement mechanism, a pressure lower than the supercharging pressure is supplied to the pressure chamber to close the bypass valve. A control device for a variable displacement turbocharger, comprising: control means for controlling the control valve.