Device for preventing the turbo-charger from over-running

A device for preventing the turbo-charger from over-running, wherein an actuator is arranged in a by-pass bypassing a turbine of the turbo-charger and operates a waste gate valve. The actuator has a positive pressure chamber communicated, via a boost pipe, with an intake air passage downstream of a compressor and a negative pressure chamber communicated with a source of negative pressure via a negative pressure pipe. The negative pressure chamber is so constituted as to be supplied with a negative pressure to have a target pressure that is set relative to the atmospheric pressure.

FIELD OF THE INVENTION

The present invention relates to a device for preventing a turbo-charger provided for an internal combustion engine from over-running.

DESCRIPTION OF THE RELATED ART

An internal combustion engine furnished with a turbo-charger is provided with a waste gate mechanism for preventing the turbo-charger from over-running. The waste gate mechanism comprises a by-pass that bypasses the turbine, a waste gate valve arranged in the by-pass, and an actuator that operates the waste gate valve by utilizing a boost pressure. In the thus constituted waste gate mechanism, the waste gate valve is opened and closed according to a balance between the boost pressure which is a source of driving the actuator and the exhaust gas pressure acting on a return spring disposed in the actuator and on the waste gate vale. In other words, the boost pressure is determined, i.e., the pressure at the outlet of the compressor of the turbo-charger is determined by the preset load of the return spring and the exhaust gas pressure acting on the waste gate valve.

By the way, in the case where the atmospheric pressure becomes low in a district of high altitudes, the pressure ratio between the inlet pressure and the outlet pressure of the compressor increases in the turbo-charger that operates in a state of a low atmospheric pressure. As a result, the rotational speed of the turbine increases and, in the worst case, the turbo-charger rotates at a speed in excess of a maximum permissible rotational speed and may be broken. When a vehicle mounting the internal combustion engine with turbo-charger is used in a region where there is a great difference in the altitude, the boost pressure must be set to be not so high to prevent the over-running in a high land where the atmospheric pressure is low, with sacrificing the performance in the low lands, or it is necessary to employ a turbo-charger of a large capacity having a sufficient margin in the pressure ratio.

In order to solve the above-mentioned problem, JP-A 8-200082 proposes a device for preventing the turbo-charger from over-running by forming a second by-pass in the exhaust passage upstream of the by-pass in which a waste gate valve is disposed, arranging a relief valve with a sonic nozzle in the second by-pass, and opening the relief valve when the rotational speed of the turbo charger reaches an over-running zone.

In the device disclosed in the above publication, however, the second by-pass is arranged on the outside of the waste gate valve, and it is needed to arrange the relief valve with the sonic nozzle in the second by-pass, causing the structure to become complex and raising the cost of production.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an inexpensive device for preventing the turbo-charger from over-running, which is capable of preventing the over-running in a high land where the atmospheric pressure is low, without sacrificing the performance in a low land, by controlling the actuator that operates the waste gate valve based on the boost pressure and the atmospheric pressure.

In order to achieve the above object according to the present invention, there is provided a device for preventing the turbo-charger from over-running, comprising a turbo-charger having a turbine arranged in an exhaust gas passage of an internal combustion engine and a compressor that is arranged in an intake air passage of the internal combustion engine and is driven by the turbine, a waste gate valve arranged in a by-pass bypassing the turbine, and an actuator that has a positive pressure chamber communicated, via a boost pipe, with the intake air passage downstream of the compressor and a negative pressure chamber communicated with a source of negative pressure via a negative pressure pipe and operates the waste gate valve; characterized in that:the device comprisesa pressure adjusting valve arranged in the negative pressure pipe and for adjusting the pressure in the negative pressure chamber;a pressure sensor for detecting the pressure in the negative pressure chamber;an atmospheric pressure sensor for detecting the atmospheric pressure; anda control means for controlling said pressure adjusting valve based on the detection signals from the atmospheric pressure sensor and the pressure sensor; and that:the control means has a storage means for storing a target pressure in the negative pressure chamber, which corresponds to the atmospheric pressure, and controls the pressure adjusting valve so as to make the pressure in the negative pressure chamber become equal to said target pressure, based on the atmospheric pressure detected by the atmospheric pressure sensor and on the pressure in the negative pressure chamber detected by the pressure sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of a device for preventing a turbo-charger from over-running constituted according to the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1is a block diagram illustrating the constitution of a device for preventing the turbo-charger from over-running, constituted according to the present invention.

In the illustrated embodiment, the internal combustion engine2is a diesel engine which includes an internal combustion engine body21, an intake manifold22and an exhaust manifold23. An intake air passage24is connected to the intake manifold22, and an exhaust gas passage25is connected to the exhaust gas manifold23. A turbo charger3is arranged in the intake air passage24and in the exhaust gas passage25. The turbo-charger3includes a turbine31arranged in the exhaust gas passage25, a compressor32arranged in the intake air passage24, and a rotary shaft33for coupling the turbine31to the compressor32.

The exhaust gas passage25is provided with a by-pass26, which communicates the upstream side of the turbine31with the downstream side thereof, i.e., bypasses the turbine31. A waste gate valve4is arranged in the by-pass26. The waste gate valve4is operated by an actuator5. In the illustrated embodiment, the actuator5is constituted by a casing51, a diaphragm52arranged in the casing51to section the interior of the casing51into a positive pressure chamber51aand a negative pressure chamber51b, an operation rod53that is coupled at its one end to the diaphragm52and is coupled at the other end to the waste gate valve4, and a return spring54arranged in the negative pressure chamber51bto urge the diaphragm52toward the left in the drawing, i.e., to urge the waste gate valve4in a direction to close the valve at all times. In the thus constituted actuator5, the positive pressure chamber51ais communicated with the intake air passage24downstream of the compressor32in the intake air passage24by a boost pipe6, and the negative pressure chamber51bis communicated with a vacuum pump7which is a source of negative pressure by a negative pressure pipe8. A pressure adjusting valve9for adjusting the pressure in the negative pressure chamber51bis arranged in the negative pressure pipe8communicating the negative pressure chamber51bwith the vacuum pump7. The pressure adjusting valve9is a three-way valve and is operated by a pulse width modulation (PWM) signal from a control means that will be described later. When the pulse width modulation (PWM) signal has a minimum pulse width, the pressure adjusting valve9works to open the negative pressure pipe8to the atmosphere while shutting it off on the side of the vacuum pump7. In a state where the pressure adjusting valve9is thus worked to open the negative pressure pipe8to the atmosphere while shutting it off on the side of the vacuum pump7, the actuator5is operated by the boost pressure only.

The device for preventing the turbo-charger from over-running of the illustrated embodiment has a pressure sensor10that is arranged in the negative pressure pipe8and detects the pressure in the negative pressure chamber51b, and an atmospheric pressure sensor11for detecting the atmospheric pressure. These sensors send their detection signals to a control means12. The control means12is constituted by a microcomputer and has a central processing unit (CPU)121that executes an arithmetic processing according to a control program, a read-only memory (ROM)122that is a storage means for storing a control program and a control map setting a target pressure in the negative pressure chamber51b, relative to the atmospheric pressure as will be described later, a random access memory (RAM)123for storing the results of operation, an input interface124and an output interface125. The thus constituted control means12receives, through the input interface124thereof, detection signals from the pressure sensor10and the atmospheric pressure sensor11, and produces a pulse width modulation (PWM) signal to transmit it to the pressure adjusting valve9through the output interface125thereof.

The device for preventing the turbo-charger from over-running according to the illustrated embodiment is constituted as described above. Described below is the operation thereof.

The exhaust gas emitted from the exhaust port of the internal combustion engine body21into the exhaust gas passage25through the exhaust manifold23works to operate the turbine31in the turbo-charger3before it is emitted. On the other hand, the intake air taken in from the atmosphere has a pressure raised by the compressor32that is driven by the rotation of the turbine31and is supplied to the engine body21, through the intake air passage24. When the rotational speed of the turbo-charger3is lower than a predetermined value, the boost pressure in the intake air passage24is maintained to be not larger than a predetermined value. Therefore, even when the boost pressure acts on the positive pressure chamber51ain the actuator5through the boost pipe6, the waste gate valve4is maintained in the closed state due to the urging force in the direction of closing the valve, produced by the return spring54and the exhaust gas pressure acting on the waste gate valve4. Then, as the boost pressure in the intake air passage24increases to exceed the predetermined value due to an increase in the rotational speed of the turbo-charger3which is caused by an increase in the energy of the exhaust gas, the diaphragm52of the actuator5moves toward the right inFIG. 1due to the boost pressure acting on the positive pressure chamber51ain the actuator5against the return sprig54and the exhaust gas pressure acting on the waste gate valve4, and the waste gate valve4is opened by the operation rod53. As a result, since part of the exhaust gas is emitted through the by-pass26bypassing the turbine31, the exhaust gas energy acting on the turbine31decreases, the rotational speed of the turbine31decreases and consequently, the turbo-charger3is prevented from over-running.

As the altitude becomes high and the atmospheric pressure becomes low, the pressure ratio between the inlet pressure and the outlet pressure of the compressor32of the turbo-charger3increases as described above. Accordingly, the rotational speed of the turbine31increases and, in the worst case, exceeds a maximum permissible rotational speed, resulting in a breakage of the turbo-charger3. In order to solve this problem, in the illustrated embodiment, a negative pressure set relative to the atmospheric pressure is caused to act on the negative pressure chamber51bin the actuator5to open the waste gate valve4even when the boost pressure is lower than the predetermined value, in case the atmospheric pressure is low, Thereby, the rotational speed of the turbine31is lowered to prevent the turbo-charger from over-running.

Next, the negative pressure acting on the negative pressure chamber51bof the actuator5will be described in detail.

The read-only memory (ROM)122in the control means12stores a control map in which the target pressure in the negative pressure chamber51bis set based on the atmospheric pressures as shown in FIG.2. In a state where the atmospheric pressure is higher than about 740 hectopascals (hPa) as will be learned from this control map, the target pressure in the negative pressure chamber51bis set to be the same value as the atmospheric pressure. And, as the atmospheric pressure becomes lower than about 740 hectopascals (hPa), the target pressure in the negative pressure chamber51bis set to become gradually lower than the atmospheric pressure. The target pressure based on the atmospheric pressure varies depending upon the characteristics of the internal combustion engine and of the turbo-charger, and is suitably set depending upon a combination of the internal combustion engine and the turbo-charger.

On the other hand, the control means12receives detection signals from the pressure sensor10and the atmospheric pressure sensor11. Based upon the atmospheric pressure detected by the atmospheric pressure sensor11, the control means12determines a target pressure in the negative pressure chamber51bwith reference to the control map shown in FIG.2. After the target pressure in the negative pressure chamber51bin the actuator5is determined as described above, the control means12sets a pulse width based on a difference between the target pressure and the pressure in the negative pressure chamber51bdetected by the pressure sensor10, and sends a pulse width modulation (PWM) signal having the thus set pulse width, to the pressure adjusting valve9. This control operation is fed back until the pressure in the negative pressure chamber51bcomes into agreement with the target pressure. For example, in a state where the atmospheric pressure is higher than about 740 hectopascals (hPa), the target pressure in the negative pressure chamber51bhas been set to be nearly equal to the atmospheric pressure. Therefore, the pulse width of the pulse width modulation (PWM) signal output to the pressure adjusting valve9is set to be a minimum and consequently, the pressure adjusting valve9opens the negative pressure pipe8to the atmosphere and shuts it off on the side of the vacuum pump7. As a result, the interior of the negative pressure chamber51bhas the atmospheric pressure, and the actuator5is operated by the boost pressure only. When the atmospheric pressure becomes lower than about 740 hectopascals (hPa), on the other hand, since the target pressure in the negative pressure chamber51bis set to be lower than the atmospheric pressure, a pulse width modulation (PWM) signal having a pulse width set based on a difference between the target pressure and the pressure in the negative pressure chamber51bdetected by the pressure sensor11is sent to the pressure adjusting valve9, as described above. As a result, the pressure adjusting valve9permits the negative pressure pipe8to be communicated with the vacuum pump7, whereby a negative pressure is supplied into the negative pressure chamber51band the pressure drops therein. This brings about the same effect as the case where the set pressure of the waste gate valve4is decreased. When the atmospheric pressure is low, therefore, the waste gate valve4is opened even when the boost pressure is lower than the predetermined value. Accordingly, since part of the exhaust gas is emitted through the by-pass26bypassing the turbine31, the exhaust gas energy acting on the turbine31decreases, the rotational speed of the turbine31decreases and consequently, the turbo-charger3is prevented from over-running in a state where the atmospheric pressure is low.

As described above, the device for preventing the turbo-charger from over-running of the illustrated embodiment drives the actuator5that operates the waste gate valve4by a boost pressure that basically acts in the positive pressure chamber51a, and, when the atmospheric pressure becomes low, effects the correction by using a negative pressure that acts on the negative pressure chamber51b. Therefore, the control operation can be executed without time lag for a change in the rotational speed of the internal combustion engine or for a change in the rotational speed of the turbo-charger3caused by variation in the load. While the internal combustion engine is in operation, the pressure in the positive pressure chamber51aof the actuator5fluctuates due to changes in the inlet pressure of the turbine31and in the outlet pressure of the compressor32stemming from a change in the rotational speed or the load. Therefore, the pressure in the negative pressure chamber51b, too, fluctuates with the fluctuation of pressure in the positive pressure chamber51a. This fluctuation, however, can be adjusted by the feedback control operation described above.

The device for preventing the turbo-charger of the engine from over-running of the invention is constituted as described above. Described below is the operation effect thereof.

Namely, the actuator for operating the waste gate valve has a positive pressure chamber communicated, through a boost pipe, with the intake air passage downstream of the compressor and a negative pressure chamber communicated with a source of negative pressure through a negative pressure pipe, the negative pressure chamber being supplied with a negative pressure so as to have a target pressure that has been set relative to the atmospheric pressure. When the atmospheric pressure is low, therefore, the waste gate valve is opened even when the boost pressure is lower than the predetermined value. According to the present invention, therefore, there is provided an inexpensive device for preventing the turbo-charger from over-running, which is capable of preventing the over-running in high lands where the atmospheric pressure is low, without sacrificing performance in low lands.