Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2002-12-13
2004-04-27
Denion, Thomas (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
Reexamination Certificate
active
06725660
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No.2001-400941 filed Dec. 28, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control device for a variable-geometry turbocharger used in vehicle engines or the like, and more particularly relates to a control device for a variable-geometry turbocharger of the type that varies the volume by varying the opening, i.e., the area, of the nozzle in the turbine inlet.
2. Description of the Related Art
Variable-geometry turbochargers (hereafter also referred to as “VGT”) which vary the opening of the variable nozzle in the turbine inlet in accordance with the operating conditions of the engine have been known in the past. In the case of such adjustment of the opening of the nozzle, a method in which variable nozzle vanes installed in the turbine inlet are opened and closed is generally used.
In such VGT control using nozzle vanes, the angle or opening of the nozzle vanes is varied by means of an actuator in accordance with the engine rotational speed and engine load. Furthermore, in the case of actual control, the nozzle vane opening or intake air pressure is set as a target value, and this target value is corrected in accordance with the atmospheric pressure, intake air temperature, water temperature and the like. Furthermore, in order to avoid damage to the VGT caused by excessive rotation or surging, a limit value is generally placed on the target value.
In a VGT, the velocity of the exhaust flowing into the turbine can be increased by closing down the opening of the nozzle vanes. Accordingly, in cases where the engine and turbocharger are accelerated from a low-rotation state during starting of the vehicle or the like, control is performed so that the opening of the nozzle vanes is closed down, thus producing as high a pressure as possible on the compressor outlet side by means of a small exhaust flow. On the other hand, in cases where the engine rotational speed is high and the amount of exhaust flow is large, control is performed so that the opening of the nozzle vanes is increased; in this way, a large amount of exhaust energy can be efficiently sent to the turbine.
In such VGT control, a closed loop is usually constructed in which a target value is basically set by means of a map in accordance with the engine operating conditions, and the actual value is fed back. Especially during transitional periods such as acceleration or deceleration, a separate target value is set independently from the basic map, or control is performed with a value that is obtained by adding a separately calculated correction value to the value of the basic map used as the target value.
For example, control during acceleration is performed as follows. In cases where the engine is in an idle state or a low-rotation, low-load steady operating state prior to acceleration, the opening of the nozzle vanes is ordinarily “full open” in order to reduce the exhaust resistance. Furthermore, the opening of the nozzle vanes may be varied because of requirements on the EGR control side. When there is a shift from this state to an acceleration operating state, since an intake air pressure target value that is abruptly higher is set from state in which the actual intake air pressure is low, the opening of the nozzle vanes is controlled so that this opening is closed down. As a result, the exhaust flow velocity into the turbine is ordinarily increased, so that the rotational speed of the turbocharger abruptly rises, thus causing an immediate rise in the intake air pressure so that the turbo lag is eliminated.
Furthermore, the amount fuel is increased during acceleration. However, if only the fuel is abruptly increased, this leads to an increase in smoke (in the case of a diesel engine); accordingly, a limit is placed on the amount of fuel injection itself so that an amount of fuel injection that is suited to the actual intake air amount is obtained. Consequently, in order to improve the acceleration characteristics (especially during starting of the vehicle into motion), it is necessary to accelerate the rise in the intake air pressure as far as possible, so that a large amount of intake air is supplied to the engine as quickly as possible, thus making it possible to increase the amount of fuel injection.
However, since the rotational speed of the turbocharger is still low immediately following acceleration, if the opening of the nozzle vanes is immediately closed down, this causes exhaust resistance so that the rise in the engine rotation may deteriorate, and thus rather cause a delay in the rise of the compressor outlet pressure (intake air pressure). Conventionally, therefore, a technique has been proposed in which the system is controlled so that the opening of the nozzle vanes is temporarily opened to a value that is greater than the basic target value immediately following the initiation of acceleration, or is held in a temporary open state, so that the exhaust resistance is reduced, after which the system is controlled so that the opening is closed down according to the map, thus ameliorating turbo lag (see Japanese Patent Application Laid-Open No. 2001-173448).
Meanwhile, for example, control during deceleration is performed as follows. Ordinarily, when the accelerator pedal is returned from a certain operating state, the amount of fuel injection that is required is reduced, and the engine rotation drops; at the same time, the amount of intake air is reduced (in the case of a diesel engine that has no throttle valve). In a VGT, the target value is calculated by means of a map using the engine rotation and engine load as input values. Accordingly, the system is controlled so that the nozzle vanes are gradually opened as the engine rotation drops; as a result, the rotation of the turbine also drops. However, if there is a deceleration due to an abrupt release of the accelerator pedal during acceleration under conditions close to the surge line determined by the compressor characteristics, since the rotational speed of the turbocharger has already increased to some extent, and is prevented from decelerating, i.e., dropping, because of inertia, a state is created in the compressor in which the amount of intake air is low in spite of the fact that the outlet side pressure is high, so that the phenomenon of surging occurs. As a result of this surging, an abnormal sound is generated in the compressor and intake air duct, and in regions where the pressure ratio is high, the compressor itself may be damaged. Accordingly, in regard to the problems that occur in the case of such abrupt deceleration as well, methods have been proposed in which surging is suppressed by temporarily opening the nozzle vanes of the VGT, or holding these vanes open for a time, immediately following deceleration, so that lowering of the turbine rotation is promoted, thus causing a lowering of the pressure on the outlet side of the compressor (see Japanese Patent Publication No. H6-72545 and Japanese Patent Application Laid-Open No. H10-77856).
Thus, in cases where there is either an abrupt acceleration or abrupt deceleration, it is desirable that the opening of the nozzle vanes be controlled so that a correction value is temporarily added to the control value on the basic map, or so that the nozzle vanes are opened independently from the basic map. However, for example, the following problems occur when temporary opening of the abovementioned type is attempted on the basis of the detected value of the acceleration or deceleration alone, e.g., the variation in the amount of depression of the accelerator pedal per predetermined unit time alone.
(1) In cases where an acceleration again occurs in a short time after a temporary deceleration that follows an initial acceleration, the rotational speed of the turbocharger itself is sufficiently high, so that there is no need for a temporary opening of the nozzle vanes (there
Denion Thomas
Isuzu Motors Limited
McCormick Paulding & Huber LLP
Trieu Thai-Ba
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