JPH0647934B2 - Exhaust gas recirculation system for engines with variable displacement turbocharger - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an exhaust gas recirculation device (hereinafter referred to as “EGR device”) in a variable displacement turbocharged engine.

2. Description of the Related Art An EGR device extracts a part of exhaust gas emitted from an engine of an automobile engine or the like from an exhaust system.
This is a device that mixes with intake air and sends it to the combustion chamber of the engine to lower the maximum temperature during combustion to reduce the amount of NOx generated. In order to mix the exhaust gas for EGR (hereinafter referred to as “recirculation exhaust gas”) into the exhaust gas, the pressure of the intake air in the mixing portion must be lower than the pressure of the recirculation exhaust gas. Therefore, in an engine with a turbocharger, the pressure on the downstream side of the blower of the turbocharger is generally higher than the exhaust pressure, so it is possible to mix the exhaust gas for recirculation on the upstream side (inlet side) of the blower where the pressure is low (atmospheric pressure). It was being appreciated. As a document relating to the EGR device of the engine with a turbocharger, there is JP-A-56-124664.

[Problems to be Solved by the Invention]

(Problem) However, the above-mentioned conventional technique has a problem that durability reliability of the blower impeller in the blower is deteriorated. (Explanation of Problems) In the above-mentioned conventional example, since the exhaust gas is supplied to the inlet side of the blower, the blower impeller is contaminated by the exhaust gas and the heat of the exhaust gas causes mechanical strength (for example, creep). Strength) is reduced. Therefore, the durability and reliability are reduced. Furthermore, if the blower discharge temperature is limited, the engine performance will be limited. Considering the recent trend toward higher output,
It becomes negative. Some exhaust gas recirculates to the discharge side of the blower, and in such a case, the blower impeller is not contaminated by the exhaust gas. However, in a place where the engine load is high, the boost pressure is generally higher than the pressure of the exhaust gas, so that the exhaust gas cannot be recirculated and NOx cannot be reduced. The present invention aims to solve the above problems.

[Means for solving problems]

In order to solve the above problems, in the exhaust gas recirculation system for a variable capacity turbocharged engine of the present invention, a means for extracting recirculation exhaust gas from the turbine inlet side of the variable capacity turbocharger and supplying it to the blower discharge side, and a turbine The turbine is movable such that the pressure on the inlet side is higher than the pressure on the blower discharge side, and the differential pressure from the pressure on the blower discharge side is a value between a predetermined lower limit value and a predetermined upper limit value. And means for controlling the nozzle.

[Work]

The means for extracting the recirculation exhaust gas from the turbine inlet side of the variable displacement turbocharger and supplying it to the blower discharge side enables the recirculation exhaust gas to flow to the engine without touching the blower impeller. As a result, the blower impeller is not contaminated and the mechanical strength is not reduced, and durability reliability is increased. The means for controlling the movable nozzles of the turbine widens or narrows the gap between the movable nozzles, which can change the pressure at the turbine inlet side. That is, the pressure on the turbine inlet side decreases when the gap is widened, and rises when the pressure is narrowed. Therefore, by the means, the pressure on the turbine inlet side can be adjusted to be higher than the pressure on the blower discharge side by a desired value.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an EGR device for a variable displacement turbocharged engine according to an embodiment of the present invention. In FIG. 1, 1 is a rotation sensor, 2 is an engine, 3 is an intake manifold, 4 is an exhaust manifold, 5 is an exhaust gas supply pipe for recirculation, 6 is a blower, 6'is a blower impeller, 7 is a turbine, 8 is Intake pipe, 9 intake manifold engine connection, 10 exhaust manifold engine connection, 11 air cleaner, 12 step motor, 13 controller, 14 load sensor,
Reference numeral 15 is an accelerator opening sensor, 16 is a flywheel housing, 17 is a boost pressure measuring pressure sensor, and 18 is an exhaust pressure measuring pressure sensor. (A) Gas flow path The flow of intake air and exhaust gas is as follows. The intake air flows in the route of air cleaner 11 → blower 6 → intake pipe 8 → intake manifold 3 → engine 2.
Then, at the discharge side of the blower 6, that is, at the intake pipe 8, the exhaust gas for recirculation extracted from the inlet side of the turbine 7 is supplied. On the other hand, the exhaust gas is discharged to the outside through the route of engine 2 → exhaust manifold 4 → turbine 7. Then, a part of the exhaust gas is supplied to the intake pipe 8 on the inlet side of the turbine 7. In a turbocharger that is not a variable displacement type, in the high load region, the pressure on the inlet side of the turbine 7 is lower than the pressure on the discharge side of the blower 6, so that the blower 6 from the inlet side of the turbine 7
Recirculation exhaust gas cannot be sent to the discharge side. However, in the variable displacement turbocharger, the pressure on the inlet side of the turbine 7 can be increased by controlling the movable nozzle of the turbine 7 as described in detail later. Therefore, the exhaust gas for recirculation can be sent from the inlet side of the turbine 7 to the discharge side of the blower 6. The movable nozzle of the turbine 7 is actuated by an actuator (step motor 12 in FIG. 1), which is controlled by a control signal from the controller 13. The controller 13 includes a rotation sensor 1, a load sensor 14,
The engine state is judged based on signals from the accelerator opening sensor 15, the boost pressure measuring pressure sensor 17, the exhaust pressure measuring pressure sensor 18, etc., and a control signal to the actuator is issued. As described above, the recirculation exhaust gas recirculates to the engine without touching the blower impeller 6 '. As a result, the durability and reliability of the blower impeller 6'is increased. (B) Configuration and operation of variable displacement turbocharger A variable displacement turbocharger is a turbocharger in which a turbine has a movable nozzle that controls the flow rate of exhaust gas. FIG. 6 shows a sectional view in the vicinity of the movable nozzle of the variable displacement turbocharger, and FIG. 7 shows a view seen from the XX direction in FIG. In these figures, 701 is an actuating link, 702 is an actuating shaft, 703 is an actuating lever, 70
4 is a control ring, 705 is a control lever, 706 is a nozzle rotating shaft, 707 is a turbine housing, 708 is a movable nozzle, 709 is a turbine wheel, 710 is a free end, and 711 is a recess. The operation link 701 is an actuator (not shown) (first
In the case shown, the control ring 704 is rotated via the actuating shaft 702 and the actuating lever 703 when actuated by the step motor 12). Recess 711 of control ring 704
Since the free end 710 of the control lever 705 is fitted on the control lever 705, when the control ring 704 rotates, the control lever 70
The movable nozzle 708 rotates around the nozzle rotation shaft 706 via the nozzle 5. Thus, the gap between the movable nozzles 708 is widened or narrowed. The exhaust gas enters through the gap, turns the turbine wheel 709, and then exits to the outside. Therefore, the flow velocity of the exhaust gas can be controlled by adjusting the opening degree of the movable nozzle 708. At the same time, the pressure on the inlet side of the turbine 7 can be controlled as described below. FIG. 3 is a diagram showing the relationship between the pressure on the turbine inlet side of the variable displacement turbocharger, the flow rate of exhaust gas, and the opening degree of the movable nozzle. In FIG. 3, θ _A to θ _C are the openings of the movable nozzle. When the flow rate of exhaust gas is increased while the opening of the movable nozzle is kept constant, the pressure gradually increases at first, but has a characteristic that it rapidly increases from the middle. It can also be seen that the pressure changes when the flow rate of exhaust gas is kept constant and the opening of the movable nozzle is changed. If the opening is such that the gap between the movable nozzles is narrowed, only a small amount of exhaust gas can flow out, and the pressure on the inlet side of the turbine 7 increases. On the contrary, if the opening is such that the gap between the possible nozzles is wide, a large amount of exhaust gas flows out, so the pressure becomes low. The present invention utilizes this characteristic of the variable displacement turbocharger to control the pressure on the inlet side of the turbine 7 to be higher than the pressure on the discharge side of the blower 6, so that the exhaust gas for recirculation flows toward the discharge side of the blower 6. It made it possible to flow. (C) Actuator for controlling the movable nozzle FIG. 2 shows the connection relationship between the turbine 7 and the step motor 12 of the variable displacement turbocharger when the step motor 12 is used as the actuator for controlling the movable nozzle 708. Indicates. The lever 21 driven by the step motor 12 moves the actuation link 701 via the link rod 19. The subsequent operation is as described with reference to FIGS. 6 and 7. The step motor 12 can be rotated step by step in the positive direction or the negative direction to control the opening degree in small steps. The return spring 20 has a movable nozzle 70 in case of a failure.
This is for rotating 8 on the safe side (so that the gap between the movable nozzles 708 becomes wide). If a failure occurs with the gap kept narrow, the flow velocity of the exhaust gas blown to the turbine wheel 709 will remain high.
Then, the blower 6 also continues to rotate at high speed, the boost pressure rises too much, and the engine may be destroyed. Conventionally, an air cylinder has been used as an actuator for controlling the movable nozzle 708, but in that case, it is general that the air cylinder is combined and controlled in several steps. However, with this number of steps, it was difficult to maximize the capacity of the variable displacement turbocharger, and the engine performance could not be fully exhibited. Therefore, it is conceivable to use a hydraulic cylinder for continuous control, but in that case it is essential to detect the absolute position of the hydraulic cylinder, and a control valve and position sensor must be provided (by closed control. control). However, such parts that require high system operation are
Installation in a bad environment where there is a corrosive gas or the like at a high temperature around the turbocharger is not preferable in terms of durability and reliability. Although the step motor is adopted as the actuator in the above-mentioned embodiment, if the step motor is used, the desired operation can be sufficiently performed by the control by the open control. Therefore, it is not necessary to install a position sensor etc. in a bad environment, and it is necessary to consider heat prevention etc.
Since it is only a step motor, it is more reliable than the above. As means for preventing heat damage, for example,
It is conceivable to provide a heat shield plate 22 as shown in FIG. (D) Operation means of the present invention FIG. 4 shows an operation procedure of the present invention. In the following description, or corresponds to or in FIG. In order to know the state of the engine, the controller 13
The signals from the rotation sensor 1, the load sensor 14, and the boost pressure measuring pressure sensor 17 are read. Further, the accelerator opening degree α ₁ at this time is read by the accelerator opening degree sensor 15 in order to use it for determining whether the driving vehicle is going to accelerate or decelerate in the process of. The position of the lever that regulates the opening of the movable nozzle of the variable displacement turbocharger is set according to the state of the engine. This setting is performed by reading from a lever position map set in advance. FIG. 5 shows an example of a lever position map of the variable displacement turbocharger. The curve M shows the curve at the maximum output.
The straight lines L ₁ , L ₂ , and L ₃ show outputs of approximately 1/4, 2/4, and 3/4 with respect to the maximum output, respectively. FIG. 5 shows that the rotation speed is N _A and the load (that is, the output) is the rotation speed N _A.
When it is in a state of 1/4 of the maximum output at, it means that the position of θ ₁ is given as the lever position. Similarly, when the output is 2/4, θ
Θ ₃ at ₂ and 3/4 output, θ _M at maximum output
give. If the rotation speed changes to N _B , another value is given. The exhaust pressure, which is the pressure on the inlet side of the turbine 7, is read by the exhaust pressure measuring pressure sensor 18. It is determined whether or not the differential pressure between the boost pressure and the exhaust pressure is equal to or higher than P _L set as the lower limit value of the differential pressure. If the differential pressure is smaller than the lower limit value, the step motor 12 is driven by one step in the direction of increasing the differential pressure. ，
The above steps are repeated until the differential pressure becomes equal to or higher than the lower limit value P _L. Differential pressure between the boost pressure and the exhaust pressure, it is determined whether or not more than P _H is set as the upper limit of differential pressure. If the differential pressure is not less than the upper limit value P _H, is driven in the direction differential pressure falls a step motor 12 by one step. , Are repeated until the differential pressure becomes equal to or lower than the upper limit value P _H. The accelerator opening α ₂ at this time is read from the accelerator opening sensor 15. It is determined whether or not the absolute value of the difference between the accelerator opening α ₁ read in step ₁ and the accelerator opening α ₂ read in step 3 is equal to or greater than a preset accelerator opening α ₀ . When the left side is large, it means that the driver suddenly accelerated or decelerated. Determine whether you have accelerated or decelerated. α ₂ -α
_{If 1} is positive, deceleration is performed, and if ₁ is negative, acceleration is performed. Check if the exhaust brake is in use. This is because the exhaust brake is performed by using the exhaust pressure, and therefore it is not preferable to operate so as to reduce the exhaust pressure during use of the exhaust brake. The movable nozzle of the turbine 7 is fully closed. The rotation of the blower 6 drops and the supply of intake air to the engine decreases. Monitor whether the engine condition has dropped to idle and has arrived. This is because if it drops more than that, the engine may stop. It is monitored whether the boost pressure does not rise above the set value B _s . This is because if it goes up too high, the engine may be destroyed.

As described above, according to the exhaust gas recirculation system for a variable capacity turbocharged engine of the present invention, the exhaust gas for recirculation is taken out from the turbine inlet side of the variable capacity turbocharger and supplied to the blower discharge side. Since the exhaust gas for recirculation does not touch the blower impeller, the durability and reliability of the blower impeller are increased. Further, since the pressure on the turbine inlet side is higher than the pressure on the blower discharge side, and the means for controlling the movable nozzle of the turbine is provided so that the differential pressure from the pressure on the blower discharge side is within a predetermined range, exhaust gas is It is always supplied smoothly to the blower discharge side, and NOx reduction is properly performed.

[Brief description of drawings]

FIG. 1 ... EGR device for variable displacement turbocharged engine according to an embodiment of the present invention FIG. 2 ... Diagram showing connection relationship between turbine and step motor of variable displacement turbocharger according to the present invention FIG. FIG. 4 is a diagram showing the relationship between the exhaust gas flow rate and the pressure ratio in the variable displacement turbocharger using the opening of the movable nozzle as a parameter. FIG. 4 is a diagram showing the operating procedure of the present invention. Lever position map FIG. 6 ... Sectional view around the movable nozzle of the variable displacement turbocharger FIG. 7 ... View seen from XX direction in FIG. 6, where 1 is a rotation sensor, 2 is an engine, 3 is intake air Manifold, 4 exhaust manifold, 5 exhaust gas supply pipe for recirculation, 6 blower, 6'blower
Impeller, 7 turbine, 8 intake pipe, 9 intake manifold engine connection, 10 exhaust manifold engine connection, 11 air cleaner, 12 step motor, 13 controller, 14 load sensor, 15 Accelerator opening sensor, 16 flywheel housing, 17 pressure sensor for boost pressure measurement,
18 is a pressure sensor for measuring exhaust pressure, 19 is a link rod,
Reference numeral 20 is a return spring, 21 is a lever, 22 is a heat shield, 701 is an operating link, 702 is an operating shaft, 703 is an operating lever, 704 is a control ring, 705 is a control lever, 706 is a nozzle rotating shaft, and 707 is a turbine. A housing, 708 a movable nozzle, 709 a turbine wheel, 710 a free end and 711 a recess.

Claims (1)

[Claims] 1. A means for extracting exhaust gas for recirculation from a turbine inlet side of a variable capacity turbocharger and supplying it to a blower discharge side, and a pressure at the turbine inlet side higher than a pressure at the blower discharge side, and said blower. A variable displacement turbocharger, comprising: a means for controlling the movable nozzle of the turbine such that the pressure difference between the discharge side pressure and the discharge side pressure is within a range between a predetermined lower limit value and a predetermined upper limit value. Exhaust gas recirculation system for engine.