JPS61205331A - Air pressure control mechanism of variable turbocharger - Google Patents

Abstract

PURPOSE:To enable a flow of exhaust gas to be automatically controlled, by changing a Mach number of gas, which passes through Venturi tubes connected with a scroll inlet part of a divided type full circumferential inflow turbine in a turbocharger, in accordance with a change of a flow of exhaust and variably generating the total static pressure ratio. CONSTITUTION:When the captioned mechanism is applied to a four-cylinder engine, the engine, considering its firing order, arranges exhaust manifolds of two front and rear cylinders and two inner side cylinders to respectively join, connecting each exhaust duct D1, D2 with an inlet of an exhaust turbine T. This exhaust turbine T, being formed in a divided type full circumferential inflow turbine, provides a gas automatic control mechanism to be interposed between two flow paths S1, S2 of a turbine scroll S. Said control mechanism, communicating with each flow path S1, S2, is constituted by providing Venturi tubes V1, V2 while a communication hole H communicating with the both tubes V1, V2 in the narrowest part wall. In this way, the air pressure is automatically controlled by changing the total static pressure ratio in accordance with a Mach number of exhaust gas passing through the Venturi tubes V1, V2 and changing by a flow of exhaust.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pneumatic control mechanism for varying the turbine capacity of a turbocharger. ``Turbine scroll or fixed nozzle vane turbochargers have a narrow operating range (off-design efficiency is low. Therefore, when matched to the high speed of the engine, low speed performance and part load performance will deteriorate, and the adoption of a wastegate valve will result in poor off-design efficiency. Matching at low speeds causes loss of exhaust energy at high speeds, resulting in poor fuel efficiency.

Various variable turbochargers have been proposed to solve this problem. However, the conventionally proposed ones have mechanically movable parts in the variable mechanism,
Since a drive system is also required to move this, the structure is complicated and expensive. Therefore, although variable turbochargers improve fuel efficiency in high engine speed ranges, they have not yet become widespread.

The present invention has been made in view of the above points, and has a simple structure in which the variable mechanism has no mechanically moving parts and automatically controls the behavior of the fluid by the gas flow itself. The aim is to provide the world with an inexpensive variable turbocharger.

The present invention provides a mechanism for automatically controlling the gas flow rate at the scroll inlet portion of a turbocharger in which the flow path of the turbine scroll is divided in the longitudinal direction of the axis of the turbine impeller.

The variable mechanism has a plurality of scroll passages each connected to a bench pipe, and a throat of the plurality of bench pipes is provided with a communication hole for allowing them to flow, and the mechanically moving parts are do not have. The control adjustment of the gas flow rate introduced into each turbine scroll passage utilizes the phenomenon that the ratio between the total fluid pressure and the static pressure changes significantly depending on the Matsuha number.
It is characterized by substantially changing the cross-sectional area of the throat portion of the turbine scroll by increasing or decreasing the gas flow rate.

FIG. 1 shows an embodiment of the present invention. In the diagram, E is the engine, M+, Me is the exhaust manifold, DI, D
, is the exhaust duct. In the illustrated example of a four-cylinder engine, the exhaust manifolds of the two front and rear cylinders and the two inner cylinders are brought together in consideration of the ignition order, and two exhaust ducts D11D-
Exhaust gas can be supplied to the exhaust turbine T separately.

The exhaust turbine T is a split type full-circle inflow turbine and till
As shown in the figure, the flow path of the turbine scroll S is divided into St and 88 in the axial longitudinal direction of the turbine wheel. Therefore, the exhaust gas supplied from the exhaust duct D1 is ejected from the passage S of the scroll S, and the exhaust gas supplied from the exhaust duct D is ejected from the passage S to the exhaust turbine T. C is a compressor coaxial with the exhaust turbine T.

The present invention provides a dynamic pressure supercharging turbocharger as described above, in which the gas flow rate is automatically controlled between the two exhaust ducts D, D, and the two flow paths S, S, of the turbine scroll S. A control mechanism is involved.

Its structure consists of two Benchelli tubes V, , V, each with a narrowed cross-sectional area, arranged in parallel, the throat of the Benchelli tube being made longer, and a communication system that allows vI%V to flow through the narrowest wall. Hole H
It is worn with. In FIG. 1, the circular part drawn out is the A-A cross section of the Venturi tube v8, and shows the arrangement of the throat and the communication hole H.

Next, the principle of how the present invention can automatically control air pressure will be explained.

In the embodiment shown in FIG. 1, the turbine capacity changes in two stages.

When the exhaust gas supplied from one exhaust duct flows through one venturi pipe in the low engine speed range, if there is almost no leakage from the communication hole H into the adjacent flow path,
Assuming that it can pass through, the exhaust gas from each cylinder is
Most of the exhaust gas is ejected from the exhaust turbine TVc from one of the flow paths of the turbine scroll S.

In the engine high speed range, if the exhaust gas supplied from one exhaust duct is distributed to the adjacent venturi pipe through the communication hole H, the exhaust gas for each cylinder will be:
Since the exhaust turbine TK is ejected from both flow paths S, , S, of the turbine scroll S, the cross-sectional area of the throat portion of the turbine scroll is substantially doubled.

If the flow rate of gas flowing through the communication hole H can be controlled by increasing or decreasing the exhaust flow rate in this way, the turbine capacity can be increased by 2.
It is possible to change it in stages.

The element devices that control the flow rate of gas flowing through this communication hole H are the turbine scroll S itself, which has a fixed shape, and the pentaeri tube V3. It is VP.

The flow velocity of the exhaust gas is the sonic velocity immediately after the exhaust valve opens. The gas flow rate during blowdown, when most of the exhaust gas flow flows out of the cylinder, is Matsuha 1. The reason for using a Venturi tube in the present invention is to increase the gas flow rate and to take advantage of the natural phenomenon that the ratio of the total pressure of the fluid to the static pressure changes significantly depending on the Matsusa number. It is.

The ratio of the total pressure P of the fluid to the static pressure P is obtained by the following equation when the gas flow velocity is expressed by the Matsush number M.

Now, in the engine's low speed rotation range (including the high speed and low load range in the case of gasoline engines), exhaust gas flows smoothly through the turbine scroll S,
Assuming that the gas flow velocity at the throat reaches Matsuha 1.8 due to the tting effect, the ratio of total pressure P to static pressure P is, assuming the specific heat ratio to be 1.3, PO93 part (1+ -X 1 .8”) = 5.5
6P 2 Therefore, in the above assumption, the flow rate of exhaust gas that passes through the venturi pipe as it is, and the flow rate of the adjacent bench from the communication hole H, I
The ratio of gas flow rate leaking into the J pipe is 5.5 from the pressure direction.
It can be considered that the ratio is 6:1.

From the above, during blowdown, most of the gas flow goes straight through the Ventili tube, but 1/6.56 of the gas flow
, about 15% is wasted.

In the latter half of the exhaust process, when the flow rate of exhaust gas decreases,
Although the leakage ratio increases, the leakage loss during blowdown, when most of the exhaust gas flows out of the cylinder, can be reduced.
It will need to be evaluated.

We believe that comparing and examining the dynamic pressure energy loss in the current hydrostatic supercharging turbocharger, in which the turbine scroll has one flow path, and the leakage loss in the present invention will serve as a guideline.

The flow rate of the exhaust gas during blowdown is Matsuha 1 as described above. If the ratio of dynamic pressure ΔP and static pressure P is expressed in Matsuh number = 1.3, then dynamic pressure ΔP reaches 39% of the total pressure P, which is compared to conventional static pressure supercharging that does not use low-speed gas pulses. It can be seen that the dynamic pressure loss of the turbocharger is larger than that of the present invention during blowdown.

In addition, when the venturi tube's restriction is strengthened and the gas flow velocity is set to Matsuha 2, the total pressure static pressure ratio is 7.65, and when the Matsuha is set to 2.5, the pressure ratio is 17.53. Needless to say, leakage loss is reduced.

Next, in a high engine speed range, the flow of exhaust gas is close to a steady state and has a large flow rate.

Since the shape of the turbine scroll S is fixed, if the throat cross-sectional area is determined by setting a design point at a small flow rate, the pressure at the scroll inlet increases. The turbine scroll S senses the gas flow rate and sends a signal to the venturi tube in the form of a pressure increase. When the pressure at the scroll inlet increases, the gas flowing through the Venturi tube can no longer be considered an incompressible fluid, and the throttle of the Venturi tube increases.
ng effect is lost. Now, the gas flow rate is Matsuha 0.51C
Assuming that, the ratio of total pressure P to static pressure P changes as follows.

In the above assumption, the exhaust gas is roughly divided into two parts by the communication hole H,
It can be seen that the exhaust turbine TK is ejected from the two flow paths 81°S of the turbine scroll S at the same time.

In other words, the cross-sectional area of the throat portion of the turbine scroll S is substantially doubled.

Since it is only one assumption that the flow velocity of exhaust gas at a large flow rate is Matsuha IO,S, how the ratio of total pressure P to static pressure P changes depending on the Matsuha number of the fluid is a second assumption. As shown in the figure. The graph was calculated using 1.3. As shown in the figure, the rate of change in P/P is significantly different between J/>1 and Af<1.

From the above, the present invention performs pneumatic pressure control by utilizing the natural phenomenon that the Matsuha number of the gas passing through the pliers pipe changes by increasing or decreasing the exhaust flow rate, and the total pressure static pressure ratio changes depending on the Matsuha number. It has many mechanical moving parts. Therefore, the variable turbocharger has a simple structure and is inexpensive, contributing to energy saving.

It goes without saying that if the turbine scroll is divided into three parts, three ventili tubes are not required, and a communication hole for communicating these three pipes can be bored in the throat wall.

[Brief explanation of the drawing]

FIG. 1 is a partial longitudinal cross-sectional schematic diagram showing an embodiment of the present invention, and FIG. 2 is a graph of the Matsuzha number and the total pressure static pressure ratio. C: Compressor, DI%D,: Exhaust duct, E: Engine, H: Communication hole, Ml, Me'', exhaust manifold, S: Turbine scroll, S, , S,: S flow path,
T: tlF air turbine V, , V, : Vencheri tube.

Claims (1)

[Claims] The number of venturi tubes equal to the number of flow paths of the scrolls is connected to the scroll inlet of a split-type all-around inflow turbine in which the flow path of the turbine scroll is divided in the longitudinal direction of the turbine wheel axis, and the throat of the venturi tube is made longer. The Mach number of the gas passing through the throat of the Venturi pipe changes depending on the engine operating conditions, and the total pressure static pressure ratio of the gas changes depending on the Mach number. A variable turbocharger pneumatic control mechanism that uses changing natural phenomena to control and adjust the flow rate of gas flowing through a communication hole, thereby changing the turbine capacity.