JPH04132832A - Intake/exhaust structure of engine - Google Patents

Abstract

PURPOSE:To prevent blow-off of fresh air by rapidly closing an exhaust valve when a variation rate of an exhaust temperature sensor detection value in relation to the time is smaller than a negative judging standard value preliminarily set. CONSTITUTION:An exhaust port 7 provided on the ceiling face of a combustion chamber 5 is opened and closed by an exhaust valve 8 in an upper course uniflow type two-cycle engine CE, and an intake port 6 provided on the side wall of a cylinder 3 is opened and closed by a piston 4. An exhaust temperature sensor 21 which detects exhaust gas temperature is provided in an exhaust passage 11. When a variation rate of a detection value of the exhaust temperature sensor 21 in relation to the time is smaller than a negative judging standard value preliminarily set, a control unit 20, rapidly closes the exhaust valve 8 by an exhaust valve opening/closing timing variation means 12. Consequently, when exhaust gas temperature starts to decrease, namely when blow-off of fresh air is generated, since a valve closing timing of the exhaust valve 8 is quickened, generation of the blow-off of the fresh air can be prevented before is happens.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an intake and exhaust structure for a two-stroke engine.

[Prior Art] In a conventional two-stroke engine, an intake port and an exhaust port are provided on the side surface of the combustion chamber (inner peripheral surface of the cylinder) near bottom dead center, and both ports are opened and closed by the side surface of the piston. (For example, JP-A-62-1
(See Publication No. 13820).

However, in such conventional two-stroke engines, ■Since the intake port and exhaust port are both located near bottom dead center, the upper part of the combustion chamber tends to become a dead space, and combustion gas remains in this area. ■The heat load around the exhaust port increases, which may cause distortion in the cylinder due to heat damage.■The oil in the cylinder is pushed out to the exhaust port by the flow of exhaust gas, causing oil There were problems such as an increase in consumption (LQC).

In order to solve the above problems, a two-stroke engine has been proposed in which an exhaust port is provided on the ceiling surface (cylinder head) of the combustion chamber, and the exhaust port is opened and closed by an exhaust valve. In such a two-stroke engine,
Since a so-called uniflow is formed in which both fresh air and combustion gas flow unilaterally upward within the combustion chamber, no dead space is generated and scavenging can be performed completely. In addition, the cylinder will not be distorted due to heat damage, and oil will not leak from the exhaust port.

[Problems to be Solved by the Invention] However, in a two-stroke engine in which the exhaust port is opened and closed by an exhaust valve, fresh air may blow into the exhaust port during scavenging. Engines in which intake air is supercharged by a charger have a problem in that fresh air blows through when the boost pressure changes. Incidentally, such a blow-by of fresh air naturally occurs in a two-stroke engine in which both ports are opened on the side of the cylinder.

When such fresh air blow-through occurs, the exhaust gas temperature decreases and the activity of the exhaust gas purification catalyst decreases.
There is a problem that the engine's emission performance deteriorates.

The present invention has been made to solve the above-mentioned problems of the conventional art, and includes an upward flow uniflow two-stroke engine in which the exhaust port is opened and closed by an exhaust valve.
An object of the present invention is to provide an intake and exhaust structure for an engine that can prevent fresh air from blowing through and improve emission performance.

[Means for Solving the Problems] In order to achieve the above object, the first invention opens and closes an exhaust port provided on the ceiling surface of a combustion chamber with an exhaust valve, and an intake port provided on a cylinder side wall with a piston. In an upward flow uniflow type two-stroke engine which is configured to open and close at the same time, an exhaust temperature sensor for detecting the exhaust gas temperature is provided, and the rate of change of the detected value of the exhaust temperature sensor over time is calculated and the rate of change is set in advance. To provide an engine intake and exhaust structure characterized in that an exhaust valve control means is provided to quickly close an exhaust valve when the value is smaller than a negative determination reference value.

The second invention is to supercharge intake air with a supercharger, open and close an exhaust port provided on the ceiling of the combustion chamber with an exhaust valve, and open and close the intake port provided on the side wall of the cylinder with a piston. In the upward flow uniflow type two-stroke engine, an exhaust temperature sensor is provided to detect the exhaust gas temperature, and a negative judgment criterion is set in advance by calculating the rate of change of the detected value of the exhaust temperature sensor over time. Provided is an engine intake and exhaust structure characterized in that a supercharging pressure control means is provided for lowering the supercharging pressure of a supercharger when the supercharging pressure is smaller than the above value.

A third invention is the first invention or the second invention, wherein an exhaust gas purification device and a catalyst temperature sensor for detecting the catalyst temperature of the exhaust gas purification device are provided, and the catalyst temperature sensor detects the catalyst temperature. An intake and exhaust structure for an engine is provided, characterized in that an intake air temperature control means for increasing the intake air temperature when the temperature is lower than a catalyst activation temperature is provided.

[Operations and Effects of the Invention] Generally, in a two-stroke engine, when fresh air blows through, the exhaust gas temperature decreases. Therefore, when the exhaust gas temperature begins to decrease, it is considered that fresh air blow-through begins to occur.

According to the first invention, the rate of change of the exhaust temperature sensor detection value with respect to time (hereinafter referred to as the exhaust temperature differential value)
is calculated, but this exhaust gas temperature differential value indicates the rate of increase or decrease in the exhaust gas temperature, so when the exhaust gas temperature differential value becomes a negative value, it means that the exhaust gas temperature is beginning to decrease. Become. Here, when the exhaust gas temperature differential value is smaller than a preset determination reference value (negative value), that is, when the rate of decrease in exhaust gas temperature is larger than the set value, the closing timing of the exhaust valve is advanced. In other words, when fresh air starts blowing through, the closing timing of the exhaust valve is immediately advanced, and the occurrence of fresh air blowing is prevented. Here, the exhaust temperature differential value has a very quick response to changes in exhaust gas temperature, so it can respond almost instantaneously to, for example, fresh air blowing caused by sudden changes in boost pressure. As a result, fresh air blow-through is almost completely prevented, and emission performance is improved.

Is it possible to consider a method that advances the closing timing of the exhaust valve when the exhaust gas temperature detected by the exhaust gas temperature itself drops?In this method, the exhaust gas temperature drops and after 1 hour, that is, the fresh air Since this will have to be corrected after a considerable amount of fresh air blows through, it is impossible to completely prevent fresh air from blowing through. In addition, the temperature detection part of the exhaust temperature sensor (for example, a thermocouple) has a heat capacity, and when the exhaust gas temperature changes during this time, there is a response delay in the detected value, so the exhaust gas temperature may fluctuate drastically. Sometimes, it is not possible to accurately detect the exhaust gas temperature, and it is not possible to effectively prevent fresh air from blowing through.

According to the second invention, the exhaust gas temperature differential value is basically calculated in the same process as the first invention, and when the exhaust gas temperature differential value is smaller than the judgment reference value (negative value), that is, when the exhaust gas temperature is When blow-by begins to occur, the supercharging pressure of the pumping machine is lowered. For this reason, the inflow velocity of fresh air into the combustion chamber or the flow velocity of fresh air within the combustion chamber is reduced, so as in the first invention, blow-by of fresh air is prevented, and emission performance is improved. It will be planned. Further, unnecessary increase in supercharging pressure is prevented, and fuel efficiency is improved.

According to the third invention, first of all, the first invention or the second invention
The same action and effect as the invention can be obtained.

Furthermore, when the temperature of the catalyst in the exhaust gas purification device is lower than the catalyst activation temperature, the intake air temperature can be raised by, for example, bypassing the intercooler in an engine equipped with a supercharger and supplying intake air. The gas temperature is raised, which quickly raises the catalyst temperature and further improves the emission performance.

[Example] Examples of the present invention will be specifically described below.

As shown in FIGS. 1 and 2, a two-stroke engine C
E includes a cylinder block 1 and a cylinder block l.
A cylinder head 2 fastened to the upper side of the cylinder head 2 is provided. A cylinder 3 is disposed within the cylinder block I, and a piston 4 is fitted into the cylinder 3 so that it can freely reciprocate in the cylinder axial direction between top dead center and bottom dead center. There is. Here, a combustion chamber 5 is defined by the lower end surface of the cylinder head 2, the inner surface of the cylinder 3, and the upper end surface of the piston 4.

An intake port 6 is provided on the side surface of the cylinder 3 at a position slightly above the upper end surface of the piston 4 at the bottom dead center position (Figures 1 and 2 show this state). The intake port 6 is opened and closed by the side surface of the piston 4. Further, an exhaust port 7 is provided on the ceiling surface (cylinder head 2) of the combustion chamber 5,
This exhaust port 7 is opened and closed at predetermined timing by an exhaust valve 8.

Here, in the stroke in which the piston 4 moves upward, after the intake port 6 is closed, the intake air in the combustion chamber 5 is compressed by the piston 4, and fuel is injected from the fuel injection valve 9 during the intake to form an air-fuel mixture. This air-fuel mixture is ignited and combusted by the spark plug 10. After passing the top dead center, the pressure generated by the combustion of the air-fuel mixture pushes down the technology stone 4, and this work is converted into rotational power of a rank shaft (not shown).

In this downward stroke of the piston 4, when the piston 4 descends to a predetermined position, the exhaust valve 8 is opened and combustion gas is discharged into the exhaust passage 11 via the exhaust port 7.

As will be explained later, the opening/closing timing of the exhaust valve 8 is controlled by the exhaust valve opening/closing timing variable means 12 in accordance with a signal from the control unit 20. Further, the exhaust gas is purified by an exhaust gas purification device 13 provided in the exhaust passage 11.

When the piston 4 further descends to near the bottom dead center, the intake port 6 is opened, and intake air (fresh air) is supplied from the intake port 6 into the combustion chamber 5, and this intake air is supercharged as explained later. Therefore, the combustion gas remaining in the combustion chamber 5 is pushed out to the exhaust port 7 for scavenging.

At this time, both the intake air and the combustion gas form a uniflow that flows unidirectionally upward, and no dead space is created.

In order to supply intake air into the combustion chamber 5, an intake passage 14 communicating with the intake port 6 is provided, and this intake passage I4 is connected to a supercharger 15 that supercharges the intake air, and a supercharger 15 that supercharges the intake air and whose temperature is reduced by adiabatic compression. An intercooler 16 is provided to cool the rising intake air. Further, a bypass intake passage 17 that bypasses the intercooler I6 is provided, and a switching valve 18 that opens and closes the bypass intake passage 17 is provided.

Then, the opening/closing timing of the exhaust valve 18 or the boost pressure of the supercharger 15 is controlled to prevent fresh air from blowing through, and the intake air temperature is controlled to prevent the catalyst temperature of the exhaust gas purification device 13 from decreasing. Performs intake and exhaust control such as
A control unit 20 is provided, and the control unit 20 contains, as control information, the exhaust gas temperature detected by a thermocouple exhaust temperature sensor 21 installed at the exhaust port 7 and the exhaust gas temperature detected by a thermocouple exhaust temperature sensor 21 installed at the catalyst of the exhaust gas purification device 13. The catalyst temperature detected by the thermocouple type catalyst temperature sensor 22 can be input. Note that the control unit 20 corresponds to the exhaust valve control means according to claim I, the boost pressure control means according to claim 2, or the intake air temperature control means according to claim 3,
It is equipped with a differentiation circuit 20a, an SCPU 20b, and the like.

Hereinafter, a method of controlling intake and exhaust gas by the control unit 20 will be explained according to the flowchart shown in FIG.

In step #1, the catalyst temperature Tc detected by the catalyst temperature sensor 22 is read.

In step #2, it is compared whether the catalyst temperature Tc is equal to or higher than the catalyst activation temperature. In this embodiment, when the catalyst temperature Tc is lower than the catalyst activation temperature, the switching valve 18 is opened to increase the intake air temperature.

As a result of the comparison in step #2, if the catalyst temperature Tc is equal to or higher than the catalyst activation temperature (YES), the activity of the catalyst has been sufficiently increased, and therefore there is no need to further increase the exhaust gas temperature, so step #2 3, the switching valve 18 is closed, and the relatively high temperature intake air discharged from the supercharger 15 is cooled by the intercooler 16. Therefore, the density of the intake air supplied to the combustion chamber 5 is increased, the charging efficiency is increased, and the engine output is increased. Thereafter, a routine for preventing fresh air from blowing in steps #5 and subsequent steps is executed.

On the other hand, as a result of the comparison in step #2, if the catalyst temperature Tc is lower than the catalyst activation temperature (NO), the switching valve 18 is opened in step #4 in order to raise the exhaust gas temperature and activate the catalyst early. It will be done. At this time, the relatively high-temperature intake air discharged from the supercharger 15 bypasses the intercooler I6 and is supplied to the combustion chamber 5, increasing the exhaust gas temperature, which increases the catalyst temperature and increases the catalyst temperature. It will be revitalized. Thereafter, a routine for preventing fresh air from blowing in step #5 and subsequent steps is executed.

In step #5, the detected value Tp of the exhaust temperature sensor 21 is read.

In step #6, the rate of change ΔTp/Δt of the exhaust temperature sensor detection value Tp with respect to time t, that is, heat flux (unit time, amount of heat flowing into the temperature detection part (thermocouple) of the exhaust temperature sensor 21 per unit area) is calculated.

As mentioned above, thermocouples have heat capacity, so when the exhaust gas temperature changes, the exhaust gas temperature sensor detection value T
Either p is inevitably accompanied by a time delay, or the heat flux responds to changes in the exhaust gas temperature with almost no time delay, so changes in the exhaust gas temperature can be detected from the heat flux without any response delay. In this embodiment, when the heat flux is smaller than a preset negative judgment reference value, that is, when the rate of decrease in exhaust gas temperature is large, it is considered that fresh air is starting to blow through, so the exhaust valve 8 The opening/closing timing of the supercharger 15 is advanced or the supercharging pressure of the supercharger 15 is lowered to prevent fresh air from blowing through.

In step #7, a comparison is made to determine whether the heat flux is smaller than a determination reference value (negative value), that is, whether fresh air is beginning to blow through.

As a result of the comparison in step #7, if fresh air is blowing through (YES), the opening/closing timing θC of the exhaust valve 8 is advanced (advanced) by a preset increment Δθ in step #9. On the other hand, if there is no fresh air blowing through (
NO), the opening/closing timing θC is retarded by 80 in step #8. In other words, if there is a blow-through of fresh air,
Feedback control is performed in which the opening/closing timing is advanced by Δθ until this does not occur, and if no fresh air blow-through occurs, the opening/closing timing is gradually retarded by Δθ.
The air inside the tank is completely scavenged and kept in an optimal state to prevent fresh air from blowing through. In Figure 4,
When such opening/closing timing control of the exhaust valve 8 is performed, the opening/closing characteristics of the intake port 6 (curve G,) and the opening/closing characteristics of the exhaust valve 8 at maximum retard (late closing) (curve C,) and the opening/closing characteristics of the exhaust valve 8 at maximum advance (early closing) (curve G
3).

Such opening/closing timing control of the exhaust valve 8 is performed, preventing fresh air from blowing through, preventing a decrease in exhaust gas temperature, and improving the emission performance of the engine CE.

Furthermore, instead of controlling the opening/closing timing of the exhaust valve 8, as shown in steps #10 to #12, the supercharging pressure of the supercharger 15 is controlled to prevent fresh air from blowing through. You can do it like this.

In this case, it is compared in step #lO whether or not fresh air blow-through has occurred, and if fresh air blow-through has occurred (Y
ES), in step #12, the supercharging pressure P is lowered by a preset increment ΔP to reduce the flow velocity of fresh air in the combustion chamber 5 to prevent blow-through, and if fresh air blow-through has not occurred (NO ), and in step #11, feedback control of the supercharging pressure is performed such that the supercharging pressure P is increased by ΔP.

In this case, as in the case of the opening/closing timing control in steps #7 to #9, occurrence of fresh air blow-through is prevented and emission performance is improved.

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram of a two-stroke engine equipped with an intake and exhaust structure according to the present invention. FIG. 2 is a partially cutaway and elevational explanatory view of the main parts of the engine shown in FIG. 1. FIG. 3 is a flowchart showing a method of controlling intake and exhaust control by the control unit. FIG. 4 is a diagram showing the characteristics of the opening/closing timing of the intake port and the opening/closing timing of the exhaust valve with respect to the crank angle. CE...Engine, ■...Cylinder block, 2.
・. Cylinder head, 3. Cylinder, 4.. Piston, 5.
・・Combustion chamber, 6・・Intake port, 7・・Exhaust port,
8 - Exhaust valve, 11... Exhaust passage, I2... Exhaust valve opening/closing timing variable means, 13... Exhaust gas purification device, 14
...Intake passage, 15...Supercharger, 16...Intercooler, 17...Bypass intake passage, 18...Switching valve, 20...Control unit, 20a...
- Differential circuit, 20b...CPU, 21...Exhaust temperature sensor, 22...Catalyst temperature sensor.

Claims (3)

[Claims] (1) In an upward flow uniflow two-stroke engine in which an exhaust valve opens and closes the exhaust port on the ceiling of the combustion chamber, and a piston opens and closes the intake port on the side wall of the cylinder, the exhaust gas temperature Exhaust valve control means is provided with an exhaust temperature sensor for detecting the exhaust temperature sensor, calculates the rate of change of the detected value of the exhaust temperature sensor over time, and closes the exhaust valve early when the rate of change is smaller than a preset negative judgment reference value. An engine intake and exhaust structure characterized by having the following features: (2) While the intake air is supercharged by the turbocharger, the exhaust port provided on the ceiling of the combustion chamber is opened and closed by an exhaust valve, and the intake port provided in the cylinder side wall is opened and closed by a piston. In a uniflow type two-stroke engine, an exhaust temperature sensor is provided to detect the exhaust gas temperature, and the rate of change of the detected value of the exhaust temperature sensor over time is calculated and the rate of change is smaller than a preset negative judgment reference value. An intake and exhaust structure for an engine, which is sometimes equipped with a boost pressure control means for lowering the boost pressure of a supercharger. (3) In the engine intake and exhaust structure according to claim 1 or 2, an exhaust gas purification device and a catalyst temperature sensor for detecting the catalyst temperature of the exhaust gas purification device are provided, and the catalyst temperature sensor detects the temperature. An intake/exhaust structure for an engine, characterized in that an intake/exhaust structure for an engine is provided, the intake/exhaust structure being provided with an intake air temperature control means for increasing the intake air temperature when the catalyst temperature is lower than the catalyst activation temperature.