Method of Controlling a Throttle Valve and a Throttle Valve Opening Control Device

The present invention relates to a method and a device for controlling the opening operation of the throttle valve of a carburetor in an internal combustion engine.

When the throttle valve of the carburetor is rapidly closed as in the case wherein a vehicle is decelerated, the vacuum level in the intake manifold becomes extremely high. As a result of this, the liquid fuel stuck to the inner wall of the intake manifold is vaporized, whereby an extremely rich air-fuel mixture is fed into the cylinder of the engine. This results in a misfire occurring and, thus, a large amount of unburned HC and CO components is discharged into the exhaust system of the engine. In addition, at this time, if there is a hot spot in the exhaust system of the engine, there occurs a problem in that an after-burn is caused.

In order to prevent an extremely rich air-fuel mixture from being fed into the cylinder of the engine particularly when a vehicle is decelerated, there has been known a throttle valve opening control device in which, when the throttle valve is rapidly closed, the throttle valve temporarily remains opened at a predetermined opening degree and, then, the throttle valve is returned to the idling position. In an engine adoping such a throttle valve opening control device, when the throttle valve is rapidly closed, the vacuum level in the intake manifold does not become so great and, as a result, the air-fuel mixture fed into the cylinder of the engine does not becomes so rich. As is mentioned above, in a conventional engine, the occurrence of misfire is prevented in such a way that, when the throttle valve is rapidly closed, the throttle valve temporarily remains opened at a predetermined opening degree for a fixed time length, irrespective of whether the warm-up of the engine is completed or not.

However, before completion of the warm-up of the engine, in general, a rich air-fuel mixture is formed into the carburetor and, in addition, a satisfactory vaporization of the fuel cannot be obtained since the temperature of the engine is relatively low. As a result of this, a large amount of liquid fuel is stuck to the inner wall of the intake manifold. Consequently, in an engine equipped with a conventional throttle value opening control device, when a vehicle is decelerated before completion of the warm-up of the engine, even if the throttle valve is returned to the idling position after the throttle valve temporarily remains opened at a predetermined opening degree for a fixed time length, the liquid fuel remains on the inner wall of the intake manifold when the throttle valve is returned to the idling position. This results in a misfire occurring and, as a result, a large amount of unburned HC and CO components is discharged into the exhaust system of the engine, thereby causing an after-burn.

On the other hand, as is known to those skilled in the art, in an engine provided with a catalytic converter used for purifying the exhaust gas, if the temperature of the catalyzer is lower than a predetermined high level, a satisfactory purifying efficiency of the catalyzer can not be obtained. Consequently, the purifying efficiency is very low before completion of the warm-up of the engine since the temperature of the catalyzer is relatively low. Consequently, even if an engine is provided with a catalytic converter, a large amount of unburned components discharged into the atmosphere.

As a method for eliminating this disadvantage, there is a method of elongating the length of time during which the throttle valve temporarily remains opened at a predetermined opening degree at the time of deceleration. However, this method causes a problem in that a satisfactory effectiveness of engine-braking can not be obtained when a vehicle is decelerated after completion of the warm-up of the engine.

An object of the present invention is to prevent the occurrence of an after-burn caused at the time before completion of the warm-up of the engine while obtaining a good drivability of a vehicle after completion of the warm-up of the engine.

According to the present invention, there is provided a throttle valve control device of an internal combustion engine which has a carburetor with a throttle valve in an intake passage, which device comprises:

control means for temporarily holding the throttle valve during a first length of time at a predetermined opening degree, which is slightly greater than an idling opening degree of the throttle valve when the throttle valve is rapidly closed after completion of the warm-up of the engine, and for temporarily holding the throttle valve at the predetermined opening degree during a second length of time, which is longer than said first length of time when the throttle valve is rapidly closed before completion of the warm-up of the engine;

first restricting means having a first restricted opening for restricting the flow rate of the air flowing in said first restricted opening; second restricting means having a second restricted opening with an opening area which is smaller than that of said first restricted opening for further restricting the flow rate of the air flowing in said second restricted opening as compared with said first restricting means;

switching means for selectively interconnecting said control means with the atmosphere via either of said first restricting means or said second restricting means in response to the temperature of the engine, and;

a resilient member for urging the throttle valve towards its idling position.

In addition, according to the present invention, there is provided a method for controlling a throttle valve of a carburetor of an internal combustion engine comprising the steps of:

temporarily holding the throttle valve during a first length of time at a predetermined opening degree, which is slightly greater than an idling opening degree of the throttle valve when the throttle valve is rapidly closed after completion of the warm-up of the engine, and temporarily holding the throttle valve at the predetermined opening degree, during or second length of time which is longer than said first length of time when the throttle valve is rapidly closed before completion of the warm-up of the engine, and;

gradually returning the throttle valve to its idling position.

The present invention may be more fully understood from the description of preferred embodiments of the invention presented below, together with the accompanying drawings.

In the drawings:

FIG. 1 is a schematic view of an embodiment of a throttle valve opening control device according to the present invention, and;

FIG. 2 is a schematic view of an alternative embodiment according to the present invention.

Referring to FIG. 1, 1 designates an engine body, 2 an intake manifold, 3 a carburetor, 4 a throttle valve, and 5 a diaphragm apparatus. This diaphragm apparatus has in its housing a damper chamber 7 and an atmospheric pressure chamber 8 which are separated by a diaphragm 6. A compression spring 9 is disposed in the damper chamber 7, and the diaphragm 6 is always biased towards the left in FIG. 1 due to the spring force of the compression spring 9. The atmospheric pressure chamber 8 is connected to the atmosphere via an opening 10 and, in addition, a control rod 11 passing through the atmospheric pressure chamber 8 and extending outwardly from the housing of the diaphragm apparatus 5 is rigidly fixed onto the diaphragm 6. An arm 13 is fixed onto a throttle shaft 12 of the throttle valve 4 so as to rotate together with the throttle valve 4. An adjust screw 14 is screwed into the upper end of the arm 13, and the control rod 11 is so arranged that its tip faces the adjust screw 14. A tension spring 15 is disposed between the arm 13 and the stationary wall of the intake manifold 2 so that the arm 13 is always urged in the clockwise direction in FIG. 1 due to the spring force of the tension spring 15. In FIG. 1, reference numeral 16 designates an electromagnetic switching valve, 17 a first delay valve, and 18 a second delay valve. The electromagnetic switching valve 16 comprises a housing 19, a valve chamber 20 formed in the housing 19, a movable plunger 21 movable in the housing 19, a solenoid 22 serving to attract the movable plunger 21, a compression spring 23 always biasing the movable plunger 21 towards the left in FIG. 1, and a valve head 24 disposed in the valve chamber 20 and connected to the movable plunger 21 via a valve stem 25. A pair of valve ports 26 and 27 arranged to face the valve head 24 open into the valve chamber 20, and this valve chamber 20 is connected to the damper chamber 7 of the diaphragm apparatus 5 via a conduit 28. The solenoid 22 of the electromagnetic valve 16 is connected to a temperature detecting switch 29 detecting the temperature of the coolant of the engine on one hand, and to a power source 31 via an ignition switch 30. The temperature detecting switch 29 is turned to the ON condition when the temperature of the coolant of the engine is lowered below a predetermined level, for example 40.degree. C, while the temperature detecting switch 29 is turned to the OFF condition when the temperature of the coolant of the engine is elevated beyond the above-mentioned predetermined level. Consequently, the solenoid 22 remains energized until the time the temperature of the coolant of the engine attains the predetermined level after the engine is started by operating the ignition switch 30 and, as a result, the movable plunger 21 moves towards the right in FIG. 1 due to the attracting force of the solenoid 22. As a result of this, the valve head 24 opens the valve port 26 and closes the valve port 27. Contrary to this, when the temperature of the coolant of the engine is elevated beyond the predetermined level, the solenoid 22 is de-energized and, as a result, the valve head 24 is returned to the position shown in FIG. 1. At this time, the valve head 24 closes the valve port 26 and opens the valve port 27.

The first delay valve 17 has in its housing an upper chamber 40 and a lower chamber 41 which are separated by a partition 39. The upper chamber 40 is connected to the valve port 27 via a conduit 42 and, on the other hand, the lower chamber 41 is connected to the atmosphere via an air filter 43. A check valve 44 permitting the outflow of air from the lower chamber 41 to the upper chamber 40 is mounted on the partition 39 and, in addition, a first restricted opening 45 is formed on the partition 39.

Similar to the first delay valve 17, the second delay valve 18 has in its housing an upper chamber 33 and a lower chamber 34 which are separated by a partition 32. The upper chamber 33 is connected to the valve port 26 via a conduit 35 and, on the other hand, the lower chamber 34 is connected to the atmosphere via an air filter 36. A check valve 37 permitting the outflow of air from the lower chamber 34 to the upper chamber 33 is mounted on the pertition 32 and, in addition, a second restricted opening 38 is formed on the partition 39. The first restricted opening 45 of the first delay valve 17 is set so as to have an opening area larger than that of the second restricted opening 38 of the second delay valve 18.

As is mentioned above, when the temperature of the coolant of the engine is higher than the predetermined level, the valve head 24 of the electromagnetic switching valve 16 is in the position shown in FIG. 1. Consequently, at this time, the damper chamber 7 of the diaphragm apparatus 5 is connected to the atmosphere via the first restricted opening 45 and, thus, the pressure in the damper chamber 7 is equal to the atmospheric pressure.

FIG. 1 shows a moment when the throttle valve 4 is closed after the throttle valve 4 is opened to a great extent and, then, the adjust screw 14 of the arm 13 abuts against the tip of the control rod 11. At this time, the throttle valve 4 is held open at an opening degree which is slightly greater than the idling opening degree shown by the broken line in FIG. 1. Then, the control rod 11 is urged towards the right in FIG. 1 due to the spring force of the tension spring 15 and, as a result, the air contained in the damper chamber 7 is gradually discharged into the atmosphere via the first restricted opening 45. Consequently, the throttle valve 4 is gradually closed and is returned to the idling position. After this, when the throttle valve 4 is opened, since air can freely enter into the damper chamber 7 from the atmosphere via the check valve 44, the diaphragm instantaneously moves towards the left in FIG. 1 due to the spring force of the compression spring 9 and the control rod 11 projects at its most projecting position. By communicating the damper chamber 7 with the atmosphere via the first restricted opening 45 as is shown in FIG. 1, the throttle valve 4 can be gradually closed from the position shown by the solid line in FIG. 1 to the idling position shown by the broken line in FIG. 1.

When the temperature of the coolant of the engine is lower than the predetermined level, the solenoid 22 is energized. Consequently, at this time, the damper chamber 7 is connected to the atmosphere via the second restricted opening 38. In this case, in the same manner as in the case wherein the damper chamber 7 is connected to the atmosphere via the first restricted opening 45, the throttle valve 7 is gradually closed after the throttle valve 4 comes into engagement with the control rod 11. However, as was stated previously, the second restricted opening 38 is set so as to have an opening area smaller than that of the first restricted opening 45. Consequently, the length of time necessary to push out the air in the damper chamber 7 into the atmosphere via the second restricted opening 38 is longer than the length of time necessary to push out the air in the damper chamber 7 into the atmosphere via the first restricted opening 45. As a result of this, when the temperature of the coolant of the engine is lower than the predetermined level, the throttle valve 4 is closed more slowly as compared with the case wherein the temperature of the coolant of the engine is higher than the predetermined level and, as a result, a large amount of air is introduced into the intake manifold 2. Therefore, in this case, while a large amount of the liquid fuel stuck to the inner wall of the intake manifold 2 is gradually vaporized into the introduced air, the air-fuel mixture fed into the cylinder of the engine does not become excessively rich because a large amount of air is introduced into the intake manifold 2. Then, when the throttle valve 4 is returned to the idling position, almost all of the liquid fuel stuck to the inner wall of the intake manifold 2 has been vaporized and, as a result, there occurs no danger that the air-fuel mixture fed into the cylinder of the engine becomes excessively rich.

FIG. 2 shows an alternative embodiment according to the present invention. In FIG. 2, similar components are indicated with the same reference numerals as used in FIG. 1. Referring to FIG. 2, a lever 50 is pivotably mounted on the housing of the intake manifold 2 by means of a pivot pin 51, and the tip of the control rod 11 is pivotably connected to the upper end of the lever 50. On the other hand, an adjust screw 52 is screwed into the lower end of the lever 50 and is arranged so as to face a cam face 53 of the arm 13. Consequently, when the throttle valve 4 is closed and the adjust screw 52 abuts against the cam face 53 of the arm 13, the lever 50 slowly rotates in the clockwise direction in FIG. 2 since the arm 13 is urged in the clockwise direction due to the spring force of the tension spring 15. As a result of this, the throttle valve 4 is gradually closed. When the lever 15 rotates to reach the position shown by the broken line in FIG. 2, the adjust screw 52 is disengaged from the cam face 53, whereby the throttle valve 4 is returned to the idling position shown by the broken line in FIG. 2. In this embodiment, in the same manner as in the embodiment shown in FIG. 1, the air contained in the damper chamber 7 is gradually pushed out into the atmosphere via the restricted opening 38 or 45 due to the spring force of the tension spring 15. Consequently, when the temperature of the coolant of the engine is lower than the predetermined level, the throttle valve 4 is closed more slowly as compared with the case wherein the temperature of the coolant of the engine is higher than the predetermined level. In the embodiments shown in FIGS. 1 and 2, the temperature of the coolant of the engine is detected by the temperature detecting switch 29. However, instead of detecting the temperature of the coolant of the engine, any other temperature, such as the temperature of the lubricating oil of the engine, the temperature of the exhaust gas, the temperature of the cylinder block of the engine, the temperature in the engine compartment and the temperature of the fuel, may be detected by the temperature detecting switch 29.

According to the present invention, when the throttle valve is rapidly closed before completion of the warm-up of the engine, an excessively rich air-fuel mixture can be prevented from being fed into the cylinder of the engine. As a result of this, the amount of unburned HC and CO components in the exhaust gas can be reduced and the occurrence of an after-burn can be prevented. In addition, when the throttle valve is rapidly closed after completion of the warm-up of the engine, the throttle valve is more rapidly closed to its idling position as compared with the case wherein the throttle valve is closed to its idling position before completion of the warm-up of the engine. As a result of this, a satisfactory effectiveness of an engine-braking can be obtained after completion of the warm-up of the engine.

While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by these skilled in the art without departing from the spirit and scope of the invention.