JPH08284668A - Engine having mechanical supercharger - Google Patents

Abstract

PURPOSE: To improve fuel consumption characteristics of acceleration responsive ness in low speed rotation area of an engine which has a mechanical super charger and is supercharged by the supercharger at least under high load, by reducing mechanical loss of the supercharger in a high speed and high load area. CONSTITUTION: An actual closing timing of an intake valve is set at the time when a crank angle is delayed by 40 to 50 degrees from a bottom dead center. An intake passage capacity on a downstream side of a mechanical supercharger 11 is set to be a value with which resonance effect of dynamic supercharge is obtained in high speed rotation area. Independent intake passages 7a to 7d of cylinders 2a to 2d are connected with a collection part 8 which does not have a volume enlargement chamber. Capacity of the independent intake passages 7a to 7d are set to be values with which inertial supercharge effect is obtained at high speed rotation area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine equipped with a mechanical supercharger, and more particularly to an improvement of its intake system.

[0002]

2. Description of the Related Art Conventionally, an engine having a supercharger for supercharging intake air has been put into practical use in order to increase the intake charge amount of the engine. As the supercharger, a turbine linked to a compressor is used. A turbocharger driven by exhaust gas and a mechanical supercharger (supercharger) in which a compressor is driven by an engine output shaft are known.

An intake system utilizing the dynamic supercharging effect of intake air such as the inertia supercharging effect or the resonance supercharging effect is known as a means for increasing the output of the engine. This intake system resonates the pressure wave of the intake.
In this system, a pressure wave is generated immediately before the intake valve is closed to enhance the charging efficiency of intake air.In such an intake system, a volume expansion chamber such as a surge tank is provided upstream of the independent intake passage. When the intake valve is opened, the intake negative pressure wave propagated from the combustion chamber through the intake port to the upstream side in the independent intake passage at the sonic velocity is reversed in the volume expansion chamber. The inertia supercharging effect is obtained by the configuration in which the inverted positive pressure wave propagates downstream and reaches the downstream end of the intake port immediately before the intake valve closes.

Further, as in the high compression ratio engine with a supercharger described in Japanese Patent Laid-Open No. 3-138416, the shape of the independent intake passage for each cylinder has an inertia supercharging action generated by the independent intake passage. Independent intake air is set in the high load range, especially in the high speed range where intake is likely to occur before the closing timing of the intake valve, by setting the tuning speed of the engine to be in the higher speed range than the engine speed that produces maximum horsepower. The adiabatic compression effect due to the absence of inertial action in the passage is reduced,
Those with improved knock resistance are also proposed.

[0005]

By the way, the turbocharger has a drawback that the efficiency is good in a high rotation and high load range, but the responsiveness is low in a low rotation range. Have difficulty. On the other hand, the mechanical supercharger has an advantage that it has excellent responsiveness in a low rotation and high load range.
There is a drawback in that the mechanical loss increases as the pressure in the discharge side intake passage increases in the high rotation and high load region, the horsepower of the engine is consumed, and the fuel consumption characteristics deteriorate.

Therefore, it can be said that the mechanical supercharger is an extremely excellent supercharger if the point that the fuel consumption characteristic in the high rotation and high load range is deteriorated is corrected.

On the other hand, if a volume expansion portion such as a surge tank for reversing the intake negative pressure wave is provided in the intake passage in order to obtain the inertia supercharging effect, the acceleration response in the low speed rotation range deteriorates. There is.

It is known that the synchronized rotational speed of inertial supercharging is determined by the volume of the intake passage downstream of the volume expansion chamber. Particularly in an engine equipped with a supercharger, the volume expansion chamber and the supercharger are used. It was found that a large volume of the intake passage between and had a negative effect on the inertia supercharging effect.

In view of the above circumstances, the present invention aims to improve the fuel consumption characteristics of the engine in the high speed and high load region by reducing the mechanical loss of the mechanical supercharger in the high speed and high load region, and to improve the fuel consumption characteristics in the low speed rotation region. It is an object of the present invention to provide an engine with a mechanical supercharger that has improved acceleration response.

[0010]

In the engine with the mechanical supercharger according to the present invention, the substantial closing timing of the intake valve is set at a time point delayed by 40 to 50 ° in crank angle from the bottom dead center, and It is characterized in that the volume of the intake passage on the downstream side of the supercharger is set to a value at which a resonance effect of dynamic supercharging can be obtained in a high speed rotation range. The substantial closing timing of the intake valve is defined as the time when the intake valve closes to the position where the valve lift amount is 0.4 mm.

In this case, the throat diameter of the intake port is such that when the average intake Mach number M _im at the maximum engine speed becomes 0.5 or more, the intake flow velocity tends to reach a peak, so that M _im is 0.3 to 0. It is preferable to set it within the range of 4.

Where M _{im is the} average intake Mach number v _{im is} the average intake velocity in the intake valve opening a is the sound velocity V _{h is the} stroke volume η _{V is the} volumetric efficiency F _{it is the} intake valve effective time area, and v _im = V _h (η _V / 100) / F _it M _im = v _im / a = V _h (η _V / 100) / (a · F _it ) (1) Further, the engine with a supercharger according to the present invention is The independent air intake passage of the cylinder may be connected to a collecting portion having no volume expansion chamber. Then, the inertial supercharging effect can be generated by the independent intake passage.

When an intercooler is provided in the intake passage on the downstream side of the mechanical supercharger, it is preferable to use a water-cooled intercooler.

[0014]

According to the present invention, the substantial closing timing of the intake valve is set at 4 crank angle after bottom dead center (ABDC).
By setting the time point from 0 to 50 °, the acceleration response in the medium to low speed rotation range can be improved, and in the high speed rotation range, the volumetric efficiency η _{V of the} intake air increases due to the dynamic supercharging. As a result of reducing the discharge pressure of the supercharger, the mechanical loss of the supercharger is reduced, and the acceleration response and fuel consumption characteristics in the high speed rotation range can be improved.

According to the present invention, the dynamic supercharging effect in the high speed rotation range is set by setting the volume of the intake system in consideration of the volume of the entire intake system on the downstream side of the mechanical supercharger. Can be increased.

Further, the independent intake passage of each cylinder is connected to the collecting portion having no volume expansion chamber, whereby the acceleration response in the low speed rotation range can be improved, and
Since the remaining independent intake passages function as volume expansion chambers for each independent intake passage and the intake negative pressure wave can be inverted at the collecting portion, an inertia supercharging effect can be obtained in the independent intake passages. it can.

Further, when the intercooler provided in the intake passage on the downstream side of the supercharger is a water-cooled type having a larger cooling capacity than the air-cooled type, the supercharged intake air is effectively cooled and the supercharge effect is obtained. And the volume is smaller than that of an air-cooled intercooler having the same cooling capacity, and the intake system volume on the downstream side of the supercharger is reduced accordingly,
The inertia supercharging effect can be improved.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a schematic structure of an in-line 4-cylinder mechanical supercharged engine according to an embodiment of the present invention.
The cylinder head 1 of this engine has cylinders 2a-2
intake ports 3a to 3d and exhaust ports 4a to 4d are formed, and the intake ports 3a to 3d and the exhaust port 4 are formed.
Each of a to 4d has its downstream end branched into two ports, and each cylinder 2a to 2d is provided with two intake valves and two exhaust valves. In this embodiment,
In order to improve the acceleration response in the medium to low speed rotation range, the actual closing timing of the intake valve, which is defined as the time when the valve is lifted to the position where the valve lift amount is 0.4 mm, is reduced by the crank angle for the reason described later. It is set to 40 to 50 ° after the dead point.

An intake manifold 6 is attached to the intake side of the cylinder head 1, and the intake manifold 6 is provided with independent intake passages 7a to 7d having upstream ends and downstream ends of the intake ports 3a to 3d, respectively. Independent intake passages 7a-7
A collecting portion 8 for collecting the upstream ends of d is formed, and in the common intake passage 9 on the upstream side of the collecting portion 8, a mechanical supercharger 11 driven by an engine via a belt 10;
An intercooler 12 that cools intake air whose temperature has risen due to compression by the supercharger 11 is arranged in order from the upstream side. The intercooler 12 is preferably a water-cooled type that cools intake air more effectively and has a smaller volume than an air-cooled type.

The collecting portion 8 is not a volume expansion chamber extending in the cylinder row direction like a surge tank in a conventional engine, but has a structure in which four independent intake passages 7a to 7d are bundled as they are. With respect to one independent intake passage, the other three independent intake passages function as a volume expansion chamber, and in the high speed rotation range, the intake valve is opened to move from the combustion chamber to the intake port 3a. The intake negative pressure wave propagated to 3d propagates in the independent intake passages 7a to 7d to the upstream side at the speed of sound and is inverted at the collecting portion 8, and the inverted positive pressure wave propagates to the downstream side, and immediately before the intake valve is closed. Intake port 3a-
It reaches the downstream side of 3d to obtain the effect of inertia supercharging.

The inertial supercharging tuning rotational speed is mainly determined by the volume V of the intake system per cylinder downstream of the collecting portion 8, that is, the volume of each intake port 3a-3d and each independent intake passage 7a-.
Since it can be determined by the sum of the volume of 7d and the throat diameter of the intake ports 3a to 3d (the diameter of the opening with respect to the combustion chamber), in order to obtain the inertia supercharging effect in the high speed rotation range, First, it is necessary to determine the throat diameters of the intake ports 3a to 3d.

The throat diameter can be determined by using a graph as shown in FIG. FIG. 2 shows each cylinder 2a
Throat diameter S (mm) with respect to bore diameter B (mm) when each of 2d has 4 valves (2 intake valves, 2 exhaust valves)
The straight line K1 (S = 0.48 × B−9.5) showing the upper limit value of the throat diameter S and the straight line K2 (S = 0.48 × B-13.2) showing the lower limit value of the throat diameter S. And are divided into three regions I, II, and III, and the throat diameter S is selected from the region II. In this embodiment, as will be described later, the point Q representing the bore diameter B = 80 mm and the throat diameter S = 27.0 mm was selected. It should be noted that the region I is a region where it is impossible to arrange four valves per cylinder, and the region III has a high average intake Mach number, so that sufficient volume efficiency η _V cannot be obtained in the high speed rotation region. Area. The average intake Mach number is the above formula
In the present embodiment, the average intake Mach number M _{im at} the maximum rotation speed is set within the range of 0.3 to 0.4.

3 (a) and 3 (b) and FIG. 4 (a),
As shown in Table 1 below, (b) has as parameters the engine synchronous speed when the bore diameter B, the throat diameter S, and the intake port diameter P (= independent intake passage diameter) are changed.
6 is a graph obtained by simulating the relationship between the volume efficiency η _{V and} the length L (cm) of the independent intake passage per cylinder.

[0025]

[Table 1]

3 (a) and 3 (b) and FIG. 4 (a),
Areas (b) indicated by hatching in the respective diagrams of (b) to
In (c), region (b) is engine speed 5500 ±
The range of inertia tuning at 500 rpm, the range (b) is the range of inertia tuning at engine speed 5000 ± 500 rpm,
Regions (C) indicate the regions where the engine speed is 4500 ± 500 rpm and the inertia is tuned. In addition, area (a) ~
The range of the intake passage length L in (C) is set from (A) to
It is shown in FIG. 3A as (C).

When the above graph is created, the substantial closing timing of the intake valve, which is defined by the time when the valve is lifted to the position of 0.4 mm, is set to 45 ° after the bottom dead center in crank angle. The valve opening timing is crank angle before top dead center 10
(Opening period 235 °). The intake air temperature on the downstream side of the intercooler 12 was set to about 70 ° C.

In this embodiment, as shown in the example of FIG. 3 (b), the bore diameter B is set as a condition for obtaining the highest volume efficiency η _V when the displacement is 1608 cc and the inertia tuning speed is 5000 rpm ± 500 rpm. = 80 mm, throat diameter S = 27.
0mm, intake port diameter P = 38.2mm, independent intake passage length L = 40cm.

FIG. 5 shows FIG. 3 (a), (b) and FIG.
From (a) and (b), it is a graph showing the relationship of the volume V of the intake system per cylinder on the downstream side of the collecting section 8 with respect to each throat diameter S at each inertial tuned rotation speed. Is represented by the following formula.

V = [(127.5−0.02N) S + O.315N−1862.5] × √ (T / 293) where N: Inertial tuning rotation speed (rpm) T: Absolute temperature (° K) (70 ° C is 343 ° K) Therefore, when tuning within the range of N ± 500 rpm,
The volume V is in the range of 0.92V to 1.08V. Also,
From FIG. 5, the volume V of the intake system per cylinder on the downstream side of the collecting portion 8 at the inertia tuning speed of 5000 rpm is 550 cm.
It becomes ³ .

FIG. 6 shows a displacement of 1608 cc and a bore diameter B = 8.
Independent intake passage length (cm) per cylinder when 0 mm
³ is a graph obtained by simulating changes in volume efficiency η _V with respect to engine speed (rpm) when the independent intake passage volume (cm ³ ) is changed. As is clear from the figure, when the independent intake passage length was 40 cm and the volume was 458 cm ³ , the highest volume efficiency η _V could be obtained at the inertia tuning speed of 5000 rpm. Therefore, the desirable volume of each intake port 3a-3d is 550
It becomes −458 = 92 cm ³ .

From the above results, the volume of the intake system on the downstream side of the supercharger 11 was determined as follows.

(1) Volume of four intake ports 3a to 3d = 92 cm ³ × 4 (diameter of each intake port 38.2 mm, length 8 cm) (2) Four independent intake passages 7a to 7d Volume = 4
58 cm ³ x 4 (diameter of each independent independent intake passage 38.2 mm, length 40 cm) (3) Volume of the common intake passage 9 downstream of the intercooler 12 = 196 cm ³ (common intake passage diameter 50 mm, length 10 cm (4) Volume of intercooler 12 = 1300 cm ³ (5) Volume of common intake passage 9 upstream of intercooler 12 = 196 cm ³ (diameter of common intake passage 50 mm, length 10 cm) The total volume of the intake system on the downstream side is
196 + 1300 + 196 + (458 + 92) × 4 = 3
It becomes 892 cm ³ .

As described above, in this embodiment, the length of the common intake passage 9 on the upstream side and the downstream side of the intercooler 12 is shortened as much as possible to reduce the volume, and a good inertia supercharging effect is obtained. I am trying.

Next, in this embodiment, in order to improve the acceleration response in the medium and low speed rotation range, the valve lift amount 0.4
In the present embodiment, the reason why the substantial closing timing of the intake valve, which is defined by the time when the valve is closed to the position of mm, is set to 40 to 50 ° after the bottom dead center in the crank angle will be described.

FIG. 7 is a graph showing the change in volume efficiency η _V (%) when the intake valve volume is kept constant and the actual closing timing (ABDC) of the intake valve is changed to 25 to 80 °. is there. As is clear from FIG. 7, the earlier the valve closing timing is closed, the higher the volume efficiency η _V at low speed is, and the engine speed is 1
If the valve closing timing is changed from 70 ° to 45 ° at 500 rpm,
The volume efficiency η _V has increased by about 9.5%. On the other hand, at the engine speed of 1500 rpm, the volume efficiency η _V at the valve closing timing of 25 ° is larger than that at 45 °, but it is about 4000 rp.
Since it sharply decreases at m or more, in this embodiment, about 450
The valve closing timing is set in the range of 40 to 50 ° (ABDC) so that the maximum volume efficiency η _V can be obtained at 0 rpm, and the inertia tuning speed is set to 5000 ± 500 rpm, so that the high speed rotation range is achieved. The volumetric efficiency η _{V of the} intake air is increased.

FIG. 8 shows the change over time in the charging efficiency η _C (%) when the throttle valve is fully closed to fully open under 1500 rpm. As apparent from FIG. 8, the rate of increase in charging efficiency eta _C enough to quickly close the closing timing and increases charging efficiency eta _C in closing timing 70 ° and 45 °
The time to reach 95% of the steady state is 7.67 respectively.
Cycles and 7.20 cycles, with a 45 ° improvement of about 6.5%. Also, by closing the valve closing timing early, the charging efficiency η _{C in} the steady state also increases in the low speed rotation range, so compare the times until the same charging efficiency (95% of the steady state at 70 ° valve closing timing). Then, the valve closing timing is 45 °
It can be seen that is shortened by about 18% with respect to the valve closing timing of 70 °.

As is clear from the above description, in the present embodiment, while reducing the volume of the intake system on the downstream side of the mechanical supercharger, the acceleration response in the low speed rotation range is improved and the acceleration response in the high speed rotation range is increased. It is possible to improve the fuel efficiency characteristics by reducing the mechanical loss of the supercharger by increasing the volumetric efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an upright 4-cylinder mechanical supercharged engine according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the bore diameter and the intake port throat diameter.

FIG. 3 is a graph showing the relationship between the volume efficiency and the independent intake passage length with the bore diameter, the throat diameter, and the intake port diameter as parameters.

FIG. 4 is a graph showing the relationship between the volume efficiency and the independent intake passage length with the bore diameter, the throat diameter, and the intake port diameter as parameters.

FIG. 5 is a graph showing the relationship between the throat diameter and the volume of the intake system per cylinder on the downstream side of the collecting portion.

FIG. 6 is a graph showing changes in volume efficiency with respect to engine speed, with independent intake passage length and volume as parameters.

FIG. 7 is a graph showing changes in volume efficiency when the closing timing of the intake valve is changed.

FIG. 8 is a graph showing a change over time in charging efficiency when the closing timing of the intake valve is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder head 2a-2d Cylinder 3a-3d Intake port 4a-4d Exhaust port 6 Intake manifold 7a-7d Independent intake passage 8 Collecting portion 9 Common intake passage 11 Mechanical supercharger 12 Intercooler

Claims (5)

[Claims] 1. An engine having a mechanical supercharger, wherein the supercharger performs supercharging at least when the load is high, in an engine, the substantial closing timing of an intake valve is from a bottom dead center to a crank angle. In 4
It is set at a time point delayed by 0 to 50 °, and the intake passage volume on the downstream side of the supercharger is set to a value at which a resonance effect of dynamic supercharging can be obtained in a high speed rotation range. An engine with a mechanical supercharger. 2. The mechanical passage according to claim 1, wherein the throat diameter of the intake port is set so that the average intake Mach number at the maximum rotation speed is 0.3 to 0.4. Engine with a feeder. 3. The mechanical supercharger according to claim 2, wherein the engine is a multi-cylinder engine, and an independent intake passage of each cylinder is connected to a collecting portion having no volume expansion chamber. Engine. 4. The engine with a mechanical supercharger according to claim 3, wherein the volume of the independent intake passage is set to a value at which an effect of inertia supercharging is obtained in a high speed rotation range. 5. A water-cooled intercooler is provided in an intake passage on the downstream side of the supercharger.
An engine with a mechanical supercharger according to any one of 1 to 4.