JPH0421051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an engine having a mechanical supercharger disposed in the intake system.

[Conventional technology]

A mechanical supercharger consists of a vane pump or a roots pump placed in the intake system of an engine, and is connected to the engine's crankshaft via a transmission belt or the like and driven by the output of the engine. It is preferable to supercharge the engine in order to obtain high output during acceleration or high load, but supercharging is generally not required at low load, and operating the supercharger at low load will cause engine output loss. grow bigger,
Fuel efficiency also worsens. Therefore, it is preferable to disconnect or connect the supercharger to the engine depending on a predetermined load, and an electromagnetic clutch is interposed in the transmission system between them. Providing an electromagnetic clutch to operate a supercharger above a predetermined load and above a predetermined rotational speed is described, for example, in Japanese Utility Model Application Publication No. 110330/1983.

[Problem that the invention seeks to solve]

When attempting to control a mechanical supercharger on-off using a constant load, there is a problem in how to set the load that becomes the on-off switching point. Normally, it is better to perform the necessary supercharging during high loads such as acceleration and not supercharge during low loads such as city driving, so it is better to turn the supercharger on and off at relatively high loads. is advantageous. However, it has been found that it is better to turn the supercharger on and off at a relatively low load when driving at high speeds. This is because when driving at high speeds, the engine speed is high, so if the supercharger is turned on and off with a relatively high engine load, the supercharger will suddenly start from a no-load state to a high rotational load state, which increases efficiency. This is because sudden supercharging occurs and the torque fluctuation shock in which the engine torque rapidly increases becomes large. Furthermore, before the supercharger is connected, the driver is unconsciously restrained by the feeling of high-speed driving and tries to step on the accelerator slowly rather than all at once. In this case, if the on-off switching point of the supercharger is on the high load side, it will be difficult to reach the switching point of the supercharger even if the accelerator is depressed slowly.
In other words, even though the driver has not actually pressed the pedal to the point where the supercharger is activated, he thinks he is accelerating the vehicle, and even then he cannot get the feeling that the supercharging is working. Figure 7 shows this as a diagram.

Therefore, when setting the load to turn the supercharger on and off, if the switching load is set to a relatively high load side, the torque fluctuation shock at high engine speeds will become large and the supercharging sensation at high speeds will be affected. If the load for switching is set to a relatively low load side to prevent this, the frequency of turning the supercharger on and off in the low engine speed range will increase, which will be disadvantageous in terms of fuel efficiency. There is a contradictory situation in which drivability deteriorates.
Setting the on-off switching point was difficult.

[Means for solving problems]

In order to solve the above problems, an engine with a mechanical supercharger according to the present invention is configured such that the supercharger performs intake supercharging when the engine load is above a predetermined value or when the engine speed is above a predetermined value. The mechanically supercharged engine is characterized in that the predetermined value of the engine load is set to be smaller as the engine rotation speed increases in a region below the predetermined value of the engine speed.

〔Example〕

In FIG. 2, the engine body consists of a cylinder block 2 and a cylinder head 4 as is well known, a piston 6 is inserted into the cylinder block 2, and a combustion chamber 8 is formed above it. The piston 6 is connected to a crankshaft 12 via a connecting rod 10. On the other hand, an intake passage 14 and an exhaust passage 16 are formed in communication with the combustion chamber 8,
A known intake valve 18 and exhaust valve 20 are arranged respectively.

As is well known, the intake passage 14 is formed by an intake pipe and an intake port, and in order from upstream,
It includes an air cleaner 22, an air flow meter 24, a throttle valve 26, a supercharger 28, and a surge tank 30, and a fuel injection valve 32 is attached to a branch pipe downstream of the surge tank 30. It will be seen that the supercharger 28 is formed by a known Roots pump. The Roots pump has two bilobed rotors 34, each of which is attached to a support shaft 3.
6. Meshing gears (not shown) are attached to one ends of the two support shafts 36, and one support shaft 36 drives the other support shaft, so that the two rotors 34 are synchronized with each other. can be rotated.

An electromagnetic clutch 38 is attached to the other end of the drive side support shaft 36. The electromagnetic clutch 38 has a pulley on its input side, and a belt 42 is stretched between the pulley and a crank pulley 40 attached to the crankshaft 12. electromagnetic clutch 3
8 is controlled by a relay 44, and the relay 44 is controlled by a control means 50.

A bypass passage 46 is connected to the intake passage 14 by bypassing the supercharger 28.
A bypass control valve 48 is disposed therein. Bypass control valve 48 is also controlled by control means 50.
The control means 50 also controls the fuel injection valve 32, and includes the aforementioned air flow meter 24, throttle position sensor 52, and cooling water temperature sensor 5.
4. In response to signals from the rotational speed sensor incorporated in the distributor 56 and other sensors, the fuel injection valve 32 and the electromagnetic clutch 38 are activated as described above.
and controls the bypass control valve 48.

As shown in FIG. 3, the control means 50 is constituted by a microcomputer system, and has a central processing unit (CPU) 6 having calculation and control functions.
0, a read-only memory (ROM) 62 for storing programs, and a random access memory (RAM) 64 for storing sensor detection values, etc., which are interconnected by a bus 66 and connected to an A/D converter 68 and an input interface 7
The detected value is taken in through the output interface 72, and the fuel injection valve 32, bypass control valve 48, and electromagnetic clutch 38 are controlled through the output interface 72. Incidentally, since the electronic control of the fuel injection valve 32 is well known, a detailed explanation thereof will be omitted.
The intake air amount Q and the engine speed N are used to control the electromagnetic clutch 38. Further, although the following explanation will only be about the control of the electromagnetic clutch 38, the bypass control valve 48 is operated at the same time as the electromagnetic clutch 38 or at a somewhat higher load side.

FIG. 4 shows a control flowchart for operating the supercharger 28, which operates according to the program stored in the ROM 62 of FIG. This flow is started by interrupting the main program for controlling the fuel injection valve 32, for example, every 20 msec. As mentioned above, in this program, the load is represented by Q/N (/rev), and Q and N are detected by the rotation speed sensor built into the air flow meter 24 and the distributor 56. , are stored in the RAM 64. Note that the load can also be determined by detecting the intake pressure.

In FIG. 4, in step 80 Q and N are read out, and in step 81 the load Q/N(/
rev). Next, in step 82, the supercharger 28
Find the predetermined value of the load that will be the switching point for on-off control. In the present invention, this predetermined value is set as a function of the engine speed, as shown in FIG. 1, and is set to become smaller as the engine speed increases. In the present invention, this predetermined value is stored as a map.

In step 83, a comparison is made to see if the detected load Q/N is greater than a stored predetermined value, and if yes, the process proceeds to step 84, where the supercharger 28 is operated. If no in step 83, the process advances to step 85, where it is compared whether the engine speed N is greater than 3400 rpm, and if yes, the supercharger 28 is checked in step 84 regardless of the load Q/N.
If the answer is NO, the process advances to step 86 and the supercharger 28 is stopped. In this case, the supercharger 28
The rotor 34 continues to rotate due to inertia, and is therefore able to pass air equivalent to the amount without supercharging.

The predetermined values shown in FIG. 1 are set such that they have a high constant value in a portion on the low engine speed side, are connected by diagonal lines, and have a low constant value in a portion on the high engine speed side. However, as shown in FIG. 5, it can also be set to decrease as the engine speed increases.

Next, referring to FIGS. 6 to 8, the supercharger 2
The feature of setting the predetermined value of the load, which is the switching point for on-off control of the engine 8, to be lower as the engine speed increases will be explained. FIG. 6 shows a case where the set value is set constant regardless of the engine speed. Considering the case where the engine is accelerating from point _A0 in a low speed state, the accelerator operation is bold at low speeds and the slot needs to be wide open for acceleration, so it is easy to exceed the high setting value. Enters the supercharging region (A ₁ ). Even with a slight throttle operation, the engine enters the lower supercharging region (A ₂ ).
Therefore, if the set value is set to a constant value on the low side, the frequency of turning on and off of the supercharger 28 will increase in the low engine speed range, and even when supercharging is not required, supercharging will occur. As a result, fuel efficiency and drivability deteriorate. Therefore, as mentioned above, in the low engine speed range,
It is better to set the setting value as high as possible.

On the other hand, when the engine is running at high speed, for example when the vehicle speed is 80.
Considering the case of accelerating from point B ₀ such as Km/H or more, the accelerator operation is careful and gradual at high speeds, so even if the driver thinks he has performed sufficient acceleration operation, the actual acceleration is It is difficult to reach the supercharging region (B ₁ ) that exceeds the higher set value,
For higher set values, it often remains in the non-supercharging region (B ₂ ). Therefore, drivers are dissatisfied with the feeling of acceleration due to supercharging. That is, if the setting value for supercharger operation is constant with respect to engine speed, the driver's feeling is that the engine speed is high enough to operate the supercharger 28, as shown in FIG. As the speed increases, the throttle opening must be increased. In fact, if the predetermined value is set high to prevent switching from A ₀ to A ₂ at low engine speeds, even if the engine accelerates at high speeds, it often only accelerates around B ₂ . .

When accelerating beyond a high predetermined value when the engine is running at high speed, it is necessary to operate the accelerator carefully, and in this case, engine torque fluctuations become large and the driver feels a shock. Supercharger 2
When switching 8 from a non-operating state to an operating state,
Torque fluctuation when transitioning from B ₀ to B ₁ from A ₀
The torque fluctuation is larger than that when shifting from A ₁ or from B ₀ to B ₂ . In other words, when transitioning from A ₀ to A ₁ , the turbocharger 28 is activated on the high load side.
This is because the amount of intake air passing through the supercharger 28 per unit time is small even when switching from B 0 to B 2 , and the amount of intake air is small when switching from B ₀ to B ₂ because the load at the time of switching is small. Referring to FIG. 8, if the supercharger 28 is activated at T ₀ , then from B ₀
When shifting to _B1 , since switching is performed at high speed and high load, a large amount of air equivalent to high speed and high load is supplied, so the engine torque increases rapidly and the shock becomes large. It will be seen that when transitioning from B ₀ to B ₂ , the intake air amount is switched within a small range, so that the shock becomes smaller.

〔Effect of the invention〕

As explained above, for example, as shown in FIGS. 1 and 5, setting the predetermined value of the load for operating the supercharger to be lower as the engine speed increases is as follows according to FIG. This means switching when the engine speed changes from A ₀ to A ₁ , and switching from B ₀ to B ₂ when the engine speed is high. Therefore, according to the present invention, when the engine speed is low, the supercharger is operated at a relatively high predetermined load value to improve fuel efficiency and drivability, and when the engine speed is high, the supercharger is operated at a relatively low predetermined load value. The supercharger can be activated to eliminate the shock feeling and give the driver a sense of acceleration. Furthermore, in the present invention, it is possible to reduce the shock feeling and improve fuel efficiency by simply setting the switching point of the supercharger operation according to the engine speed, and there is no need to provide a shock absorbing mechanism to the clutch. Furthermore, the electrical control device can be constructed using simple on-off control without using duty ratio control or the like.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a predetermined load value for supercharger switching according to the present invention, FIG. 2 is a sectional view of an engine to which the present invention is applied, and FIG. 3 is a configuration diagram of a control means.
FIG. 4 is a diagram showing a control flowchart, FIG. 5 is a diagram showing another example of the predetermined value of load, and FIG. 6 is a diagram explaining the characteristics when the predetermined value of load is kept constant.
FIG. 7 is a diagram illustrating the feeling of the throttle opening when the predetermined value of the load is kept constant, and FIG. 8 is a diagram illustrating the shock when the supercharger is switched at high speed. 14...Intake passage, 28...Supercharger, 38...Electromagnetic clutch.

Claims (1)

[Claims] 1. In an engine with a mechanical supercharger, the intake system is equipped with a mechanical supercharger, and the supercharger performs intake supercharging at an engine load of a predetermined value or higher or an engine speed of a predetermined value or higher, An engine with a mechanical supercharger, characterized in that the predetermined value of the engine load is set to be smaller as the engine speed increases in a region below the predetermined value of the engine speed.