JP2828470B2 - Engine output control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an engine output control device that switches the valve timing of an intake valve related to the output characteristics of an engine based on a predetermined engine speed. It is.

(Prior Art) In an engine, from the viewpoint of securing a high level of output performance in the entire rotation speed range, the output characteristics of the engine are conventionally made variable, and the output characteristics are switched at a predetermined engine rotation speed. There is something like that. As a method of switching the output characteristics, for example,
As disclosed in Japanese Patent Application Laid-Open No. 60-27711, there are known a method of switching the opening and closing timing of an intake valve and a method of switching a compression ratio of an engine.

(Problems to be Solved by the Invention) However, these methods have the following problems.

A. In the case of the method by switching the valve timing As shown in FIG. 5, this method uses a high-speed cam having a large valve lift and a long valve-opening period as a cam for driving the intake valve, and a small valve lift. A low speed cam having a short valve opening period is provided, and the two cams are selectively switched at a predetermined engine speed as shown in FIG.

The technical idea of this method is as follows. That is, in order to obtain a high output, it is sufficient to introduce a large amount of intake air into the combustion chamber by using a cam capable of obtaining a larger valve lift and having a long valve opening period like a high-speed cam. According to such a setting, in practice, a high output can be obtained in the actual high rotation speed range. However, when the high-speed cam is used in a low-speed range, the output greatly decreases because the overlap between the intake valve and the exhaust valve is large and the amount of residual gas in the combustion chamber increases (see FIG. 4). reference characteristic diagram L ₁ a). Accordingly, in the low-speed range, the use of the low-speed cam having a small overlap between the intake valve and the exhaust valve results in a higher output because the residual gas amount is reduced (see FIG. 4). reference characteristic diagram L ₁ b).

Such view of the fact, as shown by the characteristic diagram L ₁ of FIG. 4, a high-speed cam and the low speed cam, a characteristic diagram L ₁ b according to the characteristic diagram L ₁ a and the low-speed cam by the high-speed cam At the intersection a
By switching at (engine speed N ₁ ), higher output characteristics can be obtained throughout the entire engine speed range. Conventionally, it is customary to set the cam switching timing fixedly.

However, in general, the engine output decreases when the engine temperature decreases because the vaporization and atomization of fuel deteriorates accordingly. In this case, such a tendency of the engine output to decrease is the same whether the high-speed cam or the low-speed cam is used, but the extent of the decrease corresponds to the difference in the overlap period with the exhaust valve. They are very different. That is, as shown by ΔT ₁ and ΔT ₂ in FIG. 4, when a high-speed cam is used, a large amount of residual gas makes combustion stability worse than when a low-speed cam is used.
The decrease in engine output is also greater than when using the low-speed cam (“ΔT ₁ ”> “ΔT ₂ ”, where “ΔT ₁ ” is the torque reduction when using the high-speed cam, “ΔT ₂ ”is the torque reduction when using the low speed cam).

As a result, in the cold state, as shown by the characteristic diagram L ₂ in Figure 4, the intersection of switching timing of the cam, the characteristic diagram L ₂ b by characteristic diagram L ₂ a and the low-speed cam by the high-speed cam The rotation speed shifts to the rotation speed N ₂ (N ₁ <N ₂ ) corresponding to b.

Therefore, as in the conventional case, the cam switching timing (rotation speed) is set to, for example, the timing (rotation speed N ₁ ) in a warm state.
Fixedly If set, the torque point in the rotational speed N ₁ with an increase in engine speed in the cold state c to
From point d to point d, and a torque shock occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to realize a driving operation with less torque shock by shifting a cam switching timing to a higher rotation side in a cold state than in a warm state.

B. In the case of a method by changing the compression ratio In this method, the compression ratio of the engine is set to a high compression ratio in a high rotation range, and to a low compression ratio in a low rotation range. It is as follows.

In general, when the engine output is viewed in relation to the ignition advance angle, the inverted V-shaped characteristic as shown in FIG. 10 is obtained. Therefore, in order to obtain a highest torque may be set to the advance amount t ₂ corresponding to spark advance to the highest output point b. However, in general, there is a knocking limit slightly closer to the advance angle than this maximum output point. Therefore, simply when the advance amount t ₂ corresponding to the maximum output point spark advance, for example, such as the actual advancing amount by variations in the manufacturing of the engine exceeds the t ₂ In that case, you will fall into the knocking limit.

Therefore, in the engine, practically optimum practical ignition angle (generally abbreviated as MBT) to t _1, the advance amount t ₂
It is obligatory to set a point on the more retarded side and at a certain interval from the knocking limit. This practical ignition advance angle changes in accordance with the engine speed, and the curve MBT in FIG. 8 shows this in correspondence with the engine speed.

It is known that the knocking limit generally moves to the retard side as the compression ratio increases, and the knocking limit at a certain high compression ratio and the knocking limit at a low compression ratio are defined by the engine speed. The knocking limit curve shown in FIG. 8 is shown by the relationship.

By the way, from the viewpoint of simply obtaining a high engine output, it is sufficient to set the compression ratio to a high compression ratio and set the ignition advance to the practical ignition advance (MBT) throughout the entire rotation range.
As can be seen from FIG. 8, in such a case, the MBT curve approaches or crosses the knocking limit at the high compression ratio at or above the regulation value in the low rotation speed range, and as a result, the engine Knocking occurs.

In order to avoid knocking in such a low rotation range,
Conventionally, as shown by a broken line in FIG. 8, the MBT curve is shifted to the retard side in a low rotation range, thereby securing an interval equal to or larger than a regulation value between the MBT curve and a knocking limit at a high compression ratio. I was trying to do it.

However, in such a case, the engine output is sacrificed in the operating range where the MBT curve is shifted to the retard side, as can be seen from FIG.

Against this background, while maintaining the MBT curve, for example, one is a high-rotation side than the engine speed N ₂ to set the compression ratio of the engine at a high compression ratio, it is in this than low-rotation low By setting the compression ratio, the interval between the MBT curve and the knocking limit is secured to a predetermined value or more, thereby achieving both high output of the engine and avoidance of knocking. This is the reason for providing a variable compression ratio mechanism. still,
Engine speed N ₂ is a switch timing of the compression ratio is fixedly set.

However, heretofore, there has been the following problem because conventionally, the whole process was only between the compression ratio and the knocking limit and the relationship between these and the engine temperature was not considered at all.

That is, as shown in FIG. 9, the knocking limit fluctuates not only with the compression ratio but also with the engine temperature. When the compression ratio is the same, the knocking limit moves to the advanced side as the engine temperature is lower. I do. Therefore, for example, if the switching timing of the compression ratio (engine speed N ₂ ) is fixedly set on the basis of the knocking limit in a warm state, the above restriction is sufficiently maintained even in a cold state even if a high compression ratio is maintained. Despite being satisfied with the value (in other words,
High Compression ratio despite a region where a high output is obtained) switches to a low compression ratio the engine speed N ₂ as the boundary, resulting in that the engine output can not be sufficiently obtained in the low speed range Becomes

Therefore, the present invention changes the valve timing of the intake valve in consideration of the engine temperature which is an influential factor of the output characteristics of the engine, so that a high-level output characteristic can be obtained in the entire temperature range and the entire rotation range of the engine. It is an object of the present invention to provide an engine output control device.

(Means for Solving the Problems) The present invention employs the following configuration as specific means for solving such problems.

According to the first aspect of the invention, the valve timings of the plurality of intake valves according to the engine speed are set and set so that a large amount of intake air is introduced into the combustion chamber from the low engine speed range to the high engine speed range. In an engine provided with valve timing changing means for executing a change from a low-speed valve timing to a high-speed valve timing that opens late to the low-speed valve timing when a predetermined engine speed is reached, Is set to a higher rotation speed as the engine temperature is lower.

According to the second aspect of the present invention, in the engine output control device according to the first aspect, the valve timing changing means may use a high-speed cam having a large valve lift and a long valve opening period. And a low-speed cam having a small valve lift and a short valve opening period.

According to a third aspect of the present invention, in the engine output control device according to the second aspect, the switching timing between the high-speed cam and the low-speed cam by the valve timing changing means is set such that the lower the engine temperature, the higher the rotation speed. Is set.

(Operation and Effect of the Invention) In the present invention, the following operation and effect can be obtained by adopting such a configuration.

According to the engine output control device of the first aspect, the change from the low-speed valve timing to the high-speed valve timing is set to the higher rotation speed as the engine temperature is lower. It is possible to secure a high level of output characteristics in the entire engine temperature range and the entire rotation range while minimizing the occurrence of torque shock due to the change of valve timing between the valve timing and the engine. is there.

According to the output control device for an engine according to the second aspect of the present invention, the valve timing changing means includes a high-speed cam having a large valve lift and a long valve opening period and a high speed cam having a small valve lift and a valve opening period. Since the valve cam is switched between the short low speed cam,
By selectively using the high-speed cam and the low-speed cam in accordance with the engine temperature, which is an influential factor of the output characteristics of the engine, both high-speed and low-speed cams provide high-level output characteristics. Is obtained.

According to the engine output control apparatus of the third aspect, the switching timing between the high-speed cam and the low-speed cam by the valve timing changing means is set to a higher rotation speed as the engine temperature is lower. Therefore, the difference in engine output when switching between the high-speed cam and the low-speed cam is reduced as much as possible, and accordingly, smooth operation with less torque shock when switching the cam is realized.

(Embodiments) Some preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment FIG. 1 shows an intake / exhaust system of an automobile engine 1 in which an output control device according to a first embodiment of the present invention has been obtained. Is an exhaust passage, is an intake valve, and 5 is an exhaust valve. The opening / closing timing of the intake valve 4 can be changed by valve timing changing means 20 described later. In FIG. 1, reference numeral 6 denotes an injector, 7 denotes a throttle valve, 8 denotes a throttle opening sensor, 9 denotes an air flow meter, 10 denotes an air cleaner, 11 denotes an air control valve, 12 denotes an O ₂ sensor, 13 denotes a water temperature sensor, 14 Denotes an engine speed sensor, and 15 denotes a control unit. The control unit 15 receives a signal from each sensor and performs fuel control, air-fuel ratio control, and the like.

This engine 1 is a three-valve engine having two intake valves and one exhaust valve (see FIG. 2). As will be described later, a high-speed cam and a low-speed cam are selectively used to achieve high engine speed and low engine speed. The output characteristics of the engine 1 are changed by changing the opening / closing timing (valve timing) of each intake valve 4, 4 at the time of rotation, so that a high output is obtained in the entire rotation range, and the valve timing is changed. Is executed in accordance with the engine temperature to realize smooth operation without torque shock. Hereinafter, the configuration of the valve timing changing means 20, which is the prerequisite technology for this control,
The operation will be described.

The valve timing changing means 20 has a well-known configuration. Specifically, as shown in FIG. 2, low-speed cams 27, 27 for intake valves are provided at both axial positions, and A camshaft 21 having a high-speed cam 28 for the intake valve and a cam 29 for the exhaust valve provided inside the low-speed cams 27, 27, and an intake valve disposed in parallel on both sides of the camshaft 21 with appropriate separation. Rocker shaft 22 and rocker shaft for exhaust valve
23. The low-speed cam 27 and the high-speed cam
The cam shapes of the exhaust cam 29 and the exhaust cam 29 are relatively set so as to have opening and closing characteristics as shown in FIG.

A pair of left and right low-speed rocker arms 24, 24 and a high-speed rocker arm 25 are rotatably attached to the intake valve rocker shaft 22. Each of the low-speed rocker arms 24, 24 has a cam roller 30 provided on one end 24a side thereof, and a low-speed cam 27 of the cam shaft 21.
In addition, the high-speed rocker arm 25 has a slider 32 provided at one end 25a thereof so as to be able to abut against the high-speed cam 28, respectively. Also, each low speed rocker arm
The head (not shown) of the intake valve 4 is associated with the other end 24b of the 24, 24.

Further, between each low-speed rocker arm 24 and each high-speed rocker arm 25, slide pins 35, 35 are provided, which are removably connected to each other by the forward and backward movements. That is, the slide pin 35 is normally housed in the high-speed side pin receiving hole 37 on the high-speed rocker arm 25 side by the spring force of the spring 36 arranged on the low-speed rocker arm 24 side, and is normally inserted into the high-speed rocker arm. When the pressure oil is supplied to the pressure chamber 39 provided behind the slide pin 35, the low-speed rocker arm 24 protrudes against the spring force of the spring 36. The low-speed rocker arm 24 and the high-speed rocker arm 25 can be integrally connected by fitting into the low-speed side pin receiving hole 38 on the 24 side. Therefore, the intake valve 4
When the low-speed rocker arm 24 and the high-speed rocker arm 25 are not connected, they are driven by the low-speed cam 27. When they are connected, they are driven by the high-speed cam 28. That is, the valve timing can be switched by controlling the operation of the slide pin 35. In the embodiment, the switching of the valve timing is performed by the control unit 15 according to the engine speed,
In addition, at that time, the change of the engine speed (that is, the change of the output characteristic of the engine) serving as the reference for this switching is performed according to the engine temperature (see FIG. 4). Specifically, as shown in FIG. 4, the switching timing is changed to a higher rotation side when the engine is cold than when it is warm.

The exhaust valve rocker shaft 23 has an exhaust valve rocker arm 26, and its cam roller 31 is attached to the exhaust cam.
It is installed in a state corresponding to 29.

Next, the actual change control of the valve timing is described in the third.
The description will be made based on the flowchart shown in FIG.

After the start of the control, first, the operating state of the engine (engine speed Ne, intake air amount Qa, engine cooling water temperature Tw, etc.) is read (step S1). Then, the switching speed Nc of the valve timing changing means 20 is calculated from these pieces of information (step S2). Specifically, as shown in FIG. 6, the switching speed Nc is expressed as a function of the water temperature Tw, and shifts to a higher rotation side as the water temperature increases.

Next, the switching speed Nc is compared with the current speed Ne (step S3), and when Nc = Ne, the cam is switched (step S4).

Thus, switching timing of the valve timing change unit 20 (i.e., change of valve timing) by performing in accordance with the engine temperature, as indicated by the curve L ₁ and the curve L ₂ in FIG. 4, the engine temperature elevation Irrespective of the above, a smooth output characteristic diagram can be obtained, thereby realizing operation with less torque shock.

Second Embodiment In this embodiment, the operation of the first embodiment having a variable cam mechanism is realized mainly by reducing torque shock by changing the switching timing according to the engine temperature. On the other hand, in an engine provided with a compression ratio variable mechanism (not shown), the compression ratio switching timing is changed according to the engine temperature, so that high output can be obtained mainly in a lower speed range. It is. Specifically, based on the technical concept described in the above-mentioned “Problems to be Solved by the Invention”, as shown in FIGS. 7A and 7B, when the engine is cold, The switching timing of the compression ratio is changed to a lower rotation side than at the time.

[Brief description of the drawings]

FIG. 1 is a system diagram of an engine provided with an output control device according to a first embodiment of the present invention, FIG. 2 is an explanatory view of a detailed structure of a valve timing changing means shown in FIG. 1, and FIG. Flowchart, FIG. 4 is an output characteristic diagram, FIG. 5 is a valve timing diagram, FIG. 6 is a map showing switching speed of the valve timing changing means with respect to engine temperature, and FIG. 7 is a second embodiment of the present invention. FIG. 8 and FIG. 9 are correlation diagrams between the practical ignition advance and the knock limit, and FIG. 10 is a correlation diagram between the engine ignition and the output torque in the output control device. 1 ... Engine 4 ... Intake valve 5 ... Exhaust valve 20 ... Valve timing changing means 21 ... Camshaft 22,23 ... Rocker shaft 24 ... Rocker arm for low speed 25 ... Rocker arm for high speed 35 ... Slide pin

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-252847 (JP, A) JP-A-64-32034 (JP, A) JP-A-64-63629 (JP, A) JP-A 64-64 69730 (JP, A) JP-A-2-176129 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 13/02

Claims (3)

(57) [Claims] A valve timing of a plurality of intake valves is set according to an engine speed so that a large amount of intake air is introduced into a combustion chamber from a low engine speed range to a high engine speed range, and the set low-speed valve timing is set. The engine having valve timing changing means for executing a change to the high-speed valve timing that opens late to the low-speed valve timing when the predetermined engine rotation speed is reached. The output control device of the engine, wherein the lower the engine temperature, the higher the rotation speed is set. 2. The valve timing changing means according to claim 1, wherein the valve timing changing means comprises a high-speed cam having a large valve lift and a long valve opening period, and a high speed cam having a large valve lift and a short valve opening period. An engine output control device configured to switch between a low speed cam and a low speed cam. 3. The engine output control according to claim 2, wherein the switching timing between the high-speed cam and the low-speed cam by the valve timing changing means is set to a higher rotation side as the engine temperature is lower. apparatus.