JPH07156691A - Power unit for vehicle - Google Patents

Abstract

PURPOSE:To markedly improve fuel consumption by using a gasoline engine with supercharger and an automatic transmission, achieving the lower fuel consumption in a low fuel consumption region in a high load side at a low speed, and also using this operating region more. CONSTITUTION:A supercharger 15 is provided in an engine, to set air-fuel ratio, in a low speed region in at least an engine supercharge region, to a value larger than theoretical air-fuel ratio, and to reduce net fuel consumption in this region, also to use an automatic transmission as a speed changer 25, and by setting a characteristic of this automatic transmission so that steady running on a flat road can be performed in a low speed region in the supercharge region, this region is more used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle power unit equipped with a gasoline engine with a supercharger and an automatic transmission.

[0002]

2. Description of the Related Art Conventionally, a gasoline engine with a supercharger in which intake air is pressurized and supplied by a supercharger such as an exhaust turbocharger is generally known.

In this type of engine with a supercharger, for example, as disclosed in Japanese Patent Laid-Open No. 3-23327, the air-fuel ratio of the air-fuel mixture in the supercharging region (the operating region where the intake pressure is increased by supercharging) is high. There has also been proposed one in which the amount of fuel supplied from the fuel supply means is controlled so as to be larger than the theoretical air-fuel ratio (on the lean side). According to this engine, in the operating region on the high load side, which is the supercharging region, lean burn (lean combustion) is performed while ensuring torque and combustion stability by supercharging, thereby reducing fuel consumption in this operating region. It

[0004]

By the way, a power unit of a vehicle is composed of an engine and a transmission. In this power unit, the running state of the vehicle is related to the operating state of the engine and the gear ratio of the transmission. Also, the fuel efficiency changes depending on the operating condition of the engine. Therefore, even if an engine with a turbocharger as described above is used and the air-fuel ratio is increased in the supercharging region to achieve low fuel consumption, fuel consumption is substantially sufficient if the operating region with low fuel consumption is used less frequently. However, there was still a problem in this respect.

In view of the above circumstances, the present invention aims to further improve the fuel consumption in the low fuel consumption region of the engine, and to improve the fuel consumption significantly by making frequent use of this operating region. It is an object of the present invention to provide a power unit of a vehicle capable of

[0006]

To achieve the above object, the present invention comprises a gasoline engine with a supercharger and an automatic transmission, and at least the supercharging region of the engine (the pressure immediately before the intake valve is atmospheric pressure). In the low speed range, the air-fuel ratio is set to a value larger than the stoichiometric air-fuel ratio, and the characteristics of the automatic transmission are set to the steady state on a flat road in the low speed range in the supercharging range. It is set to run.

In the present invention, preferably, the automatic transmission is a continuously variable transmission, and the gear ratio control characteristic for changing the gear ratio of the continuously variable transmission in accordance with the operating state has a flat ratio in the low speed region in the supercharging region. Set so that steady running is performed at.

The supercharger is effectively an exhaust turbo supercharger.

Alternatively, the supercharger is a mechanical supercharger, and a valve timing variable mechanism for varying the valve opening overlap period of the intake / exhaust valve is compared with a low speed high load range and a low speed low load range. It is also effective to provide control means for controlling the variable valve timing mechanism so as to increase the valve opening overlap period.

The geometric compression ratio of the engine is preferably set to 9 or more.

Further, the intake valve closing timing is set so that the effective compression ratio of the engine becomes smaller than the expansion ratio at least in the low speed region of the supercharging region. It is preferable that the valve closing timing is set to a crank angle of 50 ° or more after bottom dead center.

Further, it is preferable that the engine is provided with exhaust gas recirculation means for recirculating exhaust gas to the intake system at least at low speed and high load.

Further, a catalyst capable of purifying nitrogen oxides is provided in the engine exhaust passage even when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, and the exhaust gas recirculation amount by the exhaust gas recirculation means is set to at least low speed and high load. It is preferable to provide means for controlling the temperature of the catalyst so that it is maintained in a temperature range where the purification performance of the catalyst becomes high.

[0014]

According to the present invention, the air-fuel ratio of the air-fuel mixture is large and the average effective pressure is high in the low speed region of the supercharging region, so that the net fuel consumption rate is low for the reason described in detail later. Moreover, by setting the automatic transmission to the above characteristics, the frequency of driving in this low fuel consumption driving range is increased.

In the present invention, particularly when the automatic transmission is a continuously variable transmission, it becomes possible to easily set the gear ratio control characteristic that enables steady running in the low speed region in the supercharging region.

When a turbocharger is used as the supercharger, the resistance of the supercharger is small, which is advantageous for reducing fuel consumption.

When a mechanical supercharger is used as the supercharger, a scavenging action can be obtained by increasing the valve opening overlap period of the intake / exhaust valve at least in the low speed and high load range.
This is advantageous for suppressing knocking in this region.

When the geometrical compression ratio of the engine is set to 9 or more, the thermal efficiency is increased and it is also advantageous for lean burn.

If the effective compression ratio of the engine is made smaller than the expansion ratio by, for example, delaying the intake valve closing timing at least in the low speed region of the supercharging region, the temperature rise during compression is suppressed. , Which is advantageous for suppressing knocking in this area.

Further, when the exhaust gas is recirculated at least under high load, the generation of nitrogen oxides under high load is suppressed, and even if the exhaust gas is recirculated in this way, fuel and air are supercharged. Combustion stability is ensured due to the increased density.

Further, the engine exhaust passage is provided with a catalyst capable of purifying nitrogen oxides even when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, and the exhaust gas recirculation amount by the exhaust gas recirculation means is at least when the load is high. By providing a means for controlling the temperature of the catalyst in a temperature range where the purification performance of the catalyst is high, the nitrogen oxides can be favorably purified under high load.

[0022]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a power unit of a vehicle according to an embodiment of the present invention. The engine (gasoline engine) in this power unit has an engine body 1, an intake passage 10, an exhaust passage 12, and the like. The engine body 1 includes a plurality of cylinders 2, and an intake port 4 and an exhaust port 5 are opened in a combustion chamber 3 of each cylinder 2, and in the illustrated example, two intake ports 4 and two exhaust ports 5 are opened. ing. The intake ports 4 and the exhaust ports 5 are opened and closed by intake valves 6 and exhaust valves 7, respectively. The intake port 4 is connected to the intake passage 11 for each cylinder on the downstream side of the intake passage 10, and the exhaust port 5 is connected to the exhaust passage 13 for each cylinder on the upstream side of the exhaust passage 12.

Further, the engine is provided with a supercharger, and in this embodiment, an exhaust turbo supercharger 15 is provided. The exhaust turbocharger 15 includes a turbine 15a arranged in the exhaust passage 12 and a compressor 15b arranged in the intake passage 10 and connected to the turbine 15a via a shaft 15c. 15a rotates, and in conjunction with this, the compressor 15b
The intake air is supercharged by rotating.

The compressor 1 in the intake passage 10
An intercooler 16 for cooling the supercharged air is provided downstream of 5b.
Is provided. Further, in the intake passage 10, an air cleaner 17, an air flow meter 18 for detecting the intake flow rate,
A throttle valve 19 for adjusting the intake flow rate according to accelerator operation and the like, an injector 20 for injecting and supplying fuel, and the like are provided. On the other hand, a catalyst 21 is provided in the exhaust passage 13. The catalyst 21 has a high NOx purification rate even in a lean combustion state in which the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 is larger than the stoichiometric air-fuel ratio.

Further, this engine is provided with an exhaust gas recirculation means 23. This exhaust gas recirculation means 23
Is an EGR passage 23a that connects the exhaust passage 12 and the intake passage 10, and an EG that is provided in the EGR passage 23a and controls the exhaust gas recirculation amount according to a control signal.
And an R valve 23b.

A transmission 25 is connected to the output shaft of the engine.
The final reducer 26 is connected to the output side of the
A wheel 28 is connected to the wheel via an axle 27.

FIG. 2 shows the structure of the transmission 25. The transmission 25 is composed of an automatic transmission, and in this embodiment, a toroidal type continuously variable transmission 40 is used. That is, the transmission 25 is connected to the output shaft of the engine to perform a torque increasing action, the planetary gear mechanism 31 as a speed reducer to which the output of the torque converter 30 is transmitted, and the rotation of the engine. Is input and the rotation thereof is continuously changed.

The planetary gear mechanism 31 includes a forward planetary gear mechanism 32 and a reverse planetary gear mechanism 33. The sun gear 34 shared by these is connected to the turbine shaft 35 of the torque converter, while the forward planetary gear mechanism 31 is connected. Gear mechanism 3
The second ring gear is connected to the output shaft 50 via the forward clutch 36 and the one-way clutch 37, and the ring gear of the reverse planetary gear mechanism 33 is connected to the output shaft 50 via the reverse clutch 38.
It is possible to switch between forward and reverse by the operation of 6, 38.

Further, the continuously variable transmission 40 has a first transmission unit 41 and a second transmission unit 42, and these transmission units 41, 42 have the same structure, and each of the output shafts has the same structure. An input disc 43 rotatably provided on the shaft 50 and the input disc 43;
And an output disk 44 which is arranged to face the output shaft 50 and rotates integrally with the output shaft 50, and a pair of rollers 45 which are arranged between the input / output disks 43 and 44. The roller 45
Is rotated in contact with both disks 43 and 44 so as to transmit the rotation of the input disk 43 to the output disk 44, and is tiltable. The roller 45 is tilted by a hydraulic drive mechanism (not shown) and its installation angle is changed, so that the contact position of the roller 45 with respect to both the disks 43 and 44 is changed to change the gear ratio. It has become so.

The input disks 43 of the transmission units 41 and 42 are arranged adjacent to each other, and an intermediate disk 46 is arranged between the input disks 43, and between the intermediate disk 46 and the input disks 43. In addition, a loading cam 47 that applies a pressing force corresponding to the input torque to the input disk 43 is interposed.

In order to input the engine output to the input disk 43 of the continuously variable transmission 40, an input shaft 51 is arranged in parallel with the output shaft 50, and a first gear 52 is provided on one end side of the input shaft 51. A gear 55 is provided, which is connected to a hollow shaft 53 directly connected to the input side of the torque converter 30 via a switching clutch 54, and an idle gear 56 meshes with the gear 55.
The first gear 52 is in mesh with 6. The input shaft 51
A second gear 57 is provided on the other end side of the second gear 57.
A gear 58 provided on the intermediate disk 46 meshes with the gear 7.

According to the transmission 25, when the switching clutch 54 is released, the hollow shaft 5 is released.
The transmission of rotation between the engine 3 and the input shaft 51 of the continuously variable transmission 40 is cut off, and the engine output is transmitted to the output shaft 50 via the torque converter 30 and the planetary gear mechanism 31. on the other hand,
When the switching clutch 54 is engaged, the engine output is transmitted from the hollow shaft 53 to the input shaft 51 and then to the output shaft 50 via the continuously variable transmission 40. When the vehicle is traveling normally except when moving backward or starting, the switching clutch 5 is
By controlling a hydraulic drive mechanism (not shown) that tilts the roller 45 in the state where 4 is fastened, the gear ratio can be changed according to the traveling state.

The control of the gear ratio and the like in the transmission 25 and the control of the engine are performed by the control unit (ECU) 60 shown in FIG.
The control unit 60 includes the air flow meter 18, a throttle opening sensor 61 for detecting the opening of the throttle valve, an engine speed sensor 62 for detecting the engine speed, and a sensor 6 for detecting the output shaft speed of the transmission.
The signal from 3rd grade is input. And the above ECU
A control unit 60 controls the fuel injection amount from the injector 20 and controls the EGR valve 23b so as to obtain a preset air-fuel ratio according to the operating conditions such as the intake air amount and the engine speed as engine control. Thus, the exhaust gas recirculation amount is controlled, and the gear ratio of the continuously variable transmission 40 is controlled according to a traveling condition according to a preset gear ratio control characteristic.

In this power unit, the air-fuel ratio of the air-fuel mixture is set to a value larger than the stoichiometric air-fuel ratio (excess air ratio λ is λ> 1) at least in the low speed region of the supercharging region of the engine, and sufficient fuel economy is achieved. Preferably for A / F>
Set to 17.

The region where the air-fuel ratio is set to a value larger than the stoichiometric air-fuel ratio may be the entire operating region of the engine. Further, as shown in FIG. 3, for example, the high rotation and high load region is excluded. Set λ> 1 in the operating range and only in the high rotation and high load range λ ≦
It may be set to 1.

Further, the geometrical compression ratio of the engine is larger than that of a general supercharged engine (8.5 or less), and is a high compression ratio of 9 or more.

Further, the intake valve closing timing is set so that the effective compression ratio becomes smaller than the expansion ratio at least in the low speed region in the supercharging region. In the present embodiment, as shown in FIG. 4, the exhaust valve is set to open near the bottom dead center and closed near the top dead center so that the expansion ratio becomes a substantially geometric compression ratio, while the intake valve It is set to open near top dead center and close some time later than bottom dead center. Specifically, intake valve closing timing I defined with 1 mm lift
C is set at a crank angle later than 50 ° after bottom dead center. By delaying the intake valve closing timing to this extent, the blowback of the intake occurs at the end of intake, and the effective compression ratio becomes sufficiently smaller than the expansion ratio, and the knocking suppression effect described later is effectively obtained. It is what is done.

Although the opening / closing timing of the intake / exhaust valve is fixed in the above example, a valve timing variable mechanism (for example, which will be described later) that can change the opening / closing timing of both the intake valve and the intake / exhaust valve. A mechanism as shown in FIG. 9) may be provided so that the effective compression ratio becomes smaller than the expansion ratio at least in the low speed region in the supercharging region, and the opening / closing timing is controlled according to the operating state. Further, as the setting such that the effective compression ratio becomes smaller than the expansion ratio, the intake valve closing timing may be set earlier than the bottom dead center.

Further, the exhaust gas recirculation means 23 recirculates the exhaust gas to the intake system at least at low speed and high load, and for example recirculates the exhaust gas in the entire operating range. The control unit 60 controls the EGR valve in accordance with the operating state to control the exhaust gas recirculation amount. Particularly, in this embodiment, the exhaust gas recirculation is controlled by the NOx purification catalyst 21 as described later in detail. It is also used for temperature adjustment, and the exhaust gas recirculation amount is controlled so as to maintain the temperature of the NOx purification catalyst 21 in a temperature range in which the purification performance of the catalyst is high at low speed and high load.

The exhaust gas recirculation amount may be controlled, for example, by providing detection means for detecting the catalyst temperature or the degree of NOx purification of the catalyst, and feedback controlling the exhaust gas recirculation amount in accordance with the detection signal. Alternatively, since the catalyst temperature is related to the operating conditions such as engine load and the exhaust gas recirculation amount, the exhaust gas recirculation amount required to keep the NOx purification catalyst in the proper temperature range is investigated in advance in various operating ranges, and The exhaust gas recirculation amount may be set according to the operating state by controlling the exhaust gas recirculation amount based on the operating state.

On the other hand, the characteristics of the continuously variable transmission 40 are set so that steady running is performed on a flat road in the low speed region of the supercharging region.

That is, in the control of the continuously variable transmission 40, for example, as shown in FIG. 5, a map of gear ratio control characteristics in which the output rotation speed and the throttle opening are associated with the input rotation speed (engine rotation speed). Based on this map, the gear ratio is controlled according to the actual output speed and throttle opening. In this case, the continuously variable transmission 40 has a relatively high degree of freedom in setting the gear ratio control characteristic, and thus the engine operating state during steady running can be adjusted relatively freely.

Therefore, the gear ratio control characteristic is set so that steady running is performed on a flat road in the low speed and high load region. That is, in the map of the operating state shown in FIG.
(Line indicated by thick solid line) is a steady running line, and the gear ratio control characteristic of the continuously variable transmission 40 is set such that the operating state follows the line D by controlling the gear ratio.

The low speed region is a region where the engine speed is at least 3000 rpm (1/2 of the rated speed) or less.

According to the power unit of this embodiment as described above, the fuel consumption is greatly improved, and its operation will be described below.

The indicated fuel consumption rate (fuel consumption rate of work for the piston) is bi, the average effective pressure is Pe, and the friction loss average effective pressure (loss effective due to friction of sliding parts such as pistons and driving of various auxiliary machines). If the pressure) is Pf, the net fuel consumption rate be of the engine be is as follows.

[0047]

## EQU1 ## be = {(Pe + Pf) / Pe} × bi Further, FIG. 6 shows the relationship between the engine shaft torque and the net fuel consumption rate be. When the air-fuel ratio in the engine is normally λ = 1, the broken line curve B is the non-supercharged engine in lean burn (λ> 1) in the normal time, and the solid curve C is the turbo as in the present embodiment. Each shows the case of lean burn with a supercharged engine.

In any of these cases, the basic tendency is that the fuel consumption rate is high on the low torque side and decreases as the shaft torque increases. This is because, as the average effective pressure Pe corresponding to the torque increases, the friction loss average effective pressure Pf decreases relatively, and {(Pe + Pf) / Pe} in the above formula 1 decreases. Is. Further, comparing the case where λ = 1 is normally used and the case where lean burn is performed, the indicated fuel consumption rate bi is smaller in the case of lean burn, and thus the net fuel consumption rate be is smaller.

By the way, in the curves A and B showing the case of the non-supercharged engine in FIG. 6, there is a tendency that the net fuel consumption rate increases when the axial torque becomes higher than a certain level.
Even if λ = 1 or lean burn at normal times,
This is because the air-fuel ratio must be made rich in order to obtain the required high torque when the load is high, and the indicated fuel consumption rate bi increases accordingly.

On the other hand, when the engine with a turbocharger is made lean burn, the amount of intake charge at high load is increased by supercharging, so that the torque obtained while maintaining lean burn is higher than that of the naturally aspirated engine. Therefore, the lean burn can be maintained even on the high torque side where the air-fuel ratio must be made rich in the naturally aspirated engine. When the lean-burn is performed to the high torque side by the supercharged engine as described above, both {(Pe + Pf) / Pe} and the indicated fuel consumption rate bi in the equation (1) become small. As shown, the net fuel economy is significantly lower on the high torque side compared to a naturally aspirated engine.

FIG. 7 (a) shows a constant fuel consumption rate line (a large number of curves shown by thin solid lines) and a steady running line (thick solid line) D of the net fuel consumption rate in the case of the power unit of this embodiment, and a conventional one. A steady running line (one-dot chain line) E using the transmission and an equal horsepower line (a large number of curves shown by broken lines) are shown. For comparison with the present embodiment, FIG. 7B shows an equal fuel consumption rate line of the net fuel consumption rate in the case of a naturally aspirated engine, and this equal fuel consumption rate line is generally known. Therefore, the net fuel consumption rate becomes the minimum value bmin 'in the low-speed, relatively high-torque side operation region, that is, this region becomes the optimum fuel consumption region.

When a turbocharged engine is used as in this embodiment and lean burn is performed at least in the supercharging range at a low speed range, the net fuel consumption rate is the minimum value bmin as shown in FIG. 7 (a). There is an optimal fuel consumption range in the supercharging range in the low speed range, compared to the naturally aspirated engine,
As is clear from FIG. 6 described above, the optimum fuel consumption region is on the higher torque side, and the minimum value bmin thereof is smaller than the minimum value bmin ′ in the case of a naturally aspirated engine.

In the power unit of this embodiment, the characteristic of the gear ratio of the continuously variable transmission 40 is set so that the steady running line D passes through the supercharging range in the low speed range, so that the turbocharger A significant fuel efficiency improvement effect can be obtained in connection with the lean burn using the attached engine.

That is, in order to improve the fuel consumption, it is required to drive a large number in a driving region where the net fuel consumption rate is small. However, according to the conventional general setting, the steady running line E is larger than the optimum fuel consumption region. Since the driving range is far away, the frequency of use of the driving range having a small net fuel consumption rate is reduced. On the other hand, in the present embodiment, the continuously variable transmission 40 is used, the gear ratio control characteristic thereof is adjusted, and the steady running line D is set so as to pass through the supercharging region in the low speed region. The frequency of driving in a low fuel consumption region with a low rate increases.

In this way, high torque is obtained by lean burn due to supercharging, the net fuel consumption rate is lowered in the low-speed high-torque operation region, and the frequency of use in this low fuel consumption region is increased. By controlling the gear ratio so that it can be increased, fuel efficiency is greatly improved.

In this case, particularly when the turbocharger 15 is used as the supercharger, the drive loss due to the resistance of the supercharger in the supercharge range is smaller than that in the mechanical supercharger, so that the turbocharger 15 in the supercharge range is reduced. It becomes even more advantageous by reducing fuel consumption. However, turbocharger 15
Is inferior to the mechanical supercharger in terms of low-speed torque and response, but this is compensated by the gear ratio control of the continuously variable transmission. Specifically, when the throttle opening (accelerator pedal depression amount) is increased, the gear ratio is changed by the gear ratio control of the continuously variable transmission according to the increase, that is, in FIG. As shown by the arrow in (a), the engine speed is increased according to the increase in the load, so that the horsepower is increased as compared with the case where only the load is increased. Therefore, even if the supercharging response is poor, the horsepower is earned by the increase in the number of revolutions due to the change in the gear ratio, and the low speed traveling performance and the acceleration performance are secured.

Further, in the present embodiment, the fuel efficiency is further reduced by increasing the geometrical compression ratio of the engine and setting the intake closing timing so that the effective compression ratio is smaller than the expansion ratio. I am trying.

That is, if the air-fuel ratio is made lean to the high torque side in the low speed range, the knock resistance in the low speed and high load range is improved, and accordingly, the geometric compression ratio of the engine can be increased. The compression ratio can be set to 9 or higher, which is higher than that of the supercharged engine. By increasing the compression ratio, the combustion efficiency is increased and the air-fuel mixture density at the time of compression is increased, which enables further leaning, which contributes to improvement of fuel efficiency. Further, if the intake valve closing timing is delayed and, for example, the intake valve closing timing defined for 1 mm lift is set to 50 ° or more after the bottom dead center in the crank angle, the effective compression ratio becomes sufficiently smaller than the expansion ratio,
The temperature rise due to compression is suppressed and the knock resistance is enhanced. The fuel consumption is further improved by increasing the expansion ratio while enhancing the knock resistance in this way.

Further, in the present embodiment, in connection with the fact that the air-fuel ratio is set to lean up to the high load side while performing supercharging,
At least when the load is high, EGR (exhaust gas recirculation) is performed to effectively reduce NOx.
The x purification catalyst 21 is used effectively.

That is, by making the air-fuel ratio lean, HC, CO, etc. are reduced, and if it is made significantly lean, NOx is also reduced, but in the high load region, the theoretical air-fuel ratio is to some extent due to output requirements. NOx tends to increase because there is no choice but to approach. However, in the high load region, sufficient air is supplied by supercharging and there is a sufficient margin in terms of combustion stability, and it is allowed to introduce exhaust gas into the combustion chamber in addition to making it lean. . Therefore,
NOx is reduced by performing EGR in this region.

Further, the catalyst 2 provided in the exhaust passage 12
1 purifies NOx in the lean operation state. However, the catalyst 21 capable of purifying NOx even in the lean state is generally much more efficient than the stoichiometric air-fuel ratio state when the temperature range where the NOx purification performance is high is in the lean state. If the catalyst temperature is out of this temperature range, the purification performance will be significantly reduced (see FIG. 8). Then, when the load is high, the exhaust gas temperature rises, so that the catalyst temperature tends to be higher than the temperature range in which the purification performance is high. On the other hand, the exhaust gas amount from the EGR passage 23a affects the exhaust gas temperature, and the exhaust gas temperature decreases as the exhaust gas recirculation amount increases. The catalyst temperature changes according to the exhaust gas temperature.

Therefore, the EGR is performed at the time of high load and the EGR valve 23b is controlled to control the exhaust gas recirculation amount so that the catalyst temperature is in the temperature range X with high purification performance. Therefore, NO by EGR
In addition to the effect of suppressing the x generation amount, the effect of promoting the NOx purification by the NOx purification catalyst is obtained, and the NOx emission amount is significantly reduced.

As described above, NOx is introduced into the exhaust passage 12.
The method of providing the purification catalyst 21 and controlling the exhaust gas recirculation amount so that the catalyst temperature is in the temperature range where the purification performance is high can be applied to other than the power unit of the present invention. In the case where the air-fuel ratio is larger than the stoichiometric air-fuel ratio and the air-fuel ratio is apt to generate NOx in a specific operation area such as a high load area or the whole operation area, the above method is applied. Is effective.

The specific structure of the power unit of the present invention is not limited to the above-mentioned embodiment, but various modifications can be made.

For example, in the above embodiment, the transmission 25 is provided with the toroidal type continuously variable transmission 40, but a belt type continuously variable transmission may be used.
Further, instead of such a continuously variable transmission, a multi-stage automatic transmission having a plurality of shift stages may be used. In this case,
It suffices to set the shift point for changing the gear according to the operating state so that the steady running line as shown in FIG. 7A can be obtained. However, the continuously variable transmission is easier to adjust the gear ratio according to the operating state, and the gear ratio changes smoothly. Therefore, the continuously variable transmission is advantageous in the above setting.

Further, as shown in FIG. 9, the supercharger provided in the intake passage 10 of the engine 1 may be a mechanical supercharger 71 such as a Risholum type supercharger. The mechanical supercharger 71 has a drive shaft connected to a crankshaft of an engine via a belt 72 or the like and is driven by the engine.

In the case of using this mechanical supercharger 71, a valve timing variable mechanism for varying the valve opening overlap period of the exhaust valve by changing the valve timing of at least one of the intake valve and the exhaust valve is provided. It is desirable to increase the valve opening overlap period at least in the low speed and high load region to enhance the scavenging action. In the example shown in FIG. 8, the valve mechanism for the intake valve 6 and the exhaust valve 7
To the cam pulleys 73 and 74, respectively.
Valve timing changing mechanisms 77 and 78 for changing the valve timing by changing the phases of the camshafts 75 and 76 with respect to. Then, each of the valve timing variable mechanisms 77 and 78 is an EC as a control means.
By controlling by U60 according to the driving state,
The valve opening overlap period is set to be larger at least in the low speed and high load range than in the low speed and low load range.

When the mechanical supercharger 71 is used as in this embodiment, it is more disadvantageous to fuel consumption than the turbocharger in terms of drive loss due to resistance of the supercharger in the high load type. However, since the supercharging pressure becomes higher than the exhaust pressure when a mechanical supercharger is used, increasing the valve opening overlap period at least in the low speed and high load region has the effect of lowering the mixture temperature by scavenging the high temperature residual gas. Is sufficiently obtained, and the knock resistance is enhanced. Therefore, higher supercharging,
A high compression ratio is possible and lean performance is enhanced, which is advantageous for obtaining high torque with lean burn.

Also in this embodiment, as compared with the naturally aspirated engine, the net fuel consumption rate becomes sufficiently small in the supercharging region on the high load side in the low speed region due to the improvement of the lean performance, etc. A steady running line D as shown in FIG.
By setting the characteristics of the transmission so as to obtain, the fuel efficiency can be significantly improved.

[0070]

The present invention is provided with a gasoline engine with a supercharger and an automatic transmission, and sets the air-fuel ratio to a value larger than the theoretical air-fuel ratio at least in the low speed region of the supercharging region of the engine, Since the characteristics of the transmission are set so that steady running is performed on a flat road in the low speed range of the supercharging range (Claim 1), the net fuel consumption rate in the low speed range of the supercharging range is greatly reduced. In addition, it is possible to make heavy use of this low fuel consumption region, and it is possible to significantly improve the fuel consumption.

In the present invention, the automatic transmission is a continuously variable transmission as described in claim 2, and the gear ratio control characteristic for changing the gear ratio of the continuously variable transmission in accordance with the operating state is set in the supercharging range. If the setting is made so that steady running is performed on a flat road in the low-speed range, the setting for making heavy use of the low fuel consumption range can be easily made as described above, and the acceleration performance etc. can be controlled by the gear ratio control. You can get better.

When the turbocharger is used as the supercharger as described in claim 3, the resistance at the time of supercharging is smaller than that of other superchargers, and the fuel consumption reducing effect can be enhanced.

When the mechanical supercharger is used as the supercharger as described in claim 4 and the valve opening overlap period of the intake / exhaust valve is increased at least in the low speed region of the supercharging region, the valve opening overrun is caused. By obtaining the scavenging action during the lap period, it is possible to enhance the knock resistance in the low speed region in the supercharging region, which is advantageous in achieving high supercharging to obtain high torque in lean burn.

When the geometrical compression ratio of the engine is set to 9 or more as described in claim 5, thermal efficiency can be improved and lean burn can be made advantageous, so that fuel consumption can be further reduced.

When the intake valve closing timing is set so that the effective compression ratio of the engine becomes smaller than the expansion ratio at least in the low speed range in the supercharging range as described in claim 6, the temperature rise during compression is reduced. It is possible to improve knocking resistance, and in particular, by sufficiently delaying the intake valve closing timing as described in claim 7, knocking can be sufficiently suppressed.

When the exhaust gas is recirculated at least under high load as described in claim 7, it is possible to suppress the generation of nitrogen oxides under high load.

Further, as described in claim 8, a catalyst for purifying nitrogen oxides is provided in the engine exhaust passage, and the exhaust gas recirculation amount by the exhaust gas recirculation means is set to at least the temperature of the catalyst at high load. Providing a means for controlling the temperature so that the purification performance of the catalyst is high, the nitrogen oxide can be favorably purified under a high load.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an overall structure of a power unit according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a transmission.

FIG. 3 is an explanatory diagram showing a map of air-fuel ratio control.

FIG. 4 is an explanatory diagram showing valve timing.

FIG. 5 is an explanatory diagram showing a control map of the continuously variable transmission.

FIG. 6 is a diagram showing a relationship between a shaft torque and a net fuel consumption rate.

FIG. 7 (a) is a diagram showing a steady running line, an equal fuel consumption line and an equal horsepower line, and FIG. 7 (b) is a diagram showing an equal fuel consumption line in the case of a naturally aspirated engine.

FIG. 8 is a diagram showing the relationship between the NOx purification rate and the temperature of the NOx purification catalyst.

FIG. 9 is a schematic view of an overall structure of a power unit according to another embodiment of the present invention.

[Explanation of symbols]

 1 Engine Main Body 6 Intake Valve 10 Intake Passage 12 Exhaust Passage 15 Exhaust Turbocharger 23 Exhaust Gas Recirculation Means 25 Transmission 40 Toroidal Continuously Variable Transmission 60 Control Unit

Claims (9)

[Claims] 1. A gasoline engine with a supercharger and an automatic transmission, wherein the air-fuel ratio is set to a value larger than the theoretical air-fuel ratio at least in the low speed range of the supercharging range of the engine, and the characteristics of the automatic transmission are set. Is set so that steady running is performed on a flat road in a low speed range in the supercharging range. 2. The automatic transmission is a continuously variable transmission, and the gear ratio control characteristic for changing the gear ratio of the continuously variable transmission in accordance with the operating state has a steady state in a low speed region in the supercharging region on a flat road. The power unit for a vehicle according to claim 1, wherein the power unit is set so as to travel. 3. The power unit for a vehicle according to claim 1, wherein the turbocharger is an exhaust turbocharger. 4. The supercharger is a mechanical supercharger, and
A variable valve timing mechanism that varies the valve opening overlap period of the intake and exhaust valves, and a valve timing variable mechanism that controls the valve opening variable period so that the valve opening overlap period is increased at least in the low speed and high load range compared to the low speed and low load range. The power unit for a vehicle according to claim 1 or 2, further comprising: 5. The power unit for a vehicle according to claim 1, wherein the geometrical compression ratio of the engine is set to 9 or more. 6. The intake valve closing timing is set so that the effective compression ratio of the engine becomes smaller than the expansion ratio at least in the low speed region of the supercharging region.
The vehicle power unit described. 7. The vehicle according to claim 6, wherein at least in the low speed region of the supercharging region, the intake valve closing timing defined with a 1 mm lift is set to 50 ° or more after bottom dead center in crank angle. Power unit. 8. A power unit for a vehicle according to claim 1, wherein the engine is provided with exhaust gas recirculation means for recirculating exhaust gas to the intake system at least when the load is high. 9. An engine exhaust passage is provided with a catalyst capable of purifying nitrogen oxides even when the air-fuel ratio is higher than the stoichiometric air-fuel ratio, and the exhaust gas recirculation amount by the exhaust gas recirculation means is at least when the load is high. 9. The power unit for a vehicle according to claim 8, further comprising means for controlling the temperature of the catalyst so as to maintain it in a temperature range in which the purification performance of the catalyst is high.