JPH07156696A - Power unit for vehicle - Google Patents

Abstract

PURPOSE:To attain improving accelerating performance or the like without causing busy shifting an automatic transmission, in a power unit for a vehicle provided with an engine with exhaust turbosupercharger and the automatic transmission. CONSTITUTION:An assist means 20 for assisting an exhaust turbosupercharger driven by energy, except exhaust energy, is provided relating to the exhaust turbo supercharger. Also by a control means 54 for receiving outputs of a speed change shift detecting means 55 and acceleration detecting means 56, by driving the assist means 20 only in an accelerating condition further with a speed change shift of an automatic transmission 40 in a high speed shift, at acceleration time in the high speed shift apt to lack horse power, supercharge action is improved to earn the horse power, so that accelerating performance can be improved even not by a shift down.

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 including an engine equipped with an exhaust turbocharger and an automatic transmission.

[0002]

2. Description of the Related Art Generally, a vehicle power unit includes an engine and a transmission. By providing the engine in the power unit of this vehicle with an exhaust turbocharger that is driven by exhaust energy and supercharges intake air,
Those designed to improve the output are generally known.

Further, since the exhaust turbo supercharger is difficult to obtain sufficient supercharging performance in a low speed range where exhaust energy is small, for example, as shown in Japanese Patent Publication No. 59-51649, a high pressure oil pump is used. It is also proposed to provide an assist means for assisting the drive of the exhaust turbocharger by the energy of the supplied hydraulic oil. This supercharger includes, as assisting means, a hydraulic turbine attached to a shaft connecting an exhaust turbine and a compressor, and a high-pressure oil pump for supplying hydraulic oil to the hydraulic turbine. In the hydraulic oil supply path between the oil pump and the hydraulic turbine,
A control valve that operates according to the boost pressure is provided. And
When the boost pressure is lower than a predetermined value, the assist means is driven, that is, the working oil from the high pressure oil pump is supplied to the hydraulic turbine to assist the rotation of the shaft and increase the boost pressure. It has become.

[0004]

By the way, in the exhaust turbo supercharger disclosed in the above publication, the assist means is driven when the boost pressure is low. However, in a power unit using an automatic transmission as the transmission. Had the following problems in relation to the characteristics of the automatic transmission and the running state.

That is, when the engine is in an operating state where it is required to increase the horsepower, specifically, when the engine is in an accelerating state due to an accelerator operation,
If the automatic transmission is in the low speed stage, the engine speed increases relatively quickly, and horsepower is earned by this increase in speed, so it is sufficient even if the turbocharger has a relatively low supercharging performance. Acceleration performance can be obtained. On the other hand, when the engine is accelerated while the automatic transmission is in the high gear, if the exhaust turbocharger has a low supercharging performance, the horsepower cannot be sufficiently obtained in the high gear.

As described above, when the horsepower is insufficient at the time of acceleration at a high speed, the shift map of the automatic transmission is set so that the downshift is performed, and the horsepower is earned by the downshift. Conceivable. However, if you downshift each time when accelerating at high speed,
This causes so-called shift busy, in which shifting of gears becomes extremely frequent, which gives the driver a feeling of strangeness due to a shift shock or the like, and is not preferable in terms of controllability and reliability of the automatic transmission.

In view of the above circumstances, the present invention provides an engine equipped with an exhaust turbocharger and an automatic transmission, and improves acceleration performance and the like without causing shift busy of the automatic transmission. It is an object of the present invention to provide a vehicle power unit capable of performing the above.

[0008]

In order to achieve the above object, the present invention provides an engine provided with an exhaust turbocharger which is driven by exhaust energy to supercharge intake air, and a multi-stage having a plurality of shift speeds. A power unit of a vehicle including an automatic transmission, and the exhaust turbocharger is provided with assist means for assisting driving of the exhaust turbocharger with energy other than exhaust energy, and A control means for driving the assist means is provided when the automatic transmission is in the operating state in which it is required to increase the horsepower of the engine in the state where the automatic transmission is in the lowest gear.

In the present invention, it is preferable to provide a gear shift stage detecting means for detecting a shift stage state of the automatic transmission and an acceleration detecting means for detecting an acceleration state of the engine, and the shift stage detecting means and the acceleration detection. According to the output of the means, the control means is configured to drive the assist means only in an accelerating state and when the shift stage of the automatic transmission is in the high speed stage.

Further, it is preferable that the characteristics of the automatic transmission are set such that steady running is performed on a flat road in a low speed and high load region in a high speed stage.

When setting the characteristics of the automatic transmission in this way, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine is
It is effective to set the value larger than the theoretical air-fuel ratio at least in the low speed and high load region.

Alternatively, it is also effective to set the air-fuel ratio to the stoichiometric air-fuel ratio at least in the low speed and high load region.

Further, it is preferable to set the intake valve closing timing of the engine so that the effective compression ratio becomes smaller than the expansion ratio at least in the low speed and high load region.

[0014]

According to the present invention, when the automatic transmission is in the operating state where it is required to increase the horsepower of the engine while the automatic transmission is in the specific shift stage, only the exhaust turbocharger is driven by the exhaust energy. Then, even if the horsepower is insufficient, the supercharging action is enhanced by the driving of the assist means, so that the horsepower is sufficiently earned. By doing so, when the required horsepower is ensured at the specific gear, the downshift of the automatic transmission becomes unnecessary, and shift busy can be avoided.

In the present invention, particularly in the acceleration state,
Further, if the assist means is driven only when the shift stage of the automatic transmission is in the high speed stage, the supercharging action is enhanced and the horsepower is earned at the time of acceleration in the high speed stage where the horsepower tends to be insufficient. Therefore, it is less likely that downshifting will be required when accelerating at a high speed, and shift busy can be avoided. In addition, since the engine speed increases relatively quickly during acceleration at low speeds, horsepower is earned,
In such a case, the driving of the assisting means is stopped, so that the assisting means can be prevented from becoming a driving resistance of the engine.

When the characteristics of the above-mentioned automatic transmission are set such that steady running is performed on a flat road in a low speed and high load region at a high speed stage, the automatic transmission is often operated in a low fuel consumption region on the low speed and high load side. This is advantageous for improving fuel efficiency. With this setting, acceleration often occurs from the state where steady running is performed in the low speed and high load range in the high speed stage, and in this case, if downshifting is performed each time, the shift frequency remarkably increases. However, such a situation can be avoided by driving the assist means.

Further, if the air-fuel ratio is set to a value (lean) larger than the theoretical air-fuel ratio at least in the low speed and high load range, it is advantageous in reducing fuel consumption, and moreover, the assist means is driven during acceleration at a high speed stage. As a result, the horsepower is sufficiently increased even in the lean burn state.

When the air-fuel ratio is set to the theoretical air-fuel ratio at least in the low speed and high load range, it is advantageous to the improvement of the emission and the fuel consumption as compared with the case where the amount of fuel is increased in the low speed and high load range. In this case as well, the horsepower is sufficiently increased by driving the assist means during acceleration at the high speed stage.

Further, if the effective compression ratio is made smaller than the expansion ratio at least in the low speed and high load region, the temperature rise during compression is suppressed in the low speed and high load region, so that the knock resistance is enhanced, Even when the boost pressure is increased by driving the assisting means, knocking is sufficiently suppressed.

[0020]

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 in this power unit includes an engine body 1, an intake passage 10, and an exhaust passage 12.
And so on. 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 two intake ports 4 are provided in the illustrated example.
And two exhaust ports 5 are open. 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 includes a cylinder-specific intake passage 11 downstream of the intake passage 10.
Is connected, and the exhaust port 5 is connected to the cylinder-by-cylinder exhaust passage 13 on the upstream side of the exhaust passage 12.

Further, the engine has an exhaust turbocharger 15
Is provided. The exhaust turbocharger 15 includes a turbine 16 arranged in the exhaust passage 12 and a compressor 17 arranged in the intake passage 10 and connected to the turbine 16 via a shaft 18, and is driven by exhaust energy. Then, the turbine 16 rotates, and the compressor 17 rotates in conjunction with this, so that the intake air is supercharged.

The exhaust turbocharger 15 is provided with assist means 20 for assisting the drive of the exhaust turbocharger 15 with energy other than exhaust energy. In the present embodiment, the assisting means 20 transfers energy by hydraulic pressure to the shaft 18 of the exhaust turbocharger 15.
The hydraulic turbine 21 for supplying the hydraulic fluid to the hydraulic turbine 21 is supplied with hydraulic oil.
That is, as shown in FIG. 2, the exhaust turbocharger 15
A hydraulic turbine 21 is attached to the shaft 18 in the housing 19, and a hydraulic oil injection nozzle 22 for injecting hydraulic oil toward the hydraulic turbine 21 is discharged to the housing 19 and the oil in the housing 19 is discharged. A discharge port 23 is provided.

The hydraulic oil injection nozzle 22 and the discharge port 23 are connected to the hydraulic oil supply passage 24 and the oil return passage 25 shown in FIG. The hydraulic oil supply passage 24 is connected via a control valve 27 to an oil pump 26 that is driven by the engine and discharges high-pressure oil. The control valve 27 can be switched between a state in which the oil discharged from the oil pump 26 is sent to the hydraulic oil supply passage 24 and a state in which the oil is released to a relief passage (not shown), and operates according to a control signal. Has become.

In FIG. 1, an intercooler 31 for cooling the supercharged air is provided downstream of the compressor 17 in the intake passage 10. Further, in the intake passage 10, an air cleaner 32, an air flow meter 33 for detecting the intake air flow rate, a throttle valve 34 for adjusting the intake air flow rate according to an accelerator operation, and an injector 35 for injecting and supplying fuel are arranged.

A multi-stage automatic transmission 40 is connected to the output shaft of the engine.
The final reducer 43 is connected to the output side of 0, and the final reducer 4
A wheel 45 is connected to the wheel 3 via an axle 44.

The automatic transmission 40 has a torque converter 41 and a transmission 42 provided on the output side thereof. The transmission 42 has a planetary gear mechanism such as a Ravigneaux type and friction elements such as various clutches and brakes. Then, the gear ratio is changed stepwise by engaging and releasing the friction element according to the supply and discharge of the hydraulic pressure to the friction element, so that, for example, four forward gears and one reverse gear can be obtained. Since such a multi-stage automatic transmission is conventionally known, illustration and description of details of the transmission 42 and the like are omitted.

A control unit (ECU) 50 controls the automatic transmission 40 and the engine. The control unit 50 includes the air flow meter 33, a throttle opening sensor 46 for detecting an opening of a throttle valve, an engine speed sensor 47 for detecting an engine speed, a vehicle speed sensor 48 for detecting a vehicle speed, and an automatic transmission 40. Inhibitor switch 4 to detect the range of
The signal from 9 etc. is input.

As shown in FIG. 3, the control unit 50 includes a transmission control section 51 and an engine control section 5.
Have two. The transmission control unit 51 includes a throttle opening sensor 46, a vehicle speed sensor 48, and an inhibitor switch 49.
And the like, and determines the gear stage by collating the operating state of the vehicle (throttle opening degree, vehicle speed, etc.) with a predetermined gear shift map, and controls the automatic transmission 40 to attain that gear stage. To do.

The engine control unit 52 controls the air-fuel ratio to a preset value by controlling the fuel injection amount from the injector 35 according to the intake air amount, the engine speed, etc. In addition to having the means 53, it also has the control means 54 for controlling the assist means 20. The control means 54 drives the assist means 20 when the automatic transmission 40 is in a specific shift speed and the operating state is required to increase the horsepower of the engine. Specifically, in accordance with the outputs of the gear shift detecting means 55 and the acceleration detecting means 56 included in the engine control unit 52, the automatic transmission 40 is in the accelerating state and the shift speed of the automatic transmission 40 is a high speed gear (four forward gear automatic shifts). The control means 54 is configured so as to drive the assist means 20 only when in the fourth gear).

Based on the information from the transmission control unit 51, the shift speed detecting means 55 detects the shift speed state of which shift speed the automatic transmission 40 is in. Further, the acceleration detecting means 56 calculates the rate of change of the throttle opening detected by, for example, the throttle opening sensor 46, and detects an acceleration state in which the rate of change becomes a predetermined value or more.

Assisting means 2 by the control means 54 and the like
The control of 0 is shown in the flow chart of FIG. That is, the gear and the throttle opening θ of the automatic transmission 40 are read in step S1, and it is determined in step S2 whether or not the gear is the fourth speed. If the determination is YES, the throttle opening is calculated in step S3. Change rate dθ / dt
Is determined to be equal to or greater than the predetermined value α. Then, if YES at both steps S2 and S3, the assisting means 20 is driven (step S4), and otherwise, the assisting means 20 is stopped (step S).
5).

The engine and the automatic transmission 40 in the power unit are set as follows.

The engine air-fuel ratio is set to a value larger than the theoretical air-fuel ratio at least in the low speed and high load range (supercharging range of the low speed range), and is preferably set to A / It is set to F> 17. Note that the air-fuel ratio may be set to a value larger than the theoretical air-fuel ratio in all operating regions of the engine, and may be set to the theoretical air-fuel ratio or lower in the high rotation and high load region, and in other regions. It may be set to a value larger than the fuel ratio.

Further, the intake valve closing timing is set so that the effective compression ratio becomes smaller than the expansion ratio. For example, as shown in FIG. 5, the exhaust valve is set to open near the bottom dead center and close near the top dead center so that the expansion ratio becomes a substantially geometric compression ratio, while the intake valve closes to the top dead center. It is set to open at a time later than a certain time later than the bottom dead center, and specifically, the intake valve closing timing IC defined with a 1 mm lift is set to a crank angle of 50 ° or more after the bottom dead center. It

In the present embodiment, the opening / closing timing of the intake / exhaust valve is fixed, but a valve timing variable mechanism for changing the opening / closing timing of both the intake valve and the intake / exhaust valve is provided, and at least the low speed The opening / closing timing may be controlled according to the operating state while making the effective compression ratio smaller than the expansion ratio in the low speed region in the high load supercharging region. 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.

In order to obtain a high expansion ratio, it is preferable that the geometrical compression ratio of the engine is made larger than that of a general supercharged engine (8.5 or less) so that the compression ratio is 9 or higher.

On the other hand, the characteristics of the automatic transmission 40 are set so that a steady running state can be obtained on a flat road in the low speed and high load range at the high speed stage. That is, in the operation state map shown in FIG. 6, which will be described in detail later, a line A (line indicated by a thick solid line) passing through the low fuel consumption region on the low speed and high load side is a steady running line at the fourth speed (high speed stage). The gear ratio of the fourth speed of the automatic transmission 40 is set so that the gear shift map is set such that steady running at the fourth speed is realized in the low speed and high load range on the line A. There is.

The low speed and high load range is specifically the full open torque when the engine speed is at least 3000 rpm (1/2 of rated speed) and the assist means 20 is not driven. A region in which the engine load is higher than the load at which the torque becomes ½ of the above.

According to the power unit of the present embodiment as described above, when the automatic transmission 40 is in the high speed stage and the throttle opening change rate is in an acceleration state of a predetermined value or more, the turbocharger 15 is operated. The assisting means 20 provided for the drive is driven. That is, the control valve 27 is switched to the hydraulic oil supply state, the high-pressure hydraulic oil sent from the oil pump 26 to the hydraulic oil injection nozzle 22 via the hydraulic oil supply passage 24 is injected toward the hydraulic turbine 21, and Energy is provided to the shaft 18 of the exhaust turbocharger 15. As a result, the drive of the exhaust turbocharger 15 is assisted, and the boost pressure is sufficiently increased by the assist means 20 even in the low speed range where the exhaust energy is relatively small.

Therefore, during acceleration in a state where the automatic transmission 40 is in the high speed stage, the torque of the drive of the exhaust turbocharger 15 is increased by the supercharging assisting action of the assist means 20 and sufficient acceleration performance is obtained. To be Therefore, it becomes less necessary to compensate for the torque shortage by downshifting, and shift busy can be avoided.

In particular, in the present embodiment, the characteristics of the automatic transmission 40 are set so that steady running can be performed on a flat road in a low speed and high load region at a high speed stage, while improving fuel efficiency and satisfying such conditions. Even under the condition, the action of ensuring the acceleration performance can be obtained without inducing the shift busy, and this action will be described with reference to FIG.

FIG. 6 shows the equal fuel consumption rate line of the net fuel consumption rate (a large number of curves indicated by thin solid lines), the equal horsepower line (a plurality of curves indicated by broken lines), and the characteristics of the automatic transmission 40 as described above. A steady running line (thick solid line) A at a high speed when set, and a steady running line (dashed line) B at a high speed by setting a conventional general automatic transmission are shown.

As shown in the figure, the net fuel consumption rate has the minimum value bmin in the high load region in the low speed region. In particular, while the turbocharger 15 is supercharging, the lean burn (the air-fuel ratio is larger than the stoichiometric air-fuel ratio) is set to further reduce the fuel consumption in the low speed and high load range. That is, the indicated fuel consumption rate (fuel consumption rate of work for the piston) is calculated as b
i, the average effective pressure is Pe, and the average friction loss effective pressure (average effective pressure of loss due to friction of sliding parts such as pistons and driving of various auxiliary machines) is Pf.

[0044]

[Mathematical formula-see original document] be = {(Pe + Pf) / Pe} * bi, and if lean burn is performed while supercharging is performed, the average effective pressure Pe in this equation is large, the indicated fuel consumption rate bi is small, and the mechanical Since the friction loss average effective pressure Pf is kept small by using the exhaust turbocharger 15 having a resistance lower than that of the type supercharger or the like, the net fuel consumption rate be is reduced.

Further, according to the characteristics of the conventional general automatic transmission, while the steady running line B passes through the operation area greatly separated from the optimum fuel consumption area, the characteristics of the automatic transmission 40 as in the present embodiment. According to this, since the steady traveling line A passes through the low fuel consumption region on the low speed and high load side, there are many opportunities for driving in this region. As a result, the fuel efficiency is greatly improved.

By the way, if the characteristics of the automatic transmission 40 are set as in this embodiment, it is disadvantageous in terms of the horsepower margin (the amount of increase in horsepower from the steady running state to the maximum torque). That is, as shown in FIG. 6, when the acceleration operation is performed from the state where steady running is performed at a high speed in a low speed range with a certain horsepower, the exhaust turbocharger 15
With only supercharging by, the horsepower margin P1 when the characteristic of the automatic transmission 40 is set as in the present embodiment is equal to the horsepower margin P1 when the characteristic of the conventional general automatic transmission is used.
It becomes smaller than 2. In addition, when the horsepower margin P1 is small at the high speed, the horsepower can be gained by downshifting, but this causes shift busy.

On the other hand, when the assist means 20 is driven at the time of acceleration in the high speed stage, the maximum torque in the low speed region is increased as indicated by the chain double-dashed line. The surplus amount P3 is obtained, and good acceleration performance is secured.

In this case, if 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 and high load region, knocking is prevented by suppressing the temperature rise during compression. In particular, the knock resistance is ensured even when the boost pressure is increased by driving the assist means 20.

In the present embodiment, the assist means 20 is driven during acceleration and the automatic transmission 40.
Is only in the high speed stage, and the driving of the assisting means 20 is stopped in other cases, so that the fuel economy and the traveling performance are kept good. That is, when the automatic transmission 40 is in the low speed stage, horsepower is earned by the engine speed increasing relatively quickly during acceleration, and in such a case, if the assist means 20 is driven, this is the engine speed. The driving resistance rather deteriorates the acceleration performance and the fuel consumption. Therefore, the driving of the assist means 20 is stopped at the low speed stage even during acceleration.

The concrete structure of the power unit of the present invention is not limited to the above-mentioned embodiment, but various modifications can be made. A modification will be described below.

In the above embodiment, the assist means 20 is driven at the time of acceleration only at the fourth speed, which is the highest speed stage of the automatic transmission 40. However, in addition to this, if the third speed or the like is effective for improving the acceleration performance, the assist is performed. The means 20 may be driven. However, the driving of the assisting means is stopped at least at the lowest speed (first speed).

Further, in the above embodiment, the air-fuel ratio of the air-fuel mixture is made larger than the theoretical air-fuel ratio at least in the low speed and high load region, but the air-fuel ratio is set to the stoichiometric air fuel ratio in at least the low speed and high load region. The stoichiometric air-fuel ratio may be set in the operating range. In this case, a three-way catalyst is provided in the exhaust passage.

As described above, when the stoichiometric air-fuel ratio is set at least in the low speed and high load region, the fuel consumption is reduced and the HC, CO, etc. are reduced as compared with the case where the fuel amount is increased in the high load region to make the fuel rich. Since the amount of emission is reduced and the purification rate of the three-way catalyst is increased by the theoretical air-fuel ratio,
Emissions are improved. Even when the stoichiometric air-fuel ratio is set in the low speed and high load region or the lean air fuel ratio is set as in the above embodiment, the torque is sufficiently increased by driving the assist means during acceleration in the high speed stage.

The assisting means for assisting the drive of the exhaust turbocharger 15 may be, for example, one shown in FIG. 7 or one shown in FIG.

That is, in the embodiment shown in FIG. 7, the compressor 1 of the exhaust turbocharger 15 in the intake passage 10
7, a mechanical supercharger 60 connected to an engine output shaft via an electromagnetic clutch (not shown) is provided, and a bypass passage 61 that bypasses the mechanical supercharger 60 and the bypass passage 61. Open / close valve 6 for opening / closing the passage 61
2 is provided, and the mechanical supercharger 60 constitutes an assist means. Then, by a control unit (not shown), the electromagnetic clutch is turned on at a predetermined time (acceleration at a high speed stage) to turn on the mechanical supercharger 60.
Is driven and the opening / closing valve 62 is closed, and the electromagnetic clutch is turned off except at a predetermined time.
The drive of 0 is stopped and the on-off valve 62 is opened.

In the embodiment shown in FIG. 8, an electromagnetic assist means 70 for applying electromagnetic energy to the shaft of the exhaust turbocharger 15 is provided, and this electromagnetic assist means 70 is provided at a predetermined time by a control unit (not shown). Power is supplied to the electromagnetic assisting means 70, and the power supply to the electromagnetic assisting means 70 is cut off except at a predetermined time.

[0057]

INDUSTRIAL APPLICABILITY The present invention relates to an exhaust turbocharger,
It is required to provide assist means for assisting the drive of the exhaust turbocharger with energy other than exhaust energy, and to increase the horsepower of the engine when the automatic transmission is in a specific gear other than the lowest gear. When the vehicle is in the operating state, the assist means is driven (claim 1).
Even when the horsepower is insufficient only by driving the exhaust turbocharger by the exhaust energy, the supercharging action is enhanced by driving the assist means, so that the horsepower can be sufficiently earned. Therefore, it is possible to reduce the case where it is necessary to earn horsepower by downshifting the automatic transmission and prevent shift busy. Moreover,
Since the assist means is driven only in an operating state in which the horsepower is required to be increased at the specific shift speed, and other than that, supercharging is performed only by a low resistance turbocharger, thereby improving fuel efficiency. be able to.

In this invention, when the assist means is driven only when the automatic transmission is in the high speed stage in the accelerating state, the horsepower is insufficient. By increasing the supercharging effect and increasing horsepower when accelerating at high speeds, it is less likely that a downshift will be required when accelerating at high speeds, effectively preventing shift busy. You can
On the other hand, at the time of acceleration at a low speed stage where the engine speed rises relatively quickly, the driving of the assisting means is stopped to prevent the assisting means from becoming a driving resistance of the engine, and to maintain good acceleration performance. , Can improve fuel economy.

Further, in addition to the structure of claim 2, as described in claim 3, the characteristics of the automatic transmission are set so that steady running can be performed on a flat road in a low speed and a high load region in a high speed stage. When set to, fuel efficiency can be further improved by increasing the use of the low fuel consumption region, and even with such automatic transmission setting, the assist means is driven during acceleration at a high speed stage. By
It is possible to improve the acceleration performance while preventing shift busy.

Further, as described in claim 4, when the air-fuel ratio is set to a value larger than the stoichiometric air-fuel ratio at least in the low speed and high load region, the fuel efficiency improving effect can be enhanced, and in claim 5 As described above, when the air-fuel ratio is set to the stoichiometric air-fuel ratio at least in the low speed and high load region, the emission can be improved. Then, even if the air-fuel ratio is set to the stoichiometric air-fuel ratio or a value larger than this in the low speed and high load range, the torque is sufficiently increased by driving the assist means during acceleration in the high speed range, and the above-described effect is obtained. .

When the intake valve closing timing of the engine is set so that the effective compression ratio becomes smaller than the expansion ratio at least in the low speed and high load range, the boost pressure is increased in the low speed and high load range. Even when the torque is increased, the knock resistance can be sufficiently ensured, and the torque can be effectively increased by driving the assist means during acceleration at the high speed stage.

[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 cross-sectional view showing the structure of assisting means.

FIG. 3 is a functional block diagram showing a configuration of a control unit.

FIG. 4 is a flowchart showing control of assisting means.

FIG. 5 is an explanatory diagram showing valve timing.

FIG. 6 is a diagram showing a steady running line, an equal fuel consumption line, and an equal horsepower line.

FIG. 7 is a schematic view showing another example of the assist means.

FIG. 8 is a schematic view showing still another example of the assist means.

[Explanation of symbols]

 1 Engine Main Body 15 Exhaust Turbocharger 20 Assisting Means 40 Automatic Transmission 50 Control Unit 54 Control Means 55 Gear Shift Detecting Means 56 Acceleration Detecting Means

Claims (6)

[Claims] 1. A power unit for a vehicle, comprising: an engine provided with an exhaust turbocharger that is driven by exhaust energy to supercharge intake air; and a multi-stage automatic transmission having a plurality of shift stages. In the case where the exhaust turbo supercharger is provided with assist means for assisting the drive of the exhaust turbo supercharger with energy other than exhaust energy, and the automatic transmission is in a specific gear stage other than the lowest speed stage, A power unit for a vehicle, comprising: a control means for driving the assist means when an operating state in which the horsepower of the engine is required to be increased is provided. 2. A shift speed detecting means for detecting a shift speed state of the automatic transmission, and an acceleration detecting means for detecting an acceleration state of the engine are provided, and the shift speed detecting means and the acceleration detecting means are provided in response to the outputs. 2. The power unit for a vehicle according to claim 1, wherein the control means is configured to drive the assist means only in an accelerating state and when the shift stage of the automatic transmission is in a high shift stage. 3. The power unit for a vehicle according to claim 2, wherein the characteristic of the automatic transmission is set so that steady running is performed on a flat road in a low speed and a high load region at a high speed stage. 4. The power unit for a vehicle according to claim 3, wherein the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine is set to a value larger than the theoretical air-fuel ratio at least in the low speed and high load region. 5. The power unit for a vehicle according to claim 4, wherein the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine is set to a stoichiometric air-fuel ratio at least in a low speed and high load range. 6. The vehicle according to claim 3, wherein the intake valve closing timing of the engine is set so that the effective compression ratio becomes smaller than the expansion ratio at least in the low speed and high load range. Power unit.