CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE WITH TURBOCHARGER

Abstract: A control system for an internal combustion engine having a turbocharger determines an amount of air commensu­ rate with an amount of fuel to be supplied which corresponds to the amount of depression of an accelerator pedal, based on the rotational speed of the engine and the amount of depression of the accelerator pedal. If a value produced by subtracting an amount of air downstream of a throttle valve from the commensurate amount of air is larger than a prede­ termined value, then an electric rotary machine combined with the turbocharger is operated as a motor to increase the amount of air supplied to the engine, and an amount of fuel corresponding to the supplied amount of air is supplied to the engine.

Description: The present invention relates to a control system for an internal combustion engine having a turbocharger drivable by the energy of exhaust gases emitted from the engine, and more particularly to a control system for an internal combustion engine, especially a gasoline engine, having a turbocharger combined with an electric rotary machine serving as a motor-generator mounted on the rotatable shaft of the turbocharger. Japanese Laid-Open Patent Publication No. 60-195329 discloses an engine system in which an electric rotary machine operable as a motor or a generator is mounted on the rotatable shaft of a turbocharger drivable by the energy of exhaust gases emitted from an engine, and the electric rotary machine is operated as a motor or a generator dependent on operating conditions of the engine. According to the disclosed arrangement, when the engine rotates at a low speed and under a high load, the electric rotary machine is operated as a motor to assist in turbocharging the engine. With a gasoline engine, unlike a diesel engine, the boost pressure produced by the turbocharger is increased up to a region upstream of a throttle valve. When the engine is under a partial load, however, the opening of the throttle valve is reduced, and the pressure near an intake valve is made lower than the atmospheric pressure. In case the electric rotary machine is operated as a motor with the turbocharged boost pressure used as a reference, since the pressure of intake air supplied to the engine is low, no optimum engine output power is available when the engine is partially loaded. FR-A-2183337 and EP-A-0217537 each disclose a turbocharged engine in which an electric rotary machine is disposed on a rotable shaft of the turbocharger, the intake air pressure being sensed and used in conjunction with the engine speed, the amount of depression of the accelerator pedal and other measured operating conditions to control operation of the electric machine. It is an object of the present invention to provide a control system for an internal combustion engine having a turbocharger, the control system being capable of supplying the engine with an amount of air commensurate with a supplied amount of fuel corresponding to the amount of depression of an accelerator pedal, even when the engine is under a partial load, so that engine output power corresponding to the amount of depression of the accelerator pedal, which represents the intention of the driver for acceleration or deceleration, can be produced. According to the present invention, a control system is provided for an internal combustion engine having a turbocharger, comprising: an electric rotary machine disposed on a rotatable shaft of the turbocharger; an accelerator pedal movement sensor for detecting the amount of depression of an accelerator pedal which controls operation of the engine; an engine speed sensor for detecting the speed of rotation of the engine; means for supplying calculated electric power to the electric rotary machine; and, means for supplying the engine with a calculated amount of fuel; is characterised by: an amount-of-air sensor for detecting the amount of air downstream of a throttle valve disposed in an intake pipe connected to the engine; means for calculating an amount of air commensurate with an amount of fuel to be supplied which corresponds to the amount of depression of the accelerator pedal, based on detected signals from the engine speed sensor and the accelerator pedal movement sensor; means for calculating the electric power to be supplied to the electric rotary machine, which corresponds to the difference between the commensurate amount of air and the amount of air detected by the amount-of-air sensor, when a value produced by subtracting the amount of air detected by the amount-of-air sensor from the commensurate amount of air is larger than a predetermined value; and, means for calculating the amount of fuel to be supplied which corresponds to the amount of air detected by the amount-of-air sensor, after the electric rotary machine is operated. The above and other objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view, partly in block form, of a control system according to the present invention; Figs. 2(a) and 2(b) are a flowchart showing an operation sequence of the control system. DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, an internal combustion engine 1 using gasoline as fuel produces combustion energy by burning fuel supplied from a fuel tank 2a through a fuel pump 2b and an injector 2c and mixed with air drawn through an intake pipe 1a, and discharges exhaust gases through an exhaust pipe 1b. Power generated by the combustion energy produced by the engine 1 is transmitted through a clutch 31, a transmission 32, a propeller shaft 33, and a final speed reducer 34 to road wheels 35 to drive a motor vehicle on which the engine 1 is mounted. The rotational speed of the engine 1 is detected by an engine speed sensor 11, which sends a detected signal to an electronic control unit 5. A throttle valve 4 is disposed in the intake pipe 1a and operated by an accelerator pedal 40. The amount of depression of the accelerator pedal 40 is detected by an accelerator pedal movement sensor 41, which issues a detected signal to the electronic control unit 5. A turbocharger 6 is coupled to the intake pipe 1a and the exhaust pipe 1b and has a turbine 6b drivable by the energy of exhaust gases emitted from the engine 1 and a compressor 6a rotatable by the turbine 6b for charging intake air into the engine 1. The turbine 6b and the compressor 6a are interconnected by a rotatable shaft 6c on which there is mounted an electric rotary machine 7 that can selectively operate as a motor or a generator. When the turbine 6b is rotated by the exhaust energy, the electric rotary machine 7 operates in a generator mode to generate electric power which is sent to a power converter 8 that charges a battery 9 mounted on the motor vehicle. The power converter 8 comprises various power control circuits such as a rectifying/smoothing circuit for converting AC electric power to DC electric power, a converter circuit for freely varying the voltage of the DC electric power, an inverter circuit for converting the DC electric power to AC electric power with adjustable frequency, and a duty cycle control circuit having semiconductor devices for controlling the voltage and current of the electric power. These various power control circuits are controlled by control commands from the electronic control unit 5. For increasing the output torque from the engine 1, the DC electric power from the battery 9 is converted to AC electric power, which is supplied to the electric rotary machine 7. The electric rotary machine 7 then operates in a motor mode to drive the compressor 6a for compressing intake air, thus increasing the boost pressure of intake air to be charged into the engine 1. An amount-of-air sensor 12 is attached to the intake pipe 1a downstream of the throttle valve 4 for detecting the amount of air supplied to the engine 1. A boost pressure sensor 13 is mounted on the intake pipe 1a upstream of the throttle valve 4. Detected signals from the sensors 12, 13 are applied to the electronic control unit 5. The rotational speed of the rotatable shaft 6c of the turbocharger 6 is detected by a turbine speed sensor 61, and the phase of the magnetic field and the output of the rotor of the electric rotary machine 7 is detected by a phase sensor 71. Detected signals from the sensors 61, 71 are also applied to the electronic control unit 5. The electronic control unit 5 comprises a microcomputer having a central processing unit for effecting arithmetic operations on signals from the various sensors and comparing coefficients, memories for storing a control program and various data, and an input/output unit for receiving various signals and transmitting control commands. The electronic control unit 5 issues commands for controlling the amount of fuel supplied from the injector 2c to the engine 1, the output power of the power converter 8, and the voltage generated by the electric rotary machine 7. The memories of the electronic control unit 5 store amounts of air to be supplied which are commensurate with amounts of fuel supplied corresponding to amounts of depression of the accelerator pedal 40, engine rotational speed data corresponding to amounts of depression of the accelerator pedal 40, and maps of these data. Operation of the control system will now be described below with reference to the flowchart of Figs. 2(a) and 2(b). A step 1 determines whether the engine 1 is idling or not based on a speed signal from the engine speed sensor 11. If the engine speed is an idling speed, then control goes to a step 2 in which the electric rotary machine 7 is operated in an idling generation mode. If the engine speed is not an idling speed in the step 1, then a signal from the accelerator pedal movement sensor 41 is checked in a step 3. If the accelerator pedal 40 is fully depressed, then control goes to a step 5, and if the accelerator pedal 40 is partly depressed, then control goes to a step 4. In the step 4, the engine rotational speed is detected by the engine speed sensor 11. Then, an amount of air (Q₁) to be burned at a proper air/fuel ratio commensurate with an amount of fuel supplied which corresponds to the amount of depression of the accelerator pedal 40 is calculated in a step 6. A present amount of air (Q p ) is then detected based on a signal from the amount-of-air sensor 12 in a step 7. A step 8 compares the difference (Q₁ - Q p ) between the amount of air (Q₁) and the amount of air (Q p ) and a predetermined amount of air (Q A ). If (Q₁ - Q p ) > (Q A ), then it is determined that the engine 1 should be accelerated, and the turbine rotational speed is measured based on a signal from the turbine speed sensor 61 in a step 9. In a next step 10, the electric power to be supplied and the phase thereof are set which correspond to the difference between the amount of air (Q₁ ) and the present amount of air (Q p ). The inverter of the power converter 8 is controlled to drive the electric rotary machine 7 in a step 11. In a step 12, the amount of air (Q p2 ) is measured based on a signal from the amount-of-air sensor 12. In a step 13, the amount of fuel to be supplied which corresponds to the amount of air (Q p2 ) is calculated, and the injector 2c is controlled to supply the calculated amount of fuel into the engine 1. A step 14 then compares the amount of air (Q p2 ) with the amount of air (Q₁) corresponding to the amount of depression of the accelerator pedal 40. If (Q p2 ) > (Q₁), then the electric power supplied to the electric rotary machine 7 is reduced in a step 15, and the amount of air (Q p3 ) is measured based on a signal from the amount-of-air sensor 12 in a step 16. The amount of fuel to be supplied which corresponds to the amount of air (Q p3 ) is calculated and the injector 2c is controlled in a step 17. A step 18 determines whether the amount of air (Q p3 ) is equal to the amount of air (Q₁). If equal, then the power converter 8 is turned off in a step 19, the voltage generated by the electric rotary machine 7 is measured in a step 20, and the generated voltage is controlled in a step 21. If (Q₁ - Q p ) < (Q A ) in the step 8, then it is determined that the engine is in a steady mode, and control goes to a step 22 in which the amount of air is measured based on a signal from the amount-of-air sensor 12. In a next step23, the amount of fuel to be supplied which corresponds to the measured amount of air is calculated and the injector 2c is controlled. Then, the voltage generated by the electric rotary machine 7 is measured in a step 24. If the measured voltage is higher than a predetermined voltage, e.g., 12 V, in a step 25, then the generated voltage is controlled in a step 26. If the accelerator pedal 40 is fully depressed in the step 3, the engine rotational speed is detected by the engine speed sensor 11 in the step 5. Then, an amount of air (Q 1M ) corresponding to a proper air/fuel ratio for the amount of fuel to be supplied which corresponds to the full depression of the accelerator pedal 40 is calculated in a step 27. Then, steps 28 through 32 effect the same processing as that in the steps 9 through 13, and a step 33 compares the amount of air (Q 1M ) and the amount of air (Q p2 ). If the measured amount of air (Q p2 ) is larger than the amount of air (Q 1M ), then the electric power supplied from the power converter 8 is reduced in a step 34, and the amount of air (Q p3 ) is measured based on a signal from the amount-of-air sensor 12 in a step 35. The amount of fuel to be supplied which corresponds to the amount of air (Q p3 ) is calculated and controlled in a step 36. A step 37 compares the difference (Q 1M - ΔQ) which is produced by subtracting a small amount ΔQ from the amount of air (Q 1M ) with the measured amount of air (Q p3 ). If (Q p3 ) > (Q 1M - ΔQ), then the electric power supplied to the electric rotary machine 7 is checked in a step 38. If the supplied amount of electric power is zero, then the voltage generated by the electric rotary machine 7 is measured in a step 39 and controlled in a step 40. If the supplied amount of electric power is not zero in the step 38, then control returns to the step 34. If the amount of air (Q p3 ) is smaller than (Q 1M - ΔQ) in the step 37, the electric power supplied to the electric rotary machine 7 is increased in a step 41, and then (Q 1M - ΔQ) and (Q p3 ) are compared in a step 42. If the amount of air (Q p3 ) is smaller than (Q 1M - ΔQ), then the electric power supplied from the power converter 8 is increased again in the step 41. With the present invention, as described above, the amount of air commensurate with the amount of fuel supplied which corresponds to the amount of depression of the accelerator pedal is determined on the basis of the engine rotational speed and the amount of depression of the accelerator pedal. If the value produced by subtracting the amount of air downstream of the throttle valve from the determined amount of air is larger than a predetermined value, then the electric rotary machine combined with the turbocharger is operated as a motor to increase the amount of air to be charged into the engine, and the amount of fuel corresponding to the supplied amount of air is controlled. Therefore, engine output power corresponding to the amount of depression of the accelerator pedal, which indicates the intention of the driver for accelerator or deceleration, can be produced even when the engine is under a partial load.

Claims: 1. A control system for an internal combustion engine (1) having a turbocharger (6), comprising: an electric rotary machine (7) disposed on a rotatable shaft (6c) of the turbocharger; an accelerator pedal movement sensor (41) for detecting the amount of depression of an accelerator pedal (40) which controls operation of the engine; an engine speed sensor (11) for detecting the speed of rotation of the engine; means (8) for supplying calculated electric power to the electric rotary machine (7); and, means (2c) for supplying the engine with a calculated amount of fuel; characterised by: an amount-of-air sensor (12) for detecting the amount of air downstream of a throttle valve (4) disposed in an intake pipe (1a) connected to the engine; means (5) for calculating an amount of air commensurate with an amount of fuel to be supplied which corresponds to the amount of depression of the accelerator pedal (40), based on detected signals from the engine speed sensor (11) and the accelerator pedal movement sensor (41); means (5) for calculating the electric power to be supplied to the electric rotary machine (7), which corresponds to the difference between the commensurate amount of air and the amount of air detected by the amount-of-air sensor, when a value produced by subtracting the amount of air (Q p ) detected by the amount-of-air sensor from the commensurate amount (Q₁) of air is larger than a predetermined value (Q A ); and, means (5) for calculating the amount of fuel to be supplied which corresponds to the amount of air detected by the amount-of-air sensor, after the electric rotary machine is operated. 2. A control system according to claim 1, wherein the engine uses gasoline as the fuel. 3. A control system according to claim 1, wherein the means (5) for calculating electric power includes means for reducing electric power to be supplied to the electric rotary machine when the amount of air detected by the amount-of-air sensor is larger than the commensurate amount of air.

Inventors: KAWAMURA, HIDEO
Applicants: ISUZU MOTORS LIMITED
Application year: 1988
Main classification: F02D33
IPC codes: F02B37, F02D41, F02B1