DESCRIPTION

ENGINE CONTROL APPARATUS

Technical Field

[0001] The present invention relates to an engine control apparatus for a vehicle or the like, with the improved control of, in particular, a stepping motor of a fuel pump in engine control.

Background Art

[0002] Conventionally, a motor for driving a fuel pump which discharges a fuel from a fuel tank of a vehicle is controlled by switching ON/OFF of energization of an electromagnetic relay. The electromagnetic relay includes a magnet which can produce an electromagnetic effect and a switch having contacts which are mechanically closed and opened by the electromagnetic effect of the magnet.

[0003] The fuel is pressure-fed by the fuel pump from the fuel tank to a pressure fuel piping. The fuel is injected into an engine cylinder by an injector. When a fuel temperature is elevated by receiving heat from neighboring components such as an engine or the motor of the fuel pump, there arises a problem that the fuel is vaporized in the pressure fuel piping to be likely to generate vapor

[0004] When the vapor is generated, the fuel cannot be pressurized, thereby destabilizing a fuel pressure. As a result, the amount of injection from the injector is also destabilized. In order to reduce a consumption current of the motor of the fuel pump to prevent the vapor from being generated, the consumption current is intended to be reduced by lowering a duty ratio of the motor of the fuel pump, for example, during idling which requires a small amount of fuel to be injected (for example, see Patent Document 1).

[0005] In the case of the fuel pump for a small vehicle such as a small two-wheel vehicle, the fuel pump is demanded to be reduced in size in view of a vehicle layout. Therefore, the motor for driving the fuel pump is required to be compactified.

[0006] [Patent Document 1] JP 2000-220548 A

Disclosure of the Invention

Problems to be solved by the Invention

[0007] The number of revolutions or the amount of discharge of the fuel pump is determined by a torque of the motor. The torque of the motor is determined by a voltage applied to the motor.
Therefore, when the voltage applied to the motor is low due to a voltage drop for engine starting or due to battery deterioration, there is a possibility that an insufficient torque of the motor delays the pressurization of the fuel to a required fuel pressure. When the insufficient pressurization lowers the fuel pressure, there is a possibility that the merchantability of the vehicle is remarkably lowered as represented by deteriorated starting performance or lowered acceleration performance because a required amount of fuel cannot be injected. Moreover, when the voltage applied to the motor is unnecessarily high, there arises a problem that the consumption current of the motor increases to cause the motor itself to generate heat. As a result, the vapor is likely to be generated.

[0008] The present invention is devised to solve the problems as described above, and has an object of obtaining an engine control apparatus which can realize the improved starting performance of an engine by ensuring the starting performance of a motor when a battery voltage failure occurs and realize the suppression of generation of vapor by reducing a consumption current of the motor during a normal operation.

Means for solving the Problems

[0009] An engine control apparatus according to the present invention includes a stepping motor corresponding to a power source of a fuel pump for sucking a fuel from a fuel tank to discharge the sucked fuel and a control unit for performing pulse width modulation control on a voltage applied to the stepping motor, the applied voltage being determined by a drive pulse rate, to control a fuel discharge amount. The control unit corrects a target drive pulse rate based on a battery voltage value of a battery to compute the drive pulse rate to make the drive pulse rate closer to the corrected target drive pulse rate, and also corrects a pulse width modulation control duty ratio of a pulse application time of the applied voltage based on the battery voltage value of the battery.

Effects of the Invention

[0010] The engine control apparatus according to the present invention has the effects of realizing, without using a special circuit as the motor of the fuel pump, the improved engine starting performance by ensuring the starting performance of the motor of the fuel pump when the battery voltage failure occurs and the suppression of generation of the vapor by reducing the consumption current of the motor during the normal operation.

Brief Description of the Drawings

[0011] [FIG. 1] A view illustrating a system configuration of an engine including an engine control apparatus according to a first embodiment of the present invention.

[ FIG. 2 ] A view illustrating the relationship between a stator and terminals of a stepping motor of the engine control apparatus according to the first embodiment of the present invention.
[ FIG. 3 ] A view illustrating an energization pattern of a drive pulse rate of the stepping motor of the engine control apparatus according to the first embodiment of the present invention.

[ FIG. 4 ] A flowchart illustrating drive control of the stepping motor of the engine control apparatus according to the first embodiment of the present invention.

[FIG. 5] A view illustrating the relation between a battery voltage value and a drive pulse rate correction amount of the engine control apparatus according to the first embodiment of the present invention.

[FIG. 6] A view illustrating the relation between the battery voltage value and a PWM control duty ratio correction amount of the engine control apparatus according to the first embodiment of the present invention.

Best Mode for carrying out the Invention

[0012] A first embodiment of the present invention will be
described below.

[First Embodiment]

[0013] An engine control apparatus according to a first embodiment of the present invention will be described referring to FIG s. lto6. FIG. 1 is a view illustrating a system configuration of an engine including an engine control apparatus according to
a first embodiment of the present invention.

[0014] In FIG. 1, a control unit 1 stores a program or a map for controlling an operation of the entire engine in a memory (not shown). The control unit 1 computes appropriate fuel injection timing and fuel injection amount based on information from an intake air temperature sensor 3 for measuring a temperature of engine intake air, which is provided for an air cleaner 2 on the intake side, a throttle position sensor 6 for measuring an opening of a throttle valve 5, which is provided for an intake pipe 4 , an intake air pressure sensor 7 for measuring an intake air pressure in the downstream of the throttle valve 5, an engine temperature sensor 9 for measuring a wall surface temperature of an engine 8, and a crank angle sensor 11 for measuring the position of a crank shaft 10. The control unit 1 then outputs a driving signal to an injector 24 corresponding to a fuel injection device.

[0015] To the exhaust side (on the left side of FIG. 1) of the engine 8, an exhaust pipe 12 and a muffler 13 are connected

[0016] In a similar manner, the control unit 1 outputs an ignition signal to an ignition coil 14 at appropriate timing based on the information from various sensors to cause an ignition plug 15 to generate sparks. As a result, a mixture of the fuel and the intake air in an engine cylinder is combusted to push out a piston of the engine 8, thereby rotating the crank shaft 10.

[0017] The fuel is injected into the engine 8 in the following manner. A motor 22 of a fuel pump 21 is driven by a driving signal from the control unit 1. The fuel pump 21 sucks the fuel from a fuel tank 20 through a filter to discharge the sucked fuel. After a pressure of the discharged fuel is adjusted to a predetermined pressure, the fuel passes through a pressure fuel piping 23 to be fed to the injector 24.

[0018] In the first embodiment of the present invention, a stepping motor is used as the motor 22 for driving the fuel pump 21.

[0019] The control unit 1 detects a battery voltage value from a battery 25 mounted in a vehicle and uses the detected battery voltage value for correcting a target drive pulse rate and a PWM (pulse width modulation) control duty ratio of the stepping motor 22 of the fuel pump 21 described below.

[0020] FIG. 2 is a view illustrating the relation between a stator and terminals of the stepping motor of the engine control apparatus according to the first embodiment of the present invention. Terminals T1, T3, T4 and T6 are phase-shifted by 90 electrical degrees . By sequentially switching an energization state in each phase, the stepping motor 22 can be rotated by each step angle. Terminals T2 and T5 are connected to the battery 25.

[0021] FIG. 3 is a view illustrating an energization pattern of a drive pulse rate of the stepping motor according to the first embodiment of the present invention. The energization pattern is two-phase full-step energization pattern in which any two of the phases are always in an energized state at any instant. As is schematically illustrated, a pulse application time (corresponding to a pulse application time illustrated in FIG. 3) corresponding to a unit time, during which a PWM-controlled drive pulse is applied to the stepping motor 22, is divided into two steps, that is, a first half period (first period) and a second half period (second period). Then, a current value for each of the periods is controlled by setting a PWM control duty ratio for each of the periods . Although the pulse application time is divided into two steps in this case, the pulse application time may be divided into a plurality of periods equal to or larger than three periods. In such a case, the control can be more sophisticated.

[0022] Next, drive control of the stepping motor according to the first embodiment of the present invention will be described referring to the drawings. FIG. 4 is a flowchart illustrating the drive control of the stepping motor of the engine control apparatus according to the first embodiment of the present invention.

[0023] First, in Step 100, the control unit 1 reads output signals from various sensors such as the intake air temperature sensor 3, the throttle position sensor 6, the intake air pressure sensor 7 , the engine temperature sensor 9 , and the crank angle sensor 11 which are connected to the control unit 1. The control unit 1 also reads a battery voltage value Vb of the battery 25.
[0024] Next, in Step 101, the control unit 1 detects a state of the vehicle from various sensors to compute a fuel injection amount required for the vehicle. For example, from a map describing the relation between a throttle position detected by the throttle position sensor 6 and an engine rotation speed calculated based on a detection signal from the crank angle sensor 11, the fuel injection amount is computed.

[0025] Next, in Step 102, the control unit 1 determines a fuel amount to be discharged from the fuel pump 21 according to the fuel injection amount computed in the previous Step 101. Because the fuel amount to be discharged varies depending on a drive pulse rate of the stepping motor 22 for driving the fuel pump 21, a target drive pulse rate of the stepping motor 22 is determined by the fuel injection amount. For example, from a map describing the relation between the fuel injection amount and the engine rotation speed, the target drive pulse rate is computed. When the fuel injection amount is large, the stepping motor 22 is driven at high rotation speed to increase the fuel discharge amount from the fuel pump 21. Therefore, the control unit 1 sets the target drive pulse rate to a high frequency. On the contrary, when the fuel injection amount is small during idling or the like, the control unit 1 sets the target drive pulse rate to a low frequency because a small fuel discharge amount from the fuel pump 21 is required.

[ 0026 ] Next, in Step 103 , the control unit 1 corrects the target drive pulse rate determined in the previous Step 102 according to the battery voltage value Vb. When the battery voltage value Vb drops, the voltage applied to the stepping motor 22 also drops to lower a motor torque. As a result, the stepping motor 22 is likely to step out. When the drive pulse rate is high, the motor torque is lowered. Therefore, the stepping motor 22 is particularly affected by the battery voltage drop to be more likely to step out. Therefore, when the battery voltage value drops, for example, when the battery voltage value drops to 12V while a normal voltage value is approximately 14V, the control unit 1 corrects the target drive pulse rate to a lower value from the relation between the battery voltage value and a drive pulse rate correction amount illustrated in FIG. 5, specifically, a map describing the relation between the battery voltage value and the drive pulse rate correction amount. More specifically, referring to FIG. 5, when the battery voltage value is 12V, a corresponding drive pulse rate correction amount is 0.8. Therefore, the target drive pulse rate is multiplied by the correction amount, 0.8. Specifically, the target drive pulse rate is set to allow the torque to be ensured even when the battery voltage value drops.

[0027] On the contrary, when the battery voltage value is high, the control unit 1 determines a large correction amount as illustrated in FIG. 5 to set a higher target drive pulse rate. For example, when the battery voltage value elevates to 16V while the normal voltage value is approximately 14V, the target drive pulse rate is corrected to a higher value. Specifically, referring to FIG. 5, when the battery voltage value is 16V, a corresponding drive pulse rate correction amount is 1.3. Therefore, the target drive
pulse rate is multiplied by the correction amount,1.3. In this manner, even when the voltage applied to the stepping motor 22 is high, the application time is reduced to reduce the consumption current. As a result, heat generation from the stepping motor 22 can be suppressed. Moreover, since the range of a settable drive pulse rate is determined depending on the type of the used stepping motor 22, the corrected target drive pulse rate is restricted to fall within the range.

[0028] Next, in Step 104, the control unit 1 compares a current drive pulse rate which is currently set and the target drive pulse rate corrected in Step 103 with each other. When the current drive pulse rate is lower than the target drive pulse rate (YES), the process proceeds to Step 105. On the other hand, when the current drive pulse rate is equal to or higher than the target drive pulse rate (NO), the process proceeds to Step 106.

[0029] Next, in Step 105, the control unit 1 increments the current drive pulse rate by a minimum resolution to make the current drive pulse rate closer to the target drive pulse rate.

[0030] On the other hand, in Step 106, the control unit 1 performs a comparison in a manner opposite to that in Step 104. When the current drive pulse rate is higher than the target drive pulse rate (YES), the process proceeds to Step 107. When the comparison is not established in Step 106 (NO) , it is determined that the current drive pulse rate is identical with the target drive pulse rate. Therefore, the process proceeds to Step 108 without changing the current drive pulse rate.

[0031] Next, in Step 107, the control unit 1 decrements the current drive pulse rate by the minimum resolution to make the current drive pulse rate closer to the target drive pulse rate.

[0032] Owing to a series of operations in Steps 104 to 107, the current drive pulse rate is not abruptly changed. Therefore, the step-out of the stepping motor 22 can be prevented. However, since it is also considered that the stepping motor 22 does not step out depending on the performance thereof even when the current drive pulse rate is greatly changed, the amount of change of the current drive pulse rate in Steps 105 and 107 is not required to be limited to the minimum resolution.

[0033] In Step 108, the control unit 1 determines the PWM control duty ratio for each of the periods obtained by dividing the application time of the pulse applied to the stepping motor 22 according to the current drive pulse rate computed in Steps 105 and 107. For example, from a map describing the relation of the current drive pulse rate and an engine temperature detected by the engine temperature sensor 9, the PWM control duty ratio is computed. When the current drive pulse rate is high, the consumption current is small because the time of application of the pulse to the stepping motor 22 is short. However, when the current drive pulse rate is low, the consumption current becomes larger because the time of application of the pulse to the stepping motor 22 is long. Therefore, by controlling the PWM control duty ratio, the duty ratio is increased to allow the consumption current to be reduced even when the current drive pulse rate is low. Although it is assumed that the PWM control duty ratio is determined for each of the periods obtained by the division in the first embodiment of the present invention, the duty ratio of the entire pulse application time may be changed at a time.
[0034] Next, in Step 109, the control unit 1 corrects the PWM control duty ratio according to the battery voltage value as in the case of Step 103. When the battery voltage value is low, the voltage applied to the stepping motor 22 drops as described for Step 103. Therefore, if the PWM control duty ratio is increased to lower the current value, the motor torque is reduced to induce the possibility of causing step-out. Therefore, from the relation between the battery voltage value and a PWM control duty ratio correction amount illustrated in FIG. 6, specifically, a map describing the relation between the battery voltage value and the PWM control duty ratio correction amount, the control unit 1 corrects the PWM control duty ratio to a larger value when the battery voltage value drops, for example, when the battery voltage value drops to 10V while the normal voltage value is approximately 14V. Specifically, referring to FIG. 6, when the battery voltage value is 10V, a corresponding PWM control duty ratio correction amount is 1.5. Therefore, the PWM control duty ratio is multiplied by the correction amount,1.5. As a result, the voltage applied to the stepping motor 22 can be increased to improve the torque.

[0035] On the contrary, when the battery voltage value is high, the control unit 1 corrects the PWM control duty ratio to a smaller value to reduce the consumption current for preventing the stepping motor 22 from generating heat. For example, when the battery voltage value is elevated to 16V while the normal voltage value is approximately 14V, the PWM control duty ratio is corrected to a smaller value. Specifically, referring to FIG. 6, when the battery voltage value is 16V, a corresponding PWM control duty ratio correction amount is 0.7. Therefore, the PWM control duty ratio is multiplied by the correction amount, 0.7. Moreover, since the range of the settable PWM control duty ratio is limited depending on the type of the used stepping motor 22, a restricting process is performed to allow the corrected PWM control duty ratio to fall within the range. The PWM control duty ratio may be corrected only for the first half period (first period) of the pulse application time or only for the second half period (second period). [0036] Next, in Step 110, when the battery voltage value indicates an abnormal voltage such as a value exceeding a predefined value, the voltage applied to the stepping motor 22 becomes extremely high. Therefore, the control unit 1 uniformly reduces the PWM control duty ratios of the respective periods obtained by dividing the pulse application time, which are determined in Steps 108 and 109, for example, by 10% when the battery voltage value exceeds, for example, 18V. In this manner, the consumption current of the stepping motor 22 can be reduced to suppress the heat generation from the stepping motor 22.

[0037] Then, in Step 111, the control unit 1 supplies the application voltage to the stepping motor 22 of the fuel pump 21 according to the current drive pulse rate and the PWM control duty ratio described above to drive the stepping motor 22.

[0038] The engine control apparatus according to the first embodiment of the present invention includes the stepping motor 22 corresponding to a power source of the fuel pump 21 for sucking the fuel from the fuel tank 20 to discharge the sucked fuel and the control unit 1 for performing the pulse width modulation control on the voltage applied to the stepping motor 22, which is determined by the drive pulse rate, to control the fuel discharge amount. The control unit 1 corrects the target drive pulse rate based on the battery voltage value of the battery 25 to compute the drive pulse rate to make the drive pulse rate closer to the corrected target drive pulse rate. At the same time, the control unit 1 corrects the pulse width modulation control duty ratio for the pulse application time of the applied voltage based on the battery voltage value of the battery 25. Thus, the improved engine starting performance can be realized by ensuring the starting performance of the stepping motor 22 of the fuel pump 21 when the battery voltage
failure occurs, while the suppression of generation of vapor can be realized by reducing the consumption current of the stepping motor 22 during the normal operation, without using a special circuit as the stepping motor 22 of the fuel pump 21.

[0039] Moreover, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the rate of the drive pulse applied to the stepping motor 22 to a low frequency when the battery voltage value of the battery 25 tends to be low. Therefore, when the battery voltage drops to induce the possibility of reducing the torque of the stepping motor 22, the current is applied to the stepping motor 22 after the drive pulse rate is switched to a low frequency. As a result, the torque of the stepping motor 22 can be ensured. By ensuring the torque, the fuel can be fed from the fuel pump even when the battery voltage drops.

[0040] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the rate of the drive pulse applied to the stepping motor 22 to a high frequency when the battery voltage value of the battery 25 tends to be high. Therefore, the voltage application time to the stepping motor 22 is reduced to allow the consumption current to be reduced. The reduction of the consumption current is effective when the stepping motor 22 generates heat.

[0041] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the PWM control duty ratio of the first period among the plurality of periods obtained by dividing the pulse application time to the stepping motor 22, based on the battery voltage value. By setting the PWM control duty ratio of the first period independently of the other period(s), a high torque can be ensured even when a large load is applied to start driving the stepping motor 22.

[0042] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the PWM control duty ratio(s) of the second and subsequent periods among the plurality of periods obtained by dividing the pulse application time to the stepping motor 22, based on the battery voltage value. Therefore, the torque is ensured in the first period to rotate the stepping motor 22 without fail. In the second and subsequent periods, the torque can be controlled to prevent the inertia of a rotor of the stepping motor 22 from being lowered. As a result, the Joule heat of a motor coil can be reduced by the reduced consumption current.

[0043] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the PWM control duty ratio to a larger value when the battery voltage value of the battery 25 tends to be low. As a result, the voltage applied to the stepping motor 22 is increased to allow the motor torque to be ensured to prevent the occurrence of step-out.

[0044] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 corrects the PWM control duty ratio to a smaller value when the battery voltage value of the battery 25 tends to be high. As a result, the applied voltage can be prevented from being increased to prevent the stepping motor 22 from generating heat due to the increased consumption current. The generation of vapor can also be suppressed.

[0045] Further, in the engine control apparatus according to the first embodiment of the present invention, the control unit 1 switches the PWM control duty ratios of all the plurality of periods obtained by dividing the pulse application time to a lower value when the battery voltage value of the battery 25 exceeds the predefined value. Therefore, an abnormally high voltage value is not applied to the stepping motor 22. As a result, the increase in consumption current, the heat generation of the stepping motor 22, and the generation of vapor can be prevented. Moreover, since the coil can be prevented from being thermally deteriorated, the engine control apparatus serves to improve the reliability of a fuel supply device.

CLAIMS

1. An engine control apparatus, comprising:

a stepping motor corresponding to a power source of a fuel pump for sucking a fuel from a fuel tank to discharge the sucked fuel; and

a control unit for performing pulse width modulation control on a voltage applied to the stepping motor, the applied voltage being determined by a drive pulse rate, to control a fuel discharge amount,

wherein the control unit corrects a target drive pulse rate based on a battery voltage value of a battery to compute the drive pulse rate to make the drive pulse rate closer to the corrected target drive pulse rate, and also corrects a pulse width modulation control duty ratio of a pulse application time of the applied voltage based on the battery voltage value of the battery.

2. An engine control apparatus according to Claim 1, wherein the control unit corrects the drive pulse rate to a low frequency when the battery voltage value of the battery is lower than a normal value.

3. An engine control apparatus according to Claim 1, wherein the control unit corrects the drive pulse rate to a high frequency when the battery voltage value of the battery is higher than a normal value.
4. An engine control apparatus according to Claim 1, wherein the control unit divides the pulse application time into a plurality of periods and corrects the pulse width modulation control duty ratio for a first period among the plurality of periods based on the battery voltage value.

5. An engine control apparatus according to Claim 1, wherein the control unit divides the pulse application time into a plurality of periods and corrects the pulse width modulation control duty ratio for a second period and those for subsequent periods among the plurality of periods based on the battery voltage value.

6 . An engine control apparatus according to Claim 4 or 5, wherein the control unit corrects the pulse width modulation control duty ratio to a higher value when the battery voltage value of the battery is lower than a normal value.

7 . An engine control apparatus according to Claim 4 or 5, wherein the control unit corrects the pulse width modulation control duty ratio to a lower value when the battery voltage value of the battery is higher than a normal value.

8. An engine control apparatus according to Claim 1, wherein the control unit sets the pulse width modulation control duty ratio in the pulse application time to a lower value when the battery voltage value of the battery exceeds a predefined value to indicate an abnormal voltage.