JPS6335831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel pump drive circuit for an internal combustion engine.

A fuel pump sends fuel from a fuel tank to a fuel injection valve, and usually includes a driving motor. The fuel pump drive circuit drives the fuel pump by operating this motor.

In conventional fuel pump drive circuits, switching elements such as relay switches and transistors are connected in series to the fuel pump motor, and when the switching element is turned on when the fuel pump is driven, power supply voltage is applied to the motor. was. In a drive circuit having such a configuration, the fuel discharge force of the fuel pump is always approximately constant as long as there is no fluctuation in the power supply voltage.

Incidentally, the pressure of the fuel discharged from the fuel pump is adjusted by a pressure regulator so that the pressure difference between the pressure and the pressure of the intake manifold of the engine is always constant.

In conventional fuel pump drive circuits, the power supply voltage when driving the fuel pump is directly applied to the motor, so when the fuel injection amount is small, such as when the engine is lightly loaded, the fuel discharge force is more than sufficient. Since the power supply voltage is wasted accordingly, it has been found that it is more desirable to be able to control the fuel discharge power in order to save power.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fuel pump drive circuit that enables control of fuel discharge power.

The fuel pump drive circuit of the present invention supplies a power supply voltage between both ends of the series circuit by making one end on the switching element side of both ends of the series circuit between the fuel pump motor and the switching element equal to ground potential, and then Integrating means for integrating the voltage across the element is provided, and when the output voltage of the integrating means exceeds the first reference voltage, the switching element is turned on to apply the power supply voltage between the terminals of the motor, and the output voltage of the integrating means is The second reference voltage is lower than the first reference voltage.
When the voltage falls below the reference voltage, the switching element is turned off.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2 a and b.

FIG. 1 is a circuit diagram of a fuel pump drive circuit according to the present invention. In FIG. 1, a voltage setting circuit 1 is capable of generating an arbitrary set voltage. An operational amplifier is connected to the output of voltage setting circuit 1.
Inverting amplifier circuit 2 consisting of OP ₁ and resistors R ₁ to R ₄
is connected. A comparator circuit 3 consisting of an operational amplifier OP ₂ , resistors R ₅ , R ₆ and a diode D ₁ is connected to the output of the inverting amplifier circuit 2 . Comparison circuit 3
The output of is connected to two inverters consisting of transistor Q ₁ and resistors R ₇ and R ₈ , transistor Q ₂ and resistors R ₉ and R ₁₀ , and the base of transistor Q ₃ via resistor R ₁₁ . . The emitter of the transistor _Q3 is grounded, and the collector is connected to one end of a fuel pump motor M and also to an integrating circuit 4 consisting of a resistor _R12 and a capacitor _C1 . The output of the integrating circuit 4, in which the voltage across the capacitor _C1 becomes the integrated output voltage, is connected to the positive input terminal of the operational amplifier _OP2 of the comparator circuit 3. Further, the collector of the transistor Q ₃ is connected to the negative input terminal of the operational amplifier OP ₂ via a hysteresis resistor R ₆ and a diode D ₁ of the comparator circuit 3.
A power supply voltage V _B is supplied to the other end of the motor M, and a smoothing capacitor C ₂ is connected between the power supply voltage V _B and the ground. Note that the capacitor _C3 connected between the collector and base of the transistor _Q3 is a negative feedback capacitor, and the diode _D2 connected in parallel to the motor M is a diode for absorbing back electromotive force.

In the fuel pump drive circuit according to the present invention having such a configuration, first, when power supply voltage _B is applied,
Transistors Q ₁ and Q ₃ are off, transistor Q ₂
is turned on, and the setting voltage _{IN is} output from voltage setting circuit 1.
occurs, and voltage ₁ is generated at the output of the inverting amplifier circuit 2. This voltage V ₁ can be expressed by the following equation since the resistors R ₁ to R ₄ have equal resistance values.

₁ = _B − _IN (1) Then, the voltage ₁ is applied to the negative input terminal of the operational amplifier OP ₂ as the first reference voltage. At this time, since the transistor _Q3 is in the off state, the output voltage of the integrating circuit 4 gradually becomes higher than the voltage ₁ , and the output of the operational amplifier _OP2 , that is, the output of the comparator circuit 3 changes from a low level to a high level. This high level becomes a drive signal that turns transistor Q ₁ on, transistor Q ₂ off, and transistor
Q ₃ are turned on and voltage _B is applied to motor M.
is applied.

Next, when the voltage _B is applied to the motor M, the output voltage of the integrating circuit 4 gradually decreases. Also, since the collector of transistor Q ₃ is almost at ground potential, the voltage applied to the negative input terminal of operational amplifier OP ₂ is a voltage V ₂ smaller than voltage ₁ due to hysteresis resistor R ₆ .
become. Therefore, when the output voltage of the integrating circuit 4 becomes smaller than the second reference voltage, voltage ₂ , the operational amplifier
The output of OP ₂ returns to low level and transistors Q ₁ ,
Since _Q3 is turned off and transistor _Q2 is turned on, voltage _B is no longer supplied to motor M.

Next, when the output voltage of the integrating circuit 4 gradually increases to voltage ₁ , the output of the operational amplifier OP becomes high level again and the voltage _B is supplied to the motor M.

In the fuel pump drive circuit according to the present invention,
The voltage supply to the motor M becomes intermittent as shown in Fig. 2a, and the output voltage of the integrating circuit 4, which is the average applied voltage of the transistor _Q3 , falls between voltages ₁ and ₂ as shown in Fig. 2b. exist. The average applied voltage _M to the motor M is the average applied voltage of the transistor _Q3 .
If the average applied voltage of _Q3 is _Q3 , it can be expressed by the following equation.

_M = _B - _Q3 (2) Also, since the average applied voltage _Q3 of the transistor _Q3 is controlled to be the output voltage ₁ of the inverting amplifier circuit 2, the following equation must hold.

_Q3 = ₁ ...(3) Therefore, from equations (1), (2), and (3), the average applied voltage _M of motor M is _M = _IN ...(4), and by changing the set voltage _IN , the voltage of motor M can be changed. The average applied voltage _M can be controlled.

Further, as shown in FIG. 2a, at the falling edge of the voltage waveform applied to the motor M, the switching operation of the transistor _Q3 is rapidly performed, so that a back electromotive peak voltage occurs. Since this peak voltage has a high frequency component, it causes noise in the output of the car's radio and reduces the S/N ratio. Therefore, the negative feedback capacitor C ₃ is used to switch the transistor Q ₃ from on to off. This slows down the operation and suppresses the peak voltage level to prevent deterioration of the car radio's S/N ratio.

As described above, in the pump drive circuit according to the present invention, the voltage across the switching element is fed back to the comparing means via the integrating means, so that the average voltage of the voltage applied to the switching element is equal to the first and second reference voltages in the comparing means. In other words, the voltage applied to the fuel pump motor by subtracting the voltage across the switching element from the power supply voltage is determined so that the average voltage is within the range between the first and second reference voltages. A drive signal is generated from the comparing means to turn the switching element on and off such that it lies within the voltage range. Therefore, when a transistor is used as the internal resistance of the motor or a switching element, for example, the voltage applied to the motor can be controlled within a desired voltage range regardless of its active characteristics. For example, by adjusting the first and second reference voltages in the comparison means according to the load condition of the engine, the voltage applied to the motor can be set, and it is possible to obtain an appropriate fuel discharge force according to the engine load. can. Furthermore, since the switching element is intermittently turned on and supplies current to the motor, power consumption can be reduced compared to conventional circuits.

Furthermore, in the fuel pump drive circuit of the present invention,
One end on the switching element side of the series circuit between the fuel pump motor and the switching element is made equal to the ground potential, and a power supply voltage is supplied between both ends of the series circuit. If the harness that connects the fuel pump motor outside the control unit comes into contact with the vehicle body due to deterioration of the outer skin, overcurrent can be prevented from flowing to the switching element, and damage to the switching element can be prevented. .

It is clear that it is desirable to supply the output signal of the electronically controlled fuel injection device to the voltage setting circuit 1 so that the set voltage generated by the voltage setting circuit 1 changes depending on the operating state of the engine.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the fuel pump drive circuit of the present invention, and FIGS. 2a and 2b are operational waveform diagrams of the circuit of FIG. 1. Explanation of symbols of main parts 1... Voltage setting circuit, 2
...inverting amplifier circuit, 3...comparison circuit, 4...integrator circuit,
M...Motor.

Claims (1)

[Claims] 1. A switching element connected in series with a fuel pump motor and turned on in response to a drive signal;
A power supply that supplies voltage between both ends of the series circuit by making one end on the switching element side of both ends of the series circuit of the motor and the switching element equal to ground potential, and a voltage between both ends of the switching element. an integrating means for integrating the output voltage of the integrating means; and generating the drive signal when the output voltage of the integrating means exceeds a first reference voltage and stops generating the drive signal when the output voltage falls below a second reference voltage that is smaller than the first reference voltage. A fuel pump drive circuit comprising: comparison means for comparing. 2. The comparing means includes a voltage setting circuit that generates a set voltage, and a voltage setting circuit that inverts and amplifies the set voltage to generate the first set voltage.
2. The fuel pump drive circuit according to claim 1, further comprising: an inverting amplifier circuit that generates a reference voltage; and a hysteresis circuit that generates the second reference voltage depending on the first reference voltage.