JPS5838366A - Driving circuit for fuel pump - Google Patents

Abstract

PURPOSE:To prevent heating of a motor as well as brakage of a circuit element by a method wherein a second switching element is annexed to the series circuit of a fuel pump motor to interrupt an over-current flowing through the motor when the over-current is flowed continuously. CONSTITUTION:When dust or the like is clogged in the fuel path of the fuel pump and a current flowing through the motor M is increased, the valtage V3 of a plus input terminal for an operational amplifier OP3 is increased gradually. When said voltage V3 becomes higher than a predetermined voltage Vr, the output level of the operational amplifier OP3 is converted into a high level. Said high level is held by a diode D3 and a resistor R15 while it is turned to a current interrupting signal and brings a transistor Q4 into ON condition through a resistor R16, threfore, the base potential of another transistor Q3 becomes to earth potential. Accordingly, the transistor Q3 becomes OFF and the over-current flowing through the motor M may be interrupted.

Description

[Detailed description of the invention] The present invention is applied 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 a conventional fuel pump drive circuit, a switching element such as a relay switch or transistor is connected in series with the fuel pump motor, and when the switching element is turned on when driving the fuel pump, power supply voltage is applied to the motor. was.

With a drive circuit configured like this, the fuel pump's fuel discharge output is always almost constant unless there is a fluctuation in the power supply voltage, so fuel injection is performed when the engine is lightly loaded; when d is low, the fuel discharge output is Although this is more than enough, that amount of power is still wasted.

Therefore, it is desirable to be able to control the fuel discharge force in order to save power, and the applicant has already proposed a fuel pump zero drive circuit as shown in FIG.

In FIG. 1, a voltage setting circuit 1 is capable of generating an arbitrary set voltage. An inverting amplifier circuit 2 consisting of an operational amplifier OP1 and resistors R1 to R4 is connected to the output of the voltage setting circuit 1.

The output of the inverting amplifier circuit 2 is an operational amplifier OP2. Resistance R,
A comparison circuit 3 consisting of a diode D, a diode D, and a diode D is connected. The output of the comparator circuit 3 includes a transistor Q,
and resistor R, , R8, transistor Q2 and resistor 11
．． , + "f O, and the base of transistor Q3 is connected through a resistor R1. The emitter of transistor Q3 is grounded,
One end of a fuel pump motor M is connected to the collector, and an integrating circuit 4 consisting of resistors R1 and R2 and a capacitor C1 is also connected. The output of an integrating circuit in which the voltage across the capacitor C4 becomes an integrated output voltage, and the output of the comparator circuit; is connected to the IF terminal of the operational amplifier OP2 of 3. In addition, the collector of the transistor (N) is connected to the negative power input of the operational amplifier OP2 via the resistor 1 for hysterinosis of the comparator circuit 3 and the diode D1. 1 (8 lB is supplied, and a capacitor C2 for damping is connected between the power supply voltage VB and the ground.
is connected. Note that a diode 1) 2 connected in parallel to the motor M is a diode for absorbing back electromotive force.

In the fuel pump drive circuit having such a configuration, first, when the electric voltage vR is applied, the transistor Q1. Q5 is turned off, transistor Q2 is turned on, a set voltage v1N is generated from the voltage setting circuit 1, and a voltage 1 is generated at the output of the inverting amplifier circuit 2. This voltage V, the resistance ``(,1
.about.It4 have the same value of O'■'L, so it can be expressed by the following equation.

v1= vR" I N ・−'−・(
1) The voltage v1 is then applied to the negative input terminal of the operational amplifier OP2. At this time, since the transistor Q3 is in the off state, the output voltage of the integrating circuit 4 gradually becomes larger 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 serves as a drive signal to turn on transistor Q1, turn off transistor Q2, and turn on transistor Q3 to apply voltage VB to motor M.

Next, when the motor Mvc voltage 8 is applied, the integrating circuit 4
output voltage gradually decreases. Furthermore, since the collector of the transistor Q3 is approximately at ground potential, the voltage applied to the negative input terminal of the operational amplifier OP2 becomes the voltage 2vC, which is smaller than the voltage 2vC, due to the hysteresis resistor R16. Therefore, when the output voltage of the integrating circuit 4 becomes smaller than the voltage ■2, the output level of the operational amplifier OP2 returns to a low level, and the transistor Q
1. Since Q3 is turned off and transistor Q2 is turned on, voltage 8 is no longer supplied to motor M.

Next, the output voltage of the integrating circuit 4 gradually increases until the voltage ■
When it becomes 1, the output level of the operational amplifier OP2 becomes high level again, and the voltage 8 is supplied to the motor M.

In such a fuel pump drive circuit, the voltage supply to the motor M is intermittent, and the output voltage of the integrating circuit 4, which is the average applied voltage of the transistor Q3, becomes a voltage 1. ■It exists between the two. The average voltage applied to the motor 1 can be expressed by the following equation, assuming that the average voltage applied to the transistor Q3 is 2 and 3.

■M-VB ``Q3 ''''-'-'・(2
) Also, since the average applied voltage Q3 of the transistor Q3 is controlled so that the output voltage of the inverting amplification plane 2 becomes 1 vC, the following equation must hold true.

V, 3-V, ・・・・・・・・・ (
3) Therefore, from equations (1), (2), and (3), the average applied voltage of motor N・1 becomes Vo vIN (4), and by changing the set voltage The average applied voltage (2) of the motor M can be controlled.

In internal combustion engines, a fuel filter is installed to eliminate dust and other particles contained in the fuel, but some internal combustion engines are installed downstream of the fuel pump, so it is difficult to remove the dust inside the fuel pump. The fuel containing it passes through. However, since the fuel passage inside the fuel pump is narrow, the passage may become clogged with fuel.

In this case, the load on the motor becomes larger than normal. However, in such a fuel pump drive circuit, since a current limiting resistor is not connected in series with the motor, when the load on the motor becomes large due to the above reasons, an overcurrent flows through the motor. This is because the resistance value of the current limiting resistor is so large that it cannot be ignored, and if such a resistor is connected in series with the motor, the circuit configuration for controlling the average applied voltage of the motor will become complicated. . Therefore, there are problems in that the motor generates heat or switching elements such as transistors are destroyed due to overcurrent.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a fuel pump X-motion circuit that prevents heat generation in the motor and destruction of switching elements.

A fuel pump fψ dynamic circuit according to the present invention (・size, fuel 7j?7
) The current flowing through the DC circuit is cut off when an overcurrent of more than a predetermined value continues for a predetermined period of time fL in the series circuit between the motor and the first switching element.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG.

In FIG. 2, parts equivalent to those in FIG.
The voltage across P3 is connected to the positive input terminal of an operational amplifier (') P3 via an integrating circuit 5 consisting of a resistor F(,4) and a capacitor C3.The negative input terminal of an operational amplifier OP, A predetermined voltage V is supplied, and a series circuit consisting of a feedback resistor R, 5 and a diode 5 is connected between the positive input terminal and the output terminal. Also, there is a resistor at the output end, 16
The base of transistor Q4 is connected through the terminal.

The emitter of transistor Q4 is grounded, and the collector is connected to the base of transistor Q3. Note that the resistance I (7) has an extremely small resistance value and can be ignored when controlling the average voltage applied to the motor.The other configuration of the fuel pump drive circuit according to the present invention is the conventional example shown in FIG. Since it is the same as that, the explanation is omitted here.

In the fuel pump drive circuit according to the present invention having the above configuration, when the transistor Q3 is turned on, the motors N1,
Between collector and emitter of transistor Q3 and resistor R+
Current flows through the series circuit of 3. The voltage across the resistors R2 and R3 is a voltage corresponding to this current, which is integrated by the resistor R114 and the capacitor C5 and supplied to the positive input terminal of the operational amplifier 01]3. Normally, since the voltage at the positive input terminal is lower than the predetermined voltage V 1 supplied to the negative input terminal, the output level of the operational amplifier OP is at a low level, and therefore the transistor Q4 is in an off state. Incidentally, an integrating circuit 5 consisting of a resistor (14) and a capacitor C3 is inserted to prevent the voltage at the positive input terminal of the operational amplifier OP3 from becoming higher than a predetermined voltage Vr due to the large current flowing when the motor M is started.

For example, the fuel passage of the fuel pump (・c-J″ Mikafuku 21
) and the blood flow to the motor 1 increases, the 3rd [tsu Ha
, ), the voltage V3 at the positive input terminal of the operational amplifier OP6 gradually increases by 1. And this voltage ■ is the predetermined voltage ~
! When it becomes greater than 7, the output level of the operational amplifier OP5 is inverted from a low level to a high level as shown in FIG. 3 (6).

This high level is held by the diode D3 and the resistors R and 5 ('coyori'), and becomes a current cutoff signal, and the resistor 1 (1
6, the transistor Q4 is turned on via Ql[4, so the base potential of the transistor Q3 is almost ground'1
l-j fI'l: と・しる. Therefore, transistor Q
6 becomes off-state and cuts off the overcurrent flowing to the 7-terminal N1.

Thus, the fuel by the present investigation,”? 7 no H, y, r
According to the dynamic circuit, it is possible to prevent heat generation in the motor and destruction of switching elements when an overcurrent flows through the motor without changing the circuit configuration for controlling the average applied voltage of the motor. It can be done.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a private pump drive circuit already proposed and disclosed by the applicant, FIG. 2 is a circuit diagram showing an embodiment of the fuel pump and drive circuit of the present invention, and FIG. 3(a). (b) is an operation waveform diagram of the circuit of FIG. 2. Explanation of symbols of main parts 1... Voltage setting circuit 2... Inverting amplifier circuit 3...
-Comparison circuit 4,5...Integrator circuit M...Motor Applicant Nippon Den Hayaki Co., Ltd. Agent Patent attorney Motohiko Fujimura

Claims (2)

[Claims] (1) a first suinochinda element connected in series with a fuel pump motor and turned on in response to a drive signal; and a power source that supplies voltage between both ends of a series circuit of the motor and the first switching element; drive signal generation means for intermittently generating the drive signal to control the average applied voltage of the motor, current detection means for generating a voltage according to the current flowing through the motor; Comparing means for generating a current cutoff signal when the output voltage continues to be equal to or higher than a predetermined voltage for a predetermined period of time, and a second switching element that operates to cut off the current flowing through the series circuit in response to the current cutoff signal. A fuel pump drive circuit characterized by: (2) The second switching element is provided between the input end of the drive signal of the first switching element and one end of the power supply, and becomes an axle-shaped fμ in response to a current cutoff signal. The fuel pump drive circuit according to item 1.