JPS6140930Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for an output transistor used in a constant speed traveling device for an automobile.

Electrical circuits for automobiles are often subjected to harsh conditions, and therefore it is necessary to adopt various methods of protection against such conditions. In particular, in actuators used in constant speed driving devices that automatically control constant speed driving of automobiles, the coil windings of plunger relays, etc., which are used to convert electrical signals into mechanical force, are at high risk of being short-circuited due to the intrusion of rainwater or careless handling.
Therefore, unless some kind of protection circuit is provided for short circuits in these coil windings, the output transistors that supply current to these coil windings can be destroyed in an instant. For this reason, protection circuits for the output transistors have traditionally been provided in automobile cruise control devices, but the protection circuit itself is configured as a circuit independent of other circuits, which tends to result in a large number of parts and an expensive circuit.

The present invention was made to correct these disadvantages of conventional circuits, and the output transistor protection circuit is configured by actively utilizing the circuit itself originally included in the constant speed driving device for automobiles. The purpose is to

That is, in the present invention, a circuit is provided that constantly detects the current flowing through the control valve coil and release valve coil, which are used in the actuator of the constant speed traveling device and have a high risk of shot. When it is detected that an excessive current has flowed,
Resets the self-holding circuit that enables constant speed running. In a constant speed running device, the self-holding circuit is set when running at a constant speed, and only at this time current flows to the control valve coil and release valve coil to control constant speed running, so if the self-holding circuit is reset, these Current will no longer flow through the coil, and the output transistor will be protected.

The present invention will be described in more detail below along with examples.

FIG. 1 shows a block diagram of a constant speed traveling device for an automobile. Now, assuming that the car is running at a given speed, a rotating magnet with two poles each (NS) is attached to the back of the speedometer (not shown), so the reed switch 1 has a frequency corresponding to the vehicle speed. Generate a signal. This vehicle speed signal is converted into a DC voltage according to the frequency by the FV conversion circuit 2, and is applied to the input terminal of the comparison circuit 4 through the line 3. On the other hand, when the driver wishes to drive the vehicle at a constant speed at the current speed, the driver presses the set switch _S1 . This generates a signal L (low) on line 5, which is converted into a signal H (high) by inverter 6 and then applied to the input terminal of NAND circuit 8 through line 7. Therefore, when the signal sent from the output line 10 of the high-speed limiter circuit 9 to the NAND circuit 8 is H, the signal L is output from the output line 11 of the NAND circuit 8. Here, the high-speed limiter circuit 9 is a circuit that prohibits constant-speed running at high speeds that are subject to legal regulations. In other words, in Japan, continuous driving at high speeds of 102 km/h or higher is prohibited by law, so high-speed limiter circuits have traditionally been used in constant-speed driving devices for automobiles. The high-speed limiter circuit 9 employed in the embodiment of the present invention, together with the NAND circuit 8 and the like, prohibits the self-holding circuit 12 from being set at high speeds. FIG. 2 is a diagram for conceptually explaining such a function. In other words, high-speed signals are prohibited in circuit 3.
When the vehicle speed is not input to 0, when the set switch _S1 is pressed, the signal L is sent directly to the self-holding circuit, the self-holding circuit is set, and constant speed driving is started, but the high speed signal is not input to the prohibition circuit. 30
, the signal L will not be input to the self-holding circuit even if the set switch _S1 is pressed. Figure 3 shows a circuit that embodies such a function, and the chime signal that is generated intermittently at high speed is smoothed by the smoothing circuit 3.
1 and input to the inverter 32 as a continuous H signal. The inverter 32 inverts this input signal and inputs the signal L to the NAND circuit 8. Therefore, even if the set signal is input through the inverter 33 during high-speed running, the signal L is input from the NAND circuit 8.
is never output. On the other hand, when driving at low speeds where no chime signal is generated, the smoothing circuit 31
Since the signal L is output from the inverter 32
The signal that is input to the NAND circuit 8 through 2 becomes H.
Therefore, in this state, by inputting the set signal,
A signal L will be sent from the NAND circuit 8. In this way, the high-speed limiter circuit used in this constant-speed running device does not release the set state of the self-holding circuit like the conventional one, so setting it for constant-speed running at high speeds is prohibited. However, even if you press the set switch while driving at high speed with the chime sounding, there is no risk that the previously activated constant speed driving function will be cleared. In other words, since the car maintains the constant speed driving function, when the accelerator is released, the car will run at the original memorized speed. Therefore, if the speed reaches such a high speed that the chime sounds for a moment on a downhill slope, or if you temporarily press the accelerator to prevent danger from overtaking, etc., each time you There is no need to worry about operating a switch, and you can drive safely for long periods of time at a constant speed.

Now, when the set switch _S1 is pressed while driving at low speed and the signal L is sent from the NAND circuit 8 to the line 11, the analog switch 13 is turned on for a moment, and the DC voltage corresponding to the vehicle speed appearing on the line 3 is turned on. is stored in the analog memory circuit 14. On the other hand, when signal L is generated on line 11, self-holding circuit 12 is set, so line 1
5, energization of the release valve coil begins. Moreover, the control valve is also in a state where it can be energized. However, while the set switch _S1 is pressed, the input signal input from the NAND circuit 8 to the AND circuit 16 is L, so the control valve coil is not energized.

Now, the release valve coil is a coil part of an electromagnet that alternately opens and closes the atmospheric communication hole of the negative pressure chamber of the actuator, and the control valve coil alternately opens and closes the negative pressure atmospheric communication hole and the communication hole to the intake manifold. It has the function of adjusting the atmospheric pressure of the negative pressure chamber inside the actuator. The actuator moves the diaphragm using negative pressure in the intake manifold, thereby controlling the throttle link system. That is, as negative pressure is introduced into the negative pressure chamber within the actuator and the pressure in the negative pressure chamber is reduced, the diaphragm mechanically moves the throttle link system to open the throttle and increase engine output. On the other hand, when the partial pressure at which the atmosphere is introduced into the negative pressure chamber increases, the negative pressure chamber approaches atmospheric pressure and the throttle is returned accordingly, reducing engine output. The atmospheric pressure in such a negative pressure chamber decreases only when both the release valve coil and the control valve coil are driven, and at other times, the atmosphere is introduced and approaches atmospheric pressure. Therefore, after the self-holding circuit 12 is set and the release valve coil is activated, the negative pressure chamber exhibits a corresponding atmospheric pressure according to the control signal output by the comparator circuit 4, and the vehicle speed is controlled. The Rukoto. Here, the advance angle compensation circuit 1 is provided between the comparison circuit 4 and the control valve coil.
Reference numeral 7 denotes a circuit for apparently eliminating control delay due to hysteresis exhibited by the throttle link system in speed control, and has the function of advancing the duty of the control signal output from the comparator circuit 4.

By the way, it is the output circuits 19 and 20 that drive the control valve coil and the release valve coil based on the control signal appearing on the output line 18 of the AND circuit 16 and the signal appearing on the output line 15 of the self-holding circuit. In this invention,
The drive current flowing through the coils such as these control valve coils is constantly detected by the overcurrent detection circuit 21. When an overcurrent is detected due to a coil shot or the like, the overcurrent detection circuit 21 resets the self-holding circuit 12 through a line 22. By the way, in a constant speed traveling device,
When the low speed limiter circuit 23 detects that the vehicle is running at an extremely low speed, it forgets the vehicle speed for constant speed driving stored in the analog memory circuit 14 in consideration of the shock when returning to constant speed driving. and reset the self-holding circuit 12 via line 24. A reset signal is also generated when the brake lamp switch S ₂ , clutch switch S ₃ or parking switch S ₄ is pressed, or when the brake lamp fuse F is disconnected, and the self-holding circuit 1
2 is set to be reset. The present invention utilizes the reset of the self-holding circuit 12 to protect the output circuits 19 and 20. In other words, when the self-holding circuit is reset, the signal sent from the output line 15 of the self-holding circuit is reversed, and the coil drive current is cut off for both the control valve coil and the release valve coil, thereby avoiding damage to the output circuit. Because you can.

FIG. 4 shows a part of a circuit using such an overcurrent detection circuit. A low impedance resistor _R1 and an output transistor for coil drive are connected between the power supply B ⁺ for coil drive and the ground terminal.
Tr ₁ and control valve coil L in this example
are connected in series. The base terminal of the transistor Tr ₁ is configured to receive a control signal sent out, for example, through the line 18 shown in FIG.
Tr ₁ switches and the drive of the coil L is controlled. In addition, the transistor Tr ₂ is a transistor for overcurrent detection, and its base potential is connected to the resistors R ₁ and R ₂
and R ₃ . Therefore, coil L
In the case where the resistor R1 is shot, an excessive current flows through the resistor _R1 and the potential difference between its ends increases, so that the base potential of the transistor _Tr2 rapidly decreases and the transistor _Tr2 becomes conductive. As a result, a reset signal is output from the power supply B ⁺ to the self-holding circuit through the resistor _R4 . Note that in this circuit, the voltage change of the resistor R ₁ is detected via the diode D ₁ and the transistor Tr ₂ is switched. However, a diode D ₂ etc. is also provided, and this is used to detect the current change of the release valve driving transistor. can also be detected simultaneously, and the transistor for overcurrent detection can be shared.

As described above, according to the circuit of the present invention, it is possible to effectively utilize the circuit originally included in the constant speed traveling device for an automobile, so that it can be manufactured at a very low cost. What's more, when the coil is shot and a large current flows, the conduction of the transistor can be interrupted in just about 1mS, sufficiently preventing damage to the circuit.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a constant speed driving device for automobiles used in the present invention, Fig. 2 is a principle diagram of a circuit that prohibits high speed setting, Fig. 3 is a circuit diagram thereof, and Fig. 4
The figure is a circuit diagram for explaining the output transistor protection circuit. In the figure, Tr ₁ is an output transistor, Tr ₂ is an overcurrent detection transistor, R ₁ is a low impedance resistor, and 12 is a self-holding circuit.

Claims (1)

[Scope of utility model registration request] The current vehicle speed of the vehicle is detected, this is compared with a memorized reference vehicle speed for constant speed driving, and the output signal of the difference is sent to the coil drive circuit which is enabled to operate by the output of the self-holding circuit. By adjusting the excitation of the coil in the actuator, the air pressure in the negative pressure chamber of the actuator is adjusted, and by moving the actuator's diaphragm according to this air pressure, the throttle link system is moved to perform constant speed running. In a vehicle having a constant speed driving function, an output transistor for driving the coil in the coil drive circuit and a drive current path of the coil are provided in order to detect the drive current of the coil driven by the output transistor. is connected to a low impedance resistor connected to both ends of this resistor, detects the potential difference between the two ends, becomes conductive when the potential difference exceeds a certain level, resets the self-holding circuit, and prohibits conduction of the output transistor. 1. An output transistor protection circuit for a constant speed vehicle for an automobile, comprising an overcurrent detection transistor that protects the output transistor.