Title of Invention

DRIVER DEVICE FOR ENGINE SYSTEM

Abstract

A high-potential side line LH and a low-potential side line LL are connected to both terminals of a battery B. Electronic driver circuits 54, 55, 56 are connected between the high-potential side line LH and the low-potential side line LL. In order to protect these driver circuits from load dump surge, a switching element 70, 70a is provided in the high-potential side line LH or the low-potential side line LL, and the switching element 70, 70a is turned off by a voltage detection circuit 80, 100, 110, when the voltage of the high-potential side line LH with respect to the low-potential side line LL rises to a threshold voltage or more.

Full Text

DRIVER DEVICE FOR ENGINE SYSTEM FIELD OF THE INVENTION The present invention relates to a driver device for an engine system having two electric pathways connected to a high potential side terminal and a low potential side terminal of a power supply means. A load dump surge, in which a high voltage is superposed on an electric pathway due to connection failure between a battery and the electric pathway or the like, occurs in the above type driver device in some cases. In this instance, a high voltage may be applied to the driver device and lowers the reliability of the driver device. Therefore, it has been proposed in JP-A-2003-37930 that a Zener diode is provided as a protection circuit for protecting the driver device from the load dump surge as shown in Figs. 7(a), 7(b) and 7(c). In Fig. 7(a), a driver circuit 1 and an electric control unit (ECU) 2 of an actuator of an engine system are connected to a battery B through a high-potential side line LH and a low-potential side line LL. In order to protect the driver circuit 1 and ECU 2, a Zener diode 3 is connected in parallel to the driver circuit 1 and the ECU 2. The Zener diode 3 has a function of short-circuiting when a voltage applied thereto in the reverse direction is equal to a predetermined value or more. Therefore, it can be avoided that the voltage of the high-potential side line LH with respect to the low-potential side line LL is set to a predetermined value or more, and further the driver circuit 1 and ECU 2 can be protected from the load dump surge. A diode 4 is an element for protecting the driver circuit 1 and ECU 2, when the high-potential side line LH and the low-potential side line LL are reversely connected (reverse-connected) to the battery B. In Fig. 7(b), a transistor 5 is used for dealing with the reverse connection iri place of the diode 4 shown in Fig. 7(a). In Fig. 7(c), only ECU 2 is connected to the Zener diode 3 in parallel. The transistor 5 is provided to protect the driver circuit 1 under the reverse connection state. According to these protection circuits, the driver circuit 1 and ECU 2 can be protected. However, in this case, a large-size Zener diode 3 is required to withstand high power. In the case of Fig. 7(c), the driver circuit 1 is not protected by the Zener diode 3, and thus it is required to be constructed by an element having a high-voltage resistant property. SUMMARY OF THE INVENTION The present invention has an object to provide a driver device for an engine system that can deal with load dump surge without using any large-size Zener diode. According to the present invention, a driver device for an engine system is characterized by comprising: a switching element that is provided in any one of the two electric pathways and conducting/interrupting a driver circuit of an actuator of the engine system and a power supply means; and a voltage detection circuit that is connected to the one electric pathway at a position nearer to the power supply means with respect to the switching element and also connected to the other electric pathway, the voltage detection circuit carrying out an off-operation of setting the switching element to turn off when a voltage applied by connection to both the two electric pathways rises to a predetermined voltage or more. In this construction, the voltage applied to the voltage detection circuit is increased to a predetermined voltage or more by the two electric pathways, the switching element is turned off. Therefore, when load dump surge occurs, the switching element is turned off by the voltage detection circuit. Accordingly, the driver circuit connected to the two electric pathways at the downstream of the switching element can be protected from the load dump surge. By using the switching element as described above, use of a large-size Zener diode can be avoided. The driver device is also characterized in that the voltage detection circuit operates a conduction control terminal of the switching element through a diode. When the power supply means is reversely connected to the two electric pathways, a reverse bias also occurs in the switching element. When this reverse bias voltage is equal to a predetermined value or more, it lowers the reliability of the switching element. In this point, according to the above construction, application of a large reverse bias to the switching element can be suitably avoided by providing the diode. The driver device is also characterized in that the switching element is a bipolar transistor. When the switching element is constructed by using a MOS transistor, a parasitic diode is formed. Therefore, when the two electric pathways and the power supply means are reversely connected to each other or the like, the reverse bias may be applied to the driver circuit through the parasitic diode. In this point, according to the above construction, such a disadvantage can be avoided by using the bipolar transistor as the switching element. The driver device is also characterized in that the voltage detection circuit has a resistance member for restricting current flowing in the circuit. In this construction, the resistance member is provided as the restricting means for restricting the current flowing in the voltage detection circuit. Therefore, it can be avoided that the elements in the voltage detection circuit are designed in a large size so as to be adaptable to high power. The driver device is also characterized in that the voltage detection circuit has a transistor through which the other electric pathway and the conduction control terminal of the switching element are connected to each other. According to this construction, the switching element can be turned on/off by turning on/off the transistor connected between the two electric pathways. Therefore, it is easy to turn on/off the switching element by utilizing the voltage between the two electric pathways. The driver device is also characterized by further comprising: a diagnosing means for diagnosing whether abnormality exists in at least one of the actuator and the driver circuit or not; and a power supply circuit that is connected to the one electric pathway at a position nearer to the driver circuit side with respect to the switching element and drops the voltage between the two electric pathways to apply the lowered voltage to the diagnosing means. When the switching element is under an OFF state, the diagnosing means prohibits the diagnosing means from determining that abnormality exists. In this construction, even when the switching element is turned off, the power supply to the diagnosing means is not necessarily interrupted immediately because the power supply circuit is provided. On the other hand, the power supply to the driver circuit trends to be interrupted when the switching element is turned off. Therefore, when the power supply is interrupted, the driver circuit and the actuator ceases to operate, and thus the diagnosing means may erroneously determine that abnormality occurs in these elements. In this point, according to the above construction, when the switching element is under the OFF state, the diagnosis of the diagnosing means is prohibited. Accordingly, the erroneous determination caused by the OFF state of the switching element can be avoided. The driver device is also characterized in that the actuator includes at least one of a brushless motor provided to a fuel pump, an idle speed control valve and an electric control type throttle valve. According to this construction, the driver circuit of the brushless motor provided to the fuel pump, the driver circuit of the idle speed control valve and the driver circuit of the electric control type throttle valve are not required to be constructed by high-voltage resistant elemerits which can endure load dump surge, and thus these driver circuits can be miniaturized. BRIEF DESCRPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: Fig. 1 is a circuit diagram showing a driver device for an engine system according to a first embodiment of the present invention; Fig. 2 is a time chart showing the operation mode of a protection circuit according to the first embodiment; Fig. 3 is a flowchart showing processing corresponding to the operation mode of a switching element according to the first embodiment; Fig. 4 is a circuit diagram showing a driver device for an engine system according to a second embodiment of the present invention; Fig. 5 is a circuit diagram showing a driver device for an engine system according to a third embodiment of the present invention; Fig. 6 is a circuit diagram showing a driver device for an engine system according to a fourth embodiment of the present invention; and Fig. 7 is a circuit diagram showing a protection circuit of a conventional driver device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be described in detail with reference to various embodiments, in which a driver device is provided for an engine system mounted on a two-wheeled motor vehicle such as a motor cycle. (First Embodiment) As shown in Fig. 1, a throttle valve 16 which is mechanically opened/closed in accordance with the operation of an acceleration grip 14 by a driver is provided at the upstream of an air intake passage 12 of a gasoline engine 10. Furthermore, an idle speed control (ISC) passage 18 through which the upstream and the downstream of the throttle valve 16 are connected to each other is provided to bypass the throttle valve 16. The ISC passage 18 is provided with an ISC valve 22 driven by an electric motor 20. A fuel injection valve 24 is provided at the downstream of the air intake passage 12. Fuel in a fuel tank 26 is pumped up and supplied to the fuel injection valve 24 by a fuel pump 28. The fuel pump 28 is an electrically-operated pump which is provided with a brushless motor 30 and pumps up fuel in the fuel tank 26. The fuel injection valve 24 injects the fuel into the air intake passage 12. The air intake passage 12 and a combustion chamber 32 are allowed to communicate with each other by the opening operation of an air intake valve 34, whereby air-fuel mixture containing air and fuel flows into the combustion chamber 32. The air-fuel mixture in the combustion chamber 32 burns by ignition of an ignition plug 36. The combustion energy is converted to rotational energy through a piston 38. The combustion chamber 32 is allowed to communicate with an exhaust passage 42 by the opening operation of an exhaust valve 40, whereby the air-fuel mixture burned in the combustion chamber 32 is discharged as exhaust gas. The motor 20, the brushless motor 30, etc. as actuators of the engine system are driven by a driver device 50. The driver device 50 has a high-potential side line LH connected to a high-potential side terminal of a battery B, and a low-potential side line LL connected to a low-potential side terminal of the battery B. The high-potential side line LH and the low-potential side line LL serve as power supply lines. A capacitor 52 for storing electric power of the battery B, an ISC driver circuit 54 for driving the motor 20, and a brushless motor driver circuit 56 for driving the brushless motor 30 are connected in parallel between the high-potential side line LH and the low-potential side line LL. Furthermore, a regulator 58 for regulating the power between the high-potential side line LH and the low-potential side line LL to a lowered power and outputting the lowered power is connected between the high-potential side line LH and the low-potential side line LL. A capacitor 60 for storing the lowered power and an electrical control unit (ECU) 62 are connected in parallel between the output of the regulator 58 and the low-potential side line LL. ECU 62 operates various kinds of actuators of the engine system. That is, it operates the opening degree of the ISC valve 22 through the ISC driver circuit 54, for example, and also operates the brushless motor 30 through the brushless motor driver circuit 56. When these operations are carried out, ECU 62 determined the presence or absence of abnormality of an operation system on the basis of the sensing of the opening degree of the ISC valve 22 or the sensing of current flowing in the brushless motor driver circuit 56, for example. According to the driver device 50, the electric energy stored in the capacitor 52 can be supplied to the ISC driver circuit 54, the brushless motor driver circuit 56, etc, and also power achieved by lowering the voltage of the battery B can be supplied to ECU 62. A load dump surge occurs in some cases, in which a high voltage is superposed between the high-potential side line LH and the low-potential side line LL due to conduction failure between the high-potential side line LH/the low-potential side line LL and the battery B. In order to protect the ISC driver circuit 54, the brushless motor driver circuit 56, ECU 62, etc. from the load dump surge, a protection circuit is provided. The protection circuit has a switching element 70 through which the high-potential side line LH is divided into two parts and these two parts are connected to each other at a position nearer to the battery B side with respect to the capacitor 52, and a voltage detection circuit 80. The voltage detection circuit 80 sets the switching element 70 to ON-state when the voltage of the high-potential side line LH with respect to the low-potential side line LL is equal to a normal voltage value. It sets the switching element 70 to OFF-state when the voltage of the high-potential side line LH with respect to the low-potential side line LL is equal to a predetermined threshold value Vth or more. The switching element 70 includes an NPN type transistor, and the emitter and collector thereof are connected to the battery B side and the capacitor 52 side, respectively. A pull-up resistor 72 is provided between the emitter and base of the switching element 70. Furthermore, a diode 74 is connected to the conduction control terminal (base) of the switching element 70 so that the direction from the high-potential side line LH to the low-potential side line LL is set to the forward direction. The cathode side of the diode 74 is connected to the collector of a PNP type bipolar transistor 81 in the voltage detection circuit 80, and the emitter of the bipolar transistor 81 is connected to the low-potential side line LL. The voltage detection circuit 80 has a serial connection of a Zener diode 82 and a resistor 83, and a serial connection of a resistor 84 and a PNP type bipolar transistor 85. These serial connections are connected in parallel between the high-potential side line LH and the low-potential side line LL. The Zener diode 82 allows current flow from the high-potential side line LH to the low-potential side line LL when the voltage of the high-potential side line LH with respect to the low-potential side line LL rises to a predetermined threshold value Vth or more. The base of the bipolar transistor 85 is connected through a resistor 86 between the Zener diode 82 and the resistor 83. Furthermore, the base of the bipolar transistor 81 is connected through a resistor 87 between the resistor 84 and the bipolar transistor 85. Fig. 2 shows the operation of the protection circuit. More specifically, Fig. 2(a) shows the voltage of the high-potential side line LH with respect to the low-potential side line LL, Fig. 2(b) shows the ON/OFF state of the bipolar transistor 85, Fig. 2(c) shows the ON/OFF state of the bipolar transistor 81, Fig. 2(d) shows the ON/OFF state of the switching element 70, Fig. 2(e) shows the ON/OFF state of the ISC driver circuit 54 and the brushless motor driver circuit 56, and Fig. 2(f) shows an abnormality determination prohibition flag. As shown in Fig. 2, before a time tl, the voltage of the high-potential side line LH with respect to the low-potential side line LL is a battery voltage Vb, and it is not more than the threshold voltage Vth. Therefore, no current flows in the Zener diode 82. Accordingly, the base and emitter of the bipolar transistor 85 are short-circuited to each other, and the bipolar transistor 85 is in the OFF state. Furthermore, the voltage corresponding to the difference between the voltage of the high-potential side line LH with respect to the low-potential side line LL and the voltage drop amount caused by the resistor 84 and the resistor 87 is applied between the base and emitter of the bipolar transistor 81, and current from the high-potential side line LH flows through the resistors 84, 87. Therefore, the bipolar transistor 81 is turned on, and thus the switching element (transistor) 70 is turned on. Accordingly, the power of the battery B can be supplied to the capacitor 52 side. On the other hand, after the time tl, if a load dump surge is superposed between the high-potential side line LH and the low-potential side line LL, the voltage of the high-potential side line LH with respect to the low-potential side line LL increases. When the voltage is increased to the threshold voltage Vth or more (time t2), the Zener diode 82 breaks down and current flows in the Zener diode 82. Accordingly, a forward bias is applied between the base and emitter of the bipolar transistor 85 and current flows in the base of the bipolar transistor A 85, so that the bipolar transistor 85 is turned on. Here, the voltage between the collector and the emitter when the bipolar transistor 85 is turned on is set to such a value that the bipolar transistor 81 is turned off. With the bipolar transistor 81 being in the OFF state, the switching element 70 is turned off. Thus, over-voltage can be avoided from being applied to the ISC driver circuit 54, the brushless motor driver circuit 56, etc. As described above, according to the first embodiment, by using the switching element 70, the protection circuit for protecting the ISC driver circuit 54, the brushless motor driver circuit 56, etc. from over-voltage without using any large-size Zener diode. Particularly with respect to the voltage detection circuit 80, it is constructed by the resistor members and the active elements, and also the resistant values of the resistor 83, the resistor 84, etc. are increased, thereby providing restricting means for restricting the current flowing in the voltage detection circuit 80. Accordingly, small-power active elements can be used. For example, the Zener diode 82 as an active element is a small-power compact element. The size reduction of the Zener diode 82 can be performed by increasing the resistance value of the resistor 83. That is, even when the voltage of the high-potential side line LH with respect to the low-potential side line LL is increased, the current flowing between the Zener diode 82 and the resistor 83 can be restricted. On the other hand, if a resistor is connected to the Zener diode 3 shown in Fig. 7 in series, the voltage drop in this resistor is increased, and the voltage of the high-potential side line LH with respect to the low-potential side line LL is increased, so that it cannot operate as a protection circuit. The abnormality determination flag shown in Fig. 2(f) is a flag for prohibiting the determination that abnormality exists in the operation system of the ICS driver circuit 54 or the brushless motor driver circuit 56 (abnormality determination) during the period when the switching element 70 is turned off due to over-voltage. That is, during this period, the power supply from the battery B is interrupted, and thus the ISC driver circuit 54 and the brushless motor driver circuit 56 cannot be driven after the stored electric charge of the capacitor 52 has been discharged or consumed. On the other hand, ECU 62 trends to keep the power supply state even after the charge of the capacitor 52 is equal to zero because it uses the capacitor 60 as a power source. Therefore, even in a case where no abnormality exists in the operation system of the ISC driver circuit 54, the brushless motor driver circuit 56 or the like, the presence or absence of abnormality is determined when the switching element 70 is turned off, so that abnormality may be determined erroneously. Therefore, according to this embodiment, the abnormality determination prohibition flag for prohibiting the abnormality determination is turned on when the switching element 70 is turned off. Specifically, ECU 62 monitors the ON/OFF state of the switching element 70 so that the abnormality determination is not erroneously made during the OFF-period of the switching element 70. Specifically, as shown in Fig. 1, the collector side of a bipolar transistor 90 is connected to the output side of the regulator 58 through a resistor 92, and also the emitter side of the bipolar transistor 90 is grounded (connected to the low-potential side line LL). The base of the bipolar transistor 90 is connected between the Zener diode 82 and the resistor 83 through the resistor 94. Accordingly, when the bipolar transistor 85 is turned on, the bipolar transistor 90 is also turned on. Therefore, the ON/OFF state of the switching element 70 can be monitored by monitoring whether current flows in the collector of the bipolar transistor 90. Fig. 3 shows the processing of ECU 62 which is executed when the switching element 70 is turned off. This processing is repetitively executed by ECU 62 at a predetermined period, for example. In this series of processing, it is checked in step S10 whether the bipolar transistor 90 is under ON-state or not. This processing is used to check in the voltage detection circuit 80 whether the switching element 70 is turned off or not. Then, if it is determined that the bipolar transistor 90 is turned on, the abnormality determination prohibition flag is set to ON in step S12, thereby prohibiting the abnormal determination of the operation system. On the other hand, if the determination is negative in step S10, it is determined in step S14 whether it is the moment at which the bipolar transistor 90 is switched from the ON-state to the OFF-state. This processing is used to determined the switching timing at which the OFF-state of the switching element 70 is switched to the ON-state because the over-voltage is eliminated. When the positive determination is made in step S14, the proceeds to step S16. In step S16, the abnormality determination prohibition flag is set to OFF, and also the brushless motor 30 is re-started, whereby the starting processing of the brushless motor 30 is executed. When the processing of step S12 or step S16 is completed or when the negative determination is made in step S14, this series of processing is temporarily finished. According to this embodiment described above, the following advantages can be achieved. (1) The driver device 50 has the switching element 70 for conducting/interrupting each of the ISC driver circuit 54 and the brushless motor driver circuit 56 to/from the battery B, and the voltage detection circuit 80 for turning off the switching element 70 when the voltage of the high-potential side line with respect to the low-potential side line LL rises to the threshold voltage Vth or more, which is higher than the voltage Vb of the battery B. Accordingly, the ISC driver circuit 54, the brushless motor driver circuit 56, etc. can be protected from load dump surge. In addition, by using the switching element 70, the voltage detection circuit 80 itself can be constructed without using any large-size Zener diode. (2) The voltage detection circuit 80 operates the conduction control terminal (base) of the switching element 70 through the diode 74. Accordingly, even when the terminal of the battery B is reversely connected to the high-potential side line LH and the low-potential side line LL (the reverse bias is applied), the driver device can suitably deal with this. Here, when the reverse bias is equal to a predetermined value or more, the reliability of the switching element 70 and the bipolar transistor 81 is lowered. Therefore, when no diode 74 is provided, the switching element 70 and the bipolar transistor 81 are required to be constructed by high-voltage resistant elements which can withstand application of the reverse bias. On the other hand, by providing the diode 74 as in the case of this embodiment, a large reverse bias can be suitably avoided from being applied to the switching element 70 and the bipolar transistor 81, and also these elements can be miniaturized. (3) The switching element 70 is constructed by the bipolar transistor. If the switching element is constructed by using an MOS transistor, a parasitic diode is formed. Therefore, when the reverse bias is applied or the like, the reverse bias may be applied to the ISC driver circuit 54 or the brushless motor driver circuit 56 through the parasitic diode. In this point, according to this embodiment, such a disadvantage can be avoided by using the bipolar transistor as the switching element 70. (4) The voltage detection circuit 80 has the resistors 83, 84, etc. for restricting the current flowing therein. Accordingly, the active elements constituting the voltage detection circuit 80 can be constructed by small-power elements. Specifically, for example, the resistor 83 is provided so as to be connected between the high-potential side line LH and the low-potential side line LL, and the voltage across both ends of the resistor 83 is detected as a voltage applied between the high-potential side line LH and the low-potential side line LL. Accordingly, the current flowing in the resistor 83 can be reduced. Thus the bipolar transistor 85 dealing with the above current can be reduced in size. (5) The voltage detection circuit 80 is provided with the bipolar transistor 81 for connecting the low-potential side line LL and the base of the switching element 70. Accordingly; the switching element 70 can be turned on/off by turning on/off the bipolar transistor 81. Therefore, the switching element 70 can be easily turned on/off by using the voltage of the high-potential side line LH with respect to the low-potential side line LL. (6) When the switching element 70 is under the OFF-state, the abnormality determination of the operation system of the ISC valve 22 and the brushless motor 30 is prohibited. Accordingly, the erroneous determination caused by the off-operation of the switching element 70 can be suitably avoided. (7) The switching element 70 is provided between each of the ISC driver circuit 54 and the brushless motor driver circuit 56 and the battery B. Accordingly, the ISC driver circuit 54 and the brushless motor driver circuit 56 are not required to be constructed by the high-voltage resistant elements for withstanding the load dump surge. (Second Embodiment) A second embodiment is shown in Fig. 4, in which elements having the same functions as the elements shown in Fig. 1 are represented by the same reference numerals for convenience. As shown in Fig. 4, the base of the switching element 70 is directly connected to the collector of the bipolar transistor 81 with no diode interposed therebetween. The switching element 70 and the bipolar transistor 81 are constructed by voltage-resistant elements which can withstand the reverse bias caused by the reverse-connection of the battery B. Accordingly, as compared with the construction shown in Fig. 1, the number of parts can be reduced. (Third Embodiment) A third embodiment is shown in Fig. 5. In this embodiment, in addition to the throttle valve 16, an electrically-controlled throttle valve 23 driven by a motor 125 is provided upstream of the throttle valve 16. The driver device 50 has a throttle driver circuit 55 for driving the motor 25. The throttle driver circuit 55 is connected between the low-potential side line LL and the high-potential side line LH. Furthermore, a voltage detection circuit 100 is provided. Here, the voltage detection circuit 100 has a serial connection member including a resistor 102 and a resistor 104, and this serial connection member is connected between the low-potential side line LL and the high-potential side line LH. The voltage of the high-potential side line LH with respect to the low-potential side line LL is divided by the resistor 102 and the resistor 104. This divisional voltage value (the voltage drop value by the resistor 104) is applied to the non-inverting input terminal of a comparator 106. On the other hand, the high-potential voltage of the capacitor 60 is applied to the inverting input terminal of the comparator 106. Here, the resistance values of the resistor 102 and the resistor 104 are set so that the voltage of the capacitor 60 under the charged condition is higher than the voltage drop amount of the resistor 104 corresponding to the battery voltage Vb. Therefore, at the normal time, the output of the comparator 106 is set to logic "L", and the switching element 70 is set to ON-state. On the other hand, when the voltage of the high-potential side line LH with respect to the low-potential side line LL increases, the output of the comparator 106 is set to logic "H" and the switching element 70 is set to OFF-state to interrupt the high voltage on the line LH from being applied to the succeeding circuits. ECU 62 takes the output of the comparator 106 to execute the same processing as the processing shown in Fig. 3. This third embodiment has the following advantages in addition to the advantages (1) to (4), (7) in the first embodiment described above. (8) The voltage detection circuit 100 has the serial connection member of the resistor 102 and the resistor 104 which is connected between the low-potential side line LL and the high-potential side line LH, and detects the voltage between both ends of the resistor 104 as the voltage of the high-potential side line LH with respect to the low-potential side line LL. Accordingly, the voltage of the high-potential side line LH with respect to the low-potential side line LL can be detected by treating a lower voltage as compared with the voltage of the high-potential side line LH with respect to the low-potential side line LL. Accordingly, an element (an element constituting the comparator 106) for sensing the voltage of the high-potential side line LH with respect to the low-potential side line LL can be reduced in size. (9) The switching element 70 is provided between the throttle driver circuit 55 and the battery B. Accordingly, the throttle driver circuit 55 is not required to be constructed by a high-voltage resistant element which can withstand load dump surge. (Fourth Embodiment) A fourth embodiment is shown in Fig. 6. In this embodiment, the low-potential side line LL is divided into two parts, and these parts are connected to each other by a switching element 70a. The switching element 70a is constructed by an N-channel MOS transistor. The conduction control terminal (base) of the switching element 70 is connected to the high-potential side line LH through the emitter and collector of the bipolar transistor 81. The bipolar transistor 81 is turned on/off by a voltage detection circuit 110. The voltage detection circuit 110 may be constructed by adjusting the resistance values of the resistor 84 and the resistor 87 in the voltage detection circuit 80 shown in Fig. 1, for example. A parasitic diode is formed in the N-channel MOS transistor, and it is set so that the direction from the ECU 62 side to the low-potential side of the battery 8*is set to a forward direction. Thus, the advantages (1), (2), (4) to (7) of the first embodiment can be achieved. (Other Embodiments) The above embodiments may be modified as follows. The voltage detection circuit is not limited to those shown in the above embodiments, and any construction may be adopted insofar as the switching elements 70, 70a are turned off when the voltage of the high-potential side line LH with respect to the low-potential side line LL rises to a predetermined voltage or more. In this case, it is preferable that the voltage detection circuit is constructed by a small-power element by providing a resistor as restricting means for restricting current flowing in the voltage detection circuit. In the first to third embodiments, the switching element is not limited to the bipolar transistor. For example, a MOS transistor may be used to deal with the load dump surge. Furthermore, if a diode is provided between the parasitic diode and the battery B so as to face the forward direction of the parasitic diode, this construction is adaptable to the application of the reverse bias. The power supply means of the driver device is not limited to the battery B, and it may be an electric generator. In this case, load dump surge also occurs. Therefore, it is effective to apply this invention to even a vehicle having no battery B in order to deal with the load dump surge. The engine system is not limited to the two-wheeled motor vehicle, and it may be applied to a four-wheeled vehicle. Furthermore, the engine system is not limited to one having the gasoline engine 10, and it may have a diesel engine. The driver circuit as a protection target is not limited to the device of the above embodiments, and the driver circuit can be reduced in size by providing the switching element between any driver circuit and the battery. WHAT IS CLAIMED IS: 1. A driver device for an engine system having two electric pathways r connected to a high-potential side terminal and a low-potential side terminal of power supply means, respectively, comprising: a driver circuit of an actuator of the engine system; a switching element that is provided in any one of the two electric pathways and conducting/interrupting the driver circuit and the power supply means; and a voltage detection circuit that is connected to the one electric pathway at a position nearer to the power supply means side with respect to the switching element and also connected to the other electric pathway, the voltage detection circuit carrying out an off-operation of setting the switching element to OFF when a voltage applied to the two electric pathways rises to a predetermined voltage or more. 2. The driver device for the engine system according to claim 1, further comprising: a diode connected to a conduction control terminal of the switching element, so that the voltage detection circuit operates the conduction control terminal of the switching element through the diode. 3. The driver device for the engine system according to claim 1 or 2, wherein the switching element is a bipolar transistor. 4. The driver device for the engine system according to any one of claims 1 to 3, wherein the voltage detection circuit has a resistance member for restricting current flowing in the voltage detection circuit. 4 5. The driver device for the engine system according to any one of claims 1 to 4, wherein the voltage detection circuit has a transistor through which the other electric pathway and the switching element are connected to each other. 6. The driver device for the engine system according to any one of claims 1 to 5, further comprising: diagnosing means for diagnosing whether abnormality exists in at least one of the actuator and the driver circuit; and a power supply circuit that is connected to the one electric pathway at a position nearer to the driver circuit side with respect to the switching element and drops the voltage between the two electric pathways to apply a lowered voltage to the diagnosing means, wherein when the switching element is in an OFF-state, the diagnosing means is prohibited from determining abnormality. 7. The driver device for the engine system according to any one of claims 1 to 6, wherein the actuator includes at least one of a brushless motor provided to a fuel pump, an electric idle speed control valve and an electric throttle valve.

Documents:

1619-CHE-2007 AMENDED CLAIMS 23-03-2011.pdf

1619-CHE-2007 EXAMINATION REPORT REPLY RECEIVED 23-03-2011.pdf

1619-CHE-2007 POWER OF ATTORNEY 23-03-2011.pdf

1619-che-2007-abstract.pdf

1619-che-2007-claims.pdf

1619-che-2007-correspondnece-others.pdf

1619-che-2007-description(complete).pdf

1619-che-2007-drawings.pdf

1619-che-2007-form 1.pdf

1619-che-2007-form 18.pdf

1619-che-2007-form 3.pdf

1619-che-2007-form 5.pdf