JP2006115557A - Switching element, motor drive circuit and buffer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable switching element in which temperature rise can be suppressed, and to enhance reliability of a motor drive circuit or a buffer while reducing the size. <P>SOLUTION: The switching element S1 having an MOSFETM1 is provided with a diode D1 having a forward voltage drop value smaller than that of a parasitic diode K1 in parallel with the parasitic diode K1 of the MOSFETM1. Since a regeneration current flows through the diode D1 as well as the parasitic diode K1, heat generation from the switching element S1 is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to improvements in switching elements, motor drive circuits, and shock absorbers.

  Generally, in a circuit that drives an inductive load with a switching element, specifically, for example, a motor driving circuit, a surge voltage is generated when the switching element is switched from closed to open.

  Normally, in such a circuit, a flywheel diode is placed in parallel with the inductive load to suppress a surge that occurs when the inductive load is cut off and protect the switching element from the surge voltage. To be done.

  In turn, a switching element having a MOS (Metal Oxide Semiconductor) field effect transistor has a built-in parasitic diode (also referred to as a body diode), and this parasitic diode is connected between the source and drain of the MOS field effect transistor. It is built in antiparallel with the field effect transistor.

This parasitic diode is generated in the manufacturing process of the MOS field effect transistor. However, when the MOS field effect transistor is used as a switching element, the parasitic diode functions as a flywheel diode, so it is often active. In particular, a parasitic diode is used as a flywheel diode (see Patent Documents 1 and 2).
JP 2001-204194 A (paragraph number 0012, FIG. 1) Japanese Patent Laying-Open No. 2003-324986 (paragraph number 0038, FIG. 4)

  In particular, when a parasitic diode in a switching element having a conventional MOS field effect transistor is used as a flywheel diode, for example, when the switching element is applied to a circuit for PWM control of a brushless motor, the switching element Thus, a regenerative current frequently flows through the parasitic diode.

  Furthermore, when a motor using the above-described PWM circuit is used in a shock absorber that uses the output torque of the motor as a damping force, or as a damping force and a thrust of an actuator, the rotor of the motor is Since it is forced to rotate, its own induced electromotive voltage may become very high, and the regenerative current flowing through the parasitic diode also increases.

  If the regenerative current that flows through the parasitic diode increases, the amount of heat generation also increases, which causes the temperature rise of the MOS field effect transistor, resulting in a decrease in the reliability of the switching element and in some cases damage to the switching element itself. There is a fear.

  In order to cope with the temperature rise of the switching element, it is customary to attach a cooling plate to the switching element. However, in the conventional switching element, the cooling plate is enlarged in response to an increase in the amount of heat generated by the parasitic diode. In addition, a plurality of switching elements must be connected in parallel to dissipate heat, which inconveniently increases the size of the motor drive circuit and the shock absorber.

  Therefore, the present invention was devised in order to improve the above-mentioned problems, and the object of the present invention is to provide a highly reliable switching element that suppresses temperature rise, and other objects are as follows. It is to improve the miniaturization and reliability of the motor drive circuit and the shock absorber.

  In order to achieve the above-described object, the switching element of the present invention is a switching element having a MOS field effect transistor, and a forward voltage drop smaller than the forward voltage drop value of the parasitic diode in parallel with the parasitic diode of the MOS field effect transistor. A diode having a value is provided.

  The motor driving circuit of the present invention is a motor driving circuit in which a plurality of arms in which switching elements having MOS field effect transistors are connected in series are connected to a power source, and the switching elements of the arms are connected to the motor windings. In the circuit, the switching element includes a MOS field effect transistor and a diode having a forward voltage drop value smaller than the forward voltage drop value of the parasitic diode in parallel with the parasitic diode of the MOS field effect transistor. It is characterized by that.

  Furthermore, the shock absorber of the present invention includes a motion converting mechanism that converts linear motion into rotational motion, a motor that transmits the rotational motion, and a motor drive circuit. A switching element including a transistor is connected in series, and a plurality of arms each having a switching element connected to a motor winding are connected to a power source. The switching element is connected to a MOS field effect transistor. A diode having a forward voltage drop value smaller than the forward voltage drop value of the parasitic diode is provided in parallel with the parasitic diode of the MOS field effect transistor.

  According to the switching element of the present invention, the calorific value thereof can be reduced as compared with the conventional switching element, whereby the temperature rise of the MOS field effect transistor can be reduced, the reliability of the switching element can be improved, and the switching element Damage to itself is also prevented.

  Furthermore, according to the switching element and the motor drive circuit of the present invention, the cooling plate for cooling the switching element can be made smaller than the conventional one, so that the entire motor drive circuit including the housing can be downsized. It becomes.

  In addition, according to the shock absorber of the present invention, the reliability of the switching element can be improved and the switching element itself can be prevented from being damaged, thereby avoiding the risk that the shock absorber cannot generate a damping force.

  Further, the cooling plate for cooling the switching element can be made smaller than the conventional one, and the entire motor drive circuit including the housing can be reduced in size, so that the shock absorber mounting this is also reduced in size. In addition, the mountability of the shock absorber to the vehicle is improved.

  The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a circuit diagram of a motor drive circuit in one embodiment. FIG. 2 is a diagram showing the flow of current flowing through the motor drive circuit when the winding is energized. FIG. 3 is a diagram showing the flow of current flowing through the motor drive circuit when the winding is not energized. FIG. 4 is a diagram conceptually showing a shock absorber using a motor.

  As shown in FIG. 1, the motor drive circuit C in one embodiment includes an arm A1 in which switching elements S1 and S4 are connected in series, an arm A2 in which switching elements S2 and S5 are connected in series, and a switching element S3 and S3. S6 The arm A3 connected in series is connected to a power source, and the output terminals to which the switching elements S1, S4, S2, S5, S3, S6 of each arm A1, A2, A3 are connected to the motor M P1, P2, and P3.

  Further, although not shown in detail, the motor M is composed of a rotor and a stator, and a permanent magnet is mounted on the outer peripheral side of the rotor in a predetermined magnetic arrangement, while the stator is wound around the stator core and the stator core. In this case, the motor M is configured as a three-phase brushless motor.

  Each of the U-phase, V-phase, and W-phase windings is Y-shaped at one end, but may be Δ-connected.

  Further, the motor M is provided with a rotational position detecting means for detecting the rotational position of the rotor. Specifically, as the rotational position detecting means, for example, a Hall element for detecting the magnetism of the permanent magnet of the rotor or the like. The magnetic sensor which consists of, a resolver, a rotary encoder, etc. can be used.

  Furthermore, a current sensor for detecting the current flowing in each of the U, V, and W windings of the motor M is separately provided, and signals output from the rotational position detecting means and the current sensor are input to a gate controller (not shown). The

  The gate controller is a control circuit that performs PWM control of the motor M, but the configuration of the gate controller and the PWM control are well known and will not be described in detail.

  On the other hand, the arm A1 is configured by connecting two switching elements S1 and S4 in series. An output terminal P1 is provided between the switching elements S1 and S4 of the arm A1, and the output terminal P1 is connected to the motor M. Connected to the U phase of the winding.

  The other arms A2 and A3 have the same configuration as the arm A1, and their output terminals P2 and P3 are connected to the V-phase and W-phase of the winding of the motor M, respectively.

  Therefore, for example, when switching element S1 and switching element S4 are turned on, the power supply E and the U phase and V phase of the winding of motor M are closed circuit, and current is supplied to U phase and V phase of the winding of motor M. Similarly, the switching elements S1, S2, S3 of any one of the arms A1, A2, A3 and one switching element S4, S5, S6 of the other two arms A1, A2, A3 are appropriately arranged in the same manner. When turned on, the winding of the motor M can be energized. Specifically, the gate controller controls the opening and closing of the motor M so that a rotating magnetic field is formed by the UVW phase winding.

  The switching element S1 includes a MOS field effect transistor (hereinafter referred to as a MOSFET) M1 and a diode D1 connected to the source electrode and the drain electrode of the MOSFET M1, and the diode D1 is antiparallel to the MOSFET M1. Connected to be.

  The MOSFET M1 includes a parasitic diode K1 between the source electrode and the drain electrode, and the parasitic diode K1 and the diode D1 are connected in parallel.

  Furthermore, the forward voltage drop value of the diode D1 is set smaller than the forward voltage drop value of the parasitic diode K1.

  The other switching elements S2, S3, S4, S5, and S6 have the same configuration as that of the switching element S1, and diodes D2, D3, D4, D5, and D6 and parasitic diodes K2, K3, K4, K5, and K6 are respectively included. It is prepared for.

  The switching elements S1, S2, S3, S4, S5 and S6 are controlled by the gate controller based on the rotational angle of the rotor detected by the rotational position detecting means and the current flowing in each winding, respectively. Thus, the motor M is driven by applying a voltage to the gate electrode and being controlled to open and close, and further, the output torque and the rotor rotational speed of the motor M are controlled by PWM control.

  In addition to PWM control, control using a continuous modulation method such as PAM (Pulse Amplitude Modulation) or PPM (Pulse Position Modulation) or a discontinuous modulation method such as a PNM (Pulse Number Modulation) circuit may be performed.

  The motor drive circuit C is configured as described above. Hereinafter, the operation of the motor drive circuit C will be described. During PWM control, each of the switching elements S1, S2, S3, S4, S5, and S6 is controlled by the gate controller. Is controlled to be turned on in a predetermined pulse width period for realizing a predetermined duty ratio and turned off in other periods. For example, as shown in FIG. 2, the switching element S1 is turned on in a certain period. When the switching element S5 is turned on, the current circulates through the power source E, the switching elements S1 and MOSFETs M1 and M5 of the switching element S5, and the windings of the motor M, whereby a current flows through the windings.

Then, in the next period, as shown in FIG. 3, the switching element S1 is turned off and no current is supplied from the power source E to the winding, but the back electromotive force is applied to the winding that has been energized until then. occur regenerative current _{I 0} flows.

At this time, the regenerative current I ₀ circulates through the MOSFET M5 of the switching element S5 that is turned on and the parasitic diode K4 and the diode D4 of the switching element S4.

  Here, since the forward voltage drop value of the diode D4 is smaller than the forward voltage drop value of the parasitic diode K4, the current flowing through the diode D4 is larger than the current flowing through the parasitic diode K4.

The heat generated by the diode D4 and the parasitic diode K4 is the product of the forward voltage drop value and the current. For example, the forward voltage drop value of the diode D4 is V and the flowing current is I. When the forward voltage drop value of K4 is a · V (a> 1), the current flowing through the parasitic diode K4 is I / a. The regenerative current I ₀ is I ₀ = I + I / a.

  Therefore, the heat generated by the diode D4 becomes V · I, and the heat generated by the other parasitic diode K4 becomes V · I / a. Therefore, the total heat generated by the diode D4 and the parasitic diode K4 is (1 + 1). / A) · V · I.

Here, for comparison with the conventional switching element, a state where the switching element S4 removed the diode D4, i.e., when only parasitic diode K4 assumed that flows the regenerative current I _0, the heat generated in the parasitic diode K4 is Since the flowing current is (1 + 1 / a) I and the forward voltage drop value is a · V, (1 + a) V · I is obtained.

  Since a> 1, since 1 + 1 / a <1 + a, the heat generated by the diode D3 can be reduced.

  This is the same when the other switching elements S2, S3, S4, S5 and S6 are switched from on to off.

  As is apparent from the above, the amount of heat generated by each of the switching elements S1, S2, S3, S4, S5, and S6 can be made smaller than that of the conventional switching element, thereby reducing the temperature rise of the MOSFET. The reliability of the switching element can be improved and the switching element itself can be prevented from being damaged.

  In addition, since the cooling plate for cooling the switching element can be made smaller than the conventional one, the entire motor drive circuit including the housing can be reduced in size.

  Next, the shock absorber 1 using the motor M equipped with the motor drive circuit described above will be described.

  As shown in FIG. 4, the shock absorber 1 basically includes a motion conversion mechanism 2 that converts linear motion into rotational motion, and a motor M to which the rotational motion is transmitted. In the case of the embodiment, the motion conversion mechanism 2 includes a ball screw nut 3 and a screw shaft 4 that is screwed to the ball screw nut 3, and the ball screw nut 3 and the screw shaft 4 are relatively linearly moved in the axial direction. Can be converted into the rotational motion of the screw shaft 4, and this rotational motion of the screw shaft 4 can be transmitted to the output shaft 5 that forms part of the rotor of the motor M.

  In the case of the shock absorber 1, torque output by driving the motor M can be applied to the screw shaft 4 to suppress or promote linear motion between the ball screw nut 3 and the screw shaft 4. In addition, when the output shaft 5 is forcibly rotated by the screw shaft 4, an induced electromotive force is generated in the winding in the motor M and energy is regenerated in the motor M to generate an electromagnetic force. As a result, the rotational movement of the screw shaft 4 can be suppressed, and the linear movement of the ball screw nut 3 can be suppressed.

  That is, the shock absorber 1 not only generates a damping force, but can also function as an actuator, and can also function as an active suspension.

  The detailed structure will be described below. The screw shaft 4 is formed in a cylindrical shape, and a helical screw groove (not shown) is formed on the outer periphery thereof. The upper end of the screw shaft 4 in FIG. 4 is the output shaft 5 of the motor M in FIG. It is connected to the tip which becomes the lower end by a coupling or the like.

  The ball screw nut 3 to be screwed onto the screw shaft 4 is provided with a spiral ball holding portion (not shown) on the inner periphery thereof so as to coincide with the spiral screw groove of the screw shaft 4. A large number of balls (not shown) are arranged in the ball holding portion, and a passage (not shown) communicates between both ends of the ball holding portion so that the ball can circulate inside the ball screw nut 3. And when the ball screw nut 1 is screwed onto the screw shaft 4, the ball of the ball screw nut 1 is fitted into the helical screw groove of the screw shaft 4, Since the ball itself is rotated by the frictional force with the screw groove of the screw shaft 4 as the screw shaft 4 rotates, there is an advantage that a smooth operation is possible compared to a mechanism such as a rack and pinion. Is composed of a ball screw nut 3 and a screw shaft 4. Instead Le screw mechanism may employ the rack and pinion or other mechanisms.

  As described above, when the screw shaft 4 is rotatably engaged with the ball screw nut 3 along the screw groove and the screw shaft 4 moves linearly in the vertical direction in FIG. The screw nut 3 is fixed to the inner periphery of the upper end of the cylinder 8 connected to one of the vehicle body side member or the axle side member of the vehicle via the bracket 7, and thereby the rotation of the ball screw nut 3 in the circumferential direction. Since it is regulated, the screw shaft 4 is forcibly rotated.

  On the other hand, the motor M has the same configuration as that described above, and in this case, is a three-phase brushless motor. Although not shown, the motor M is connected to the other of the vehicle body side member or the axle side member of the vehicle.

  Therefore, the shock absorber 1 in the present embodiment is interposed between the vehicle body side member and the axle side member of the vehicle by the motor M and the bracket 7.

 In the shock absorber 1 configured as described above, as described above, the motor M is driven and / or by energy regeneration, or both, the axial direction between the ball screw nut 3 and the screw shaft 4 is increased. By suppressing the relative linear motion, the relative linear motion between the vehicle body and the axle of the vehicle is attenuated.

 The damping force generated when the shock absorber 1 expands and contracts is controlled by controlling the current flowing through the winding of the motor M. This current is controlled by the motor drive circuit C and the gate controller described above. Is called.

 In addition to the current caused by the power source E, the current flowing in the winding is caused by the induced electromotive force generated in the winding when the motor M is forcibly driven by the screw shaft 4, that is, the induced electromotive force due to energy regeneration. There is something to do.

 Therefore, the motor M is based on the torque generated by the energy regeneration, that is, the induced electromotive force generated by forcibly driving the output shaft 5, and the torque generated by the power source E is adjusted to reduce the damping force of the shock absorber 1. However, when the two torques are in the same direction, the current flowing through the winding also increases, and when any of the switching elements S1, S2, S3, S4, S5, S6 is turned off, the power source E A large regenerative current is generated in the motor driving circuit C mounted on the shock absorber 1 that can be applied to the windings, in comparison with the motor driving circuit C when the motor M is simply driven. .

 Here, as described above, the regenerative current flows through the diodes D1, D2, D3, D4, D5, D6 and the parasitic diodes K1, K2, K3, K4, K5, K6.

  In this case as well, the amount of heat generated by the switching elements S1, S2, S3, S4, S5, and S6 is reduced, so that the temperature rise of the MOSFET can be reduced, and the reliability of the switching element can be improved. Since damage is also prevented, the danger that the shock absorber 1 will not be able to generate a damping force is avoided.

  Further, the cooling plate for cooling the switching element can be made smaller than the conventional one, and the entire motor drive circuit including the housing can be reduced in size, so that the shock absorber 1 on which the shock absorber 1 is mounted is also reduced in size. Furthermore, the mountability of the shock absorber 1 on the vehicle is improved.

  In the above description, the motor M is a three-phase brushless motor. However, a motor having a two-phase winding may be used. In this case, two arms having the above-described switching elements connected in series are connected in parallel. What is necessary is just to comprise a motor drive circuit by connecting.

  The motor M is not limited to the brushless motor described above, and may be another motor.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

It is a circuit diagram of the motor drive circuit in one embodiment. It is the figure which showed the flow of the electric current which flows through the motor drive circuit at the time of winding energization. It is the figure which showed the flow of the electric current which flows through the motor drive circuit at the time of winding non-energization. It is the figure which showed notionally the buffer using a motor.

Explanation of symbols

1 shock absorber 2 motion conversion mechanism 3 ball screw nut 4 screw shaft 5 output shaft 7 bracket 8 cylinder A1, A2, A3 arm C motor drive circuit D1, D2, D3, D4, D5, D6 diode E power supply K1, K2, K3 , K4, K5, K6 Parasitic diode M Motor M1, M2, M3, M4, M5, M6 MOSFET
P1, P2, P3 output terminals S1, S2, S3, S4, S5, S6 switching elements

Claims (3)

A switching element comprising a MOS field effect transistor, wherein a diode having a forward voltage drop value smaller than the forward voltage drop value of the parasitic diode is provided in parallel with the parasitic diode of the MOS field effect transistor. In a motor driving circuit in which a plurality of arms each having a switching element having a MOS field effect transistor connected in series are connected to a power source, and the switching elements of the arms are connected to a winding of a motor, the switching element has a MOS electric field. A motor drive circuit comprising: an effect transistor; and a diode having a forward voltage drop value smaller than the forward voltage drop value of the parasitic diode in parallel with the parasitic diode of the MOS field effect transistor. In a shock absorber having a motion conversion mechanism for converting linear motion into rotational motion, a motor to which the rotational motion is transmitted, and a motor drive circuit, the motor drive circuit includes a switching element having a MOS field effect transistor in series. A plurality of arms formed by connecting and connecting switching elements to a winding of a motor are connected to a power source, and the switching element includes a MOS field effect transistor, a parasitic diode of the MOS field effect transistor, and A buffer comprising: a diode having a forward voltage drop value smaller than the forward voltage drop value of the parasitic diode.

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