Patent ID: 12212268

DETAILED DESCRIPTION

A set of a pair of a positive side (or upper arm) switching element and a negative side (or lower arm) switching element corresponding to the “half bridge circuit” according to the conceivable technique is referred to as a “leg” in this specification. The three-leg bridge circuits disclosed in Patent Literatures 1 and 2 includes one shared leg and two unshared legs. In the three-leg bridge circuit, the number of switch elements is reduced from eight to six compared to two H-bridge circuits. Also, the circuit area of the power converter is reduced.

However, when two motors are energized at the same time, a larger current flows through the shared leg than the non-shared leg, so there may be a risk of failure due to heat generation.

The present embodiments provide a motor control device that reduces heat generation in a shared leg in a configuration in which one leg of a bridge circuit is shared by two DC motors.

A motor control device according to the present embodiments drives a first motor and a second motor that output torque in a braking direction or a non-braking direction in accordance with the direction of energization in a vehicle braking device. This motor control device includes a power converter and a control unit.

The power converter is accommodated in one casing and has three legs, a first leg, a second leg, and a third leg, which are connected in parallel between a positive terminal and a negative terminal of the DC power supply. In each leg, a positive side switch element connected to the positive terminal and a negative side switch element connected to the negative terminal are connected in series via an inter-element connection point. The power converter can convert the electric power of the DC power supply and supply the converted power to the first motor and the second motor. The control unit operates the positive side switch element and the negative side switch element of each leg to control energization of the first motor and the second motor.

The inter-element connection point of the first leg is connected to one terminal of the first motor. The inter-element connection point of the third leg is connected to one terminal of the second motor. The inter-element connection point of the second leg is connected to the other terminal of the first motor and to the other terminal of the second motor. That is, the second leg is a shared leg, and the first and third legs are non-shared legs.

When the control unit energizes the positive side switch element of the first leg to the negative side switch element of the second leg and energizes the positive side switch element of the third leg to the negative side switch element of the second leg, the first The motor and the second motor are configured to output torque in the same direction, either the braking direction or the non-braking direction.

When the absolute value of the current flowing or estimated to flow in at least one of the first motor and the second motor exceeds the current threshold, the control unit switches and drives the positive side switch element and the negative side switch element of the second leg. The “current estimated to flow” means current expected based on circuit specifications and experimental data, or future current expected from changes in current detection values from the past to the present.

In the present embodiments, one of the positive side switch element or the negative side switch element of the second leg is not always in an on state, but is switching and driven so that the return current flows. As a result, even if the maximum instantaneous current does not change, the flowing current is shared temporally by both switch elements, so that heat generation per element can be reduced.

A motor control device according to the present disclosure will be described with reference to plural embodiments based on the drawings. The motor control device of this embodiment functions as an “electric parking brake motor control device” that drives two electric parking brake motors for locking the right and left rear wheels when the vehicle is parked.

[Overall Configuration of Brake Device]

First, with reference toFIGS.1and2, the overall construction of a vehicle braking system will be described. The brake device90has an “electric hydraulic control function” and an “electric parking brake function”. In the automotive technical field, “Electric Hydraulic Control” is commonly known as “ESC” or control related to Electric Stabilization Control. In addition to braking control in a narrow sense, stabilization control may include antilock brake control, vehicle behavior stabilization control, slope start assist control, traction control, vehicle following control, lane departure avoidance control, obstacle avoidance control, and the like. The electric parking brake (hereinafter “EPB”) function is a function that locks the wheels when the vehicle is parked.

As shown inFIG.1, the brake device90includes a brake control ECU10, a hydraulic pressure generator80, a brake pedal91, an EPB switch94, brake units95R,95L,96R, and96L for each wheel, a wheel speed sensor97, and the like. In the so-called “motor-on-caliper type” brake device shown inFIG.1, two EPB motors71and72are provided, one for each of the right and left rear wheels.

InFIG.1, thick solid lines indicate hydraulic pressure paths, and dashed arrows indicate electrical signals. When the brake pedal91is stepped on, hydraulic pressure is supplied to the hydraulic pressure generator80and an electric signal is transmitted to the brake control ECU10. When the EPB switch94is operated, an electric signal is sent to the EPB motor control device400in the brake control ECU10.

The brake control ECU10includes an ESC (electric hydraulic pressure) control unit20and an ESC power converter25as components related to electric hydraulic pressure control. The ESC control unit20rotates the ESC motor83by power supply from the ESC electric power converter25to drive the hydraulic pressure actuator85, thereby controlling the brake hydraulic pressure of the hydraulic pressure generator80. The hydraulic pressure is typically oil pressure, and the hydraulic pressure actuator is a hydraulic pump or hydraulic cylinder. Also, the ESC motor83is, for example, a three-phase motor, and the ESC electric power converter25is a three-phase inverter circuit.

The brake control ECU10also includes an EPB control unit40and an EPB electric power converter45as components related to EPB control. The EPB control unit40drives the two EPB motors71and72by power supply from the EPB power converter45, and locks the right and left rear wheels when parking. In this embodiment, the EPB motors71and72are configured to include DC motors. The EPB power converter45is configured to include a “three leg bridge circuit” which will be described later. A portion of the brake control ECU10that includes the EPB control unit40and the EPB electric power converter45is referred to as an “EPB motor control device400.”

A hydraulic pressure actuator85of the hydraulic pressure generator80is driven by the output of the ESC motor83and supplies braking hydraulic pressure to the front wheel brake units95R and95L and the rear wheel brake units96R and96L. The outputs of the first EPB motor71and the second EPB motor72respectively act on the rear wheel brake unit96R and96L during parking. A wheel speed sensor97detects the rotational speed of each wheel and notifies the brake control ECU10of the detected rotational speed.

FIG.2illustrates the configuration of the right rear wheel brake unit96R. The brake pad965of the rear wheel brake unit96R is pressed against the brake disc966by the output of the first EPB motor71, thereby locking the wheels. In addition, the wheels are locked by pressing the brake pads965against the brake discs966by the hydraulic pressure supplied from the hydraulic pressure generator80throughout the stop and running operations.

[Configuration of EPB Motor Control Device]

Next, referring toFIG.3, the configuration of the EPB motor control device400will be described. Hereinafter, “EPB” in the element names inFIG.1will be omitted. In other words, the EPB motor control device400, the EPB control unit40and the EPB electric power converter45are referred to as “motor control device400”, “control unit40” and “electric power converter45”. Also, the first EPB motor71is referred to as “first motor71”, and the second EPB motor72is referred to as “second motor72”.

The control unit40includes a microcomputer, a driving circuit, and the like, and has a CPU, a ROM, a RAM, an I/O, a bus line connecting these configurations, and the like (not shown). The control unit40performs required control by executing software processing or hardware processing. The software processing may be implemented by causing the CPU to execute a program. The program may be stored beforehand in a memory device such as a ROM, that is, in a readable non-transitory tangible storage medium. The hardware processing may be implemented by a special purpose electronic circuit.

The electric power converter45has three legs, a first leg51, a second leg52and a third leg53, connected in parallel between a positive terminal Tp and a negative terminal Tn of the DC power supply Bt. The voltage of the DC power supply Bt is, for example, 12 [V]. The three legs51,52,53are housed in one casing600and mounted on the same substrate, for example. As described above, the electric power converter45is configured as a “three-leg bridge circuit” and can convert the electric power of the DC power supply Bt and supply the converted electric power to the first motor71and the second motor72.

In the first leg51, a positive switch element S1H connected to the positive terminal Tp and a negative switch element S1L connected to the negative terminal Tn are connected in series via an inter-element connection point N1. In the second leg52, a positive switch element S2H connected to the positive terminal Tp and a negative switch element S2L connected to the negative terminal Tn are connected in series via an inter-element connection point N2. In the third leg53, a positive switch element S3H connected to the positive terminal Tp and a negative switch element S3L connected to the negative terminal Tn are connected in series via an inter-element connection point N3. The positive switch elements S1H, S2H, S3H and the negative side switch elements S1L, S2L, S3L are configured by MOSFETs, for example.

The inter-element connection point N1of the first leg51is connected to one terminal of the first motor71. The inter-element connection point N3of the third leg53is connected to one terminal of the second motor72. The inter-element connection point N2of the second leg52is connected to the other terminal of the first motor71and to the other terminal of the second motor72. The control unit40operates the positive switch elements S1H, S2H, S3H and the negative switch elements S1L, S2L, S3L of the legs51,52,53to control the energization of the first motor71and the second motor72.

A connection point on the positive terminal Tp side of the positive switch elements S1H, S2H, and S3H of the three legs51,52, and53is defined as a positive connection point N0u. A connection point on the negative terminal Tn side of the negative switch elements S1L, S2L, and S3L of the three legs51,52, and53is defined as a negative connection point N0d. In the configuration example ofFIG.3, between the element connection points N1, N2, N3of each leg and the positive connection point N0u, and between the element connection points N1, N2, N3of each leg and the negative connection point N0d, shunt resistors R1u, R1d, R2u, R2d, R3u, R3das “current detectors” are arranged. Details regarding current detection will be described later. Note that the arrangement configuration of the shunt resistors inFIG.3corresponds toFIG.14B.

Here, as indicated by the solid line arrow, the direction of current flowing from the positive switch element S1H of the first leg51through the first motor71to the negative switch element S2L of the second leg52is defined as the positive direction. Similarly, the direction of current flowing from the positive switch element S3H of the third leg53to the negative switch element S2L of the second leg52through the second motor72is defined as the positive direction.

Here, as indicated by the dashed line arrow, the direction of current flowing from the positive switch element S2of the second leg52through the first motor71to the negative switch element S1L of the first leg51is defined as the negative direction. Similarly, the direction of current flowing from the positive switching element S2H of the second leg52through the second motor72to the negative switching element S3L of the third leg53is defined as the negative direction.

To “energize the first motor71and the second motor72in the positive direction” means that energization from the positive switching element51H of the first leg51to the negative switching element S2L of the second leg52and energization from the positive switch element S3H of the third leg53to the negative switch element S2L of the second leg52are performed. To “energize the first motor71and the second motor72in the negative direction” means that energization from the positive switch element S2H of the second leg52to the negative switch element S1L of the first leg51and energization from the positive switch element S2H of the second leg52to the negative switch element S3L of the third leg53are performed.

In one configuration example, when the control unit40energizes in the positive direction, both the first motor71and the second motor72output torque in the braking direction, and when the control unit40energizes in the negative direction, both the first motor71and the second motor72output torque in the non-braking direction. When the motors71,72output torque in the braking direction, the rear wheel brake units96R,96L lock the wheels, and when outputting torque in the non-braking direction, the rear wheel brake units96R,96L unlock the wheels.

In another configuration example, oppositely, when the control unit40energizes in the positive direction, both the first motor71and the second motor72may output torque in the non-braking direction, and when the control unit40energizes in the negative direction, both the first motor71and the second motor72may output torque in the braking direction.

In short, the motor control device400of this embodiment is designed so that when the control unit40is energized in the positive direction, the first motor71and the second motor72output torque in the same direction, either the braking direction or the non-braking direction. Further, when the control unit40energizes in the negative direction, the first motor71and the second motor72are configured to output torque in the direction opposite to when energized in the positive direction.

Next, with reference toFIG.4, difficulties in the power converter45having a three-leg bridge circuit configuration will be described. The upper side ofFIG.4shows the current path and the amount of current during positive direction energization, and the lower side shows the current path and current amount during negative direction energization. A thick block arrow indicates a large amount of current. In the three-leg bridge circuit, when the two motors71and72are energized at the same time, the current flowing through the switch elements S2H and S2L of the second leg52, which is the shared leg, increases, and there may be a difficulty of failure due to heat generation.

Therefore, in the present embodiment, in a configuration in which one leg of a bridge circuit is shared by two DC motors, an object is to reduce heat generation in the shared leg. In the first and second embodiments, heat generation in the shared leg is reduced by changing the energization method. In the third and fourth embodiments, in addition to the energization method, measures in terms of hardware configuration are added.

First and Second Embodiments

The energization method according to the first and second embodiments will be described with reference toFIGS.5to12, focusing on time charts. In the following description of the energization method, reference numerals for the control unit, the first to third legs, the first motor, the second motor, and the like will be omitted. The time charts ofFIGS.8and12schematically show the operation using a time axis divided by unit time. One scale of the time axis corresponds to two units (2τ) of the time unit [τ], and even times such as t0, t2, . . . are marked on each scale. The points in the middle of each scale correspond to odd-numbered times.

It is assumed that the positive side and negative side switch elements are turned on and off complementarily, and the duty ratio of each leg on the vertical axis means “the ratio of the on time of the positive side switch element to the switching cycle”. When the duty ratio is 0%, the positive side switch element is off and the negative side switch element is on, and when the duty ratio is 100%, the positive side switch element is on and the negative side switch element is off. Each time chart shows an example of energization in the positive direction when the duty ratio of the first leg and the third leg is 100%. Alternatively, the energization in the positive direction may be performed when the duty ratio of the first leg and the third leg is 0%. In that case, 100% and 0% in the drawing are reversed.

Before describing the first and second embodiments, an energization method of a comparison example will be described with reference to the time charts ofFIGS.5and6. In the comparison example 1 shown inFIG.5, each leg operates only at a duty ratio of 0% or 100%. That is, during rotation of each motor, the switch element in the corresponding leg is either always off or always on. Further, in the comparison example 1, the first motor and the second motor start rotating (that is, activated) at the same time from a stop state, and finish rotating at the same time.

During the period from time t0 to t12, the first and third legs are energized with a duty ratio of 100% and the second leg is energized with a duty ratio of 0%, and a positive current flows through the first and second motors. During the period from time t16 to t28, the first and third legs are energized with a duty ratio of 0% and the second leg is energized with a duty ratio of 100%, and a negative current flows through the first and second motors. As indicated by shaded areas, the absolute values of the positive current immediately after time t0 and the negative current immediately after time t16 exceed the current threshold.

That is, the current peak timings of the first motor and the second motor overlap, and a large current flows through the switch element of the second leg. The upper part of the drawing shows changes in the motor rotation amounts θm1 and θm2 when a positive current is applied. In the comparison example 1, the line representing the rotation amount θm1 of the first motor from the initial position θ0 to the control target θtgt overlaps with the line representing the rotation amount θm2 of the second motor.

In the comparison example 2 shown inFIG.6, each leg operates only at a duty ratio of 0% or 100% as in the comparison example 1. Further, in the comparison example 2, the activation timings of the first motor and the second motor are shifted by 2τ as a predetermined time. The significance of shifting the activation timing will be described later in the description of the first embodiment.

As a difference from the comparison example 1, the duty ratio of the third leg is 0% from time t0 to t2, 100% from time t12 to t14, and 100% from time t16 to t18. Also, the duty ratio of the first leg is 100% from time t28 to t30. As a result, a positive current flows through the first motor during the period from t0 to t12, while a positive current flows through the second motor during the period from t2 to t14. Further, negative current flows through the first motor during the period from time t16 to t28, while negative current flows through the second motor during the period from time t18 to t30.

In the comparison example 2, while maintaining the length (12τ) of the energization period of the second motor, the energization period of the first motor is offset by a predetermined time. Therefore, the line of the rotation amount θm1 of the first motor from the initial position θ0 to the control target θtgt and the line of the rotation amount θm2 of the second motor are parallel. That is, the end time difference Δe has a length of 2τ equal to the activation time difference Δs. Therefore, there may be a possibility that the braking timing of the right and left wheels in the EPB would be shifted.

The details of the switch operation during the period in which the energization timing is shifted will be supplemented with reference toFIG.7. Since the negative switch element S3L of the third leg is turned on during the period from time t0 to t2, a current path indicated by a dashed line is formed in the upper side of the drawing. Further, since the positive switch S3H of the third leg is turned on during the period from time t16 to t18, the current path indicated by the dashed line is formed in the lower side of the drawing. The similar feature is applied to the first leg in the period from time t12 to t14 and the period from time t28 to t30.

However, since the resistance of the switch element is much smaller than the resistance of the motor winding, the current flowing through the dashed line path is ignored in the comparison example 2. Here, if the current in the dashed line path cannot be completely ignored due to the resistance of the circuit, it may be possible to turn off both the positive switch element and the negative switch element of the first leg or the third leg during these periods.

Next, with reference toFIG.8, the energization method of the first embodiment will be described. The format of the timing chart conforms toFIGS.5and6of the comparison example. First, as a matter common to the first and second embodiments, the control unit40starts energization when the EPB switch94is operated. For example, when the current flowing through the motor reaches a predetermined value or more, or the integrated value of the current reaches a predetermined value or more, the control unit40determines that the parking brake is sufficiently locked or unlocked, and terminates energization.

In this embodiment, in order to reduce heat generation in the shared leg, when the absolute value of the current flowing or estimated to flow in at least one of the first motor and the second motor exceeds the current threshold, the control unit switches and drives the positive switch element and the negative switch element of the second leg. The “flowing current” is determined based on the current detection value or estimated value by a current detector such as a shunt resistor, or the detected value or estimated value of other physical quantity correlated with the current.

The “current estimated to flow” means current expected based on circuit specifications and experimental data, or future current expected from changes in current detection values from the past to the present. For example, if it is known that the peak current when the motor is energized always exceeds the current threshold, the control unit may always perform switching drive operation when the motor is energized.

As described in the comparison example, in this energization method, a configuration is established in which the control unit performs a PWM control for each switch element of the power converter and performs the switching drive operation based on the duty ratio. For example, it is defined that the ratings of the positive switch element and the negative switch element of the second leg are the same, and that the heat receiving characteristics and the heat dissipation characteristics due to the substrate arrangement are also the same. In this case, it may be preferable to set the duty ratio of the switching drive operation to approximately 50% so that the on-state times of the positive switch element and the negative switch element are approximately the same.

Specifically, referring toFIG.8, in the first embodiment, the duty ratio of the second leg is set to 50% during the period from time t0 to t3 and the period from time t11 to t19, and the switching drive operation is performed. In particular, the control unit of the first embodiment disperses current and heat by switching and driving the second leg once per one-directional energization, with reference to the second embodiment described below. When the motor starts to move, a large current flows, but the voltage is low. In other words, since a high voltage is not required at the start of energization, it is considered that setting the duty ratio of the second leg to 50% has no influence.

FIG.9shows the relationship between the applied voltage for energizing the motor and the torque-rotational speed characteristics. The torque at activation, i.e., when the rotation speed is 0, increases as the voltage increases. The high voltage region characteristics at voltage of V are indicated by a line connecting no-load rotation speed No and activation torque Ts. The low voltage region characteristics at voltage of ½V are indicated by a line connecting the no-load rotational speed (No/2) and the activation torque (Ts/2). Therefore, if the required torque at activation is (Ts/2), activation is possible with a duty ratio of 50%. Further, as indicated by the arrow, by changing the duty ratio to 100% after activation, it is possible to shorten the time required to lock and secure the lock torque equivalent to that of the above-described comparison example.

Further, the control unit energizes the first motor and the second motor so as to shift the timing of the current peaks. Specifically, the control unit shifts the activation timing of the first motor and the second motor from stop to rotation. In the example shown by the solid line inFIG.8, the control unit activates the first motor at time t0 and activates the second motor at time t2 after a predetermined time 2τ during positive direction energization. Further, the control unit activates the first motor at time t16 during negative direction energization, and activates the second motor at time t18 after a predetermined time 2τ. This feature is the same as the comparison example 2 shown inFIG.6. Thus, the amount by which the activation timing is shifted may be a fixed value.

Alternatively, as indicated by the two-dot chain line, when the absolute value of the current of one of the first motor and the second motor (in this example, the first motor) that has started to be energized first exceeds the threshold value temporarily, and then, falls below the threshold, the control unit may start energizing the other motor (i.e., the second motor in this example).

Further, in the example ofFIG.8, the control unit shifts the duty ratio of the second leg from 50% to 0% at time t3 when the positive current value of the second motor falls below the threshold, and changes the duty ratio of the second leg from 50% to 100% at time t19 when the absolute value of the negative current falls below the threshold. Not limited to this example, the timing of shifting the duty ratio from 50% to 0% or 100% may be set to a fixed value.

Furthermore, in the example ofFIG.8, the first leg51and the third leg53, which are non-shared legs, are also switched and driven at a duty ratio of 50% during the period from time t13 to t16 when the positive energization shifts to the negative energization. During the period from time t13 to t16, the three legs51,52,53are synchronously switched and driven, so that no current flows through the motors71,72. Note that during the period from t12 to t13 when the duty ratio of the first leg51is 0% and the period from t28 to t29 when the duty ratio of the third leg53is 100%, the current along the dashed line path inFIG.7is ignored as in the comparison example 2.

In the diagram showing the changes in the motor rotation amounts θm1 and θm2 during the positive direction energization, since the voltage is low during the period from time t0 to t3 when the duty ratio of the second leg is 50%, the slope of changes in the motor rotation amounts θm1 and θm2 becomes relatively small. Therefore, the motor rotation amounts θm1 and θm2 appear as broken lines. In addition, a period in which the duty ratio of the second leg is 50% is provided in comparison with the comparison example 2, and the proportion of the second motor driven with a duty ratio of 100% is greater than that of the first motor. Therefore, the rotation amount θm2 of the second motor increases faster than the rotation amount θm1 of the first motor, and the end time difference Δe(1τ) to reach the control target θtgt becomes smaller than the activation time difference Δs(2τ).

As described above, in the first embodiment, one of the positive switch element and the negative switch element of the second leg is not always turned on, but it is switched and driven so that the return current flows. As a result, even if the maximum instantaneous current does not change, the flowing current is shared temporally by both switch elements, so that heat generation per element can be reduced. Further, by setting the duty ratio of the switching drive operation to 50%, the heat generation of the positive side switch and the negative side switch becomes almost equal, and the heat generation peak can be effectively reduced. In other words, switching is performed so that the temperatures of the positive switch element and the negative switch element approach each other.

Moreover, it may be preferable that the switching drive operation is performed only during a period when the current value is large and the voltage is low. If switching drive operation is performed in a low-current high-rotation region, the motor rotation speed may decrease. Therefore, by performing the switching drive operation only during the period when the current value is large and the voltage is low, it is possible to suppress the decrease in the motor rotation speed in the low current high rotation region.

Furthermore, in the first embodiment, the maximum instantaneous current can be reduced by shifting the energization timings so that the timings at which the drive currents of the motors are large do not overlap. Therefore, heat generation in the second leg is suppressed. Also, by energizing so that the end time difference Δe is smaller than the activation time difference Δs, even if the start timing is shifted, the difference in brake timing between the right and left wheels in the EPB can be reduced.

Next, the flow charts ofFIGS.10and11show the energization method according to this embodiment. In the following flowchart, a symbol S indicates a step. In S11ofFIG.10, the control unit determines whether the absolute value of the current flowing or estimated to flow in at least one of the first motor and the second motor exceeds the current threshold.

When the determination in S11is “yes”, in S12the control unit performs switching drive operation so that the temperatures of the positive side switch S2H and the negative side switch S2L of the second leg approach each other. Specifically, the control unit switches and drives the second leg at a duty ratio of 50%, for example. In the case of “no” in S11, in S13, the control unit performs fixed energization to the second leg, that is, energization corresponding to a duty ratio of 0% or 100%.

In S21ofFIG.11, it is determined whether the EPB switch has been operated. When “yes”, the process proceeds to S22to start driving the first motor and the second motor simultaneously. In S22, the control unit energizes the first motor and the second motor so as to shift the timing of the current peak, specifically, the activation timing from stop to rotation. At this time, it may be shifted by a predetermined time. Alternatively, when the absolute value of the current of one of the motors to which energization has started earlier exceeds the threshold value temporarily and then falls below the threshold, energization of the other motor may be started.

Second Embodiment

Next, with reference toFIG.12, the energization method of the second embodiment will be described. In the second embodiment, the second leg is switched and driven to dissipate the current and heat by switching the second leg twice, at the initial stage and the final stage, per one-directional energization.

It is the same as the first embodiment shown inFIG.8in that the second leg is switched at a duty ratio of 50% during the period from t0 to t3 in the positive direction energization. In the subsequent end of energization, the positive current exceeds the current threshold during the period from t8 to t12 for the first motor and from t10 to t14 for the second motor. Therefore, the control unit further switches and drives the second leg at a duty ratio of 50% during the period from t8 to t14. As a result, the second leg continues the switching operation with a duty ratio of 50% over the period from t8 to t19 after the period in which both motors are stopped.

Similarly, during the negative direction energization, the absolute value of the negative current exceeds the current threshold during the period from t24 to t28 for the first motor and from t26 to t30 for the second motor at the end of the energization. Therefore, the control unit further switches and drives the second leg at a duty ratio of 50% for a period after t24. In the second embodiment, it is possible to further reduce heat generation in the second leg due to the large current in the final stage of the energization, as compared with the first embodiment.

[Arrangement Example of Current Detector]

Next, with reference toFIGS.13A to17C, an example arrangement of shunt resistors as “current detectors” will be described. In this embodiment, the current detector is used for current detection to determine whether the switching drive operation of the second leg52is implemented. Regarding the code of the shunt resistor arranged in each leg, the first letter is “R”, the second letter is the number of the leg, and the third letter is “u” for the positive side and “d” for the negative side. A shunt resistor arranged between the positive side connection point N0uof the three legs and the positive terminal Tp is represented as a “positive path shunt resistor R0u”, and a shunt resistor arranged between the negative side connection point N0dof the three legs and the negative terminal Tn is represented as “the negative path shunt resistor R0d”.

The symbols of the shunt resistors connected in series with the motors71and72are defined as “Rm1and Rm2”. A current flowing through each shunt resistor is represented by a symbol in which “R” of the shunt resistor is replaced with “I”. The current flowing through the shunt resistor R0uin the positive path is called “total positive current I0u”, and the current flowing through the shunt resistor R0din the negative path is called “total negative current I0d”.

FIGS.13A and13Bshow a configuration for directly detecting the first motor current Im1and the second motor current Im2as an arrangement example of the first category. In the basic configuration461shown inFIG.13A, one shunt resistor Rm1is arranged in series with the first motor71between the inter-element connection point N1of the first leg51and the inter-element connection point N2of the second leg52. Another shunt resistor Rm2is arranged in series with the second motor72between the inter-element connection point N3of the third leg53and the inter-element connection point N2of the second leg52. Hereinafter, “configuration” such as “basic configuration461” means a three leg bridge circuit (or a power converter).

In a configuration462ofFIG.13B, a positive path shunt resistor R0uand a negative path shunt resistor R0dare added to the basic configuration461. A first motor current Im1is detected by a shunt resistor Rm1, and a second motor current Im2is detected by a shunt resistor Rm2.

FIGS.14A to14Cshow an arrangement example of the second category, in which the currents flowing through the first leg51and the third leg53are detected, and the first motor current Im1and the second motor current Im2are calculated from the detected currents. In the basic configuration471shown inFIG.14A, shunt resistors R1u, R1d, R3u, and R3dare arranged at four locations between the inter-element connection points N1, N3of the first leg51and the third leg53and the positive side connection point N0u, and between the inter-element connection points N1, N3of the first leg51and the third leg53and the negative side connection point N0d. In another arrangement example of the second category, the shunt resistor may be arranged between the inter-element connection point of at least two legs among the three legs51,52,53and the positive side connection point N0u, and between the inter-element connection point of at least two legs and the negative connection point N0d.

Currents I1u, I1d, I3uand I3dare detected by the shunt resistors R1u, R1d, R3uand R3d. Motor currents Im1and Im2are calculated by equations (1.1) and (1.2).
Im1=I1u−I1d(1.1)
Im2=I3u−I3d(1.2)

In the basic configuration471, the currents I2uand I2dof the second leg52are not directly detected, and can be calculated by the following equations. When the equation of “Im1+Im2≥0” is satisfied, the positive side current I2uof the second leg52is represented by equation (2.1a) according to the switching timing of the negative side switching element S2L. Negative current I2dis represented by equation (2.2).

I2u=0⁢(when⁢S⁢2⁢L⁢is⁢on)=-I⁢m⁢1-I⁢m⁢2⁢(when⁢S⁢2⁢L⁢is⁢off)(2.1a)I⁢2⁢d=I⁢m⁢1+I⁢m⁢2+I⁢2⁢u(2.2)

When the equation of “Im1+Im2<0” is satisfied, the positive current I2uof the second leg52is represented by the equation (2.1b) according to the switch timing of the positive switching S2H. Negative current I2dis represented by equation (2.2).

I⁢2⁢u=-Um⁢1-I⁢m⁢2⁢(when⁢S⁢2⁢H⁢is⁢on)=0⁢(when⁢S⁢2⁢H⁢is⁢off)(2.1b)I⁢2⁢d=I⁢m⁢1+I⁢m⁢2+I⁢2⁢u(2.2)

In the configuration472ofFIG.14B, shunt resistors R2uand R2dare added to the basic configuration471at two locations between the inter-element connection point N2of the second leg52and the positive side connection point N0uand between the inter-element connection point N2of the second leg52and the negative side connection point N0d. Thus, the currents I2u, I2din the second leg52are directly detected.

In a configuration473ofFIG.14C, a positive path shunt resistor R0uand a negative path shunt resistor R0dare added to the basic configuration471, and the positive total current I0uand the negative total current I0dare detected. The currents I2uand I2dof the second leg52can also be calculated by equations (3.1) and (3.2).
I2u=I0u−I1u−I3u(3.1)
I2d=I0d−I1d−I3d(3.2)

Next,FIGS.15A to17Cshow other layout examples of shunt resistors. Other arrangement examples are not limited to the configuration capable of calculating the motor currents Im1and Im2. The arrangement examples inFIGS.13A-14Care comprehensively summarized such that the shunt resistor is arranged in series with one or more of the positive or negative switch elements of any of the three legs51,52,53, or arranged in series with one or more of the first motor71or the second motor72. It is understood that the shunt resistors R0u, R0dof the positive path and the negative path are provided in series commonly to the positive side switch element or the negative side switch element of the three legs51,52,53. InFIGS.15to17, the symbols of the connection points N1, N2, N3, N0u, and N0dare omitted.

In configuration481ofFIG.15A, shunt resistors R1d, R2d, R3dare provided in series with the negative switch elements S1L, S2L, S3L of each leg. In configuration482ofFIG.15B, a shunt resistor R0uin the positive path is further added to the configuration481.

In configuration483ofFIG.16A, shunt resistors R1u, R2u, R3uare provided in series with the positive switch elements S1H, S2H, S3H of each leg. In configuration484ofFIG.16B, a shunt resistor R0din the negative path is further added to the configuration483.

In configuration485ofFIG.17A, shunt resistors R0uand R0dof the positive path and the negative path are provided. In configuration486ofFIG.17B, only the positive path shunt resistor R0uis provided. In configuration487of FIG.17C, only the negative path shunt resistor R0dis provided.

Third and Fourth Embodiments

Next, with reference toFIGS.18and19, third and fourth embodiments will be described in which, in addition to the energization methods according to the first and second embodiments, measures for reducing heat generation in terms of hardware configuration are added. The third and fourth embodiments focus on the feature such that the second leg, which is a shared leg, to generate more heat than the first and third legs, which are non-shared legs.

In the third embodiment, regarding the current or temperature ratings of the positive side switch element and the negative side switch element, the rating of the element of the second leg52is set higher than the rating of the elements of the first leg51and the third leg53. As shown inFIG.18, the current rating of the elements in the second leg52is approximately twice the current rating of the elements in the first leg51and the third leg53. Alternatively, the temperature rating of the elements in the second leg52is higher than the temperature rating of the elements in the first leg51and the third leg53. Specifically, an element having a physical size larger than that of the first leg51and the third leg53is used as the element of the second leg52.

As a result, the circuit area and cost can be reduced compared to uniformly increasing the ratings of all elements in accordance with the required specifications of the second leg52. In addition, when a thermal failure occurs, one of the first leg51or the third leg53is estimated to fail first. Thus, it is possible to lower the possibility such that two motors71and72are not operable at the same time due to the one failure.

In the fourth embodiment, regarding the arrangement of the legs on the substrate, the second leg52is arranged at a location that receives less heat or has better heat dissipation than the first leg51and the third leg53. For example, as shown inFIG.19, a heat sink (or a connector)58is provided at one end of the substrate50, and a second leg52and a first leg51and a third leg53are arranged in the vicinity thereof from the heat sink (or connector)58side, in this order. On the side of the third leg53opposite to the heat sink (or connector)58, another heat-generating component59(for example, a shunt resistor, or the like) is arranged.

the second leg52is arranged such that the distance D21between the second leg52and the first leg51and the distance D23between the second leg52and the third leg53are larger than the distance D13between the first leg51and the third leg53(i.e., the equations of D21>D13, and D23>D13are satisfied). That is, the second leg52is arranged at a location where the heat is least received with respect to the mutual heat reception between the three legs51,52,53and the heat reception from the other heat-generating component59.

In addition, the second leg52is arranged at a location closer to the heat sink (or connector)58than the first leg51and the third leg53, that is, at a location with good heat dissipation. In the fourth embodiment, by designing the substrate arrangement so as to be advantageous for heat generation reduction and heat dissipation of the second leg52, even when combined with the third embodiment, the increase in the rating of the elements of the second leg52is reduced. Alternatively, it is permissible to use elements of the same rating for all legs51,52,53without combination with the third embodiment.

Other Embodiments

(a) The duty ratio in the switching drive operation of the second leg may not be limited to 50%, and may be any value greater than 0% and less than 100%. For example, the duty ratio may be set such that the temperatures of the positive side switch element and the negative side switch element of the second leg are approximately the same. Specifically, considering the difference in heat reception characteristics due to the heat generation of peripheral elements according to the layout of the substrate, the heat generation of the elements on the side that easily receives heat is reduced, and the more current flows in the elements on the side that are less likely to receive heat. Thus, overall optimization is established.

(b) The switching drive control method may not be limited to PWM control. For example, one of preset switching patterns may be selected according to conditions.

(c) When the non-shared leg is duty-driven in addition to the shared leg, the switching frequency of the shared leg may be less than that of the non-shared leg. As a result, switching loss in the shared leg is relatively reduced, and heat generation in the shared leg can be suppressed more effectively. Alternatively, instead of reducing the number of times of switching, the carrier frequency may be lowered, or predetermined duty driving may be repeated in synchronization with the carrier.

(d) In the above embodiment, in addition to detecting or calculating the motor current based on the current detection value of the shunt resistor and the like, a temperature detector may be used to detect the environmental temperature and the temperature of the switch element. For example, depending on the environmental temperature and the temperature of the switch element, the higher the temperature, the lower the current threshold, and the second leg may be switched and driven more effectively.

(e) Current detectors may not be limited to shunt resistors, and other current detectors may be used.

The present disclosure is not limited to such embodiments but can be implemented in various forms without deviating from the spirit of the present disclosure.

The controllers (control units) and method described in the present disclosure may be implemented by a special purpose computer which is configured with a memory and a processor programmed to execute one or more particular functions embodied in computer programs of the memory. Alternatively, the controllers (control units) described in the present disclosure and the method thereof may be realized by a dedicated computer configured as a processor with one or more dedicated hardware logic circuits. Alternatively, the controllers (control units) and the method according to the present disclosure may be achieved using one or more dedicated computers constituted by a combination of the processor and the memory programmed to execute one or more functions and the processor with one or more hardware logic circuits. The computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by a computer.

It is noted that a flowchart or the processing of the flowchart in the present application includes sections (also referred to as steps), each of which is represented, for instance, as S11. Further, each section can be divided into several sub-sections while several sections can be combined into a single section. Furthermore, each of thus configured sections can be also referred to as a device, module, or means.

The present disclosure has been made in accordance with the embodiments. However, the present disclosure is not limited to such embodiments and configurations. The present disclosure also encompasses various modifications and variations within the scope of equivalents. Furthermore, various combination and formation, and other combination and formation including one, more than one or less than one element may be made in the present disclosure.