JP5024618B2 - Electric motor control device and electric booster - Google Patents

Description

  The present invention relates to an electric motor control device and an electric booster used in a vehicle brake system.

As an example of a conventional vehicle brake system, there is an electric booster disclosed in Patent Document 1.
An electric booster disclosed in Patent Document 1 includes an input member that moves forward and backward by operation of a brake pedal, an assist member that is arranged to be relatively movable with respect to the input member, and an electric motor that moves the assist member forward and backward. And the brake fluid pressure boosted in the master cylinder is generated by the assist thrust applied to the assist member in accordance with the movement of the input member by the brake pedal.
By the way, in the above-described prior art, when the rotational speed of the electric motor reaches the upper limit value due to the influence of the driving voltage of the electric motor and the power source current (power source voltage), etc., there is a limit. On the other hand, when emergency braking is intended, an increase in the rotation speed of the electric motor is required. In response to this requirement (in order to increase the number of revolutions during emergency braking or the like), it is considered to prepare a power supply with a larger supply voltage or to provide a capacitor for the power supply.
JP 2007-112426 A

  However, the electric motor used in the electric booster requires high-speed rotation in order to shorten the operation time at the initial stage of operation (note that the load torque is small), while obtaining a high braking force at the end of the operation. High torque is required. For this reason, as described above, preparing a power supply with a larger supply voltage or further providing a capacitor for the power supply leads to an increase in the size of the apparatus. Met. These problems are the same not only in the electric booster but also in the vehicle brake system provided with an electric motor such as an electric disc brake, an electric parking brake, and a hydraulic system for controlling the vehicle attitude.

  The present invention has been made in view of the above circumstances, and provides an electric motor control device and an electric booster capable of ensuring an appropriate rotational speed and high torque of an electric motor without causing an increase in the size of the device. The purpose is to provide.

The present invention is applied to the electric motor in an electric motor control device that controls the electric motor used in a vehicle brake system including an electric motor that operates by receiving power supplied from a power source by operating a brake pedal. A booster circuit that boosts a voltage from the power source to generate a boosted voltage is provided so as to supply the boosted voltage to the electric motor, and the number of rotations of the electric motor to be operated in accordance with the operation of the brake pedal The target value of the physical data in the corresponding relationship with the power supply is expected to exceed the upper limit value of the physical data in the relationship corresponding to the rotation speed of the electric motor by the power supply voltage when the voltage from the power supply is applied . If, the boosted voltage which the boosting circuit has occurred is supplied to the electric motor, the maximum output current of the boosting circuit at this time of the electric motor drive And limits the current of a value smaller than the flow.

  According to the present invention, it is possible to secure an appropriate rotation speed and high torque of an electric motor without causing an increase in size of the apparatus.

Hereinafter, an electric booster according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing an electric booster (an example of a vehicle brake system) according to a first embodiment of the present invention, including a master cylinder, a brake pedal, and an ECU (control circuit, electric motor control device). It is. FIG. 2 is a block diagram schematically showing the ECU of FIG.
FIG. 3 is a block diagram showing the DC-DC converter of FIG. 4 shows the drive current of the electric motor of FIG. 1, the characteristics of the electric motor, and the current-voltage characteristics of the power supply. FIG. 4A shows the drive current of the electric motor, and FIG. 4B shows the torque and rotation speed of the electric motor. The figure which shows a characteristic (TN characteristic), (c) is a figure which shows the current voltage characteristic of a motor driver power supply.
FIG. 5 is a diagram showing load characteristics of the electric booster of FIG. 6 is a waveform diagram for illustrating the operation of the electric booster of FIG. 1, in which (a) is a deceleration characteristic, (b) is a hydraulic pressure characteristic, (c) is a Q-axis current characteristic, and (d). (E) is a step-up control signal generation, (f) is a diagram showing the brake pedal depression amount.

In FIG. 1, reference numeral 1 denotes an electric booster provided in an automobile brake system (vehicle brake system). The electric booster 1 has an input member 5 (input rod) that is slidably guided by a case 4 held on the front seat wall 3 of the automobile by operating the brake pedal 2 and moves forward and backward. The electric booster 1 has a piston 6 including a primary piston 6a and a secondary piston 6b, and is pressurized by an electric motor (hereinafter referred to as a motor 8) provided in the input member 5 and the electric booster 1. A tandem master cylinder 9 is connected.
The electric booster 1 presses the piston 6 (primary piston 6a and secondary piston 6b) of the master cylinder 9 as the input member 5 moves forward. The primary piston 6a is arranged to be movable relative to the input member 5. In the present embodiment, the primary piston 6a constitutes an assist member.

An electric booster 1 that is an example of an automobile brake system (vehicle brake system) has load characteristics as described below.
That is,
(1) A master cylinder 9 that uses brake fluid pressure is used, and this master cylinder 9 is provided with a communication passage for supplying brake fluid in the reservoir tank 10 to the piping system during non-braking, as shown in FIG. It has an invalid stroke δ for closing the communication path at the start of braking.
(2) A disc brake 11 is used as a brake device in relation to the electric booster. In the disc brake 11, the disc rotor (not shown) swings out of plane due to fluctuations in the vertical and lateral loads of the wheels. Even so, the caliper 13 returns by an amount called a rollback amount so that the brake pad (not shown) does not contact the disk rotor 12. There is a stroke that does not generate the hydraulic pressure indicated by RB in FIG. Further, the brake pad is made of resin and deforms non-linearly, and particularly has a small elastic coefficient in a region where the surface pressure is low (deceleration is small).
(3) There are low rigidity parts such as high pressure rubber hoses, ABS units and caliper seal rings in the piping, and the amount of liquid consumed in the low pressure part is large.
In FIG. 5, the stroke reaching the brake fluid pressure of 10 MPa (corresponding to a sudden brake with a deceleration of about 1G in a normal system) is assumed to be 1, and the stroke is normalized. However, even if the normalized stroke reaches 0.5. The hydraulic pressure is slight. It rises rapidly after 7.

The electric booster 1 is further connected to the motor 8 and a rotor (not shown) of the motor 8, and converts the rotation of the motor 8 into a linear motion in the horizontal direction in FIG. And a motor control device (hereinafter referred to as ECU) 18 for controlling each control target (including the motor 8) and the ABS unit 17 in the electric booster 1. ing. In the present embodiment, the ECU 18 constitutes an electric motor control device. The screw mechanism 15 includes a male screw portion 15a connected to a rotor (not shown) of the motor 8 and a nut portion 15b screwed into the male screw portion 15a. The nut portion 15b is fixed to the primary piston 6a.
The motor 8 is a surface magnet type three-phase (Y-connection) DC brushless (DCBL) motor, and is PWM driven. Between the nut portion 15b of the screw mechanism 15 and the input member 5, a relative displacement sensor 19 for detecting the relative displacement of both is interposed.
The master cylinder 9 causes the master cylinder 9 to generate a hydraulic pressure corresponding to the operating force of the brake pedal 2 and / or the assisting force of the motor 8, and applies a braking force having a magnitude corresponding to the hydraulic pressure via the ABS unit 17. It is generated by a brake device (disc brake 11) provided corresponding to the four wheels.

  2, the ECU 18 includes a 5V power supply circuit 20, a CPU 21 (control circuit), a motor driver 22, a motor current sensor 23, an insulated DC-DC converter (hereinafter referred to as a DC-DC converter) 24 (a boost circuit). ) And a diode 25. The 5V power supply circuit 20, the CPU 21, the motor driver 22, the motor current sensor 23, and the DC-DC converter 24 operate by receiving the supply of the battery voltage Vb from the battery 26. The ECU 18 controls the motor 8 according to the depression of the brake pedal 2. Specifically, the CPU 21 detects the depression amount of the input member 5 by the CPU 21 and controls the rotation of the motor 8 via the motor driver 22. To do.

  The phase current of the motor 8 can be determined from the detection result of the current sensor 23, the electrical angle is obtained from the signal of a rotation angle detector (not shown) built in the motor 8, and the current Q-axis current, that is, the output torque is calculated. The difference from the target torque is converted / amplified into a PWM signal and output to the motor driver 22.

  As shown in FIG. 3, the DC-DC converter 24 includes an insulating transformer 30, an output voltage detection amplifier 31, an output current sensor 32, a converter control circuit 33, and a switching element 34. The converter control circuit 33 is a control terminal. 35 is ON / OFF controlled by receiving an ON / OFF signal input. When ON-controlled, the DC-DC converter 24 operates at the voltage (battery voltage) Vb of the battery 26, and a constant voltage (hereinafter referred to as a boosted voltage) ΔV, preferably 6-12V is desirably set to the battery voltage Vb. When the OFF control is performed, the output (the output to the motor driver 22 via the diode 25) is cut off without causing any switching loss.

The motor driver 22 has a battery voltage Vb and an output voltage of the DC-DC converter 24 (hereinafter referred to as a DC-DC converter output voltage) “Vb + ΔV” [corresponding to the boosted voltage of claim 1. Corresponds to the motor driver power supply voltage. Is supplied through an OR connection of a diode 25 having a low voltage loss. For this reason, when the control terminal 35 receives an ON signal input to the motor driver 22 (hereinafter, this is referred to as the control terminal 35 is appropriately turned ON), the DC-DC converter output voltage “Vb + ΔV”. [Step-up voltage] is supplied (in other words, the motor driver power supply voltage Vs becomes the DC-DC converter output voltage “Vb + ΔV”) and receives an OFF signal (hereinafter, this is appropriately controlled by the control terminal 35. Battery voltage Vb is supplied (in other words, the motor driver power supply voltage Vs becomes the battery voltage Vb).
Hereinafter, for convenience, the motor driver power supply voltage Vs corresponding to the DC-DC converter output voltage “Vb + ΔV” will be referred to as a step-up motor driver power supply voltage Vs ′. The motor driver power supply voltage Vs corresponding to the battery voltage Vb is referred to as a non-boosting motor driver power supply voltage Vs.
Since the diode 25 is present, the voltage (0.5 to 0.7 V) drops in the forward direction of the diode 25 from the battery voltage Vb. In order to avoid complicated explanation of this voltage drop, For convenience, it will be ignored.

  The output current limit value Ilim of the DC-DC converter 24 is set to about 1/3 of the power supply current “0.81 × Iqmax” at the maximum output of the motor 8. The reason why the output current limit value Ilim is set in this way is to reduce the size and loss of the insulating transformer 30 and the switching element 34 in the DC-DC converter 24. For example, when the output power is roughly calculated, in the present embodiment, since the output current limit value Ilim is set as described above, the boosted divided voltage ΔV is boosted in this way as compared with boosting from 0V to 24V. The voltage that is approximately ½ of the applied voltage (24V) may be set to 12V. Furthermore, by setting the output current Ilim to 1/3 of “0.81 × Iqmax”, the output power becomes 1/6, the size of the insulating transformer 30 and the current capacity of the switching element 34 are greatly reduced to 1/6. Can be made smaller. Due to such effects, in the present embodiment, the output current limit value Ilim is set as described above.

In the brake system, the hydraulic pressure of the brake fluid supplied to the brake device may be maintained for several minutes or more in a high pressure state, and it is desired to reduce the heat generation of the motor and the motor driver as much as possible. As described above, reduction of the heat generation of the motor and the heat generation of the motor driver is also demanded from the aspect of motor miniaturization and circuit miniaturization.
In order to meet this demand, in this embodiment, as described above, a surface magnet type DC brushless (DCBL) motor is used as the motor 8, and the motor 8 is PWM driven.

  In this embodiment, the magnet (not shown) of the motor 8 is configured using Fe—Nd—B, thereby increasing the torque constant Kt. Further, the motor 8 has a surface magnet structure, so that the coil inductance (L) is reduced and the rise of current is accelerated. Further, the stator (not shown) of the motor 8 is set so as to increase its volume, thereby reducing the coil resistance. Further, in the motor driver 22, a MOSFET having a low ON resistance is PWM-driven to minimize other than the switching loss.

The motor 8 is a three-phase DC brushless motor that is Y-connected as described above. As shown in FIG. 4 (a), the motor 8 is configured such that a current shifted by 120 ° flows through each UVW phase of the motor 8 at an electrical angle (a mechanical angle of 90 ° corresponds to an electrical angle of 360 ° when the rotor has 8 poles) 8 is controlled.
When the UVW phase current of the motor 8 is I [Arms], the DC component (Q-axis current) Iq that becomes the driving force is
Iq = (√3) × I
The drive torque T is calculated using the torque constant Kt [Nm / A]
T = Kt × Iq
It is represented by

Further, when the voltage of the motor driver 22 power supply (hereinafter referred to as the motor driver power supply voltage) Vs, the line voltage Vm is:
Maximum voltage Vmmax = (Vs / 2) × {√ (3/2)} [Vrms]
The no-load rotation speed Nmax is determined using the induced voltage constant Ke [V / (1 / s)]
Nmax = (Vs / Ke) × (1 / √3) × {1 / (2π)} × 60 [rpm]
It is represented by Although the torque constant Kt and the induced voltage constant Ke are physically the same, they are generally used separately, and will be described separately in the present specification along general examples.

  FIG. 4B is a diagram showing the operable range of the motor 8. When the rough hatching region does not operate the DC-DC converter 24 (boost circuit) (the boost voltage is not obtained) [the DC-DC converter 24 is OFF. In the case of control], the range of fine hatching indicates the range of operation in the case where the DC-DC converter 24 is operated (a boost voltage is obtained) [when the DC-DC converter 24 is ON-controlled] Yes. In FIG. 4B, the horizontal axis is the torque, but here, it is displayed using the Q-axis current Iq corresponding to the torque. The vertical axis represents the rotation speed of the motor 8.

In FIG. 4B, a line segment 40 connecting points ◯, △, and ▽ indicates the rotation of the motor 8 when the control terminal 35 is OFF and the battery voltage Vb (maximum voltage Vmmax) is supplied to the motor driver 22. This is a line segment indicating a number N (rpm). A point ◯ is a characteristic point indicating the maximum output of the motor 8. The point ▽ is a characteristic point indicating the maximum rotation speed (non-boosting maximum rotation speed) Nmax that can be operated when the drive voltage of the motor 8 is Vmmax and the current of the motor 8 is Iq (Q-axis current). As can be seen from this line segment 40, when the motor current Iq (output torque) increases, the rotational speed N of the motor 8 decreases linearly. This reduction in the rotational speed is caused by a voltage loss of motor current × coil resistance.
The rotational speed when the output torque (and thus the Q-axis current Iq) is 0 is the non-boosting maximum rotational speed Nmax. It also corresponds to).

The motor rotation speed N is expressed by the following equation.
N = {(Nmax−Vs) / Ke} × (1 / √3) × {1 / (2π)} × 60 [rpm]

In FIG. 4B, the line segment 41 connecting the points □, ◎, and ◇ is supplied with the DC-DC converter output voltage “Vb + ΔV” [boosted voltage] to the motor driver 22 when the control terminal 35 is turned ON. This is a line segment showing the motor rotation speed (appropriately referred to as the motor rotation speed during boosting) N ′ (rpm).
The motor rotation speed N when the battery voltage Vb is supplied to the motor 8 without the DC-DC converter 24 being operated with respect to the motor rotation speed N ′ at the time of boosting is hereinafter referred to as non-boosting motor rotation speed. Also called N.
The point ◇ is a characteristic point indicating the maximum rotational speed (maximum rotational speed during boosting) Nmax ′ operable when the motor voltage is Vmmax ′ and the motor current is Iq (Q-axis current). As can be seen from this line segment 41, when the motor current Iq (output torque) increases, the motor rotation speed N ′ decreases linearly as in the case of the non-boosting motor rotation speed N.
The rotation speed when the output torque (and thus the Q-axis current Iq) is 0 is the maximum rotation speed Nmax ′ during boosting, and this rotation speed is the no-load rotation speed (hereinafter referred to as the no-load rotation speed Nmax ′ during boosting as appropriate). It also corresponds to).

The maximum rotation speed during boosting (no-load rotation speed during boosting) Nmax '
Nmax ′ = Nmax × Vs ′ / Vs
Vs ′: Motor driver power supply voltage during boosting Vs: Motor driver power supply voltage during non-boosting (= battery voltage Vb)
It is shown by the relational expression.
The line segment 41 connecting the rotation speed corresponding to Vmmax, that is, the line segment 41 connecting the points □, ◎, and ◇, connects the line segment indicating the rotation speed corresponding to Vmmax, that is, the points ○, Δ, and ▽. It becomes parallel to the line segment 40.

When the maximum voltage Vmmax of the motor voltage is determined by the motor driver power supply voltage Vs, the rotation speed of the motor 8 is limited by the no-load rotation speed Nmax, and as the torque (Q-axis current Iq) increases, the phase current × coil resistance The effective motor voltage is lowered by the amount, and the operable speed range is gradually reduced accordingly. Further, the motor 8 and the motor driver 22 have a limitation on the instantaneous maximum current, and the Q-axis current is limited by the maximum Q-axis current Iqmax.
Since the motor 8 is affected by heat generation, the torque (motor current) that can be continuously generated by the motor 8 is usually about 1/2 to 1/3 of the maximum Q-axis current Iqmax. Considering this, the present embodiment is designed such that the torque when the maximum hydraulic pressure is generated is equal to or less than the above torque [torque corresponding to about 1/2 to 1/3 of the maximum Q-axis current Iqmax].

FIG. 4 (c) shows the power supply voltage (motor driver power supply voltage Vs) and power supply current (motor driver power supply current Is) at each point Δ, ○, □, ◇, ▽, ◎, ● in FIG. 4 (b). Are drawn for the vertical axis and the horizontal axis, respectively. In FIG. 4 (c), the motor 8 outputs the maximum motor output [point. 4 (b) is generated, the motor 8 has about 80% of the maximum current Iqmax as described on the horizontal axis corresponding to the point ○ in FIG. 4 (c). % Motor driver power supply current Is flows.
In addition, the maximum rotation speed [point ▽. In the case of [corresponding to the point ▽ in FIG. Even when the maximum torque is generated, the rotation speed is kept at 0 [point ●. When this corresponds to the point ● in FIG. 4B, the motor driver power supply current Is is small due to the effect of PWM driving. At this time, all of the energy of the power supply current × the battery voltage is consumed by the resistance ripening of the motor coil, and the power generated by the motor is O.

FIG. 6 illustrates operation waveforms when the brake system having the above-described load characteristics in the drive system described above is stepped on suddenly. In FIG. 6, the solid line waveform is an operation waveform when the control terminal 35 of the DC-DC converter 24 (boost circuit) is OFF, and the dotted line waveform is when the control terminal 35 of the DC-DC converter 24 (boost circuit) is ON. Is an operation waveform.
In the present embodiment, the rotational speed is grasped, and when the rotational speed is equal to or higher than a predetermined value, the control terminal 35 of the DC-DC converter 24 (boost circuit) is turned on, thereby increasing the motor driver power supply voltage. The rotational speed is increased as indicated by the dotted line in FIG. Prior to this description, when the control terminal 35 of the DC-DC converter 24 (boost circuit) is OFF (that is, when the DC-DC converter 24 (boost circuit) is not ON-controlled), the DC-DC converter 24 is provided. Will be described.

  When the sudden braking operation is performed, the pedal depression amount [FIG. 6 (f)] almost instantaneously reaches a stroke corresponding to the maximum hydraulic pressure (flat portion on the right side of FIG. 6 (b)). In order to accelerate the rotor (rotor) of the motor 8 that has stopped, the Q-axis current Iq [FIG. 6 (c)] is Iqmax (near the point ● in FIG. 4 (b)) at a change rate of dI / dt≈Vs / L. Iqmax is maintained until the rotational speed N [FIG. 6 (d)] reaches the point O in FIG. 4 (b). However, only the light weight rotor without load is accelerated. It reaches near the ▽ point of (b) and reaches a steady speed slightly smaller than Nmax.

Thereafter, as the stroke increases, the hydraulic pressure gradually increases, and accordingly, the Q-axis current increases and the rotational speed decreases. When the hydraulic pressure reaches the target hydraulic pressure (maximum hydraulic pressure, the flat portion on the right side of FIG. 6B), the rotational speed becomes 0, and the Q-axis current is maintained at a value corresponding to the hydraulic pressure.
It can be seen from the history (operating characteristics) shown in FIG. 6 that shortening the time to reach the maximum hydraulic pressure cannot be achieved even if Iqmax is increased, and it is effective by increasing Nmax. Decreasing the reduction ratio also shortens the time, but the reduction ratio cannot be lowered because the Q-axis current at the time of holding the hydraulic pressure is limited by the heat generated by the motor 8. Further, if the induced voltage constant Ke is reduced, Nmax can be increased, but since it is synonymous with decreasing Kt, the Q-axis current also increases. Although it is effective to reduce the reduction ratio at the time of low addition by providing a variable speed reduction mechanism, it is possible to reduce the size and cost by increasing the power supply voltage and increasing Nmax, rather than providing a complicated speed change mechanism. .

In the present embodiment, in consideration of the above circumstances, when the DC-DC converter 24 (step-up circuit) is provided and the DC-DC converter 24 is used to increase the rotational speed, the rotational speed is required. The voltage supplied to the motor 8 is increased so as to increase.
Here, the waveform of the dotted line in FIG. 6, that is, the case where the control terminal 35 of the DC-DC converter 24 (boost circuit) is ON will be described.

In FIG. 6, the CPU 21 in the control circuit 10 predicts that the depression speed of the brake pedal 2 is equal to or higher than a predetermined value and the speed (the number of revolutions) is insufficient (this prediction corresponds to the target speed in advance by the battery voltage obtained by monitoring the battery voltage If the battery voltage is smaller than the voltage threshold, it is predicted that the speed is insufficient.) When the voltage is increased, the DC-DC converter 24 starts a boost operation. .
In order to accelerate the inertia of the rotor (rotor) of the motor 8 at the initial stage of braking, it is necessary to energize the current Iqmax as shown in FIG. 6 (c). The boosted voltage (high voltage) is supplied from the DC-DC converter 24 (boosting circuit) to the motor 8 until the rotational speed increases and the speed limitation due to the induced voltage occurs. When the piston of the booster moves forward and the brake fluid is supplied from the master cylinder 9 to the caliper of the brake device, the load on the motor 8 increases and reaches the predetermined fluid pressure (load set value) shown in (b). As shown in (e), the control signal is turned OFF and the operation of the DC-DC converter 24 is stopped.
By passing through the low load torque region at high speed, the target hydraulic pressure in (b), in other words, the target deceleration in (a) can be reached in a short time.

FIG. 7A shows an operation locus when the booster circuit is not used (no supply of boosted voltage to the motor 8), and FIG. 7B shows the use of the booster circuit (supply of boosted voltage to the motor 8). Shows the movement trajectory.
As shown in FIG. 7 (a), when the booster circuit is not used (no boosted voltage is supplied to the motor 8), the maximum speed is limited to a speed slightly lower than the no-load rotation speed Nmax at Vb. Is done. On the other hand, as shown in FIG. 7 (b), in the case of using the booster circuit (the boosted voltage is supplied to the motor 8), the boosting no-load speed is increased from the vicinity of the non-boosting no-load rotation speed Nmax. It increases substantially in the vicinity of the rotational speed Nmax ′. From FIG. 6 (d), it can be seen that the high-speed rotation time near the no-load rotation speed Nmax ′ at the time of boosting is considerably long, and the time to reach the target deceleration can be greatly shortened.

Further, in order to reduce power consumption and heat generation, the CPU 21 limits the operation time of the DC-DC converter 24. Normally, the control terminal 35 is turned off. Since the CPU21 has the ability to detect the amount of depression of the brake pedal 2, the depression speed by the time difference, the target speed to be rotated in Sunawa Chimo over data 8 can be calculated.
As described above, when the CPU 21 watches the battery voltage Vb and predicts that the target speed exceeds the no-load rotation speed at the battery voltage Vb, the CPU 21 turns on the control terminal 35.
Since the motor 8 has a rotor inertia, it has a time to accelerate to near the no-load rotation speed even though it is a short time, and it is sufficiently in time to start boosting from the time when the control terminal 35 is turned on. In addition, since the CPU 21 has a function of detecting the rotation angle of the motor 8, the current rotation speed can be calculated from the time difference, and the load torque can also be calculated by subtracting the torque required for acceleration from the Q-axis current. If the current rotational speed does not reach the target speed even though the load torque is small, the control terminal 35 is turned ON.

  Since the DC-DC converter 24 has a current limiting function, there is no problem in operation even if the control terminal 35 is turned on until the brake fluid pressure reaches the target fluid pressure, but the target speed is the battery voltage Vb. When the rotation speed is equal to or less than the no-load rotation speed-load torque or the current exceeds I1im, the voltage is not boosted, so the control terminal 35 is turned OFF. As a result, the operation time of the DC-DC converter 24 in one sudden brake can be suppressed to a short time of a predetermined value (for example, about 0.2 seconds), and the loss of the DC-DC converter 24 (boost circuit) is reduced. Further, since it is possible to achieve prevention of heat generation, further miniaturization is possible.

As described above, when the target speed is predicted to exceed the no-load rotation speed at the battery voltage Vb, the voltage applied to the motor driver power supply and thus the motor 8 is increased by turning on the control terminal 35 (DC −DC converter output voltage “Vb + ΔV”), the rotational speed can be increased in the initial stage of operation. At the end of operation, the control terminal 35 is turned OFF, so that the motor driver power supply voltage uses the battery voltage Vb to lower the motor drive voltage and generate high torque. In this way, the DC-DC converter 24 is provided, a large voltage is supplied to the motor 8 at the initial stage of operation to increase the rotational speed, and at the end of the operation, the control terminal 35 is turned OFF, thereby As the driver power supply voltage, a battery voltage is used so that the motor driving voltage is lowered and high torque is generated. Thus, required for the motor 8 of the electric booster, the functions of both the initial time of the speed and operation end stage of the high torque generation can be achieved with a simple configuration.

In the above embodiment, the case where the insulated DC-DC converter 24 incorporating the converter control circuit 33 is used is taken as an example. However, it is easy to give the CPU 21 an equivalent function, and this configuration is adopted. Thus, the circuit scale can be reduced.
In the above embodiment, the case where the physical data corresponding to the rotational speed of the motor 8 is the battery voltage Vb is taken as an example. However, instead of this, the detection value of the motor current sensor 23 may be used. Good.

In the above operation explanation brake fluid pressure is decided to stop the boosting operation when reaching the predetermined value, when reaches the target hydraulic pressure, or booster piston displacement stops operating upon reaching the target position You may control as follows. In this case, the increase in loss is small because of a short time increase.
Further, FIG. 4B shows line segments 40 and 41 indicating the non-boosting motor rotation speed N and the boosting motor rotation speed N ′ corresponding to the maximum voltages Vmmax and Vmmax ′, respectively. 41, when the power supply voltage is boosted, the rotational speeds N and N ′ increase in proportion to Vmmax and Vmmax ′, and as the battery voltage Vb decreases, the rotational speed decreases approximately in proportion. That is, the rotation speed is greatly affected by the battery voltage Vb (and hence the motor driver 22 power supply voltage). And the fall of battery voltage Vb, ie, the fall of rotation speed, will extend the arrival time to target deceleration significantly. On the other hand, the battery voltage Vb is monitored by the CPU 21, and when the battery voltage Vb falls below a predetermined voltage (for example, 12V), the boost operation is started unconditionally, thereby reaching the target deceleration described above. You may make it prevent the bad influence of the postponement of time largely. In this case, considering that it is difficult in terms of heat capacity to keep the high hydraulic pressure holding current flowing, it is desirable to devise such that the pressure increase is stopped and the holding hydraulic pressure is lowered when the vehicle stops.

Depending on the vehicle, there is a case where an auxiliary battery is mounted as a countermeasure for a battery down and a dual power supply system using the battery and the auxiliary battery is employed.
As shown in FIG. 8, the electric booster 1 </ b> A (second embodiment) can be configured using such a dual power supply system.
In the electric booster 1A according to the second embodiment, the ECU 18A is configured to boost the auxiliary battery 45 from the battery voltage Vb by using an insulated DC-DC converter 24A as shown in FIG. . When the battery 26 is normal, about 24 V can be supplied at the maximum, and when the battery 26 fails, about 12 V can be supplied from the auxiliary battery 45. In this case, it is desirable that the DC-DC converter 24 be fed directly from the alternator 46 and be independent of the battery 26.

  In each of the above-described embodiments, the electric booster for the brake is taken as an example to explain the effect of boosting the power source, and reducing the size and loss of the DC-DC converter 24 (boost circuit). However, the present invention is not limited to this, and the present invention may be applied to a brake system having other electric motors such as an electric disc brake, an electric parking brake, and a boosting pump used in a hydraulic system for controlling the vehicle attitude.

1 is a cross-sectional view schematically showing an electric booster according to a first embodiment of the present invention including a master cylinder, a brake pedal, and an ECU. It is a block diagram which shows typically ECU of FIG. It is a block diagram which shows the DC-DC converter of FIG. 1 shows the drive current of the electric motor, the characteristics of the electric motor, and the current-voltage characteristics of the power source. FIG. 1 (a) shows the drive current of the electric motor, and FIG. 1 (b) shows the torque / rotational speed characteristics (TN characteristics) of the electric motor. (C) is a figure which shows the current-voltage characteristic of a motor driver power supply. It is a figure which shows the load characteristic of the electric booster of FIG. It is a wave form diagram for showing an operation of the electric booster of Drawing 1, (a) is deceleration characteristics, (b) is fluid pressure characteristics, (c) is Q axis current characteristic, (d) is rotation speed characteristics. (E) is a figure which shows pressure | voltage rise control signal generation | occurrence | production, (f) is a figure which shows brake pedal depression amount, respectively. The operation | movement locus | trajectory of the electric motor displayed with the rotation speed and electric current of an electric motor is shown, (a) is a figure which shows the operation | movement locus | trajectory at the time of operating a booster circuit, when (a) is not operating the booster circuit. It is a figure which shows FCU of the electric booster comprised using the auxiliary battery.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1A ... Electric booster, 2 ... Brake pedal, 5 ... Input member, 6a ... Primary piston (assist member), 8 ... Motor (electric motor), 18 ... ECU (electric motor control device), 21 ... CPU ( Control circuit), 24 ... DC-DC converter (boost circuit), 26 ... battery (power supply).

Claims (4)

In an electric motor control device that controls an electric motor used in a vehicle brake system including an electric motor that operates by receiving power supply from a power source by operating a brake pedal ,
A booster circuit for boosting a voltage from the power source applied to the electric motor to generate a boosted voltage is provided so as to supply the boosted voltage to the electric motor;
Target value of the physical data in the corresponding relationship between the rotational speed of the electric motor to be operated in response to operation of the brake pedal, the rotational speed of the electric motor by the power supply voltage during application of a voltage from said power supply expect to see if it exceeds the upper limit of the physical data in the corresponding relationship,
The step-up voltage generated by the step-up circuit is supplied to the electric motor, and the output current of the step-up circuit at this time is limited to a current smaller than the maximum current for driving the electric motor. Control device. 2. The electric motor control device according to claim 1, wherein the prediction is a voltage threshold value for a target speed of the electric motor in which the target value is set according to a depression speed of the brake pedal, and the power supply An electric motor control device characterized in that the upper limit voltage value by voltage is smaller than the voltage threshold value . 3. The electric motor control device according to claim 1, wherein when a motor torque that increases with the operation of the electric motor reaches a predetermined load set value, the boost voltage applied to the electric motor by the boost circuit is increased. An electric motor control device characterized by stopping supply. An electric motor for advancing and retracting the piston of the master cylinder by operating the brake pedal, a thrust to grant to the piston depending on the operation of the brake pedal performed by controlling the current supply of the electric Motahe from the power supply In the electric booster,
A booster circuit for boosting a voltage from the power source applied to the electric motor to generate a boosted voltage is provided so as to supply the boosted voltage to the electric motor;
Target value of the physical data in the corresponding relationship between the rotational speed of the electric motor to be operated in response to operation of the brake pedal, the rotational speed of the electric motor by the power supply voltage during application of a voltage from said power supply expect to see if it exceeds the upper limit of the physical data in the corresponding relationship,
Supplying the boosted voltage to the booster circuit occurs in the electric motor, providing the control circuitry that limits the output current to the current of the value smaller than the maximum current of the electric motor drive of the booster circuit of this time Electric booster characterized by.

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