JP5691428B2 - Electric brake control system - Google Patents

Description

  The present invention relates to an electric brake control system that generates a brake fluid pressure to a wheel cylinder by using an electric booster as a booster during a brake operation.

  Conventionally, an electric booster that generates brake fluid pressure (master cylinder pressure) to a wheel cylinder by inputting pedal depression force by a driver and assist thrust force by an electric booster to a primary piston and a secondary piston during brake operation is known. (For example, refer to Patent Document 1).

  In the conventional electric booster, the pedaling force of the driver is input from the input rod and the input piston to the primary piston through a pair of coil springs. On the other hand, the assist thrust is generated by a ball screw mechanism that converts the rotational force of the electric motor into an axial force, and is input from the ball screw movable shaft of the ball screw mechanism to the primary piston.

JP 2009-154814 A

  However, in the conventional electric booster, when the brake pedal is raised and the brake fluid pressure is raised from the state where the brake pedal is depressed and held in a fixed position (= the hydraulic pressure is kept constant), The static friction coefficient acts on the screw mechanism, and the conversion efficiency of the ball screw mechanism decreases. For this reason, the necessary current for driving the ball screw mechanism from the state where the brake pedal is held at a fixed position is larger than the current for driving the ball screw mechanism when the brake pedal position is fluctuating. Therefore, when a step-up operation is performed from the pedal holding state at the full load point (assist limit point in the electric motor) that consumes the full current, the time until the ball screw mechanism shifts from the static friction state to the dynamic friction state. It is necessary to cover the gap with only the pedal effort. Therefore, after the full load point, there is a problem that the hydraulic pressure does not increase until the pedal depression force exceeds the gap, and the characteristic of the brake hydraulic pressure (output) with respect to the pedal depression force (input) flows laterally.

  The present invention has been made paying attention to the above-mentioned problem, and at the time of a brake operation for holding the brake pedal at all load points, it is possible to suppress a decrease in the output hydraulic pressure while preparing for a re-depression from the pedal holding state. An object of the present invention is to provide an electric brake control system capable of improving pedal feeling at all load points.

In order to achieve the above object, the electric brake control system of the present invention is a means including a brake pedal, an electric booster, a master cylinder, a cut valve, and an electric brake control means.
The brake pedal applies a pedaling force of the driver when the brake is operated.
The electric booster converts the rotational force of the electric motor into an axial assist thrust via a ball screw mechanism during a brake operation.
The master cylinder pushes the hydraulic piston with a force obtained by adding an assist thrust by the electric booster to the pedal depression force to generate a master cylinder pressure.
The cut valve is provided in the middle of the liquid path from the master cylinder to the wheel cylinder provided in each wheel, and performs opening / closing control of the liquid path.
The electrically powered brake control unit, during braking operation, the electric motor is already determined that the full-load point which consumes a current of full current region, and, when it is determined that the pedal holding state, full load Assuming that the point holding condition is satisfied, the liquid path is closed by the cut valve disposed downstream of the master cylinder, the current applied to the electric motor is lowered, and the ball screw movable shaft of the ball screw mechanism is opposite to the assist direction. Return to the direction.

Therefore, when the full load point holding condition is satisfied during the brake operation , the electric brake control means closes the fluid path by the cut valve disposed downstream of the master cylinder, lowers the current applied to the electric motor, and the ball screw mechanism. The ball screw movable shaft is returned to the direction opposite to the assist direction.
In other words, even when the return control of the ball screw movable shaft is performed by closing the fluid passage downstream of the master cylinder in the pedal-holding state at all load points, the master cylinder pressure (output fluid) when the fluid passage is closed is controlled. Pressure) is maintained. Along with this, fluctuations in the pedal effort are suppressed, and a stable pedal holding state is ensured.
Then, by lowering the current applied to the electric motor and returning the ball screw movable shaft, the motor current that can be used for re-depression is ensured by reducing the current consumption, while the ball screw mechanism A running section for realizing the dynamic friction state is secured. In other words, in preparation for the next re-depression, a state in which “insufficient motor current” and “static state of the ball screw mechanism” that cause the lateral flow of the depressing force-hydraulic characteristic at the time of re-depression can be created in advance and wait.
As a result, during brake operation to hold the brake pedal at the full load point, the pedal feeling at the full load point is improved by suppressing the decrease in the output hydraulic pressure while preparing for the re-depression from the pedal holding state. Can do.

1 is an overall system diagram illustrating an electric brake control system according to a first embodiment. It is sectional drawing which shows the electric control brake unit in the electric brake control system of Example 1. FIG. It is a flowchart which shows the structure and flow of an electric brake control process performed with the brake controller in the electric brake control system of Example 1. FIG. It is operation | movement explanatory drawing which shows the electric control brake unit before the brake operation in the electric brake control system of a comparative example. It is operation | movement explanatory drawing which shows the electric control brake unit in all the load points in the electric brake control system of a comparative example. It is operation | movement explanatory drawing which shows the electric control brake unit by the full stroke in the electric brake control system of a comparative example. It is a pedaling force-hydraulic pressure characteristic diagram showing the relation between the pedaling force (input) and the hydraulic pressure (output) in which the lateral flow characteristic is observed after the full load point by the electric brake control system of the comparative example. FIG. 3 is an operation explanatory diagram illustrating an electric control brake unit before a brake operation in the electric brake control system according to the first embodiment. It is an operation explanatory view showing an electric control brake unit at the time of reaching all load points in the electric brake control system of Example 1. It is an operation explanatory view showing an electric control brake unit when control is added after reaching all load points in the electric brake control system of Example 1. It is a characteristic comparison figure which shows the comparison of the disc spring characteristic and coil spring characteristic of a disc spring employ | adopted as the electric type control brake unit in the electric brake control system of Example 1. FIG. FIG. 4 is a pedal force-hydraulic pressure characteristic diagram showing a relationship between a pedaling force (input) and a hydraulic pressure (output) based on a boost characteristic up to a full load point and a non-boost characteristic after the full load point according to the electric brake control system of Example 1; .

  Hereinafter, the best mode for realizing an electric brake control system of the present invention will be described based on Example 1 shown in the drawings.

First, the configuration will be described.
FIG. 1 shows an electric brake control system according to a first embodiment applied to an electric vehicle (electric vehicle, hybrid vehicle, etc.). The overall system configuration will be described below with reference to FIG.

  As shown in FIG. 1, the electric brake control system of the first embodiment includes a driver operation input member 1, an electric booster 3, a master cylinder 5, a brake controller 7, an ABS brake hydraulic actuator 8, and a front wheel left wheel. A cylinder 9FL, a front wheel right wheel cylinder 9FR, a rear wheel left wheel cylinder 9RL, and a rear wheel right wheel cylinder 9RR are provided. The driver operation input member 1, the electric booster 3, and the master cylinder 5 are integrally configured to constitute the electric control brake unit A.

  The driver operation input member 1 is an input member that inputs a driver's pedal effort to the electric control brake unit A during a brake operation. As shown in FIG. 1, the driver operation input member 1 includes a brake pedal 10, a clevis pin 11, a clevis 12, and an input rod 13. Then, when the driver applies a pedaling force to the brake pedal 10, it is transmitted to the input rod 13 via the clevis pin 11 and the clevis 12, and the input rod 13 is stroked in the left direction in FIG.

  The electric booster 3 is an electric booster that can assist the pedal depression force by using an electrically generated force during a brake operation. As shown in FIG. 1, the electric booster 3 has an electric motor 30. And at the time of brake operation, the rotational force of the electric motor 30 is converted into the axial direction assist thrust via the ball screw mechanism 36 (FIG. 2) mentioned later.

  The master cylinder 5 is a cylinder member that converts an input applied to the hydraulic piston to a master cylinder pressure during a brake operation. As shown in FIG. 1, the master cylinder 5 has a reserve tank 50 that stores brake hydraulic oil. When the brake is operated, the hydraulic piston is pushed by the force obtained by adding the assist thrust by the electric booster 3 to the pedal depression force, the port from the reserve tank 50 is closed, and the master cylinder pressure (primary hydraulic pressure, secondary hydraulic pressure) is generated. .

  The brake controller 7 is an electronic control device that outputs control commands to the solenoids of the electric motor 30 of the electric booster 3 and the ABS brake hydraulic pressure actuator 8 in various situations where braking force is required. As shown in FIG. 1, the brake controller 7 receives control necessary information from a pedal stroke sensor 70, a resolver 71, a master cylinder pressure sensor 72, and the like. Then, arithmetic processing is performed based on the necessary control information, and a control command based on the arithmetic processing result is output to each solenoid of the electric motor 30 and the ABS brake hydraulic pressure actuator 8.

  The pedal stroke sensor 70 is a potentiometer that detects the absolute displacement amount of the input rod 13 with respect to the dash panel to which the electric control brake unit A is fixed. The resolver 71 is a rotation angle sensor that detects the rotation angle of the electric motor 30. The sensor information from the resolver 71 is used not only as motor rotation information but also as relative displacement amount information of the assist member. The master cylinder pressure sensor 72 detects the hydraulic pressure level of the primary hydraulic pressure.

  As shown in FIG. 1, the ABS brake hydraulic pressure actuator 8 is interposed between the electric control brake unit A and the wheel cylinders 9FL, 9FR, 9RL, 9RR of each wheel. The brake fluid pressure (wheel cylinder pressure) to 9FR, 9RL, and 9RR is controlled independently. The ABS brake hydraulic pressure actuator 8 and the electric control brake unit A are connected by a primary hydraulic pressure pipe 61 and a secondary hydraulic pressure pipe 62. The ABS brake hydraulic pressure actuator 8 and the wheel cylinders 9FL, 9FR, 9RL, 9RR of the respective wheels include a left front wheel pressure pipe 63, a right front wheel pressure pipe 64, a left rear wheel pressure pipe 65, and a right rear wheel. It is connected by a pressure pipe 66.

  Each component of the ABS brake hydraulic pressure actuator 8 will be described. As shown in FIG. 1, the ABS brake hydraulic actuator 8 includes two hydraulic pumps 80, 80, one pump motor 81, four ABS in valves 82, 82, 82, 82, and four ABS out valves. 83, 83, 83, 83. And it has two cut valves 84, 84, two suction valves 85, 85, two reservoirs 86, 86, and two dampers 87, 87.

  The hydraulic pumps 80 and 80 return the brake fluid stored in the reservoir 86 to the master cylinder 5 by decompression. The pump motor 81 drives the hydraulic pump 80 according to a drive command sent from the brake controller 7. The ABS in valves 82, 82, 82, 82 are switched to a pressure increasing or holding hydraulic path in accordance with a solenoid command sent from the brake controller 7. The ABS out valves 83, 83, 83, 83 are switched to a pressure increasing / holding / depressurizing hydraulic path in accordance with a solenoid command sent from the brake controller 7.

  The cut valves 84 and 84 block the normal brake path from the master cylinder 5 when the VDC function, TCS function, brake LSD function, brake assist function, and left / right braking force distribution function are activated. The suction valves 85, 85 open the path from the master cylinder 5 to the hydraulic pump 80 when the VDC function, TCS function, brake LSD function, brake assist function, and left / right braking force distribution function are activated. The reservoirs 86, 86 temporarily store brake fluid extracted from the wheel cylinders 9FL, 9FR, 9RL, 9RR of each wheel during decompression. The dampers 87 and 87 suppress the pulsation of the brake fluid and the vibration transmitted to the brake pedal 10 when the VDC function, TCS function, ABS function, EBD function, brake LSD function, brake assist function, and left / right braking force distribution function are activated. Weaken.

  Each of the wheel cylinders 9FL, 9FR, 9RL, 9RR is set to a caliper of the brake disc of each front and rear wheel, and the brake fluid pressure (wheel cylinder pressure) from the ABS brake fluid pressure actuator 8 is applied. Then, when the brake fluid pressure is applied to the wheel cylinders 9FL, 9FR, 9RL, and 8RR, the brake disc is clamped by the brake pad, thereby applying a hydraulic braking force to the front and rear wheels.

  FIG. 2 shows an electric control brake unit A in the electric brake control system of the first embodiment. Hereinafter, specific configurations of the driver operation input member 1, the electric booster 3, and the master cylinder 5, which are components of the electric control brake unit A, will be described with reference to FIG.

  As shown in FIG. 2, the driver operation input member 1 includes an input rod 13, an input piston 14, and a pair of coil springs 15 and 16.

  The input rod 13 is a pedal effort transmission member to which the brake pedal 10 is connected. That is, when the driver applies a pedal depression force to the brake pedal 10, the pedal depression force is transmitted to the input rod 13, and the input rod 13 is stroked in the left direction in FIG.

  The input piston 14 is a pedal depression force transmission member that extends to the position inside the primary piston 51 of the master cylinder 5. The input piston 14 is coaxially connected to the input rod 13 by spherical coupling, and moves forward and backward following the input rod 13 integrally.

  The pair of coil springs 15 and 16 are interposed between the flange portion of the input piston 14 and the primary piston 51 of the master cylinder 5 to keep the input piston 14 in the biased neutral position when the brake is not operated. That is, at the time of brake operation, a hydraulic reaction force due to the pressure receiving area of the piston end surface and the primary hydraulic pressure acts on the input piston 14 in the right direction in FIG. 2, and a pedal depression force acts on the left direction in FIG. In addition, when there is a relative displacement amount of the coil springs 15 and 16 during the brake operation, the spring force corresponding to the relative displacement amount of the coil springs 15 and 16 and the spring constant is applied to the input piston 14 in the right direction of FIG. Or it works in the left direction.

  As shown in FIG. 2, the electric booster 3 includes an electric motor 30, a booster housing 31, a housing cover 32, a spring receiving cover 33, bearings 34 and 35, a ball screw mechanism 36, and a return spring 37. And a disc spring 38 (elastic body).

  The booster housing 31 is fixed to the driver operation input member 1 side by a bolt 40 with a housing cover 32 in an oil-tight state, and a spring receiving cover 33 is oil-tight by a bolt / nut 42 via a connecting plate 41 on the master cylinder 5 side. Fixed in state. And the housing member by 3 components structure is fixed to the dash panel outside a figure with the stud volt | bolt 43 provided in the housing cover 32. FIG.

  The electric motor 30 includes a motor stator 30a built in the housing member and fixed to the housing cover 32, and a motor rotor 30b disposed with respect to the motor stator 30a via an air gap. In the motor stator 30a, a motor coil is wound around stator teeth made of a laminated plate. The motor rotor 30 b is a hollow cylindrical member having a permanent magnet, and is rotatably supported by the booster housing 31 and the housing cover 32 via bearings 34 and 35. A resolver 71 composed of a resolver stator 71a and a resolver rotor 71b is disposed adjacent to the electric motor 30.

  The ball screw mechanism 36 is a mechanism that converts the rotational force of the electric motor 30 into an axial assist thrust, and includes a ball screw fixing shaft 36a, a ball 36b, and a ball screw movable shaft 36c. Is done. The ball screw fixing shaft 36a is an axial fixing member that is fixed to the motor rotor 30b and rotates together with the motor rotor 30b, but is restricted from moving in the axial direction. A plurality of balls 36b are interposed in a semicircular spiral groove formed on the inner peripheral surface of the ball screw fixing shaft 36a and a semicircular spiral groove formed on the outer peripheral surface of the ball screw movable shaft 36c. The ball screw movable shaft 36c is an axially movable member that is arranged to receive a biasing force from the return spring 37 with respect to the spring receiving cover 33 and whose rotational operation is restricted but is movable in the axial direction. A disc spring 38 having a non-linear characteristic in which the spring constant decreases as the load increases is interposed between the opposing surfaces of the flange surface of the ball screw movable shaft 36c and the end surface of the primary piston 51 of the master cylinder 5. Yes.

  As shown in FIG. 2, the master cylinder 5 includes a reservoir tank 50, a primary piston 51 (hydraulic piston), a secondary piston 52 (hydraulic piston), a cylinder housing 53, a port cylinder 54, and an interlocking spring. 55, a primary return spring 56, and a secondary return spring 57.

  The reservoir tank 50 is a tank that stores brake fluid, and is fixed to the cylinder housing 53. The fluid chamber in the reservoir tank 50 communicates with the primary fluid pressure chamber 58 formed by the primary piston 51 and the secondary fluid pressure chamber 59 formed by the secondary piston 52 through a port when the brake is not operated. . When the brake is operated, the port communication is blocked by the leftward stroke of the primary piston 51 and the secondary piston 52 in FIG. 2, and the primary hydraulic pressure and the secondary hydraulic pressure are increased according to the piston thrust. The ports are formed at necessary positions of the primary piston 51, the secondary piston 52, the cylinder housing 53, and the port cylinder 54.

  The primary piston 51 is arranged at the port communication position as shown in FIG. 2 by the urging force of the primary return spring 56 when the brake is not operated. When the brake is operated, a driver's pedaling force is applied from the input piston 14 through the pair of coil springs 15 and 16, and an assist thrust is applied from the ball screw movable shaft 36c through the disc spring 38. The sum of the pedal depression force and the assist thrust becomes the piston thrust to the primary piston 51.

  The secondary piston 52 is arranged at the port communication position as shown in FIG. 2 by the urging force of the secondary return spring 57 when the brake is not operated. When the brake is operated, a pedal depression force and an assist thrust are applied from the primary piston 51 via the interlocking spring 55. The sum of the pedal depression force and the assist thrust becomes the piston thrust to the secondary piston 52.

  FIG. 3 shows the configuration and flow of the electric brake control process executed by the brake controller 7 of the first embodiment (electric brake control means). Hereinafter, each step of FIG. 3 will be described. This electric brake control process is started when the brake is depressed by the equal magnification control, and is terminated when the brake return operation is performed or when the full stroke is reached by the brake depression.

  In step S1, it is determined whether or not the brake operation is started based on a brake switch signal or the like indicating the presence or absence of the brake operation. If YES (start brake operation), the process proceeds to step S2. If NO (brake non-operating state), the determination in step S1 is repeated.

In step S2, following the determination that the brake operation is started in step S1 or the determination that the full load point holding condition is not satisfied in step S3, a constant multiplication is performed by a rotational drive command to the electric motor 30. The same-magnification control is performed in which the pedal depression force is boosted by the assist thrust to obtain the force ratio, and the process proceeds to step S3.
During execution of this equal magnification control, the cut valves 84 and 84 of the ABS brake hydraulic pressure actuator 8 are in an open state as shown in FIG.

In step S3, following execution of the equal magnification control in step S2, it is determined whether or not the full load point holding condition that the pedal is held at the full load point that is the assist limit point in the electric motor 30 is satisfied. To do. If YES (all load point holding conditions are satisfied), the process proceeds to step S4. If NO (all load point holding conditions are not satisfied), the process returns to step S2.
Here, the total load point is determined based on whether or not the electric motor 30 is already consuming a current in the full current region (for example, 40 A region). The pedal holding state is determined based on whether or not a predetermined pedal holding determination time has elapsed while the pedal stroke signal from the pedal stroke sensor 70 remains unchanged. Then, it is assumed that the full load point holding condition is satisfied when it is determined that the load point is the full load point and the pedal is held.

  In step S4, following the determination that the full load point holding condition is satisfied in step S3, a command to close the open cut valves 84, 84 of the ABS brake hydraulic actuator 8 is output, and the process proceeds to step S5.

In step S5, following the command output for closing the cut valves 84, 84 in step S4, or the determination that the pedal re-depressed state is not detected in step S6, a command for reducing the applied current to the electric motor 30 is issued. Output and go to step S6.
Here, the command for reducing the current applied to the electric motor 30 is a command for generating a stroke for returning the ball screw movable shaft 36c of the ball screw mechanism 36 to the direction opposite to the assist direction.

  In step S6, following the motor applied current decrease command output in step S5, it is determined whether or not the pedal holding state at all load points has shifted to the re-depressing state of the brake pedal 10. If YES (detection of transition to pedal re-depression state), the process proceeds to step S7, and if NO (non-detection of transition to pedal re-depression state), the process returns to step S5.

  In step S7, following the determination that the shift to the pedal re-depressed state is detected in step S6, a command to immediately open the cut valves 84, 84 of the ABS brake hydraulic pressure actuator 8 is output, and the process proceeds to step S8.

  In step S8, following the command output for opening the cut valves 84, 84 in step S7 or the determination that the full stroke has not been reached in step S9, the electric motor is interlocked with the detection of the transition to the pedal re-depressed state. A command to increase the applied current to 30 is output, and the process proceeds to step S9.

  In step S9, it is determined whether or not the pedal stroke has reached the full stroke, following the motor applied current increase command output in step S8. If YES (full stroke has been reached), the process proceeds to the end. If NO (full stroke has not been reached), the process returns to step S8.

Next, the operation will be described.
First, “the problem of the comparative example” will be described. Subsequently, the effects of the electric brake control system of the first embodiment are “electric brake control action up to the full load point during brake operation”, “electric brake control action when the full load point pedal is held”, “full load point pedal” The description will be divided into “disc spring action in the holding state” and “electric brake control action in the pedal depressing state”.

[Problems of comparative example]
An electric booster disclosed in Japanese Patent Application Laid-Open No. 2009-154814 is used as a comparative example.
A feature of the electric booster of the comparative example is that when the ball screw mechanism is stationary, the dynamic friction state until then is switched from the static friction state to the static friction state, so that the conversion efficiency from the rotation operation by the ball screw mechanism to the linear operation is lowered. That is, until the ball screw mechanism starts moving from the stationary state, a current larger than the current in the dynamic friction state in which the ball screw mechanism is moving is required because of the static friction state.

  For this reason, in the electric booster of the comparative example, when the ball screw mechanism is stopped at all load points that are assist limit points of the electric motor, the full current (for example, 40 A) is already consumed. There is a problem that the (input) -hydraulic pressure (output) characteristic flows laterally.

  That is, the brake pedal is depressed from the brake non-operating state shown in FIG. 4 and is held at all load points (= hydraulic pressure is kept constant) which is the assist limit point in the electric motor shown in FIG. In this full load point pedal holding state, a hydraulic reaction force obtained by multiplying the pressure receiving area of the input piston and the primary hydraulic pressure acts in the right direction of FIG. On the other hand, the hydraulic reaction force is shared by both the pedaling force of the driver applied from the input rod and the static frictional resistance force by the ball screw movable shaft of the ball screw mechanism, and is applied at the full load point state shown in FIG. Keep the balance.

  When the driver re-depresses the brake pedal from the full load point pedal holding state shown in FIG. 5, the increase in the pedal depression force applied to the driver is used as a force to reduce the static frictional resistance force by the ball screw movable shaft. It is done. In other words, since it is necessary to cover the gap until the ball screw mechanism transitions from the static friction state to the dynamic friction state only with the pedal depression force, increasing the pedal depression force does not cause the primary piston to be pushed in, but the brake fluid. The pressure does not increase. Therefore, as shown in FIG. 7, out of the characteristics of the brake fluid pressure (output) with respect to the pedal depression force (input), the pedal depression force F1 in the state where the full load point pedal is held becomes the pedal depression force F2 exceeding the static friction resistance force. It shows the cross-flow characteristics in which the brake fluid pressure remains unchanged without changing.

  Then, when the increase in the pedal effort exceeds the static frictional resistance and becomes the pedal effort F2, the brake performance pressure rises from the brake fluid pressure P1 to the brake fluid pressure P2 at all load points, and then the assist performance is improved as shown in FIG. The brake fluid pressure rises slowly due to the characteristic proportional to the increase in pedal effort. Then, when the pedal effort becomes the pedal effort maximum value Fmax and reaches the full stroke, as shown in FIG. 6, the strokes of the primary piston and the secondary piston are restricted, and the brake fluid pressure becomes the brake fluid pressure maximum value Pmax.

  As described above, the electric booster of the comparative example needs a countermeasure against the lateral flow of the pedaling force-hydraulic pressure characteristic at all load points. In contrast, the current applied to the electric motor is dithered to constantly vibrate the ball screw movable shaft, thereby preventing a stationary state. That is, it is conceivable that the ball screw movable shaft does not create a static friction state and always waits in a dynamic friction state. However, in this case, there is a rebound to sound vibration due to minute vibrations, and there is a problem that abnormal noise is always generated while the brake pedal is held, which is not practical.

[Electric brake control action up to full load point during brake operation]
Until the full load point is reached during the brake operation, the process proceeds from step S1 to step S2 to step S3 in the flowchart of FIG. 3, and the equal magnification control is executed in step S2. Then, until it is determined in step S3 that the pedal is held at all load points, the flow from step S2 to step S3 is repeated, and execution of the equal magnification control is maintained.

  That is, the brake pedal 10 is depressed from the brake non-operating state shown in FIG. 8, and the input rod 13 and the input piston 14 are moved forward by the pedal depression force. When the electric motor 30 is rotated according to the forward movement of the input piston 14, the rotational movement is converted into a linear movement by the ball screw mechanism 36, and the assist thrust is transmitted to the primary piston 51. Then, the primary piston 51 and the secondary piston 52 move forward by the pedal depression force and the assist thrust accompanying the brake operation, the primary hydraulic pressure is generated in the primary hydraulic pressure chamber 58, and the secondary hydraulic pressure is generated in the secondary hydraulic pressure chamber 59. To do.

  At this time, if the rotation of the electric motor 30 is controlled so as to relatively displace the primary piston 51 in the direction of increasing the brake fluid pressure (front side), the boost ratio is increased by the addition of the assist thrust, and the electric motor 30 Brake assist action is realized. That is, by controlling the rotation of the electric motor 30 so as to maintain a constant boost ratio, the equal magnification control action is realized. At the same magnification control, the reaction force (pedal reaction force) to the brake pedal 10 tends to increase as the brake fluid pressure increases. However, the spring force of the coil spring 16 on the brake pedal 10 side (rear side) of the pair of coil springs 15 and 16 increases in accordance with the relative displacement of the primary piston 51 to the front side. The increase in reaction force is offset. By this pedal reaction force adjusting action, the pedal feeling during execution of the equal magnification control can be improved.

  If the rotation of the electric motor 30 is controlled so as to relatively displace the primary piston 51 in the direction of decreasing the brake fluid pressure (rear side), the boost ratio (= braking force) is reduced, and regenerative coordination during regenerative braking is performed. Operation can be realized. At this time, since the spring force of the coil spring 15 of the pair of coil springs 15 and 16 is increased, the decrease in the pedal reaction force is offset by this spring force, and the pedal feeling during the regenerative cooperative control is improved. Can do.

[Electric brake control action when the pedal is fully loaded]
If the pedal holding state is detected at all load points during the brake operation, the process proceeds from step S3 to step S4 → step S5 → step S6 in the flowchart of FIG. Then, in step S4, a command to close the cut valves 84, 84 is output, and in step S5, a command to reduce the applied current to the electric motor 30 is output. Then, until it is determined in step S6 that the pedal is depressed again, the flow from step S5 to step S6 is repeated, and the output of the command for reducing the applied current to the electric motor 30 is maintained.

That is, as shown in FIG. 9, the master cylinder pressure (output liquid at the time of holding the pedal) is closed by closing the liquid path by the cut valves 84 and 84 disposed downstream of the master cylinder 5 in the pedal holding state at all load points. Pressure) is maintained.
In this full load point pedal holding state, a hydraulic reaction force obtained by multiplying the pressure receiving area of the input piston 14 and the primary hydraulic pressure acts in the right direction of FIG. 9, but by maintaining the primary hydraulic pressure at a constant pressure. The fluctuation of the hydraulic reaction force is eliminated. Therefore, a stable pedal holding state in which fluctuation of the pedal depression force is suppressed is ensured without giving the driver an uncomfortable feeling of pedal operation like when the hydraulic pressure reaction force is fluctuated by the pedal depression force. In particular, when the pedal holding state is detected at all load points, control is performed to return the ball screw movable shaft 36c to the brake pedal 10 side (rear side). The fluctuation of the hydraulic pressure is suppressed, and a stable pedal holding state is ensured.

  Then, in the pedal holding state at all load points, the current applied to the electric motor 30 is lowered, and the ball screw movable shaft 36c is returned to the brake pedal 10 side (rear side) as shown in FIG. This ensures a running section for realizing the dynamic friction state of the ball screw mechanism 36 at the time of re-depression while ensuring a motor current that can be used at the time of re-depression as much as the consumption current of the electric motor 30 is reduced. Is done. In other words, the stroke corresponding to the return of the ball screw movable shaft 36c is a running section for the ball screw movable shaft 36c to run through all the load points when the pedal is depressed again. In this way, in the state where the pedal is held at all load points, in preparation for the next pedal re-depression operation, “motor current shortage” and “ball screw mechanism 36 stationary, Create a state that can remove "" in advance and wait.

As described above, in the first embodiment, when the pedal holding state is detected at all load points, the fluid path downstream of the master cylinder 5 is closed, the current applied to the electric motor 30 is lowered, and the ball screw movable shaft 36c is assisted. A configuration is adopted in which control is performed to return to the direction opposite to the direction.
Therefore, the pedal feeling at the full load point is improved by suppressing the decrease in the output hydraulic pressure while preparing for the re-depression from the pedal holding state during the brake operation for holding the brake pedal 10 at the full load point. .

[Belleville spring action when pedaling at full load point]
As described above, when the operation of returning the ball screw movable shaft 36c of the ball screw mechanism 36 is performed while maintaining the depression position of the brake pedal 10, the ball screw movable shaft 36c and the primary piston 51 are separated. As a result, all the hydraulic reaction force that the ball screw movable shaft 36c has received is handled by the pedal depression force, so that the pedal depression force of the driver suddenly increases and may not be covered by the pedal depression force.

  Therefore, a disc spring 38 having a non-linear spring characteristic is sandwiched between the ball screw movable shaft 36c and the primary piston 51. The disc spring 38 is in a contracted state in the maximum range so as to be crushed near the entire load point. When the ball screw movable shaft 36c is returned, the return spring 38 is designed to extend while maintaining a contact that suppresses a decrease in spring force. Arranged.

  Therefore, even when the ball screw movable shaft 36c is returned, as shown in FIG. 10, the contact between the ball screw movable shaft 36c and the primary piston 51 can be secured, and the hydraulic reaction force acting in the right direction in FIG. A configuration in which both the pedal depression force and the support force by the ball screw movable shaft 36c are used can be adopted.

  With this configuration, the ball screw movable shaft 36c is moved back as if the hydraulic reaction force is all handled by the pedal depression force by receiving the hydraulic reaction force by both the pedal depression force and the support force by the ball screw movable shaft 36c. It is possible to suppress a sudden increase in the pedaling force at a time point away by In addition, by adopting the disc spring 38 having a non-linear spring characteristic, even if the return amount of the ball screw movable shaft 36c is increased, the change in the supporting force by the ball screw movable shaft 36c is suppressed, and the pedal effort Fluctuations can be kept small.

  That is, in the case of a coil spring, as shown by the dotted line characteristic in FIG. 11, the spring constant is a linear coil spring characteristic. For example, when the ball screw movable shaft returns from the maximum contraction displacement Xmax to the contraction displacement X1, the spring force is ΔF. It changes with the change width of '. On the other hand, in the case of the disc spring 38, as shown by the solid line characteristic in FIG. 11, the disc constant becomes a non-linear disc spring characteristic in which the spring constant decreases as the load (= contraction displacement X) increases. Even when the ball screw movable shaft 36c returns to the displacement X1, the spring force is suppressed to a change width of ΔF (<ΔF ′).

As described above, in the first embodiment, the disc spring 38 having a non-linear characteristic is interposed between the ball screw movable shaft 36c and the primary piston 51, and the hydraulic reaction force is transmitted via the pedal depression force and the disc spring 38. The structure which takes charge of both with the support force of the ball screw movable shaft 36c was adopted.
With this configuration, it is possible not only to suppress a sudden increase in the pedal effort due to the return of the ball screw movable shaft 36c, but also to suppress a fluctuation in the pedal effort even if the return amount of the ball screw movable shaft 36c increases.
Therefore, even when the return control of the ball screw movable shaft 36c in which the ball screw movable shaft 36c and the primary piston 51 are separated in the state where the pedal is held at the full load point, the pedal depression force is suppressed from changing.

[Electric brake control action when the pedal is depressed again]
If pedal depression is detected from the pedal holding state at all load points, the process proceeds from step S6 to step S7 → step S8 → step S9 in the flowchart of FIG. In step S7, a command for opening the cut valves 84, 84 is output, and in step S8, a command for increasing the current applied to the electric motor 30 is output. Then, until it is determined that the full stroke has been reached, the flow from step S8 to step S9 is repeated, and the output of the increase command of the applied current to the electric motor 30 is maintained.

  Therefore, if the pedal is stepped on again while the ball screw mechanism 36 is being returned, the return operation of the ball screw mechanism 36 is immediately stopped and priority is given to pedal depression, so that the brake that does not hold the pedal at all load points is applied. A pedaling force-hydraulic pressure characteristic similar to the operation is realized.

  That is, the closed fluid passage is opened in conjunction with the re-depression of the pedal, the electric motor 30 is rotated using the motor current secured in preparation for the re-depression of the pedal, the ball screw mechanism 36 is advanced, and the primary piston 51 is moved. Controlled to extrude. As a result, the ball screw movable shaft 36c of the ball screw mechanism 36 pushes the primary piston 51 from the return position shown in FIG. 10 to push out the primary piston 51, and a dynamic friction state of the ball screw mechanism 36 is created when passing through all the load points. .

  Then, after the ball screw mechanism 36 passes through all the load points while maintaining the dynamic friction state, the rotation of the electric motor 30 is controlled so that no relative displacement occurs between the input piston 14 and the primary piston 51. By this motor rotation control, the pair of coil springs 15 and 16 interposed between the pistons 14 and 51 maintain the biased neutral position. The boost ratio after passing through all the load points is uniquely determined by the area ratio between the pressure receiving area of the input piston 14 and the pressure receiving area of the primary piston 51 because the relative displacement is zero.

  Therefore, as shown in FIG. 12, the pedaling force-hydraulic pressure characteristic when the pedal is depressed again from the pedal holding state at the full load point is improved regardless of the pedal holding at the full load point. . That is, an assist characteristic having a large boost ratio by equal magnification control up to the full load point and a non-assist characteristic having a small boost ratio depending on the pedal effort after the full load point are continuously connected.

As described above, in the first embodiment, when the re-depression from the pedal holding state at the full load point is detected, the closed fluid path is opened in conjunction with the re-depression of the pedal, and the applied current to the electric motor 30 is reduced. The ball screw movable shaft 36c is advanced in the assist direction to push out the primary piston 51.
Therefore, regardless of re-depression from the pedal holding state at all load points, the lateral flow of the pedaling force-hydraulic pressure characteristic can be improved by setting the ball screw mechanism 36 in a dynamic friction state using a motor current secured in advance. The

Next, the effect will be described.
In the electric brake control system of the first embodiment, the effects listed below can be obtained.

(1) A brake pedal 10 that applies the driver's pedaling force when operating the brake;
An electric booster 3 that converts the rotational force of the electric motor 30 into an axial assist thrust through a ball screw mechanism 36 during a brake operation;
A master cylinder 5 for generating a master cylinder pressure by pushing a hydraulic piston (primary piston 51, secondary piston 52) by a force obtained by adding an assist thrust by the electric booster 3 to the pedal depression force;
A fluid path (primary hydraulic pressure) is provided in the middle of a fluid path (primary hydraulic pressure pipe 61, secondary hydraulic pressure pipe 62) from the master cylinder 5 to the wheel cylinders 9FL, 9FR, 9RL, 9RR provided on each wheel. Cut valves 84 and 84 for controlling the opening and closing of the pipe 61 and the secondary hydraulic pipe 62);
When the pedal holding state is detected at all load points, which are assist limit points in the electric motor 30, the cut valve 84, 84 disposed downstream of the master cylinder 5 causes a fluid path (primary hydraulic pipe 61, secondary fluid). The pressure brake 62) is closed, the electric current applied to the electric motor 30 is lowered, and the electric brake control means for returning the ball screw movable shaft 36c of the ball screw mechanism 36 to the direction opposite to the assist direction (steps S3 to S3 in FIG. 3) S5)
Is provided.
For this reason, during brake operation for holding the brake pedal 10 at the full load point, the pedal feeling at the full load point is improved by suppressing the decrease in the output hydraulic pressure while preparing for the re-depression from the pedal holding state. be able to.

(2) In the electric booster 3, an elastic body (a disc spring 38) having a spring constant that decreases as the load increases is interposed between the ball screw movable shaft 36c and the hydraulic piston (primary piston 51). .
For this reason, in addition to the effect of (1), the pedal depression force changes in spite of performing the return control of the ball screw movable shaft 36c in which the ball screw movable shaft 36c and the primary piston 51 are separated in the state where the full load point pedal is held. Can be suppressed.

(3) When the electric brake control means (FIG. 3) detects re-depression from the pedal holding state at all load points, the liquid path (closed by the cut valves 84, 84 in conjunction with the re-depression of the pedal) The primary hydraulic pipe 61 and the secondary hydraulic pipe 62) are opened, the current applied to the electric motor 30 is increased, the ball screw movable shaft 36c of the ball screw mechanism 36 is advanced in the assist direction, and the hydraulic piston (primary The piston 51) is pushed out (steps S6 to S8).
For this reason, in addition to the effect of (1) or (2), the ball screw mechanism 36 is brought into a dynamic friction state by using a motor current secured in advance, regardless of whether the pedal is held down from the pedal holding state at all load points. As a result, the lateral flow of the pedaling force-hydraulic pressure characteristic can be improved.

  As mentioned above, although the electric brake control system of the present invention has been described based on the first embodiment, the specific configuration is not limited to the first embodiment, and the invention according to each claim of the claims is not limited thereto. Design changes and additions are allowed without departing from the gist.

  In Example 1, the example provided with the electric motor 30 by coaxial arrangement | positioning with the input rod 13 as the electric booster 3 was shown. However, the electric booster may be an example in which the electric motor is disposed outside the housing.

  In the first embodiment, an example in which a solenoid valve built in the ABS brake hydraulic actuator 8 is used as the cut valves 84 and 84 has been described. However, as a cut valve, a solenoid valve incorporated in a VDC brake hydraulic actuator other than the ABS brake hydraulic actuator may be used. Moreover, the example which uses the cut valve newly added in the middle position of the liquid path from the master cylinder to the wheel cylinder provided in each wheel may be used.

  In Example 1, the example which uses the disc spring 38 as an elastic body interposed between a ball screw movable shaft and a hydraulic piston was shown. However, an example of using an elastic body having a single structure other than a disc spring or an elastic body having a composite structure may be used as long as it has a characteristic that the spring constant decreases as the load increases.

  In Example 1, the example which applied the electric brake control system of this invention to the electric vehicle was shown. However, it can of course be applied to an engine vehicle provided with an electric control brake unit.

A Electric control brake unit 1 Driver operation input member 10 Brake pedal 3 Electric booster 30 Electric motor 36 Ball screw mechanism 36a Ball screw fixed shaft 36b Ball 36c Ball screw movable shaft 38 Disc spring (elastic body)
5 Master cylinder 51 Primary piston (hydraulic piston)
52 Secondary piston (hydraulic piston)
61 Primary hydraulic piping (liquid passage)
62 Secondary hydraulic piping (liquid passage)
7 Brake controller 8 ABS brake hydraulic actuator 84, 84 Cut valve 9FL Front wheel left wheel cylinder 9FR Front wheel right wheel cylinder 9RL Rear wheel left wheel cylinder 9RR Rear wheel right wheel cylinder

Claims (3)

A brake pedal that applies the driver's pedal effort when braking,
An electric booster that converts the rotational force of the electric motor into an axial assist thrust via a ball screw mechanism during braking operation;
A master cylinder for generating a master cylinder pressure by pushing a hydraulic piston by a force obtained by adding an assist thrust by the electric booster to the pedal depression force;
A cut valve that is provided at an intermediate position in the liquid path from the master cylinder to the wheel cylinder provided in each wheel, and controls the opening and closing of the liquid path;
When the brake operation is performed, it is determined that the electric motor is at the full load point that has already consumed the current in the full current range , and the full load point holding condition is satisfied when it is determined that the pedal is being held. Electric brake control means for closing the liquid path by the cut valve disposed downstream of the master cylinder, reducing the current applied to the electric motor, and returning the ball screw movable shaft of the ball screw mechanism to the direction opposite to the assist direction. When,
An electric brake control system comprising: In the electric brake control system according to claim 1,
The electric booster is characterized in that an elastic body having a spring constant that decreases as a load increases is interposed between the ball screw movable shaft and the hydraulic piston. In the electric brake control system according to claim 1 or 2,
When the electric brake control means detects re-depression from the pedal holding state at all load points, the electric brake control means opens the liquid path closed by the cut valve in conjunction with the pedal re-depression, and applies an electric current to the electric motor. And the hydraulic screw piston is pushed out by advancing the ball screw movable shaft of the ball screw mechanism in the assist direction.