Control device for an electric parking brake

Abstract

A control device for an electric parking brake, comprising an electric motor for generating a braking force through contacting friction materials upon a request for braking, a sensing unit for detecting a no-load current when no load is applied to the electric motor; a voltage monitoring unit for detecting a voltage applied to the electric motor and detectable between two points on a power line; a resistance calculation unit for calculating a resistance between two points based on the no-load current and the detected voltage; and a voltage calculation unit for calculating a voltage required between the two points to drive the electric motor to generate the braking force, based on the resistance and a target current.and a control unit for allowing a current above the target current to flow in the electric motor based on a comparison between the required and the detected voltages.

Description

Area

[0001] The present invention generally relates to a control device for an electric parking brake, in particular for an electric parking brake which has an electric motor which, after a request for a parking brake operation, is driven to generate a braking force to limit the rotation of a wheel by friction between a friction-providing material and a friction-affected material on the wheel, wherein the friction is generated by the friction-providing material being in contact with the friction-affected material. Background of the invention

[0002] Conventional control devices for electric parking brakes are known, which incorporate electric motors (see, for example, JP 2010-76479A). In response to a request for a parking brake application, such an electric motor is driven to generate a pressure force that presses a pressure-applying material against a friction-affected material on the wheel. When the electric motor is driven in this way, friction between the pressure-applying material and the friction-affected material generates a braking force to limit the rotation of the wheel. Furthermore, a control device detects a no-load current flowing in the electric motor before the pressure-applying material contacts the friction-affected material and sets a control setpoint current by adding this no-load current to a setpoint current value for the motor.If the amount of motor current increased by the unloaded current exceeds the target current value to be increased for the motor, the drive of the electric motor is stopped.

[0003] Furthermore, for the electric parking brake system described above to provide sufficient parking performance, the required voltage must be applied to the electric motor. If the voltage applied to the electric motor is insufficient, it will not provide adequate parking performance. It should be noted that even if the positive and negative terminals have the same voltage, a situation can arise where the braking force necessary for parking is not generated by the electric motor. This is because the voltage applied to the electric motor decreases as the resistance of the circuit increases.

[0004] However, the control device described in JP 2010-76479A does not take into account the magnitude of the circuit resistance of the power line driving the electric motor; the voltage applied to the electric motor is not measured; and no measures are taken to generate the braking force required for parking when the circuit resistance is high. Therefore, depending on the circuit resistance of the power line, the voltage applied to the electric motor may not reach the necessary level, so that the intended motor current does not flow in the electric motor, which can lead to a situation where the parking performance is insufficient.

[0005] In view of the problem described above, it is an object of at least one embodiment of the present invention to provide a control device for an electric parking brake which generates a braking force required for parking by an electric motor even when the circuit resistance of the power line is relatively large. Summary of the present invention

[0006] According to at least one embodiment of the present invention, a control device for an electric parking brake with an electric motor for generating a braking force to limit the rotation of a wheel by friction between a friction-providing material and a friction-affected material on the wheel, wherein the electric motor is driven upon a request for a parking brake operation and the braking force is generated by bringing the friction-providing material into contact with the friction-affected material, a detection unit for detecting a no-load current, which detects a consumed current in a no-load state in which no load is applied to the electric motor, after a starting current has been generated after the start of the drive of the electric motor, until the friction-providing material is in contact with the friction-affected material;A voltage monitoring unit that detects the voltage applied to the electric motor between two points on the power line as the monitored voltage; a resistance calculation unit that calculates a circuit resistance between the two points based on the current consumed in the no-load state, as detected by the detection unit for detecting a no-load current, and the monitored voltage detected by the voltage monitoring unit; a calculation unit for calculating a required voltage, which calculates a voltage required between the two points to drive the electric motor to generate the braking force, based on the circuit resistance calculated by the resistance calculation unit and a control setpoint current;and a control unit which executes a method for the flow of a current which is greater than or equal to the control set current in the electric motor based on a comparison result between the required voltage calculated by the calculation unit for calculating the required voltage and the monitored voltage detected by the voltage monitoring unit.

[0007] According to at least one embodiment of the present invention, it is possible to generate a braking force required for parking by an electric motor even when the circuit resistance of the power line is relatively large. Brief description of the characters Fig. Figure 1 is a configuration diagram of a control device for an electric parking brake according to an embodiment of the present invention; Fig. Figure 2 is a cross-sectional view of an electric parking brake system according to the present embodiment; Fig. Figure 3 is a circuit configuration diagram of the electric parking brake system according to the present embodiment; Fig. Figure 4 is a general view of a waveform of consumed current when the electric motor in the electric parking brake system according to the present embodiment is driven; and Fig. Figure 5 is a flowchart of an example of a control routine which is implemented in the electric parking brake system according to the present embodiment. Description of the embodiments

[0008] In the following, embodiments of the present invention are described with reference to the figures.

[0009] Fig. Figure 1 shows a configuration diagram of a control device 10 for an electric parking brake according to an embodiment of the present invention. Figure 1 also shows Fig. 2 a cross-sectional view of an electric parking brake system 12 according to the present embodiment.

[0010] The electric parking brake system of the present embodiment (hereinafter referred to simply as the "system") 12 is installed in a vehicle and is a trigger for limiting the rotation of the vehicle's wheels when the vehicle is parked. The system 12 includes an electric motor 14. The system 12 generates a braking force and thereby limits the rotation of the wheels by driving the electric motor 14 to rotate into a predetermined position. It should be noted that in the present embodiment, the system 12 is a trigger partially shared with a servo braking system, which serves to generate a braking force for limiting the rotation of the wheels by means of a pedal actuation force dependent on the actuation of a brake pedal by the vehicle driver.

[0011] The control device for the electric parking brake (referred to below simply as the "control device") 10 includes an electronic control unit (referred to below simply as an "electric parking brake ECU") 18, which is directly connected to the electric motor 14 via a wire 16. The electric parking brake ECU 18 has a microcomputer as its main component and controls the drive of the electric motor 14 following a program previously stored in a ROM memory. The electric motor 14 is driven to rotate when a voltage is applied to the electric motor 14 following a drive command from the electric parking brake ECU 18.

[0012] The electric parking brake ECU 18 is connected to an operating switch 22 via a wire 20, which is a direct line. The operating switch 22 can be actuated by a vehicle driver to park the vehicle and outputs an operating signal to the electric parking brake ECU 18 via wire 20 when an operating operation is initiated. The electric parking brake ECU detects whether a parking brake operation is requested by the vehicle driver based on the signal output by the operating switch 22 via wire 20.

[0013] The electric parking brake ECU 18 is also connected to various ECU sensors (referred to as "the other ECU elements") 26 via a communication bus 24, for example, a CAN bus. The other ECU elements 26 include a sensor to output information about a temperature 26a currently generated in the vehicle (for example, the temperature of the electric motor 14), a sensor to output information about the current incline of the vehicle in the forward-backward direction 26b, and a sensor to output information about an oil pressure 26c generated in a brake oil pressure system of the vehicle.Based on the signals from the other ECU elements 26, the electric parking brake ECU 18 receives information via the communication bus 24 indicating the various states currently generated for the vehicle, and then, based on the acquired information, calculates a braking force to be generated by the electric motor 14 and a control set current to flow in the electric motor 14 to generate the braking force, and controls the drive of the electric motor 14 so that the braking force is generated.

[0014] System 12 includes a body 30, which forms a wheel cylinder. The body 30 is cylindrical with a cavity and designed to allow hydraulic brake pressure to be introduced into the cavity. A rotary shaft 32, a propeller shaft 34, and a piston 36 are housed within the cavity of the body 30.

[0015] The rotating shaft 32 is an elongated, rod-like component. One end of the rotating shaft 32 is inserted into an insertion hole 38 formed on an end surface of the body 30 and is centrally mounted within it. A shaft bearing 40 is arranged at the insertion hole 38 to support the rotating shaft 32, and a sealing element 42, such as an O-ring, is also arranged there to prevent the hydraulic brake pressure in the cavity in the body 30 from leaking outwards through the insertion hole 38. The rotating shaft 32 is inserted into the insertion hole 38 and supported for rotation by the shaft bearing 40.

[0016] A spur gear unit 44 is arranged at one end of the rotating shaft 32. The spur gear unit 44 is engaged with the spur gear unit 46. The spur gear units 44 and 46 rotate with a predetermined rotational ratio relative to each other. The spur gear unit 46 is connected to an output shaft of the electric motor 14. The spur gear unit 46 rotates when the electric motor 14 is driven to rotate. The aforementioned rotating shaft 32 rotates when the spur gear units 44 and 46 rotate when the electric motor 14 is driven to rotate. Furthermore, male threaded slots 48 are formed on the outer surface of the other end of the rotating shaft 32.

[0017] The propeller shaft 34 is a cylindrical component with an internal cavity. It is designed in the form of a cylinder or a polygonal column so that it does not rotate around the center of rotation of the rotating shaft 32, even when the rotating shaft 32 is rotating. An insertion hole 50 is formed on one end surface of the propeller shaft 34. Female threaded slots 52 are formed on the inner surface of the insertion hole 50. The rotating shaft 32 is inserted into the insertion hole 50, and the male threaded slots 48 of the rotating shaft 32 are screwed into the female threaded slots 52 of the body 30. The other end of the rotating shaft 32 can be extended into the cavity of the propeller shaft 34.

[0018] The rotating shaft 32 and the propeller shaft 34 are spaced apart from each other in the shaft direction by the engagement of the male screw slots 48 and the female screw slots 52 when the rotating shaft 32 rotates. Specifically, when the rotating shaft 32 is driven by the rotary drive of the electric motor 14, the engagement between the male screw slots 48 and the female screw slots 52 prevents the propeller shaft 34 from rotating, and the rotational force of the rotating shaft 32 is converted into a force that displaces the propeller shaft 34 in the shaft direction, thus causing the propeller shaft 34 to be displaced in the shaft direction.Furthermore, when the rotary drive of the electric motor 14 is stopped, the rotation of the rotary shaft 32 is stopped, the displacement of the propeller shaft 34 in the shaft direction is stopped, and the propeller shaft 34 is held in the stop position by a frictional force generated by the engagement of the male screw slots 48 and the female screw slots 52.

[0019] The piston 36 is a component of cylindrical or polygonal column shape that encloses the circumference of the propeller shaft 34. The propeller shaft 34 is inserted into the cylinder of the piston 36 at the point where it can be displaced in the shaft direction. At one end (the left end in Fig. 2) The piston 36 has a lower part 54 designed to close the cylindrical part of the inner circumference. The lower part 54 can form one end (the left end in Fig. 2) contact the propeller shaft 34. Furthermore, the piston 36 is designed such that its outer wall surface contacts the inner wall surface of the body 30. A sealing element 56 is formed in the inner wall of the body 30, which prevents the hydraulic brake pressure in the cavity in the body 30 from leaking outwards through the space between the outer wall surface of the piston 36 and the inner wall surface of the body 30.

[0020] The piston 36 can move towards one end in the wave direction relative to the body 30 (to the left in Fig. 2) can be displaced if, due to the displacement of the propeller shaft in the wave direction, its lower part 54 is displaced towards one end of the propeller shaft 34. Furthermore, independently of the propeller shaft 34, the piston 36 can be displaced towards one end in the wave direction relative to the body 30 (to the left). Fig. 2) can be displaced when the hydraulic brake pressure is introduced into the cavity in the body 30. The piston 36 can be moved towards one end in the shaft direction relative to the body 30 (to the left). Fig. 2) be displaced both by the pressure of the propeller shaft 34 and by the hydraulic brake pressure.

[0021] If the hydraulic brake pressure is not introduced into the cavity in the body 30 when the propeller shaft 34 is in an initial position before the electric motor 14 is driven to rotate, the piston 36 is displaced and at the other end in the shaft direction in the cavity (to the right in Fig. 2) held by the elastic force of a return spiral (not shown) or by negative pressure in the cavity. In addition, the displaced propeller shaft 34 limits the displacement of the piston 36 towards the other end in the shaft direction, even when the hydraulic brake pressure in the cavity in the body 30 decreases after the propeller shaft 34 has been displaced from its initial position towards the other end in the shaft direction while the electric motor 14 is driven to rotate.

[0022] A brake pad 58 is mounted at one end of the piston 36. The brake pad 58 is a component that can be brought into contact with an end face of a brake disc 59 oriented in the shaft direction, the brake disc 59 being fixed to a wheel and rotating together with the wheel. Braking is applied to the brake disc 59 by two brake pads 58 that surround the brake disc 59 from both sides in the shaft direction. The brake pad 58 is moved by the displacement of the piston 36 in the shaft direction (to the left or right). Fig. 2) moves and the movement is stopped and held when the displacement of piston 36 is stopped.

[0023] When the system 12 is switched on using the operating switch 22, the electric parking brake ECU 18 receives this as a request for a parking brake operation and performs a locking control to generate a braking force. Specifically, it calculates the braking force to be generated by the electric motor 14 based on the vehicle's condition and issues a drive command to the electric motor 14. When the electric motor 14 is driven by the electric parking brake ECU 18 to rotate in one direction (positive direction) following the drive command, the spur gear 44 and the rotary shaft 32 rotate in the positive direction with the rotation of the spur gear 46. When the rotary shaft 32 rotates in the positive direction, the engagement of the male screw slots 48 and the female screw slots 52 displaces the propeller shaft 34 towards one end in the shaft direction.

[0024] The displacement of the propeller shaft 34 towards one end in the shaft direction causes the propeller shaft 34 to come into contact with the lower part 54 of the piston 36. As the propeller shaft 34 continues to be displaced towards one end in the shaft direction, it presses against the lower part 54 of the piston 36, and the piston 36 is moved towards one end in the shaft direction. The displacement of the propeller shaft 34 towards one end in the shaft direction then continues until the brake pad 58 at the end of the piston 36 contacts the brake disc 59, whereupon the brake pad 58 contacts the brake disc 59, thereby generating a braking force.

[0025] When the brake pad 58 contacts the brake disc 59 to generate braking force, the load on the electric motor 14 increases, and consequently, so does the current consumption. After the anti-lock braking system is activated, the electric parking brake ECU 18 detects a current I flowing in the power line between a positive terminal (power terminal) and a negative terminal (ground terminal), which are used to apply voltage to the electric motor 14. The ECU determines whether the detected current I reaches a set control current based on a vehicle condition. If the current I reaches the control current, it is detected that the electric motor 14 is generating the desired braking force, and the anti-lock braking system is activated by stopping the voltage applied to the electric motor 14 and thus stopping its rotation.It should be noted that even when the stall control has been completed by stopping the rotary drive of the electric motor 14, the propeller shaft 34 is held in the stop position to maintain the braking force.

[0026] When the operating switch 22 is set to off, the electric parking brake ECU 18 receives this as a release request for a parking brake operation or for a parking brake release and executes a release control to enable or disable the generation of braking force. Specifically, it issues a drive enable command to the electric motor 14. When the electric motor 14 is driven to rotate in the opposite direction (reverse direction) after the drive enable command from the electric parking brake ECU 18, the spur gear 44 and the rotary shaft 32 rotate in reverse, together with the rotation of the spur gear 46. When the rotary shaft 32 rotates in reverse, the engagement of the male screw slots 48 and the female screw slots 52 displaces the propeller shaft 34 towards the other end in the shaft direction.

[0027] When the propeller shaft 34 is displaced from the position in which the brake pad 58 contacts the brake disc 59 towards its opposite end in the shaft direction, the piston 36 is allowed to move towards its opposite end in the shaft direction, thereby releasing the contact between the brake pad 58 and the brake disc 59 and ceasing to generate any braking force. The displacement of the propeller shaft 34 towards its opposite end in the shaft direction, and thus the reverse rotation of the electric motor 14, continues until a predetermined distance between one end of the propeller shaft 34 and the lower part 54 of the piston 36 is established. Once this distance is established, the electric parking brake ECU 18 stops applying voltage to the electric motor 14, thus halting its reverse rotation and completing the release control.

[0028] Furthermore, when the brake pedal in system 12 is operated, a hydraulic brake pressure is introduced into the cavity in the body 30 by a pedal force dependent on the pedal operation. When the hydraulic brake pressure is introduced into the cavity in the body 30, it moves the piston 36 towards one end in the shaft direction, causing the brake pad 58 to contact the brake disc 59 to generate the braking force.

[0029] Furthermore, in the present embodiment, the electric parking brake ECU 18 in the system 12 calculates the braking force to be generated by the electric motor 14 depending on a vehicle state and controls the drive of the electric motor 14 to generate the calculated braking force when the electric parking brake ECU 18 detects that a request for a parking brake operation has been made by the operating switch 22. Specifically, it applies a predetermined voltage to the electric motor 14 so that a current flows in the electric motor 14 to drive it to rotate.

[0030] If the control set current flows into the electric motor 14 by applying a required voltage to the electric motor 14, the electric motor 14 can be driven to rotate as requested, and the system 12 can provide sufficient vehicle parking power. On the other hand, if the voltage applied to the electric motor 14 does not reach the required voltage, the current flowing in the electric motor does not reach the control set current, and the electric motor 14 is not driven to rotate as requested, which may result in insufficient vehicle parking power from the system 12.

[0031] Specifically, the circuit resistance of the power line between the power terminal and the ground terminal for applying voltage to the electric motor 14 can fluctuate. In this case, if the voltage between the power terminal and the ground terminal is the same, the actual voltage applied between the two ends of the main body of the electric motor 14 will decrease as the circuit resistance increases. Therefore, depending on the magnitude of the circuit resistance, there may be cases in which the braking force required for parking cannot be generated by the electric motor using normal control.

[0032] Subsequently, in system 12 of the present embodiment, the required braking force for parking the vehicle can be generated by the electric motor 14 by bringing a control setpoint current appropriately into flow in the electric motor 14, even if the circuit resistance of the current line is relatively high. The characterizing parts of the present embodiment are described below with reference to the Fig. 3 to 5 described.

[0033] Fig. Figure 3 shows a circuit configuration diagram of the electric parking brake system 12 according to the present embodiment. Fig. Figure 4 shows a general view of a waveform of the current consumed when the electric motor 14 is operated in the electric parking brake system 12 according to the present embodiment. Fig. Figure 5 shows a flowchart of an example of a control routine performed by the electric parking brake system 18 according to the present embodiment.

[0034] In the present embodiment, the electric parking brake ECU 18 applies a voltage to the electric motor 14 when it detects a request for a parking brake operation via the operating switch 22, and then it detects the voltages V generated at two points on the power line between the power terminal 60 and the earth terminal 62 to apply a voltage assumed to be the applied voltage to the electric motor 14. Überwachung1 and V Überwachung2and detects the current I flowing in the power line as the circulating current. It can be assumed that the detection of the circulating current is carried out, for example, based on the voltage between the two terminals of a shunt resistor (not shown) with a known resistance value, formed on the power line between the power terminal 60 and the earth terminal 62 (for example, between resistor R3 and input terminal B, as described below).

[0035] In the above-mentioned embodiment, in which the voltage on the power line between the power terminal 60 and the earth terminal 62 is measured at two points as V Überwachung1 and V Überwachung2 , as in Fig. As shown in Figure 3, resistances are generated at the following points: A resistor R1 between the current terminal 60 and the input terminal (specifically the terminal where the voltage V is applied). Überwachung1(is recorded) A of the electric parking brake ECU 18; a resistor R2 between the input terminal A and the electric motor 14; a resistor R3 between the electric motor 14 and the input terminal (specifically the terminal at which the voltage V is applied) Überwachung2 (is recorded) B of the electric parking brake ECU 18 and a resistor R4 between the input terminal B and the ground terminal 62. If the resistance values ​​of resistors R1 to R4 are greater than expected, the voltage applied to the two terminals of the main body of the electric motor 14 will not reach an expected value and there is a risk that the braking force required for parking the vehicle will not be generated.

[0036] In contrast to the above, the electric parking brake ECU 18 in the present embodiment performs the following steps after a request for a parking brake operation has been entered by the operating switch 22 and the application of voltage to the electric motor 14 has been started: (1) Calculating the values ​​of the resistances R1 to R4 (specifically the resistances R2 and R3) of the power line; (2) based on the values ​​of the resistances R2 and R3 and a control setpoint current I Soll to generate a braking force required for vehicle parking, calculating the voltage V required for a rotary drive of the electric motor 14 to generate the braking force necessary for vehicle parking nötig ; (3) Comparing the required voltage V nötig with the voltage difference between the measured voltages V Überwachung1 and V Überwachung2 (V Überwachung1 - V Überwachung2); and (4) based on the comparison result, controlling the drive of the electric motor 14.

[0037] The resistances R2 and R3 of the power line can be determined based on the current flowing in the power line (current consumed) I0 in a load-free state, in which no load is applied to the electric motor 14, and the voltage difference between the measured voltages (V). Überwachung1 - V Überwachung2 ) will be calculated.

[0038] Soon after voltage is applied to the electric motor to start the rotary drive of electric motor 14, a starting current, which has a large current value, circulates in electric motor 14 as a pulse (region A, which is represented by a dashed line in Fig. 4 is circled). After the starting current has been generated, and until the brake block 58 comes into contact with the brake disc 59 through the rotation of the electric motor 14 (specifically from a state in which the predetermined distance between one end of the propeller shaft 34 and the lower part 54 of the piston 36 is ensured, to a state in which one end of the propeller shaft 34 comes into contact with the lower part 54 of the piston 36), a certain period of time (region B, which is marked with a dashed line in Fig. (Circled in 4) is the no-load state, in which essentially no load is applied to the electric motor 14, and therefore the current consumption on the power line is kept at an almost fixed value, which is greater than or equal to zero. The values ​​of resistors R2 and R3 can thus be calculated if the current consumption (no-load current) I0 in the no-load state can be determined based on the voltage between the two terminals of the shunt resistor.

[0039] Then, starting from a state in which the predetermined distance between one end of the propeller shaft 34 and the lower part 54 of the piston 36 is ensured, the brake pad 58 comes into contact with the brake disc 59 (specifically, one end of the propeller shaft 34 comes into contact with the lower part 54 of the piston 36), and then the load applied to the electric motor 14 gradually increases, whereby the current consumption on the power line becomes proportional to the magnitude of the load (region C, which is shown with a dashed line in Fig. (4 is circled) increased.

[0040] The electric parking brake ECU 18 detects, based on the signal from the operating switch 22, whether a request for a parking brake operation is being made and, if it detects that the request for the parking brake operation has been made, it starts applying voltage to the electric motor 14 to perform the locking control (step 100).

[0041] After initiating the locking control, the electric parking brake ECU 18 detects the current I in the power line based on the voltage between the two terminals of the shunt resistor to measure a waveform of the detected current I. Based on this instantaneous waveform, it then detects the no-load current I0, which assumes a nearly constant value after the activation current has been generated. While detecting the no-load current I0, the electric parking brake ECU 18 also detects the voltages V Überwachung1 and V Überwachung2on the power line to increase the voltage difference (V Überwachung1 - V Überwachung2 ) to calculate these voltages. Then, based on the no-load current I0 and the voltage difference (V) Überwachung1 -V Überwachung2 ) calculates, as shown in the following formula (1), the resistance (R2 + R3) between the two points where the voltages V Überwachung1 and V Überwachung2 on the power line between power connection 60 and earth connection 62 (step 102). (R2+R3)=(VU monitoring1−VU monitoring2) / I0

[0042] Next, based on the calculated resistance (R2+R3), the control setpoint current I soll to generate the braking force required for vehicle parking and a known internal resistance value R tatThe electric parking brake ECU 18 calculates the voltage V required for the rotary drive of the electric motor 14 to generate the braking force required for parking the vehicle. nötig between the two points on the power line according to the following formula (2) (Step 104). Vno¨tig=Isoll×(R2+R3+Rtat)

[0043] Then the electric parking brake ECU 18 compares the calculated required voltage V nötig with the voltage difference between the voltages V Überwachung1 and V Überwachung2 , which were detected on the power line (step 106). As a result of this comparison, if V nötig ≤ (V Überwachung1 -V Überwachung2 ) is fulfilled, namely, if V Überwachung1 ≥ V Überwachung2 - I soll × I0 × R tat / (I soll- I0) is fulfilled, the instantaneous application of voltage to the electric motor 14 is maintained unchanged so that a current circulates to generate the braking force required for normal vehicle parking which is greater than or equal to the control set current and therefore the drive control for the electric motor 14 is carried out normally (step 108).

[0044] However, if V nötig > (V Überwachung1 -V Überwachung2 ) is fulfilled, namely when V Überwachung1 < V Überwachung2 - I soll x I0 × R tat / (I soll - I0) is fulfilled, maintaining the instantaneous application of voltage cannot set the current to be greater than or equal to the control set current flow in the electric motor 14.

[0045] Therefore, in the next step, it is determined whether a predetermined safety control of the application of voltage to the electric motor 14 can make the current greater than or equal to the control set current flow in order to ensure the power to generate the braking force necessary for normal vehicle parking (step 110).

[0046] It is noted that the safety control is intended to increase the current in the electric motor 14 by setting the voltage applied to the electric motor 14 higher than in the normal control, for example by increasing the supply voltage between the power terminal 60 and the earth terminal 62, or, if there are electric motors 14 each for the left and right wheels and there is a common part for these electric motors, such as a wiring harness, by operating the electric motors 14 individually (for example a duty cycle control using the reverse phase) without operating both electric motors at the same time.

[0047] If the electric parking brake ECU 18 determines in step 110 that the power requirement can be met by the safety control, it executes the safety control (step 112). When the safety control is executed, a current greater than or equal to the control set current flows in the electric motor 14 to generate the braking force required for normal vehicle parking. However, if the electric parking brake ECU 18 determines that the power requirement cannot be met by the safety control, it detects that a fault is occurring in system 12 and therefore registers an abnormality (also referred to below as "abnormality detection") (step 114).When the abnormality is detected, a diagnostic memory is activated to store information about the system abnormality, a visual and an audible warning are issued to the driver, and a procedure is carried out to induce the driver to perform other steps necessary for parking the vehicle instead of operating the operating switch 22 in the On position.

[0048] By the above-mentioned method, a current which is greater than or equal to the control set current can flow in the electric motor 14 by applying voltage as usual, if the voltage difference (V) Überwachung1 - V Überwachung2 ) between the measured voltages V Überwachung1 and V Überwachung2 is greater than or equal to the required voltage V nötig .

[0049] On the other hand, a current which is greater than or equal to the control set current can flow in the electric motor 14 if the voltage difference (V Überwachung1 -V Überwachung2 ) between the measured voltages V Überwachung1 and V Überwachung2 is lower than the required voltage V nötig and the power to generate the braking force necessary for normal vehicle parking is ensured by using the safety control instead of the normal control with a current flow which is greater than or equal to the control set current of the safety control.

[0050] Furthermore, if the voltage difference (V Überwachung1 -V Überwachung2 ) between the measured voltages V Überwachung1 and V Überwachung2 is lower than the required voltage V nötigand if performance is not ensured by the safety control, it detects that a fault is occurring in system 12 and diagnostic information about this abnormality can be registered.

[0051] As described above, according to the present embodiment, by designing the safety control, it is possible to ensure that a current greater than or equal to the control setpoint current flows in the electric motor to generate the braking force necessary for vehicle parking, even if the circuit resistance between the power terminal 60 and the ground terminal 62 on the power line is high. Furthermore, a current greater than or equal to the control setpoint current cannot flow in the electric motor 14 to generate the braking force necessary for vehicle parking due to a lack of applied voltage by the normal control system. In this respect, the lack of applied voltage to the electric motor 14 due to a voltage drop caused by a temperature characteristic or similar can be interpreted by the normal control system as a diagnostic abnormality due to a component or...Component failures can be differentiated. Therefore, even if a deficiency in the applied voltage occurs, the parking power can be adequately executed by executing the safety control, preventing unnecessary detection of a diagnostic abnormality and reducing the frequency of diagnostics.

[0052] Furthermore, in the present embodiment, during the calculation of the circuit resistance on the current line between the current terminal 60 and the earth terminal 62, the consumed current I0 and the measured voltages V are recorded. Überwachung1 and V Überwachung2The current I0 consumed is measured in a no-load state, which exists as long as the current value is stable after the generation of an initial current, until the brake pad 58 comes into contact with the brake disc 59 via the rotary drive of the electric motor 14 (specifically, until one end of the propeller shaft 34 comes into contact with the lower part 54 of the piston 36). Furthermore, the current I0 consumed in the no-load state is measured using the shunt resistor employed for current measurement in the anti-lock control. Therefore, according to the present embodiment, the circuit resistance on the current line can be accurately calculated in real time without adding any components or modifying the circuit.

[0053] Therefore, based on the circuit resistance of the power line, the voltage V required for the rotational drive of the electric motor 14 to generate the braking force required for vehicle parking can be determined. nötig The voltage between the two points on the power line can be calculated, and it can be determined whether the voltage applied between the two points on the power line during the control of the drive of the electric motor 14 is greater than or equal to the required voltage V. nötig Therefore, the safety control can be executed correctly and the parking performance can be carried out sufficiently if the performance is ensured by the safety control.

[0054] In the embodiment described above, the brake pad 58 corresponds to a "friction-providing material" as described in the claims, and the brake disc 59 corresponds to a "friction-affected material" as described in the claims. Furthermore, the electric parking brake ECU 18 implements the following units as described in the claims: a "detection unit for detecting a no-load current" as described in the claims, for detecting the current I consumed in a no-load state in which virtually no load is applied to the electric motor 14; a "voltage monitoring unit" as described in the claims, for detecting the voltages V Überwachung1 and V Überwachung2; a “resistance calculation unit”, as described in the claims, for calculating the resistance (R2 + R3) between the two points on the current line between the power terminal 60 and the earth terminal 62 in step 102; a “calculation unit for calculating a required voltage”, as described in the claims, for calculating the voltage V required for the rotary drive of the electric motor 14 to generate the braking force necessary for parking the vehicle nötig in step 104; and a “control unit” as described in the claims for performing the drive control of the electric motor 14 in steps 108 and 112.

[0055] Furthermore, in the above embodiment, the electric parking brake ECU 18 implements the following units defined in the claims: a “power fulfillment detection unit”, as described in the claims, for detecting whether the power to generate the braking force necessary for normal vehicle parking is ensured by the safety control in step 110 with a current which is greater than or equal to the control setpoint current flow; and an “abnormality detection unit”, as described in the claims, for performing an abnormality detection after a fault has been generated in the system 12 in step 114.

Claims

[1] Control device for an electric parking brake, comprising an electric motor for generating a braking force to limit the rotation of a wheel by friction between a friction-providing material and a friction-affected material on the wheel, wherein the electric motor is driven after a parking brake request and the braking force is generated by bringing the friction-providing material into contact with the friction-affected material, comprising: a detection unit for detecting a no-load current, which detects the consumed current in a no-load state in which no load is applied to the electric motor after a starting current has been generated following a start of the drive of the electric motor, until the friction-inducing material contacts the friction-affected material; a voltage monitoring unit which detects a voltage applied to the electric motor between two points on a power line as a monitored voltage; a resistance calculation unit which calculates a circuit resistance between the two points based on the current consumed in the no-load state as detected by the detection unit for detecting a no-load current and the monitored voltage detected by the voltage monitoring unit; a voltage calculation unit for calculating the voltage required between the two points to drive the electric motor to generate the braking force, based on the circuit resistance calculated by the resistance calculation unit and a control setpoint current; and a control unit which performs a procedure to allow a current greater than or equal to the control set current to flow in the electric motor based on a comparison result between the required voltage calculated by the voltage calculation unit and the monitored voltage detected by the voltage monitoring unit. [2] Control device for an electric parking brake according to claim 1, wherein the control unit performs normal control to allow current to flow in the electric motor by a normal method when the voltage monitored by the voltage monitoring unit is greater than or equal to the required voltage calculated by the voltage calculation unit, whereas the control unit performs a safety control to allow a current to flow to the electric motor that is greater than the current allowed to flow into the electric motor by the normal control, if the monitored voltage detected by the voltage monitoring unit is less than the required voltage calculated by the voltage calculation unit. [3] Control device for an electric parking brake according to claim 2, further comprising: a performance measurement unit which detects whether the current to flow in the electric motor through the safety control is greater than or equal to the control set current, if the monitored voltage detected by the voltage monitoring unit is less than the required voltage calculated by the voltage calculation unit, wherein the control unit performs the safety control when the performance detection unit detects that the current flowing through the electric motor via the safety control is greater than or equal to the control set current. [4] Control device for an electric parking brake according to claim 3, further comprising: an abnormality detection unit which detects an abnormality occurring in an electric parking brake system when the performance detection unit detects that the current allowed to flow in the electric motor through the safety control is greater than or equal to the control set current. [5] Control device for an electric parking brake according to one of claims 2 to 4, wherein the safety control increases the voltage applied to drive the electric motor such that the voltage between the two points becomes greater than or equal to the required voltage.

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