JP6168659B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

2. Description of the Related Art Conventionally, in an electric power steering apparatus, there has been proposed a technique for obtaining a steering feeling that is safe and free from a sense of incongruity even when a vehicle speed sensor provided in a vehicle fails.
For example, a control device for an electric power steering device described in Patent Document 1 includes a control vehicle speed setting unit that updates and outputs a control vehicle speed signal based on a detection signal of a vehicle speed sensor to a target current value setting unit every predetermined time. Have. The control vehicle speed setting unit, based on the detection signal of the engine speed sensor, increases the control vehicle speed signal value updated immediately before it as a reference value according to the engine speed when the vehicle speed sensor fails. The addition value is sequentially added and corrected every predetermined time, and the correction value is updated and output as a control vehicle speed signal to the target current value setting unit every predetermined time.

JP 2001-233228 A

  Due to recent measures for improving fuel efficiency, there are cases where the vehicle travels at a low engine speed even during high-speed travel, and therefore it may be inaccurate to estimate the vehicle speed using addition that increases in accordance with the engine speed. If the target current supplied to the motor is set based on the actual vehicle speed and the vehicle speed having an error, the steering feeling is deteriorated.

  An object of the present invention is to provide an electric power steering apparatus that can suppress deterioration of steering feeling when a failure occurs in a vehicle speed sensor.

For this purpose, the present invention provides a motor for applying an assisting force to the steering wheel of a vehicle, failure determination means for determining failure of a vehicle speed sensor provided in the vehicle, and an engine provided in the vehicle. A vehicle speed calculating means for calculating a vehicle speed based on a rotational speed and a gear ratio of the transmission; and when the failure determination means determines that the vehicle speed sensor has failed, the motor is calculated based on the vehicle speed calculated by the vehicle speed calculation means. Setting means for setting a target current to be supplied, and the setting means switches when the failure determination means determines that the vehicle speed sensor is defective, or when the gear position of the transmission is switched. The electric power steering apparatus is characterized in that the target current is set based on the vehicle speed calculated by the vehicle speed calculation unit immediately before switching after the predetermined period .

Here, the setting means may set the target current based on the vehicle speed detected by the vehicle speed sensor when the failure determination means does not determine that the vehicle speed sensor has failed.
Also, the setting means, wherein after the predetermined period of time is gradually changed from a vehicle speed, wherein said vehicle speed calculating means immediately before switched is calculated to the starting the target current set based on the vehicle speed the vehicle speed calculating means for calculating The target current may be set based on the vehicle speed.

  ADVANTAGE OF THE INVENTION According to this invention, when a failure arises in a vehicle speed sensor, it can suppress that a steering feeling deteriorates.

It is a figure showing the schematic structure of the electric power steering device concerning an embodiment. It is a schematic block diagram of a control apparatus. It is a schematic block diagram of a target current calculation part and a control part. It is the schematic of the control map which shows a response | compatibility with steering torque, vehicle speed, and base current. It is a schematic block diagram of a vehicle speed setting part. It is a timing chart which shows the relationship with the vehicle speed according to the vehicle speed signal which an engine speed, the gear position of a transmission, a calculated vehicle speed, and the vehicle speed calculation part outputs. It is a flowchart which shows the procedure of the vehicle speed signal output process which a vehicle speed calculation part performs.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an electric power steering apparatus 100 according to an embodiment.
The electric power steering device 100 (hereinafter sometimes simply referred to as the “steering device 100”) is a steering device for arbitrarily changing the traveling direction of the vehicle. In the present embodiment, a configuration applied to an automobile 1 having an engine 2, a transmission 3, and the like is illustrated.

  The steering device 100 includes a wheel-like steering wheel 101 that is operated by a driver to change the traveling direction of the automobile 1, and a steering shaft 102 that is provided integrally with the steering wheel 101. Yes. The steering device 100 includes an upper connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a lower connecting shaft 108 connected to the upper connecting shaft 103 via a universal joint 103b. . The lower connecting shaft 108 rotates in conjunction with the rotation of the steering wheel 101.

  Steering device 100 includes tie rods 104 connected to left and right front wheels 150 as rolling wheels, and rack shaft 105 connected to tie rods 104. Further, the steering device 100 includes a pinion 106 a that constitutes a rack and pinion mechanism together with rack teeth 105 a formed on the rack shaft 105. The pinion 106 a is formed at the lower end portion of the pinion shaft 106.

  The steering device 100 also has a steering gear box 107 that houses the pinion shaft 106. The pinion shaft 106 is connected to the lower connection shaft 108 via a torsion bar (not shown) in the steering gear box 107. A torque sensor 109 that detects the steering torque of the steering wheel 101 based on the relative rotation angle between the lower connecting shaft 108 and the pinion shaft 106, in other words, based on the torsion amount of the torsion bar, is provided in the steering gear box 107. It has been.

  Further, the steering device 100 includes an electric motor 110 supported by the steering gear box 107 and a speed reduction mechanism 111 that reduces the driving force of the electric motor 110 and transmits it to the pinion shaft 106. The reduction mechanism 111 includes, for example, a worm wheel (not shown) fixed to the pinion shaft 106, a worm gear (not shown) fixed to the output shaft of the electric motor 110, and the like. The electric motor 110 applies a driving force for rolling the front wheel 150 to the rack shaft 105 by applying a rotational driving force to the pinion shaft 106. Electric motor 110 according to the present embodiment is a three-phase brushless motor.

  The steering device 100 includes a control device 10 that controls the operation of the electric motor 110. The control device 10 receives a torque signal Td obtained by converting the torque detected by the torque sensor 109 described above into an output signal. In addition, the control device 10 outputs an output signal from a vehicle speed sensor 170 that detects a vehicle speed, which is a moving speed of the automobile 1, via a network (CAN) that performs communication for sending signals of various devices mounted on the automobile 1. Is entered. Information such as an engine rotation speed sensor 180 that detects the rotation speed Ne of the engine 2 and a position sensor 190 that detects the gear position P of the transmission 3 is input to the control device 10 via the CAN. The vehicle speed sensor 170 generates a pulse signal in proportion to the rotational speed of the axle 4 provided in the automobile 1, and outputs information corresponding to the vehicle speed in proportion to the number of pulse signals to the control device 10.

  In the steering device 100 configured as described above, the steering torque applied to the steering wheel 101 is detected by the torque sensor 109, and the control device 10 drives and controls the electric motor 110 in accordance with the detected torque. The generated torque 110 is transmitted to the pinion shaft 106. Thereby, the torque generated by the electric motor 110 assists the driver's steering force applied to the steering wheel 101.

Next, the control device 10 will be described.
FIG. 2 is a schematic configuration diagram of the control device 10.
The control device 10 includes a CPU that performs arithmetic processing when controlling the electric motor 110, a ROM that stores programs executed by the CPU, various data, and the like, and a RAM that is used as a working memory of the CPU, and the like. , An arithmetic logic circuit having an EEPROM (Electrically Erasable & Programmable Read Only Memory).

  The control device 10 converts the torque signal Td output from the torque sensor 109, the vehicle speed signal vcd output from the vehicle speed sensor 170, and the engine rotation speed Ne detected by the engine rotation speed sensor 180 into output signals. The engine rotational speed signal Nes, the gear position P of the transmission 3 detected by the position sensor 190 is converted into an output signal, and a position signal p or the like is input.

  Then, the control device 10 calculates the target current It as an example of a setting unit that calculates (sets) the target current It necessary for the electric motor 110 to supply based on the steering torque and the vehicle speed, and calculates the target current. And a control unit 30 that performs feedback control based on the target current It calculated by the unit 20. In addition, the control device 10 includes a vehicle speed setting unit 70 that sets a vehicle speed used when the target current calculation unit 20 calculates the target current It.

Next, the target current calculation unit 20 and the control unit 30 will be described in detail.
FIG. 3 is a schematic configuration diagram of the target current calculation unit 20 and the control unit 30.
The target current calculation unit 20 calculates a base current calculation unit 21 that calculates a base current Ib that serves as a reference for setting the target current It, and inertia compensation that calculates an inertia compensation current Is for canceling the inertia moment of the electric motor 110. A current calculation unit 22 and a damper compensation current calculation unit 23 that calculates a damper compensation current Id that limits the rotation of the motor are provided. The target current calculation unit 20 includes a target current determination unit 25 that determines the target current It based on values calculated by the base current calculation unit 21, the inertia compensation current calculation unit 22, and the damper compensation current calculation unit 23. ing. Further, the target current calculation unit 20 includes a phase compensation unit 26 that compensates for the phase of the steering torque detected by the torque sensor 109.
The target current calculation unit 20 detects the torque signal Td, the vehicle speed signal (vehicle speed signal vcd or vehicle speed signal vcc described later) output from the vehicle speed setting unit 70, and the rotational position of the rotor (rotor) of the electric motor 110. A motor rotation speed signal Nms corresponding to the motor rotation speed of the electric motor 110 calculated based on the output signal from the resolver is input.

FIG. 4 is a schematic diagram of a control map showing the correspondence between the steering torque and the vehicle speed and the base current Ib.
The base current calculation unit 21 is based on a torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26, a vehicle speed signal (vehicle speed signal vcd or vehicle speed signal vcc described later) output from the vehicle speed setting unit 70, and the like. A base current Ib is calculated. In other words, the base current calculation unit 21 is based on the steering torque phase-compensated by the phase compensation unit 26 (see FIG. 3) and the vehicle speed corresponding to the vehicle speed signal output from the vehicle speed setting unit 70. Ib is calculated. Note that the base current calculation unit 21 generates, for example, a phase-compensated steering torque (torque signal Ts) and vehicle speed (vehicle speed signal), and a base current Ib, which are previously created based on empirical rules and stored in the ROM. The base current Ib is calculated by substituting the steering torque and the vehicle speed into the control map illustrated in FIG. 4 showing the correspondence.

  The inertia compensation current calculation unit 22 is based on a torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26, a vehicle speed signal output from the vehicle speed setting unit 70 (a vehicle speed signal vcd or a vehicle speed signal vcc described later), and the like. Inertia compensation current Is is calculated. In other words, the inertia compensation current calculation unit 22 performs inertia compensation based on the steering torque phase-compensated by the phase compensation unit 26 (see FIG. 3) and the vehicle speed corresponding to the vehicle speed signal output from the vehicle speed setting unit 70. The current Is is calculated. For example, the inertia compensation current calculation unit 22 creates a control map indicating the correspondence between the phase compensated steering torque and vehicle speed and the inertia compensation current Is, which is previously created based on an empirical rule and stored in the ROM. The inertia compensation current Is is calculated by substituting the phase compensated steering torque and vehicle speed.

  The damper compensation current calculation unit 23 includes a torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26, a vehicle speed signal (vehicle speed signal vcd or vehicle speed signal vcc described later) output from the vehicle speed setting unit 70, and motor rotation. A damper compensation current Id is calculated based on the speed signal Nms and the like. In other words, the damper compensation current calculation unit 23 includes the steering torque phase compensated by the phase compensation unit 26 (see FIG. 3), the vehicle speed corresponding to the vehicle speed signal output from the vehicle speed setting unit 70, and the motor rotation speed Nm. A damper compensation current Id corresponding to the above is calculated. The damper compensation current calculation unit 23, for example, the correspondence between the phase compensated steering torque, vehicle speed, and motor rotation speed Nm, which is created based on empirical rules in advance and stored in the ROM, and the damper compensation current Id. The damper compensation current Id is calculated by substituting the phase-compensated steering torque, vehicle speed, and motor rotational speed Nm into the control map indicating.

  The target current determination unit 25 includes the base current Ib calculated by the base current calculation unit 21, the inertia compensation current Is calculated by the inertia compensation current calculation unit 22, and the damper compensation calculated by the damper compensation current calculation unit 23. A target current It is determined based on the current Id. For example, the target current determination unit 25 determines the current obtained by adding the inertia compensation current Is to the base current Ib and subtracting the damper compensation current Id as the target current It.

Next, the control unit 30 will be described in detail.
As shown in FIG. 3, the control unit 30 includes a motor drive control unit 31 that controls the operation of the electric motor 110, a motor drive unit 32 that drives the electric motor 110, and an actual current Im that actually flows through the electric motor 110. And a motor current detection unit 33 for detection.
The motor drive control unit 31 is based on a deviation between the target current It finally determined by the target current calculation unit 20 and the actual current Im supplied to the electric motor 110 detected by the motor current detection unit 33. A feedback (F / B) control unit 40 that performs feedback control, and a PWM signal generation unit 60 that generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110.

  The feedback control unit 40 includes a deviation calculating unit 41 for obtaining a deviation between the target current It finally determined by the target current calculating unit 20 and the actual current Im detected by the motor current detecting unit 33, and the deviation is A feedback (F / B) processing unit 42 that performs feedback processing so as to be zero.

The feedback (F / B) processing unit 42 performs feedback control so that the target current It and the actual current Im match. For example, the feedback (F / B) processing unit 42 is proportional to the deviation calculated by the deviation calculating unit 41. Is proportionally processed, integrated by an integral element, and these values are added by an addition operation unit.
The PWM signal generation unit 60 generates a PWM signal for driving the electric motor 110 by PWM (pulse width modulation) based on the output value from the feedback control unit 40, and outputs the generated PWM signal.

The motor drive unit 32 is a so-called inverter, and includes, for example, six independent transistors (FETs) as switching elements. Three of the six transistors are a positive line of a power source, an electric coil of each phase, The other three transistors are connected to the electric coil of each phase and the negative side (ground) line of the power source. Then, the driving of the electric motor 110 is controlled by driving the gates of two transistors selected from the six and switching the transistors.
The motor current detection unit 33 detects the value of the actual current Im flowing through the electric motor 110 from the voltage generated at both ends of the shunt resistor connected to the motor drive unit 32.

Next, the vehicle speed setting unit 70 will be described in detail.
FIG. 5 is a schematic configuration diagram of the vehicle speed setting unit 70.
The vehicle speed setting unit 70 includes a failure determination unit 71 as an example of a failure determination unit that determines whether or not the vehicle speed sensor 170 has failed, an engine rotation speed Ne (rpm) detected by the engine rotation speed sensor 180, and a position. A vehicle speed calculation unit 72 as an example of a vehicle speed calculation unit that calculates the vehicle speed based on the gear position P of the transmission 3 detected by the sensor 190. Further, the vehicle speed setting unit 70 uses either the vehicle speed signal vcd from the vehicle speed sensor 170 or the vehicle speed signal vcc output from the vehicle speed calculation unit 72 as the vehicle speed used when the target current calculation unit 20 calculates the target current It. A vehicle speed selection unit 73 is provided for selecting whether to use.

  The failure determination unit 71 acquires the vehicle speed signal vcd from the vehicle speed sensor 170 every predetermined period, and according to the detected vehicle speed Vcd (n−1) corresponding to the vehicle speed signal vcd acquired last time and the vehicle speed signal vcd acquired this time. The vehicle speed when the state in which the detected vehicle speed Vcd corresponding to the vehicle speed signal vcd is zero continues for a predetermined time (for example, 5 seconds) after the difference from the detected vehicle speed Vcd (n) exceeds a predetermined vehicle speed deviation ΔVc. It is determined that the sensor 170 has failed. When the failure determination unit 71 determines that the vehicle speed sensor 170 has failed, the failure determination unit 71 outputs a failure determination signal f to the vehicle speed selection unit 73.

The vehicle speed calculation unit 72 calculates the vehicle speed based on the following equation (1).
Vehicle speed = (engine rotation speed Ne (rpm) × diameter of front wheel 150 (m) × π × 60/1000) / (gear ratio of transmission 3 × final gear ratio) (1)
Here, when the vehicle speed calculation unit 72 calculates the vehicle speed based on the equation (1), a value detected by the engine rotation speed sensor 180 is used as the engine rotation speed Ne. As the diameter of the front wheel 150, a value stored in advance in the ROM is used. The gear ratio of the transmission 3 is grasped based on the correlation between the gear position P and the gear ratio stored in advance in the ROM while grasping the gear position P of the transmission 3 from the position sensor 190 based on the position signal p. A gear ratio corresponding to the gear position P is used. As the final gear ratio, a value stored in advance in the ROM is used.
The vehicle speed calculation unit 72 outputs a vehicle speed signal vcc corresponding to the calculated vehicle speed Vcc, which is the calculated vehicle speed, to the vehicle speed selection unit 73.

  The vehicle speed selection unit 73 selects the vehicle speed signal vcd acquired from the vehicle speed sensor 170 and outputs it to the target current calculation unit 20 while the failure determination signal f is not acquired from the failure determination unit 71. On the other hand, when acquiring the failure determination signal f from the failure determination unit 71, the vehicle speed selection unit 73 selects the vehicle speed signal vcc acquired from the vehicle speed calculation unit 72 and outputs it to the target current calculation unit 20.

  In the control device 10 configured as described above, the target current calculation unit 20 determines the vehicle speed while the vehicle speed sensor 170 has not failed (when the failure determination unit 71 does not output the failure determination signal f). A target current It is calculated (set) based on the detected vehicle speed Vcd corresponding to the vehicle speed signal vcd output from the sensor 170. On the other hand, when a failure occurs in the vehicle speed sensor 170 (when the failure determination unit 71 outputs the failure determination signal f), the target current calculation unit 20 is based on the calculated vehicle speed Vcc calculated by the vehicle speed calculation unit 72. It is calculated (set). Since the vehicle speed calculation unit 72 calculates based on the engine rotation speed Ne (rpm) and the gear position P of the transmission 3, the calculated vehicle speed Vcc is a highly accurate value. Therefore, according to the steering device 100 according to the present embodiment, even when a failure occurs in the vehicle speed sensor 170, the target current It is set based on the vehicle speed with little error from the actual vehicle speed. It is possible to suppress the deterioration of the steering feeling due to the failure.

<Modification of vehicle speed calculation unit 72>
When the vehicle speed calculation unit 72 calculates the vehicle speed based on the equation (1), there is a possibility that an error occurs between the actual vehicle speed and the calculated vehicle speed Vcc when the gear position P of the transmission 3 is changed.
FIG. 6 shows the engine speed Ne, the gear position P of the transmission 3, the calculated vehicle speed Vcc calculated by the vehicle speed calculation unit 72 based on the equation (1), the vehicle speed corresponding to the vehicle speed signal vcc output by the vehicle speed calculation unit 72, and It is a timing chart which shows the relationship.
For example, as shown in FIG. 6, when the gear position P of the transmission 3 changes from the first speed to the second speed and the second speed to the third speed when the engine rotational speed Ne is increasing, the gear of the transmission 3 is changed. Immediately after the position P is changed, the calculated vehicle speed Vcc temporarily increases because the gear ratio generally decreases significantly compared to the decrease in the engine speed Ne. As a result, an error occurs between the calculated vehicle speed Vcc calculated by the vehicle speed calculation unit 72 based on the equation (1) and the actual vehicle speed Vc.

Therefore, when the gear position P of the transmission 3 is switched, the vehicle speed calculation unit 72 outputs a vehicle speed signal vcc corresponding to the calculated vehicle speed Vcc immediately before the gear position P is switched for a predetermined period T1. Then, after the elapse of the predetermined period T1, the calculated vehicle speed Vcc immediately before the change of the gear position P is smoothly changed from the calculated vehicle speed Vcc immediately after the elapse of the predetermined period T2 until the predetermined period T2 elapses after the elapse of the predetermined period T1. A vehicle speed signal vcc that switches to is output. For example, during the period from the elapse of the predetermined period T1 to the elapse of the predetermined period T2, the vehicle speed calculation unit 72 adds the calculated vehicle speed Vcc, a predetermined correction coefficient α, and a predetermined value to the calculated vehicle speed Vcc immediately before the gear position P is switched. A vehicle speed signal vcc corresponding to the corrected vehicle speed Vch (= Vcc × (1 + α × t / T2)) obtained by adding the value obtained by multiplying the ratio of the elapsed time t to the period T2 (= t / T2) is output. To do. Then, after the elapse of the predetermined period T2 (after the elapse of the predetermined period (T1 + T2) from when the gear position P is switched), the vehicle speed signal vcc corresponding to the calculated vehicle speed Vcc calculated based on the equation (1) is output.
The correction coefficient α may be a single value, or may be a different value depending on which position the gear position P is switched from.

Next, the procedure of the vehicle speed signal output process performed by the vehicle speed calculation unit 72 will be described using a flowchart.
FIG. 7 is a flowchart showing a procedure of a vehicle speed signal output process performed by the vehicle speed calculation unit 72. The vehicle speed calculation unit 72 repeatedly executes this vehicle speed signal output process for each predetermined period.
First, the vehicle speed calculation unit 72 determines whether or not it is within a predetermined period (T1 + T2) after switching the gear position P of the transmission 3 (step (hereinafter simply referred to as “S”) 101). If it is not within the predetermined period (T1 + T2) (No in S101), the vehicle speed is calculated by substituting the current parameter (engine speed Ne or the like) by equation (1), and the vehicle speed signal corresponding to the calculated vehicle speed Vcc. vcc is output (S102). On the other hand, if it is within the predetermined period (T1 + T2) (Yes in S101), it is determined whether it is within the predetermined period T1 (S103).

  When it is within the predetermined period T1 (Yes in S103), the calculated vehicle speed Vcc immediately before the gear position P of the transmission 3 is switched is read from a storage area (for example, RAM) and the vehicle speed signal vcc corresponding to the calculated vehicle speed Vcc immediately before the switching is read. Is output (S104). On the other hand, if it is not within the predetermined period T1 (No in S103), it is considered to be within the predetermined period T2 after the lapse of the predetermined period T1, so that the correction coefficient α is read from the storage area (for example, ROM) and the calculated vehicle speed immediately before switching is calculated. A corrected vehicle speed Vch (= Vcc × (1 + α × t / T2)) obtained by adding a value obtained by multiplying Vcc by the calculated vehicle speed Vcc, the correction coefficient α, and the ratio of the elapsed time t to the predetermined period T2. A corresponding vehicle speed signal vcc is output (S105).

  When the vehicle speed calculation unit 72 executes the vehicle speed signal output process, the vehicle speed Vcc can be calculated with high accuracy even when the gear position P of the transmission 3 changes. As a result, even when a failure occurs in the vehicle speed sensor 170, the target current It is set on the basis of the actual vehicle speed and the vehicle speed with less error, so that deterioration of the steering feeling can be more reliably suppressed.

DESCRIPTION OF SYMBOLS 1 ... Automobile, 10 ... Control apparatus, 20 ... Target electric current calculation part, 30 ... Control part, 70 ... Vehicle speed setting part, 71 ... Failure determination part, 72 ... Vehicle speed calculation part, 73 ... Vehicle speed selection part, 100 ... Electric power steering Device, 110 ... electric motor

Claims (3)

A motor for applying an assisting force to the steering wheel of the vehicle;
Failure determination means for determining failure of a vehicle speed sensor provided in the vehicle;
Vehicle speed calculation means for calculating the vehicle speed based on the rotational speed of the engine provided in the vehicle and the gear ratio of the transmission;
A setting means for setting a target current to be supplied to the motor based on the vehicle speed calculated by the vehicle speed calculation means when the failure determination means determines that the vehicle speed sensor has failed;
Equipped with a,
When the failure determination unit determines that the vehicle speed sensor has failed, or when the gear position of the transmission is switched, the setting unit determines that the vehicle speed calculation unit immediately before the switch for a predetermined period after the switch. An electric power steering device, wherein the target current is set based on the calculated vehicle speed . The said setting means sets the said target electric current based on the vehicle speed which the said vehicle speed sensor detected, when the said failure determination means does not determine with the failure of the said vehicle speed sensor. Electric power steering device. After the predetermined period has elapsed, the setting means sets the vehicle speed to be gradually changed from the vehicle speed calculated by the vehicle speed calculation means immediately before the switching until the target current starts to be set based on the vehicle speed calculated by the vehicle speed calculation means. 2. The electric power steering apparatus according to claim 1 , wherein the target current is set based on the target current.

Images