JP5728424B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus and the like, and more particularly to a technique capable of generating a pseudo vehicle speed based on a steering torque when a vehicle speed sensor fails or a CAN (controller area network) is disconnected.

  A vehicle such as an automobile can include an electric power steering device, and the electric power steering device assists a steering torque (assist torque) in a steering system (steering system) generated by an operation by a driver on the steering handle. ). Due to the generation of the assist torque, the electric power steering device can assist the driver's steering and reduce the burden on the driver.

  For example, FIG. 1 of Patent Document 1 discloses a controller C for obtaining a steering assist force in the electric motor 1 based on both the steering torque detected by the torque detector 3 and the vehicle speed detected by the vehicle speed detector 2. According to FIG. 2 of Literature 1, the motor current of the electric motor 1 that is the source of the steering assist force is determined by both the curve or characteristic (one-dot chain line) determined for each vehicle speed and the steering torque. In other words, the storage unit 4 in FIG. 1 of Patent Document 1 stores a variable control map (one-dot chain line) as shown in FIG. 2 of Patent Document 1, and according to this variable control map, the steering torque and the vehicle speed are stored. The motor current can be determined based on both of the above, and a steering assist force is generated when the motor current flows to the electric motor 1.

JP-A-01-215667 Japanese Patent Laid-Open No. 06-127420 JP 2001-233228 A

  FIG. 2 of Patent Document 1 shows a fixed map (solid line) that can determine the motor current based on the steering torque when the vehicle speed detector 2 fails, but the fixed map (solid line) does not depend on the vehicle speed. As a result, the driver feels uncomfortable. In other words, according to step 15 of FIG. 3 of Patent Document 1, the vehicle speed is fixed to X, which gives the driver a feeling of strangeness.

  For example, FIG. 6 of Patent Document 2 discloses a vehicle speed coefficient KV corresponding to the vehicle speed V. According to the description of paragraph [0017] of Patent Document 2, when an abnormality occurs in the vehicle speed sensor 24, the vehicle speed coefficient KV Is fixed to the maximum value KV0 without depending on the vehicle speed. In other words, since the vehicle speed is fixed to 0, the driver feels uncomfortable in the medium speed region and the high speed region.

  Further, for example, FIG. 6 of Patent Document 3 discloses that when a failure of the vehicle speed sensor 11 is determined while the vehicle is running, the control vehicle speed signal VEL1 is updated based on the control vehicle speed signal VEL1 immediately before the failure. Yes. In other words, when an abnormality occurs in the vehicle speed sensor 11, a pseudo vehicle speed signal is generated, and the pseudo vehicle speed signal (the updated control vehicle speed signal VEL1) increases to, for example, Vmax according to the engine speed NE. FIG. 4 of Patent Document 3 discloses control vehicle speed fade coefficients K1, K2, and K3 based on the engine speed NE, and the pseudo vehicle speed signal (the updated control vehicle speed signal VEL1) is determined by these coefficients K1, K2, and K3. Increase or decrease. Although the driver's steering is assisted based on the engine speed NE, it is possible to reduce a sense of discomfort given to the driver, but the present inventors have recognized the need for further improvement of the electric power steering device. .

  One object of the present invention is to provide an electric power steering apparatus capable of reducing the uncomfortable feeling given to the driver. Other objects of the present invention will become apparent to those skilled in the art by referring to the aspects and preferred embodiments exemplified below and the accompanying drawings.

  In the following, in order to easily understand the outline of the present invention, embodiments according to the present invention will be exemplified.

A first aspect according to the present invention includes a torque detector that detects a steering torque of a steering system of a vehicle,
An electric motor for applying assist torque to the steering system;
A motor controller that controls a motor current of the electric motor with reference to the steering torque;
With
When the steering torque that is equal to or greater than the first predetermined torque is detected as the current steering torque, the motor control unit is more than the previous motor current set immediately before at the same torque as the current steering torque. The present invention relates to an electric power steering apparatus characterized by increasing the current motor current set by the current steering torque.

  The electric power steering apparatus determines whether or not the steering torque is equal to or greater than a first predetermined torque. When the steering torque is equal to or greater than the first predetermined torque, the motor current for the same steering torque can be increased. In other words, when the steering torque increases, the motor current can be increased, and the driver's steering can be assisted with the increased assist torque. Thus, since the assist torque is set according to the steering torque or the driver's burden, it is possible to reduce the uncomfortable feeling given to the driver.

In the first aspect,
The motor control unit may refer to the vehicle speed together with the steering torque, increase the motor current as the steering torque increases, and increase the motor current as the vehicle speed decreases.
When the steering torque that is equal to or higher than the first predetermined torque is detected as the current steering torque in a state where an abnormality in the vehicle speed is detected, the motor control unit does not refer to the vehicle speed from the vehicle speed detection unit. Thus, the current motor current may be larger than the previous motor current.

  Since the assist torque is set according to the steering torque, the electric power steering device does not need to use the vehicle speed in a state where an abnormality in the vehicle speed is detected by the electric power steering device. In other words, the vehicle speed can be used only when the vehicle speed is normal.

  In the first aspect, when the steering torque that is less than a second predetermined torque that is smaller than the first predetermined torque is detected as the current steering torque, the motor control unit is configured to use the previous motor current. Alternatively, the current motor current may be reduced.

  The electric power steering device determines whether or not the steering torque is less than the second predetermined torque, and when the steering torque is less than the second predetermined torque, the motor current for the same steering torque can be reduced. In other words, when the steering torque is reduced, the motor current can be reduced and the driver's steering can be assisted with the reduced assist torque. Since the steering torque is set within a certain range in accordance with the steering torque or the driver's burden, it is possible to reduce the sense of discomfort given to the driver.

  In the first aspect, when the steering torque that is equal to or higher than the first predetermined torque is detected as the current steering torque in a state where the abnormality in the vehicle speed is detected, the motor control unit The current motor current larger than the previous motor current may be controlled by changing the relationship between the vehicle speed and the motor current.

  When the steering torque is equal to or higher than the first predetermined torque in the state where the abnormality in the vehicle speed is detected, the relationship between the steering torque, the vehicle speed, and the motor current can be updated so as to increase the motor current for the same steering torque. .

  In the first aspect, in the state where the abnormality of the vehicle speed is detected, the motor control is performed when the steering torque that is less than the second predetermined torque that is also smaller than the first predetermined torque is detected as the current steering torque. The unit may update the relationship between the steering torque, the vehicle speed, and the motor current to control the current motor current that is smaller than the previous motor current.

  When the steering torque is less than the second predetermined torque in a state where an abnormality in the vehicle speed is detected, the relationship between the steering torque, the vehicle speed, and the motor current can be updated so as to reduce the motor current for the same steering torque. .

  In the first aspect, when the steering torque that is equal to or greater than the first predetermined torque is detected as the current steering torque in a state where the abnormality in the vehicle speed is detected, the motor control unit is The pseudo vehicle speed is obtained, the pseudo vehicle speed is referred to as the vehicle speed together with the steering torque, and the motor control unit determines the current steering torque to be higher than the previous vehicle speed associated with the same torque as the current steering torque. The current motor current may be greater than the previous motor current by reducing the associated current vehicle speed.

  Since the pseudo vehicle speed can be obtained from the steering torque, when the steering torque is equal to or higher than the first predetermined torque, the motor current for the same steering torque can be increased by reducing the pseudo vehicle speed. Further, it is not necessary to use a detection unit other than the torque detection unit, for example, the engine speed sensor 15 of Patent Document 3. In other words, if the electric power steering apparatus includes the engine speed sensor 15 of Patent Document 3, for example, if an abnormality occurs in the engine speed sensor 15, the pseudo vehicle speed can be obtained from the engine speed NE of Patent Document 3. Can not. When obtaining the simulated vehicle speed from the steering torque, the simulated vehicle speed can be obtained as long as no abnormality occurs in the torque detector.

  In the first aspect, when the abnormality in the vehicle speed is detected and the steering torque that is less than a second predetermined torque smaller than the first predetermined torque is detected as the current steering torque, the motor The control unit obtains a pseudo vehicle speed from the steering torque, refers to the pseudo vehicle speed as the vehicle speed together with the steering torque, and the motor control unit uses the vehicle speed before being associated with the same torque as the current steering torque. Instead, the current motor current may be made smaller than the previous motor current by increasing the current vehicle speed associated with the current steering torque.

  Since the pseudo vehicle speed can be obtained from the steering torque, when the steering torque is less than the second predetermined torque, the motor current for the same steering torque can be reduced by increasing the pseudo vehicle speed. Further, the pseudo vehicle speed can be obtained from the steering torque as long as no abnormality occurs in the torque detector.

  In the first aspect, the difference between the previous vehicle speed and the current vehicle speed when the steering torque that is equal to or greater than the first predetermined torque is detected as the current steering torque is the first predetermined torque. It may be smaller than the difference between the previous vehicle speed and the current vehicle speed when the steering torque that is less than a second predetermined torque smaller than the torque is detected as the current steering torque.

  When the steering torque is equal to or higher than the first predetermined torque, the pseudo vehicle speed can be decreased gradually, and the motor current for the same steering torque can be increased gradually. A sudden decrease in the simulated vehicle speed can be suppressed, and the vehicle can be driven more safely.

  Those skilled in the art will readily understand that the illustrated embodiments according to the present invention can be further modified without departing from the spirit of the present invention.

1 shows a schematic configuration example of an electric power steering apparatus according to the present invention. An example of the relationship between steering torque, vehicle speed, and motor current is shown. FIG. 3A shows a temporal change example when the steering torque changes with time, and FIG. 3B shows a temporal change example when the pseudo vehicle speed or the internal control vehicle speed changes with time. Show. The example of a transition of an internal control vehicle speed state is shown. The flowchart showing the operation example of the motor control part shown by FIG. 1 is shown. The specific structural example of the motor control part shown by FIG. 1 is shown.

  The preferred embodiments described below are used to facilitate an understanding of the present invention. Accordingly, those skilled in the art should note that the present invention is not unduly limited by the embodiments described below.

  FIG. 1 shows a schematic configuration example of an electric power steering apparatus according to the present invention. In the example of FIG. 1, the electric power steering apparatus 10 is also referred to as a torque detector 41 that detects a steering torque T of a vehicle steering system 20 (also referred to as a steering system), and assist torque (also referred to as auxiliary torque). ) And a motor control unit 42 that controls the motor current of the electric motor 43 with reference to the steering torque T. The motor control unit 42 can refer to the steering torque T and can refer to the vehicle speed detected by the vehicle speed detection unit 107, but the motor control unit 42 does not need to refer to the vehicle speed from the vehicle speed detection unit 107. Good. Although the electric power steering device 10 uses the vehicle speed from the vehicle speed detection unit 107 instead of including the vehicle speed detection unit 107, the electric power steering device 10 may include the vehicle speed detection unit 107.

  For example, the electric power steering device 10 or the motor control unit 42 determines whether or not the steering torque T is equal to or higher than the first predetermined torque. When the steering torque T is equal to or higher than the first predetermined torque, the same steering torque is determined. The motor current can be increased. The specific operation of the motor control unit 42 will be described later. When the steering torque T increases, the motor current can be increased to assist the driver with the increased assist torque. Thus, since the assist torque is set according to the steering torque T or the driver's burden, the electric power steering device 10 can reduce the uncomfortable feeling given to the driver.

  In the example of FIG. 1, the electric power steering apparatus 10 includes an assist torque mechanism 40 that applies assist torque to a steering system 20 that extends from a steering handle (for example, a steering wheel) 21 of a vehicle to steered wheels (for example, front wheels) 29 and 29 of the vehicle. (Also referred to as an auxiliary torque mechanism). Further, the electric power steering apparatus 10 includes, for example, a rack and pinion mechanism 25 as a steering mechanism.

  In the example of FIG. 1, the steering system 20 connects a rotating shaft 24 (also referred to as a pinion shaft) to a steering handle 21 via a steering shaft 22 (also referred to as a steering column) and universal shaft joints 23, 23. A rack shaft 26 is connected to the shaft 24 via a rack and pinion mechanism 25, and left and right steered wheels are connected to both ends of a rotating shaft 26 (also referred to as a rack shaft) via left and right tie rods 27 and 27 and knuckle 28 and 28. 29 and 29 are connected. The rack and pinion mechanism 25 includes a pinion 31 provided on the pinion shaft 24 and a rack 32 provided on the rack shaft 26.

  According to the steering system 20, when the driver steers the steering handle 21, the steered wheels 29 and 29 can be steered by the steering torque via the rack and pinion mechanism 25.

  In the example of FIG. 1, the auxiliary torque mechanism 40 detects a steering torque T generated in the steering system 20 by steering the steering handle 21 with a torque detection unit 41 such as a steering torque sensor, and detects this detection signal (both the torque signal). The control signal is generated by the motor control unit 42 based on the control signal, the assist torque corresponding to the steering torque T is generated by the electric motor 43 based on the control signal, and the assist torque is transmitted via the speed reduction mechanism 44 (for example, a worm gear mechanism). Is transmitted to the rotating shaft 24, and the assist torque is transmitted from the rotating shaft 24 to the rack and pinion mechanism 25 of the steering system 20.

  Preferably, the auxiliary torque mechanism 40 is detected by a vehicle speed detection unit 107 such as a vehicle speed sensor or an electronic control unit (ECU), and uses a vehicle speed V generated in the vehicle as the vehicle moves forward. Based on both, the motor control unit 42 can generate a control signal. As a result, the assist torque shows a value corresponding to the steering torque T and the vehicle speed V. Further, as will be described later, more preferably, the assist torque is determined or corrected together with the steering torque T and the vehicle speed V by, for example, the rotation angle (rotation signal) of the rotor of the electric motor 43.

  Note that the electric power steering device 10 can be classified into a pinion assist type, a rack assist type, a column assist type, and the like, depending on the location where the assist torque is applied to the steering system 20. Although the electric power steering apparatus 10 of FIG. 1 shows a pinion assist type, the electric power steering apparatus 10 may be applied to a rack assist type, a column assist type, or the like.

  According to the electric power steering device 10, the steered wheels 29 and 29 can be steered by the rack shaft 26 by a combined torque obtained by adding the assist torque of the electric motor 43 to the steering torque of the steering system 20.

  The electric motor 43 is, for example, a brushless motor, and the brushless motor incorporates a rotation sensor such as a resolver. This rotation sensor detects a rotation angle (also referred to as a motor rotation signal) of a rotor in a brushless motor.

  The motor control unit 42 includes, for example, a power supply circuit, a current sensor that detects a motor current, an input interface circuit, a microprocessor, an output interface circuit, an FET bridge circuit, and the like. For example, the input interface circuit can take in a torque signal, a vehicle speed signal, a motor rotation signal, and the like from the outside. For example, the microprocessor can perform vector control of the electric motor 43 based on a torque signal, a vehicle speed signal, and the like captured by the input interface circuit. The output interface circuit can convert, for example, a microprocessor output signal into a drive signal to the FET bridge circuit. The FET bridge circuit is configured by, for example, a switching element that supplies a drive current (three-phase alternating current) to the electric motor 43 (brushless motor).

  Such a motor control unit 42 generally includes a steering torque T (torque signal) detected by the torque detection unit 41, a vehicle speed (vehicle speed signal) detected by the vehicle speed detection unit 107, and a rotor detected by a rotation sensor. The target current value is set based on the rotation angle (rotation signal). The motor control unit 42 can drive the electric motor 43 so that the motor current detected by the current sensor matches the target current value. When the motor control unit 42 does not have a current sensor, the motor control unit 42 may control the target current value by regarding the target current value as the motor current. Note that a current sensor that detects the motor current may be attached to the electric motor 43 side, and the motor control unit 42 may capture the motor current from the electric motor 43. In addition, part or all of the motor rotation angle detection unit that detects a motor rotation signal such as the rotation angle of the rotor in the brushless motor may be provided outside the electric motor 43.

  FIG. 2 shows an example of a base map in which the target current value can be determined based on the relationship between the steering torque T and the vehicle speed V and the motor current, that is, both the steering torque T and the vehicle speed V. In the example of FIG. 2, for example, six curves are shown, and each of the six curves corresponds to the vehicle speed. When the vehicle speed is 0 [km / h] and the vehicle is stopped, the target current value or the motor current is maximum for the same steering torque, while the vehicle speed is the maximum vehicle speed [km / h]. Sometimes, the target current value or motor current is minimized for the same steering torque. By reducing the target current value or the motor current when the vehicle speed is high, the assist torque is reduced in the high speed region, and rapid steering can be suppressed. The maximum vehicle speed depends on vehicle characteristics such as the weight and size of the vehicle, and can be set according to the type of vehicle. The maximum vehicle speed that the vehicle can actually drive may be set in the base map. It may be the maximum vehicle speed.

  In the example of FIG. 2, the base map includes, for example, six curves. However, the number of curves included in the base map may be two, three to five, or seven or more. Good. Further, the curve included in the base map may be changed to one or a plurality of straight lines, for example, and the base map only needs to have characteristics determined for each vehicle speed. In the example of FIG. 2, the base map describes the relationship between the steering torque and the vehicle speed and the target current value (or motor current). The larger the steering torque, the larger the target current value, and the smaller the vehicle speed, the target current value. Is getting bigger. The motor control unit 42 in FIG. 1 can determine the target current value by referring to both the steering torque and the vehicle speed in the base map. Specifically, the characteristic as shown in FIG. 2 may be expressed by a mathematical formula, and the target current value may be calculated or determined by substituting the steering torque and the vehicle speed into the mathematical formula, or as shown in FIG. Such characteristics may be represented by a table, and a target current value corresponding to the steering torque and the vehicle speed may be extracted or determined from the table.

  The base map shows the relationship between the steering torque, the vehicle speed, and the motor current. However, instead of the vehicle speed, the base map is constructed by using a travel parameter that represents the travel state of the vehicle, for example, the engine speed. Alternatively, a base map indicating the relationship between the steering torque and the motor current may be constructed by omitting travel parameters such as vehicle speed.

  FIG. 3A shows a temporal change example when the steering torque T changes with time. In the example of FIG. 3A, the motor control unit 42 of FIG. 1 determines whether or not the steering torque T is equal to or greater than a first predetermined torque (for example, 4 [N · m]), for example, from time t1. When the steering torque T that is equal to or greater than the first predetermined torque is detected by the torque detection unit 41 between time t2 and time t3 to time t4, the motor control unit 42 calculates the motor current for the same steering torque. Can be bigger.

  Specifically, for example, a vehicle speed V (six curves) representing a vehicle speed lower than the maximum vehicle speed from a vehicle speed V (the lowest curve among the six curves) in the base map of FIG. When changing to (the second curve from the bottom), the motor current for the same steering torque is large, and the travel parameters such as the vehicle speed V can be changed, for example, at time t1 so that such a motor current is generated. it can.

  For example, assuming that the time t1 is the current time, the motor control unit 42 uses the same torque as the steering torque (current steering torque) at the time t1 based on characteristics such as the base map of FIG. The current target current value that is set based on the characteristics of the steering torque (current steering torque) at time t1 rather than the previous target current value that was set immediately before (target current value before update at time t1) (The updated target current value at time t1) is increased. When the steering torque T equal to or higher than the first predetermined torque is generated and the burden on the driver is large, the assist torque is increased by setting the motor current for the same steering torque large. Thus, since the assist torque is set according to the steering torque T or the driver's burden, the uncomfortable feeling given to the driver can be reduced.

  When the assist torque increases from time T1 and the burden on the driver is reduced, the increase in the steering torque T becomes moderate, and the steering torque T gradually begins to decrease. At time t2, the steering torque T is No more than the predetermined torque. When the steering torque T again becomes equal to or higher than the first predetermined torque at time t3, the motor control unit 42 in FIG. 1 is again set immediately before at the same torque as the current steering torque (for example, the steering torque T at time t3). The current target current value set by the current steering torque (the updated target current value at time t3) is made larger than the previous target current value (the target current value before updating at time t3). Can do.

  In the example of FIG. 3A, the motor control unit 42 of FIG. 1 determines whether or not the steering torque T is less than a second predetermined torque (for example, 2 [N · m]) that is smaller than the first predetermined torque. For example, when the steering torque T that is less than the second predetermined torque is detected by the torque detection unit 41 from time t5 to t6, the motor control unit 42 determines the motor current for the same steering torque. Can be reduced. The motor control unit 42 does not determine whether the steering torque T is less than the second predetermined torque, but reduces the motor current for the same steering torque, for example, when a predetermined time has elapsed from time t2 or t4. May be.

  For example, assuming that the time t5 is the current time, the motor control unit 42 uses the same torque as the steering torque (current steering torque) at the time t5, for example, based on characteristics such as the base map of FIG. Current target current value that is set based on the characteristics of the steering torque (current steering torque) at time t5, rather than the previous target current value that was set immediately before (target current value before update at time t5) (Target current value after update at time t5) is reduced. When the steering torque T that is less than the second predetermined torque is generated and the burden on the driver is small, the assist torque is reduced by setting the motor current for the same steering torque small. Thus, since the assist torque is set according to the steering torque T or the driver's burden, the uncomfortable feeling given to the driver can be reduced. In particular, since the steering torque T is controlled so as to fall between the first predetermined torque and the second predetermined torque, the steering torque T becomes larger than the first predetermined torque, or the steering torque T is the second predetermined torque. Even if there is a period during which the torque becomes smaller than the predetermined torque, the steering torque T is attracted within a certain range.

  FIG. 3B shows a temporal change example when the pseudo vehicle speed V ′ or the internal control vehicle speed changes with time. For example, when an abnormality of the vehicle speed detection unit 41 is detected, such as when the vehicle speed detection unit 41 fails or when the CAN is disconnected, the motor control unit 42 in FIG. 1 can obtain the pseudo vehicle speed V ′ from the steering torque T. it can. By using the simulated vehicle speed V ′ instead of the vehicle speed V detected by the vehicle speed detection unit 41, even when an abnormality of the vehicle speed detection unit 41 is detected, for example, based on characteristics such as the base map of FIG. The motor control unit 42 can continue to obtain the target current value or the motor current. In particular, by changing the pseudo vehicle speed V ′ without fixing it, the uncomfortable feeling given to the driver can be reduced. As will be described later, the simulated vehicle speed V ′ can be used not only when generating the target current value but also, for example, when generating inertia correction related to the moment of inertia, damper compensation related to the damping coefficient, etc. Like the vehicle speed V, it can be used as an internal control vehicle speed.

  For example, when an abnormality of the vehicle speed detection unit 41 is detected at time t0, the motor control unit 42 can set the pseudo vehicle speed V ′ or the internal control vehicle speed to, for example, the maximum vehicle speed (for example, 180 [km / h]). . By setting the internal control vehicle speed to the maximum vehicle speed, the assist torque is reduced, and rapid steering can be suppressed. From time t0 to time t6 shown in FIG. 3 (b), the steering torque T changes as shown in FIG. 3 (a), for example. For example, when the steering torque T that is equal to or higher than the first predetermined torque is detected by the torque detection unit 41 from time t1 to t2, the motor control unit 42 reduces the pseudo vehicle speed V ′ to reduce the same steering torque. The motor current can be increased. In the example of FIG. 3B, the pseudo vehicle speed V ′ or the internal control vehicle speed can be gradually decreased linearly from the maximum vehicle speed from time t1 to time t2. In addition, since it is preferable that the internal control vehicle speed is changed to a low speed in this way from the viewpoint of reducing the uncomfortable feeling given to the driver, the internal control vehicle speed is not linear from time t1 to time t2, for example, It may be gradually changed stepwise or curvedly.

  For example, when the steering torque T that is greater than or equal to the second predetermined torque and less than the first predetermined torque is detected by the torque detection unit 41 from time t2 to t3, the pseudo vehicle speed V ′ or the internal control vehicle speed is set to Can be kept constant. In the example of FIG. 3B, the internal control vehicle speed maintains the internal control vehicle speed at time t2 from time t2 to time t3. For example, when the steering torque T that is equal to or higher than the first predetermined torque is detected again from the time t3 to the time t4 by the torque detector 41, the internal control vehicle speed is gradually increased from the internal control vehicle speed at the time t2 or the time t3. Can be reduced. For example, when the steering torque T that is greater than or equal to the second predetermined torque and less than the first predetermined torque is detected by the torque detection unit 41 from time t4 to t5, the internal control vehicle speed is the time at time t4. Maintain internally controlled vehicle speed.

  For example, when the steering torque T that is less than the second predetermined torque is detected by the torque detector 41 from time t5 to t6, the pseudo vehicle speed V ′ or the internal control vehicle speed can be gradually increased. In the example of FIG. 3B, the decrease rate or slope of the internal control vehicle speed between time t1 and t2 and between time t3 and t4 is the increase rate of internal control vehicle speed between time t5 and t6 or Smaller than the slope. When the steering torque T is equal to or higher than the first predetermined torque, the pseudo vehicle speed V ′ can be decreased gradually, and the motor current for the same steering torque can be increased gradually. A sudden decrease in the simulated vehicle speed V ′ can be suppressed, and the vehicle can be driven more safely.

  Note that the first predetermined torque and the second predetermined torque depend not only on the vehicle characteristics but also on the transmission characteristics such as the performance of the electric motor 43 and the setting of the speed reduction mechanism 44, for example. It can be set according to the type.

  FIG. 4 shows a transition example of the internal control vehicle speed state. As shown in FIG. 4 or FIG. 3 (a) and FIG. 3 (b), when the steering torque T belongs, for example, between 0 and a second predetermined torque, the internal control vehicle speed is changed to a high speed. Can do. For example, at time t0 in FIG. 3A, the steering torque T is less than the second predetermined torque, so that the internal control vehicle speed can be increased. However, at time t0, the internal control vehicle speed has already reached the maximum vehicle speed. In such a case, the internal control vehicle speed is increased to the maximum vehicle speed.

  Next, for example, when the steering torque T becomes large and the steering torque T belongs, for example, between the second predetermined torque and the first predetermined torque, the internal control vehicle speed stops changing to the high speed side. Can do. Next, for example, when the steering torque T is further increased and the steering torque T is, for example, not less than the first predetermined torque, the internal control vehicle speed can be changed to a low speed. For example, even after time t4 in FIG. 3A, if the steering torque T continues to be equal to or higher than the first predetermined torque, the internal control vehicle speed is further decreased until reaching, for example, 0 (stopped vehicle speed). be able to.

  FIG. 5 is a flowchart showing an operation example of the motor control unit 42 shown in FIG. In the example of FIG. 5, for example, an ignition key is turned on, and the electric power steering apparatus 10 is activated. The motor control unit 42 inputs the steering torque T detected by the torque detection unit 41, for example, at a predetermined timing (step S1).

  For example, the motor control unit 42 determines whether or not the steering torque T (N) input at time t (N) is a normal value (step S2). The torque detection unit 41 can detect, for example, a failure of the torque detection unit 41 itself. For example, when a sensor unit of the torque detection unit 41 has failed, a failure signal indicating that the torque detection unit 41 has failed. Can be transmitted to the motor control unit 42. Alternatively, the motor control unit 42 may store or calculate an effective range of the steering torque T when the torque detection unit 41 operates normally, and determine whether or not the steering torque T is within the effective range. it can. For example, when the steering torque T (N) input at time t (N) is a normal value, the motor control unit 42 can perform step S4 described later. As a method for determining whether or not the steering torque T is a normal value, for example, a method disclosed or taught in Japanese Patent Application Laid-Open No. 2009-264812 can be employed.

  For example, when the steering torque T (N) input at time t (N) is not a normal value, that is, when an abnormality occurs in the torque detection unit 41, the motor control unit 42 determines that the torque detection unit 41 has failed. (Step S3). For example, when the vehicle has a warning lamp, the motor control unit 42 can light the warning lamp to notify the driver of a failure of the torque detection unit 41 or the electric power steering device 10. When an abnormality occurs, the motor control unit 42 sets the target current value or the motor current to, for example, 0, and the electric power steering device 10 does not generate assist torque.

  In step S2, for example, when the steering torque T (N) input at time t (N) is a normal value, the motor control unit 42 also inputs the vehicle speed V detected by the vehicle speed detection unit 107 at a predetermined timing, for example. (Step S4). For example, the motor control unit 42 determines whether or not the vehicle speed V (N) input at time t (N) or time t (N ′) synchronized with time t (N) is a normal value (step S5). ).

  For example, the vehicle speed detection unit 107 can detect a failure of the vehicle speed detection unit 107 itself. When a sensor unit of the vehicle speed detection unit 107 fails, for example, a failure signal indicating that the vehicle speed detection unit 107 has failed. Can be transmitted to the motor control unit 42. Or the motor control part 42 can memorize | store or calculate the effective range of the vehicle speed V when the vehicle speed detection part 107 operate | moves normally, and can judge whether the vehicle speed V exists in the effective range. For example, when the vehicle speed V (N) input at time t (N) is a normal value, the motor control unit 42 can perform step S6 described later, while the vehicle speed V (N) is not a normal value. In this case, the motor control unit 42 can perform step S8 described later. In the example of FIG. 5, the motor control unit 42 can execute step S1 and step S4 at the same time, for example, and may process step S2 and step S5 in parallel. As a method for determining whether or not the vehicle speed V is a normal value, for example, a method disclosed or taught in Japanese Patent Application Laid-Open No. 2002-331554 can be employed.

  For example, when the vehicle speed V (N) input at time t (N) is a normal value in step S5, for example, the motor control unit 42 depends on the vehicle speed V (N), for example, as shown in FIG. Alternatively, a mathematical expression is determined (step S6). Here, when the vehicle speed V (N) is a vehicle speed corresponding to, for example, the second curve from the top of the six curves in the base map of FIG. 2, for example, the motor control unit 42 is the second from the top. Adopt that curve. Alternatively, when the vehicle speed V (N) is a vehicle speed corresponding to, for example, the second curve from the bottom in the base map of FIG. 2, for example, the motor control unit 42 adopts the second curve from the bottom. For example, in the base map of FIG. 2, when the vehicle speed V (N) is large, the target current value or the motor current is set small with respect to the same steering torque.

  In step S6, when, for example, the second curve from the bottom in the base map of FIG. 2 is determined as the characteristic or formula depending on the vehicle speed V (N), the motor control unit 42 determines the second curve from the bottom. For example, the target current value (N) is determined by the steering torque T (N) input at time t (N) (step S7). As described above, the motor control unit 42 refers to or selects, for example, the second curve from the bottom shown in the base map of FIG. 2 corresponding to the vehicle speed V (N) as the relationship between the steering torque, the vehicle speed, and the target current value. To do. The motor control unit 42 refers to or selects the steering torque T (N) on the reference or selected curve (or vehicle speed V (N)), and corresponds to the reference or selected steering torque T (N). The target current value (N) can be determined or updated. When the target current value (N) is determined or updated, the motor control unit 42 drives the electric motor 43 so that the motor current matches the target current value (N), and executes, for example, step S2.

  In step S2, for example, when the steering torque T (N + 1) input at time t (N + 1) is a normal value, or when the steering torque T (N + 1) is input at time t (N + 1), for example, the motor control unit 42 For example, the vehicle speed V (N + 1) is simultaneously input at time t (N + 1) (step S4). For example, the motor control unit 42 determines whether or not the vehicle speed V (N + 1) input at time t (N + 1) is a normal value (step S5).

  For example, when the vehicle speed V (N + 1) input at time t (N + 1) is not a normal value at step S5, for example, when an abnormality occurs in the vehicle speed detection unit 107, the motor control unit 42, for example, at time t (N + 1) ) Is determined whether or not the steering torque T (N + 1) input in step S8 is equal to or greater than the first predetermined torque (step S8). When the electric power steering device 10 is activated, when it is first determined that the vehicle speed V is not a normal value, the motor control unit 42 preferably initializes the pseudo vehicle speed V ′ to the maximum vehicle speed. When the pseudo vehicle speed V ′ is initially set to the maximum vehicle speed, the generation of the assist torque is suppressed and the vehicle can be driven more safely.

  For example, in step S8, when the steering torque T (N + 1) input at time t (N + 1) is greater than or equal to the first predetermined torque, for example, the motor control unit 42, for example, from time t1 to time t2 in FIG. The pseudo vehicle speed V ′ is decreased at a decrease rate or a slope as shown in between, or the pseudo vehicle speed V ′ (N) at the time t (N) or the maximum vehicle speed that is initially set is, for example, the time t (N + 1). ) Is changed or updated to the simulated vehicle speed V ′ (N + 1) (step S9). The motor control unit 42 can use the changed or updated pseudo vehicle speed V ′ (N + 1) at time t (N + 1), for example, as the vehicle speed V (N + 1) at time t (N + 1) (step S9).

  Next, the motor control unit 42 depends on the pseudo vehicle speed V ′ (N + 1) at time t (N + 1) as the vehicle speed V (N + 1) at time t (N + 1), for example, as shown in FIG. A mathematical formula is determined (step S6). Here, the simulated vehicle speed V ′ (N) or the initially set maximum vehicle speed is, for example, the vehicle speed corresponding to the lowermost curve of, for example, six curves in the base map of FIG. For example, when V ′ (N + 1) is the vehicle speed corresponding to the second curve from the bottom among, for example, six curves in the base map of FIG. 2, the motor control unit 42 moves downward from the bottom curve. To the second curve and adopt the second curve from the bottom. Thus, the motor control unit 42, for example, the previous pseudo vehicle speed V ′ (N) associated with the same torque as the steering torque T (N + 1) (= current steering torque) input at time t (N + 1) or the initial setting. The current simulated vehicle speed V ′ (N + 1) associated with the current steering torque can be set smaller than the maximum vehicle speed that is set.

  By the way, in step S8, for example, when the steering torque T (N + 2) input at time t (N + 2) is not equal to or higher than the first predetermined torque, the motor control unit 42, for example, inputs the steering torque T input at time t (N + 2). It is determined whether (N + 2) is less than a second predetermined torque (step S10).

  For example, in step S10, when the steering torque T (N + 2) input at time t (N + 2) is less than the second predetermined torque, for example, the motor control unit 42, for example, from time t5 to time t6 in FIG. The pseudo vehicle speed V ′ is increased at an increase rate or slope as shown in between, or the pseudo vehicle speed V ′ (N + 1) at time t (N + 1) is changed to, for example, the pseudo vehicle speed V ′ at time t (N + 2). Change or update to (N + 2) (step S11). Here, for example, the simulated vehicle speed V ′ (N + 1) is a vehicle speed corresponding to the third curve from the bottom among, for example, six curves in the base map of FIG. 2, and the simulated vehicle speed V ′ (N + 2) is For example, when the vehicle speed corresponds to the lowermost curve of, for example, six curves in the base map of FIG. 2, the motor control unit 42 changes the third curve from the bottom to the lowermost curve. Then, the bottom curve is adopted. Thus, the motor control unit 42, for example, than the previous pseudo vehicle speed V ′ (N + 1) associated with the same torque as the steering torque T (N + 2) (= current steering torque) input at time t (N + 2). The current simulated vehicle speed V ′ (N + 2) associated with the current steering torque can be set large.

  Here, when the steering torque T equal to or greater than the first predetermined torque is detected as the current steering torque, the difference between the previous simulated vehicle speed V ′ and the current simulated vehicle speed V ′ (for example, V ′ (N) described above) V ′ (N + 1) is a difference between the previous simulated vehicle speed and the current simulated vehicle speed when the steering torque T that is less than the second predetermined torque is detected as the current steering torque (for example, V ′ described above) (Difference between (N + 1) and V ′ (N + 2)). As a result, when the steering torque T is equal to or higher than the first predetermined torque, the pseudo vehicle speed V ′ can be gradually decreased, and the target current value for the same steering torque can be gradually increased.

  Alternatively, for example, in step S10, when the steering torque T (N + 2) input at time t (N + 2) is not less than the second predetermined torque, for example, the motor control unit 42 performs, for example, from time t2 to time t3 in FIG. Or the pseudo vehicle speed V ′ (N + 1) at time t (N + 1), for example, is changed to the pseudo vehicle speed V at time t (N + 2), for example. '(N + 2) is adopted or updated (step S12). Here, when the pseudo vehicle speed V ′ (N + 1) and the pseudo vehicle speed V ′ (N + 2) are vehicle speeds corresponding to, for example, the third curve from the bottom among, for example, six curves in the base map of FIG. The motor control unit 42 adopts the third curve from the bottom as it is. In this way, the motor control unit 42, for example, calculates the previous pseudo vehicle speed V ′ (N + 1) associated with the same torque as the steering torque T (N + 2) (= current steering torque) input at time t (N + 2). The current pseudo vehicle speed V ′ (N + 2) associated with the steering torque can be set.

  FIG. 6 shows a specific configuration example of the motor control unit 42 shown in FIG. In the example of FIG. 6, the motor control unit 42 preferably includes a simulated vehicle speed generation unit 200, a switching unit 210, and an abnormality detection unit 201. The motor control unit 42 is disclosed in, for example, Japanese Patent Application Laid-Open No. 2010-47238. Differential processing unit 102, phase correction unit 103, inertia correction unit 104, damper correction unit 105, target current setting unit 108, addition calculation unit 109, subtraction calculation unit 110, deviation calculation unit 111, PI setting unit 112, non-interference The control unit 113, the calculation unit 114, the dq-3 phase conversion unit 115, the motor drive unit 116, the motor current detection units 118 and 119, and the three phase-dq conversion unit 120 are further included. In the example of FIG. 6, the simulated vehicle speed generation unit 200 can generate the simulated vehicle speed V ′ as shown in FIG. 3B, for example, based on the steering torque T. The switching unit 210 can switch from the vehicle speed V to the simulated vehicle speed V ′ in a state where an abnormality in the vehicle speed V is detected. The vehicle speed detection unit 107 is configured by, for example, an electronic control unit (ECU), and the ECU is connected to the motor control unit 42 via an in-vehicle network 202 such as CAN. The motor control unit 42 or the abnormality detection unit 201 can receive the vehicle speed V from the vehicle speed detection unit 107 by any method including wired and wireless.

  In the example of FIG. 6, the abnormality detection unit 201 determines whether or not the vehicle speed V is abnormal, specifically, whether or not the vehicle speed V detected by the vehicle speed detection unit 107 is a normal value. At this time, the vehicle speed detection unit 107 (ECU) can send, for example, the engine speed to the abnormality detection unit 201 via the in-vehicle network 202. In addition, the abnormality detection unit 201 can receive parameters such as a shift position and a gear ratio from the vehicle speed detection unit 107 (ECU) or another electronic control unit (ECU) 203 different from the vehicle speed detection unit 107. In addition, the electronic control unit 203 may be configured to include the vehicle speed detection unit 107. The vehicle speed detection unit 107 may be configured by a vehicle speed sensor instead of the electronic control unit. The abnormality detection unit 201 can receive a failure of the vehicle speed detection unit 107 (ECU, vehicle speed sensor, etc.) itself from the vehicle speed detection unit 107, or uses parameters such as engine speed, shift position, gear ratio, and the like. Thus, it is possible to determine the effective range of the vehicle speed V when the vehicle speed detection unit 107 operates normally, or to identify disconnection of the in-vehicle network 202 (such as no reception of the vehicle speed V from the vehicle speed detection unit 107). it can. When the vehicle speed V is not a normal value due to factors such as failure of the vehicle speed detection unit 107 or disconnection of the in-vehicle network 202, the abnormality detection unit 201 determines that the vehicle speed V is abnormal, and the switching unit 210 detects the vehicle speed detection unit. The switching unit 210 is instructed to output the simulated vehicle speed V ′ from the simulated vehicle speed generation unit 200 instead of the vehicle speed V from 107. In a state in which an abnormality in the vehicle speed V is detected, the simulated vehicle speed V ′ from the switching unit 210 is input as the internal control vehicle speed V by, for example, the target current setting unit 108, the inertia correction unit 104, the damper correction unit 105, etc. The current setting unit 108 can generate a target current value obtained by a base map such as shown in FIG. 2 based on the pseudo vehicle speed V ′. In a state where no abnormality in the vehicle speed V is detected, the internal control vehicle speed V is the vehicle speed V from the vehicle speed detection unit 107.

  In the example of FIG. 6, the motor rotation angle detection unit 130 calculates an angle (rotation angle) θ of the inner rotor with respect to the outer stator in the brushless motor 43 and outputs a signal corresponding to this angle θ to the dq-3 phase conversion units 115 and 3. Output to phase-dq converter 120. Further, the motor rotation angle detection unit 130 calculates a rotation angular velocity ω of the inner rotor with respect to the outer stator in the brushless motor 43, and outputs a signal corresponding to the rotation angular velocity ω to the differential processing unit 102, the damper correction unit 105 and the non-interacting control. Output to the unit 113.

  In the example of FIG. 6, the phase correction unit 103 uses the steering torque signal T input from the steering torque detection unit 41 (steering torque sensor 41) as the vehicle speed signal V input from the vehicle speed detection unit 107 (or an abnormality in the vehicle speed V). In the detected state, the phase is corrected based on the simulated vehicle speed signal V ′) from the simulated vehicle speed generation unit 200, and the corrected steering torque signal T ′ is output to the target current setting unit 108. The inertia correction unit 104 outputs the steering torque signal T input from the steering torque detection unit 41 and the vehicle speed signal V input from the vehicle speed detection unit 107 (or from the pseudo vehicle speed generation unit 200 in a state where an abnormality in the vehicle speed V is detected. This corresponds to the angular acceleration (that is, the time differential value of the rotational angular velocity ω) obtained by differentiating the pseudo vehicle speed signal V ′) and the signal corresponding to the rotational angular velocity ω by the differentiation processing unit 102 (differential computation unit 102). From the signal, an inertia correction signal di for performing inertia correction related to the moment of inertia is generated, and the inertia correction signal di is output to the addition operation unit 109. The damper correction unit 105 receives the steering torque signal T input from the steering torque detection unit 41 and the vehicle speed signal V input from the vehicle speed detection unit 107 (or from the pseudo vehicle speed generation unit 200 in a state where an abnormality in the vehicle speed V is detected. From the pseudo vehicle speed signal V ′) and the signal corresponding to the rotational angular velocity ω, a damper correction signal dd for performing damper correction related to the damping coefficient is generated, and this damper correction signal dd is output to the subtraction operation unit 110.

  In the example of FIG. 6, the target current setting unit 108 includes a corrected steering torque signal T ′ and a vehicle speed signal V (or a simulated vehicle speed signal V ′ from the simulated vehicle speed generation unit 200 in the state where an abnormality in the vehicle speed V is detected). Based on the above, the two-phase target currents Id1, Iq1 are calculated and output. The target currents Id1 and Iq1 correspond to the d-axis in the same direction as the permanent magnet and the q-axis orthogonal thereto in the rotating coordinate system synchronized with the rotating magnetic flux created by the permanent magnet on the inner rotor of the brushless motor 43, respectively. . These target currents Id1 and Iq1 are referred to as “d-axis target current Id1” and “q-axis target current Iq1”, respectively.

  The addition operation unit 109 adds the inertia correction signal di (inertia correction current di) to the target currents Id1 and Iq1, and outputs the added value, that is, the target currents Id2 and Iq2 after the inertia correction. The subtraction operation unit 110 subtracts the damper correction signal dd (damper correction current dd) from the inertia corrected target currents Id2 and Iq2, and outputs the subtraction value, that is, the damper corrected target currents Id3 and Iq3. The damper-corrected target currents Id3 and Iq3 are referred to as “d-axis final target current Id *” and “q-axis final target current Iq *”, respectively. The deviation calculator 111 subtracts the d-axis and q-axis detected currents Id and Iq input from the three-phase-dq converter 120 from the d-axis and q-axis final target currents Id * and Iq *, respectively, and the subtraction value That is, the deviations DId and DIq are output to the PI setting unit 112.

  In the example of FIG. 6, the PI setting unit 112 performs the calculation using the deviations DId and DIq so that the detection currents Id and Iq of the d-axis and the q-axis follow the final target currents of the d-axis and the q-axis. The d-axis and q-axis target voltages Vd and Vq are respectively calculated. The non-interacting control unit 113 and the calculation unit 114 correct the d-axis and q-axis target voltages Vd and Vq to the corrected d-axis and q-axis target voltages Vd ′ and Vq ′, and a dq-3 phase conversion unit 115. More specifically, the non-interference control unit 113 sets the d-axis and q-axis detection currents Id and Iq input from the three-phase-dq conversion unit 120 and the inner rotor rotation angular velocity ω input from the motor rotation angle detection unit 130. Based on this, non-interacting control correction values for the target voltages Vd and Vq for the d-axis and the q-axis are calculated. The calculation unit 114 calculates the d-axis and q-axis correction target voltages Vd ′ and Vq ′ by subtracting the non-interacting control correction values from the d-axis and q-axis target voltages Vd and Vq, respectively. The data is output to the dq-3 phase converter 115.

  In the example of FIG. 6, the dq-3 phase conversion unit 115 converts the d-axis and q-axis correction target voltages Vd ′ and Vq ′ into three-phase target voltages Vu *, Vv *, and Vw * to drive the motor. To the unit 116. The motor drive unit 116 includes a PWM voltage generation unit and an inverter circuit (not shown). The PWM voltage generator generates PWM control voltage signals UU, VU, WU corresponding to the three-phase target voltages Vu *, Vv *, Vw * and outputs them to the inverter circuit. The inverter circuit generates three-phase AC drive currents Iu, Iv, and Iw corresponding to the PWM control voltage signals UU, VU, and WU, and supplies these to the brushless motor 43 via the three-phase drive current path 117, respectively. To do. The three-phase AC drive currents Iu, Iv, and Iw are sine wave currents for driving the brushless motor 43 by PWM.

  In the example of FIG. 6, motor current detectors 118 and 119 are provided in two of the three-phase drive current paths 117. The motor current detection units 118 and 119 detect two drive currents Iu and Iw out of the three-phase drive currents Iu, Iv and Iw supplied to the brushless motor 43, and the three-phase-dq conversion unit 120. Output to. The three-phase-dq conversion unit 120 calculates the remaining drive current Iv based on the detected drive currents Iu and Iw. Further, the three-phase-dq converter 120 converts these three-phase detection drive currents Iu, Iv, Iw into two-phase d-axis and q-axis detection currents Id, Iq.

  For convenience of explanation, FIG. 6 shows a set of addition calculation unit 109, subtraction calculation unit 110, deviation calculation unit 111, PI setting unit 112, and calculation unit 114, respectively. Actually, these sets of circuit elements are provided individually for each of the two target currents Id1 and Id2.

  The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will be able to easily modify the above-described exemplary embodiments to the extent included in the claims. .

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Steering system (steering system), 21 ... Steering handle, 22 ... Steering shaft, 23 ... Universal joint, 24 ... Rotating shaft (pinion) Axis), 25 ... rack and pinion mechanism, 26 ... rotating shaft (rack shaft), 27 ... tie rod, 28 ... knuckle, 29 ... steered wheel, 31 ... pinion, 32 ... Rack, 40 ... Assist torque mechanism (auxiliary torque mechanism), 41 ... Torque detector (steering torque sensor), 42 ... Motor controller, 43 ... Electric motor, 44 ... Deceleration mechanism 52 ... Ball joint 104 ... Inertia correction unit 105 ... Damper correction unit 108 ... Target current setting unit 107 ... Vehicle speed detection unit 200 ... Similar vehicle speed generation unit, 201 ... abnormality detection unit, 202 ... in-vehicle network, 203 ... electronic control unit, 210 ... switching unit 210, T ... steering torque, V ... vehicle speed, V '... Simulated vehicle speed (internally controlled vehicle speed).

Claims (3)

A torque detector for detecting a steering torque of a vehicle steering system;
An electric motor for applying assist torque to the steering system;
A motor that controls the motor current of the electric motor so that the motor current increases as the steering torque increases, and the motor current increases as the vehicle speed decreases, with reference to the vehicle speed together with the steering torque. A control unit;
With
When the steering torque that is equal to or higher than the first predetermined torque is detected as the current steering torque in a state where the abnormality in the vehicle speed is detected, the motor control unit obtains a pseudo vehicle speed from the steering torque, and the steering torque In addition, the pseudo vehicle speed is referred to as the vehicle speed, and the motor control unit has a current that is associated with the current steering torque rather than the previous motor current set immediately before at the same torque as the current steering torque. An electric power steering apparatus characterized by increasing the current motor current set by the current steering torque by decreasing the pseudo vehicle speed. When the steering torque that is less than the second predetermined torque smaller than the first predetermined torque is detected as the current steering torque in a state where the abnormality in the vehicle speed is detected, the motor control unit 2. The electric power steering apparatus according to claim 1, wherein the current motor current is made smaller than the previous motor current by increasing the current pseudo vehicle speed associated with a steering torque. Difference between the first of said steering torque to a predetermined torque or more of the previous in case of said detected as currently steering torque the pseudo vehicle speed and the current of the pseudo vehicle speed is less than said first predetermined torque claim 1 or the steering torque second is less than the predetermined torque is equal to or smaller than the difference between the previous the pseudo speed and the current of the pseudo rate when said detected as currently steering torque The electric power steering apparatus according to claim 2.

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