JP3775978B2 - Electric power steering device - Google Patents

Description

【００２７】
上記の式（１）は、次のようにして導出される。図４は、関数１２のみを表した図３の部分図である。図４において、あるＥｐｓの値に対するモータ電圧の値をＶとしたとき、三角形ＰＱＲと三角形ＰＳＴとは相似であるから、
ＰＱ：ＲＱ＝ＰＳ：ＴＳ
の関係が成立する。これより、
ＲＱ＝ＴＳ・ＰＱ／ＰＳ
ここで、
ＲＱ＝Ｖ
ＴＳ＝Ｖｏ
ＰＱ＝Ｅｐｓ−（Ｃｎｔ＋δ）
ＰＳ＝Ａｏ−（Ｃｎｔ＋δ）
であるから、これらを上式に代入すれば式（１）が得られる。なお、ここでは関数１２に基づいて式（１）を導出したが、関数１３に基づいても式（１）と同じ結果が得られる。
【００２８】
次に、ステップＳ９においてＥｐｓ＞Ｃｎｔ＋δでなければ（ステップＳ９；ＮＯ）、続いてステップＳ１１において、Ｅｐｓの値が不感帯Ｘよりも負方向側にあるか否かを判定する。すなわち、図３において、Ｅｐｓ＜Ｃｎｔ−δであれば（ステップＳ１１；ＹＥＳ）、Ｅｐｓは不感帯Ｘの範囲内にはなく、これよりも負方向側（左側）にあるので、ＥＰＳモータ５を駆動するためのモータ電圧Ｖを次式によって計算する（ステップＳ１２）。
【式２】

この式（２）も、式（１）と同様の原理に従って、幾何学的に算出することができる。
【００２９】
また、ステップＳ１１において、Ｅｐｓ＜Ｃｎｔ−δでなければ（ステップＳ１１；ＮＯ）、Ｅｐｓの値は不感帯Ｘの範囲内にあることになり、この場合は、モータ電圧Ｖを出力しないので、Ｖ＝０に設定する（ステップＳ１３）。こうして、Ｅｐｓの値に応じてモータ電圧Ｖの値を求めた後、制御部１はモータ電圧ＶをＥＰＳモータ５へ出力し（ステップＳ１４）、以後ステップＳ１〜Ｓ１４の動作を反復する。
【００３０】
このように、上記の例では、制御部１によるソフトウエア処理によって、不感帯Ｘの中心位置Ｃｎｔをシフトさせ、ステアリング後にＥＰＳモータ５が駆動されるようにしているので、新たなハードウエアや機構部品を付加する必要がなく、従来と同じ構成で制御部１のソフトウエアだけを変更することで、車両を自動的に直進状態に戻す機能が実現される。
【００３１】
なお、図５の処理においては、不感帯Ｘの中心位置Ｃｎｔを計算により求めたが（ステップＳ４〜Ｓ８）、図２の関数１０をあらかじめ制御部１のメモリにテーブルとして記憶しておき、走行速度とステアリング角の積の値に対応する中心位置Ｃｎｔの値を、テーブルを参照することにより求めてもよい。
【００３２】
また、以上の実施形態ではフォークリフトに搭載される装置を例に挙げたが、本発明はフォークリフト以外の各種車両に搭載される電気式パワーステアリング装置にも適用することが可能である。
【００３３】
【発明の効果】
本発明によれば、センサの不感帯の中心位置をシフトさせることで、ステアリングが終了したときにモータ電圧が出力され、モータの回転によって操舵輪が元に戻るので、車両の走行状態を自動的に直進状態に復帰させることができる。
【図面の簡単な説明】
【図１】本発明に係る電気式パワーステアリング装置の構成図である。
【図２】不感帯の中心位置をシフトさせるための関数を示した図である。
【図３】本発明におけるＥＰＳセンサの検出値とモータ電圧との関係を示した図である。
【図４】モータ電圧の値を算出する原理を示した図である。
【図５】本発明に係る電気式パワーステアリング装置の動作を示したフローチャートである。
【図６】キングピンを用いた従来の機構の正面図である。
【図７】従来例におけるＥＰＳセンサの検出値とモータ電圧との関係を示した図である。
【符号の説明】
１ 制御部
２ 角度センサ
３ 速度センサ
４ ＥＰＳセンサ
５ ＥＰＳモータ（ステアリングモータ）
６ ハンドル
７ ステアリング機構
８ 操舵輪
Ｖ モータ電圧
Ｘ 不感帯
Ｃｎｔ 中心位置
Ｓｐｄ 走行速度
Ａｎｇ ステアリング角
Ｅｐｓ ＥＰＳセンサ検出値[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device mounted on a forklift or the like.
[0002]
[Prior art]
In a forklift, when a steering wheel is turned during steering to perform steering (steering) and then a handle is loosened, it is required for safety to automatically return the vehicle to a straight traveling state. For this reason, as shown in FIG. 6, a mechanism has been conventionally employed in which the tire 20 is automatically returned to the straight state after steering by movably supporting the tire 20 on a kingpin 21 having a kingpin angle φ. ing. In addition, 22 is an axle, 23 is a rod, and 24 is a center arm pin.
[0003]
On the other hand, many forklifts are equipped with an electric power steering device that drives a steering motor in conjunction with the operation of the steering wheel and assists steering by the steering wheel by the force of the motor. Japanese Patent Application Laid-Open No. 8-253158 and Japanese Patent Application Laid-Open No. 5-185936 describe an electric power steering device mounted on a forklift.
[0004]
[Problems to be solved by the invention]
By the way, in the case of a forklift equipped with an electric power steering device, since the steering motor is generally a small motor, the gear ratio is set large. For this reason, even if the king pin 21 as shown in FIG. 6 is provided, since the gear ratio of the steering motor is large, a force sufficient to rotate the steering motor after steering is not generated, and the steering motor becomes a friction obstacle. There arises a problem that the tire cannot return to the straight traveling state.
[0005]
In this case, if the steering motor can rotate, the tire can be returned to the straight traveling state by the action of the king pin. However, in the conventional apparatus, the relationship between the detected value of an EPS (Electric Power Steering) sensor that detects the amount of deviation between the operation angle of the steering wheel and the steering angle of the steering wheel and the motor voltage applied to the steering motor is shown in FIG. It is like that. As can be seen, there is a dead zone X in which the motor voltage is not output due to the offset δ in the vicinity where the detected value of the EPS sensor is 0, so when the detected value of the EPS sensor becomes almost 0 after steering. It is impossible to obtain a driving force for the steering motor.
[0006]
As described above, the conventional apparatus has a problem in that even if the king pin is provided, the steering motor cannot rotate, so that the vehicle does not automatically return straight after the steering.
[0007]
The present invention solves the above-described problems, and provides an electric power steering device capable of automatically returning a vehicle to a straight-ahead state after steering, regardless of the presence or absence of a kingpin. Is an issue.
[0008]
[Means for Solving the Problems]
In order to solve the above problem, in the present invention, the dead zone is not fixed as shown in FIG. 7, but the dead zone is shifted. That is, the electric power steering apparatus according to the present invention shifts the center position of the dead zone based on the traveling speed of the vehicle and the steering angle of the steering wheel, and in the vicinity where the detected value of the sensor becomes 0 by this shift, A motor voltage for returning the steered wheels is output (claim 1).
[0009]
By doing so, when the steering is finished and the detection value of the sensor becomes almost zero, the motor voltage is output and the steering motor rotates, and this rotation gives a return force to the steering wheel. The traveling state of the vehicle can be automatically returned to the straight traveling state.
[0010]
The shift of the center position of the dead zone can be linearly shifted within a certain range based on the product of the traveling speed of the vehicle and the steering angle of the steered wheels. By limiting the shift range, it is possible to prevent the force for returning the steered wheels from becoming too large and to ensure safety. In addition, when the detected value of the sensor is outside the range of the dead zone after the shift, the voltage of the steering motor is calculated by a predetermined arithmetic expression, and when the detected value of the sensor is within the range of the dead zone after the shift, The voltage is set to 0 (Claim 3). The traveling speed of the vehicle can be detected by a speed sensor, and the steering angle of the steered wheels can be detected by an angle sensor.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an electric power steering apparatus according to an embodiment of the present invention, and shows an example of an apparatus mounted on a forklift. A control unit 1 controls the entire apparatus, and includes a controller including a CPU, a memory (ROM and RAM), an input / output port, a voltage output circuit, and the like. 2 is an angle sensor for detecting the steering angle of the steering wheel 8, 3 is a speed sensor for detecting the traveling speed of the vehicle, and 4 is a deviation amount between the operation angle of the steering wheel 6 and the steering angle of the steering wheel 8. The detected value of each of these sensors 2 to 4 is input to the control unit 1 in an EPS (Electric Power Steering) sensor.
[0012]
Reference numeral 5 denotes a steering motor (hereinafter referred to as an EPS motor) driven by a voltage output from the control unit 1, which is composed of, for example, a DC motor, and assists the steering of the steered wheels 8 in conjunction with the operation of the handle 6. Reference numeral 6 denotes a steering wheel operated by the driver, 7 denotes a steering mechanism including gears for steering the steering wheel 8, and 8 denotes a steering wheel (steering tire) provided at the rear portion of the forklift. In FIG. 1, only elements related to the present invention are illustrated as elements connected to the input / output of the control unit 1.
[0013]
2 and 3 are diagrams for explaining the principle of the present invention. FIG. 2 is a diagram showing a function for shifting the center position of the dead zone X shown in FIG. 7, and FIG. It is a figure showing the relationship between detection value Eps and motor voltage (input voltage given to EPS motor 5) V. FIG.
[0014]
In FIG. 2, the horizontal axis represents the product of the absolute value of the traveling speed Spd of the vehicle and the steering angle Ang of the steered wheels 8, and the vertical axis represents the center position Cnt of the dead zone of the EPS sensor 4. As shown in the figure, the function 10 is such that the center position Cnt changes linearly while the value of | Spd | × Ang is within a certain range Y, and outside the range of Y, the center position Cnt has a constant value K1 (> 0), K2 (<0). The absolute values of K1 and K2 are selected to be equal.
[0015]
When the vehicle traveling speed Spd detected by the speed sensor 3 and the steering angle Ang of the steered wheels 8 detected by the angle sensor 2 are input to the control unit 1, the control unit 1 follows the function 10 to | Spd | × Ang From this value, the center position Cnt of the dead zone of the EPS sensor 4 is obtained. Then, based on the obtained center position Cnt, a function of the motor voltage is set as shown in FIG.
[0016]
In FIG. 3, the solid line 11 is the same as the function shown in FIG. 7, and represents the relationship between the EPS sensor detection value Eps and the motor voltage V when the center of the dead zone of the EPS sensor 4 is at the 0 position. Further, 12 and 13 represent the relationship between the EPS sensor detection value Eps and the motor voltage V when the center position Cnt of the dead zone X is shifted from the 0 position according to the function 10 of FIG. When shifted in the direction (right direction), 13 represents the relationship between Eps and V when the center position Cnt is shifted in the negative direction (left direction). 7 is an offset shown in FIG. 7, Ao is an EPS sensor detection value (maximum point value) when the motor voltage V is a constant value Vo, and Bo is an EPS sensor detection value when the motor voltage V is a constant value −Vo. (Minimum point value).
[0017]
Now, when steering is performed by operating the handle 6 during traveling, the control unit 1 reads the traveling speed Spd detected by the speed sensor 3 and the steering angle Ang detected by the angle sensor 2, and | Spd | × Ang Calculate the value. When this calculation result is a positive value (Ang> 0), as can be seen from FIG. 2, the center position Cnt of the dead zone becomes a positive value, and the control unit 1 is as shown by the one-dot chain line 12 in FIG. The center position Cnt of the dead zone X of the EPS sensor 4 is shifted in the positive direction. This shift amount increases as the travel speed Spd and the steering angle Ang increase.
[0018]
By shifting the center position Cnt of the dead zone X in the positive direction, a motor voltage is output in the vicinity of Eps = 0, and a voltage of −Vε is output from the control unit 1 when Eps = 0. When the hand of the handle 6 is loosened after the steering, the operation angle of the handle 6 and the steering angle of the steered wheel 8 are almost the same, so the detection value Eps of the EPS sensor 4 is almost zero, Thus, the EPS motor 5 is rotated by the voltage of −Vε. Since this voltage is opposite in polarity to the voltage V (0 <V ≦ Vo) applied to the EPS motor 5 during steering, the EPS motor 5 rotates in the opposite direction to that during steering, thereby the steering mechanism. 7, the steered wheel 8 receives a force to return to the original position. As a result, the vehicle automatically returns to the straight traveling state. At this time, the force to return the steering wheel 8 to the original is transmitted to the handle 6 via the steering mechanism 7, so that the handle 6 also follows the steering wheel 8 and returns to the neutral position.
[0019]
On the other hand, when the value of | Spd | × Ang is a negative value (Ang <0), the control unit 1 makes the center position Cnt of the dead zone negative as shown by the broken line 13 in FIG. Shift in direction. By shifting the center position Cnt in the negative direction, the motor voltage is output in the vicinity of Eps = 0, and the voltage Vε is output from the control unit 1 when Eps = 0. Since this voltage is opposite in polarity to the voltage V (0> V ≧ −Vo) applied to the EPS motor 5 at the time of steering, the EPS motor 5 rotates in the opposite direction to that at the time of steering. Via the mechanism 7, the steered wheel 8 receives a force for returning to the original position. As a result, the vehicle automatically returns to the straight traveling state. Also in this case, the handle 6 follows the steering wheel 8 and returns to the neutral position.
[0020]
In this way, by shifting the center position Cnt of the dead zone in the positive direction and the negative direction, the steering wheel 8 can be returned to the straight traveling state by the rotation of the EPS motor 5 regardless of the direction of steering. . Here, even when a conventional king pin is provided, since the EPS motor 5 rotates, there is no resistance in the motor portion, and the steered wheel 8 can return to the straight traveling state by the action of the king pin. It becomes. Further, even if the king pin is not provided, the steering wheel 8 returns to the straight traveling state by the action of the EPS motor 5 described above. Therefore, as long as the EPS device is provided, the vehicle automatically goes straight regardless of the presence or absence of the king pin. It is possible to return to
[0021]
In FIG. 2, since the center position Cnt of the dead zone is shifted according to the product of the traveling speed Spd of the vehicle and the steering angle Ang of the steering wheel 8, the vehicle is not traveling (Spd = 0). The center position Cnt is not shifted no matter how much the steering angle Ang is, and therefore the steering wheel 8 does not return straight. Even if the vehicle is traveling, if the steering is not performed (Ang = 0), the center position Cnt is not shifted, and the force to return the steered wheels 8 to the straight traveling state does not work. That is, only when the vehicle is running and steering is performed, the EPS motor 5 exerts a force for returning the steered wheels 8 to the straight traveling state.
[0022]
Further, if the shift amount of the center position Cnt of the dead zone becomes too large, the value of Vε increases, so that the force to return the steered wheels 8 is excessively dangerous, but in FIG. 2, the shift amount of the center position Cnt is Since the fixed value (K1, K2) is not exceeded, the EPS motor 5 does not receive an excessive return force by the EPS motor 5, and safety can be ensured.
[0023]
FIG. 5 is a flowchart showing the operation of the electric power steering apparatus as described above, and shows a procedure executed by the control unit 1. The details of the operation will be described below based on this.
[0024]
The control unit 1 reads the steering angle Ang of the steered wheels 8 detected by the angle sensor 2 (step S1), reads the traveling speed Spd of the vehicle detected by the speed sensor 3 (step S2), and further detects the EPS sensor 4. A deviation amount Eps between the steering wheel angle and the steering angle is read (step S3). Next, the center position Cnt of the dead zone of the EPS sensor 4 is calculated by the following equation based on the read travel speed Spd and steering angle Ang value (step S4).
Cnt = G · | Spd | · Ang
Here, G is the slope of the straight line in the linear portion (range Y) of the function 10 in FIG.
[0025]
Subsequently, the control unit 1 compares the calculated value of the center position Cnt with the value of K1 in FIG. 2 (step S5). If Cnt> K1 as a result of the comparison (step S5; YES), the value of K1 is set as the value of the center position Cnt (step S6). If Cnt> K1 is not satisfied (step S5; NO), then Cnt and K2 are compared (step S7). As a result of the comparison, if Cnt <K2 (step S7; YES), the value of K2 is set as the value of the center position Cnt (step S8). If Cnt <K2 is not satisfied (step S7; NO), the process proceeds to step S9.
[0026]
In step S9, it is determined whether or not the Eps value read in step S3 is on the positive direction side of the dead zone X of the EPS sensor 4. That is, in FIG. 3, if Eps> Cnt + δ (step S9; YES), since Eps is not within the dead zone X range and is on the positive direction side (right side), the EPS motor 5 is driven. Is calculated by the following equation (step S10).
[Formula 1]

[0027]
The above equation (1) is derived as follows. FIG. 4 is a partial view of FIG. 3 showing only the function 12. In FIG. 4, when the motor voltage value for a certain Eps value is V, the triangle PQR and the triangle PST are similar.
PQ: RQ = PS: TS
The relationship is established. Than this,
RQ = TS ・ PQ / PS
here,
RQ = V
TS = Vo
PQ = Eps− (Cnt + δ)
PS = Ao− (Cnt + δ)
Therefore, if these are substituted into the above equation, equation (1) is obtained. Here, although the formula (1) is derived based on the function 12, the same result as the formula (1) can be obtained based on the function 13.
[0028]
Next, if Eps> Cnt + δ is not satisfied in step S9 (step S9; NO), then in step S11, it is determined whether or not the value of Eps is on the negative side with respect to the dead zone X. That is, in FIG. 3, if Eps <Cnt−δ (step S11; YES), Eps is not in the dead zone X range and is on the negative direction side (left side), so the EPS motor 5 is driven. The motor voltage V to be calculated is calculated by the following equation (step S12).
[Formula 2]

This equation (2) can also be calculated geometrically according to the same principle as equation (1).
[0029]
If Eps <Cnt−δ is not satisfied in step S11 (step S11; NO), the value of Eps is within the dead zone X. In this case, since the motor voltage V is not output, V = Set to 0 (step S13). Thus, after determining the value of the motor voltage V according to the value of Eps, the control unit 1 outputs the motor voltage V to the EPS motor 5 (step S14), and thereafter repeats the operations of steps S1 to S14.
[0030]
As described above, in the above example, the center position Cnt of the dead zone X is shifted by software processing by the control unit 1 so that the EPS motor 5 is driven after steering. The function of automatically returning the vehicle to the straight traveling state is realized by changing only the software of the control unit 1 with the same configuration as the conventional one.
[0031]
In the process of FIG. 5, the center position Cnt of the dead zone X is obtained by calculation (steps S4 to S8), but the function 10 of FIG. The value of the center position Cnt corresponding to the product of the steering angle and the steering angle may be obtained by referring to a table.
[0032]
Moreover, although the apparatus mounted in the forklift was mentioned as an example in the above embodiment, this invention is applicable also to the electric power steering apparatus mounted in various vehicles other than a forklift.
[0033]
【The invention's effect】
According to the present invention, by shifting the center position of the dead zone of the sensor, the motor voltage is output when the steering is completed, and the steered wheels are returned to the original state by the rotation of the motor. It is possible to return to the straight running state.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an electric power steering apparatus according to the present invention.
FIG. 2 is a diagram showing a function for shifting the center position of a dead zone.
FIG. 3 is a diagram showing a relationship between a detected value of an EPS sensor and a motor voltage in the present invention.
FIG. 4 is a diagram illustrating a principle of calculating a value of a motor voltage.
FIG. 5 is a flowchart showing the operation of the electric power steering apparatus according to the present invention.
FIG. 6 is a front view of a conventional mechanism using a king pin.
FIG. 7 is a diagram showing a relationship between a detection value of an EPS sensor and a motor voltage in a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Control part 2 Angle sensor 3 Speed sensor 4 EPS sensor 5 EPS motor (steering motor)
6 Steering wheel 7 Steering mechanism 8 Steering wheel V Motor voltage X Dead zone Cnt Center position Spd Traveling speed Ang Steering angle Eps EPS sensor detection value

Claims (4)

A steering motor that steers the steering wheel in conjunction with the steering wheel operation, a sensor that detects the amount of deviation between the steering wheel steering angle and the steering angle of the steering wheel, and the motor voltage of the steering motor based on the detected value of this sensor An electric power steering device having a dead zone in which a motor voltage is not output in a certain range of a detection value of the sensor,
The control unit shifts the center position of the dead zone based on the traveling speed of the vehicle and the steering angle of the steered wheel, and returns the steered wheel to the original position in the vicinity where the detection value of the sensor becomes 0 by this shift. An electric power steering apparatus characterized in that the motor voltage is output. The electric power steering apparatus according to claim 1, wherein the control unit linearly shifts the center position of the dead zone within a certain range based on a product of a traveling speed of the vehicle and a steering angle of the steered wheels. The control unit calculates a motor voltage by a predetermined arithmetic expression when the detection value of the sensor is outside the range of the dead band after the shift, and when the detection value of the sensor is within the range of the dead band after the shift, the motor voltage The electric power steering device according to claim 1, wherein is set to 0. The electric power steering apparatus according to any one of claims 1 to 3, further comprising a speed sensor that detects a traveling speed of the vehicle and an angle sensor that detects a steering angle of the steered wheels.

Images