JPS62163863A - Motor driven power steering device - Google Patents

Abstract

PURPOSE:To obtain a stable returning characteristic of a steering system by providing means for detecting that the steering system is released from hands and returned, and braking a power assist motor when a returning condition is detected. CONSTITUTION:The motor driven power steering device in the caption comprises means 21 for detecting the steering torque of a steering system and a motor control signal detecting means 50 for determining a motor control signal on the basis of a signal fed from means 22 for detecting the rotary speed of the steering system. Then a motor 11 is controlled through a drive means 34 in accordance with said motor control signal. Here, a released hand returning condition detecting means 60 comprising a zero torque rotation detecting means 61 and a reduced steering rotation detecting means 62 for producing respective outputs when the steering torque and the steering rotary speed fed from both detecting means 21, 22 are lower than predetermined values is provided. When a released hand returning condition is detected, the motor 11 is braked by a braking means 70.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric power steering device that generates auxiliary torque by a steering force booster using an electric motor.

(Prior Art) Conventional electric power steering devices include a steering force booster powered by an electric motor and a control device composed of a microcomputer unit, and the electric motor generally operates at low output torque and high rotation speed. Therefore, when used in an electric power steering device, it is equipped with a deceleration device that decelerates the rotation to a low rotation speed with high output torque.During steering, it detects the steering torque and steering rotation speed applied to the steering system. The electric motor is driven and controlled based on the detection signal, and the electric motor power is applied to the steering system to reduce the steering force.As a result, drivability is improved and the steering feeling is improved. 80
-9545” and “Patent Application No. 130-954Ei”
has been filed by the applicant.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional electric power steering device, when the steering wheel is steered while the vehicle is running, when the steering system returns, tire reaction force including caster trail causes the electric motor to The steering system tries to return to the middle position by rotating the motor, but since the reduction gear is rotated from its output side, the electric motor is rotated at an increased speed.

In this case, the moment of inertia of the electric motor in the steering system is as large as the square of the reduction ratio, so when the steering system returns, the inertia of the device opening causes the steering system to
The oscillation of going beyond the intermediate position in the opposite direction and returning again is repeated over a long period of time, which may make it difficult to converge to the intermediate position in a short period of time. In other words, in terms of convergence characteristics in a manual steering system, as shown in Figure 6 (A), which shows the steering angle characteristic curve in text, if the steering system is turned α degrees from the middle position while driving and then released, the steering The vibration of the system converges in 11 hours, but in the electric power steering device, as shown in Fig. 6 (B), the period of vibration is long due to its own inertia force, and the vibration becomes large, so the convergence time T2 is This was larger than in the case of a manual steering system, reducing the return stability of the steering system.

(Objective of the Invention) Therefore, in the present invention, when the steering wheel is in the returning state without the hands being released, this is detected and the electric motor is electrically braked, thereby shortening the time for the steering system to converge at the middle position. The object of the present invention is to provide an electric power steering device that provides stable return characteristics of the steering system.

(Means for solving problems and their effects) FIG. 1 is an overall configuration diagram of the present invention.

In FIG. 1, when the key switch of the ignition key is turned on and the steering wheel is steered, the electric Jll (11) is driven and controlled in accordance with the steering force. When the steering wheel is operated to return, the state of the steering system returned by the reaction force of the tires is detected by the release state detection means.

Based on this detection signal, the electric motor (
11) Both terminals of the '7rL armature winding are short-circuited to perform self-braking of the motor. Therefore, since the electric motor (11) is braked during the return operation of the steering system, the time for convergence at the intermediate position of the steering system is shortened, the influence of the inertia of the electric motor itself can be eliminated, and stable return characteristics can be obtained.

Furthermore, as shown in the overall configuration diagram shown in FIG. 2, there is a steering torque detection means for detecting the steering torque of the steering system, a steering rotation detection means for detecting the rotational speed of the steering system, and a detection signal from both of these detection means. a motor control signal generating means for determining a motor control signal based on the control signal; a motor driving means for driving the motor based on the control signal of the control signal generating means; and a motor driven by the motor; , is composed of a zero torque rotation detection means and a steering rotation reduction detection means, and the zero torque rotation detection means detects the steering based on both detection signals from the steering torque detection means (21) and the steering rotation detection means (22). While detecting that the torque is below a predetermined value and the steering rotation speed is above a predetermined value, the steering rotation reduction detection means detects that the steering rotation speed is reduced based on a detection signal from the steering rotation detection means (22). To detect. Braking control of the electric motor is performed in the motor braking means based on both detection signals from the zero torque rotation detection means and the steering rotation reduction detection means. Therefore, in this case,
When the steering system returns, the electric motor is braked within the range in which the steering rotational speed decreases, allowing the steering system to return to the intermediate position within a short period of time, resulting in stable return. characteristics are obtained.

(Example) An example of the present invention will be described below based on the accompanying drawings. In this embodiment, a case will be explained in which the hand-off return state detection means is configured by a zero-torque rotation detection means and a steering rotation reduction detection means.

Figure 3 shows the electric power steering device (1) of this embodiment.
) is a schematic plan view. In the figure, (2) is a steering wheel, (3) and (4) are an input shaft and an output shaft, and these input shaft (3) and output shaft (4) are arranged coaxially with each other. The inner ends of the output shaft (4) are connected by a torsion bar, and the other end of the output shaft (4) is connected to a constant velocity joint (not shown) or a rack-and-binion,
Rotation of the steering wheel (2) is converted and transmitted as a linear change in the rack. Further, a steering rotation sensor (7) is provided around the input shaft (3), and a steering rotation sensor (7) is provided around the input shaft (3).
) and (4) are provided with a steering torque sensor (10), and an electric motor (11) is provided around the output shaft (4).
and a deceleration device are provided, each sensor (7), (
1G) and a power supply circuit (13) thereof.

The above-mentioned steering rotation sensor (7) includes a DC power generation a (8), a toothed pulley pivoted thereon, a toothed pulley integrally pivoted on the input shaft (3), and a toothed pulley suspended between these. The timing belt (9) rotates the DC generator (8) as the input shaft (3) rotates.

The above steering rotation sensor (7) is located on the output shaft side (electric motor).
may be provided.

The steering torque sensor (10) is connected to the input/output shaft (3) and (
4) a movable iron core that is displaced in the axial direction with the relative rotation;
It consists of a differential transformer, which is arranged with a gap around the outer circumference of this movable core and consists of a primary winding and a secondary winding, and the angular difference between the input and output shafts (3) and (4) is The next coil converts it into an electrical signal and outputs it.

The electric motor (11) is arranged along the output shaft (4),
A toothed pulley is attached to the rotating shaft, and a timing belt (14) is passed between the toothed pulley and the toothed pulley attached to the output shaft (4). In addition, a toothed pulley attached to the output shaft (4) is formed to have a large diameter, and both toothed pulleys and a timing belt are configured so that the rotation of the electric motor (11) is decelerated and transmitted to the output shaft (4). (14) constitutes a speed reduction device.

The input shaft (3), the output shaft (4), the DC generator (8) of the steering rotation sensor, the differential transformer and electric motor (11) of the steering torque sensor (10) are connected to the input/output shaft (3). .

(4) is supported by a steering column (not shown) that covers the periphery.

The control device (12) and its power supply circuit (13) will be explained based on FIG. 4. In the figure, (20) is a microcomputer unit, and the microcomputer unit (20) includes a steering torque detection means (
21), detection signals 51-33 from the steering rotation detection means (22) and the current detection circuit (23) are inputted through the A/D converter (24) according to instructions from the microcomputer.

The steering torque detection means (21) divides the frequency of the reference clock pulse TI of the steering torque sensor (lO) and the microcomputer unit, converts it into an alternating current signal, and supplies it to the primary winding of the differential transformer. It consists of a steering torque interface circuit (25) that rectifies and smoothes the output from the secondary winding of the transformer, and outputs a steering torque detection signal Sl indicating the direction and magnitude of the steering torque.

The steering rotation detection means (22) includes a steering rotation sensor (7).
) and a steering rotation interface (26) that converts and amplifies the output from the DC generator (8) of the steering rotation sensor (7) into an absolute value according to the polarity, and determines the steering rotation direction of the steering system. A steering rotation detection signal S2 indicating the steering speed is output.

Microcomputer φ22) (20) If I10
It is composed of a board, memory, arithmetic unit, control unit, registers, clock generator, etc., and operates based on Glock pulses. microcomputer unit) (
20), etc., the power supply circuit (13) that drives the in-vehicle battery (29) has a fuse circuit (30) and a relay circuit (32) connected to the key switch (31) of the ignition key. and a constant voltage circuit (33) connected to the input side of this relay circuit (32). ),
A microcomputer unit (20) and each detection means (
21), (22) and other interface circuits (25, 213). Therefore, when the key switch (31) is turned on, the microcomputer unit (20) sends each detection signal SI"S3 based on the command.
is digitally converted by the A/D converter (24), processed according to the old program stored in the memory, and outputs control signals T3 and T4 for driving the electric motor (11) to the electric motor drive circuit (34). (11) Drive control.

The motor drive circuit (34) includes a bridge circuit consisting of FETs (field effect transistors) (35, 36, 37, 38) and control signals T:1.1 from the microcomputer unit (20). It is composed of an interface circuit (39) that drives a bridge circuit by T4. In the bridge circuit, the respective drain terminals of FET (35) and (a8) are connected to the B terminal of the power supply circuit (13), while their source terminals are connected to the other FET (
38) and (37), respectively. The source terminals of FE T (3El) and (37) are each connected to the common side through a resistor (R) and connected to the battery (29).
) is connected to one terminal of the FET (35, 36, 3
7, 38) are connected to the output side of the interface circuit (39), and the source terminal of the FET (35) which is the output side of the bridge circuit and the FET (3
The interface circuit (39), whose source terminal (8) is connected to the armature winding of the motor a (11), receives the motor rotation direction control signal from the microcomputer φ22 (20). Based on T3, F E T (3
At the same time as turning on the FET (37), drive the FET (37) based on the motor drive signal T4 consisting of a PWM signal, or drive the FET (37) using the control signal T3. 38) is turned on, the FET (3B) is enabled to drive, and P
Based on the motor drive signal T4 consisting of the WM signal
Drive T (36). Therefore, in the motor drive circuit (30), one FET (35) is turned on and FET (37) is turned on, or the other FET (38) is turned on and FET (38) is turned on and FET (37) is turned on.
e)+7) P By WM drive, the electric motor a(11) receives the control signal T3. The rotation direction and its power (rotation speed and torque) are controlled according to T4.

In addition, in this example, the control bag! (12) Abnormality detection means for detecting the abnormality is provided. This abnormality detection means includes a current detection circuit (2) that detects the current flowing through the resistor (R).
3), whose output S3 is input through the A/D converter (24), and in the event of an abnormality, a relay control signal T2 is sent to the relay circuit (32) of the power supply circuit (13) to the microcomputer control unit. (20) and stops the supply of power from the power supply circuit (13).

Next, the effect will be explained.

m 5 Figure 1f Microcomputer Units) (20
) is a flowchart showing an outline of the motor control process in FIG.

When the key switch (31) of the ignition key is turned on, power is supplied to the microcomputer unit (20) and other circuits, and control is started (step Pa). First, the microcomputer unit) (2
0) Internally, set the I10 port, clear the data in each register and RAM, and initialize (P
+), then in step P2, initial failure diagnosis is performed,
The reading of the input signal from the A/D converter (24) is stopped and the internal circuit is checked. If there is an abnormality, the operation of the control bag 21 (12) is immediately stopped, and if there is no abnormality, the 1/- circuit ( 32) to drive the motor drive circuit (34
), and further diagnoses whether the detection signal S3 from the current detection circuit (23) is zero, and if it is not zero, it is determined that there is an abnormality and the relay circuit (32) is stopped. - Stop the control, and if it is zero, read the steering torque detection signal S1 in the next step P3, and then read the steering torque detection signal S1.
1, calculate the direction and magnitude of the steering torque, set a torque direction flag indicating the direction of torque action, and convert the magnitude to an absolute value T and store it (P+).Next, in step P5, a failure is detected. Diagnosis is performed, and if it is abnormal, the relay circuit (32) stops the drive in the same way as above, and if it is normal, it is determined in step P6 whether the absolute value T of the torque is smaller than a preset predetermined value a. , T≦
In case a, it is assumed that no steering torque is applied to the steering wheel (2), and a zero flag F1 indicating this is set.
(P7) If L, T>a, the flag is not set and the process proceeds to step P8.

In step P8, the steering rotation detection signal S2 is read, and in step P9, the steering rotation direction and the magnitude of its rotation speed are calculated, and a rotation direction flag indicating one rotation direction is set and the magnitude thereof is converted into an absolute value N. memorize it. Then, in step PIG, a failure diagnosis is performed in the same manner as above, and if normal, it is determined whether the steering rotation speed N is larger than a preset value at step pH, and if N≧b, Assuming that the steering system is being rotated, set the rotation flag F2 indicating this state) (PI3
)L, Nib, the rotation flag is not set and the process proceeds to step P+3. In step P13, it is determined whether both the zero flag F1 and the rotation flag F2 are set.

In step PI3, unless both flags Fl and F2 are set, the process proceeds to step PI4, the previous value NO of the rotational speed is zero, and the process proceeds to step P15.In step P15, the process proceeds to step P15. The rotation control direction of the electric motor (11) is determined from the torque direction flag of the steering torque at step P16, and the electric motor control duty is determined based on the absolute value T of the steering torque and the absolute value N of the steering rotation at step P8. Decide, step PI7
The motor control signal T3. is sent from the microphone computer O unit (20) to the interface circuit (39). T
4 (T3: rotation direction signal, T4: drive signal) is output, and this control signal T3. Bridge circuit FET (35) by interface circuit (39) based on T4
, 3B, 37, 38) to control the electric motor (11). That is, the torque direction flag of the steering torque and the rotation direction flag of the steering rotation are used to control the F E of the electric motor drive circuit (34) during forward operation of the steering system.
Turn on T (35) and give motor control duty to FET (37), or turn on FET (3B
) is turned on and a motor control duty is given to FET (H), and the electric motor (11) is controlled by PWM drive. On the other hand, when returning the steering system, F E
T (35) is given a component of the motor control duty that corresponds to the steering rotation speed, and FET (37) is given a component of the motor control duty that corresponds to the absolute value of the steering torque, or FET (38) By applying similar signals to and (3B), the electric motor (11) is driven and controlled. In this case, the FET to be driven is, for example, FET, depending on the rotation control direction determined in step PI5.
E T (35) and (37), F E T (3B) and (36) are determined. Then, the torque generated by the electric motor (11) is transmitted to the output shaft (4) via the timing belt (14), thereby reducing the steering force.

Next, in step FIB, the signal output to the FET of the bridge is converted into a DC voltage by the current detection circuit (23) and read, the armature current is calculated in step pH, and in step P20, the armature current is changed to the above-mentioned steering voltage. It is checked whether the torque is within a set range corresponding to the absolute value of the torque, and if it is not within the range, it is determined that there is an abnormality and the relay circuit (32) is turned off and control is stopped. For example, a fault diagnosis is performed at step P3.

In addition, in step P13 above, if both are set, the steering wheel (2) is rotating without any steering torque being applied to it, so when the steering wheel (2) is released, the reaction force of the tires is applied. Assuming that the steering system has been returned, step P2
1, that is, in step 7 PI3. 6th
It is determined that the steering system is in a state where the steering system has returned to its original state, resulting in the characteristics shown in FIG. 3(B).

In step P21, the current value N of the steering rotation speed is changed to the previous value N.
O is subtracted, and this difference is set as the change ΔN in the rotational speed. In step P22, it is determined whether the change ΔN is zero, positive, or negative.

In other words, when ΔN≧0, the steering rotational speed is increasing or remains constant, so the steering wheel (2) is released at the steering angle α, as shown by O to t1 in FIG. 6(B). The range in which you are trying to return to the middle position, and the range from t2 to tff
, t4-t5. This is ignored as it is within the range of t6 to t7, and the current value N is set to the previous value No of the rotation speed at step P2°, and the process returns to step P15. On the other hand,
When ΔN<0, the steering rotation speed is decreasing, so in FIG. 6(B), tl"tz, t3 to t4.t5
~ts, t7 to t8, the process proceeds to step P24 to brake the electric motor (11), and outputs the motor braking control signal Ts. In other words, in this embodiment, even when the steering wheel is returned to the middle position without hands, the steering speed to return to the middle position decreases from the maximum to zero, as shown by the curve m in FIG. 6(B). is detected and the electric motor (11) is braked in each of these ranges, and in step P24, as shown in FIG.
At such time, the motor braking control signal T5 is outputted as shown in FIG. 6(C), and the previous value NO is set to zero in step P25, and the process returns to step P3.

Note that, as in this embodiment, if the electric motor (11) is not braked only in the range where the steering speed decreases, and, for example, a state in which the steering wheel (2) is released and returned is detected, the state shown in FIG.
) at any point in the cycle T2, or in the range 0-1. The electric motor (11
) may be braked, and further the change is ΔN=
Braking may be performed at the intermediate position by detecting that the position is O.

Then, when the motor braking control signal T5 is output from the microcomputer unit (20) in step P24, the interface circuit (39) turns on the FETs (38) and (37) of the bridge circuit, and turns on the motor. (11) Short-circuit the armature winding. Therefore, in the electric motor (11), due to the back electromotive force generated by its own rotation, a braking flow M flows in the armature winding in a direction according to the rotation direction, as shown in FIG. 6 (D). , self-braking. As a result, when the steering system is returned to its original position, the electric motor (11) is self-braked at the middle position between the first and second vibrations of the steering system, as shown by T3 in FIG. The convergence time T3 of the system can be significantly shortened compared to manual steering, and the inertia of the electric motor can be reliably prevented.

(Effects of the Invention) As explained above, according to the present invention, when the steering wheel is released and returned, the electric motor is electrically braked to bring the steering system in the returned state to the intermediate position for a short period of time. It can be converged quickly and stable return characteristics of the steering system can be obtained. In addition, in the above embodiment, since the electric motor can be reliably braked at the middle position of the vibration of the steering system, the influence of the inertia of the electric motor can be removed, the convergence time can be greatly shortened, and good return characteristics of the steering system can be achieved. Obtainable.

[Brief explanation of drawings]

FIGS. 1 and 2 are overall configuration diagrams of the present invention, FIGS. 3 to 5, and FIGS. 6 (G), (D), and (E) relate to one embodiment of the present invention, and FIG. 4 is a block configuration diagram of the control head; FIG. 5 is a flowchart illustrating the outline of control processing; Figure 56 (C), CD) and (E ) are explanatory diagrams showing the electric motor braking Mj control signal, electric motor braking electric control signal, and convergence characteristics, respectively. Figures 6 (A) and (B) relate to the conventional example, and Figure 6 (A) shows the convergence characteristics of manual steering. FIG. 6(B) is a diagram showing the convergence characteristics of the electric power steering device. In the drawings (3) and (4) are input and output shafts, (11) is an electric motor, (20) is a microcomputer unit,
(21) is a steering torque detection means, (22) is a steering rotation detection means, and (34) is an electric motor drive means.

Claims (2)

[Claims] (1) In an electric power steering device that applies power from an electric motor to a steering system to reduce steering force, there is a hand-held return state detection means for detecting that the steering system is returned in a hand-off state, and this hand-held return state detection means. An electric power steering device comprising: electric motor braking means for braking the electric motor based on a detection signal from a state detecting means. (2) The above-mentioned hand-off return state detection means includes a zero torque rotation detection means that detects that the steering torque of the steering system is below a predetermined value and the steering rotation speed is above a predetermined value, and a zero torque rotation detection means that detects that the steering rotation speed is reduced. 2. The electric power steering apparatus according to claim 1, further comprising a steering rotation reduction detection means for detecting a decrease in steering rotation, and wherein the electric motor is braked by the motor braking means based on detection signals from both of these detection means.