JPH0639262B2 - Electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric power steering apparatus that reduces the steering force by applying the power of an electric motor to a steering system.

(Prior Art) In a conventional electric power steering apparatus, electric power of an electric motor is applied to a steering system through a speed reducer such as a gear mechanism or a ball screw mechanism to reduce a steering force.
In addition, since the electric power steering apparatus has friction elements such as electric motors and reduction gears in addition to the friction elements such as many bearings in the steering system itself, smooth operation, improvement in durable life, and prevention of Due to rust and the like, a lubricating member such as grease is injected into each friction element. Then, when controlling the electric motor, in order to prevent deterioration of the steering feeling of the steering system due to the friction element, the torque control signal among the control signals for controlling the electric power of the electric motor is divided into a road surface load component and a friction component, By adding these components, it is possible to control the electric motor to cope with the friction of the device, and it is possible to adjust the friction component of the torque control signal from the outside according to the user's preference to improve the steering feeling. I am trying to

(Problems to be Solved by the Invention) However, in the above-described conventional electric power steering apparatus, there is a problem that the viscosity of the lubricating oil injected into the friction element changes with the temperature change. That is,
Generally, the viscosity of the lubricating oil is high in the low temperature range and low in the high temperature range. Therefore, when the vehicle runs in the low temperature range, the friction increases and the friction component of the torque control signal becomes insufficient, resulting in a steering system. The start of turning is felt heavy, while the friction is reduced when traveling in a high temperature region, and the friction component of the torque control signal is excessively large, which may make the steering system unresponsive.

(Object of the Invention) Therefore, in the present invention, the temperature of the lubricating oil in the device is detected, and the temperature correction value is set based on the detected temperature so as to compensate the friction component of the torque control signal corresponding to the temperature change of the lubricating oil. It is an object of the present invention to provide an electric power steering apparatus which determines the steering feeling variation with respect to the temperature change of the lubricating oil in the apparatus and can obtain a light steering feeling.

(Means for Solving Problems and Their Actions) FIG. 1 is an overall configuration diagram of the present invention. As shown in FIG. 1, the electric power steering apparatus of the present invention is a steering torque detecting means for detecting the steering torque of the steering system.
(1), temperature detection means to detect the temperature of the lubricating oil in the device
(2), based on the detection signal from the temperature detecting means (2), a motor control signal generating means (4) for determining a motor control signal for compensating for a change in steering system friction corresponding to a change in lubricating oil temperature. ) And an electric motor drive means (5) for driving and controlling the electric motor (41) by the electric motor control signal from the electric motor control signal generating means (4).

This electric power steering device can compensate for a change in the temperature of the lubricating oil in the device, that is, a change in friction due to a change in the viscosity of the lubricating oil in the device, and the electric motor is controlled without being affected by the change in the viscosity of the lubricating oil. As a result, it is possible to reduce the variation in the steering feeling due to the temperature change of the lubricating oil.

(Embodiment) An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a vertical sectional view showing the electric power steering device. In FIG. 2, (6) is a pinion shaft, and the pinion shaft (6) is coaxial with the first shafts (6).
A) and the second shaft (6B) are divided, and the inner end of the first shaft (6A) is a bearing
By (7), it is supported in the inner end of the second shaft (6B). These inner ends are connected by a torsion bar (8) so that they can rotate relative to each other to a certain extent, but further rotate integrally. Also pinion shaft (6)
Is supported by bearings (10), (11) and (12) on a pinion holder (14) integrally provided on the rack case (13).
A pinion gear (6c) is formed on the second shaft (6B), and this pinion gear (6c) meshes with rack teeth (15a) formed on the back surface of the rack shaft (15), and Converts rotation into linear motion of the rack axis (15). The pinion shaft (6) is connected to the steering wheel via a universal joint (not shown) and the steering shaft, and the rack shaft (15) is connected to a knuckle that rotatably supports the wheels via a tie rod (not shown) to rotate the steering wheel. Is converted into the swinging motion of the wheels to enable steering of the vehicle. A steering rotation sensor (16) and a steering torque sensor (20) are provided around the pinion shaft (6). On the other end side of the rack teeth (15a) of the rack shaft (15), a ball screw mechanism (30) and a large diameter toothed pulley (40),
A timing belt (43) and an electric motor (41) with a small-diameter toothed pulley (42) mounted on the shaft are provided.The rotation of the electric motor (41) is controlled by the pulley (42), the timing belt (43), and the pulley. (40)
To the ball screw mechanism (30) via the ball screw mechanism (30) to reduce the rotation of the electric motor (41) and
It is transmitted to (15) and converted into linear motion of the rack shaft (15).
Incidentally, (9) in the figure is a seal member.

More specifically, the steering rotation sensor (16) is a pinion shaft.
It is composed of a DC generator (17) fixed to the pinion holder (14) so that the rotation axis is orthogonal to the first shaft (6A) of (6),
A bevel gear (19) that meshes with a bevel gear (18) pivotally attached to the first shaft (6A) is pivotally attached to the rotating shaft, and the generator (17) is rotated along with the rotation of the pinion shaft (6). ) Rotates, and the polarity (+,-) according to the rotation direction of the pinion shaft (6) and the DC voltage according to the rotation speed are output to the control device (26).

The steering torque sensor (20) is the first shaft of the pinion shaft (6).
(6A) and the second shaft (6B) are fitted to the outer periphery of the fitting portion of the movable core (21) made of a magnetic material so as to be displaceable in the axial direction, and the differential transformer (22) fixed in the pinion holder (14). ) And.
Grooves (21a, 21a) parallel to the axial direction are formed 180 degrees apart on the side surface of the movable iron core (21), and each groove (21a, 21a) is separated by 90 degrees from the axial direction. There are formed slanted grooves (21b, 21b) having a constant angle with respect to. Furthermore, the first axis
(6A) has pins (23a) respectively engaged with the parallel grooves (21a, 21a).
a, 23a) are integrally provided, and the slanted grooves (21b, 21b) are also provided.
The pins (23b, 23b) that engage with each other are integrally provided. Therefore, the movable iron core (21) includes the first shaft (6A) and the second shaft (6A).
Displaces in the axial direction due to relative rotation with B).

The differential transformer (22) is composed of a primary coil (22a) and secondary coils (22b) and (22c), and the primary coil (22a) has an AC pulse generated by a control device (26). Signal is applied, 2
Analog pulse electric signals are differentially output from the following coils (22b) and (22c). Then, the output signals of the secondary coils (22b) and (22c) change according to the displacement direction and the displacement amount of the movable iron core (21). Therefore, the steering torque sensor (20) determines the magnitude of the steering torque and its action. The direction is detected. In the figure, (24) is a coil spring that biases the movable iron core (21).

The rack shaft (15) is swingably and axially supported by the rack case (13) by a bearing (27) and a spherical bearing (28). A ball screw groove (15b) is formed on the outer periphery of the rack shaft (15), and a similar screw groove is mounted on the ball screw groove (15b).
A plurality of balls (32) are fitted between the ball nut (311 and the ball screw groove (15b) having (31a) on the inner peripheral surface thereof, and the space between the screw grooves (15b) and (31a) is increased. Rolling the ball nut
The circulation path provided in (31) is obtained to circulate, and the thread groove (15b),
A ball screw mechanism (30) is configured by the (31a), the ball (32), and the ball nut (31). Therefore, the rotation of the ball nut (31) smoothly moves through the balls (32) to the rack shaft (1
5) is converted into linear motion. The ball nut (31) is connected to the pulley case A (35) from both ends through elastic members (33) and (34).
It is elastically engaged by being sandwiched between A) and the pulley case B (35B). Pulley cases A, B (35A), (35
B) is rotatably supported by the rack case (13) by the angular contact bearings (36) and (37). A large diameter pulley (40) is integrally provided on the outer circumference of the pulley case A (35A), and a small diameter pulley of the electric motor (41) controlled by the control device (26).
The rotation of the electric motor (41) through the timing belt (43) wound between the large diameter pulley (40) and the ball screw mechanism (42).
It is transmitted to the rack shaft (15) through (30).

Furthermore, the ball screw mechanism (30), the pulleys (40, 42) and the timing belt (43) form the pulley case (35) described above.
A, 35B) and the pulley cases (35C) and (35D) that are integrally fixed to the rack case (13), and are covered with the temperature on the inner wall surface of the pulley case (35C) in this embodiment. A sensor (44) is provided. In this embodiment, the temperature sensor (44) uses a thermistor whose resistance value changes according to the temperature change, and detects the temperature inside the case, that is, the temperature of the lubricating oil. As is well known, the temperature inside the case is detected as a voltage characteristic that decreases with an increase in temperature due to the characteristic of the thermistor.

Next, the control device (26) will be described.

FIG. 3 shows an example of the control device (26). In the figure, (4
9) is an A / D converter, and (50) is a microcomputer unit. The microcomputer unit (50) is provided with steering torque detecting means (1), temperature detecting means (2) and steering rotation detecting means (3). The respective detection signals S _{1 to} S ₅ are input through the A / D converter (49) according to the instruction of the microcomputer unit (50).

The steering torque detecting means (1) is a steering torque sensor (20).
And the differential clock (22) by dividing the reference clock pulse T ₁ from the microcomputer unit (50) and converting it to an AC signal.
Supply to the primary coil (22a) of the differential transformer (22)
And a steering torque interface circuit (46) for rectifying and smoothing the output from the secondary coils (22b, 22c) of the steering coil, and outputs steering torque detection signals S ₁ and S ₂ indicating the operating direction and the magnitude of the steering torque. Output.

The steering rotation detection means (3) is a steering rotation sensor (16),
A steering rotation / interface circuit that amplifies the output from the DC generator (17) of the steering rotation sensor (6) according to the polarity.
(48) and outputs steering rotation speed signals S ₃ and S ₄ indicating the steering rotation direction and steering speed of the steering system.

The temperature detection means (2) is composed of a temperature / interface circuit (47) including a resistance bridge circuit including the temperature sensor (44) and an amplifier circuit for amplifying the output of the bridge circuit, and the temperature sensor ( The bridge equilibrium is broken due to the resistance change in (44), and the voltage difference at this time is output as the detection signal S ₅ of the temperature θ.

The microcomputer unit (50) is composed of an I / O port, a memory, an arithmetic unit, a control unit, each register, a clock generator, etc., and operates based on a clock pulse. The power supply circuit (52) for driving the microcomputer unit (50), etc., is connected to the + terminal of the vehicle-mounted battery (51) via the fuse circuit and the key switch of the ignition key, and the output side of this circuit. It is composed of a relay circuit and a constant voltage circuit to be connected, and supplies power from an output B terminal to a motor driving means (5) described later, and an output A terminal of the constant voltage circuit supplies a microcomputer unit (50) and each Power is supplied to the detection means (1), (2), (3), etc. Therefore, when the key switch is turned on, the microcomputer unit (50) is a respective detection signals S ₁ to S ₅ on the basis of the instructions digitally converted by the A / D converter (49), processed in accordance with a program written in the memory Then
Output the motor control signals T ₃ and T ₄ to the motor drive means (5),
Drive and control the electric motor (41). The motor control signal determining means (4) shown in FIG. 1 is composed of an A / D converter (49) and a microcomputer unit (50).

The electric motor driving means (5) is composed of a bridge circuit composed of FETs (field effect transistors) and an interface circuit for driving the bridge circuit by control signals T ₃ and T ₄ from the microcomputer unit (50). Then, in the motor driving means (5), one interface FET is turned on and the other FET is turned on by the interface circuit, or the other FET is turned on, or one FET is turned on. By the PWM driving of the other FET, the electric motor (41) controls the rotation direction and its power (rotation speed and torque) according to the control signals T ₃ and T ₄ .

Next, the operation will be described.

FIG. 4 is a flowchart showing an outline of electric motor control processing in the microcomputer unit (50).
P _{1 to} P ₁₉ show steps of the flowchart.

When the key switch of the ignition key is turned on, power is supplied to the microcomputer unit (50) and other circuits to start control (step P ₀ ). First,
I / O inside the microcomputer unit (50)
Set the port, clear each register and data in RAM to initialize (P ₁ ). Then read the steering torque detection signal S _1, S ₂ in Step P _2, these detection signals S _1,
The acting direction and the magnitude of the steering torque are calculated from S _2, and a set of the torque direction flag indicating the acting direction of the torque and the magnitude thereof are converted into an absolute value T and stored (P ₃ , P ₄ ). Next, in step P ₅ , the road surface load component control signal determining means (4A) of the electric motor control signal generating means (4) is provided with a memory such as a ROM, and this memory has a preset absolute value T of the steering torque and road surface load component. It reads the corresponding data of the control signal D _L (T) (table 1), and outputs the road load amount control signal D _L (T). Table 1
Stores the road surface load component control signal D _L (T) of the torque control signals corresponding to the absolute value T of the steering torque as shown in FIG.

Next, in step P ₆ , the temperature detection signal S ₅ is read, and in step P ₇ , the temperature correction value determination means (4B) of the motor control signal generation means (4) is provided with a memory such as a ROM and is preset in this memory. The corresponding data (Table 2) of the temperature θ corresponding to the detected signal S ₅ and the friction temperature correction value D _F (θ) is read out, and the temperature correction value D _F (θ) is output. Table 2 shows the temperature correction value D corresponding to the temperature θ as shown by the solid line in FIG.
_{Stores F} (θ). The correction value D _F (θ) is a duty value corresponding to a temperature change in consideration of the friction of the device. That is, the friction of the device is obtained by combining the viscous drag component due to the viscosity of the lubricating oil, which changes so as to become smaller at high temperature, as shown by the chain double-dashed line in FIG. 6, and the substantially constant mechanical friction loss component. It is considered that the friction as a whole has the temperature characteristic as shown by the solid line in FIG. Therefore, as shown by the solid line in FIG. 6, the correction value D _F (θ) has a temperature-versus-temperature characteristic that decreases as the temperature rises and conversely increases as the temperature lowers. It is set to compensate for the fluctuation of friction and maintain a constant steering feeling.

In step P _8, road load component control signal D _L (T) is either equal to or less than a predetermined value a, i.e. whether D _L (T) ≦ a or not. The predetermined value a indicates the dead zone in the friction control signal as shown in FIG. If D _L (T) ≧ a, it is not in the region a, so in step P ₉ , the operation of D _F (θ) + D _L (T) is performed and this is designated as D (T). Therefore, the duty ratio of the torque control signal D (T) is excessively reduced as the temperature θ increases, while it is excessively increased as the temperature θ decreases. When D _L (T) <a, it is within the area a, so the road surface load component control signal D _L (T)
Becomes zero, and in order to maintain the dead zone, D _F in step P ₁₀
(Theta) = 0 and then, the process proceeds to step P _9, is not performed addition of the correction value corresponding to the temperature theta step P ₉ D _F (θ).

In Step P ₁₁ , the steering rotation speed detection signals S ₃ and S ₄ are read,
The acting direction and magnitude of the steering rotation from these detection signals S _3, S ₄ calculates and stores a set and its magnitude of the rotational direction flag indicating the direction of action of the rotation is converted into an absolute value N (P ₁₂ , P ₁₃ ). Next, in step P ₁₄ , the contents of the memory whose address is the absolute value N of the steering speed are called from the table 3. The table 3 stores the steering rotation control signal D (N) corresponding to the absolute value N of the steering rotation speed shown in FIG.

In step P _15, the forward operation at the time of the steering system by the torque direction flag and the rotational direction flag,
It is determined whether it is the return operation. In step P ₁₆ in the case at the time of forward _{operation, D D = D (T)} + D (N), and D _u = 1, in the case when the return operation in step _{P 17 D D = D (T} ), D _u = 1-D (N)
And These D _D and D _u are duty values that are the contents of the control signal T ₄ that determines the power of the electric motor (41). For example, D _D is one of a pair of FETs in the bridge, and D _u is the other. They are given and both are PWM signals. Also, step P ₁₈
Then, the rotation directions R and L are determined by the torque direction flag. These R and L are symbols indicating the rotation direction of the control signal T ₃ that determines the rotation direction of the electric motor (41), for example, R indicates right rotation and L indicates left rotation. Then, in step P ₁₉ ,
Control signal T ₃ consisting of R and L and control signal consisting of D _D and D _u
And outputs the T _4, the process returns to step P _2, repeats the series of processing.

Therefore, the amount of friction constituting the torque control signal of the electric motor control signal is set in consideration of the temperature correction value in advance regardless of the steering torque component, and when the temperature correction value decreases as the temperature increases, the temperature decreases. Since the setting is made to increase, the influence of the viscosity of the lubricating oil that fluctuates due to the temperature change is reduced, and the deterioration of the steering feeling due to the temperature change can be reduced.

In this embodiment, the steering rotation detecting means is added and the electric motor control signal is formed by using the steering rotation control signal. However, the present invention is not limited to this, and the electric motor control signal is generated by at least the steering torque detecting means and the temperature detecting means. It can also be formed.

(Effects of the Invention) As described above, according to the present invention, the friction component of the motor control signal is set to the temperature correction value D corresponding to the temperature change.
By setting to _F (θ), the influence of the viscous resistance of the lubricating oil that fluctuates with the temperature change of the lubricating oil inside the device is compensated, so the deterioration of the steering feeling due to temperature change is prevented and the temperature of the device is reduced. It is possible to obtain a steering feeling that is not affected by.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the present invention, FIGS. 2 to 7 show an embodiment of the present invention, FIG. 2 is a vertical sectional view of an electric power steering device, and FIG. 3 is a control device thereof. FIG. 4 is a block diagram, FIG. 4 is a flow chart showing an outline of control processing, and FIGS. 5, 6, and 7 are characteristic diagrams for explaining each operation of the microcomputer unit.

Claims (1)

[Claims] 1. An electric power steering system for reducing steering force by applying power of an electric motor to a steering system, wherein steering torque detecting means for detecting steering torque of the steering system and temperature of lubricating oil in the system are controlled. A temperature control means for detecting and a motor control signal based on the detection signal from each detection means so as to compensate the change in the friction of the steering system corresponding to the temperature change of the lubricating oil based on the detection signal from the temperature detection means. An electric power steering apparatus comprising: an electric motor control signal generating means for determining the electric motor control signal; and an electric motor drive means for driving and controlling the electric motor according to the electric motor control signal from the electric motor control signal generating means.