JPH0834359A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE:To prevent the overload electric current of a motor by operating a steering rotary speed by means of a steering rotary speed operating means provided at a control means by using the detection outcomes of a motor electric current detecting means and a motor voltage detecting means. CONSTITUTION:A steering rotary speed operating means 24 is inputted with motor detection voltage VMD detected by means of a motor voltage detecting means 21; a motor detection electric current IMD detected by means of a motor electric current detecting means 22; and a steering torque signal T detected by means of a steering torque sensor 13. A motor rotational speed operating means 27 calculates a motor rotational speed NM on the basis of the motor detection voltage VMD and the motor detection electric current IMD. The differential processing of the detected steering torque T is conducted by means of a steering torque differential means 26, and the multiplication processing of the reciprocal 1/KT of a spring coefficient memorized at a spring coefficient memorizing means 28 is conducted by means of a multiplication processing means 29, and its outcome is fed to a steering rotary speed calculating means (a calculating means) 30. The calculating means 30 operates an operation rotary speed N from the motor rotary speed NM, and feeds it to a target electric current setting means and controls the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering system for reducing the steering force of a driver by directly applying the power of an electric motor as a steering assist force to a steering system.

[0002]

2. Description of the Related Art Generally, an electric power steering system has an electric motor that generates an auxiliary steering force when the steering wheel is operated further even after reaching the rack end. Drive current tends to increase corresponding to the steering torque.

In addition, the tire may hit a curb,
If the tire cannot be steered to the left or right even if it is fitted in a groove or rut and the steering wheel is operated, if the steering wheel is tried to be operated further, the electric current of the electric motor increases with an increase in steering torque. To do.

A conventional electric power steering system is disclosed in Japanese Patent Application Laid-Open No. 64-9064 disclosed by the present applicant, in which a steering torque sensor (for example, a differential transformer) and a steering rotation speed sensor (for example, a tacho generator). ) And a microprocessor, the electric motor is activated when the torque signal from the steering torque sensor exceeds a predetermined value and the steering rotation speed (steering speed) from the steering rotation speed sensor is below a predetermined value. It is configured to reduce the driving current.

FIG. 6 shows an overall configuration of a conventional general electric power steering apparatus. The electric power steering apparatus 1 includes a rack and pinion mechanism provided in a steering gear box 5 via a connecting shaft 4 having universal joints 4a and 4b on a steering shaft 3 integrally provided on a steering wheel 2. The manual steering force generation means 7 is configured by being connected to the pinion 6a of the steering wheel 6.

The rack shaft 8 is provided with rack teeth 8a that mesh with the pinion 6a, and reciprocates by these meshes.
Are connected to left and right front wheels 10 as rolling wheels via tie rods 9 at both ends thereof. In this way, when steering the steering wheel 2, the front wheels 10 are rolled to change the direction of the vehicle through the normal rack-and-pinion type steering.

In order to reduce the steering force by the manual steering force generating means 7, a motor 11 for supplying a steering assist force is arranged coaxially with the rack shaft 8, and a ball screw mechanism provided substantially parallel to the rack shaft 8. The steering assist force is converted into a thrust force via 12 to act on the rack shaft 8.

The rotor of the electric motor 11 has a helical drive side.
The gear 11a is integrally provided, and the drive-side helical gear 11a is meshed with the driven-side helical gear 12a that is integrally provided at the shaft end of the screw shaft of the ball screw mechanism 12. The nut of the ball screw mechanism 12 is connected to the rack shaft 8.

In the steering gear box 5, a steering torque sensor 13 for detecting a manual torque acting on the pinion 6a, and a steering rotation speed sensor for detecting a steering rotation speed corresponding to the rotation speed of the steering shaft 3. 14 are provided respectively, and the steering torque signal T and the steering rotation speed signal N are provided to the control means 15.

A steering wheel 2 and a front wheel 10 which is a steered wheel are mechanically connected to each other, and a steering torque signal T detected by a steering torque sensor 13 and a steering rotation speed signal N detected by a steering rotation speed sensor 14 are provided. A motor control voltage V _O (for example, a PWM signal) obtained by processing the combined signal by the control unit 15 generates a motor voltage V _M through the motor driving unit 16 (for example, a bridge circuit using FET). The electric motor 11 is PWM-driven to obtain a steering assist force corresponding to the operation of the steering wheel 2.

The control means 15 is composed of a microprocessor and is provided with an overload prevention means. The steering torque signal T detected by the steering torque sensor 13 exceeds a predetermined value and the steering rotation speed signal detected by the steering rotation speed sensor 14 is detected. When N is equal to or less than a predetermined value, the reduced-corrected motor control voltage V _O is output to the motor drive means 16, and the motor drive means 16 uses the motor voltage V _M to reduce the motor current I _M.
To prevent an overload current of the electric motor 11.

As described above, the conventional electric power steering apparatus is provided with the independent steering torque sensor and the steering rotation speed sensor, and the tire cannot hit the curb or the groove or the rut to prevent steering. In the steering operation in this state, the overload current of the electric motor that applies the steering assist force to the steering system is controlled to be decreased by detecting that the steering torque is high and the steering rotation speed is low.

[0013]

The conventional electric power steering system has two independent sensors for detecting an overload state of a motor, a differential transformer (steering torque sensor) and a tacho generator (steering rotational speed). Since the sensor is required, the space occupied by the sensor becomes large, which limits the degree of freedom in designing the vehicle interior and raises the cost.

In particular, unlike the steering torque sensor which is also used for other functions, the steering rotation speed sensor is rarely used for other functions other than the overload state detection, so it is desirable to delete it. .

The present invention has been made to solve the above problems, and its purpose is to construct a steering rotation speed detecting means by diverting an existing sensor installed therein, and to provide a function of preventing an overload current of a motor. An object of the present invention is to provide a compact and economical electric power steering device.

[0016]

Means for Solving the Problems In order to solve the above-mentioned problems, a steering rotation speed detecting means of an electric power steering apparatus according to the present invention comprises a motor current detecting means for detecting a motor current and a motor voltage detecting means for detecting a motor voltage. In addition to the above, the control section is provided with steering rotation speed calculation means for calculating the steering rotation speed based on signals from the electric motor current detection means and the electric motor voltage detection means.

[0017]

The electric power steering apparatus according to the present invention is provided with the steering rotation speed detecting means composed of the electric motor current detecting means, the electric motor voltage detecting means, and the steering rotation speed calculating means provided in the control means, and is independent of the steering rotation speed sensor. Instead, since the steering rotation speed can be calculated, the overcurrent of the electric motor can be prevented based on the steering rotation speed and the steering torque detected by the steering torque sensor.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an essential part of an electric power steering apparatus according to the present invention. In FIG.
The electric power steering apparatus 1 includes a steering torque sensor 13 that detects a steering torque of a steering system and a control unit 2.
0, an electric motor voltage detecting means 21 for detecting an electric motor voltage V _M for driving the electric motor 11, an electric motor current detecting means 22 for detecting an electric motor current I _M flowing in the electric motor 11, an electric motor driving means 16, and an electric motor 11.

The control means 20 is basically composed of a microprocessor and comprises a target current setting means 23, a steering rotation speed calculation means 24, and a drive control means 25.

The target current setting means 23 has a memory such as a ROM, and is preset based on design values and experimental values.
The steering torque T with the steering rotation speed N shown in FIG.
Of the target current I _MS characteristic for the target current data is stored, and the corresponding target current data is selected based on the steering torque signal T from the steering torque sensor 13 and the steering rotation speed signal N calculated by the steering rotation speed detection means 17, The current I _MS is provided to the drive control means 25.

The target current I _MS characteristic with respect to the steering torque T shown in FIG. 4 is P1 of the target current I _MS which increases corresponding to the steering torque T when the steering rotation speed N exceeds a predetermined value N _K.
When the steering torque T is equal to or _larger than a predetermined value T _K and the steering rotation speed N is equal to or _smaller than a predetermined value N _K , the steering rotation speed N has a value (= N _K >...> N _M > N _O ). Of the target current I _MS that decreases corresponding to each of the above.

The steering speed calculating means 24 is composed of a hard various arithmetic means and soft computing programs, the motor voltage detection means 21 detects the motor detected voltage V _MD (= motor voltage V _M), the motor current detecting means 22 Calculates the steering rotation speed N based on the motor detection current I _MD (= motor current I _M ) and the steering torque signal T, and supplies the steering rotation speed signal N to the target current setting means 23.

FIG. 2 is a block diagram of the essential portions of the steering rotation speed calculating means of the electric power steering apparatus according to the present invention. In FIG. 2, the steering rotation speed calculating means 24 is a steering torque differentiating means 26, an electric motor rotation speed calculating means 27,
The spring coefficient storage means 28, the multiplication processing means 29, and the steering rotation speed calculation means 30 are provided.

Generally, the steering rotation speed N of the electric power steering apparatus can be expressed by the following equation 1. However,
k _T is the spring coefficient, T is the steering torque, N _M is the motor rotation speed.

[0025]

## EQU1 ## N = (1 / k _T ) * dT / dt + N _M

The motor voltage of the motor (armature voltage)
V _M is the motor resistance R _M, the induced voltage coefficient of the motor k,
The motor current is I _{M and} is approximately expressed by Equation 2.

[0027]

[Formula 2] V _M = R _M * I _M + k * N _M

By rearranging the equation 2 with respect to the motor rotation speed N _M and substituting it into the equation 1, the steering rotation speed N can be calculated by the equation 3
Can be obtained from

[0029]

[Number 3] _{N = (1 / k T)} * dT / dt + (V M -R M *
I _M ) / k

The steering torque differentiating means 26 is composed of a differentiating circuit and differentiating software, performs a differentiating process on the torque signal T and outputs the differential signal dT / dt to the multiplying process means 29, and the multiplying process means 29 stores the spring coefficient. Reciprocal of spring coefficient k _T (1 / k _T ) stored in advance in the means 28 (memory such as ROM)
And the differential signal dT / dt are multiplied and the calculation result {(1 / k _T ) * dT / dt} is supplied to the steering rotation speed calculation means 30.

On the other hand, the electric motor rotation speed calculation means 27 has a memory, arithmetic functions such as subtraction and multiplication / division, and the electric motor resistance R _M and the electric motor current detection means 2 stored in advance in the memory.
Motor detection current I _MD from 2 (= motor current I _M), and the electric motor detected voltage V _MD from the motor voltage detection means 21
Based on (= motor voltage V _M ), the motor rotation speed N _M is calculated from Equation 2, and the calculation result N _M is calculated as the steering rotation speed calculation means 3
Supply 0.

The steering rotation speed calculation means 30 calculates the result {(1 / k _T ) * dT / dt} from the multiplication processing means 29.
Then, the motor rotation speed N _M from the motor rotation speed calculation means 27 is added to calculate the steering rotation speed N shown in Formula 3, and the steering rotation speed signal N is provided to the target current setting means 23.

The drive control unit 25 is a current - includes a voltage converter and a pulse width modulator or the like, the target current setting unit 23 motor drives the motor control voltage V _O to the target current I _MS was converted to the PWM control signal supplied from the output to unit 16, configured to PWM control the motor voltage V _M that drives the electric motor 11 from the motor driving means 16.

Incidentally, the steering rotation speed detecting means 17 which replaces the conventionally used steering rotation speed sensor (for example, a tacho generator) includes a motor voltage detecting means 21, a motor current detecting means 22 and a steering rotation speed calculating means 24. Configure.

FIG. 3 is a circuit diagram of an embodiment of the electric motor drive means, the electric motor voltage detection means and the electric motor current detection means, which is generally adopted in an electric power steering apparatus. The motor driving means 16 is an embodiment constituted by a bridge circuit composed of four FETs (field effect transistors) Q1 to Q4, and a DC power source E _O (battery) is applied,
The FETs Q1 to Q4 are PWM-driven by inputting the motor control voltage V _O of FIG. 1 to the gates a to d, and the output ends of the bridge circuit (FETs Q1 and Q2 and FET
Electric motor 11 connected between the sources of Q3 and Q4)
The motor voltage V _M is output to.

[0036] For example, if rotated to the right electric motor 11 (e.g., corresponding to the right steering), on control gate terminal a of FETQ1 by the direction signal of the motor control voltage V _O, PWM signal duty ratio of the motor control voltage V _O Controls the gate terminal d of FET Q4, while the FET
When Q2 and Q3 are turned off, the electric motor current I _M flows in the direction of the arrow, and the electric motor voltage V _M is set to plus (+) on the FET Q1 side and minus (−) on the FET Q4 side.

On the contrary, when the electric motor 11 is rotated counterclockwise (for example, corresponding to the steering to the left), the FETQ is used.
ON control of the gate terminal c of 3 and FETQ2 gate terminal b
By PWM controlling the electric current I _M flowing in the direction opposite to the arrow, the electric motor voltage V _M is set to be positive (+) on the FET Q3 side and negative (-) on the FET Q2 side.

The electric motor voltage detecting means 21 and the electric motor current detecting means 22 are respectively constituted by differential amplifiers OP1 and OP2, and the inter-terminal voltage of the electric motor 11 (motor voltage V _M ),
The potential difference V _D of the motor current I _M flowing through the resistor Rd connected in series with the motor 11 is amplified and detected.

The differential amplifier OP1, OP2 and driven by a power source (DC power source E _O), since the set E _O / 2 in which the virtual ground (bias) is divided by two resistors R, the E _O / 2 As a reference (corresponding to the neutral position of the steering), the linear characteristic of the voltage increasing the steering right direction (motor current I _M , plus side of the motor voltage V _M ) from E _O / 2, the steering left direction (motor current I _M , the negative side of the motor voltage V _M ) is detected as the linear characteristic of the voltage decreasing from E _O / 2.

The motor voltage detecting means 21 controls the motor voltage V _M.
Is amplified by gain (R2 / R1) to detect the motor detection voltage V _MD
(= Motor voltage V _M ) is output and motor current detection means 2
2 is a gain (Rb / Ra) for the potential difference V _D of the motor current I _M
Is amplified and converted into a current by a current converter (not shown) to output a motor detection current I _MD (= motor current I _M ) which is provided to the steering rotation speed calculation means 24 of FIG. The electric motor voltage detection means 21 and the electric motor current detection means 22 are detection means normally used to monitor the state of the electric motor 11.

In this way, the existing motor voltage detecting means 2
1 and electric motor current detection means 22, and steering rotation speed detection means 17 in place of a steering rotation speed sensor such as a tacho generator from the steering rotation speed calculation means 24 provided in the control means 20.
Can be configured.

Further, based on the steering rotation speed signal N detected by the steering rotation speed detecting means 17 and the steering torque signal T detected by the steering torque sensor 13, a target current I _MS for generating a steering assist force necessary for steering. Or the steering torque signal T is equal to or greater than a predetermined value T _K (T ≧ T _K ).
In, the target current I _MS steering torque signal T when the steering speed N is simultaneously satisfy the conditions below a predetermined value N _K (N ≦ N _K)
The steering assist is performed by reducing the value corresponding to only the value, and steering operation after reaching the rack end, or steering operation when the tire hits a curb or is stuck in a groove or rut and cannot be steered. Reduces the overload current of the motor that exerts force on the steering system.

FIG. 5 shows a steering characteristic explanatory diagram of the electric power steering apparatus according to the present invention. In FIG. 5, the characteristics when there is no overload countermeasure function are shown by F1, and the characteristics when there is an overload countermeasure function are shown by F2 and F3. In the F1 characteristic without the overload countermeasure function, when the steering wheel is operated to perform normal steering (normal steering state), the steering torque T and the illustrated steering rotation speed N increase, and along with this, the motor current I. _M also increases, and steering speed N is maintained while maintaining steering wheel operation.
And the motor current I _M is kept constant.

Next, while the steering wheel is being operated, the rack end is reached, the tire hits a curb, etc., or is fitted into a groove or rut (abutting state).
Then, since the tire is not steered even though the steering torque T is increasing, the steering rotation speed N is reduced to near zero. On the other hand, the electric motor current I _M increases in accordance with the steering torque T, and thus reaches the peak in the butting state.

In the abutting state, the tire is not steered even if a large force is applied to the steering wheel operation. Therefore, if the tire is held in a weakened state (holding state), the tire does not steer and the steering rotation speed N is near zero. Since the steering torque T is lower than that in the butting state, the electric motor current I _M is also smaller than the peak value, but the electric current is still large and the large electric motor current I _M is generated when the electric motor 11 is not rotating.
Keep flowing overloaded.

F2 and F with overload countermeasure function of the present invention
In the three characteristics, when the abutting state and the hold state (the steering torque T is a predetermined value or more and the steering rotation speed N is a predetermined value or less), the motor current I _M is reduced and corrected, and the value is equal to or less than the motor current I _M before the abutting ( For example, the F2 characteristic of the correction amount ΔI _M1 ),
In particular, the value is greatly reduced to a value like the F3 characteristic (correction amount Δ
I _M2 ), power loss and motor 1
1 can be prevented from being overloaded.

[0047]

As described above, the electric power steering apparatus according to the present invention includes the steering rotation speed detection means including the electric motor voltage detection means, the electric motor current detection means, and the steering rotation speed calculation means provided in the control means. Since the steering rotation speed can be obtained by calculation instead of the independent steering rotation speed sensor, the device can be downsized and the cost can be reduced.

Further, since the overcurrent of the electric motor can be prevented on the basis of the calculated steering rotational speed and the steering torque detected by the steering torque sensor, the electric motor is prevented from being overloaded and the power loss of the device is reduced. It can be reduced.

Therefore, it is possible to provide a compact and economical electric power steering device having a function of preventing an overload current of the electric motor.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of an electric power steering device according to the present invention.

FIG. 2 is a block diagram of a main portion of a steering rotation speed calculation means of the electric power steering device according to the present invention.

FIG. 3 is a circuit diagram of an embodiment of an electric motor drive means, an electric motor voltage detection means, and an electric motor current detection means.

[4] the target current I _MS characteristic diagram relative to the steering torque T that is the steering rotational speed N parameter

FIG. 5 is an explanatory diagram of steering characteristics of the electric power steering device according to the present invention.

FIG. 6 is an overall configuration diagram of a conventional general electric power steering device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 3 ... Steering shaft, 4 ... Connection shaft, 4a, 4b
... universal joint, 5 ... steering gear box, 6 ... rack and pinion mechanism, 6a ... pinion, 7 ... manual steering force generating means, 8 ... rack shaft, 8a ... rack teeth, 9 ... tie rod, 10 ... front wheel, 11 ... electric motor , 11a ... Drive side helical gear, 12 ... Ball screw mechanism, 12a ... Driven side helical gear, 13 ... Steering torque sensor, 14 ... Steering rotation speed sensor, 15, 20 ... Control means, 16 ... Electric motor drive means, 17 Steering rotation speed detecting means, 21 ... Electric motor voltage detecting means, 22 ... Electric motor current detecting means, 23 ... Target current setting means, 24 ... Steering rotation speed calculating means, 25 ... Drive control means, 26 ... Steering torque differentiating means, 27 ... motor rotation speed calculating means, 28 ... spring coefficient storage unit, 29 ... multiplication means, 30 ... steering speed calculation means, E _O ... power (battery), I _M Motor current, I _MD ... motor detection current, I _MS ... target current, N ... steering rotational speed (signal), N _M
… Motor rotation speed, OP1, OP2… Differential amplifier, Q
1, Q2, Q3, Q4 ... FET ( field effect transistor), T ... steering torque (signal), V _M ... motor V oltage, V
_MD : Motor detection voltage, V _O : Motor control voltage.

Claims (1)

[Claims] 1. A steering torque sensor for detecting a steering torque of a steering system, a steering rotation speed detecting means for detecting a steering rotation speed of the steering system, an electric motor for applying a steering assist force to the steering system, and a drive of the electric motor. The steering torque detected by the steering torque sensor is equal to or greater than a predetermined value, and the steering rotation speed detected by the steering rotation speed detection means is a predetermined value. In the electric power steering device configured to correct the steering assist force generated by the electric motor at the following times, the steering rotation speed detecting means includes an electric motor current detecting means for detecting an electric motor current and an electric motor voltage for detecting an electric motor voltage. A detection unit is provided, and the motor current detection unit and the motor voltage detection unit are provided in the control unit. An electric power steering apparatus comprising the steering speed calculating means for calculating the steering speed based on a signal from the stage.