JP2777420B2 - Power steering control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention provides an assist force by changing a steering characteristic between an input shaft and an output shaft according to an applied current according to a vehicle speed, a steering angle, a steering wheel torque and the like. The present invention relates to a control device for a power steering device provided with a variable mechanism for controlling the power steering.

<Prior Art> In a power steering device, a servo valve that operates between an input shaft and an output shaft by relative rotation of both shafts, and a variable mechanism that changes a steering characteristic between both shafts according to an applied current. The servo valve controls the supply and discharge of working fluid to both working chambers of a power cylinder that provides an assist force. At this time, the current applied to the variable mechanism is changed in accordance with a running state such as a vehicle speed and a steering angle. ing.

As one of them, when it is determined that the steering wheel is in the returning state by the return detecting means for detecting that the steering angle is changing in the direction approaching the neutral position, the assist force is reduced and the return of the steering wheel is improved. The handle return control which is controlled as described above is disclosed in Japanese Patent Application Laid-Open No. 62-279170.

<Problems to be Solved by the Invention> In the conventional steering wheel return control, if the steering angle changes in a direction approaching the neutral position, it is determined that the steering wheel is in the steering wheel return state, and the assist force is applied to the variable mechanism. The control is performed so as to reduce the applied current. In this case, the applied current is constant regardless of the magnitude of the steering angle or the steering angular velocity. Therefore, when returning the steering wheel from a position where the steering angle is large, or when returning the steering wheel with a large steering angular velocity, it is felt that the steering wheel return is bad.

<Means for Solving the Problems> The present invention has been made to solve the problems described above, and includes a steering angle sensor that detects a steering angle of a steering wheel,
Steering angular velocity calculating means for calculating a steering angular velocity from the steering angle; determining means for determining whether or not the steering angle is returned from the steering angular velocity and the steering angle; a predetermined steering angle lower limit value and a predetermined steering angular speed lower limit value When the determining means determines that the steering wheel is in the returning state, the steering angle is larger than a predetermined lower limit of steering angle and the steering angular velocity is larger than a lower limit of predetermined steering angular velocity, The applied current is controlled so as to reduce the assist force, and when the steering angle is smaller than a predetermined lower limit of steering angle or the steering angular speed is smaller than a lower limit of the predetermined steering angular speed, the ratio of decreasing the assist force is set. It is characterized by having control means for controlling the applied current in a direction in which the applied current decreases in accordance with a decrease in the steering angle and the steering angular velocity.

<Operation> The steering angle sensor detects the steering angle of the steering wheel, and the steering angular velocity calculating means calculates the steering angular velocity by differentiating the steering angle. The judging means judges whether the steering wheel is in the returning state or the turning state based on the direction of the steering angle and the direction of the steering angular velocity. The control means, when the determining means determines that the steering wheel is in the returning state, when the steering angle is larger than the predetermined lower limit value of the steering angle and the steering angular velocity is larger than the lower limit value of the predetermined steering angular speed, the control means enters the running state of the vehicle. An applied current controlled so as to minimize the assist force with respect to the applied current calculated in response thereto is output so as to optimize the return of the steering wheel. If the steering angle is smaller than the predetermined steering angle or the steering angular speed is smaller than the predetermined steering angular speed, the assist current is applied to the applied current calculated according to the driving state of the vehicle in accordance with the decrease in the steering angle and the steering angular speed. An applied current controlled so as to reduce the rate of reduction of the force is output to weaken the return of the steering wheel.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. In FIGS. 1 and 2, the input shaft 14 and the output shaft
The power steering device 10 having 15 includes a servo valve 11 and a reaction force mechanism 13 provided between both shafts 14 and 15, and a power cylinder 12 connected to an output shaft 15 by a rack and pinion mechanism. 14 is a steering wheel 46 via a handle shaft 47
The rack bar 12a of the power cylinder 12 is connected to a steering wheel (not shown) via a steering link mechanism.

A supply pump 20 such as a vane pump driven by an automobile engine has a built-in bypass valve 21, which allows a working fluid having a constant flow rate Q to flow through a discharge passage 23 through a branch valve 22.
Supplied to The flow dividing valve 22 distributes the working fluid having the constant flow rate Q to the servo valve passage 23a and the reaction force control passage 23b at constant flow rates Q1 and Q2, respectively. Servo valve passage
23a is connected to the power cylinder 12 via the servo valve 11, and the reaction force control passage 23b is connected to the reaction force mechanism 13 and the electromagnetic control valve 30.
Is connected.

The servo valve 11 is formed of a known rotary open center type 4-port throttle switching valve, and is operated by relative rotation between the input shaft 14 and the output shaft 15 based on the steering wheel torque applied to the steering wheel 46. In the neutral state where no steering wheel torque is generated, the working fluid supplied from the supply port 11a flows evenly through the left and right passages and the discharge port
It is discharged from 11b to the reservoir 25. In this state, since the two distribution ports 11c and 11d have the same low pressure, the power cylinder 12 is not operated. When the steering handle 46 is operated, the servo valve 11 is deviated from the neutral state, so that the servo valve 11 is connected between one distribution port (for example, 11c) and the discharge port 11b and between the other distribution port (for example, 11d) and the supply port 11a. The passage area between them is reduced, and the pressure generated in the gear generated in the servo valve passage 23a increases. This working fluid is supplied to one distribution port (eg, 11
c), flows into one chamber of the power cylinder 12 through one distribution passage (for example, 24a) to generate an assist force, and the working fluid in the other chamber flows from the other distribution passage (for example, 24a) to the other distribution port. (For example, 11d), and is discharged from the discharge port 11b to the reservoir 25. This assist force is output shaft 15
The steering output torque is increased and transmitted to the steered wheels.

The reaction force mechanism 13 has a plunger 13b fitted into an insertion hole 13c provided on the output shaft 15 side of the servo valve 11, and a circle provided on the input shaft 14 side of the servo valve 11 and engaged with the tip of the plunger 13b. It is a well-known device having an inclined surface 13d inclined on both sides in the circumferential direction as a main component. Then, the pressure of the working fluid introduced into the rear part of the plunger 13b through the port 13a is changed by the electromagnetic control valve 30 to change the characteristics of the torsion spring between the input shaft 14 and the output shaft 15 and to operate the servo valve 11 By changing the characteristics, the characteristics of the steering output torque with respect to the steering wheel torque are changed. The opening of the electromagnetic control valve 30 is usually the smallest, and the opening is gradually increased by increasing the current applied to the solenoid 30a, and is finally fully opened.

As shown in FIG. 2, the electric control device 50 includes a microprocessor (hereinafter referred to as CPU) 51, a read-only memory (hereinafter referred to as ROM) 52, and a writable memory (hereinafter referred to as RAM) 53 as main components. The solenoid 51a of the electromagnetic control valve 30 is connected to the CPU 51 via an unillustrated interface and a solenoid drive circuit, and controls a current applied to the solenoid. The steering angle sensor 45 and the vehicle speed sensor 40 are connected to the CPU 51 via an unillustrated fence. The steering angle sensor 45 is the handle shaft
47, the steering angle θ of the steering wheel 46 is detected. The vehicle speed sensor 40 is constituted by a tachometer connected to an output shaft 43 of a transmission 42 for transmitting the driving force of the engine 41 to the rear wheels 44. The vehicle speed v
Is to be detected.

The ROM 52 stores control characteristics of the applied current i applied to the solenoid 30a of the electromagnetic control valve 30 with respect to the steering angle θ and the vehicle speed v. The control characteristics are such that the applied current i decreases with an increase in the steering angle θ, and the applied current i decreases with an increase in the vehicle speed v, and is stored as a characteristic map or a functional expression. I have.

In the present embodiment, in a normal running state, the applied current i is increased to increase the opening of the electromagnetic control valve 30 in accordance with the decrease in the vehicle speed v and the decrease in the steering angle θ, and the applied force is applied to the reaction force mechanism 13. This reduces the working fluid pressure to soften the torsional spring characteristics between the input shaft 14 and the output shaft 15. Therefore, as the vehicle speed v decreases and the steering angle θ decreases, the assist force ratio increases.

Then, for example, NEGA is determined by the determination means 2 based on the flowchart disclosed in Japanese Patent Application Laid-Open No. 62-279170.
1, that is, when it is determined that the steering wheel is in the returning state,
Reduce the applied current to reduce the opening of the solenoid control valve 30,
By increasing the working fluid pressure applied to the reaction force mechanism 13, the input shaft
The torsion spring characteristic between the output shaft 14 and the output shaft 15 is made rigid, the ratio of the assist force is reduced, and the return control for improving the return of the steering wheel by the restoring force from the tire is performed.

At that time, the control unit 4 applies the applied current determined as described below to the solenoid 30a of the electromagnetic control valve 30. That is, in the initial state, the electric control device 50 sets each variable to a predetermined initial value, and the vehicle speed v and the steering angle θ, which change every moment in the running state of the vehicle, are determined by the vehicle speed sensor 40.
The current values are detected by the steering angle sensor 45 and input to respective registers (not shown). The CPU 51 executes the processing operation shown in FIG. 3 every time an interrupt signal is input every predetermined short time.

In step 100 of the flowchart of FIG. 3, the vehicle speed v and the steering angle θ are read. In step 101, the base current I obtained from a map (not shown) according to the vehicle speed v and the steering angle θ is read. , Steering angle θ
To calculate the steering angular velocity θ. Then step 10
At 3, the above-mentioned judging means 2 judges whether the steering direction is the turning direction or the returning direction.

When it is determined that the steering direction is the return direction, in step 104, a variable Xθ corresponding to the steering angle θ is read. As variable Xθ shown in Figure 4, when 0 of the steering angle theta is 0, it becomes 1 when theta is greater than _1, up to 0 <theta <variable Xθ As increased theta ₁ in the steering angle theta is 0 1 It increases linearly. Further, in step 105, a variable X corresponding to the steering angular velocity is read. Variable X as shown in FIG. 5, becomes zero when the steering angular velocity is 0, ₁ <<
_The variable X becomes ₁ at 0, and at 0 << ₁ , the variable X linearly increases from 0 to 1 as the steering angular velocity increases, and ₂ <
In < ₃ , the variable X linearly decreases from 0 to 1 as the steering angular velocity increases.

In step 106, the control current Δi is calculated by multiplying the variable Xθ read in step 104 and the variable X read in step 105 by the return current correction value Icom.
The correction value Icom changes so as to decrease as the vehicle speed increases, and is stored in the ROM 52 as a map. If it is determined in step 103 that the steering direction is the turning direction, the control current Δi is set to 0 in step 107.

Then, in step 108, the control current Δi is subtracted from the base current I read in step 101 to calculate the output current I ₀ , and in step 109, the output for applying the output current I ₀ to the solenoid 30a of the electromagnetic control valve 30 is performed. The CPU 51 stops executing the processing operation according to the flowchart of FIG. Thereafter, each time an interrupt signal is output at predetermined time intervals, the CPU 51 repeatedly executes the processing operation according to the flowchart of FIG.

As described above, when the steering wheel is in the returning state, the steering angle θ is larger than θ ₁ and the steering angular velocity is ₁ <<
_In the case of ₂ , the correction value Icom of the return current is subtracted from the base current I, and the assist force is controlled to be the smallest, so that the steering wheel return is the best. Also, the steering angle θ
In the vicinity There θ ₁ is less than neutral, the steering angular velocity
₁ When the steering wheel is stopped outside the range of << ₂ and when the steering is suddenly performed, the control current Δi reduced according to the steering angle θ and the steering angular velocity with respect to the correction value Icom of the return current is changed to the base current I.
And the degree of reduction of the assist force is reduced so that the degree of steering wheel return is reduced. That is, the return current is adjusted according to the magnitude of the steering angle θ and the magnitude of the steering angular velocity, so that the degree to which the steering wheel returns can be changed.

In the present embodiment, the steering force is changed by changing the opening of the electromagnetic control valve 30 by the applied current and increasing or decreasing the working fluid pressure applied to the reaction force mechanism 13, but is not limited to this. Instead, the present invention can be applied to a bypass control in which the steering force is changed by controlling a variable valve disposed between a high-pressure chamber and a low-pressure chamber of a hydraulic cylinder with a control current.

According to the present invention as above described <Effect of the Invention>, when in the handle return state, when large and the steering angular velocity than theta ₁ steering angle theta is greater than _1, the correction of the current return from the base current I The value Icom is reduced so that the assist force is controlled to be the smallest so that the steering wheel return is the best. Also, in less than _one neutral near the steering angle theta is theta, if the steering angular velocity is small handle small steering than _1, it was reduced according to the decrease of the steering angular velocity and the steering angle theta with respect to the correction value Icom current return The control current Δi is subtracted from the base current I so that the rate of decrease in assist force is reduced, so that the degree of steering wheel return is reduced. In this manner, the return current is adjusted according to the magnitude of the steering angle θ and the magnitude of the steering angular velocity, and it is possible to change the degree of the steering wheel return to an optimum weight.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a control device for a power steering device according to the present invention, and FIGS. 2 to 5 show one embodiment of the present invention.
FIG. 3 is an overall explanatory diagram, FIG. 3 is a flowchart of a control program in a judgment means, and FIG. 4 is a steering angle θ and a variable Xθ.
FIG. 5 is a relationship diagram between the steering angular velocity and the variable X. DESCRIPTION OF SYMBOLS 1 ... Steering angular velocity calculation means, 2 ... Judgment means, 4 ... Control means, 5 ... Output means, 11 ... Servo valve, 12 ... Power cylinder, 13 ... Variable mechanism, 14 ... Input shaft, 15 ... output shaft, 20 ... supply pump, 30 ... electromagnetic control valve, 40 ... vehicle speed sensor, 45 ... steering angle sensor, 46 ... steering wheel.

Continuation of front page (56) References JP-A-63-312268 (JP, A) JP-A-62-37274 (JP, A) JP-A-62-279170 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) B62D 6/00

Claims (1)

(57) [Claims] An input shaft connected to a steering wheel, an output shaft connected to a steered wheel, a power cylinder for applying an assist force to the output shaft, and a relative rotation between the two shafts A servo valve for controlling supply and discharge of working fluid sent from a supply pump to both working chambers of the power cylinder, and an electromagnetic valve for changing a steering characteristic between the two shafts according to an applied current. A power steering apparatus comprising: a variable mechanism; and an output unit configured to output the applied current controlled according to a traveling state of the vehicle to the variable mechanism. A steering angle sensor for detecting a steering angle of the steering wheel; Steering angular velocity calculating means for calculating a steering angular velocity from an angle; determining means for determining whether the steering wheel is in a return state from the steering angular velocity and the steering angle; a predetermined lower steering angle value and a predetermined lower steering angular velocity value When the determination unit determines that the steering wheel is in the returning state, the steering angle is larger than a predetermined lower limit of steering angle and the steering angular speed is larger than a lower limit of predetermined steering angular speed, The applied current is controlled so as to reduce the assist force, and when the steering angle is smaller than a predetermined lower limit of steering angle or the steering angular speed is smaller than a lower limit of the predetermined steering angular speed, the ratio of decreasing the assist force is set. A control device for a power steering device, further comprising control means for controlling the applied current in a direction in which the applied current is reduced in accordance with a decrease in the steering angle and the steering angular velocity.