JPS604466A - Control of steering power for power steering device - Google Patents

Abstract

PURPOSE:To obtain the optimum steering power correctly at all times by a method wherein the equivalent value for transversal acceleration, anticipated to be applied to a vehicle from a vehicle speed, a steering a angle and steering angular speed, is operated and feedback control is effected by the steering power comming from an objective steering power obtained from the value of the operation. CONSTITUTION:The output signal itself of a steering angle sensor 11 and a steering angular velocity signal, obtained by differentiating the output signal in a differentiating circuit 14 with respect to time, are inputted into the transversal acceleration corresponding value operating circuit 15 of a controller 10 together with the output signal of a vehicle speed sensor 12. Here, the transversal acceleration corresponding value (g) is computed from siad three input signals, and the objective steering power F1, corresponding to a present running condition, is operated in accordance with the output signal of the corresponding value (g) based on the objective steering power characteristics of an objective steering power operating circuit 16. Subsequently, a difference between the objective steering power F1 and an actual steering power F0, detected by a steering detector 13, is operated in a subtractor 17 and the value of electric current for a steering power controlling actuator 9 is corrected in increasing or decreasing it through a steering power correcting electric current control circuit 18 in accordance with the defference.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steering force control method for a power steering device used for the purpose of light power steering of a vehicle.

A power steering device uses a control valve that responds to the steering load to throttle the flow of working fluid toward the control valve, generates assist pressure on the upstream side, and guides this assist pressure to one chamber of a power cylinder provided in the steering operation system. This power cylinder provides power assist to steering operations, enabling nimble power steering.

By the way, in a power steering system that does not control steering force, the assist pressure P is determined solely by the steering force (steering load) F as shown in Fig. 6, but when lateral acceleration is applied to the vehicle due to steering. To generate the same lateral acceleration of the vehicle, a high assist pressure is required at low vehicle speeds, and a low assist pressure is sufficient at high vehicle speeds, so the steering force F for the lateral acceleration of the vehicle varies depending on the vehicle speed, as shown in Figure 1. Change. As a result, the steering force becomes too heavy during turning at low vehicle speeds, and the steering force becomes too light during turning at high vehicle speeds, resulting in unstable steering.

In order to solve this problem, the power steering system [ilL] is usually of the steering force control type, and the steering force control device for this purpose generally uses the control system as disclosed in, for example, Japanese Patent Application Laid-Open No. 54-100082. The flow rate is controlled by partially draining (bypassing the control valve and returning to the reservoir) the amount of working fluid directed toward the valve using an electrohydraulic actuator. Then, the actuator changes the bypass (drain) flow rate QB according to the vehicle speed as shown in FIG. The aim is to reduce the steering force F in the direction of the arrow in the figure so that the steering force F with respect to the lateral acceleration of the vehicle does not vary depending on the vehicle speed as shown in FIG.

However, in such a steering force control system, variations in the amount of working fluid discharged from the pump (amount of working fluid to the control valve) due to manufacturing errors, variations in the amount of working fluid bypassed by the electro-hydraulic actuator, It is directly affected by variations in the operating characteristics of the fluid, variations in viscosity due to temperature changes in the working fluid, etc.
The assist pressure change characteristic should be maintained as shown by the solid line in Figure 11 at the vehicle speed of The reality is that it is not possible to obtain the desired steering force characteristics as shown. Furthermore, in order to obtain at least the steering force characteristics shown in Fig. 1O, it is necessary to tune the electrohydraulic actuator to the vehicle part after the power steering device is assembled, which greatly impairs the workability of installing the power steering device. I couldn't avoid it.

In the case of the above-mentioned type of steering force control type power steering device, the present invention calculates an equivalent value of lateral acceleration expected to be applied to the vehicle from the vehicle speed, steering angle, and steering angular velocity, and uses this lateral acceleration equivalent value to set a target value. By determining the steering force and controlling the electrohydraulic actuator in feedback so that the actual steering force becomes the target steering force, the desired steering force characteristics can always be accurately obtained without being affected by the various variations described above. In addition, from the viewpoint that the above-mentioned problems can be solved all at once by eliminating the need to tune the electro-hydraulic actuator attached to the power steering device for each vehicle, we developed a method for controlling the steering force of a power steering device that embodies this idea. This is what we are trying to provide.

Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows an example of a power steering device that controls steering force using the method of the present invention. In the figure, 1 is a pump, 2 is a control valve, 8 is a power cylinder, and the pot is a reservoir.
The pump 1 sucks working fluid from the reservoir 4 and supplies it to the supply path 5.
Discharge to. When the control valve 2 is not in operation, the port arrangement is as shown by 2a, and the working fluid from the supply path 5 is directly returned to the reservoir 4 via the return path 6. However, during steering operation, the working fluid flows in response to the steering load. is throttled and generates assist pressure on the upstream side thereof, and this assist pressure is supplied to one chamber 3a or 8b of the power cylinder 3 by being arranged in the boat arrangement 2b or 2C depending on the steering direction, and is supplied to the other chamber 8b. Alternatively, 3a can be connected to the return path 6. Thus, the power cylinder 8 provided in the steering operation system has both chambers 8
a.

Steering operation is power assisted by the pressure difference between 3b and nimble power steering is possible.

The steering force control device includes a pressure compensation valve 8 and an electro-hydraulic flow rate adjustment valve (1-air hydraulic actuator) 9 in a bypass path 7 which bypasses the control valve 2 and is connected between the supply path 5 and the return path 6, and a controller. 10. The flow rate regulating valve 9 has a variable throttle part 9a located in the bypass passage 7, and its opening degree is made variable by the stroke of the valve body 9b. The stroke of the valve body 9b is determined by the magnetic force of the linear solenoid 9e that extends to the plunger 9d, which is supported movably in the axial direction by a pair of linear linear ball bearings 9C;
This is done by the plunger 9d, which is displaced to a position where the spring force of the opposing spring 9f is balanced, and the magnetic force of the linear solenoid 9e is controlled by the current value from the controller IO.

The controller 10 receives a signal θ from a steering angle sensor 11, a signal V from a vehicle speed sensor 12, and a signal F from a steering force detector 13. is input, and from the calculation results of these long sword signals, the amount of current applied to the linear solenoid 9e, and therefore the generated magnetic force, is determined, and according to this magnetic force, the plunger 9d is moved to the left in the figure together with the valve body 9b to open the variable throttle portion 9a. determine the degree.

Thus, a portion of the working fluid flowing from the pump l toward the control valve 2 bypasses the control valve 2 by an amount determined by the opening degree of the variable restrictor 9a and is returned to the reservoir 4.
The steering force can be controlled by the bypass amount of the working fluid (the opening degree of the variable throttle section 9a). Note that the amount of bypass changes as the differential pressure across the variable throttle section 9a changes, so this differential pressure across the variable throttle section 9a is kept constant by the pressure compensating valve 8, and the amount of bypass is determined only by the opening degree of the variable throttle section 9a. The above steering force control is performed accurately.

By the way, the controller 10 is configured as shown in FIG. 2 so as to be able to carry out the method of the present invention. That is, the controller 10 includes a differentiating circuit 14, a lateral acceleration equivalent value calculating circuit 15, a target steering force calculating circuit 16, a subtractor 17, and a steering force correction current control circuit 18. The steering angle signal θ from the sensor 11 is inputted, and the signal is differentiated with respect to time to output the steering angular velocity θ. The lateral acceleration equivalent value calculation circuit 15 calculates a value based on the steering angular velocity signal θ from the differentiating circuit 14, the steering angle signal θ from the steering angle sensor 11, and the vehicle speed signal ■ from the vehicle speed sensor 12, using a function of these as described below. The lateral acceleration equivalent value g is calculated and output. The reason why it is called the lateral acceleration equivalent value here is that the lateral acceleration applied to the vehicle due to steering occurs with a slight time delay from the steering as described later, and when the above calculation is performed in circuit 15, the lateral acceleration is actually not yet applied to the vehicle. This is because the calculation result is the lateral acceleration expected to be applied to the vehicle.

The target steering force calculation circuit 16 stores the target steering force characteristics (different for each vehicle) shown in FIG. 10, for example, and calculates the current vehicle running state (
A target steering force F0 corresponding to the steering state) is calculated. The steering force detector 13 detects the actual steering force F. This actual steering force F is detected. The difference between Fknee F and the target steering force F1. is calculated by the subtractor 17 and then supplied to the steering force correction current control circuit 18.

This circuit 18 corrects the current value (in some cases the pulse width) to the actuator 9 by increasing or decreasing it so that it becomes F, -Fo-0, and corrects the bypass amount QB by the actuator 9. Note that the steering force is controlled by the working fluid bypass ffi QB by the actuator 9, so in order to clearly indicate it as a feedback control system, it is shown by a broken line as if a signal corresponding to the bypass amount QB is input to the steering force detector 13. be.

Thus, this bypass amount QB is feedback-controlled so that the target steering force shown in FIG. 10 is always obtained.

In addition, in the present invention, the circuit 15 calculates the lateral acceleration equivalent value g.
The reason for calculating this and using this as the standard for calculating the target steering force is as follows. That is, instead of this, it is possible to directly detect the lateral acceleration actually applied to the vehicle by steering, but in this case, as shown in Figure 8, the lateral acceleration does not actually occur at the same time as the steering; In the method of the invention, the above-mentioned steering force control is actually inconsistent because it occurs with a time delay with respect to the steering angle and steering force that are used as calculation standards. Therefore, in the present invention, the circuit 15 calculates the lateral acceleration equivalent value g, and based on this, the circuit 16 calculates the target steering force F.
A method of calculating □ was adopted.

Next, the reason why the lateral acceleration equivalent value g is expressed as a function of the steering angle θ, the steering angular velocity θ, and the vehicle speed ■ as described above will be explained with reference to FIG. Figure 4 shows vehicle 19 (its center of gravity is indicated by P)
is turning at a constant vehicle speed V in the horizontal plane indicated by the X-Y coordinates (however, rolling motion of the vehicle body is ignored), the x-y coordinates have the center of gravity P as the origin and the longitudinal direction of the vehicle 19. This is a coordinate system in which the y-axis is the width direction of the vehicle 19.

If the position vector of the center of gravity P in the X-Y coordinate system is IR, its time differential value, that is, the velocity vector IR is IR−ui+ +vjl −−−−−(1) (however, u
, v are components of the vehicle speed V in the X and y directions, respectively, and +j is a unit vector in the X and y directions, respectively.Acceleration vector /R obtained by further differentiating this equation with respect to time is expressed by the following equation.

Next, let the yaw angular velocity γ of the vehicle 19 in the vertical vertical line passing through the center of gravity P (however, counterclockwise in the figure is positive), Δ be it, and the change in j+ in seconds be Δ11. When Δj1 is Δ11−γΔtjl, Δj+−−γΔti, +, it and j+ are respectively expressed by the following equations.

Therefore, the above equation (2) can be replaced as follows.

Also, if the slip angle at the center of gravity P is βraaian, then β
-tan-1(v-), V-i-constan
t, since normally β<< 1raaian,
u and v can be respectively replaced by the approximate expressions u-Vcosβ-■ v-Vsinβ4yβ, and from these two equations, the above (
8) Formula can be replaced as shown in the following formula.

IR! -i -V (β+γ)β+V(β+γ)jl
-------(4) From this equation (4), the equivalent value g of the lateral acceleration expected to be applied to the vehicle is g'=iV(β+γ) -------(5). By the way, the lateral acceleration that occurs while the vehicle is making a steady circular turn (turning with a constant steering angle β) is expressed as β− in the above equation.
0, but it is determined only by the vehicle speed V and yaw angular velocity γ, and while the vehicle is changing the steering angle θ, <'tj''-=
vo > The lateral acceleration that occurs during turning is not β~0,
This is also different. Therefore, the lateral acceleration equivalent value g is a function of the vehicle speed V, the steering angle θ, and the steering angular velocity θ, g −f, taking into account the specific characteristics of the vehicle involved, such as weight, wheel base, tire performance, and other road friction coefficients. (V
(t), θ(t), θ(t)). Therefore, in the method of the present invention, as described above, the vehicle speed v
The validity of calculating the lateral acceleration equivalent value g from the steering angle θ and the steering angular velocity θ can be understood.

Thus, as described above, the steering force control method of the present invention calculates the equivalent value g of the lateral acceleration expected to be applied to the vehicle from the vehicle speed ■, the steering angle θ, and the steering angular velocity θ, and calculates the target value from this lateral acceleration equivalent value. Steering force F□ is actual steering force F. Since the actuator 9 is feedback-controlled so that the steering force becomes the target steering force F0, even if there are variations in performance among the components of the power steering device and the steering force control device, or variations in the viscosity of the working fluid due to temperature changes, , the steering force can always be accurately controlled to the target value without being influenced by these factors, and for the same reason, there is no need for tuning, which was indispensable in the past, after the power steering device is assembled, and the power steering device can be used for a long time. The installation workability can be improved.

In the above example, the case where there is one target steering force characteristic as shown in FIG.
The driver may be able to freely select and use these according to his/her preference.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a power steering device that controls steering force according to the method of the present invention, Fig. 2 is a block diagram showing a controller of the power steering device configured to implement the method of the present invention, and Fig. 3 is a diagram during steering. A line showing the timing of lateral acceleration occurrence [j14 Figure 4 is a vector diagram used to calculate lateral acceleration, Figure 5 is a target steering force characteristic diagram when multiple target steering forces are set, Figure 6 is a diagram of target steering force characteristics when multiple target steering forces are set. Figure 7 is a characteristic diagram of assist pressure change in a power steering device that does not control steering force. Figure 7 is a characteristic diagram of steering force change in the same power steering device. Figure 8 is a characteristic diagram of working fluid bypass amount change in a power steering device that controls steering force. , Fig. 9 and Fig. 1O are respectively an assist pressure change characteristic diagram and a steering force change characteristic diagram of the same power steering device, and Fig. 11 is a diagram showing a problem in which the assist pressure change characteristic of the same power steering device deviates from the set characteristic. It is. 1...Pump 2...Control pulp 3...
Power cylinder 4...Reservoir 5...Working fluid supply path 6...Working fluid return path 7...Bypass path 8
... Pressure compensation valve 9 ... Flow rate adjustment valve (electro-hydraulic actuator) 10 ... Controller 11 ... Steering angle sensor 12 ... Vehicle speed sensor 18 ... Steering force detector 14 ... Differentiation Circuit 15...Lateral acceleration equivalent value calculation circuit 16...Target steering force calculation circuit 17...Subtractor 18...Steering force correction current control circuit 19...Vehicle. Patent applicant Nissan Motor Co., Ltd. Figure 6 Figure S Figure 7 Figure 9 Figure 1 O Figure ■ Figure 4 Nabi, IY Bipno (F)

Claims (1)

[Claims] When controlling the steering force of the power steering device by changing the amount of working fluid supplied by the hydraulic actuator, calculate the equivalent value of the lateral acceleration that is expected to be applied to the vehicle from the vehicle speed, steering angle, and steering angular velocity. A method for controlling a steering force of a power steering device, comprising: calculating a target steering force from the lateral acceleration equivalent value, and feedback-controlling the electro-hydraulic actuator so that the actual steering force becomes the target steering force.