JP3890199B2 - Power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power steering device that generates a steering assist force for assisting steering by a hydraulic pressure generated by a pump driven by an electric motor.
[0002]
[Prior art]
Conventionally, there has been used a power steering device that supplies hydraulic oil from an oil pump to a power cylinder coupled to a steering mechanism, thereby generating a steering assist force from the power cylinder. Among such power steering devices, for example, there is one in which an oil pump is driven by an electric motor such as a brushless motor.
[0003]
In this motor-driven pump type power steering device, stop-and-go control of an electric motor is performed. In other words, when the steering wheel operating speed (steering speed) is less than a predetermined speed, the electric motor is driven at a constant low rotational speed (including zero), and the flow rate of hydraulic oil sent from the oil pump is kept small. It is done. On the other hand, when the steering speed is equal to or higher than the predetermined speed, the electric motor is driven at a rotational speed corresponding to the vehicle speed so that an appropriate steering assist force corresponding to the vehicle speed is generated. This stop-and-go control can improve energy saving.
[0004]
[Problems to be solved by the invention]
However, in the above-described stop-and-go control, when the steering speed decreases from a speed larger than the predetermined speed and becomes lower than the predetermined speed, the rotation speed of the electric motor is changed to the vehicle speed in response to this. By suddenly lowering from the corresponding rotational speed to the constant low rotational speed, the flow rate of hydraulic oil supplied from the oil pump to the power cylinder is sharply reduced, and accordingly, the steering given from the power cylinder to the steering mechanism. There is a problem that the assisting power decreases rapidly. If the steering assist force rapidly decreases, not only does the driver feel uncomfortable with steering, but the steering wheel cannot be maintained and the vehicle may fluctuate from side to side.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a power steering device that solves the above technical problems and can prevent a sudden decrease in steering assist force.
[0006]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, the invention according to claim 1 is used by being mounted on a vehicle and supplying hydraulic oil sent from a pump (23) driven by an electric motor (27) to a power cylinder (26). A power steering device for supplying a steering assist force according to the operation of the operation member (11) for steering the vehicle from the power cylinder, the vehicle speed detecting means (5) for detecting the vehicle speed (V) ), Steering angle data output means (4) for outputting the steering angle data corresponding to the change in the steering angle by the operation of the operation member, and the operation member based on the steering angle data output from the steering angle data output means Steering speed calculation means (3, S1) for calculating the steering speed (dθ / dt), which is the time change rate of the steering angle, and a threshold value (S) where the steering speed calculated by the steering speed calculation means is predetermined. Above If the steering speed is equal to or higher than the threshold value, the flow rate (Qv; Qv + ΔQ) set based on the vehicle speed detected by the vehicle speed detection means is set as a new target flow rate. If the steering speed is less than the threshold value, a flow rate (QK) obtained by subtracting a predetermined reduced flow rate (K) from the current target flow rate is set as a new target flow rate with a predetermined standby flow rate as a lower limit. Drive control of the electric motor so that the target flow rate setting means (3, S2, S3, S4, S5, S6, S7) and the hydraulic fluid of the target flow rate set by the target flow rate setting means are sent from the pump. Motor control means (3, 6) for controlling the steering angle detection means (3, S1) for detecting the steering angle (θ) of the operating member based on the steering angle data output from the steering angle data output means. In addition The target flow rate setting means sets a reduced flow based on the steering angle detected by the steering angle detection means when the steering speed calculated by the steering speed calculation means is less than the threshold, A power steering device characterized in that a flow rate obtained by subtracting a set reduced flow rate from a current target flow rate is determined as a new target flow rate .
[0007]
In addition, the alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies hereinafter.
According to the present invention, after the steering speed decreases and reaches a predetermined threshold value, the reduced flow rate is set for each predetermined control period while the steering speed is less than the threshold value. Then, the target flow rate is decreased gradually until the target flow rate reaches a predetermined standby flow rate. As a result, the target flow rate is gradually reduced at the rate of the reduced flow rate / control cycle, and accordingly, the steering assist force generated from the power cylinder is gradually reduced. Therefore, it is possible to prevent the driver from feeling uncomfortable due to the sudden decrease in the steering assist force, and to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force.
[0009]
According to a second aspect of the present invention, the target flow rate setting means adjusts the vehicle speed detected by the vehicle speed detection means when the steering speed calculated by the steering speed calculation means is equal to or greater than the threshold value. A flow rate obtained by adding an additional flow rate corresponding to the steering speed calculated by the steering speed calculation means to the corresponding basic flow rate may be set as a new target flow rate (31, 32, 33).
Further, as described in claim 3, the additional flow rate is preferably generated by multiplying the magnitude of the steering speed by a predetermined proportional term, and the proportional term is determined by the piston (263) of the power cylinder. Is more preferably the product of the pressure receiving area (Ap) and the ratio (r) of the piston movement amount to the steering angle change.
[0010]
In this case, the additional flow rate is set to a value substantially equal to the volume change rate (volume change amount per unit time) of the oil chamber of the power cylinder corresponding to the steering speed. Therefore, when the addition value of the basic flow rate and the additional flow rate is set as the target flow rate, and the electric motor is driven and controlled based on this target flow rate, the speed is almost equal to the volume change rate with the volume change of the oil chamber of the power cylinder. The flow rate of hydraulic fluid delivered from the pump increases or decreases. As a result, the hydraulic oil having an appropriate flow rate according to the steering speed can be sent out from the pump, and the steering oil feels uncomfortable due to insufficient or excessive flow rate of the hydraulic oil supplied to the power cylinder. The torque loss feeling when the steering speed is reduced can be eliminated.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a conceptual diagram showing a basic configuration of a power steering apparatus according to an embodiment of the present invention. This power steering device is provided in association with the steering mechanism 1 of the vehicle, and is for applying a steering assist force to the steering mechanism 1.
[0012]
The steering mechanism 1 includes a steering wheel 11 that is operated by a driver, a steering shaft 12 coupled to the steering wheel 11, a pinion gear 13 provided at a tip portion of the steering shaft 12, and a left-right direction of the vehicle. Rack shaft 14. A rack gear portion 14a is formed on the rack shaft 14, and the pinion gear 13 is engaged with the rack gear portion 14a. Further, tie rods 15 are coupled to both ends of the rack shaft 14, and the tie rods 15 are coupled to knuckle arms 16 that support the front left wheel FL and the front right wheel FR as steering wheels, respectively. The knuckle arm 16 is rotatably provided around the kingpin 17. With this configuration, when the steering wheel 11 is operated and the steering shaft 12 is rotated, this rotation is converted into a linear motion along the left-right direction of the vehicle by the pinion gear 13 and the rack shaft 14, and this linear motion is converted into the knuckle arm 16. The rotation of the front left wheel FL and the front right wheel FR is achieved by converting the rotation around the king pin 17.
[0013]
In the middle part of the steering shaft 12, a torsion bar 21 that twists according to the direction and magnitude of the steering torque applied to the steering wheel 11, and an opening degree according to the direction and magnitude of the torsion bar 21 are twisted. And a hydraulic control valve 22 that changes.
The hydraulic control valve 22 is provided with four ports 221, 222, 223, and 224, and hydraulic oil pumped from the reservoir tank 24 by the oil pump 23 is supplied to the port 221 through the oil pipe 251. It has come to be. The port 222 communicates with the reservoir tank 24 via the oil pipe 252. The ports 223 and 224 are communicated with oil chambers 261 and 262 of the power cylinder 26 that generate steering assist force via oil pipes 253 and 254, respectively. Between the oil chambers 261 and 262 of the power cylinder 26, a piston 263 that moves in the vehicle width direction due to a hydraulic pressure difference in the oil chambers 261 and 262 is provided. The piston 263 is configured integrally with the rack shaft 14.
[0014]
When the steering wheel 11 is rotated in either the left or right direction, the torsion bar 21 is twisted, and the oil chambers 261 and 262 of the power cylinder 26 are supplied from the hydraulic control valve 22 by an amount corresponding to the twist of the torsion bar 21. Hydraulic oil is supplied to one of these. As a result, a hydraulic pressure difference is generated between the oil chambers 261 and 262, and the piston 263 of the power cylinder 26 moves in accordance with the hydraulic pressure difference, whereby the application of the steering assist force to the rack shaft 14 is achieved. At this time, the excess hydraulic oil is returned from the hydraulic control valve 22 to the reservoir tank 24 via the oil pipe 252. When the torsion bar 21 is hardly twisted, the hydraulic control valve 22 is in an equilibrium state, and the hydraulic oil supplied from the oil pump 23 to the hydraulic control valve 22 is not supplied to the power cylinder 26. The oil is returned to the reservoir tank 24 through the oil pipe 252.
[0015]
The oil pump 23 is driven by an electric motor 27. The electric motor 27 is driven and controlled by the electronic control unit 3 including a microcomputer.
The electronic control unit 3 is provided with steering angle data output from the steering angle sensor 4. The steering angle sensor 4 is provided in association with the steering wheel 11. The steering angle of the steering wheel 11 when the ignition key switch is turned on and the engine is started is set to an initial value “0”. Steering angle data with a code corresponding to the relative steering angle and corresponding to the steering direction is output. The electronic control unit 3 obtains a rudder angle midpoint that is a rudder angle when the vehicle is in a straight traveling state based on the rudder angle data, and further, based on the rudder angle midpoint and the rudder angle data, the wheel FR, An absolute steering angle (steering angle) θ corresponding to the FL direction is obtained. The steering angle midpoint is detected, for example, by sampling the steering angle data output from the steering angle sensor 4, creating a histogram of the steering angle data values, and generating the most frequent data after collecting a predetermined number of samples. This is achieved by obtaining the rudder angle data as rudder angle data at the midpoint of the rudder angle. The electronic control unit 3 obtains the steering speed dθ / dt by differentiating the steering angle θ with respect to time.
[0016]
The electronic control unit 3 is further provided with vehicle speed data output from the vehicle speed sensor 5. The vehicle speed sensor 5 may directly detect the traveling speed (vehicle speed) V of the vehicle, and obtains the vehicle speed V by calculation based on the output pulse of the wheel speed sensor provided in association with the wheel. There may be.
Furthermore, the electronic control unit 3 is supplied with current data output from the motor current detection circuit 6. The motor current detection circuit 6 outputs current data proportional to the current (motor current) flowing through the electric motor 27.
[0017]
The electronic control unit 3 sets a target flow rate Q of hydraulic oil to be supplied from the oil pump 23 to the hydraulic control valve 22 based on the steering angle data given from the steering angle sensor 4 and the vehicle speed data given from the vehicle speed sensor 5. . Then, the rotation speed of the electric motor 27 corresponding to the target flow rate Q is set, and the motor current is fed back based on the output signal of the motor current detection circuit 6 so that the electric motor 27 is driven at the set rotation speed. Control.
[0018]
FIG. 2 is a flowchart showing a process flow for setting the target flow rate Q of the hydraulic oil to be supplied from the oil pump 23 to the hydraulic control valve 22. The target flow rate setting process shown in FIG. 2 is repeatedly executed at regular control cycles by the microcomputer of the electronic control unit 3. First, based on the steering angle data output from the steering angle sensor 4, the steering angle θ and the steering speed dθ / dt of the steering wheel 11 are obtained by calculation, and the vehicle speed data is taken in from the vehicle speed sensor 5 to obtain the vehicle speed. V is acquired (step S1).
[0019]
Next, it is determined whether or not the absolute value of the steering speed dθ / dt is greater than or equal to a predetermined threshold value S (step S2). If the absolute value of the steering speed dθ / dt is equal to or greater than the threshold value S, the flow rate Qv corresponding to the vehicle speed V is set, and the set vehicle speed-corresponding flow rate Qv is set as the target flow rate Q (step S3). ), The target flow rate setting process is returned. For example, according to the vehicle speed-target flow rate characteristic line shown in FIG. 3, the vehicle speed corresponding flow rate Qv is set to a smaller value as the vehicle speed V increases within a predetermined flow rate range.
[0020]
On the other hand, when the absolute value of the steering speed dθ / dt is less than the threshold value S (NO in step S2), a reduced flow K corresponding to the steering angle θ is set (step S4). The reduced flow rate K is set to an upper limit value Kmax so that it decreases monotonously (in this embodiment, decreases linearly) with respect to an increase in the absolute value of the steering angle θ according to the steering angle-reduced flow characteristic line shown in FIG. It is determined between zero. When the reduced flow rate K is set, the reduced flow rate K is subsequently subtracted from the current target flow rate Q, and the value Q-K obtained thereby is set as a new target flow rate Q (step S5).
[0021]
Thereafter, it is determined whether or not the newly set target flow rate Q is less than a predetermined standby flow rate Qu (step S6). If the target flow rate Q is equal to or higher than the standby flow rate Qu, the target flow rate setting process is immediately returned. On the other hand, if the target flow rate Q is less than the standby flow rate Qu, the target flow rate Q is reset to the standby flow rate Qu (step S7), and then this target flow rate setting process is returned. As a result, while the state where the absolute value of the steering speed dθ / dt is less than the threshold value S continues, the target flow rate Q is gradually reduced until the standby flow rate Qu is reached.
[0022]
FIG. 5 is a time chart for explaining the characteristic operation of the power steering apparatus according to this embodiment. FIG. 5A shows the change over time of the steering speed dθ / dt of the steering wheel 11, and FIG. 5B shows the change over time of the target flow rate Q. FIG. 5 shows an example in which the vehicle speed V is kept constant.
In the period from time t1 to time t2 when the steering speed dθ / dt is equal to or higher than the threshold value S, the target flow rate Q is set to the vehicle speed corresponding flow rate Qv. When the steering speed dθ / dt reaches the threshold value S at time t2, and then the steering speed dθ / dt falls below the threshold value S, the reduced flow rate K corresponding to the steering angle θ at that time (immediately after time t2) is obtained. Is set. Then, a value Q-K obtained by subtracting the reduced flow rate K from the current target flow rate Q (target flow rate immediately before the steering speed dθ / dt reaches the threshold value S) is set as a new target flow rate Q. In the period from time t2 to t3 when the steering speed dθ / dt is less than the threshold value S, the reduced flow rate K is set and the target flow rate Q is determined in advance for each control cycle of the processing shown in FIG. The reduced flow rate K is decreased until reaching Qu.
[0023]
Therefore, after time t2, the target flow rate Q is gradually reduced at the rate of the reduced flow rate K / control cycle, and accordingly, the steering assist force applied from the power cylinder 26 to the steering mechanism 1 (rack shaft 14). Is gradually reduced. As a result, it is possible to prevent the driver from feeling uncomfortable due to a sudden decrease in the steering assist force, and it is possible to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force. Further, during the period from time t3 to t4, the target flow rate Q is set to the standby flow rate Qu, and the electric motor 27 is driven at a constant low rotational speed (including zero), so energy saving by stop-and-go control is achieved. Sex can be secured.
[0024]
When the steering speed dθ / dt reaches the threshold value S at time t4, the target flow rate Q is set to the vehicle speed corresponding flow rate Qv, and the flow rate of the hydraulic oil supplied from the oil pump 23 to the hydraulic control valve 22 is set to the standby flow rate Qu. To the target flow rate Q = Qv. Thereafter, during the period from time t4 to time t5 when the steering speed dθ / dt is equal to or higher than the threshold value S, the target flow rate is set to the vehicle speed corresponding flow rate Qv.
When the steering speed dθ / dt reaches the threshold value S at time t5 and further the steering speed dθ / dt becomes less than the threshold value S, the target flow rate Q is gradually reduced from the vehicle speed-corresponding flow rate Qv. If the steering speed dθ / dt exceeds the threshold value S at time t6 before the target flow rate Q reaches the standby flow rate Qu, the target flow rate Q is the target flow rate Q immediately before time t6. To the vehicle speed corresponding flow rate Qv.
[0025]
As described above, according to this embodiment, the target flow rate Q of hydraulic fluid to be supplied from the oil pump 23 to the hydraulic control valve 22 is responded to when the steering speed dθ / dt is less than the threshold value S. Instead of being suddenly reduced to the standby flow rate Qu, the flow rate is gradually reduced from the vehicle speed corresponding flow rate Qv to the standby flow rate Qu at a reduced flow rate K / control cycle speed. As a result, it is possible to prevent the driver from feeling uncomfortable due to a sudden decrease in the steering assist force, and it is possible to prevent the vehicle from wobbling due to the sudden decrease in the steering assist force.
[0026]
In this embodiment, in the state where the steering speed dθ / dt is equal to or higher than the threshold value S, the target flow rate Q is set to the vehicle speed-corresponding flow rate Qv. (Basic flow rate) The flow rate Qv + ΔQ may be set by adding an additional flow rate ΔQ corresponding to the steering speed dθ / dt to Qv. The configuration for this is shown in FIG.
Each part shown by this FIG. 6 is implement | achieved when the microcomputer of the electronic control unit 3 performs a program process, for example. That is, the electronic control unit 3 sets the target flow rate Q = Qv + ΔQ in a state where the steering speed dθ / dt is equal to or greater than the threshold value S, so that the basic flow rate generation unit 31 that generates the basic flow rate Qv corresponding to the vehicle speed V, the steering An additional flow rate generation unit 32 that generates an additional flow rate ΔQ corresponding to the absolute value of the velocity dθ / dt and an addition unit 33 that adds the basic flow rate Qv and the additional flow rate ΔQ to generate a target flow rate Q = Qv + ΔQ are included.
[0027]
In the additional flow rate setting unit 32, the additional flow rate ΔQ is generated by multiplying the absolute value of the steering speed dθ / dt by a predetermined proportional term. In the proportional term, for example, Ap is the pressure receiving area of the piston 263 of the power cylinder 26 (contact area with the hydraulic oil in one oil chamber), and the rate of change in the movement amount x of the piston 263 with respect to the change in the steering angle θ ( The ratio is set to a constant value Ap · r obtained by multiplying the pressure receiving area Ap and the ratio r when r = x / θ. Therefore, the additional flow rate ΔQ is set to a value substantially equal to the volume change rate (volume change amount per unit time) of the oil chambers 261 and 262 of the power cylinder 26 according to the steering speed dθ / dt.
[0028]
Therefore, when the addition value of the basic flow rate Qv and the additional flow rate ΔQ is set as the target flow rate Q, and the electric motor 27 is driven and controlled based on the target flow rate Q, the volume of the oil chambers 261 and 262 of the power cylinder 26 is changed. The flow rate of the hydraulic oil supplied to the hydraulic control valve 22 increases or decreases at a speed approximately equal to the volume change rate. As a result, hydraulic oil having an appropriate flow rate corresponding to the steering speed dθ / dt can be sent from the oil pump 23, and the steering oil feels strange due to insufficient or excessive flow rate of the hydraulic oil supplied to the power cylinder 26 (during sudden steering). , Etc., and the feeling of torque loss when the steering speed is reduced.
[0029]
Although the embodiments of the present invention have been described above, the present invention can be implemented in other forms and various design changes can be made within the scope of the matters described in the claims. It is.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a basic configuration of a power steering apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a flow of processing for setting a target flow rate.
FIG. 3 is a characteristic diagram showing a correspondence relationship between a vehicle speed and a target flow rate.
FIG. 4 is a characteristic diagram showing a correspondence relationship between a steering angle and a reduced flow rate.
FIG. 5 is a time chart for explaining a characteristic operation of the power steering apparatus according to the embodiment.
FIG. 6 is a block diagram showing a configuration for setting a target flow rate to a flow rate corresponding to a vehicle speed and an additional flow rate of an additional flow rate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering mechanism 3 Electronic control unit 4 Steering angle sensor 5 Vehicle speed sensor 6 Motor current detection circuit 11 Steering wheel 23 Oil pump 26 Power cylinder 261,262 Oil chamber 263 Piston 27 Electric motor 31 Basic flow rate generation unit 32 Additional flow rate setting unit 33 Addition Part

Claims (4)

Steering assist force according to the operation of the operation member for steering the vehicle from the power cylinder by supplying hydraulic oil sent from a pump mounted on the vehicle and driven by an electric motor to the power cylinder. A power steering device for generating
Vehicle speed detection means for detecting the vehicle speed;
Rudder angle data output means for outputting rudder angle data according to the rudder angle change caused by operation of the operation member;
Steering speed calculation means for calculating a steering speed that is a time change rate of the steering angle of the operation member based on the steering angle data output from the steering angle data output means;
It is determined whether the steering speed calculated by the steering speed calculating means is equal to or higher than a predetermined threshold value. If the steering speed is equal to or higher than the threshold value, the vehicle speed detected by the vehicle speed detecting means is determined. If the steering speed is lower than the threshold value, the flow rate set based on the flow rate obtained by subtracting a predetermined decrement from the current target flow rate is set to a predetermined standby flow rate as the lower limit. A target flow rate setting means for determining a new target flow rate;
Motor control means for driving and controlling the electric motor so that hydraulic oil at the target flow rate set by the target flow rate setting means is delivered from the pump ;
Steering angle detection means for detecting the steering angle of the operating member based on the steering angle data output from the steering angle data output means,
The target flow rate setting means sets a reduced flow based on the steering angle detected by the steering angle detection means when the steering speed calculated by the steering speed calculation means is less than the threshold, A power steering device characterized in that a flow rate obtained by subtracting a set reduced flow rate from a current target flow rate is determined as a new target flow rate . When the steering speed calculated by the steering speed calculation means is equal to or greater than the threshold value, the target flow rate setting means sets the basic flow rate corresponding to the vehicle speed detected by the vehicle speed detection means to the basic flow rate by the steering speed calculation means. power steering apparatus according to claim 1, characterized in that to determine the flow rate obtained by adding an additional flow rate corresponding to the steering speed that is calculated on the new target flow rate.   The additional flow rate is generated by multiplying the magnitude of the steering speed calculated by the steering speed calculation means by a predetermined proportional term,
  3. The power steering apparatus according to claim 2, wherein the proportional term is a product of a pressure receiving area of the power cylinder and a ratio of a piston moving amount with respect to a steering angle change.   The target flow rate setting means subtracts the reduced flow rate from the current target flow rate every predetermined control period when the steering speed is below the threshold value, thereby reducing the current flow rate to the current flow rate. 4. The power steering device according to claim 1, wherein the power steering device is gradually decreased from the target flow rate at a rate of the reduced flow rate / the control cycle until a predetermined standby flow rate is reached.

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