JP4639146B2 - Power steering device - Google Patents

Description

  The present invention relates to a power steering device that assists a driver's steering with an electric hydraulic pump.

Conventionally, in a power steering apparatus as disclosed in Patent Document 1, a power cylinder includes a power cylinder, a bidirectional pump connected to the power cylinder, and an electric motor that drives the bidirectional pump to rotate forward and backward. Steering assist force is obtained by supplying hydraulic pressure to the right and left pressure chambers. Further, in order to improve the steering response, a check valve that always keeps the hydraulic pressure in the apparatus at a predetermined pressure or higher is provided. As a result, when the hydraulic pressure is supplied to the power cylinder by the bidirectional pump, the hydraulic pressure held above the predetermined pressure immediately reaches the assist pressure, and the assist can be started.
JP 2004-306721 A

  However, in normal hydraulic power steering, the residual pressure is all returned to the reservoir tank at the time of switching back, while the pressure reduction to the reservoir tank at the time of switching back is a check valve for ensuring the above-mentioned cutting response. Since it is limited, there is basically no choice but to return to the opposite cylinder via a pump. For example, when transitioning from the right-side cut state to the back-turn state, the decrease in the hydraulic pressure of the raised right cylinder is delayed, resulting in a residual pressure, and the switch-back response is poor when transitioning from handle return and switch-back to switch-back. Will occur.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a power steering device that can achieve steering assist without causing the driver to feel uncomfortable even when the steering direction is switched.

In order to achieve the above object, in the power steering apparatus of the present invention, the hydraulic power cylinder for assisting the steering force of the steering mechanism connected to the steering wheel and the first and second pressure chambers of the hydraulic power cylinder are respectively first. , A bidirectional pump having a pair of discharge ports for supplying hydraulic pressure through the second passage, an electric motor connected to the bidirectional pump and rotating the bidirectional pump forward and reverse, and the steering wheel. Steering load detection means for detecting or estimating a steering load of a steering wheel for rudder control, and an electric motor that outputs a drive signal to the electric motor to generate a desired hydraulic pressure based on the steering load. and control means, and the electric motor rotation direction detecting means for detecting a rotational direction of the electric motor, the steering and direction of the load and the electric motor rotational direction mismatch Rutoki, the first than the driving torque of the electric motor, and determines Families around judging means and drag motion state is a state reaction force is large acting on the electric motor by a pressure difference between the second pressure chamber, wherein And a correction unit that corrects the drive signal to the accompanying side when the accompanying determination unit determines that the accompanying state is in the accompanying state .

  If the direction of the steering force does not match the direction of rotation of the electric motor, that is, if the reaction force acting on the motor due to the pressure difference between the left and right cylinders exceeds the electric motor driving torque, the motor rotates. At this time, since the driver can determine that the steering wheel is turned back or the steering force is reduced, it is necessary to quickly reduce the pressure difference between the left and right cylinders. The pressure reduction response is delayed because it acts in a direction that hinders the pressure reduction for removing the pressure difference, and as a result, the steering wheel turn-back response and the assist force response at the time of turn-back are deteriorated. Accordingly, by correcting the electric motor driving force in the follower direction, the pressure difference can be quickly reduced, and the steering wheel return response and the steering response at the turn-back can be improved.

  Hereinafter, the best mode for realizing the power steering apparatus of the present invention will be described based on an embodiment shown in the drawings.

  FIG. 1 is a system diagram showing the overall configuration of a power steering apparatus according to Embodiment 1 of the present invention. First, the configuration will be described. 1 is a steering wheel, 2 is a steering shaft, 3 is a rack and pinion mechanism, 5 is a power steering mechanism that assists the steering force of the driver, and 6 is an external gear type driven by an electric motor 6a. A bidirectional pump, 7 is a steering wheel, 8 is a warning lamp for notifying the driver that a failure has occurred in the steering system, and 10 is a control unit (corresponding to the electric motor control means described in the claims). The electric motor 6a is a brushless motor, and is provided with an electric motor rotation speed sensor 6b including three Hall elements that detect the rotation angle of the electric motor.

  A bidirectional pump 6 that is a hydraulic source of the power steering mechanism 5 includes a first cylinder chamber 51 (a first pressure chamber described in the claims) of a power cylinder 5a (corresponding to a hydraulic power cylinder described in the claims). And a second cylinder chamber 52 (corresponding to the second pressure chamber described in the claims) and a hydraulic pipe 61 (corresponding to the first and second passages described in the claims). It has been. When the driver operates the steering wheel 1, the rotation direction of the electric motor 6 a is switched according to the operation direction, and the oil between the first cylinder chamber 51 and the second cylinder chamber 52 is supplied and discharged to thereby change the driver's direction. Assist steering force. Specifically, when the steering wheel 1 is steered to the right in the figure, the electric motor 6a is driven in the direction in which the hydraulic pressure is supplied from the second cylinder chamber 52 to the first cylinder chamber 51 to move integrally with the rack shaft 54. Assisting the piston 53 to the second cylinder chamber 52 side.

  The hydraulic pipe 61 is provided with a bypass circuit 62 that communicates the first cylinder chamber 51 and the second cylinder chamber 52 without passing through the bidirectional pump 6. On the bypass circuit 62, an electronically controlled fail-safe valve 4 that operates based on a command signal from the control unit 10 is provided.

  The fail-safe valve 4 uses a normally open valve that is closed when a voltage is supplied in response to a command signal from the control unit 10 and is open when no voltage is supplied. As a result, even if some abnormality occurs in the steering system and the power supply is shut down, the first cylinder chamber 51 and the second cylinder chamber 52 can be in communication with each other. Steering can be ensured.

  Further, the steering shaft 2 is provided with a torque sensor 12 for detecting the steering torque of the driver.

  The control unit 10 includes a steering torque signal from the torque sensor 12, an IGN signal from the ignition switch 13, an engine speed signal from the engine speed sensor 14, a vehicle speed signal from the vehicle speed sensor 15, and an electric motor speed sensor 6b. The electric motor rotation signal is input. Based on these input signals, command signals are output to the electric motor 6a, the fail safe valve 4 and the warning lamp 8 of the bidirectional pump 6.

  FIG. 2 is a block diagram showing the configuration inside the control unit 10. The power supply circuit watchdog timer 101 receives a voltage signal from the power supply 11 and an IGN signal from the ignition switch 13 and transmits / receives a signal to / from the main microcomputer 107.

  The engine speed processing circuit 102 outputs an engine speed signal from the engine speed sensor 14 to the main microcomputer 107. The torque sensor processing circuit 103 outputs a torque signal from the torque sensor 12 (corresponding to the steering load detecting means described in claims) to the main microcomputer 107 and also to the sub-microcomputer 108. The vehicle speed signal processing circuit 104 outputs a vehicle speed signal from the vehicle speed sensor 15 to the main microcomputer 107. The diagnostic circuit 105 outputs a diagnostic signal input via the connector 16 to the main microcomputer. The CAN communication circuit 106 outputs a signal transmitted by the vehicle system CAN to the main microcomputer 107.

  The sub microcomputer 108 monitors the main microcomputer 107. When a failure occurs in the main microcomputer 107, a control signal can be output to the fail safe relay 109, the fail safe valve driving circuit 116, and the warning lamp driving circuit 117.

  The fail safe relay 109 cuts off the power supply for driving the electric motor when any failure occurs. The EEPROM 110 is configured to store various data necessary for control and update the data. The fail safe relay diagnosis input circuit 111 outputs an operation diagnosis signal of the fail safe relay 109 to the main microcomputer 107. The electric motor drive circuit 112 supplies a voltage to the electric motor 6a based on a command signal from the main microcomputer 107. The current monitor circuit 113 detects the current value of the electric motor 6 a and outputs it to the main microcomputer 107. The electric motor terminal voltage circuit 114 outputs the terminal voltage of the electric motor 6a to the main microcomputer 107.

  The electric motor rotation signal processing circuit 115 outputs the rotation speed of the electric motor 6a to the main microcomputer 107. The fail safe valve drive circuit 116 outputs a drive signal to the fail safe valve 4 based on a command signal from the main microcomputer 107 or the sub microcomputer 108. The warning lamp drive circuit 117 outputs a command signal to the warning lamp 8 based on a command signal from the main microcomputer 107 or the sub-microcomputer 108.

  FIG. 3 is a schematic diagram illustrating the configuration of the pump unit according to the first embodiment. First, the configuration will be described. The hydraulic pipes 61a, 61b, 61c, 61d connect the cylinder chambers 51 to the bidirectional pump 6. The bypass oil passages 62a, 62a ′, 62b, 62b ′ communicate with the hydraulic pipes 61b, 61c. The reservoir tanks 202a, 202b, and 205 supply oil to the bidirectional pump 6 and store drained oil. For convenience of explanation, a plurality of reservoir tanks are shown, but one reservoir tank may be provided. The check valves 201a and 201b are closed when hydraulic pressure is generated by the bidirectional pump 6, and are opened when negative pressure is generated.

  Details of the return check valve 203 will be described later. The check valve 204 (corresponding to the check valve described in the claims) supplies drained oil to the reservoir tank 205, and the drain oil passage 63 passes through the return check valve 203, the reservoir tank 205, and the check valve 204. Connect.

  Here, the return check valve 203 will be described. The return check valve 203 includes a first return check valve 203a (corresponding to a first bypass valve described in claims) and a second return check valve 204a (corresponding to a second bypass valve described in claims). And a spool valve 210 and return springs 206a and 206b for biasing the spool valve 210 to the center.

  The first return check valve 203a is provided with a first hydraulic chamber 207a having a connection port for the hydraulic pipes 61a and 61b, and a first piston chamber 208a having a connection port for the drain oil passage 63 and the bypass oil passage 62a ′. It has been. Similarly, the second return check valve 203b includes a second hydraulic chamber 207b having a connection port for the hydraulic pipes 61c and 61d, and a second piston chamber 208b having a connection port for the drain oil passage 63 and the bypass oil passage 62b ′. Is provided.

  The spool valve 210 is acted on by the urging force on the right side in the figure by the urging force of the return spring 206a, the oil pressure of the first hydraulic chamber 207a, and the oil pressure of the first piston chamber 208a. On the other hand, as the biasing force on the opposite side (left side in the figure), the biasing force by the return spring 207a, the hydraulic pressure in the second hydraulic chamber 207b, and the hydraulic pressure in the second piston chamber 208b act. Thereby, the position of the spool valve 210 is determined.

  The spool valve 210 is acted on by the urging force on the right side in the figure by the urging force of the return spring 206a, the oil pressure of the first hydraulic chamber 207a, and the oil pressure of the first piston chamber 208a. On the other hand, as the biasing force on the opposite side (left side in the figure), the biasing force by the return spring 207a, the hydraulic pressure in the second hydraulic chamber 207b, and the hydraulic pressure in the second piston chamber 208b act. Thereby, the position of the spool valve 210 is determined.

  FIG. 4 is a diagram illustrating the flow of oil during normal torque assist control, and FIG. 5 is an operation explanatory diagram illustrating the movement of the return check valve. In FIG. 4, a thick solid line indicates a high oil pressure, and a thick dotted line indicates a low oil pressure.

(When steering from the neutral position)
A description will be given of steering from a position where the hydraulic pressure in the first cylinder chamber 51 and the hydraulic pressure in the second cylinder chamber 52 are balanced. At the start of steering, the hydraulic pressure in the first cylinder chamber 51 and the hydraulic pressure in the second cylinder chamber 52 are in a balanced state. When assisting the rack shaft 54 to the right side in the figure by the steering of the driver, the bidirectional pump 6 is driven to supply hydraulic pressure to the second cylinder chamber 52. Then, the hydraulic pipe 61c and the hydraulic pipe 61d become high hydraulic pressure.

  This high oil pressure is also supplied to the bypass oil passages 62b and 62d ', and the second piston chamber 208b becomes a high oil pressure. At this time, since the fail safe valve 4 is closed, as shown in FIG. 5B, the first piston chamber 208a and the second piston chamber 208b, and the first hydraulic chamber 207a and the second hydraulic chamber 207b are different. Pressure is generated and the spool valve 210 is moved to the left in FIG. Thereby, the bypass oil passage 62a ′ and the drain oil passage 63 are communicated with each other, and the first cylinder chamber 51 has a low hydraulic pressure released to the atmosphere. Torque assist steering is executed using this differential pressure.

[Control unit control configuration]
The main microcomputer 107 includes a torque signal from the torque sensor processing circuit 103, an ignition signal from the power circuit watchdog timer 101 (corresponding to the signals of the ignition switch 13 and the power supply 11), a vehicle speed signal from the vehicle speed signal processing circuit 104, electric An electric motor rotation signal or the like from the motor rotation signal processing circuit 115 is input. In the main microcomputer 107, there is provided a target electric motor torque calculator 70 for calculating a target electric motor torque T * of the electric motor 6a based on each signal. A current command value corresponding to the target electric motor torque T * is output to the electric motor drive circuit 112.

  FIG. 6 is a control block diagram showing the configuration of the target electric motor torque calculation unit 70. The target electric motor torque calculation unit 70 is a first target electric motor torque calculation unit 71 that calculates the first target electric motor torque T1 * based on the steering torque, the vehicle speed, and the electric motor rotation speed, and the steering torque and the electric motor rotation speed. Based on (the electric motor rotation direction), based on the rotation determination unit 72 (corresponding to the rotation determination unit described in the claims) that determines whether or not the electric motor 6a is in the rotation state. Based on the correction torque calculation unit 73 (corresponding to the correction means described in the claims) and the accompanying determination unit 72, the correction amount 0 and the calculation result of the correction torque calculation unit 73 are calculated. And a switching unit 74 that switches between the first target electric motor torque T1 * and the correction torque Thos (or 0).

  The first target electric motor torque calculation unit 71 performs calculation so that the assist force increases as the steering torque increases, and the assist force increases as the vehicle speed decreases. Furthermore, when the rate of change of the steering torque is large, the inertia torque associated with the increase in the rotation speed of the electric motor itself is taken into account. For example, when the rotation speed of the electric motor is decreased, the torque in the direction in which the rotation speed of the electric motor decreases. When increasing the electric motor rotation speed, the torque in the direction of increasing the electric motor rotation speed is increased.

  The accompanying determination unit 72 determines whether or not the direction of the steering torque and the direction of the electric motor rotational speed are inconsistent. When the directions are not consistent, the driving torque is output to the electric motor 6a in the same direction as the steering torque. Nevertheless, it is determined whether or not the electric motor 6a is rotated in the direction opposite to the steering torque due to the hydraulic pressure difference, that is, whether the electric motor 6a is rotating. When it is determined that it is in the accompanying state, the switching unit 74 is switched to the correction torque side, and when it is determined that it is not in the accompanying state, the switching unit 74 is switched to the 0 side.

  The correction torque calculation unit 73 detects the electric motor rotation direction and calculates the correction torque from the torque signal detected by the torque sensor 12 and the electric motor rotation speed detected by the electric motor rotation speed sensor 6b.

  The adder 75 adds the first target electric motor torque T1 * and the correction torque Thos, and outputs the result as a final target electric motor torque T * to a block for calculating a current command value.

FIG. 7 is a flowchart showing the control contents of the target electric motor torque calculation unit 70.
In step 201, the first target electric motor torque T1 * is calculated.

  In step 202, the electric motor rotation direction is detected. The electric motor rotation direction is determined based on the electric motor rotation signal from the electric motor rotation signal processing circuit 115.

  In step 203, it is determined whether or not the electric motor rotation direction matches the torque direction. On the other hand, if they match, it is determined that correction is not necessary, and the process proceeds to step 208.

In step 204, the correction torque Thos is calculated from the following equation.
Tdmhos ＝ Motrev × Dmg × Gtmp
Thos ＝ Tdmhos
Motrev: Electric motor speed
Dmg: Dynamic friction coefficient
Gtmp: A temperature correction coefficient. The dynamic friction coefficient is a value set in advance by calculation, experiment, or the like for the friction between the bidirectional pump 6 and the cylinder chambers 51 and 52. Further, the temperature correction coefficient is a value set in the map shown in FIG. 8, and is set to be a small temperature correction coefficient corresponding to the decrease in the viscous resistance as the temperature rises.

  In Step 205, it is determined whether the electric motor rotation direction is the right direction or the left direction. If the rotation direction is the left direction, the process proceeds to Step 206, and a correction torque calculation value is set as the correction torque. On the other hand, in the case of the right direction, the process proceeds to step 207, and a value obtained by multiplying the correction torque calculation value by minus is set as the correction torque.

  In step 209, the first target electric motor torque T1 * and the correction torque Thos are added to calculate the final target electric motor torque T *.

  The effect by the said control process is demonstrated based on the time chart of FIG. In FIG. 9, the solid line represents the first cylinder chamber 51 (right cylinder pressure) without correction processing, the thick solid line represents the second cylinder chamber 52 (left cylinder pressure) without correction processing, and the one-dot chain line represents the correction processing. The first cylinder chamber 51 (right cylinder pressure) is provided, and the thick dashed line represents the second cylinder chamber 52 (left cylinder pressure) with correction processing.

[Without correction processing]
First, the operation in the case of the prior art that does not include the correction process will be described.
When the driver steers the steering wheel 1 to the right at time t1, the steering torque increases to the right. Along with this, a target electric motor torque corresponding to the steering torque is calculated, a current command value corresponding to the target electric motor torque T * is output to the electric motor 6a, and the pressure in the first cylinder chamber 51 increases.

  When the driver starts to weaken the steering torque to the right at time t2, an assist force corresponding to the small steering torque is applied. That is, in order to reduce the pressure in the first cylinder chamber 51, a target electric motor torque in a direction opposite to that during assisting is temporarily set for the electric motor 6a. The target electric motor torque in the opposite direction absorbs inertia torque of the electric motor 6a in order to lower the electric motor rotation speed, and does not reverse the electric motor rotation direction.

  At this time, since the hydraulic pressure in the first cylinder chamber 51 is higher than the hydraulic pressure in the second cylinder chamber 52 at time t2 ′, a large differential pressure acts on the bidirectional pump 6, and the bidirectional pump 6 It will be accompanied in the direction in which hydraulic fluid flows from the cylinder chamber 51 to the second cylinder chamber 52 side.

  Here, when the driver reduces the steering torque, the driver is in a state of turning back the steering wheel 1. If the hydraulic pressure in the first cylinder chamber 51 cannot be quickly reduced at the time of turning back, the self-aligning torque input from the steered wheels 7 is reached. Etc. will be canceled out, and feedback information from the road surface cannot be transmitted to the driver, which may give a sense of incongruity. Details will be described later.

  When the driver weakens the steering torque to the right side at time t3 and then applies the steering torque to the left side, the steering torque increases to the left side. Accordingly, a target electric motor torque corresponding to the steering torque is calculated, and a current command value corresponding to the target electric motor torque is output to the electric motor 6a. As a result, hydraulic oil is supplied to the second cylinder chamber 52. However, at time t3, the operating hydraulic pressure in the first cylinder chamber 51 has not yet been reduced, and the lowering of the operating hydraulic pressure in the first cylinder chamber 51 ends slightly later, and the operating hydraulic pressure in the second cylinder chamber 52 increases. To start.

  Here, the balance relationship between the forces of the steering system at time t3 will be described. In general, the steering system has an equation of motion based on steering torque input by the driver to the steering wheel 1, various frictions, assist force by the power steering mechanism 5, and road surface reaction force generated between the steering wheel 7 and the road surface. It is made up. Here, a self-aligning torque is generated between the steered wheel 7 and the road surface in accordance with the generation of the tire slip angle (or the twisting force of the steered wheel 7).

  Normally, the driver senses road surface feedback information such as self-aligning torque from the steering wheel 1 and performs steering in accordance with the traveling state. At this time, when shifting from the right assist state as described above to the left assist state, if the decrease of the hydraulic pressure in the right first cylinder chamber 51 is prevented, the self-aligning torque generated in the steered wheel 7 is There is a possibility that it will be canceled out by the hydraulic pressure in the one cylinder chamber 51 and sufficient road surface feedback information cannot be given to the driver.

  That is, if the hydraulic pressure in the cylinder chamber on the side where the assist is being performed cannot be quickly reduced when the steering wheel 1 is turned back, the driver cannot be provided with appropriate road surface feedback information, and the steering feeling is deteriorated. There is a risk of inviting.

[With correction processing]
Next, an operation when the correction process of the first embodiment is provided will be described.
When the driver steers the steering wheel 1 to the right at time t1, the steering torque increases to the right. Accordingly, a target electric motor torque corresponding to the steering torque is calculated, a current command value corresponding to the target electric motor torque is output to the electric motor 6a, and the pressure in the first cylinder chamber 51 increases.

  When the driver starts to weaken the steering torque to the right at time t2, an assist force corresponding to the small steering torque is applied. That is, in order to reduce the pressure in the first cylinder chamber 51, a target electric motor torque in a direction opposite to that during assisting is temporarily set for the electric motor 6a. The target electric motor torque in the opposite direction absorbs inertia torque of the electric motor 6a in order to lower the electric motor rotation speed, and does not reverse the electric motor rotation direction.

  At this time, since the hydraulic pressure in the first cylinder chamber 51 is higher than the hydraulic pressure in the second cylinder chamber 52 at time t2 ′, a large differential pressure acts on the bidirectional pump 6, and the bidirectional pump 6 The hydraulic oil is rotated in the direction in which the hydraulic oil flows from the cylinder chamber 51 toward the second cylinder chamber 52, and the steering torque direction and the electric motor rotation direction do not match. At this time, in order to reduce the hydraulic pressure in the first cylinder chamber 51 to an appropriate value, the correction torque Tdmhos is calculated and subtracted (or added) to the target electric motor torque. This correction torque is a correction amount assuming system friction in the electric motor rotation direction. It is desirable to avoid a sudden change in the driving force of the electric motor by performing a gradual increase correction at the start of applying the correction torque and a gradual decrease correction at the end of applying the correction torque.

  The system represents an oil flow path including the first cylinder chamber 51, the second cylinder chamber 52, oil passages 61 and 62 that are pipes connecting the cylinder chambers, and the bidirectional pump 6. This friction represents the ease of oil flow with respect to the electric motor rotation speed. By correcting in consideration of this friction, the hydraulic pressure in the first cylinder chamber 51 can be quickly reduced, and information relating to the self-aligning torque can be transmitted to the driver.

  When the driver weakens the steering torque to the right side at time t3 and then applies the steering torque to the left side, the steering torque increases to the left side. Accordingly, a target electric motor torque T * corresponding to the steering torque is calculated, and a current command value corresponding to the target electric motor torque T * is output to the electric motor 6a. As a result, hydraulic oil is supplied to the second cylinder chamber 52. At this time, the hydraulic pressure in the first cylinder chamber 51 has already decreased, and the hydraulic pressure in the second cylinder chamber 52 starts to increase immediately after time t3.

  Therefore, when the steering direction is switched, the self-aligning torque is not canceled by the hydraulic pressure in the cylinder chamber, and sufficient road surface feedback information can be given to the driver.

(Contrast with power steering device using rotary valve)
Here, a description will be given based on comparison with an existing power steering apparatus in which a pump driven by an engine is used as a hydraulic pressure source and the hydraulic pressure supplied from the hydraulic pressure source is switched by a rotary valve. In general, in a conventional power steering apparatus having a rotary valve that switches an oil passage according to torsion of a torsion bar, the steering direction is switched, and hydraulic pressure is supplied from the assisting cylinder chamber to the other cylinder chamber. When is started, the assisting cylinder chamber is connected to the drain circuit. Therefore, since the hydraulic pressure can be reduced relatively quickly, the information on the self-aligning torque can be fed back to the driver.

  On the other hand, as in the first embodiment, the first cylinder chamber 51 and the second cylinder chamber 52 are sealed via the bidirectional pump 6, and the hydraulic pressure in the cylinder chamber is not connected to the drain circuit, and the bidirectional pump In the case of a system that controls the assist force by supplying and discharging 6 (hereinafter referred to as the system of the first embodiment), there are the following problems. That is, when the hydraulic pressure drop in the assisting cylinder chamber is insufficient, the hydraulic pressure in the assisting cylinder chamber does not rise, and the relationship between the steering torque applied to the steering wheel 1 and the steering wheel 7 is lost. There is a fear, and it gives the driver a sense of incongruity. In particular, when the above-described self-aligning torque feedback information is lost, a sense of incongruity occurs.

(Contrast between prior art and Example 1)
Therefore, the applicant of the present invention separately provides a fail-safe valve for connecting the assisting cylinder chamber to the drain circuit or the other cylinder chamber when the steering direction is switched in the system of the first embodiment. Proposed system (equal to conventional technology). This system detects the driver's turn-back based on the rate of change of the steering torque, and when turning-back is detected, the fail-safe valve is temporarily opened to lower the hydraulic pressure in the cylinder chamber.

  In the prior art, basically, a fail-safe valve is used to perform ON / OFF control. This fail-safe valve is intended to allow the left and right cylinder chambers to communicate with each other at the time of failure so that the steering can be performed only by the driver's steering force, and an inexpensive valve is used. In this case, if both cylinder chambers are connected at once, the hydraulic pressure is applied at a stroke from the higher hydraulic pressure to the lower hydraulic pressure, which may cause an oil hammer or a sudden torque fluctuation. If a proportional control valve or the like is mounted in order to avoid this problem, fine pressure reduction control or the like must be performed, which may increase the cost of the entire system.

10 and 11 are time charts showing the ON / OFF control of the fail-safe valve. The prior art has the problem shown in FIG.
Problem (1) Since turning-back is determined based on the rate of change of steering torque, it is unstable, for example, it is determined that turning-back is caused by a slight change in steering torque.
Problem (2) The valve opening pressure of the fail-safe valve becomes a resistance and may not be able to be quickly reduced.

Further, the conventional technique has a problem shown in FIG.
Problem (3) When a delay in response of the fail-safe valve occurs, a delay in response from the fail-safe valve opening command to the actual start of pressure reduction occurs, which tends to cause discomfort.
Problem (4) When the cylinder pressure is reduced and the electric motor 6a is driven to supply hydraulic pressure to the other cylinder chamber, the fail-safe valve is opened, so that no load is generated in the cylinder chamber, and the electric motor rotation speed is reduced. May rise at a stretch.
Problem (5) When such a state is repeated, the steering torque changes in accordance with the fluctuation, which may cause control hunting.

  On the other hand, in the first embodiment, it is possible to make a stable switching determination by determining the rotation based on both the electric motor rotation direction and the steering torque (solving the problem (1)). In addition, by correcting the target electric motor torque T * of the electric motor 6a that drives the bidirectional pump 6, problems (2), problems (3), problems (4), problems of the fail-safe valve itself are corrected. All of (5) can be eliminated, and a good steering feeling can be provided without causing a delay in response or control hunting.

  Next, Example 2 will be described. Since the basic configuration is the same as that of the first embodiment, only different points will be described. FIG. 12 is a control block diagram illustrating the configuration of the target electric motor torque calculation unit 70 according to the second embodiment. In the first embodiment, the correction torque is calculated based on the number of revolutions of the electric motor in order to compensate for the friction of the system. On the other hand, the second embodiment is different from the first embodiment in that the compensation torque is calculated based on the change rate of the steering torque for the purpose of compensating for the inertia of the system.

That is, in step 202, the correction torque Thos is calculated from the following equation.
Thos ＝ Tdmhos ＋ Tlmhos
However,
Tdmhos ＝ Motrev × Dmg × Gtmp
Tlmhos = (d (TTrq) / dt) × lmg
Motrev: Electric motor speed
Dmg: Dynamic friction coefficient
Gtmp: Temperature correction coefficient
d (TTrq) / dt: Steering torque differential value
lmg is the inertia characteristic coefficient of the system. The inertia characteristic coefficient of the system is an inertia characteristic between the bidirectional pump 6 and each of the cylinder chambers 51 and 52, and may be obtained in advance by experiments or the like.

  That is, when the steering torque changes, the steering system moves along with the change. The driver usually steers based on the relationship between the steering torque applied to the steering wheel 1 and the steering wheel 7. Therefore, when the steering torque changes, the delay due to the inertia is suppressed by compensating for the inertia corresponding to the motion generated in the system due to this change.

  The effect by the said control process is demonstrated based on the time chart of FIG. In FIG. 13, the solid line represents the relationship without correction processing, the dotted line represents the relationship of Example 1, and the alternate long and short dash line represents the relationship of Example 2.

  When the driver steers the steering wheel 1 to the right at time t21, the steering torque increases to the right. Accordingly, a target electric motor torque corresponding to the steering torque is calculated, a current command value corresponding to the target electric motor torque is output to the electric motor 6a, and the pressure in the first cylinder chamber 51 increases.

  When the driver starts to weaken the steering torque to the right at time t22, it is necessary to apply an assist force corresponding to a small steering torque (substantially neutral state). Therefore, in order to reduce the pressure in the first cylinder chamber 51, a target electric motor torque in the opposite direction to that during assisting is set for the electric motor 6a.

  When the driver starts to weaken the steering torque to the right side, an assist force corresponding to a small steering torque is applied. That is, in order to reduce the pressure in the first cylinder chamber 51, a target electric motor torque in a direction opposite to that during assisting is temporarily set for the electric motor 6a. The target electric motor torque in the opposite direction absorbs inertia torque of the electric motor 6a in order to lower the electric motor rotation speed, and does not reverse the electric motor rotation direction.

  At this time, since the hydraulic pressure in the first cylinder chamber 51 is higher than the hydraulic pressure in the second cylinder chamber 52, a large differential pressure acts on the bidirectional pump 6. The hydraulic oil is rotated in the direction in which the hydraulic oil flows to the two-cylinder chamber 52 side, and the steering torque direction and the electric motor rotation direction do not match. At this time, correction torques Tdmhos and Tlmhos are calculated and subtracted (or added) to the target electric motor torque in order to reduce the hydraulic pressure in the first cylinder chamber 51 to an appropriate value.

  This correction torque is calculated as a correction torque assuming system friction and system inertia in the electric motor rotation direction. That is, a large correction torque is added when the steering torque change rate is large, and a small correction torque is added when the steering torque change rate is small. Thereby, compared with Example 1, the transient response of the hydraulic pressure fall of the 1st cylinder chamber 51 can be improved further. When the rate of change of the steering torque is large, the movement of the system becomes faster, so that the correction torque is increased according to the rate of change of the steering torque.

  At time t23, when the driver weakens the steering torque to the right side and then applies the steering torque to the left side, the steering torque increases to the left side. Accordingly, a target electric motor torque corresponding to the steering torque is calculated, and a current command value corresponding to the target electric motor torque is output to the electric motor 6a. As a result, hydraulic oil is supplied to the second cylinder chamber 52. At this time, the hydraulic pressure in the first cylinder chamber 51 has already decreased, and the hydraulic pressure in the second cylinder chamber 52 starts to increase immediately from time t23.

  Therefore, it is possible to improve the transient response at the time of switching the steering direction, etc., and the self-aligning torque is not canceled by the hydraulic pressure in the cylinder chamber, and sufficient road surface feedback information can be given to the driver.

  Next, Example 3 will be described. Since the basic configuration is the same as that of the second embodiment, only different points will be described. FIG. 14 is a control block diagram illustrating a control configuration of the target electric motor torque calculation unit 70 of the third embodiment. In Example 2, when calculating the correction torque Thos, values (Tdmhos and Tlmhos) in consideration of both system friction and inertia were used. On the other hand, the third embodiment is different in that a vehicle speed sensitive gain Gvsp is applied to the correction torque Thos.

That is, in step 202, the correction torque Thos is calculated from the following equation.
Thos = (Tdmhos + Tlmhos) x Gvsp
However,
Tdmhos ＝ Motrev × Dmg × Gtmp
Tlmhos = (d (TTrq) / dt) × lmg
Motrev: Electric motor speed
Dmg: Dynamic friction coefficient
Gtmp: Temperature correction coefficient
d (TTrq) / dt: Steering torque differential value
lmg: System inertia characteristic coefficient
Gvsp: Vehicle speed sensitivity gain.

  FIG. 15 is a map showing the vehicle speed sensitivity gain. As described above, the reaction force (self-aligning torque or the like) acting on the steered wheels 7 has a correlation with the tire slip angle. The tire slip angle has a correlation with the steering angle, lateral acceleration, yaw rate, vehicle speed, and the like. The vehicle speed sensitivity gain is set to a small gain because the self-aligning torque decreases at high vehicle speeds, and is set to a large gain at low vehicle speeds because the self-aligning torque increases. In this way, by setting the vehicle speed sensitive gain, even in the high vehicle speed range, even when the driver turns the steering wheel 1 back, the force to suddenly return to the neutral position is suppressed, so Can be improved. Further, in the low vehicle speed region, by reproducing the self-aligning torque more, the reaction force acting on the steering wheel 7 can be accurately fed back to the driver, and the steering feeling can be further improved.

  In the third embodiment, the vehicle speed sensitive gain Gvsp is applied to the sum of Tdmhos and Tlmhos, but the vehicle speed sensitive gain for friction compensation and the vehicle speed sensitive gain for inertia compensation may be set separately. .

  The technical ideas other than the claims based on the above embodiments are listed below.

(1) In the power steering device according to claim 1 or 2,
The electric motor is a brushless motor,
The power steering device according to claim 1, wherein the electric motor rotation direction detecting means is position detecting means for detecting a position of a stator of the electric motor.

  By using a brushless motor position detection sensor (such as a resolver) as the electric motor rotation direction detection means, there is no need to provide a special sensor or the like.

(2) In the power steering device according to claim 1 or 2,
The electric motor rotation direction detecting means detects a rotation direction of the electric motor based on an electric motor drive signal of the electric motor control means.

  By detecting the rotation direction of the electric motor based on the electric motor drive signal, it is not necessary to provide a special sensor or the like.

(3) In the power steering device according to claim 1 or 2,
The electric motor control means corrects the drive signal gradually when the follow-up determination means determines that the direction of the steering load and the rotation direction of the electric motor do not coincide with each other. .

  By gradually increasing the driving signal, a sudden change in the driving force of the electric motor can be avoided, and the uncomfortable steering caused by the change in the hydraulic pressure can be suppressed.

  (4) In the power steering apparatus according to claim 1 or 2, the electric motor control means is configured such that the follow-up determination means is in a state in which the direction of the steering load and the rotational direction of the electric motor do not coincide with each other. A power steering device characterized by gradually reducing the drive signal when it is determined that the shift has been made.

  When the steering load direction and the electric motor rotation direction are matched, the drive signal is gradually lowered and returned to the normal drive signal, thereby avoiding an abrupt change in the electric motor drive force, An uncomfortable feeling of steering due to a change in pressure can be suppressed.

1 is a system configuration diagram of a power steering device in Embodiment 1. FIG. FIG. 3 is a block diagram illustrating a configuration within a control unit according to the first embodiment. FIG. 3 is a schematic diagram illustrating a configuration of a pump unit in the first embodiment. It is a figure showing the flow of the oil at the time of the normal torque assist control in Example 1. FIG. FIG. 6 is an operation explanatory diagram illustrating the movement of the return check valve according to the first embodiment. It is a control block diagram showing the structure of the target electric motor torque calculating part in Example 1. It is a flowchart showing the control content of the target electric motor torque calculating part in Example 1. 3 is a map showing a temperature correction coefficient in the first embodiment. 6 is a time chart illustrating a case where correction processing is not performed and a case where correction processing is performed in the first embodiment. It is a time chart showing the problem in a prior art. It is a time chart showing the problem in a prior art. It is a control block diagram showing the structure of the target electric motor torque calculating part in Example 2. 6 is a time chart illustrating a case where correction processing is performed in the second embodiment, a case where correction processing is performed in the first embodiment, and a case where correction processing is not performed. FIG. 10 is a control block diagram illustrating a configuration of a target electric motor torque calculation unit according to a third embodiment. 10 is a map showing a vehicle speed sensitivity gain in the third embodiment.

Explanation of symbols

1 Steering wheel 4 Fail-safe valve 5 Power steering mechanism 5a Power cylinder (hydraulic power cylinder)
6 Bi-directional pump 6a Electric motor 6b Electric motor rotational speed sensor 7 Steering wheel 10 Control unit 12 Torque sensor 13 Ignition switch 14 Engine rotational speed sensor 15 Vehicle speed sensor 51 First cylinder chamber (first pressure chamber)
52 Second cylinder chamber (second pressure chamber)
61 Oil passage (first passage, second passage)
62 Bypass circuit 63 Drain oil passage 72 Accompanying judgment unit 73 Correction torque calculation unit
115 Electric motor rotation signal processing circuit
203a First return check valve (first bypass valve)
204 Check valve
204a Second return check valve (second bypass valve)
205 Reservoir tank

Claims (3)

A hydraulic power cylinder for assisting the steering force of the steering mechanism connected to the steering wheel;
A bidirectional pump having a pair of discharge ports for supplying hydraulic pressure to the first and second pressure chambers of the hydraulic power cylinder via the first and second passages, respectively;
An electric motor connected to the bidirectional pump and rotating the bidirectional pump forward and reverse;
Steering load detection means for detecting or estimating a steering load of a steering wheel for steering control of the steering wheel;
Electric motor control means for outputting a drive signal to the electric motor in order to generate a desired hydraulic pressure in the electric motor based on the steering load;
Electric motor rotation direction detecting means for detecting the rotation direction of the electric motor;
When the steering load direction and the electric motor rotation direction do not match , the reaction force acting on the electric motor is larger than the driving torque of the electric motor due to the pressure difference between the first and second pressure chambers. A follow-up judging means for judging that the accompanying state is
When the accompanying determination unit determines that the accompanying state is in the accompanying state , a correcting unit that corrects the driving signal to the accompanying side;
A power steering apparatus comprising: The power steering apparatus according to claim 1, wherein
An electric motor rotation number detecting means for detecting the rotation number of the electric motor is provided;
The power steering device according to claim 1, wherein the correction means calculates a correction amount of the drive signal based on a value obtained by multiplying a rotation speed of the electric motor by a predetermined dynamic friction coefficient. A hydraulic power cylinder for assisting the steering force of the steering mechanism connected to the steering wheel;
A bidirectional pump having a pair of discharge ports for supplying hydraulic pressure to the first and second pressure chambers of the hydraulic power cylinder via the first and second passages, respectively;
An electric motor connected to the bidirectional pump and rotating the bidirectional pump forward and reverse;
Steering load detection means for detecting or estimating a steering load of a steering wheel for steering control of the steering wheel;
Electric motor control means for outputting a drive signal to the electric motor in order to generate a desired hydraulic pressure in the electric motor based on the steering load;
A reservoir tank for storing hydraulic oil;
A first bypass valve that switches between communication and blocking between the first pressure chamber and the reservoir tank based on the hydraulic pressure of the bidirectional pump;
A second bypass valve that switches between communication and blocking between the second pressure chamber and the reservoir tank based on the hydraulic pressure of the bidirectional pump;
Provided between the first bypass valve and the second bypass valve and the reservoir tank, the pressure on the first bypass valve and second bypass valve side is higher than the pressure on the reservoir tank side by a predetermined value or more. A check valve that allows the flow of oil from the first bypass valve side and the second bypass valve side to the reservoir tank side,
Electric motor rotation direction detecting means for detecting the rotation direction of the electric motor;
When the steering load direction and the electric motor rotation direction do not match , the reaction force acting on the electric motor is larger than the driving torque of the electric motor due to the pressure difference between the first and second pressure chambers. A follow-up judging means for judging that the accompanying state is
When the accompanying determination unit determines that the accompanying state is in the accompanying state, a correcting unit that corrects the driving signal to the accompanying side;
A power steering apparatus comprising:

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