JP2008213669A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly increase a temperature by circulating working fluid over a wide range in a hydraulic system when a temperature of a working fluid is low. <P>SOLUTION: A hydraulic circuit for imparting moving force to a steering rod 14 is constituted by connecting a two-way pump 31 with a first hydraulic chamber 24 and second hydraulic chamber 25 in a hydraulic cylinder device 21 by a first piping 41 and second piping 42, respectively, and provided with a bypass pipe 48 for communicating with the first hydraulic chamber 24 and second hydraulic chamber 25 independently from the circuit. When the temperature Th of the working fluid becomes a reference temperature Th0 or lower, the two-way pump 31 is driven besides opening a solenoid opening/closing valve 49 provided to a bypass pipe 48. By so doing, the working fluid is circulated over the entire system including the hydraulic cylinder device 21. As a result, the temperature of the working fluid is uniformly increased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steering device that generates a hydraulic pressure difference in a hydraulic cylinder by a bidirectional pump to generate a moving force in a steered rod.

  2. Description of the Related Art Conventionally, there is known a steering device that applies assist torque to steered wheels by operating a hydraulic cylinder with a bidirectional pump. For example, in the power steering device proposed in Patent Document 1, a power cylinder is provided in a rack of a rack and pinion type steering device, and a first pressure chamber and a second pressure chamber partitioned by a piston of the power cylinder are provided in the first flow chamber. It connects with a bidirectional pump via a channel and the 2nd channel. And an assist torque is given to a steered wheel by controlling the electric motor which drives a bidirectional pump, and supplying hydraulic pressure selectively to two pressure chambers.

In such a power steering device using hydraulic pressure, if the temperature of the hydraulic oil is low, the force required for steering becomes large and the steering operation becomes heavy. Therefore, in the apparatus proposed in Patent Document 1, a communication path that connects the first flow path and the second flow path is provided, and a tank is connected to the communication path via an electromagnetic valve, so that the temperature of the hydraulic oil is increased. When the engine pressure is low, the solenoid valve is opened and the bidirectional pump is driven to circulate the hydraulic oil through the tank.
JP 2006-82568 A

  However, in the apparatus proposed in Patent Document 1, the hydraulic oil existing in the first flow path or the second flow path only circulates through the tank, and the hydraulic oil does not circulate in a wide range in the system. Absent. For example, hydraulic fluid in the power cylinder (first pressure chamber, second pressure chamber) with a large amount of oil does not circulate. For this reason, the temperature of the hydraulic oil in the entire system cannot be increased uniformly.

  The present invention has been made to cope with the above-described problem, and an object of the present invention is to uniformly raise the temperature of a working fluid over a wide range in a hydraulic system when the temperature of the working fluid is low.

  In order to achieve the above object, the present invention is characterized by comprising a steered rod for connecting steerable wheels so as to be steerable, and a first hydraulic pressure chamber and a second hydraulic pressure chamber on the left and right sides of the piston. A hydraulic cylinder that generates a moving force in the steered rod due to a hydraulic pressure difference between the hydraulic chambers, and a first pipe that communicates with the first hydraulic chamber and a second pipe that communicates with the second hydraulic chamber are connected. Then, a bidirectional pump that selectively supplies hydraulic pressure to the first hydraulic pressure chamber and the second hydraulic pressure chamber, an electric motor that drives the bidirectional pump in forward rotation and reverse rotation, and steering of the steering handle A steering apparatus comprising: a steering detection means for detecting a state; and a motor control means for driving the bidirectional pump by controlling the electric motor in accordance with the detected steering state. The first hydraulic chamber and the first hydraulic chamber of the hydraulic cylinder are independent of the piping. A bypass pipe communicating with the hydraulic pressure chamber, an on-off valve provided in the bypass pipe, a temperature detection means for detecting the temperature of the hydraulic fluid or the environmental temperature of the hydraulic fluid, and a detected temperature detected by the temperature detection means are predetermined. And a circulation control means for opening the on-off valve and driving the two pumps to circulate the working fluid when the temperature is lower than the temperature.

  According to this invention, the motor control means controls the electric motor according to the steering state of the driver to drive the bidirectional pump. The bidirectional pump communicates with the first hydraulic chamber and the second hydraulic chamber of the hydraulic cylinder through the first pipe and the second pipe. When the bidirectional pump is driven, the hydraulic fluid is pumped from one hydraulic chamber (first hydraulic chamber or second hydraulic chamber) of the hydraulic cylinder and the other hydraulic chamber (second hydraulic chamber or To the first hydraulic pressure chamber). Thereby, a hydraulic pressure difference is generated between the hydraulic pressure chambers, and a moving force is applied to the steered rod. The turning force is applied to the steered wheels by the moving force applied to the steered rod. In this case, for example, by controlling the height of the hydraulic chamber of the hydraulic cylinder, the size of the hydraulic pressure difference, the inflow / outflow amount of hydraulic fluid, etc., the moving direction, moving force, moving speed, etc. of the steered rod are controlled. can do.

  Incidentally, examples of the steering detection means for detecting the steering state of the steering handle include a torque detection means for detecting a steering torque acting on the steering handle, and a steering angle detection means for detecting the steering angle of the steering handle. Further, the moving force applied to the steered rod may be used as, for example, steering assist torque, or generated by a steering-by-wire steering actuator that mechanically separates the steering operation unit and the steered drive unit. It may be used as a turning force.

  When the temperature of the hydraulic fluid is low, the force required for steering increases and the steering operation becomes heavy. Therefore, in the present invention, a bypass pipe that communicates the first hydraulic pressure chamber and the second hydraulic pressure chamber, and an on-off valve that opens and closes the flow path of the bypass pipe, the temperature of the hydraulic fluid or the environmental temperature of the hydraulic fluid is provided. When the temperature is below a predetermined temperature, the on-off valve is opened and the bidirectional pump is driven. The bypass pipe is provided to communicate the first hydraulic pressure chamber and the second hydraulic pressure chamber independently of the first pipe and the second pipe. That is, apart from the first pipe and the second pipe, a bypass pipe is provided as an independent flow path that connects the first hydraulic pressure chamber and the second hydraulic pressure chamber. Therefore, one end of the bypass pipe is connected to the first hydraulic chamber, and the other end is connected to the second hydraulic chamber.

In such a flow path configuration, the circulation control means maintains the open / close valve in a closed state if the temperature of the hydraulic fluid or the environmental temperature of the hydraulic fluid exceeds a predetermined temperature, but if the temperature is below the predetermined temperature, Is opened and the bidirectional pump is driven.
When the on-off valve is opened and the bidirectional pump is driven, hydraulic fluid is pumped from one hydraulic pressure chamber and supplied to the other hydraulic pressure chamber. In this case, since the two hydraulic chambers communicate with each other by the bypass pipe, the working fluid flows through the bypass pipe so as to cancel the hydraulic pressure difference between the hydraulic chambers. That is, hydraulic fluid flows from the high-pressure side hydraulic pressure chamber to the low-pressure side hydraulic pressure chamber via the bypass pipe due to the hydraulic pressure difference generated by the pump drive. This flow continues while the bi-directional pump is being driven.

  As a result, for example, the working fluid pumped from the first hydraulic chamber flows in the order of the first pipe → the bidirectional pump → the second pipe → the second hydraulic chamber → the bypass pipe → the first hydraulic chamber →. Circulate with. When the direction of rotation of the bidirectional pump is reversed, the hydraulic fluid is pumped from the second hydraulic pressure chamber, and the second pipe → bidirectional pump → first pipe → first hydraulic chamber → bypass pipe → second liquid It circulates in the flow of pressure chamber →. Accordingly, the working fluid can be circulated in a wide range in the system including the hydraulic cylinder. During the circulation of the hydraulic fluid, the hydraulic pressure is released and the hydraulic pressure difference between the hydraulic chambers is reduced, so that the moving force acting on the steered rod is small. Therefore, the problem that the steered wheels are steered does not occur.

Thus, according to the present invention, the temperature of the working fluid can be raised uniformly over a wide range in the system.
In the present invention, for example, when the steering detection means detects that the steering handle is operated, a prohibition means for prohibiting the operation of the circulation control means may be provided. When the steering operation is performed, if the circulation control is performed by opening the flow path of the bypass pipe, the steering rod cannot generate the moving force due to the hydraulic pressure. A certain amount of moving force can be generated.

  Further, vehicle speed detection means for detecting the vehicle speed and prohibition means for prohibiting the operation of the circulation control means when the vehicle speed is equal to or higher than a predetermined vehicle speed (for example, during traveling) may be provided. For example, the operation of the circulation control unit may be permitted while the vehicle is stopped, and the operation of the circulation control unit may be prohibited when the vehicle starts to travel and reaches a predetermined vehicle speed. This predetermined vehicle speed may determine whether the vehicle is running or stopped. Also in this case, a moving force can be generated on the steered rod in accordance with the steering of the steering wheel during traveling.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a power steering apparatus for a vehicle as an embodiment of a steering apparatus of the present invention.

  The power steering device of this vehicle is roughly classified into a steering mechanism 10 that steers the left and right front wheels FW1 and FW2 that are steered wheels by steering the steering handle 11, and a liquid that generates a steering assist torque in response to a driver's steering operation. The pressure assist device 20 includes an assist control device 50 that controls the operation of the hydraulic pressure assist device.

  The steering mechanism 10 is a mechanism for steering the left and right front wheels FW1 and FW2 by a rotating operation of the steering handle 11, and includes a steering shaft 12 connected so as to rotate integrally with the upper end of the steering handle 11. A pinion gear 13 is connected to the lower end of the steering shaft 12 so as to rotate integrally. The pinion gear 13 meshes with the rack teeth 15 formed on the steered rod 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the steered rod 14 via a tie rod 16 and a knuckle arm 17. As a result, the left and right front wheels FW1 and FW2 are steered to the left and right according to the axial displacement of the steered rod 14 accompanying the rotation of the steering shaft 12 around the axis.

  The steering shaft 12 is provided with a steering torque sensor 61. The steering torque sensor 61 is one of the components of the assist control device 50 described later, and outputs a signal corresponding to the steering torque that acts on the steering shaft 12 when the steering handle 11 is turned. The value of the steering torque detected from the signal output from the steering torque sensor 61 is hereinafter referred to as steering torque Tr. As for the steering torque Tr, the operation direction of the steering wheel 11 is identified by positive and negative values. In the present embodiment, the steering torque Tr when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Tr when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, the magnitude of the steering torque Tr is the absolute value thereof.

  The hydraulic pressure assist device 20 constitutes an actuator that applies a moving force in the rod axis direction to the steered rod 14, and includes a hydraulic cylinder device 21 and a pump that supplies the hydraulic pressure to the hydraulic cylinder device 21. The apparatus 30 and the piping part 40 which forms the flow path of the hydraulic fluid (hydraulic oil) which flows with the pump apparatus 30 are provided.

  The hydraulic cylinder device 21 includes a cylinder body 22 fixed to the vehicle body, and a piston 23 fitted in the cylinder body 22 so as to be fluid-tight and slidable. A steering rod 14 is inserted coaxially in a liquid-tight and slidable manner in the cylinder body 22, and a piston 23 is provided so as not to move relative to the steering rod 14. Thus, the cylinder body 22 and the piston 23 divide the inside of the cylinder body 22 into two hydraulic chambers, the first hydraulic chamber 24 and the second hydraulic chamber 25.

  The pump device 30 includes a bidirectional pump 31 and a pump motor 32 that drives the bidirectional pump 31. The bidirectional pump 31 includes a first port 31a and a second port 31b that serve as an inflow / outflow portion of the working fluid. Accordingly, the hydraulic pressure supply direction of the hydraulic oil is switched according to the rotation direction of the pump motor 32.

  The piping section 40 includes a first pipe 41 that communicates the first port 31a of the bidirectional pump 31 and the first hydraulic chamber 24 of the hydraulic cylinder device 21, and the second port 31b of the bidirectional pump 31 and the hydraulic cylinder. And a second pipe communicating with the second hydraulic chamber 25 of the device. The first pipe 41 is connected to the first suction pipe 43 in the middle thereof. The first suction pipe 43 is connected to a tank 45 with a suction check valve 44 provided on the way. Similarly, the second pipe 42 is also connected to the tank 45 by a second suction pipe 47 provided with a suction check valve 46. The two suction tech valves 44 and 46 are each opened when the pressure in the bidirectional pump 31 is lower than the pressure in the tank 45.

  The tank 45 is provided with a temperature sensor 62 that detects the temperature of the hydraulic fluid. The temperature sensor 62 is one of the components of the assist control device 50 described later, and outputs a signal corresponding to the detected temperature. Hereinafter, the temperature value detected by the signal output from the temperature sensor 62 is referred to as a hydraulic fluid temperature Th. The temperature sensor 62 is not limited to the one that directly detects the temperature of the hydraulic fluid, but can also calculate the environmental temperature of the hydraulic fluid that affects the temperature of the hydraulic fluid by detection or estimation. For example, the atmospheric temperature of the hydraulic assist device 20 may be detected.

  The piping unit 40 further includes a bypass pipe 48 that communicates the first hydraulic chamber 24 and the second hydraulic chamber 25 of the hydraulic cylinder device 21. The bypass pipe 48 forms a flow path independently communicating with the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25 separately from the first pipe 41 and the second pipe 42, and one end of the bypass pipe 48 is formed. The first hydraulic chamber 24 is connected, and the other end is connected to the second hydraulic chamber 25. Further, the bypass pipe 48 is provided with an electromagnetic on-off valve 49 that controls opening and closing of the flow path.

The assist control device 50 controls the operation of the hydraulic pressure assist device 20, calculates a target energization control amount of the pump motor 32 in accordance with the steering operation state, and controls the pump motor 32 with the calculated target energization control amount. An electronic control unit 51 that performs drive control and a motor drive circuit 52 that energizes the pump motor 32 in accordance with a control command from the electronic control unit 51 are configured.
The electronic control unit 51 is mainly composed of a microcomputer composed of a CPU, a ROM, a RAM and the like. The electronic control unit 51 receives a detection signal from the steering torque sensor 61, a detection signal from the temperature sensor 62, and a detection signal from the vehicle speed sensor 63. The vehicle speed sensor 63 outputs a vehicle speed detection signal indicating the traveling speed V of the vehicle.

  For example, the motor drive circuit 52 forms a bridge circuit by a plurality of switching elements (not shown), and supplies a drive current for normal rotation or reverse rotation to the pump motor 32 by energization control to each switching element. In the motor drive circuit 52, for example, the magnitude of the motor current is also controlled by energizing the switching element at a duty ratio corresponding to the PWM control signal from the electronic control unit 51.

  In the pump device 30, the bidirectional pump 31 is rotated by energization from the motor drive circuit 52 to the pump motor 32, and either from the first hydraulic chamber 24 or the second hydraulic chamber 25 of the hydraulic cylinder device 21. Pump the hydraulic fluid and supply it to the other. As a result, a hydraulic pressure difference is generated between the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25, and a moving force corresponding to the hydraulic pressure difference acts on the steered rod 14. For example, when the steered rod 14 is moved in the right direction of the drawing, the hydraulic fluid is pumped from the second hydraulic pressure chamber 25 and supplied to the first hydraulic pressure chamber 24. Further, the operation state of the bidirectional pump 31, for example, the rotation direction, the discharge flow rate, the discharge pressure, and the like can be controlled by the energization control of the pump motor 32.

  The electronic control unit 51 controls not only the pump device 30 but also the opening / closing operation of the electromagnetic opening / closing valve 49. The electromagnetic on-off valve 49 is a normally closed type urged in the valve closing direction by a spring or the like, and is maintained in an open state only in a state where the solenoid is energized from the electronic control unit 51 and is not energized in the solenoid. In this case, the valve is kept closed.

  Next, pump control processing performed by the assist control device 50 will be described. FIG. 2 shows a pump control routine performed by the assist control device 50. The pump control routine is stored in the ROM of the electronic control unit 51 as a control program and repeatedly executed in a short cycle. This control routine is executed after an ignition switch (not shown) is turned on and a predetermined initial diagnosis is completed. The pump control routine includes assist control and circulation control for circulating the working fluid at a low temperature.

  When this control routine is started, the electronic control unit 51 determines in step S11 that the steering torque Tr detected by the steering torque sensor 61, the hydraulic fluid temperature Th detected by the temperature sensor 62, and the vehicle speed V detected by the vehicle speed sensor 63. Is read. Subsequently, in step S12, it is determined whether the hydraulic fluid temperature Th is equal to or lower than the reference temperature Th0. The reference temperature Th0 is set to a very low temperature at which the performance of the hydraulic pressure assist device 20 is reduced due to the increase in the viscosity of the hydraulic fluid and the handle operation becomes heavier than the reference level.

  In step S12, when it is determined that the hydraulic fluid temperature Th exceeds the reference temperature Th0 (S12: NO), the assist control from step S13 is performed. In step S13, the target assist torque Tr * is calculated based on the steering torque Tr and the vehicle speed V read in step S11. The target assist torque Tr * is calculated with reference to an assist torque table shown in FIG. 3, for example. This assist torque table is stored in the ROM of the electronic control unit 51 and is set so that the target assist torque Tr * increases as the steering torque Tr increases, and increases as the vehicle speed V decreases. Is done.

The characteristic graph of FIG. 3 shows only the relationship between the positive region, that is, the steering torque Tr in the right direction and the target assist torque Tr *, but the negative region, that is, the steering torque Tr in the left direction, and the target assist torque Tr *. 3 is moved to a point-symmetrical position around the origin. In this embodiment, the target assist torque Tr * is calculated using the assist torque table. However, instead of the assist torque table, a target assist torque T * that changes according to the steering torque Tr and the vehicle speed V is defined. You may make it calculate with the prepared function.
The target assist torque Tr * is not necessarily calculated from the combination of the vehicle speed V and the steering torque Tr, and may be calculated based on at least a detection signal corresponding to the steering state.

  Subsequently, the electronic control unit 51 calculates the target current I * necessary for generating the target assist torque Tr * in step S14, and in step S15, the motor drive circuit 52 causes the motor corresponding to the target current I * to be calculated. A control signal (for example, PWM control signal) is output. Thus, the target current I * flows through the pump motor 32. As a result, the bidirectional pump 31 is driven, and a hydraulic pressure difference corresponding to the target assist torque Tr * is generated between the two hydraulic chambers 24 and 25 of the hydraulic cylinder device 21. Movement force is applied. This moving force acts as an assist torque that assists the driver's steering operation.

  The electronic control unit 51 ends the present control routine once when the process of step S15 is performed, but repeatedly executes the same process at a predetermined short period until the ignition switch is turned off. Therefore, the optimum assist torque according to the driver's steering wheel operation and the vehicle speed can be obtained.

  In a system using such hydraulic pressure, when the temperature of the hydraulic fluid becomes extremely low, the force required for steering becomes large and the steering operation becomes heavy. Therefore, when the electronic control unit 51 determines in step S12 that the hydraulic fluid temperature Th is equal to or lower than the reference temperature Th0 (S12: YES), the electronic control unit 51 does not perform the assist control in steps S13 to S15 described above. Circulation control of the hydraulic fluid is performed through S16 to S17.

  The electronic control unit 51 energizes the solenoid of the electromagnetic on-off valve 49 in step S16. As a result, the electromagnetic on-off valve 49 is opened, and the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25 of the hydraulic cylinder device 21 are communicated via the bypass pipe 48. Accordingly, a circulation path through which the hydraulic fluid circulates by the bidirectional pump 31 is formed including the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25.

  Subsequently, the electronic control unit 51 energizes the pump motor 32 to rotate the bidirectional pump 31 in step S17. The energization amount to the pump motor 32 may be a preset value, and the rotation direction of the bidirectional pump 31 can be arbitrarily set. When the bidirectional pump 31 rotates, hydraulic fluid is pumped from one of the two hydraulic chambers 24 and 25 and supplied to the other. In this case, since the two hydraulic pressure chambers 24 and 25 are communicated with each other by the bypass pipe 48, the working fluid flows to the bypass pipe 48 so as to cancel the hydraulic pressure difference between the hydraulic pressure chambers 24 and 25. That is, the hydraulic fluid flows from the high-pressure side hydraulic chamber 24 (or 25) to the low-pressure side hydraulic chamber 25 (or 24) through the bypass pipe 48 due to the hydraulic pressure difference generated by the rotation of the bidirectional pump 31.

  As a result, for example, when the bidirectional pump 31 is rotated so as to send the working fluid from the first port 31a to the second port 31b, the working fluid is the first as shown by the solid arrow in FIG. Circulation is performed in the flow of piping 41 → bidirectional pump 31 → second piping 42 → second hydraulic pressure chamber 25 → bypass pipe 48 → first hydraulic pressure chamber 24 → first piping 41 →. When the direction of rotation of the bidirectional pump 31 is reversed, as indicated by a broken line arrow in FIG. 1, the second pipe 42 → the bidirectional pump 31 → the first pipe 41 → the first hydraulic pressure chamber 24 → the bypass pipe. It circulates in the flow of 48 → second hydraulic pressure chamber 25 → second pipe 42 →. Therefore, the working fluid can be circulated in a wide range in the system including the hydraulic cylinder device 21.

  During the circulation of the hydraulic fluid, the hydraulic pressure is released and the hydraulic pressure difference between the hydraulic chambers 24 and 25 is reduced, so that the moving force acting on the steered rod 14 is small. Therefore, the problem that the left and right front wheels FW1, FW2 are steered does not occur.

  The rotational direction of the bidirectional pump 31 during the circulation control in step S17 is the direction in which the driver is operating the steering handle 11, that is, the direction in which the steering torque detected by the steering torque sensor 61 is working. It may be set so that the moving force acts on the steered rod 14 in the same direction. Further, the rotational direction of the bidirectional pump 31 may be set so that the moving force acts on the steering rod 14 in the direction in which the steering angle of the steering handle 11 returns to the neutral position. In this case, a steering angle sensor (not shown) for detecting the steering angle θ of the steering handle 11 is provided, and for example, the detected value θ of the steering angle sensor is also read in step S11 of FIG. Then, when the pump motor 32 is energized in step S17, the motor rotation direction is determined so that the moving force acts on the steered rod 14 in the direction to return the steering handle 11 to the neutral position. By setting the rotation direction of the bidirectional pump 31 during the circulation control in this way, even if a slight steering torque is applied due to the circulation hydraulic pressure, the driver does not feel uncomfortable.

  The electronic control unit 51 once exits from this control routine when performing the process of step S17. Then, similar processing is repeated at a predetermined short cycle. Accordingly, during the period in which the hydraulic fluid temperature Th is equal to or lower than the reference temperature Th0, the above-described hydraulic fluid circulation control is continued. The temperature of the hydraulic fluid rises uniformly by this circulation control. And if hydraulic fluid temperature Th exceeds reference temperature Th0 (S12: NO), circulation control of Steps S16-S17 will be ended, and assist control of Steps S13-S15 will be performed.

  According to the vehicle power steering apparatus of the embodiment described above, the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25 of the hydraulic cylinder device 21 are communicated with each other by the bypass pipe 48 and are normally closed to the bypass pipe 48. A type of electromagnetic on-off valve 49 is provided, and the electromagnetic on-off valve 49 is opened only when the hydraulic fluid is at a reference temperature Th 0 or less and the hydraulic fluid is circulated by the bidirectional pump 31. In this case, since the first hydraulic pressure chamber 24 and the second hydraulic pressure chamber 25 constitute a part of the circulation path of the hydraulic fluid, the hydraulic fluid can be circulated throughout the hydraulic system. Accordingly, the temperature of the hydraulic fluid can be increased uniformly. For this reason, the desired steering assist performance can be obtained at an early stage even at extremely low temperatures.

Next, a first modification related to pump control will be described. As shown in FIG. 4, the first modification is obtained by adding the process of step S18 to the above-described pump control routine (FIG. 2). Since other processes are the same as those in the previous embodiment, the description of the same parts is omitted.
In this modified example 1, when it is determined in step S12 that the hydraulic fluid temperature Th detected by the temperature sensor 62 is equal to or lower than the reference temperature Th0, the steering torque detected by the steering torque sensor 61 is further determined in step S18. It is determined whether Tr is less than or equal to the reference torque Tr0. The determination in step S18 is to determine whether or not the driver is operating the steering wheel.

  If it is determined in step S18 that Tr ≦ Tr0, it can be determined that the driver is not operating the steering wheel. In this case, circulation control of the hydraulic fluid in steps S16 to S17 is performed to increase the temperature of the hydraulic fluid. On the other hand, if it is determined in step S18 that Tr> Tr0, it can be determined that the driver is operating the steering wheel. In this case, assist control in steps S13 to S15 is performed.

  That is, in the first modification, two conditions are set as conditions for performing the circulation control of the hydraulic fluid. One is that the hydraulic fluid temperature Th is equal to or lower than the reference temperature Th0, and the other is that the driver is not operating the steering wheel. Therefore, in a situation where the hydraulic fluid is in an extremely low temperature state, the circulation control of the hydraulic fluid is continued while the handle is not operated, and the circulation control is prohibited and the assist control is performed while the handle control is being performed. Done.

  If the circulation control is performed by opening the flow path of the bypass pipe 48 when the steering wheel operation is performed, the steered rod 14 cannot generate a moving force due to the hydraulic pressure, but the process of step S18 is performed. By adding, a certain amount of assist torque can be generated when the steering wheel is operated, which is easy to use. Further, since the circulation control of the hydraulic fluid is started when the steering wheel operation is completed, the desired steering assist performance can be obtained at an early stage.

Next, a second modification related to pump control will be described. As shown in FIG. 5, the second modification is obtained by adding the process of step S <b> 19 to the above-described pump control routine (FIG. 2). Since other processes are the same as those in the previous embodiment, the description of the same parts is omitted.
In this modified example 2, when it is determined in step S12 that the hydraulic fluid temperature Th detected by the temperature sensor 62 is equal to or lower than the reference temperature Th0, the vehicle speed V detected by the vehicle speed sensor 63 is further determined in step S19. It is determined whether or not the reference vehicle speed is V0 or less. The determination in step S19 is to determine whether or not the vehicle is traveling, and it is desirable to set the reference vehicle speed V0 to 0 km / h or a low speed close thereto.

  If it is determined in step S19 that V ≦ V0, it can be determined that the vehicle is stopped. In this case, circulation control of the hydraulic fluid in steps S16 to S17 is performed to increase the temperature of the hydraulic fluid. On the other hand, if it is determined in step S19 that V> V0, it can be determined that the vehicle is traveling. In this case, assist control in steps S13 to S15 is performed.

  That is, in the second modification, two conditions are set as conditions for performing the circulation control of the hydraulic fluid. One is that the hydraulic fluid temperature Th is equal to or lower than the reference temperature Th0, and the other is that the vehicle is stopped. Therefore, in a situation where the hydraulic fluid is in a very low temperature state, the hydraulic fluid circulation control is continued while the vehicle is stopped, and the circulation control is prohibited and the assist control is performed while the vehicle is traveling. .

  If the circulation control is performed by opening the flow path of the bypass pipe 48 when the handle operation is performed, the steering rod 14 cannot generate a moving force due to the hydraulic pressure, but the process of step S19 is performed. By adding, it is possible to generate a certain amount of assist torque when operating the steering wheel during traveling, which is convenient. Further, when the vehicle is stopped, the hydraulic fluid circulation control is performed prior to the assist control, so that the desired steering assist performance can be obtained at an early stage.

  The power steering device for a vehicle according to this embodiment has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in the present embodiment, a power steering device that generates assist torque in response to a driver's steering wheel operation has been described. However, a steer-by-wire system that mechanically separates the steering operation unit and the steering driving unit of the steering wheel. It can also be applied to a steering device. That is, the hydraulic cylinder device and the pump device can be used as the actuator of the steered drive unit without providing the rack and pinion mechanism of the present embodiment. In this case, a steering angle detection means for detecting the steering angle of the steering wheel may be provided, and the drive rod position may be controlled by driving the pump device so that the steered wheels have the target turning angle based on the detected steering angle. .

1 is an overall configuration diagram of a vehicle power steering apparatus according to an embodiment of the present invention. It is a flowchart showing a pump control routine. It is a characteristic view showing an assist torque map. It is a flowchart showing the modification 1 of a pump control routine. It is a flowchart showing the modification 2 of a pump control routine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 13 ... Pinion gear, 14 ... Steering rod, 15 ... Rack tooth, 20 ... Hydraulic pressure assist device, 21 ... Hydraulic cylinder device, 22 ... Cylinder body, 23 ... Piston, 24 ... First hydraulic chamber, 25 ... Second hydraulic chamber, 30 ... Pump device, 31 ... Bidirectional pump, 32 ... Pump motor, 40 ... Piping section, 41 ... First piping, 42 ... Second Piping 48. Bypass pipe 49 49 Electromagnetic on-off valve 50 Assist control device 51 Electronic control unit 52 Motor drive circuit 61 Steering torque sensor 62 Temperature sensor 63 Vehicle speed sensor

Claims (1)

A steered rod for connecting steerable wheels so as to be steerable;
A hydraulic cylinder having a first hydraulic chamber and a second hydraulic chamber on the left and right sides of the piston, and generating a moving force on the steered rod by a hydraulic pressure difference between the two hydraulic chambers;
A first pipe that communicates with the first hydraulic chamber and a second pipe that communicates with the second hydraulic chamber are connected to selectively select the first hydraulic chamber and the second hydraulic chamber. A bi-directional pump that supplies hydraulic pressure;
An electric motor for driving the bidirectional pump forward and backward, and
Steering detection means for detecting the steering state of the steering wheel;
A motor control means for controlling the electric motor in accordance with the detected steering state to drive the bidirectional pump;
A bypass pipe communicating the first hydraulic chamber and the second hydraulic chamber of the hydraulic cylinder independently of the first pipe and the second pipe;
An on-off valve provided in the bypass pipe;
Temperature detection means for detecting the temperature of the hydraulic fluid or the environmental temperature of the hydraulic fluid;
And a circulation control means for opening the on-off valve and driving the both pumps to circulate the working fluid when the detected temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature. .

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