JP2015081032A - Hydraulic power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic power steering device that can increase a reduction range of a total flow of hydraulic fluid discharged from a plurality of motor pumps.SOLUTION: A first motor pump and a second motor pump have a first motor and a second motor, respectively. The first motor and the second motor are controlled by using an identical motor rotation speed control map. The motor rotation speed control map is provided to calculate a motor rotation speed command value Nbased on a vehicle speed and a steering speed. When motor rotation speed command values Nof the first motor and the second motor are equal to or less than a rotation speed determination threshold Nset based on a predetermined minimum rotation speed, the second motor is made stop. At the same time, the first motor is driven at a rotation speed twice as high as the original motor rotation speed command value N.

Description

  The present invention relates to a hydraulic power steering apparatus that assists steering by using hydraulic pressure.

  For example, Patent Document 1 describes a hydraulic power steering apparatus having two electric pumps. In this apparatus, two electric pumps are driven during steering when the pump load increases. Further, at the time of non-steering when the pump load is small, at least one of the two electric pumps is maintained in a state of being driven at a lower rotational speed than during steering. Thereby, the hydraulic response at the start of steering is ensured. Patent Documents 2 and 3 describe the use of an electric gear pump as a hydraulic power source of a hydraulic power steering apparatus.

JP-A-9-95251 Japanese Patent Laid-Open No. 11-218084 Japanese Patent Laid-Open No. 11-50974

  In the gear pump, an oil film is formed, for example, in a gap between the two gears and the case as the two gears meshing with each other rotate. The oil film reduces the rotational load on both gears. Whether or not the oil film is formed depends on the rotational speeds of both gears. For this reason, in a gear pump, the minimum allowable number of rotations may be set based on the minimum number of rotations at which the oil film is formed. Further, the discharge flow rate of the gear pump is substantially proportional to the rotational speed of both gears. For this reason, the minimum discharge amount of the gear pump is determined by setting the minimum rotation speed of the gear pump.

  When two electric pumps having gear pumps are used as the hydraulic power source of the hydraulic power steering apparatus, hydraulic oil discharged from the two electric pumps is supplied to the hydraulic actuators that are the sources of assist force. The hydraulic actuator generates an assist force corresponding to the total flow rate of hydraulic oil supplied from the two electric pumps. In the hydraulic power steering apparatus, the assist force is usually reduced as the vehicle speed increases. That is, the number of rotations of the two electric pumps is reduced to reduce the amount of hydraulic oil supplied to the hydraulic actuator. The assist force generated by the hydraulic actuator is reduced by the amount that the hydraulic oil supply amount is reduced.

  However, since the two electric pumps must be maintained at a rotational speed equal to or higher than the minimum rotational speed, the lower limit of the total flow rate of the hydraulic oil supplied to the hydraulic actuator is naturally determined. For this reason, it may be difficult to cope with a situation where an assist force that is weaker than the assist force corresponding to the lower limit of the total flow rate is required.

  An object of the present invention is to provide a hydraulic power steering device capable of expanding a reduction range of a total flow rate of hydraulic oil discharged from a plurality of electric pumps.

  The hydraulic power steering apparatus that can achieve the above object includes a hydraulic actuator that generates an assist force, a plurality of electric pumps that supply hydraulic oil to the hydraulic actuator, and a control device that controls each electric pump. While the control device normally drives each electric pump, a control command value correlated with any one discharge flow rate among the electric pumps is set based on a lower limit of the control command value allowed for each electric pump. When it is less than the threshold value, at least one electric pump is stopped and the control command value for the remaining electric pumps is increased so as to compensate for the decrease in the discharge flow rate accompanying the stop.

  For some reason, a lower limit may be set for the control command value correlated with the discharge flow rate of each electric pump. In this case, the discharge flow rate of each electric pump, and hence the lower limit of the total flow rate of the working flow supplied to the hydraulic actuator, is naturally determined. However, there may be situations where the total flow rate is desired to be less than the lower limit. In this regard, according to the above configuration, by stopping at least one electric pump and increasing the control command value for the remaining electric pumps, the control command value for each electric pump can be reduced below its lower limit, The reduction range of the total flow rate of the hydraulic oil supplied to the hydraulic actuator can be expanded. That is, it becomes possible to supply the hydraulic actuator with a flow rate that is lower than the lower limit of the total flow rate on the assumption that all the electric pumps are operated.

  In the hydraulic power steering apparatus described above, each electric pump may include a motor whose rotational speed is controlled by the control device and a gear pump driven by the motor. In this case, the command value correlated with the discharge flow rate is based on the rotational speed command value of the motor, and the threshold is based on the minimum rotational speed at which an oil film is formed between the gear of the gear pump and the housing that houses the gear. It is preferable that the rotation speed determination threshold is set.

  In the gear pump, an oil film is formed between the gear and the housing along with the rotation of the gear, thereby reducing the rotational load on the gear. Whether or not the oil film is formed depends on the number of rotations of the gear, and hence the number of rotations of the motor. For this reason, a lower limit may be set for the rotational speed of the motor. In view of this point, according to the above configuration, when the rotation speed command value of any one of the motors of each electric pump is less than the rotation speed determination threshold, at least one of the electric pump motors is stopped, The rotational speed command value for the motors of the remaining electric pumps is increased so as to compensate for the decrease in the discharge flow rate due to the stop. Thereby, the reduction width | variety of the total flow volume of the hydraulic fluid with respect to a hydraulic actuator can be expanded, without making the rotation speed command value of each motor fall below the minimum.

  In the hydraulic power steering device described above, the control device may include a storage unit that stores a motor rotation speed control map that calculates the rotation speed command value based on a vehicle speed and a steering speed. In this case, it is preferable that the control device controls each motor using the same motor rotation speed control map.

  According to this configuration, the control device can easily calculate the rotational speed command value by using the same motor rotational speed control map.

  According to the present invention, in the hydraulic power steering apparatus having a plurality of electric pumps, it is possible to expand the reduction range of the total flow rate of the hydraulic oil discharged from each electric pump.

The block diagram which shows schematic structure of a hydraulic power steering apparatus and its periphery. The block diagram which shows the structure of the 1st and 2nd electric pump. Sectional drawing of the pump part in the 1st and 2nd electric pump. The graph which shows an example of the change of the total flow volume of the hydraulic fluid supplied to a hydraulic actuator. (A) is a flowchart which shows the process sequence at the time of controlling the rotation speed of a 1st motor, (b) is a flowchart which shows the process sequence at the time of controlling the rotation speed of a 2nd motor. (A) is a graph showing an example of a change in the total flow rate of hydraulic oil supplied to the hydraulic actuator, (b) is a graph showing an example of a change in the discharge flow rate of the first electric pump, and (c) is The graph which shows an example of the change of the discharge flow volume of a 2nd electric pump. The graph which shows the characteristic of a motor rotation speed map. The flowchart which shows the process sequence at the time of controlling the rotation speed of the 1st and 2nd motor in other embodiment. The flowchart which shows the process sequence at the time of controlling the rotation speed of the 1st and 2nd motor in other embodiment.

Hereinafter, an embodiment of a hydraulic power steering apparatus will be described. The hydraulic power steering device assists the operation of the steering mechanism of the vehicle.
<Steering mechanism>
As shown in FIG. 1, the steering mechanism 10 includes a steering wheel 11 and a steering shaft 12 to which the steering wheel 11 is coupled. The steering shaft 12 includes a column shaft 12a, an intermediate shaft 12b, and a pinion shaft 12c that are connected in order from the steering wheel 11 side. The pinion shaft 12c is meshed with a rack shaft 13 extending in a direction intersecting with the axial direction. Therefore, the rotational motion of the steering shaft 12 is converted into the reciprocating linear motion of the rack shaft 13 by the rack and pinion mechanism 14 including the pinion shaft 12 c and the rack shaft 13. The reciprocating linear motion is transmitted to the left and right steered wheels 16 and 16 via tie rods 15 and 15 respectively connected to both ends of the rack shaft 13, whereby the steered angles of the steered wheels 16 and 16 are changed. The

<H-EPS>
The hydraulic power steering device 20 assists the steering operation by assisting the operation of the rack shaft 13. The hydraulic power steering apparatus 20 includes a hydraulic actuator 21, a steering valve 22, a first electric pump 23, a second electric pump 24, and an oil tank 25 as a configuration for assisting the steering operation. The first and second electric pumps 23 and 24 each function as a hydraulic pressure source for the hydraulic actuator 21. The first and second electric pumps 23, 24 suck in the hydraulic oil (working fluid) stored in the oil tank 25 and increase the pressure of the sucked hydraulic oil for discharge. The hydraulic fluid discharged from the first and second electric pumps 23 and 24 is supplied to the hydraulic actuator 21 via the steering valve 22.

<Hydraulic actuator>
The hydraulic actuator 21 has a hollow cylinder 31 and a piston 32. The cylinder 31 is also used as a housing for the rack shaft 13. A rack shaft 13 that also functions as a piston rod is inserted into the cylinder 31. Inside the cylinder 31, a piston 32 is fixed to the rack shaft 13 in a penetrating manner. By the piston 32, the inside of the cylinder 31 is partitioned into a first chamber 31a and a second chamber 31b. The piston 32 is integrated with the rack shaft 13 and slides in the cylinder 31 along the axial direction of the rack shaft 13. Further, the rack shaft 13 moves in the first direction LA or the second direction RA indicated by the arrow in FIG. 1 due to the differential pressure between the first chamber 31a and the second chamber 31b. The displacement of the rack shaft 13 due to the differential pressure functions as an assist force that assists the steering operation.

<Steering valve>
The steering valve 22 is provided on the pinion shaft 12c. The steering valve 22 is a rotary valve that switches the hydraulic oil supply path and the discharge path to the hydraulic actuator 21 (first and second chambers 31a and 31b) in conjunction with the operation of the steering wheel 11, that is, the rotation of the pinion shaft 12c. It is. More specifically, the steering valve 22 has a pump port 41, a tank port 42, a first cylinder port 43, and a second cylinder port 44. The pump port 41 is connected to discharge ports (not shown) of the first and second electric pumps 23 and 24 via a supply pipe 45 that branches into a bifurcated way. The tank port 42 is connected to the oil tank 25 through a discharge pipe 46. The first cylinder port 43 is connected to the first chamber 31a via the first supply / exhaust pipe 47, and the second cylinder port 44 is connected to the second chamber 31b via the second supply / exhaust pipe 48. Yes. The suction ports (not shown) of the first and second electric pumps 23 and 24 are connected to the oil tank 25 via suction pipes 45a and 45b, respectively.

  The first and second electric pumps 23 and 24 suck the working oil stored in the oil tank 25 through the suction pipes 45a and 45b, respectively, and discharge the sucked working oil with the increased pressure. The hydraulic oil discharged from the first and second electric pumps 23 and 24 is supplied to the steering valve 22 via the supply pipe 45. The steering valve 22 supplies first and second hydraulic oil supplied via the supply pipe 45 in accordance with the direction (steering direction) and magnitude (steering resistance) of the steering torque applied to the steering wheel 11. It distributes to either of the exhaust pipes 47 and 48. That is, the hydraulic oil is supplied to any one of the first and second chambers 31a and 31b via one of the first and second supply / discharge pipes 47 and 48.

  For example, when hydraulic oil is supplied to the first chamber 31a via the first supply / discharge pipe 47, the hydraulic actuator 21 generates an oil pressure corresponding to a hydraulic pressure difference generated between the hydraulic actuator 21 and the second chamber 31b. The oil pressure acts on the rack shaft 13 as an assist force. At this time, the hydraulic oil in the second chamber 31b is pushed out, and the pushed-out hydraulic oil returns (circulates) to the steering valve 22 through the second supply / discharge pipe 48 and further flows through the discharge pipe 46. Return to tank 25. Here, since the oil pressure acts in the second direction RA (rightward in FIG. 1) via the piston 32, the rack shaft 13 moves in the second direction RA together with the piston 32. The steering operation is assisted by the movement of the rack shaft 13.

<Electric pump>
As shown in FIG. 2, the first electric pump 23 includes a first motor 51, a first pump 52 driven by the first motor 51, and a first ECU that controls the operation of the first motor 51. (Electronic control unit) 53 is provided. A brushless motor is employed as the first motor 51, and a circumscribed gear pump is employed as the first pump. The first ECU 53 drives the first pump 52 by rotating the first motor 51 in a predetermined direction. The second electric pump 24 is the same product as the first electric pump 23, and includes a second motor 61, a second pump 62, and a second ECU 63.

As shown in FIG. 3, the first pump 52 has a housing 71, a drive gear 72, and a driven gear 73.
A housing chamber 74 in which the drive gear 72 and the driven gear 73 are housed is provided inside the housing 71. Two circular arc surfaces 75a and 75b corresponding to the outer diameters of the drive gear 72 and the driven gear 73 are provided on the inner peripheral surface 75 of the housing 71 (the storage chamber 74). In addition, the housing 71 is provided with a suction port 76 and a discharge port 77 that pass through the housing 71 from between the two arcuate surfaces 75a and 75b in the housing chamber 74 toward the outside. The suction port 76 is connected to the suction pipe 45a, and the discharge port 77 is connected to the supply pipe 45.

  The drive gear 72 and the driven gear 73 are accommodated in the accommodation chamber 74 in a state of being engaged with each other. The drive gear 72 rotates integrally with a shaft 78 that is linked to the first motor 51. The driven gear 73 rotates about the shaft 79 as the drive gear 72 rotates through meshing with the drive gear 72. A gap D1 is formed between the outer peripheral surface of the drive gear 72 and the arc surface 75a, and a gap D2 is formed between the outer peripheral surface of the driven gear 73 and the arc surface 75b. The drive gear 72 rotates along the arc surface 75a of the storage chamber 74, and the driven gear 73 rotates along the arc surface 75b.

  When the first motor 51 is rotated in a predetermined direction, the drive gear 72 rotates in the clockwise direction indicated by the arrow RB in FIG. Further, the driven gear 73 rotates in the counterclockwise direction indicated by the arrow LB in FIG. 3 in conjunction with the drive gear 72. As a result, the hydraulic oil is sucked into the storage chamber 74 through the suction port 76. The working oil on the suction port 76 side to be sucked is separated in such a manner as to be confined between the teeth and the inner peripheral surface 75 of the housing 71 as the drive gear 72 and the driven gear 73 rotate, and the inner peripheral surface 75. Are moved to the discharge port 77 side. Then, when the drive gear 72 and the driven gear 73 are engaged with each other, the hydraulic oil filled between the teeth is discharged through the discharge port 77.

Since the second pump 62 is the same product as the first pump 52, a detailed description of the second pump 62 is omitted.
<Electrical configuration>
Next, the electrical configuration of the hydraulic power steering apparatus will be described.

  As shown in FIG. 1, the first and second electric pumps 23 and 24 are connected to each other via a communication network 81 such as a CAN (Controller Area Network). A steering sensor 82 and a vehicle speed sensor 83 are also connected to the communication network 81. The steering sensor 82 detects the steering speed ω of the steering wheel 11. The vehicle speed sensor 83 detects a vehicle speed (vehicle traveling speed) V. The first and second electric pumps 23 and 24 obtain the steering speed ω that is the detection result of the steering sensor 82 and the vehicle speed V that is the detection result of the vehicle speed sensor 83 via the communication network 81.

  As shown in FIG. 2, the first and second ECUs 53 and 63 take in the steering speed ω and the vehicle speed V, and control the first and second motors 51 and 61 based on the taken in steering speed ω and the vehicle speed V, respectively. To do. The first ECU 53 includes a first microcomputer (hereinafter referred to as “first microcomputer”) 54 and a first drive circuit (PWM inverter) 55. The first microcomputer 54 generates a motor control signal Sc (PWM signal) based on the steering speed ω and the vehicle speed V. The first drive circuit 55 converts the DC power supplied from the DC power supply 70 into three-phase AC power based on the motor control signal Sc. The AC power is supplied to the first motor 51 as drive power.

  The first microcomputer 54 calculates a motor rotation speed command value (target rotation speed of the first motor 51) based on the vehicle speed V and the steering speed ω, and generates a motor control signal Sc according to the motor rotation speed command value. To do. The first microcomputer 54 uses the motor rotational speed control map Mp stored in its own storage unit 54a to obtain an appropriate motor rotational speed command value according to the vehicle state at that time.

As shown in the graph of FIG. 7, the motor rotation speed control map Mp is a three-dimensional map that defines the relationship among the steering speed ω, the vehicle speed V, and the motor rotation speed command value N ^* . The motor rotation speed control map Mp calculates a smaller value of the motor rotation speed command value N ^* as the vehicle speed V is higher and the steering speed ω is lower. The motor rotation speed command value N ^* shown in the graph of FIG. 7 is an example, and is set as appropriate according to the vehicle type or product specifications.

  A first current sensor 56 and a first rotation angle sensor 57 are connected to the first microcomputer 54. The first current sensor 56 is provided between the first drive circuit 55 and the ground, and detects a first current value Im1 that is a value of a current supplied to the first motor 51. The first rotation angle sensor 57 detects a first rotation angle θm1 that is the rotation angle of the first motor 51.

The first microcomputer 54 takes in the first current value Im1 and the first rotation angle θm1 at a predetermined sampling period. The first microcomputer 54 monitors the actual rotational speed of the first motor 51 based on the first rotational angle θm1. Then, the first microcomputer 54 performs rotation speed feedback control for the first motor 51 based on the motor rotation speed command value N ^* and the actual rotation speed. The first microcomputer 54 detects an abnormality such as an overcurrent based on the first current value Im1.

The second ECU 63 has the same configuration as the first ECU 53. That is, the second ECU 63 has a second microcomputer (hereinafter referred to as “second microcomputer”) 64 and a second drive circuit 65. A motor rotation speed control map Mp shown in the graph of FIG. 7 is also stored in the storage unit 64a of the second microcomputer 64. The second microcomputer 64 uses the same motor rotational speed control map Mp as the first microcomputer 54 to calculate an appropriate motor rotational speed command value N ^* according to the vehicle state at that time, and the motor rotational speed command value. A motor control signal Sc is generated according to N ^* . The second microcomputer 64 is connected to a second current sensor 66 and a second rotation angle sensor 67. Similar to the first microcomputer 54, the second microcomputer 64 performs rotation speed feedback control for the second motor 61 based on the motor rotation speed command value N ^* and the actual rotation speed.

<Amount of oil supplied to the hydraulic actuator>
Next, the amount of oil supplied to the hydraulic actuator 21 will be described.
As shown in the following equation (1), the hydraulic actuator 21 is supplied with hydraulic oil having a total flow rate Q that is the sum of the discharge flow rate Q1 of the first electric pump 23 and the discharge flow rate Q2 of the second electric pump 24. .

Q = Q1 + Q2 (1)
Here, the first and second microcomputers 54 and 64 each calculate a motor rotation speed command value N ^* using the same motor rotation speed control map Mp. The same applies to the vehicle speed V and the steering speed ω used for calculating the motor rotation speed command value N ^* . For this reason, as shown in the following equation (2), the rotation speeds of the first and second motors 51 and 61, and hence the discharge flow rates Q1 and Q2 of the first and second electric pumps 23 and 24 are basically determined. Will be the same. Therefore, as shown in the following equation (3), the hydraulic actuator 21 has hydraulic oil twice as large as the discharge flow rate Q1 of the first electric pump 23 or twice as large as the discharge flow rate Q2 of the second electric pump 24. Is supplied.

Q1 = Q2 ………………… (2)
Q = 2 · Q1 = 2 · Q2 (3)
The discharge flow rates Q1, Q2 of the first and second electric pumps 23, 24 are determined by the rotation speeds of the first and second motors 51, 61. The discharge flow rates Q1 and Q2 of the first and second electric pumps 23 and 24 are expressed by the following equation (4).

Q1 = Q2 = Q ₀ · N (4)
However, “Q ₀ ” is the discharge flow rate (unit: cc) per rotation of the first and second pumps 52, 62. “N” is the rotation speed (unit: rpm) of the first and second motors 51 and 61.

  The first and second microcomputers 54 and 64 control the total flow rate Q of the hydraulic oil supplied to the hydraulic actuator 21 by controlling the rotational speeds of the first and second motors 51 and 61. The hydraulic actuator 21 generates a hydraulic pressure corresponding to the total flow rate Q, and thus assist force. For this reason, as the total flow rate Q decreases, the hydraulic pressure generated by the hydraulic actuator 21 becomes lower, and the assist force becomes weaker.

  In the hydraulic power steering apparatus 20, due to the characteristics of the motor rotation speed control map Mp, the hydraulic pressure generated by the hydraulic actuator 21, and hence the assist force, decreases as the vehicle speed V increases and the steering speed ω decreases. That is, the amount of hydraulic oil supplied to the hydraulic actuator 21 is reduced by reducing the rotational speeds of the first and second electric pumps 23 and 24 according to the vehicle speed V and the steering speed ω. The assist force generated by the hydraulic actuator 21 is also reduced by the amount that the hydraulic oil supply amount is reduced.

Here, the hydraulic power steering apparatus 20 has the following concerns.
That is, normally, in the first pump 52, with the rotation of the drive gear 72 and the driven gear 73, for example, the gap D1 between the drive gear 72 and the inner peripheral surface 75 (arc surface 75a) of the housing 71, and the driven gear 73. Oil films are respectively formed in the gaps D2 between the inner peripheral surface (arc surface 75b) of the housing and the housing. With this oil film, the rotational loads on the drive gear 72 and the driven gear 73 are reduced. Whether the oil film is formed depends on the rotational speeds of the drive gear 72 and the driven gear 73. The rotational speed correlates with the rotational speed of the first motor 51. For this reason, the first electric pump 23 sets a minimum rotation speed that is a lower limit of the rotation speed allowed for the first motor 51. This minimum rotational speed is determined by experiments or the like based on the minimum rotational speed of the first motor 51 on which the oil film is formed. Further, the discharge flow rate Q1 of the first pump 52 is substantially proportional to the rotational speeds of the drive gear 72 and the driven gear 73. For this reason, by setting the minimum rotation speed of the first motor 51, the lower limit flow rate Q1 _min which is the lower limit of the discharge flow rate Q1 of the first pump 52 is also determined. This also applies to the second electric pump 24 having the same configuration as the first electric pump 23 and executing the same control. That is, by setting the minimum rotation speed of the second motor 61, the lower limit flow rate Q2 _min that is the lower limit of the discharge flow rate Q2 of the second pump 62 is also determined.

As described above, the first and second electric pumps 23 and 24 need to maintain the rotation speeds of the first and second motors 51 and 61 at a value equal to or higher than the minimum rotation speed, and are supplied to the hydraulic actuator 21. the lower limit flow rate, which is the lower limit of the total flow rate Q of the hydraulic fluid Q _min is also naturally determined. For this reason, it may be difficult to cope with a situation where an assist force that is weaker than the assist force according to the lower limit flow rate _Qmin is required.

The relationship between these lower limit flow rates Q _min , Q1 _min , and Q2 _min is expressed by the following equations (5) and (6) based on the previous equations (1) and (2).
Q _min = Q1 _min + Q2 _min (5)
Q1 _min = Q2 _min (6)
As indicated by a broken line in the graph of FIG. 4, a situation is assumed in which the amount of oil supplied to the hydraulic actuator 21 is desired to be smaller than the lower limit flow rate _Qmin . Although this differs depending on the vehicle type or product specifications, for example, when the vehicle is traveling at a high speed, the total flow rate Q of hydraulic oil required to obtain a more suitable assist force is less than the lower limit flow rate _Qmin . But it can not be made smaller than the lower limit flow rate Q _min total flow Q from the viewpoint of maintaining the state of the oil film described above is formed. Therefore, as shown by the solid line in the graph of FIG. 4, so that the supply amount of oil for the hydraulic actuator 21 is slightly more than the lower limit flow rate Q _min for example, the discharge of the first and second pumps 52 and 62 flow Q1 , Q2 are set.

Specifically, when the minimum number of rotations of the first and second motors 51 and 61 in which the oil film is formed is 1000 rpm and the discharge flow rate per pump rotation is 1.7 cc, the following expression (7) is given. as such, the lower limit flow rate _{Q min} per unit time is 3400Cc.

Q _min = 1.7 cc × 1000 rpm × 2 units = 3400 cc / min (7)
Can not be less than the lower limit flow rate _{Q min} also 3400cc it is not possible to the rotational speed of the first and second pumps 52 and 62 to less than the minimum speed. For this reason, for example, the discharge flow rates Q1 and Q2 of the first and second pumps 52 and 62 are lower than the lower limit flow rates Q1 _min and Q2 _min so that the total flow rate Q is larger than 3400 cc which is the lower limit flow rate Q _min. Therefore, the rotational speed of the first and second motors 51 and 61 must be set to a value (for example, 1300 rpm) larger than the minimum rotational speed (here, 1000 rpm). That is, the assist force cannot be made weaker than the assist force according to 3400 cc, which is the lower limit flow rate Q _min .

  Thus, even if it is desired to lower the total flow rate Q in order to obtain a more suitable assist force, a situation in which it cannot be reduced may occur. For this reason, for example, when driving at a high speed, the actual assist force with respect to a more suitable assist force is the actual total flow rate Q indicated by the solid line in the graph of FIG. 4 and the originally required total amount indicated by the broken line in the graph of FIG. It becomes stronger by the difference ΔQ from the flow rate Q.

  Therefore, in order to generate a more suitable assist force, in this example, the total flow rate is controlled through the rotational speed control of the first and second electric pumps 23 and 24 (more precisely, the first and second motors 51 and 61). Increase the Q reduction range.

<Rotational speed control of first motor>
Next, the processing procedure of the rotational speed control of the first motor 51 by the first microcomputer 54 will be described with reference to the flowchart of FIG. Each process of the flowchart is executed at a predetermined control cycle in accordance with a control program stored in the storage unit 54a of the first microcomputer 54.

As shown in the flowchart of FIG. 5A, the first microcomputer 54 calculates a motor rotation speed command value N ^* for the first motor 51 (step S101). The first microcomputer 54 calculates a motor rotation speed command value N ^* using the motor rotation speed control map Mp based on the vehicle speed V and the steering speed ω.

Then, the first microcomputer 54 is motor rotation speed command value ^{N *} calculated in step S101 to determine whether it is less than the rotational speed determination threshold _{N th} (Step 102). Rotational speed determining threshold N _th is a value determined by an experiment as the minimum rotational speed or reference the rotational speed of the first motor 51 oil film described above is formed. The rotation speed determination threshold value N _th is stored in the storage unit 54a.

The first microcomputer 54 when the motor rotation speed command value ^{N *} is determined that not less than the rotational speed determination threshold _{N th} (NO at step S102), and executes the normal control of the first motor 51 (step S103) . That is, the first microcomputer 54 generates the motor control signal Sc based on the normal motor rotation speed command value N ^* calculated in step S101.

Usually the contrary, the first microcomputer 54 when the motor rotation speed command value ^{N *} is determined that is less than the rotational speed determination threshold _{N th} (YES at step S102), the rotational speed of the first motor 51 Rotation speed double control is performed to double the time (step S104). That is, the first microcomputer 54 doubles the normal motor rotation speed command value N ^* calculated in step S101 and generates a motor control signal Sc based on the doubled motor rotation speed command value N ^* . When the rotation speed of the first motor 51 is twice that of the normal time, the discharge flow rate Q1 of the first pump 52 is twice that of the normal time.

<Rotational speed control of second motor>
Next, the processing procedure of the rotational speed control of the second motor 61 by the second microcomputer 64 will be described with reference to the flowchart of FIG. Each process of the flowchart is executed in a predetermined control cycle according to a control program stored in the storage unit 64a of the second microcomputer 64.

As shown in the flowchart of FIG. 5B, the second microcomputer 64 calculates a motor rotation speed command value N ^* for the second motor 61 (step S201). The second microcomputer 64 calculates the motor rotation speed command value N ^* using the motor rotation speed control map Mp based on the vehicle speed V and the steering speed ω.

Then, the second microcomputer 64 has the motor rotation speed command value ^{N *} calculated in step S201 to determine whether it is less than the rotational speed determination threshold _{N th} (Step 202). The rotation speed determination threshold value N _th is the same value as that stored in the storage unit 54 a of the first microcomputer 54 and is stored in the storage unit 64 a of the second microcomputer 64.

Second microcomputer 64 when the motor rotation speed command value ^{N *} is determined that not less than the rotational speed determination threshold _{N th} (NO at step S202), and executes the normal control of the second motor 61 (step S203) . That is, the second microcomputer 64 generates the motor control signal Sc based on the normal motor rotation speed command value N ^* calculated in step S201.

In contrast, the second microcomputer 64 when the motor rotation speed command value ^{N *} is determined that is less than the rotational speed determination threshold _{N th} (YES at step S202), for stopping the second motor 61 Control is executed (step S204). When the second motor 61 is stopped, the discharge flow rate Q2 of the second pump 62 becomes “0 (zero)”.

<Operation of motor rotation speed control>
Next, an operation by executing the rotation speed control of the first and second motors 51 and 61 will be described.

As shown in the graph of FIG. 6 (a), wherein in a state of being maintained at a total flow rate Q a lower limit flow rate Q is greater than _min first total flow rate Q _U of hydraulic fluid than the lower limit flow rate Q _min assume that controls the small second total flow rate Q _L as a target value of the flow rate control.

As shown in FIG. 6B, the discharge flow rate Q1 of the first electric pump 23 is maintained at a discharge flow rate Q1 _U larger than the lower limit flow rate Q1 _min through normal control. Further, as shown in FIG. 6C, the discharge flow rate Q2 of the second electric pump 24 is maintained at a discharge flow rate Q2 _U larger than the lower limit flow rate Q2 _min through normal control. The first electric pump 23 and the second electric pump 24 are subjected to the same flow rate control based on the same motor rotation speed control map Mp. Therefore, the discharge flow rate Q2 _U of the first discharge flow rate Q1 _U and a second electric pump 24 of the electric pump 23 at this time is the same flow rate. And these discharge flow rate _Q1 U, the flow rate which is the sum of Q2 _U is the first total flow rate _{Q U.}

As shown in FIGS. 6B and 6C, in this state, for example, triggered by vehicle acceleration (time t1), the discharge flow rates Q1 and Q2 gradually decrease. When these discharge flow rates Q1 and Q2 reach the lower limit flow rates Q1 _min and Q2 _min corresponding to the rotation speed determination threshold N _th (time t2), the first electric pump 23 performs the rotation speed double control, In the electric pump 24, stop control is executed.

  Here, for convenience of explanation, when the execution of the double rotation speed control is started, the discharge flow rate Q1 twice that of the normal control is immediately obtained, and when the stop control execution is started, the discharge flow rate Q2 is It is assumed that it reaches “0” immediately.

As shown by the two-dot chain line in FIGS. 6B and 6C, if it is an original situation (during normal control) in which both the first and second electric pumps 23 and 24 are operated, the time t2 and after. The discharge flow rate Q1 of the first and second electric pumps 23 and 24 needs to be controlled to a flow rate smaller than the lower limit flow rates Q1 _min and Q2 _min. Such flow rate control is difficult from the viewpoint of the oil film described above. is there.

In this regard, in this example, the discharge flow rate Q1 _U, which is twice the originally required discharge flow rate Q1 indicated by a two-dot chain line in FIG. can get. The discharge flow rate Q1 _U is equal to the second total flow rate Q _L is a target value of the flow rate control. Further, as shown in FIG. 6C, after time t2, the discharge flow rate Q2 becomes “0” through the stop control of the second electric pump 24. Therefore, after time t2, the discharge flow rate Q1 _U of the first electric pump 23 directly becomes the second total flow rate _{Q L.}

In this manner, the first electric pump 23 compensates for the decrease in the total flow rate Q accompanying the stoppage of the second electric pump 24. Thus, without oil film respectively above the rotational speed of the first and second motors 51, 61 is less than the minimum rotational speed to be formed, the total flow rate Q is below the lower limit flow rate Q _min, where the second the total flow rate _{Q L} is obtained. That is, the reduction range of the total flow rate Q is expanded to a flow rate that is less than the lower limit flow rate _Qmin .

<Effect of Embodiment>
Therefore, according to the present embodiment, the following effects can be obtained.
(1) In the first and second electric pumps 23 and 24, when the motor rotation speed command value N ^* for the first and second motors 51 and 61 is equal to or less than a predetermined minimum rotation speed, the second motor 61 is stopped. The first motor 51 is driven at a rotational speed exceeding the minimum rotational speed, that is, a rotational speed that is twice the original motor rotational speed command value N ^* . For this reason, the reduction width of the total flow rate Q can be expanded while suppressing the oil film breakage. Over-assist in high vehicle speed range is also suppressed.

(2) The first and second microcomputers 54 and 64 can easily calculate the motor rotational speed command value N ^* by using the same motor rotational speed control map Mp.
<Other embodiments>
In addition, you may implement the said embodiment as follows.

  In this example, the first and second microcomputers 54 and 64 are provided in the first and second electric pumps 23 and 24, respectively. However, the first and second microcomputers 54 and 64 are integrated as a single microcomputer. May be. In this example, the first and second motors 51 and 61 are controlled using the same motor speed control map Mp. However, the first and second motors 51 and 61 are controlled using different motor speed control maps Mp. Also good. Also in this case, it is preferable to drive the first and second motors 51 and 61 so that the total rotation speed does not change.

  The first and second motors 51 and 61 may be controlled using the same motor rotation speed control map Mp by a single microcomputer. An example of the processing procedure in this case is as follows.

As shown in the flowchart of FIG. 8, the microcomputer calculates a motor rotation speed command value N ^* for the first and second motors 51 and 61 (step S301). Then, microcomputer calculated motor rotation speed command value N ^* to determine whether it is less than the rotational speed determination threshold N _th at step S301 (step 302). Microcomputer when the motor rotation speed command value ^{N *} is determined that not less than the rotational speed determination threshold _{N th} (NO at step S302), executes normal control of the first and second motors 51 and 61 (step S303 ). In contrast, when the microcomputer is to be determined that the motor rotation speed command value N ^* is less than the rotational speed determination threshold N _th (YES at step S302), the rotational speed twice the control for the first motor 51 While performing (step S304), the 2nd motor 61 is stopped. Even if it does in this way, the effect similar to this Embodiment is acquired.

  The first and second motors 51 and 61 may be controlled by a single microcomputer using different motor speed control maps Mp. An example of the processing procedure in this case is as follows.

As shown in the flowchart of FIG. 9, the microcomputer calculates first and second motor rotation speed command values N1 ^* and N2 ^* for the first and second motors 51 and 61, respectively (step S401). Then, the microcomputer first motor rotation speed command value N1 ^* calculated in step S401 to determine whether it is less than the rotational speed determination threshold N _th (Step 402). When microcomputer is determined that ^* the first motor rotation speed command value N1 or less rotational speed determination threshold _{N th} (YES at step S402), stops the first motor 51 (step S403). Then, the microcomputer drives the second motor 61 at a rotational speed greater than the original second motor rotational speed command value N2 ^* (step S404). Specifically, the microcomputer is a value obtained by adding the first motor rotation speed command value N1 ^* calculated in the previous step S401 to the original second motor rotation speed command value N2 ^* calculated in the previous step S401. was a new second motor rotation speed command value N2 ^*, the new second motor rotation speed command value by using N2 ^* to drive the second motor 61. In contrast, the second motor microcomputer is (NO in step S402), the microcomputer when the motor rotation speed command value ^{N *} is determined that not less than the rotational speed determination threshold _{N th} in step S402 that has been calculated in step S401 rotation speed command value N2 ^* to determine whether it is less than the rotational speed determination threshold _{N th} (step 405). When microcomputer is determined that ^* the second motor rotation speed command value N2 or less rotational speed determination threshold _{N th} (YES at step S405), stops the second motor 61 (step S406). Then, the microcomputer drives the first motor 51 at a rotational speed greater than the original first motor rotational speed command value N1 ^* (step S407). Specifically, the microcomputer is a value obtained by adding the second motor rotation speed command value N2 ^* calculated in the previous step S401 to the original first motor rotation speed command value N1 ^* calculated in the previous step S401. was the first motor rotation speed command value new N1 ^*, the new first motor rotation speed command value by using the N1 ^* to drive the first motor 51. Incidentally, when the microcomputer is the motor rotation speed command value ^{N *} in the previous step S405 is determined that not less than the rotational speed determination threshold _{N th} (NO at step S405), the normal of the first and second motors 51 and 61 Control is executed (step S408). Even if it does in this way, the effect similar to this Embodiment is acquired. In the present embodiment, the first and second motors 51 and 61 may be controlled using different motor speed control maps Mp. In this case, the first and second microcomputers 54 and 64 mutually exchange the first and second motor rotation speed command values N1 ^* and N2 ^* via the communication network 81.

In this example, the first and second electric pumps 23 and 24 are provided, but three, four, or more electric pumps may be provided. For example, three electric pumps may be provided, and the motors of these electric pumps may be controlled using the same motor rotation speed control map Mp. An example of control in this case is as follows. That is, the microcomputer when the motor rotation speed command value N ^* is determined that is less than the rotational speed determination threshold value N _th, and executes the rotation speed 3 times the control for one motor, stopping the other two motors Let Moreover, you may control three electric pumps as follows. That is, when it is determined that the motor rotation speed command value N ^* is equal to or less than the rotation speed determination threshold value N _th , the microcomputer executes, for example, 1.5 times rotation speed control for the two motors, and the remaining one Stop the motor. An appropriate number of electric pumps may be driven so that the required discharge flow rate can be obtained. The same applies when four or more electric pumps are provided.

In this example, the motor rotation speed command value N ^* is used to determine whether or not the motor rotation speed double control is performed (steps S102 and S202). However, the discharge of the first and second pumps 52 and 62 is performed. The determination may be made using other control command values correlated with the flow rates Q1 and Q2. For example, first and second microcomputers 54 and 64 accurately convert motor rotation speed command value N ^* into a current command value, and generate motor control signal Sc based on the current command value. It may be determined whether or not the motor rotation speed double control is performed based on the current command value.

  In addition, a flow rate sensor that detects the actual flow rate (actual total flow rate Q) of the hydraulic oil flowing through the supply pipe 45 is provided in the supply pipe 45, and the first and second microcomputers 54 and 64 indicate the detection result of the flow rate sensor. Based on this, flow rate feedback control for the first and second motors 51 and 61 may be performed. When performing the flow rate feedback control, it may be determined whether to perform the motor rotation speed double control based on a flow rate command value that is a control command value generated by the first and second microcomputers 54 and 64.

  In addition, a pressure sensor for detecting the pressure in the supply pipe 45 is provided in the supply pipe 45, and the first and second microcomputers 54 and 64 are connected to the first and second motors 51 and 61 based on the detection result of the pressure sensor. Pressure feedback control may be performed. When performing the pressure feedback control, it may be determined whether to perform the motor rotation speed double control based on the pressure command value that is the control command value generated by the first and second microcomputers 54 and 64.

  In this example, the first and second electric pumps 23 and 24 are configured to include the first and second ECUs 53 and 63. However, the first and second ECUs 53 and 63 are configured as the first and second electric pumps. It may be provided separately from the pumps 23 and 24. Moreover, you may give the function of 1st and 2nd ECU53,63 to ECU of another vehicle-mounted system.

<Other technical ideas>
Next, a technical idea that can be grasped from the above embodiment will be added below.
(A) The control device controls each motor using different motor rotation speed control maps.

  (B) The control device is provided in each electric pump.

  DESCRIPTION OF SYMBOLS 20 ... Hydraulic power steering apparatus, 21 ... Hydraulic actuator, 23 ... 1st electric pump, 24 ... 2nd electric pump, 51 ... 1st motor, 52 ... 1st pump (gear pump), 53 ... 1st ECU (control device), 54a ... storage unit, 61 ... second motor, 62 ... second pump (gear pump), 63 ... second ECU (control device), 64a ... storage unit, Mp ... motor rotation Number control map.

Claims (3)

A hydraulic actuator that generates assist force, a plurality of electric pumps that supply hydraulic oil to the hydraulic actuator, and a control device that controls each electric pump,
While the control device normally drives each electric pump, a control command value correlated with any one discharge flow rate among the electric pumps is set based on a lower limit of the control command value allowed for each electric pump. A hydraulic power steering device that stops at least one electric pump and increases a control command value for the remaining electric pumps to compensate for a decrease in discharge flow rate associated with the stop. In the hydraulic power steering device according to claim 1,
Each electric pump includes a motor whose rotational speed is controlled by the control device, and a gear pump driven by the motor,
The command value correlated with the discharge flow rate is set based on the rotational speed command value of the motor, and the threshold value is set based on the minimum rotational speed at which an oil film is formed between the gear of the gear pump and the housing that houses the gear. A hydraulic power steering device that is a rotation speed determination threshold value. In the hydraulic power steering device according to claim 2,
The control device has a storage unit storing a motor rotation speed control map for calculating the rotation speed command value based on a vehicle speed and a steering speed,
The control device is a hydraulic power steering device that controls each motor using the same motor rotation speed control map.