CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serial no. 2019-205048, filed on Nov. 12, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to a hydraulic control device in which a second pump and a bypass valve are connected in parallel between a first pump and a hydraulic operation part, and which supplies a first oil from the first pump to the hydraulic operation part via the bypass valve, or which pressurizes the first oil with the second pump and supplies the pressurized first oil as a second oil to the hydraulic operation part.

Description of Related Art

For example, Patent Document 1 discloses a hydraulic control device of a vehicle transmission in which a second pump (electric pump) and a bypass valve (check valve) operated by the drive of a motor are connected in parallel between a first pump (mechanical pump) and a hydraulic operation part of the transmission. In this case, when the engine is started, first, a first oil is supplied from the first pump to the hydraulic operation part via the bypass valve (first state). After that, the second pump is driven by the drive of the motor, and the first oil supplied from the first pump is pressurized by the second pump, and the pressurized first oil is supplied as the second oil from the second pump to the hydraulic operation part (second state). The hydraulic operation part includes, for example, an oil chamber of pulleys (drive pulley and driven pulley) of a belt-type continuously variable transmission.

In the hydraulic control device having the above configuration, switching between the first state in which the first oil is supplied to the hydraulic operation part (continuously variable transmission) and the second state in which the second oil is supplied is performed by opening and closing the bypass valve. That is, when the discharge amount (flow rate) of the second oil from the second pump exceeds the flow rate (discharge amount of the first oil from the first pump) of the first oil passing through the bypass valve, the hydraulic pressure (line pressure PH) in the downstream oil passage of the bypass valve becomes higher than the hydraulic pressure (output pressure P1) in the upstream oil passage. In this way, the bypass valve is closed, and the supply of the first oil from the first pump to the hydraulic operation part via the bypass valve is switched to the supply of the second oil from the second pump to the hydraulic operation part. As a result, the flow of the first oil to the oil passage is blocked, and the second oil is pumped to the hydraulic operation part by the second pump. On the other hand, when the discharge amount of the second pump is reduced due to the stop or the low rotation state of the second pump, the bypass valve is in the valve open state, and the first oil is supplied to the hydraulic operation part.

In the above hydraulic control device, the work load of the first pump is reduced by driving the second pump in the second state. At that time, the target rotation speed of the second pump is calculated by performing a feedback control using the hydraulic pressure of the oil (discharge pressure of the first pump) detected by the hydraulic sensor provided on the suction side of the second pump. (Patent Document 2)

By the way, in the above hydraulic control device, it ends the feedback control and transitions to the control which keeps the target rotation speed of the second pump constant when a required discharge pressure, which is a required value of the discharge pressure of the second pump, becomes less than or equal to a predetermined pressure by the above feedback control. However, in the control which keeps the target rotation speed of the second pump constant, even if the rotation speed of the second pump is maintained at a rotation speed which keeps the required discharge pressure less than or equal to the predetermined pressure, there is a possibility that the required discharge pressure cannot be maintained below the predetermined pressure due to changes in the operation state of the hydraulic operation part from that state. As a result, if the required discharge pressure cannot be maintained below the predetermined pressure in the fixed mode, the effect of reducing the work load of the first pump is reduced by that amount, and the effect of reducing the fuel consumption of the vehicle may not be fully obtained. Therefore, in the above-mentioned fixed mode, a control is required for more reliably maintaining a state where the required discharge pressure is less than or equal to the predetermined pressure.

RELATED ART

Patent Document

[Patent Document 1] Japanese Laid-open No. 2015-200369[Patent Document 2] Japanese Laid-open No. 2019-35426

The disclosure has been made in view of the above-mentioned problems of the conventional technology, and the disclosure provides a hydraulic control device in which in the rotation control of the second pump, the required discharge pressure of the second pump can be more reliably maintained in a state of being less than or equal to the predetermined pressure in the control which keeps the target rotation speed constant after the end of the feedback control, whereby it can more reliably obtain the effect of reducing the work load of the first pump and the effect of reducing the fuel consumption of the vehicle.

SUMMARY

In view of the foregoing, a hydraulic control device (10) according to the disclosure, in which a second pump (30) and a bypass valve (58) that are driven by a motor (32) are connected in parallel between a first pump (20) and a hydraulic operation part (56) of a transmission, and which is switchable between a first state of supplying a first oil from the first pump (20) to the hydraulic operation part (56) via the bypass valve (58) and a second state of pressurizing with the second pump (30) the first oil supplied from the first pump (20) and supplying the pressurized first oil as a second oil to the hydraulic operation part (56), includes: a hydraulic pressure detection part (26) which detects an oil pressure (P1) of the first oil on a suction side in the second pump (30); and a control part (28) which controls a rotation speed of the second pump (30) in the second state. The control part (28) controls the rotation speed of the second pump (30) based on a required flow rate, which is a required value of a flow rate of the second oil, and a required discharge pressure, which is a required value of a discharge pressure of the second pump (30), and at this time, performs a feedback control with respect to the required discharge pressure by using the oil pressure detected by the hydraulic pressure detection part (26), thereby calculating a target rotation speed (NA) of the second pump (30) by using the required discharge pressure after the feedback control and the required flow rate, and controlling a rotation of the second pump (30) with the calculated target rotation speed (NA), ends the feedback control and transitions to a control which keeps the target rotation speed (NA) constant when the required discharge pressure has become less than or equal to a predetermined pressure, and in the control which keeps the target rotation speed (NA) constant, controls the rotation of the second pump (30) by adding a predetermined addition rotation speed (N4) to the target rotation speed (NA) corresponding to the required discharge pressure.

