Hydraulic circuit for transmission

A hydraulic circuit for a transmission includes a friction element that engages or disengages an operating element of the transmission, a pump that pumps oil to form preliminary pressure that allows the friction element to be maintained in a standby state in which the friction element is ready to operate, and a direct control valve that receives the oil that has passed through the pump and adjusts the preliminary pressure to form operating pressure that allows the friction element to operate, when operating the friction element. The friction element includes a hydraulic chamber into which the oil is introduced, a first supply hole through which the oil that has passed through the pump is supplied to the hydraulic chamber, and a second supply hole through which the oil that has passed through the direct control valve is supplied to the hydraulic chamber.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority to Korean Patent Application No. 10-2017-0065537, filed on May 26, 2017, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a hydraulic circuit for a transmission.

BACKGROUND

An automatic transmission for a vehicle automatically converts power generated from a prime mover (such as an engine, an electric motor, or the like) into torque and rotational speeds in RPM that are appropriate for facilitating the driving of the vehicle.

The automatic transmission includes: a torque converter to which the power of the prime mover is supplied; a plurality of operating elements capable of converting the power supplied through the torque converter into torque and rotational speeds in RPM appropriate for driving the vehicle; a plurality of friction elements that engage or disengage rotations of operating elements to implement a plurality of shifting stages; a hydraulic circuit that selectively operates the friction elements by using hydraulic pressure; and a control unit that controls the overall operation of the automatic transmission to selectively adjust the shifting stages depending on a driving state of the vehicle.

A hydraulic circuit for a transmission in the related art may supply oil to at least one of friction elements at a predetermined hydraulic pressure to selectively operate at least one of the friction elements.

To this end, the hydraulic circuit for a transmission in the related art may include: a pump that pumps oil stored in an oil pan; a regulator valve that forms line pressure by adjusting the pressure of the oil pumped by the pump; a reducing valve that receives the oil that has passed through the regulator valve and reduces the line pressure to form reducing pressure; a line solenoid valve that controls the regulator valve by using the reducing pressure; and a proportional control solenoid valve that receives the oil that has passed through the regulator valve and fouls control pressure to selectively control one of the friction elements.

Since the hydraulic circuit for a transmission in the related art controls the friction elements by using the plurality of valves, as described above, the hydraulic circuit has a complex circuit structure. Due to this, the hydraulic circuit for a transmission in the related art has problems in terms of high installation cost and high flow loss.

SUMMARY

The present disclosure has been made to solve the above-mentioned problems occurring in the related art while advantages achieved by the related art are maintained intact.

An aspect of the present disclosure provides a hydraulic circuit for a transmission, the hydraulic circuit having a structure improved to simplify the circuit structure thereof.

Another aspect of the present disclosure provides a hydraulic circuit for a transmission, the hydraulic circuit having an improved structure to rapidly operate a friction element.

According to an aspect of the present disclosure, a hydraulic circuit for a transmission may include a friction element configured to engage or disengage an operating element of the transmission, a pump configured to pump oil to form preliminary pressure that allows the friction element to be maintained in a standby state in which the friction element is ready to operate, and a direct control valve configured to receive the oil that has passed through the pump and to adjust the preliminary pressure to form operating pressure that allows the friction element to operate, when operating the friction element. The friction element may include a hydraulic chamber into which the oil is introduced, a first supply hole through which the oil that has passed through the pump is supplied to the hydraulic chamber, and a second supply hole through which the oil that has passed through the direct control valve is supplied to the hydraulic chamber.

According to an embodiment, the hydraulic circuit may further include a hydraulic line configured to supply, to the friction element, the oil that has passed through the pump and the oil that has passed through the direct control valve. The hydraulic line may include a first hydraulic line connecting the pump and the first supply hole, a second hydraulic line configured to deliver the oil that has passed through the friction element to the direct control valve, and a third hydraulic line connecting the direct control valve and the second supply hole.

According to an embodiment, the friction element may further include a drain hole through which the oil introduced into the hydraulic chamber is drained from the hydraulic chamber. The second hydraulic line may connect the drain hole and the direct control valve.

According to an embodiment, the hydraulic circuit may further include a relief valve placed on the third hydraulic line to restrict the operating pressure such that the operating pressure becomes lower than a maximum allowable pressure determined in advance.

According to an embodiment, the hydraulic circuit may further include a hydraulic line configured to supply, to the friction element, the oil that has passed through the pump and the oil that has passed through the direct control valve. The hydraulic line may include a first hydraulic line connecting the pump and the first supply hole, a second hydraulic line configured to deliver the oil that has passed through the pump to the direct control valve, and a third hydraulic line connecting the direct control valve and the second supply hole.

According to an embodiment, the second hydraulic line may connect the first hydraulic line and the direct control valve.

According to an embodiment, the hydraulic circuit may further include a controller configured to control driving of the pump and the direct control valve. The controller may close the direct control valve when allowing the friction element to stand ready for operation and may open the direct control valve to a predetermined opening degree when operating the friction element.

According to an embodiment, the hydraulic circuit may further include a pressure sensor configured to measure the operating pressure. The controller may adjust at least one of an RPM of the pump and a degree to which the direct control valve is open, based on a pressure value measured by the pressure sensor.

According to an embodiment, the direct control valve may be a proportional control solenoid valve configured to linearly control the operating pressure.

According to an embodiment, the pump may be an electric oil pump.

According to an embodiment, the friction element may be either an overdrive clutch or an overdrive brake.

The hydraulic circuit for a transmission, according to the present disclosure, has the following effects:

First, the hydraulic circuit for a transmission according to the present disclosure may reduce the number of valves required to operate a friction element, compared to a hydraulic circuit for a transmission in the related art, and may thus reduce the amount of oil supplied by a pump, valve installation cost, flow loss, and the like.

Second, the hydraulic circuit for a transmission according to the present disclosure may rapidly operate a friction element since the hydraulic circuit may maintain the friction element in a standby state in which the friction element is ready to operate.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numbers will be used throughout to designate the same or equivalent elements. In addition, a detailed description of well-known features or functions will be ruled out in order not to unnecessarily obscure the gist of the present disclosure.

Terms, such as “first”, “second”, “A”, “B”, “(a)”, “(b)”, and the like, may be used herein to describe elements of the present disclosure. Such terms are only used to distinguish one element from another element, and the substance, sequence, order, or number of these elements is not limited by these teams. Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by those skilled in the art to which the present disclosure pertains. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application.

FIG. 1is a schematic view illustrating a configuration of a hydraulic circuit for a transmission according to a first embodiment of the present disclosure.FIG. 2is a block diagram for explaining a control system of the hydraulic circuit illustrated inFIG. 1.FIG. 3is a schematic view illustrating a configuration of a friction element illustrated inFIG. 1.

A hydraulic circuit1for a transmission, according to the first embodiment of the present disclosure, is a device for supplying hydraulic pressure to a friction element10of an automatic transmission of a vehicle. The hydraulic circuit1for a transmission is applicable to all types of vehicles without any specific limitation. For example, the hydraulic circuit1for a transmission may be applied to a hybrid electric vehicle driven by power supplied from an engine and an electric motor. Hereinafter, a description of the hydraulic circuit1for a transmission will be given, assuming that the hydraulic circuit1for a transmission is applied to a hybrid electric vehicle.

Referring toFIGS. 1 to 3, the hydraulic circuit1for a transmission may include the friction element10, a pump20, a direct control valve30, a hydraulic line40, a controller50, and the like.

The controller50is an electric circuitry that executes instructions of software which thereby performs various functions described hereinafter.

The friction element10may be either a clutch or a brake that may engage or disengage an operating element included in a planetary gear set of the automatic transmission of the vehicle. For example, the friction element10may be either an overdrive clutch or an overdrive brake. For the convenience of description, a description of the hydraulic circuit1for a transmission will hereinafter be given with a clutch as an example of the friction element10.

The friction element10may include clutch plates11, clutch discs12, a piston13, a return spring14, and the like, as illustrated inFIG. 3.

The clutch plates11may be arranged with a predetermined interval therebetween. The clutch plates11may be coupled with a clutch retainer16and may be connected to an input shaft (not illustrated) of the automatic transmission of the vehicle. The clutch discs12may be arranged with a predetermined interval therebetween to correspond to the clutch plates11. The clutch discs12may be coupled with a clutch hub15and may be connected to an output shaft (not illustrated) of the automatic transmission of the vehicle. As illustrated inFIG. 3, the clutch plates11and the clutch discs12may be alternately arranged with a pre-determined interval therebetween.

The piston13may be located to be movable between the clutch retainer16and the clutch plates11. The piston13may be supported by a piston retainer17. As illustrated inFIG. 3, a hydraulic chamber18into which oil is introduced may be formed between the piston13and the clutch retainer16.

The friction element10may further include a first supply hole19a,a drain hole19b,and a second supply hole19cthat are formed through a sidewall of the clutch retainer16to be communicatively connected to the hydraulic chamber18. As illustrated inFIG. 1, the first supply hole19amay be connected with the pump20through a first hydraulic line42, which will be described below. The drain hole19bmay be connected with an inlet of the direct control valve30through a second hydraulic line44, which will be described below. The second supply hole19cmay be connected with an outlet of the direct control valve30through a third hydraulic line46, which will be described below. Accordingly, oil supplied from the pump20and the direct control valve30may be introduced into the hydraulic chamber18through the first and second supply holes19aand19c,respectively. The oil introduced into the hydraulic chamber18may be drained from the hydraulic chamber18through the drain hole19b.

As the oil is introduced into, or drained from, the hydraulic chamber18, a hydraulic pressure may be applied to the hydraulic chamber18. The hydraulic pressure may be exerted on the piston13to move the piston13toward the clutch plates11.

The return spring14may be interposed between the piston13and the piston retainer17. The return spring14may elastically press the piston13in the direction in which the piston13moves away from the clutch plates11. The elastic pressure of the return spring14may increase in proportion to the degree to which the return spring14is compressed.

As described above, the hydraulic pressure applied to the hydraulic chamber18and the elastic pressure of the return spring14may be exerted on the piston13in opposite directions. Accordingly, a difference between the hydraulic pressure and the elastic pressure may cause the piston13to move or stop.

For example, the piston13may stop when the hydraulic pressure is equal to the elastic pressure.

For example, when the hydraulic pressure is higher than the elastic pressure, the piston13may move toward the clutch plates11. The piston13having moved forward, as described above, may press the clutch plates11to allow the clutch plates11and the clutch discs12to be locked together. The friction element10may engage an operating element by allowing the clutch plates11and the clutch discs12to be locked together.

For example, when the hydraulic pressure is lower than the elastic pressure, the piston13may move away from the clutch plates11. Due to this, the pressure exerted on the clutch plates11by the piston13may be released, and thus the clutch plates11and the clutch discs12may be unlocked from one another. The friction element10may disengage the operating element by allowing the clutch plates11and the clutch discs12to be unlocked from one another. Furthermore, the piston13, which has moved as far as possible from the clutch plates11, may move backward while being supported by the clutch retainer16, and at this time, the hydraulic chamber18may have a minimum volume.

The pump20may pump oil out of an oil pan60and may deliver the oil to the first hydraulic line42. An oil filter70may preferably be located between the pump20and the oil pan60to filter the oil, but the present disclosure is not limited thereto.

The pump20may preferably be an electric oil pump driven by power supplied from a high-voltage battery (not illustrated), but the pump20is not limited thereto.

The pump20may be driven at a predetermined RPM to form preliminary pressure by which the friction element10may be maintained in a standby state, in which the friction element is ready to operate: As illustrated inFIG. 2, the controller50may control driving of the pump20and may adjust the magnitude of the preliminary pressure by adjusting the RPM of the pump20.

Here, the standby state where the friction element10is ready to operate may refer to a state right before the friction element10is operated by hydraulic pressure applied to the hydraulic chamber18. That is, the standby state may refer to a state in which hydraulic pressure and elastic pressure are equal to each other with the piston13that has maximally moved backward so as to be supported by the clutch retainer16. The preliminary pressure may refer to hydraulic pressure when the friction element10is in the standby state.

The oil pumped by the pump20may be supplied to the first supply hole19aof the friction element10through the first hydraulic line42and may be introduced into the hydraulic chamber18to apply preliminary pressure to the piston13, thereby maintaining the friction element10in the standby state in which the friction element10is ready to operate.

The direct control valve30may be configured to: receive the oil, which has passed through the pump20, via the second hydraulic line44, which will be described below; adjust the pressure of the oil; and deliver the oil to the third hydraulic line46, which will be described below.

As illustrated inFIG. 1, the inlet of the direct control valve30may be connected with the second hydraulic line44. The oil introduced into the hydraulic chamber18may flow into the second hydraulic line44through the drain hole19b,and the oil that has passed through the second hydraulic line44may be delivered to the inlet of the direct control valve30. That is, the oil that has passed through the pump20may be delivered to the inlet of the direct control valve30via the hydraulic chamber18.

The direct control valve30may adjust the pressure of the oil delivered thereto. For example, in the case where preliminary pressure is formed by pumping, the direct control valve30may adjust the preliminary pressure to foam operating pressure by which the friction element10is to be operated. To this end, the direct control valve30may be a normally low (N/L) type proportional control solenoid valve that preliminarily adjusts hydraulic pressure. As illustrated inFIG. 2, the controller50may control driving of the direct control valve30and may adjust the magnitude of the operating pressure by adjusting the degree to which the direct control valve30is open.

Here, an operation of the friction element10may refer to a state in which the clutch plates11and the clutch discs12are locked together so that the operating element is engaged by the friction element10. The operating pressure may refer to hydraulic pressure when the friction element10operates.

The oil, the pressure of which has been adjusted by the direct control valve30, may be supplied to the second supply hole19cof the friction element10through the third hydraulic line46and may be introduced into the hydraulic chamber18again to apply the operating pressure to the piston13, thereby operating the friction element10.

The hydraulic line40may be configured to supply, to the friction element10, the oil that has passed through the pump20and the direct control valve30. For example, as illustrated inFIG. 1, the hydraulic line40may include the first hydraulic line42, the second hydraulic line44, and the third hydraulic line46.

The first hydraulic line42may be configured to connect an outlet of the pump20and the first supply hole19a. Accordingly, oil pumped by the pump20may be supplied to the first supply hole19athrough the first hydraulic line42to apply preliminary pressure to the hydraulic chamber18.

The hydraulic circuit1for a transmission may further include a mechanical oil pump100configured to supply oil to a lubrication element80and a cooled element90. The lubrication element80may refer to a component (such as a bearing, a bush, a gear, or the like) that needs to be lubricated by using oil, and the cooled element90may refer to a component (such as an electric motor) that needs to be cooled by using oil. The mechanical oil pump100may be connected with the lubrication element80through a lubricant line110and may be connected with the cooled element90through a cooling line120branching from the lubricant line110. Accordingly, oil pumped by the mechanical oil pump100may be supplied to the lubrication element80and the cooled element90through the lubricant line110and the cooling line120.

However, depending on a driving state of a vehicle, there may be lack of oil supplied from the mechanical oil pump100to the lubrication element80and the cooled element90. To solve this problem, a manual valve130may be coupled to the first hydraulic line42to switch a flow path and may be connected with the lubricant line110and the cooling line120through a connecting line140. When there is lack of oil supplied from the mechanical oil pump100to the lubrication element80and the cooled element90, the manual valve130may switch a flow path to route oil passing through the first hydraulic line42to the connecting line140, thereby supplementing the oil supplied from the mechanical oil pump100to the lubrication element80and the cooled element90.

The second hydraulic line44may be configured to connect the drain hole19band the inlet of the direct control valve30. Accordingly, oil introduced into the hydraulic chamber18may be supplied to the direct control valve30through the second hydraulic line44.

The third hydraulic line46may be configured to connect the outlet of the direct control valve30and the second supply hole19c.Accordingly, oil, the pressure of which has been adjusted by the direct control valve30, may be supplied to the second supply hole19cthrough the third hydraulic line46to apply operating pressure to the hydraulic chamber18.

The third hydraulic line46may be provided with a pressure sensor150configured to measure the operating pressure and a relief valve160configured to restrict the operating pressure such that the operating pressure becomes lower than a maximum allowable pressure determined in advance.

The pressure sensor150may be constituted by a pressure sensor generally used to measure hydraulic pressure. The pressure sensor150may measure the pressure of oil passing through the third hydraulic line46and may transmit the measured oil pressure to the controller50.

The relief valve160may be constituted by a relief valve generally used to restrict a maximum hydraulic pressure. The relief valve160may restrict the maximum operating pressure of oil passing through the third hydraulic line46to a maximum allowable pressure to prevent the piston13and the other components from being damaged when operating pressure higher than the maximum allowable pressure is applied to the hydraulic chamber18.

Hereinafter, a method of controlling the hydraulic circuit1for a transmission will be described with reference to the drawings.

First, when the controller50allows the friction element10to stand ready for operation, the controller50may apply preliminary pressure to the hydraulic chamber18by closing the direct control valve30and driving the pump20. To this end, the controller50may control the RPM of the pump20such that the pressure of oil pumped by the pump20reaches the preliminary pressure.

Next, when the controller50operates the friction element10, the controller50may apply operating pressure to the hydraulic chamber18by opening the direct control valve30and driving the pump20. To this end, the controller50may adjust the RPM of the pump20while adjusting the degree to which the direct control valve30is open, to allow the pressure of oil adjusted by the direct control valve30to reach the operating pressure. Furthermore, the controller50may adjust at least one of the RPM of the pump20and the degree to which the direct control valve30is open, based on a pressure value measured by the pressure sensor150. That is, the controller50may receive an operating pressure change from the pressure sensor150in real time and may adjust at least one of the RPM of the pump20and the degree to which the direct control valve30is open, to allow the operating pressure to have a predetermined pressure value.

As described above, the hydraulic circuit1for the transmission may apply the preliminary pressure to the hydraulic chamber18of the friction element10to maintain the friction element10in the standby state in which the friction element10is ready to operate, and may then apply the operating pressure to the hydraulic chamber18by using the direct control valve30to operate the friction element10.

The hydraulic circuit1for a transmission may achieve a reduction in the number of valves required to supply hydraulic pressure to the friction element10, compared to a hydraulic circuit for a transmission in the related art that controls the pressure of oil to be supplied to a friction element by using a plurality of valves. Accordingly, the hydraulic circuit1for the transmission may reduce the amount of oil supplied by the pump20, valve installation cost, flow loss, and the like.

Furthermore, the hydraulic circuit1for the transmission may reduce time necessary for operating the friction element10since the hydraulic circuit1is capable of maintaining the friction element1in a standby state in which the friction element10is ready to operate.

FIG. 4is a schematic view illustrating a configuration of a hydraulic circuit for a transmission according to a second embodiment of the present disclosure, andFIG. 5is a schematic view illustrating another exemplary configuration of a friction element compared to the one illustrated inFIG. 3.

A hydraulic circuit2for a transmission, according to the second embodiment of the present disclosure, differs from the above-described hydraulic circuit1for a transmission in terms of the structure in which the pump20and the direct control valve30are connected together, and the remaining configuration of the hydraulic circuit2is the same as that of the hydraulic circuit1for a transmission. The following description of the hydraulic circuit2for a transmission will be focused on the difference. Furthermore, identical elements included in both the hydraulic circuit2for a transmission and the hydraulic circuit1for a transmission described above are provided with identical reference numbers, which have been used in describing the hydraulic circuit1for a transmission.

A friction element10′ differs from the above-described friction element10in that the friction element10′ includes only the first and second supply holes19aand19cbut does not include the drain hole19b,as illustrated inFIGS. 4 and 5.

A hydraulic line40′ differs from the above-described hydraulic line40in that a second hydraulic line44′ is directly connected with the first hydraulic line42, as illustrated inFIG. 4.

The hydraulic circuit2for a transmission differs from the above-described hydraulic circuit1for a transmission in that oil supplied from the pump20is directly supplied to the direct control valve30without passing through the hydraulic chamber18. Likewise to the above-described hydraulic circuit1for a transmission, the hydraulic circuit2for a transmission may apply preliminary pressure to the hydraulic chamber18through the control of the pump20and the direct control valve30to maintain the friction element10′ in a standby state in which the friction element10′ is ready to operate, or may apply operating pressure to the hydraulic chamber18to operate the friction element10′.