Shift control method for a vehicle

Abstract

The present disclosure relates to a shift control method for a transmission, the transmission including an electric oil pump (EOP) directly connected to a friction clutch of a vehicle, and the shift control method may include: when a shift starts, setting, by a controller, a predetermined first target RPM for controlling the EOP; determining, by the controller, a target current based on the first target RPM; maintaining, by the controller, the first target RPM until an EOP drive current reaches the target current; when the EOP drive current is greater than or equal to the target current, linearly reducing, by the controller, the RPM of the EOP from a predetermined second target RPM to a third target RPM; and increasing, by the controller, the EOP driving force to increase the frictional force of the friction clutch such that the slip of the friction clutch is less than a predetermined reference slip.

Description

Technical Field

[0001] The present invention relates to a shift control method for a vehicle. Background Art

[0002] Figure 1 The configuration of a transmission for an electric vehicle to which the present invention can be applied is shown.

[0003] An input shaft IN rotated by the power of an electric generator MG can drive a first-stage drive gear D1 through a one-way clutch OWC. The connection state of a second-stage drive gear D2 relative to the input shaft IN can be changed by a friction clutch FC. An output shaft OUT is provided with a first-stage driven gear P1 engaged with the first-stage drive gear D1 and a second-stage driven gear P2 engaged with the second-stage drive gear D2, so that the power transmitted through the first-stage driven gear P1 or the second-stage driven gear P2 can be transmitted to a differential DF through an output gear OG.

[0004] The input shaft IN is provided with a dog clutch DC (or a synchronizer) for achieving reverse gear by rotating the electric generator MG in the reverse direction when the first-stage drive gear D1 is fixed to the input shaft IN.

[0005] When the transmission having the above configuration performs a shift from the first stage to the second stage, the shift to the second stage is completed by engaging the friction clutch FC only in the first-stage drive state.

[0006] That is, the shift from the first stage to the second stage is achieved by engaging only one friction clutch FC.

[0007] The information included in the background section of the present invention is only for enhancing the understanding of the general background of the present invention, and should not be regarded as an admission or an implication in any form that the information forms the prior art known to those skilled in the art. Summary of the Invention

[0008] Aspects of the present invention are directed to providing a shift control method for a vehicle equipped with a transmission that performs shifting by engaging a friction clutch, having a simpler configuration when controlling the friction clutch, so that the components required for the transmission can be reduced and appropriate shifting performance can be obtained, ultimately further improving the marketability of the vehicle.

[0009] According to various exemplary embodiments of the present invention, a shift control method for a transmission including an electric oil pump (EOP) directly connected to a friction clutch of a vehicle includes: when a shift implemented by engaging the friction clutch starts, setting, by a controller, a predetermined first target RPM for controlling the EOP; determining, by the controller, a target current based on the first target RPM; maintaining, by the controller, the first target RPM until an EOP drive current, which is a current for driving the EOP, reaches the target current; when the EOP drive current is greater than or equal to the target current, linearly reducing, by the controller, the RPM of the EOP from a predetermined second target RPM to a third target RPM; and increasing, by the controller, an EOP driving force to increase the frictional force of the friction clutch such that the slip of the friction clutch is less than a predetermined reference slip, where the EOP driving force is a force for driving the EOP.

[0010] The first target RPM can be set based on an automatic transmission fluid (ATF) temperature and an accelerator position sensor (APS) signal, and the first target RPM can be set higher as the ATF temperature is higher or the APS signal indicates a greater amount of accelerator pedal depression.

[0011] The target current based on the first target RPM can be set as the EOP drive current that flows when a piston starts to move when the flow path from the EOP to the friction clutch is fully filled with ATF when the EOP rotates at the first target RPM.

[0012] The controller can be configured to: set the third target RPM based on the ATF temperature; set a piston stroke time of the friction clutch based on the APS signal; and set the second target RPM using the third target RPM and the piston stroke time.

[0013] As the ATF temperature is higher, the third target RPM can be set higher, and as the APS signal indicates a greater amount of accelerator pedal depression, the piston stroke time can be set shorter.

[0014] When the RPM of the EOP linearly changes from the second target RPM to the third target RPM during the piston stroke time, the controller can set the second target RPM to obtain a flow rate of ATF that fills the space generated by the piston stroke.

[0015] In the increase of the EOP driving force, the controller can increase the EOP driving force according to a predetermined pressure curve selected based on the APS signal.

[0016] As the APS signal indicates a greater amount of accelerator pedal depression, a pressure curve with a higher pressure level can be selected.

[0017] After the EOP driving force increases, when the slip of the friction clutch is greater than or equal to a predetermined reference slip, the shift control method may further include additionally increasing the EOP driving force until the slip of the friction clutch is less than the predetermined reference slip.

[0018] During the additional increase of the EOP driving force, the controller may learn the additional increase of the EOP driving force until the slip of the friction clutch is less than the predetermined reference slip, so as to reflect the additionally increased EOP driving force in the EOP driving force according to the pressure curve during the next shift control.

[0019] The method and apparatus of the present invention have other features and advantages that are obvious in the accompanying drawings incorporated herein for explaining the specific principles of the present invention together and in the following detailed description or are more particularly set forth therein. Description of the Drawings

[0020] Figure 1 is a view exemplarily showing the structure of a transmission of an electric vehicle to which various exemplary embodiments of the present invention can be applied;

[0021] Figure 2 is exemplarily showing the control Figure 1 of a hydraulic control device of a transmission to which various exemplary embodiments of the present invention can be applied;

[0022] Figure 3 is a flowchart showing a shift control method of a vehicle according to various exemplary embodiments of the present invention;

[0023] Figure 4 is a graph explaining a shift control method of a vehicle according to various exemplary embodiments of the present invention.

[0024] It can be understood that the drawings are not necessarily drawn to scale, showing a slightly simplified depiction of various features illustrating the basic principles of the present invention. Specific design features of the present invention as included herein, including for example specific dimensions, orientations, positions, and shapes, will be determined in part by the particular intended application and use environment.

[0025] In the drawings, throughout the several views of the drawings, reference numerals indicate the same or equivalent parts of the present invention. Detailed Description of the Invention

[0026] Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. When the present invention is described in connection with the exemplary embodiments of the present invention, it will be understood that this specification is not intended to limit the present invention to those exemplary embodiments. On the other hand, the present invention is intended to cover not only the exemplary embodiments of the present invention, but also various alternatives, modifications, equivalents or other embodiments, which may be included within the spirit and scope of the present invention as defined by the appended claims.

[0027] Referring Figure 1 and Figure 2 , the friction clutch FC is controlled by directly receiving the pressure of the oil discharged from the electric oil pump (EOP), and the motor M of the EOP is controlled by the controller CLR. Figure 1

[0028] A part of the automatic transmission fluid (ATF) is used to lubricate and cool not only the friction clutch FC but also other gears through the orifice OF, where the automatic transmission fluid (ATF) is the oil discharged from the EOP.

[0029] Referring Figure 3 , a shift control method of a transmission including an EOP directly connected to a friction clutch FC according to various exemplary embodiments of the present invention includes: when a shift implemented by engaging the friction clutch FC starts, setting, by the controller CLR, a predetermined first target RPM V1 for controlling the EOP (S10); determining, by the controller CLR, a target current based on the first target RPM V1 (S20); maintaining, by the controller CLR, the first target RPM V1 until the EOP drive current reaches the target current, where the EOP drive current is the current for driving the EOP (S30); when the EOP drive current is greater than or equal to the target current, linearly decreasing, by the controller CLR, the RPM of the EOP from a predetermined second target RPM V2 to a third target RPM V3 (S40); and increasing, by the controller CLR, the EOP driving power to increase the frictional force of the friction clutch FC such that the slip of the friction clutch FC is less than a predetermined reference slip, where the EOP driving power is the power for driving the EOP (S50).

[0030] That is, according to various exemplary embodiments of the present invention, the hydraulic pressure directly acting on the friction clutch FC can be adjusted by controlling the EOP without a separate solenoid valve or the like for controlling the hydraulic pressure. Therefore, the number of components can be reduced and the shift operation can be performed smoothly.

[0031] Here, "the EOP is directly connected to the friction clutch" means that as in Figure 2No separate solenoid valve or the like is provided in the flow path from the EOP to the friction clutch FC, so that the hydraulic pressure of the ATF discharged from the EOP can directly act on the friction clutch FC.

[0032] In addition, "shifting implemented by engaging the friction clutch" means that shifting is implemented by engaging only one friction clutch, just like the shifting from the first stage to the second stage implemented when the friction clutch FC is engaged in the transmission as Figure 1 shown.

[0033] That is, in a conventional transmission that uses hydraulics to implement shifting, shifting is usually performed by disengaging one clutch while engaging another clutch, which is the so-called clutch to clutch shifting. However, in the case of shifting applying various exemplary embodiments of the present invention, shifting is implemented by engaging only one friction clutch without disengaging another clutch.

[0034] The first target RPM V1 can be set based on the ATF temperature and the accelerator position sensor (APS) signal; and as the ATF temperature is higher or as the APS signal indicates a greater depression amount of the accelerator pedal, the first target RPM V1 is set higher.

[0035] This is because as the ATF temperature is higher, the viscosity of the ATF is lower, increasing the leakage amount, and as the APS signal indicates a greater depression amount of the accelerator pedal, the driver shows an intention to accelerate the vehicle faster. Therefore, for faster shifting, the first target RPM V1 is set relatively higher.

[0036] The target current based on the first target RPM V1 is set as the EOP drive current that flows when the piston starts to move when the flow path from the EOP to the friction clutch FC is completely filled with ATF when the EOP rotates at the first target RPM V1.

[0037] When starting to shift, the controller CLR monitors the EOP drive current until the target current is reached, while controlling the EOP to rotate at the first target RPM V1. The EOP drive current that has reached the target current indicates that the flow path from the EOP to the friction clutch FC is completely filled with ATF and the piston of the friction clutch FC is now in a state of starting to move.

[0038] That is, this process corresponds to Figure 4Part A, in which, when starting to shift gears, the pressure chamber where the piston of the friction clutch FC is located is completely filled with ATF from the EOP to engage the friction clutch FC. As described above, when the EOP is continuously driven while the controller CLR maintains the RPM of the EOP at the first target RPM V1, the ATF discharged from the EOP completely fills the pressure chamber, and then the pressure in the flow path increases until the piston overcomes the elastic force of the return spring and starts to move, so the EOP drive current increases. Using such a principle, it is determined that the flow path from the EOP to the pressure chamber of the friction clutch FC is completely filled with ATF.

[0039] According to various exemplary embodiments of the present invention, the friction clutch FC includes a plurality of clutch discs and clutch plates installed between two rotating bodies of power adjustment to generate frictional force between the two rotating bodies when the clutch discs and clutch plates are pressed against each other. In the pressure chamber, the clutch discs and clutch plates are pressed by the linear sliding of the piston by means of hydraulic pressure. In the case where no hydraulic pressure is supplied to the pressure chamber, the return spring does not allow the piston to press the clutch discs and clutch plates, thereby cutting off the power transmission between the two rotating bodies.

[0040] When the flow path from the EOP to the friction clutch FC is completely filled with ATF as described above and the piston is in the state of starting to move and the EOP drive current is greater than the first target RPM V1, the controller CLR linearly reduces the RPM of the EOP from the second target RPM V2 to the third target RPM V3 (S40).

[0041] This process corresponds to Figure 4 Part B, in which the piston of the friction clutch FC overcomes the elastic force of the return spring and starts to move, and the piston moves to a position where it starts to press the clutch discs and clutch plates.

[0042] The movement of the piston as described above is called the piston stroke. The RPM of the EOP when the piston starts to generate frictional force in the friction clutch FC by pressing the clutch discs and clutch plates after completing the piston stroke corresponds to the third target RPM V3.

[0043] The controller CLR sets the third target RPM V3 based on the ATF temperature, sets the piston stroke time of the friction clutch FC based on the APS signal, and sets the second target RPM V2 using the third target RPM V3 and the piston stroke time.

[0044] As the ATF temperature is higher, the third target RPM V3 is set higher, and as the APS signal indicates a greater amount of accelerator pedal depression, the piston stroke time is set shorter.

[0045] That is to say, considering that the higher the ATF temperature, the more leakage in the hydraulic circuit, as the ATF temperature increases, the third target RPM V3 is set higher. Moreover, as the APS signal indicates a greater amount of accelerator pedal depression, the piston stroke time is set shorter to facilitate faster gear shifting.

[0046] When the RPM of the EOP linearly changes from the second target RPM V2 to the third target RPM V3 during the piston stroke time, the controller CLR sets the second target RPM V2 to obtain the flow rate of the ATF that fills the space generated by the piston stroke.

[0047] That is to say, through design based on multiple experiments and their analysis, the volume of the space generated by the piston stroke, that is, the space that needs to be filled with ATF due to the piston stroke, is pre-input into the controller CLR. When determining the third target RPM V3 and the piston stroke time, the controller CLR sets the second target RPM V2 to obtain the flow rate that fills the volume during the piston stroke time.

[0048] When setting the second target RPM V2 as described above, the controller CLR quickly adjusts the RPM of the EOP from the first target RPM V1 to the second target RPM V2, and then gradually adjusts the RPM of the EOP from the second target RPM V2 to the third target RPM V3 to complete the piston stroke.

[0049] Thereafter, during the increase in the EOP driving force (S50), the controller CLR increases the EOP driving force according to a predetermined pressure curve selected based on the APS signal.

[0050] The pressure curve is a curve that increases the frictional force of the friction clutch FC over time. Based on multiple experiments and analysis of the pressure curve, multiple pressure curves based on the APS signal are pre-input into a storage device or the like so that the controller CLR can refer to the pressure curve, thereby not only suppressing the occurrence of shift shock but also facilitating fast gear shifting. Thus, as the APS signal indicates a greater amount of accelerator pedal depression, a pressure curve with a higher pressure level is selected, so that the friction clutch FC is engaged faster to facilitate faster gear shifting.

[0051] Here, the reason for adjusting the EOP driving force according to the pressure curve is that the pressure exerted by the piston on the clutch disc and clutch plate is determined by the EOP driving force.

[0052] This process corresponds to Figure 4 part C. In Figure 4 Considering the continuity with other parts, the RPM of the EOP is shown in part C. Here, the RPM of the EOP obviously refers to the RPM that allows the EOP driving force to follow the pressure curve.

[0053] When the EOP driving force is gradually increased according to the selected pressure curve as described above, the friction clutch FC engages, so that the slip of the friction clutch FC can be less than the reference slip. When the slip of the friction clutch FC is less than the reference slip, the gear shift is basically completed.

[0054] The reference slip can be determined by design based on multiple experiments and analyses of the reference slip, where the reference slip is a value used to judge that the gear shift as described above has been completed.

[0055] However, when the slip of the friction clutch FC is greater than or equal to the reference slip even after the EOP driving force is increased, the EOP driving force is additionally increased until the slip of the friction clutch FC is less than the reference slip (S60) to reduce the slip of the friction clutch FC to less than the reference slip, so that the gear shift is terminated.

[0056] When the EOP driving force is additionally increased as described above, the controller CLR learns that the EOP driving force is additionally increased until the slip of the friction clutch FC is less than the reference slip, so as to reflect the additionally increased EOP driving force in the EOP driving force according to the pressure curve during the next gear shift control, thereby promoting a quick gear shift under the same conditions next time.

[0057] As described above, according to various exemplary embodiments of the present invention, the hydraulic pressure required to engage the friction clutch FC for performing a gear shift can be formed by directly controlling the EOP without a separate solenoid valve or the like for adjusting the hydraulic pressure. Therefore, the number of required components can be reduced, thereby not only improving the assembly efficiency and promoting cost reduction, but also realizing a smooth and stable gear shift operation, which greatly contributes to improving the marketability of the vehicle.

[0058] According to various exemplary embodiments of the present invention, a vehicle equipped with a transmission that performs a gear shift by engaging a friction clutch can have a relatively simple configuration in controlling the friction clutch, so that the components required for the transmission can be reduced and appropriate gear shift performance can be obtained, ultimately further improving the marketability of the vehicle.

[0059] In addition, terms related to a control device such as "controller", "control unit", "control device", or "control module" refer to a hardware device including a memory and a processor configured to run one or more steps described as an algorithmic structure. The memory stores the algorithm steps, and the processor runs the algorithm steps to execute one or more processes of a method according to various exemplary embodiments of the present invention. The controller according to various exemplary embodiments of the present invention can be implemented by a non-volatile memory configured to store algorithms for controlling the operation of various components of a vehicle or data of software commands for running the algorithms and a processor configured to perform the operations described above using the data stored in the memory. The memory and the processor can be separate chips. Optionally, the memory and the processor can be integrated on one chip. The processor can be implemented as one or more processors.

[0060] The control device can be at least one microprocessor operated by a predetermined program that can include a series of commands for implementing the methods included in the above-described various exemplary embodiments of the present invention.

[0061] The above invention can also be implemented as computer-readable code on a computer-readable recording medium. A computer-readable recording medium is any data storage device that can store data that can be read by a computer system thereafter. Examples of computer-readable recording media include hard disk drives (HDDs), solid state drives (SSDs), silicon disk drives (SDDs), read-only memories (ROMs), random access memories (RAMs), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, etc. and are implemented as carrier waves (e.g., transmitted over the Internet).

[0062] In various exemplary embodiments of the present invention, each of the above operations can be performed by a controller, and the controller can be configured by multiple controllers or an integrated single controller.

[0063] For the convenience of explanation and accurate definition of the appended claims, the terms "above", "below", "inside", "outside", "upper", "lower", "upward", "downward", "front", "rear", "back", "inside", "outside", "inward", "outward", "inner", "outer", "internal", "external", "inner", "outer", "forward", and "backward" are used to describe the features of the exemplary embodiments with reference to the positions of such features as shown in the drawings. It will be further understood that the term "connected" or its derivatives refer to both direct connection and indirect connection.

[0064] In addition, the term "fixedly connected" means that the fixedly connected members always rotate at the same speed. In addition, the term "selectively connectable" means that "when the selectively connectable members are not engaged with each other, the selectively connectable members rotate separately, when the selectively connectable members are engaged with each other, the selectively connectable members rotate at the same speed, and when at least one of the selectively connectable members is a fixed member and the remaining selectively connectable members are engaged with the fixed member, the selectively connectable members are fixed".

[0065] For purposes of illustration and description, the foregoing description of specific exemplary embodiments of the invention has been provided. They are not intended to be exhaustive or to limit the invention to the exact forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described to explain some principles of the invention and its practical application to enable others skilled in the art to implement and utilize the invention in its various exemplary embodiments, as well as various alternatives and modifications thereof. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A shift control method for a transmission, the transmission including an electric oil pump (EOP) directly connected to a friction clutch of a vehicle, the shift control method comprising: When it is determined that a shift to be achieved by engaging the friction clutch starts, setting, by a controller, a first target revolutions per minute (RPM) for controlling the EOP, i.e., a first target RPM; Determining, by the controller, a target current based on the first target RPM; Maintaining, by the controller, the first target RPM until an EOP drive current reaches the target current, wherein the EOP drive current is a current for driving the EOP; When it is determined that the EOP drive current is greater than or equal to the target current, linearly decreasing, by the controller, the RPM of the EOP from a second target RPM to a third target RPM; and Increasing, by the controller, an EOP driving force to increase a frictional force of the friction clutch such that a slip of the friction clutch is less than a predetermined reference slip, wherein the EOP driving force is a force for driving the EOP.

2. The shift control method according to claim 1, wherein The first target RPM is set according to an automatic transmission fluid (ATF) temperature and an accelerator position sensor (APS) signal, and As the ATF temperature is higher or the APS signal indicates a greater depression amount of an accelerator pedal, the first target RPM is set higher.

3. The shift control method according to claim 1, wherein The target current based on the first target RPM is set as an EOP drive current that flows when a piston starts to move when the ATF completely fills a flow path from the EOP to the friction clutch when the EOP rotates at the first target RPM.

4. The shift control method according to claim 1, wherein The controller is configured to: Set the third target RPM according to the ATF temperature; Set a piston stroke time of the friction clutch according to the APS signal; and Set the second target RPM by using the third target RPM and the piston stroke time.

5. The shift control method according to claim 4, wherein As the ATF temperature is higher, the third target RPM is set higher, and As the APS signal indicates a greater depression amount of the accelerator pedal, the piston stroke time is set shorter.

6. The shift control method according to claim 4, wherein The controller is configured to set the second target RPM to obtain a flow rate of the ATF that fills a space generated by a piston stroke when it is determined that the RPM of the EOP linearly changes from the second target RPM to the third target RPM during the piston stroke time.

7. The shift control method according to claim 1, wherein In the increase of the EOP driving force, the controller is configured to increase the EOP driving force according to a predetermined pressure curve selected based on the APS signal.

8. The shift control method according to claim 7, wherein As the APS signal indicates a greater amount of accelerator pedal depression, a pressure curve with a higher pressure level is selected.

9. The shift control method according to claim 1, further comprising: After the EOP driving force increases, when it is determined that the slip of the friction clutch is greater than or equal to a predetermined reference slip, the EOP driving force is additionally increased until the slip of the friction clutch is less than the predetermined reference slip.

10. The shift control method according to claim 9, wherein In additionally increasing the EOP driving force, the controller is configured to learn the additional increase in the EOP driving force until the slip of the friction clutch is less than the predetermined reference slip, so as to reflect the additionally increased EOP driving force in the EOP driving force according to the pressure curve during the next shift control.

11. The shift control method according to claim 1, wherein The controller includes: A processor; and A non-transitory storage medium on which a program for executing the shift control method according to claim 1 is recorded and run by the processor.

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