Transmission for electric vehicle and control method thereof

文档序号：826486 发布日期：2021-03-30 浏览：25次中文

阅读说明：本技术 用于电动车辆的变速器及其控制方法 (Transmission for electric vehicle and control method thereof ) 是由李在峻黄真荣金珍镐金钟成闵盛焕朴钟述将旭镇孔镇亨于 2020-03-05 设计创作，主要内容包括：本发明提供一种用于电动车辆的变速器。该用于电动车辆的变速器可以包括：第一行星齿轮组；第一马达,被构造为将动力输入到第一行星齿轮组的第一转动元件；差速器,被构造为接收从第一行星齿轮组的第二转动元件输出的动力；第二马达,被构造为将动力选择性地提供到第一行星齿轮组的第三转动元件；第二行星齿轮组,包括直接连接到差速器的第一转动元件和被构造为从第二马达选择性地接收动力的第二转动元件；以及第三行星齿轮组,包括直接连接到第二行星齿轮组的第三转动元件的第三转动元件、固定的第二转动元件和直接连接到差速器的被选择输出轴的第一转动元件。(The invention provides a transmission for an electric vehicle. The transmission for an electric vehicle may include: a first planetary gear set; a first motor configured to input power to a first rotating element of the first planetary gear set; a differential configured to receive power output from the second rotating element of the first planetary gear set; a second motor configured to selectively supply power to a third rotating element of the first planetary gear set; a second planetary gear set including a first rotating element directly connected to the differential and a second rotating element configured to selectively receive power from the second motor; and a third planetary gear set including a third rotating element directly connected to the third rotating element of the second planetary gear set, a fixed second rotating element, and a first rotating element directly connected to the selected output shaft of the differential.)

1. A transmission for a vehicle, the transmission comprising:

a first planetary gear set including three rotating elements, i.e., a first rotating element, a second rotating element, and a third rotating element;

a first motor connected to a first rotating element of the first planetary gear set and inputting power to the first rotating element of the first planetary gear set;

a differential connected to the second rotating element of the first planetary gear set and receiving power output from the second rotating element of the first planetary gear set;

a second motor selectively supplying power to a third rotating element of the first planetary gear set;

a second planetary gear set including a first rotating element connected to a differential case of the differential and a second rotating element selectively receiving power from the second motor; and

a third planetary gear set including a third rotating element connected to the third rotating element of the second planetary gear set, a fixed second rotating element, and a first rotating element connected to a selected output shaft, which is one of the output shafts of the differential.

2. The transmission for a vehicle according to claim 1, further comprising:

a first clutch selectively connecting the third rotating element of the first planetary gear set to a transmission housing; and

a second clutch selectively connecting two of the three rotating elements of the first planetary gear set directly with each other.

3. The transmission for a vehicle according to claim 2,

the first planetary gear set includes a first sun gear as a first rotating element of the first planetary gear set, a first carrier as a second rotating element of the first planetary gear set, and a first ring gear as a third rotating element of the first planetary gear set and selectively connected to the first clutch, and

the second clutch selectively connects the first sun gear and the first ring gear to each other.

4. The transmission for a vehicle according to claim 3,

the second motor is selectively connected to the first ring gear of the first planetary gear set through a third clutch.

5. The transmission for a vehicle according to claim 4,

a second rotating element of the second planetary gear set is selectively connected to the second motor through a fourth clutch.

6. The transmission for a vehicle according to claim 3,

the ratio of the number of teeth of the second sun gear of the second planetary gear set to the number of teeth of the second ring gear of the second planetary gear set and the ratio of the number of teeth of the third sun gear of the third planetary gear set to the number of teeth of the third ring gear of the third planetary gear set are identical to each other.

7. A transmission for a vehicle, the transmission comprising:

a first planetary gear set including three rotating elements, i.e., a first rotating element, a second rotating element, and a third rotating element;

a first motor connected to a first rotating element of the first planetary gear set and inputting power to the first rotating element of the first planetary gear set;

a differential connected to the second rotating element of the first planetary gear set and receiving power output from the second rotating element of the first planetary gear set;

a second motor selectively supplying power to a third rotating element of the first planetary gear set; and

a multiple planetary gear set installed between a differential case of the differential and a selected output shaft to distribute power supplied from the second motor to the differential case and the selected output shaft, and to reverse directions of torques distributed to the differential case and the selected output shaft, which is one of the output shafts of the differential, to each other.

8. The transmission for a vehicle according to claim 7,

the compound planetary gear set includes:

a second planetary gear set including a first rotating element connected to the differential case and a second rotating element selectively connected to the second motor; and

9. A transmission for a vehicle comprising two or more motors, two or more clutches and one or more planetary gear sets and having two or more gears, wherein,

a first motor of the two or more motors is connected to a first rotating element of a first planetary gear set of the one or more planetary gear sets, the first planetary gear set including three rotating elements, i.e., the first rotating element, a second rotating element, and a third rotating element,

the third rotating element of the first planetary gear set is selectively connected to the transmission housing through the first clutch,

the second rotating element of the first planetary gear set is connected to the output shaft,

a second motor of the two or more motors is connected to a third rotating element of the first planetary gear set,

a second clutch selectively connecting two rotating elements among the three rotating elements of the first planetary gear set, and

allowing transmission control via the second motor.

10. The transmission for a vehicle according to claim 9,

the second motor is always connected to the third rotating element of the first planetary gear set through a speed reducer.

11. A control method of a transmission for a vehicle according to claim 5, the control method comprising:

in a first-gear running state where the first clutch is engaged and the first motor drives, the controller releases the first clutch after controlling the second motor to supply the same torque as that of the first clutch supporting the third rotating element of the first planetary gear set to the third rotating element of the first planetary gear set;

the controller decreases the speed of the first motor and increases the speed of the second motor to synchronize the speeds of the three rotating elements of the first planetary gear set with each other while maintaining the torque of the first motor and the torque of the second motor constant; and

the controller releases torque of the second motor to establish a second gear state while maintaining a speed of the first motor after engaging the second clutch.

12. The control method according to claim 11, wherein,

the controller engages a third clutch before torque is supplied from the second motor to a third rotating element of the first planetary gear set, and releases the third clutch after the second clutch is engaged.

13. The control method according to claim 11, wherein,

after engaging the fourth clutch, the controller controls the second motor to apply torque in opposite directions to the differential case and the selected output shaft to perform torque vectoring.

14. The control method according to claim 11, further comprising:

in the second gear state where the second clutch is engaged and the first motor is driven, the controller releases the second clutch after increasing the torque of the second motor to the first clutch torque while maintaining the speed of the first motor;

the controller reduces the speed of the second motor to 0 and increases the speed of the first motor while maintaining the torque of the first motor and the torque of the second motor constant; and

the controller releases the torque of the second motor to establish the first-gear running state after the first clutch is engaged.

15. The control method according to claim 14, wherein,

the controller engages a third clutch before releasing the second clutch and increasing the torque of the second motor, and releases the third clutch after releasing the torque of the second motor.

16. The control method according to claim 14, wherein,

after engaging the fourth clutch, the controller controls the second motor to apply torque in opposite directions to the differential case and the selected output shaft to perform torque vectoring.

17. A control method of a transmission for a vehicle according to claim 9, the control method comprising:

the controller releases torque of the second motor to establish a second gear state while maintaining a speed of the first motor after engaging the second clutch.

18. The control method according to claim 17, further comprising:

the controller reduces the speed of the second motor to 0 and increases the speed of the first motor while maintaining the torque of the first motor and the torque of the second motor constant; and

the controller releases the torque of the second motor to establish the first-gear running state after the first clutch is engaged.

Technical Field

The present invention relates to a transmission that can be mounted in an electric vehicle and a control method thereof.

Background

An electric vehicle, which is a vehicle that provides power of an electric motor as driving force, does not discharge exhaust gas, and thus can contribute to reduction of environmental pollution in large cities.

There is a need for improvement of various technologies to achieve popularization of electric vehicles, and in particular, there is a need for a technology capable of significantly increasing a travel distance of one charge.

In order to increase the travel distance, it is necessary to achieve the maximum climbing performance and the maximum speed performance required for the vehicle while improving energy efficiency (travel distance per unit power, km/kWh) by reducing the size and capacity of a motor mounted in an electric vehicle. For this reason, a transmission is mounted in an electric vehicle.

For the above reasons, the transmission mounted in the electric vehicle has a simple configuration, no shift shock occurs, and heat generation is small.

The information disclosed in this background section is only for enhancement of general background of the invention and may not be taken as an acknowledgement or any form of suggestion that this information forms the prior art known to a person skilled in the art.

Disclosure of Invention

Various aspects of the present invention are directed to providing a transmission for an electric vehicle configured to provide a plurality of gear ratios to reduce a capacity of a motor, to achieve maximum hill climbing performance and maximum speed performance required for the vehicle, to improve energy efficiency of the vehicle with a relatively simple configuration and a small weight, to prevent shift shock, to significantly reduce heat generation, and to implement a torque vectoring (torque vectoring) function to improve high-speed curve running performance of the vehicle, and a control method thereof.

According to an exemplary embodiment of the present invention, a transmission for an electric vehicle includes: a first planetary gear set; a first motor configured to input power to a first rotating element of the first planetary gear set; a differential configured to receive power output from the second rotating element of the first planetary gear set; a second motor configured to selectively supply power to a third rotating element of the first planetary gear set; a second planetary gear set including a first rotating element connected to a differential case of the differential and a second rotating element configured to selectively receive power from a second motor; and a third planetary gear set including a third rotating element connected to the third rotating element of the second planetary gear set, a fixed second rotating element, and a first rotating element connected to a selected output shaft, the selected output shaft being any one of output shafts of the differential.

A first clutch configured to selectively connect the third rotating element of the first planetary gear set to the transmission housing and a second clutch configured to directly connect two of the three rotating elements of the first planetary gear set to each other may be connected to the first planetary gear set.

The first planetary gear set may include a first sun gear directly connected to the first motor as an input element, a first carrier directly connected to the differential case as an output element, and a first ring gear connected to the first clutch, and the second clutch may connect the first sun gear and the first ring gear to each other.

The second motor may be connected to the first ring gear of the first planetary gear set through a third clutch.

The second rotating element of the second planetary gear set may be connected to the second motor through a fourth clutch.

The ratio of the number of teeth of the second sun gear of the second planetary gear set to the number of teeth of the second ring gear of the second planetary gear set and the ratio of the number of teeth of the third sun gear of the third planetary gear set to the number of teeth of the third ring gear of the third planetary gear set may be identical to each other.

According to various exemplary embodiments of the present invention, a transmission for an electric vehicle includes: a first planetary gear set; a first motor configured to input power to a first rotating element of the first planetary gear set; a differential configured to receive power output from the second rotating element of the first planetary gear set; a second motor configured to selectively supply power to a third rotating element of the first planetary gear set; and a double planetary gear set installed between a differential case of the differential and a selected output shaft to distribute power supplied from the second motor to the differential case and the selected output shaft, and to make directions of torques distributed to the differential case and the selected output shaft, which is any one of the output shafts of the differential, opposite to each other.

The compound planetary gear set may include: a second planetary gear set including a first rotating element connected to a differential case of the differential and a second rotating element configured to be connected to a second motor; and a third planetary gear set including a third rotating element connected to the third rotating element of the second planetary gear set, a fixed second rotating element, and a first rotating element connected to the selected output shaft.

According to various exemplary embodiments of the present invention, a transmission for an electric vehicle includes two or more motors, two or more clutches, and one or more planetary gear sets and has two or more gears, wherein a first motor is connected to a first rotating element of a first planetary gear set, a third rotating element of the first planetary gear set is selectively connected to a transmission case through the first clutch, a second rotating element of the first planetary gear set is connected to an output shaft, a second motor is connected to the third rotating element of the first planetary gear set, includes a second clutch connecting any two elements of the first planetary gear set, and allows transmission control through the second motor.

The second motor may be constantly connected to the third rotating element of the first planetary gear set through a speed reducer.

According to various exemplary embodiments of the present invention, a control method for a transmission of an electric vehicle includes: in a low-speed drive state in which the first clutch is engaged and the first motor is driven, the controller releases the first clutch after controlling the second motor to supply the same torque as that of the first clutch supporting the third rotating element of the first planetary gear set to the third rotating element of the first planetary gear set; the controller reduces the speed of the first motor and increases the speed of the second motor to synchronize the speeds of the three rotating elements of the first planetary gear set with each other while maintaining the torque of the first motor and the torque of the second motor constant; and the controller releases the torque of the second motor to establish the high-speed drive state while maintaining the speed of the first motor after engaging the second clutch.

The controller may engage the third clutch before torque is provided from the second motor to the third rotating element of the first planetary gear set, and release the third clutch after the second clutch is engaged.

After engaging the fourth clutch, the controller may be configured to control the second motor to apply torque in opposite directions to the differential case and the selected output shaft to perform torque vectoring.

The control method may further include: in a high-speed drive state in which the second clutch is engaged and the first motor is driven, the controller releases the second clutch after increasing the torque of the second motor to the first clutch torque while maintaining the speed of the first motor; the controller reduces the speed of the second motor to 0 and increases the speed of the first motor while maintaining the torque of the first motor and the torque of the second motor constant; and the controller releases the torque of the second motor to establish a low-speed travel state after the first clutch is engaged.

The controller may engage the third clutch before releasing the second clutch and increasing the torque of the second motor, and release the third clutch after releasing the torque of the second motor.

The method and apparatus of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following detailed description, which together serve to explain certain principles of the invention.

Drawings

FIG. 1 is a schematic illustration of a transmission for an electric vehicle according to an exemplary embodiment of the present invention;

FIG. 2 is a table describing the operating modes of the transmission of FIG. 1;

FIG. 3 is a flow chart illustrating a control method for shifting the transmission of FIG. 1 from low gear to high gear;

FIG. 4 is a motor map illustrating a process for shifting the transmission of FIG. 1 from low gear to high gear;

FIG. 5 is a table showing torque variation of the motor and clutch during the shift of FIG. 3;

FIG. 6 is a graph depicting a process for shifting the transmission of FIG. 1 from low gear to high gear;

FIG. 7 is a flowchart illustrating a control method for shifting the transmission of FIG. 1 from high gear to low gear;

FIG. 8 is a motor map illustrating a process for shifting the transmission of FIG. 1 from high gear to low gear;

FIG. 9 is a table showing the torque variation of the motor and clutch during the shift of FIG. 7;

fig. 10 is a table showing the rotation speed of each portion in the transmission of fig. 1 in a state where the fourth clutch is engaged and the second motor is stopped;

FIG. 11 is a table showing the rotational speeds of each portion in the transmission of FIG. 1 in a state where the fourth clutch is engaged and the second motor is driven at a speed of 100 RPM;

FIG. 12 is a diagram for describing a torque vectoring function by comparing the state of FIG. 10 and the state of FIG. 11 with each other using lever diagrams of a second planetary gear set and a third planetary gear set;

FIG. 13 is a schematic illustration of a transmission for an electric vehicle according to another exemplary embodiment of the present invention;

FIG. 14 is a schematic illustration of the transmission of FIG. 13 with the addition of a retarder according to an exemplary embodiment of the present invention; and

fig. 15 is a diagram provided for comparison with the graph of fig. 6 and describing a process of shifting a general transmission for an electric vehicle from a low gear to a high gear according to the related art.

It is to be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the invention, including, for example, specific dimensions, orientations, locations, and shapes, as embodied herein, will be determined in part by the particular intended application and use environment.

In the drawings, like or equivalent parts of the invention are designated by reference numerals throughout the several views of the drawings.

Detailed Description

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

Hereinafter, a transmission for an electric vehicle and a control method thereof according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

Referring to fig. 1, a transmission for an electric vehicle according to an exemplary embodiment of the present invention includes: a first planetary gear set PG 1; a first motor MG1 that inputs power to a first rotating element of the first planetary gear set PG 1; a differential DF receiving power output from the second rotating element of the first planetary gear set PG 1; a second motor MG2 that supplies power to the third rotating element of the first planetary gear set PG 1; and a double planetary gear set CG mounted between a differential case of the differential DF and a selected output shaft as any one of the output shafts of the differential DF to distribute power supplied from the second motor MG2 to the differential case and the selected output shaft and to reverse directions of torques distributed to the differential case and the selected output shaft to each other.

That is, according to an exemplary embodiment of the present invention, the output speed of the power input from the first motor MG1 is changed by the first planetary gear set PG1, and then the power may be output through the differential DF, the second motor MG2 applies an appropriate torque to the third rotating element of the first planetary gear set PG1 to achieve smooth shifting without a shift shock, and the power supplied from the second motor MG2 is distributed through the double planetary gear set CG to implement a torque vectoring function.

Note that the output shafts of the differential DF are provided with a right output shaft OR and a left output shaft OL, respectively, and an output shaft selected to receive power supplied from the second motor MG2 among the right output shaft OR and the left output shaft OL is referred to as a "selected output shaft". Although fig. 1 illustrates the case where the right output shaft OR is the selected output shaft, the left output shaft OL may of course also become the selected output shaft according to an exemplary embodiment of the present invention.

The first clutch CL1, which may fix the third rotating element to the transmission case CS, and the second clutch CL2, which may directly connect two of the three rotating elements with each other, are connected to the first planetary gear set PG 1.

That is, the first planetary gear set PG1 includes a first sun gear S1 directly connected to the first motor MG1 as an input element, a first carrier C1 directly connected to the differential DF as an output element, and a first ring gear R1 connected to the first clutch CL1, and the second clutch CL2 may connect the first sun gear S1 and the first ring gear R1 to each other.

In the first planetary gear set PG1, switching between a state in which the output speed of power is reduced by the first carrier C1 and power is output through the differential DF when the first sun gear S1 is driven by the first motor MG1 in a state in which the first clutch CL1 is engaged to fix the first ring gear R1, and a state in which the first clutch CL1 is released and the second clutch CL2 is engaged to rotate all the rotary elements of the first planetary gear set PG1 together so that the power transmitted from the first motor MG1 is output as it is through the differential DF, may be performed, and thus the input power may be output at a speed equal to or less than a predetermined speed.

Meanwhile, the second motor MG2 may be connected to the first ring gear R1 of the first planetary gear set PG1 through a third clutch CL3 to selectively transmit power to the first ring gear R1.

The compound planetary gear set CG includes: a second planetary gear set PG2 that includes a first rotary element directly connected to the differential case of the differential DF and a second rotary element that receives power from the second motor MG 2; and a third planetary gear set PG3 including a third rotary element directly connected to the third rotary element of the second planetary gear set PG2, a second rotary element fixed to the transmission case CS, and a first rotary element directly connected to the selected output shaft.

That is, according to the exemplary embodiment of fig. 1, it may be considered that the second planetary gear set PG2 forming the multiple planetary gear set CG is configured to distribute power supplied from the second motor MG2 to the differential case and the selected output shaft, and the third planetary gear set PG3 is configured to reverse the direction of power distributed to the selected output shaft so that the directions of torques distributed to the differential case and the selected output shaft are opposite to each other.

The second carrier C2, which is the second rotating element of the second planetary gear set PG2, is connected to the second motor MG2 through the fourth clutch CL4, and the third carrier C3, which is the second rotating element of the third planetary gear set PG3, is fixed to the transmission case CS.

Further, the ratio of the number of teeth of the second sun gear S2 of the second planetary gear set PG2 to the number of teeth of the second ring gear R2 of the second planetary gear set PG2 and the ratio of the number of teeth of the third sun gear S3 of the third planetary gear set PG3 to the number of teeth of the third ring gear R3 of the third planetary gear set PG3 are set to be equal to each other.

According to an exemplary embodiment of the present invention, the second planetary gear set PG2 and the third planetary gear set PG3 are implemented by substantially identical planetary gear sets having the same number of teeth as each other.

Note that the controller CLR in fig. 1 may control the first motor MG1, the second motor MG2, the first clutch CL1, the second clutch CL2, the third clutch CL3, and the fourth clutch CL4, and may be implemented by a Transmission Control Unit (TCU) or the like.

Fig. 13 shows a transmission for an electric vehicle according to another exemplary embodiment of the present invention. The transmission is a transmission for an electric vehicle including two or more motors, two or more clutches, and one or more planetary gear sets and having two or more gears, and has the following configuration: the first motor MG1 is connected to a first rotary element of the first planetary gear set PG1, a third rotary element of the first planetary gear set PG1 is selectively connected to the transmission case CS by a first clutch CL1, a second rotary element of the first planetary gear set PG1 is connected to the output shaft OUT, the second motor MG2 is always connected to a third rotary element of the first planetary gear set PG1, the second clutch CL2 connecting any two elements of the first planetary gear set PG1 is included, and transmission control can be performed by the second motor MG 2.

In fact, the configuration according to the exemplary embodiment of fig. 13 may be considered to be different from the configuration according to the exemplary embodiment of fig. 1 in that the double planetary gear set CG is removed and the second motor MG2 is directly connected to the first planetary gear set PG 1. The first rotating element of the first planetary gear set is the first sun gear S1, the second rotating element is the first carrier C1, and the third rotating element is the first ring gear R1.

Fig. 14 shows a transmission for an electric vehicle according to still another exemplary embodiment of the present invention. Actually, the configuration of the exemplary embodiment according to fig. 14 and the configuration of the exemplary embodiment according to fig. 13 are substantially the same as each other. The configuration of the exemplary embodiment according to fig. 14 differs from the configuration of the exemplary embodiment according to fig. 13 only in that the second motor MG2 is always connected to the third rotating element of the first planetary gear set PG1 through a speed reducer.

Except for the above-described differences, the exemplary embodiment of fig. 13 and 14 is substantially the same as the exemplary embodiment of fig. 1, and thus a detailed description of the exemplary embodiment of fig. 13 and 14 will be omitted.

A process of performing transmission control of a transmission for an electric vehicle according to an exemplary embodiment of the present invention configured as shown in fig. 1 will be described.

Referring to fig. 3, 4, 5 and 6, a control method of shifting the transmission from a low gear (first gear) to a high gear (second gear) includes: in a low-speed travel state in which the first clutch CL1 is engaged and the first motor MG1 is driven, the controller CLR releases the first clutch CL1 after controlling the second motor MG2 to supply the same torque as that of the first clutch CL1 supporting the third rotating element of the first planetary gear set PG1 to the third rotating element of the first planetary gear set PG1 (S10); the controller CLR reduces the speed of the first motor MG1 and increases the speed of the second motor MG2 to synchronize the speeds of the three rotating elements of the first planetary gear set PG1 with each other while maintaining the torque of the first motor MG1 and the torque of the second motor MG2 constant (S20); and the controller CLR releases the torque of the second motor MG2 to form a high-speed drive state while maintaining the speed of the first motor MG1 after engaging the second clutch CL2 (S30).

Hereinafter, the process will be described in more detail.

In the first speed state corresponding to a low gear, in a state where the first clutch CL1 is engaged, the output speed of the power supplied from the first motor MG1 to the first sun gear S1 is reduced, and the power is output to the differential DF through the first carrier C1, so that the first clutch CL1 fixes the first ring gear R1 of the first planetary gear set PG 1.

At this time, as shown in fig. 4, the first motor MG1 supplies a torque T _ MG1a relatively smaller than T _ MG1b to the first sun gear S1.

To shift to the second speed state corresponding to a high gear, the torque applied to the first ring gear Rl to release the first clutch CL1 while maintaining the state of fixing the first ring gear R1 is referred to as "first clutch torque T _ CL 1". The second motor MG2 is controlled to produce the first clutch torque T _ CL1, and then the first clutch CL1 is released so that a first torque phase begins in which the torque of the second motor MG2 changes while the speed of the first motor MG1 is unchanged.

Therefore, the torque of the first motor MG1 and the torque of the second motor MG2 are maintained, the speed of the first motor MG1 is decreased and the speed of the second motor MG2 is increased to start an inertia phase that synchronizes the rotation speeds of all the rotating elements of the first planetary gear set PG 1.

Therefore, when the second clutch CL2 is engaged, since all the rotating elements of the first planetary gear set PG1 are engaged with each other to rotate integrally, the power supplied from the first motor MG1 is changed from 1: a gear ratio of 1 is output to the differential DF, and in this state, a second torque phase in which the speed of the first motor MG1 is maintained and the torque of the second motor MG2 is released is started, thereby completing the shift to the second speed state corresponding to the high gear.

In the second torque phase, as described above, the speed of the first motor MG1 is maintained and the torque of the second motor MG2 is released such that the torque of the first motor MG1 is increased.

The torque of the first motor MG1 may be increased to T _ MG1b in fig. 4. It can be considered that the shifting process shown in fig. 4 describes the following process: the transmission according to the example embodiment of the invention shifts from the state of outputting T _ MG1a as the maximum torque in the first speed state to the state of outputting T _ MG1b as the maximum torque in the second speed state, thereby achieving a shift between two points on the iso-power curve of the first motor MG 1.

Note that the torque that the second clutch CL2 provides to maintain the state in which all the rotating elements of the first planetary gear set PG1 are engaged with each other to rotate integrally is referred to as second clutch torque T _ CL 2.

The shifting process described above can be represented by the graph in fig. 6. As shown in fig. 15, in a general transmission according to the related art, the torque output through the differential DF is reduced during a period corresponding to the first torque phase according to an exemplary embodiment of the present invention, so that shift quality is deteriorated. However, as shown in fig. 6, in the transmission according to the exemplary embodiment of the present invention, the output torque is maintained without significant change before and after shifting, so that it is possible to ensure excellent shift quality without occurrence of shift shock.

Further, in the case of the transmission for an electric vehicle according to the related art, heat generation due to the clutch that plays a major role in shifting becomes the biggest problem in developing the transmission. However, in the example embodiment of the invention, the second motor MG2 plays a major role in shifting, so that shift shock and clutch heating can be prevented, and durability of the clutch and the transmission can also be significantly improved.

Meanwhile, in the first torque phase, the third clutch CL3 is engaged before torque is supplied from the second motor MG2 to the third rotating element of the first planetary gear set, and in the second torque phase, the third clutch CL3 is released after the second clutch CL2 is engaged.

That is, the third clutch CL3 may be engaged only at the time of gear shifting to supply the power of the second motor MG2 to the first planetary gear set PG1 to perform the above-described action, and the third clutch CL3 may be released in other states, and the fourth clutch may be engaged as needed to control the second motor MG2 to implement the torque vectoring function.

The torque vectoring control is a technique of actively controlling the drive torque output from the differential DF to the output shafts on both sides to effectively reduce understeer and the like when the vehicle is running on a high-speed curve or when the right and left drive wheels are running on an uneven road having friction coefficients different from each other with respect to the ground, thereby improving the drivability and stability of the vehicle. In the example embodiment of fig. 1, after engaging the fourth clutch CL4, the controller CLR may control the second motor MG2 to apply torque in opposite directions to the differential case and the selected output shaft to perform torque vectoring.

Meanwhile, referring to fig. 7 to 9, the control method of shifting the transmission from the high gear (second gear) to the low gear (first gear) includes: in a high-speed travel state in which the second clutch CL2 is engaged and the first motor MG1 is driven, the controller CLR releases the second clutch CL2 after increasing the torque of the second motor MG2 to the first clutch torque while maintaining the speed of the first motor MG1 (S50); the controller CLR reduces the speed of the second motor MG2 to 0 and increases the speed of the first motor MG1 while maintaining the torque of the first motor MG1 and the torque of the second motor MG2 constant (S60); and the controller CLR releases the torque of the second motor MG2 to establish a low-speed drive state after engaging the first clutch CL1 (S70).

Hereinafter, the process will be described in more detail.

In the second speed state corresponding to a high gear, the second clutch CL2 is engaged and all the rotary elements of the first planetary gear set PG1 rotate at the same speed. In this state, to shift to the first speed, the controller CLR increases the torque of the second motor MG2 to the first clutch torque T _ CL1 while maintaining the speed of the first motor MG 1.

That is, the torque of the second motor MG2 is increased to cause the second motor MG2 to provide a torque corresponding to the first clutch torque T _ CL1 to achieve the first speed state by fixing the first ring gear R1, the first clutch torque T _ CL1 being a torque to be applied to the first ring gear R1.

The torque of the first motor MG1 decreases as the torque of the second motor MG2 increases, so that the speed of the first motor MG1 is maintained as the torque of the second motor MG2 increases as described above.

In practice, the present process corresponds to a first torque phase in the transmission control, and the torque represented as the first motor MG1 in fig. 8 is reduced from T _ MG1b to T _ MG1 a.

When the torque of the second motor MG2 increases to the first clutch torque, the second clutch CL2 is released.

Therefore, the torque of the first motor MG1 and the torque of the second motor MG2 are maintained constant, the speed of the second motor MG2 is reduced to 0, and the inertia phase in which the speed of the first motor MG1 is increased starts.

When the speed of the second motor MG2 becomes 0, the first clutch CL1 is engaged to fix the first ring gear R1, and then the torque of the second motor MG2 is released to start the second torque phase, thereby completing the shift from high gear to low gear.

Even during the above-described shifting process, the output torque is maintained substantially constant, so that no shift shock occurs and excellent shift quality can be ensured, eventually contributing to improvement in the marketability of the vehicle. Further, since the clutch involved in shifting does not generate heat, durability of the clutch and the transmission is improved.

Even in this case, in the first torque phase, the third clutch CL3 is engaged before torque is supplied from the second motor MG2 to the first ring gear R1, and in the second torque phase, the third clutch CL3 is released after torque of the second motor MG2 is released.

As described above, the transmission for an electric vehicle according to the exemplary embodiment of the invention provides two speed ratios (low gear and high gear) to achieve maximum hill climbing performance requiring relatively high torque and maximum speed performance requiring relatively high-speed power while improving energy efficiency by reducing the weight of the vehicle even in the case of using the first motor MG1 having a relatively small capacity.

Further, in the case where the first clutch CL1 and the second clutch CL2 are engaged and released after the second motor MG2 generates the first clutch torque T _ CL1 or the second clutch torque T _ CL2, a state in which friction hardly occurs and heat hardly generates can be theoretically achieved. Therefore, it is possible to prevent the transmission and the clutch from generating heat and improve durability.

Meanwhile, fig. 10, 11, and 12 are diagrams describing a torque vectoring function implemented by the transmission of fig. 1. Fig. 10 is a table showing the rotation speed of each portion in the transmission of fig. 1 in a state where the fourth clutch CL4 is engaged and the second motor MG2 is stopped.

That is, in the case where the second motor MG2 is not driven and thus the speed of the second motor MG2 is 0, the speed of the left output shaft OL and the speed of the right output shaft OR of the differential DF are both 3000.

Note that the rotational speed of each portion is determined on the assumption that the number of teeth of the second ring gear R2 is 60, the number of teeth of the second sun gear S2 is 30, the number of teeth of the third ring gear R3 is 60, and the number of teeth of the third sun gear S3 is 30.

Fig. 11 is a table showing the rotation speed of each portion in the transmission of fig. 1 in a state where the fourth clutch CL4 is engaged and the second motor MG2 is driven at a speed of 100 RPM.

That is, in the case where the second motor MG2 is driven at 100RPM, the speed of the left output shaft OL of the differential DF becomes 3300, and the speed of the right output shaft OR becomes 2700. Therefore, each of the speed deviation from the differential case of the differential DF to the right side and the speed deviation from the differential case of the differential DF to the left side becomes 300RPM, thereby achieving the torque vectoring control.

Fig. 12 is a diagram describing a torque vectoring function by comparing the state of fig. 10 and the state of fig. 11 with each other using lever diagrams of a second planetary gear set and a third planetary gear set. In fig. 12, the solid line indicating the state of fig. 10 and the broken line indicating the state of fig. 11 show the execution of the torque vectoring control.

Note that fig. 12 shows a case where the speed of the third sun gear S3 connected to the right output shaft OR of the differential DF is reduced by 300RPM relative to the speed of the second sun gear S2 connected to the differential case, and thus, although not shown, the left output shaft of the differential DF is increased by 300RPM relative to the speed of the differential case according to the configuration and action of the differential DF.

As described above, in the transmission according to the exemplary embodiment of the invention, the second motor MG2 participates in shifting in the state where the third clutch CL3 is engaged to realize smooth shifting, and the torque vectoring function is implemented in the state where the fourth clutch CL4 is engaged, so that the running stability at the time of high-speed curve running of the vehicle can be improved.

Meanwhile, the shift control of the transmission of fig. 13 and 14 according to the exemplary embodiment is substantially the same as the shift control of the transmission of fig. 1 except for the torque vectoring control, and thus a detailed description of the shift control of the transmission of fig. 13 and 14 will be omitted.

According to exemplary embodiments of the present invention, it is possible to provide a plurality of gear ratios to reduce the capacity of a motor, achieve maximum hill climbing performance and maximum speed performance required for a vehicle, improve energy efficiency of the vehicle with a relatively simple configuration and a small weight, increase a travel distance of one charge, prevent shift shock, significantly reduce heat generation, and achieve torque vectoring to improve high-speed curve travel performance of the vehicle.

For convenience in explanation and accurate definition in the appended claims, the terms "upper", "lower", "inner", "outer", "upward", "downward", "upwardly", "downwardly", "front", "rear", "inner", "outer", "inwardly", "outwardly", "inner", "outer", "inner", "outer", "forwardly" and "rearwardly" are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. It will be further understood that the term "connected," or derivatives thereof, refers to both direct and indirect connections.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the following claims and their equivalents.

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Transmission for electric vehicle and control method thereof

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