Method for learning touch point of engine clutch for hybrid electric vehicle

Abstract

A method for learning a touch point of an engine clutch for a hybrid electric vehicle includes controlling a speed of an engine to have an idle speed. A fluid pipe of a clutch actuator is refilled with a working fluid by driving a driving motor in an idle control state of the engine, a speed of the driving motor is synchronized with the speed of the engine, and then the engine clutch is engaged. The engine clutch is released after the refill is performed, and the speed of the driving motor is decreased. A working fluid is applied so that the engine clutch is operated in an engagement direction by operating the clutch actuator, and a state change of the driving motor is detected. The touch point of the engine clutch is determined based on the state change of the driving motor.

Claims

1. A method of learning a touch point for an engine clutch of a hybrid electric vehicle, the method comprising steps of: controlling a speed of an engine to be an idle speed; refilling a fluid pipe of a clutch actuator with a working fluid by driving a driving motor in an idle control state of the engine, synchronizing a speed of the driving motor with the speed of the engine, and then engaging the engine clutch; releasing the engine clutch after the step of refilling and decreasing the speed of the driving motor; applying the working fluid to operate the engine clutch in an engagement direction by operating the clutch actuator and detecting a state change of the driving motor; and determining the touch point of the engine clutch based on the state change of the driving motor.

2. The method of claim 1, wherein when a value of a state of charge (SOC) of a battery is equal to or smaller than a reference value so that the engine is driven for charging the battery, the method for learning the touch point of the engine clutch is performed.

3. The method of claim 1, wherein when a temperature of the engine is equal to or lower than a reference temperature, the engine is driven for warming up the engine and the steps for learning the touch point of the engine clutch are performed.

4. The method of claim 1, wherein the step of detecting the state change of the driving motor includes maintaining the idle control state of the engine.

5. The method of claim 1, wherein the step of detecting the state change of the driving motor includes detecting a torque change of the driving motor.

6. The method of claim 5, wherein in the step of detecting the state change of the driving motor, the touch point is stored as a learning value when a torque variation value of the driving motor is equal to or larger than a set value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure.

(2) FIG. 1 is a diagram schematically illustrating a power train of a hybrid electric vehicle according to the related art.

(3) FIG. 2 is a diagram schematically illustrating a dry clutch and an actuator for driving the clutch according to the related art.

(4) FIG. 3 is a diagram for describing a problem in the related art.

(5) FIG. 4 is a flowchart illustrating a touch point learning process according to the present disclosure.

(6) FIG. 5 is a diagram illustrating an example of an engine speed, a motor speed, a stroke position value, and a touch point learning value during the touch point learning process according to the present disclosure.

(7) It should 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 present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

DETAILED DESCRIPTION

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

(9) Hereinafter, an exemplary embodiment of the present inventive concept will be described in detail with reference to the accompanying drawings so that those with ordinary skill in the art to which the present disclosure pertains may easily carry out the exemplary embodiment.

(10) The present disclosure provides a touch point learning method for an engine clutch of a hybrid electric vehicle, which changes a refill time point and a touch point learning time point, thereby accurately estimating and learning a touch point that is a start position of a torque transmission.

(11) An aspect of the present inventive concept is to synchronize a speed of an engine and a speed of a driving motor by controlling the engine and the driving motor to have an idle speed, perform engagement of an engine clutch and refill of a fluid pipe, engage the engine clutch again in a state where the speed of the driving motor is decreased after the engine clutch is released, and update a start position of a torque transmission as a new touch point.

(12) The touch point learning method of the present disclosure may be usefully applied as a learning method of a dry clutch widely applied to a parallel hybrid electric vehicle.

(13) FIG. 4 is a flowchart illustrating a touch point learning process according to the present disclosure, and FIG. 5 is a diagram illustrating an example of an engine speed, a motor speed, a stroke position value, and a touch point learning value during the touch point learning process according to the present disclosure.

(14) A power train of a hybrid electric vehicle including an engine 1, an engine clutch 2, a driving motor 3, and a transmission 4 described below will be referred to FIG. 1, and an actuator for operating the engine clutch 2 will be referred to FIG. 2.

(15) In FIG. 5, a stroke position value represents a stroke position value of a piston 14 installed at a master cylinder 15 of the actuator of the engine clutch, and may be detected by a travel sensor 16 installed at the master cylinder 15.

(16) A touch point learning value represents a previous learning value stored in a memory and a newly updated learning value, and the learning value is a piston stroke position (torque transmission start point) value detected by the travel sensor 16 when both ends of the engine clutch are in contact so that the torque transmission starts, and a touch point value obtained whenever the touch point learning process is performed is stored as a learning value in the memory and updated.

(17) When a refill process and the touch point learning process are continuously performed by simply rotating the driving motor and operating the actuator and the engine clutch 2 while the engine is driven for travelling of the vehicle, a driver may feel uncomfortable.

(18) Accordingly, the refill process and the touch point learning process may be set to be performed when the engine is driven for other reasons, not for the purpose of the travelling of the vehicle.

(19) For example, a driving state of the engine in which the refill process and the touch point learning process are performed may be a case where the engine is driven for charging a battery because a value of a state of charge (SOC) of the battery is equal to or smaller than a reference value, or a case where the engine is driven for warming up the engine because a temperature of the engine is equal to or lower than a reference temperature.

(20) According to the present disclosure, when the engine 1 is driven due to a low SOC of the battery, a low temperature of the engine, or the like, an engine control unit 11 first controls the engine to have an idle speed for learning a touch point.

(21) Then, when the engine 1 enters an idle control state, the driving motor 3 is also driven at the same speed as that of the engine to be in an idle state.

(22) In general, in order to learn the touch point, the driving motor 3 needs to rotate, and a high frequency noise is generated when the driving motor rotates. However, the engine 1 and the driving motor 3 are driven together, so that the high frequency noise of the driving motor is not heard due to an engine noise.

(23) Next, when the speed of the engine and the speed of the driving motor are controlled to be the same and then are synchronized as described above, the engine clutch 2 is engaged, and the refill process for completely filling the fluid pipe 18 with a fluid is performed.

(24) In this case, a pressure of a working fluid is transmitted to a slave cylinder 19 by moving the piston 14 of the master cylinder 15 forwardly, and a piston 20 of the slave cylinder 19 moves forward by the transmitted pressure of the working fluid, so that friction surfaces of the engine clutch 2 are engaged.

(25) As a matter of course, a piston stroke position of the master cylinder 15 is controlled so that the fluid pipe 18 becomes a refilled state in which the fluid pipe 18 is completely filled with the fluid.

(26) When the engagement of the engine clutch 2 and the refill are performed as described, the engine clutch is released, and in this case, in order to release the engine clutch, the piston 14 of the master cylinder 15 moves backward.

(27) Subsequently, the speed of the driving motor 3 is decreased to a rotational speed, at which a torque may be detected, during the idle control of the engine 1, and a change time point of a motor torque is searched by slowly operating the engine clutch 2 in an engagement direction to determine and learn thd touch point.

(28) When the driving motor 3 rotates at a minimum specific speed (for example, 500 rpm) or more at the time of the learning of the touch point, a torque may be accurately detected, and the engine clutch 2 is slowly operated in the engagement direction by applying a pressure of the working fluid to the slave cylinder 19 by moving the piston 14 of the master cylinder 15 forwardly and moving the piston 20 of the slave cylinder 19 forwardly with the pressure of the working fluid applied to the slave cylinder 19.

(29) Here, a state change of the driving motor 3 is detected, and the touch point of the engine clutch 2 is determined based on the state change of the driving motor 3. When a torque variation value of the driving motor is equal to or larger than a set value, a piston stroke position value at this time is determined as a new touch point and is stored in the memory.

(30) When the new touch point is determined and the touch point learning process is performed as described above, the engine clutch 2 is then controlled by using the learning value.

(31) As described above, in the related art, a refill state of a fluid within a fluid pipe is be determined before a touch point is learned, but in the present disclosure, it is possible to accurately estimate and learn a touch point based on a completely refilled state of the fluid through the control process.

(32) In the present disclosure, any driving uncomfortableness is not incurred to a driver during the refill process and the touch point learning process, so that it is possible to improve operability when the touch point learning process is performed.

(33) The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.