METHOD FOR CONTROLLING START OF ISG VEHICLE

Abstract

A method for controlling start of an ISG (idle stop and go) vehicle may include an operation of limiting, when an ISG mode of the vehicle is turned off, an engine torque to less than a preset value for a predetermined time from a point of time at which the IGS mode is turned off.

Claims

1. A method for controlling start of an idle stop and go (ISG) vehicle, comprising: limiting, when an ISG mode of the vehicle is turned off, an engine torque to less than a preset value for a predetermined time from a point of time at which the IGS mode is turned off.

2. The method according to claim 1, further comprising, after limiting the engine torque, increasing the engine torque at a pre-mapped gradient in response to an accelerator opening degree.

3. The method according to claim 2, wherein increasing the engine torque further comprises controlling a clutch torque to be variable based on at least one of the engine torque and the accelerator opening degree.

4. The method according to claim 1, wherein after an ignition is turned on by releasing a brake pedal or pressing an accelerator pedal while the ISG mode is turned on, the ISG mode of the vehicle is turned off when an RPM of the engine is increased to a reference value or more.

5. The method according to claim 1, wherein the vehicle is provided with an automated manual transmission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a graph showing variation in characteristic values as a function of vehicle start control according to a conventional technique.

[0023] FIG. 2 is a flowchart showing a method for controlling start of an ISG vehicle according to an embodiment of the present invention.

[0024] FIG. 3 is a graph showing variation in characteristic values according to an embodiment of the present invention.

[0025] 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.

[0026] In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

[0027] Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are 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.

[0028] Hereinbelow, a method for controlling start of an ISG vehicle according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0029] FIG. 2 is a flowchart showing the method for controlling start of the ISG vehicle according to the exemplary embodiment of the present invention. FIG. 3 is a graph showing variation in characteristic values according to the exemplary embodiment of the present invention. Referring to FIGS. 2 and 3, the start control method of the vehicle includes operation S240 of, when an ISG function of a vehicle is turned off, limiting an engine torque to less than a preset value for a predetermined time from a point of time at which the ISG function is turned off.

[0030] When the ISG function of the vehicle is turned on, the engine is stopped to reduce fuel consumption resulting from unnecessary idling. In operation S240, when a driver presses an acceleration pedal to accelerate the vehicle, the IGS function is turned off and the ignition of the vehicle is turned on to operate the engine, whereby the vehicle begins to move.

[0031] However, depending on characteristics of the driver or driving conditions, the vehicle may be excessively quickly started and rapidly accelerated. In this case, because the engine torque is rapidly increased, the RPM of the engine is excessively increased, and excessive slip occurs in a clutch. Here, when the clutch is engaged to move the vehicle, an excessive load may be applied to the engine because the engine is connected to an input shaft of a transmission while the engine rotates at high speed. Thereby, an engine overshooting or clutch burning phenomenon may be caused.

[0032] To avoid the above problems, the present invention is configured such that, when the IGS function is turned off before the clutch is engaged to move the vehicle, the engine torque is limited to less than a preset value for a predetermined time. That is, in the conventional technique, when the driver quickly starts the vehicle while the ISG function of the vehicle is in the turn-on state, the engine torque is rapidly increased after the ISG function is turned off. However, the present invention restricts a rapid increase of the engine torque just after the ISG function is turned off and thus enables the clutch to be engaged while the engine rotates comparatively slowly. Thereby, even when an excessive load is input, a jerk phenomenon is not caused, and the clutch can be prevented from burning.

[0033] The preset value is a value that is set by a designer to prevent the engine torque from rapidly increasing and may be changed depending on the kind of vehicle.

[0034] The start control method according to the present embodiment further includes operation S250 of increasing the engine torque at a pre-mapped gradient in response to an accelerator opening degree after the torque limit operation S240 has been conducted.

[0035] In the case where the engine torque is limited to less than the preset value after the ISG function is turned off, even if the driver variably manipulates the accelerator pedal, there is no unfamiliarity in driving. For this, in an exemplary embodiment of the present invention, after the torque limit operation S240 is conducted, the engine torque is controlled to be increased in proportion to the degree of opening of the accelerator pedal, thus providing linear start acceleration in response to the accelerator opening degree.

[0036] Here, the engine torque is increased at a pre-mapped gradient in response to the accelerator opening degree. This differs from the conventional configuration in which the engine torque is increased only in response to the accelerator opening degree. In detail, in the conventional technique, the engine torque may be rapidly increased in response to the accelerator opening degree without limit. However, in the present embodiment, the engine torque is increased in proportion to the accelerator opening degree, wherein the engine torque is controlled to be increased at a gradient limited as a function of the accelerator opening degree. Therefore, the engine torque can be prevented from being excessively rapidly increased. Moreover, because the present embodiment is also configured such that the engine torque is increased in response to the accelerator opening degree, satisfactory acceleration effect can be provided.

[0037] The pre-mapped gradient is a gradient that is set by a designer to a predetermined value depending on the kind of vehicle such that the engine torque is appropriately increased. Although the gradient is mapped such that it is increased in proportion to the accelerator opening degree, it is preferable that the gradient of the present embodiment be less than an actual gradient at which the engine torque is increased in response to the accelerator opening degree in the conventional technique.

[0038] The torque increase operation S250 further includes operation S260 of controlling a clutch torque to be variable based on at least one of the engine torque and the accelerator opening degree.

[0039] In other words, when the torque increase operation S250 is conducted, the clutch torque is increased in proportion to at least one of the accelerator opening degree and the engine torque that increases in response to the accelerator opening degree. Thereby, the engagement operation of the clutch can be smoothly conducted. For instance, the clutch torque may also be controlled to be increased at a pre-mapped gradient in response to the accelerator opening degree in the same manner as that of controlling the engine torque. Alternatively, the clutch torque may be controlled in such a way that it is applied in proportion to the engine torque.

[0040] In brief, in the present embodiment, after the ISG function of the vehicle is turned off, the engine torque is controlled to be less than a preset value for a predetermined time. Subsequently, the engine torque and the clutch torque are controlled to be linearly increased in response to the accelerator opening degree. Thereby, when the vehicle moves after the ISG function is turned off, a jerk phenomenon can be prevented from occurring due to a rapid increase in RPM of the engine, and the clutch can be prevented from burning because of excessive slip. Moreover, linear start-acceleration effect can be provided.

[0041] The engine torque is controlled by an engine management system (EMS) or engine control unit (ECU). The clutch torque is controlled by a transmission control unit (TCU).

[0042] That is, the EMS, which is used for electronic control of every engine, may autonomously control the engine torque. Alternatively, the ECU provided in the EMS may conduct the start control method according to the present embodiment.

[0043] The TCU is a control unit which controls the clutch torque to be variable depending on driving conditions of the vehicle. As stated above, the TCU provides clutch torque which varies depending on at least one of the accelerator opening degree and the engine torque.

[0044] Here, the ISG function of the vehicle is characterized in that after the ignition is turned on (S210) by releasing the brake pedal or pressing the accelerator pedal while the ISG function is turned on (S200), the ISG function is turned off when the RPM of the engine is increased to a reference value or more (S220).

[0045] In detail, when the driver releases the brake pedal or presses the accelerator pedal to accelerator the vehicle, the RPM of the engine is increased to restart the engine of the vehicle that has been stopped. When the RPM of the engine becomes a reference value or more, it begins to control the engine torque depending on the accelerator opening degree. For this, the ISG function is turned off (S230), and the torque limit operation S240 is conducted. Here, the reference value refers to the minimum value of the RPM of the engine that is required to start the vehicle.

[0046] Furthermore, the vehicle according to the present embodiment is a vehicle provided with a dual clutch transmission (DCT) or an automated manual transmission (AMT).

[0047] Referring to FIG. 3, when the driver presses the accelerator pedal while the ISG function is turned on, the accelerator opening degree is greatly increased, whereby the engine torque is increased to restart the engine. When the ignition of the engine is turned on and the engine torque becomes a predetermined value or more, the ISG function is turned off because it is determined that the ignition of the engine has been completed. Here, the EMS or ECU outputs an engine torque control signal so that the engine torque is maintained less than the preset value for a predetermined time. After the predetermined time has passed, the engine torque is increased at a pre-mapped gradient in response to the accelerator opening degree. Thereafter, after the predetermined time has passed or the clutch has been engaged, the EMS or ECU stops outputting the engine torque control signal. It can be appreciated that, in the same manner as the engine torque, the clutch torque is controlled to be increased in response to the accelerator opening degree or the engine torque

[0048] In accordance with the present embodiment, as shown in the lower portion of FIG. 3, the RPM of the engine is gently increased. Therefore, a difference between the RPM of the engine and the RPM of the input shaft is reduced, whereby when the clutch is engaged, the vehicle can smoothly and rapidly start to move. This can be understood by the fact that the acceleration is gently increased without changing greatly.

[0049] As described above, in accordance with a method for controlling start of an ISG vehicle according to an exemplary embodiment of the present invention, after an ISG function is turned off, the engine torque is controlled. Therefore, when the vehicle starts, a jerk phenomenon, which results from engagement of the clutch when the vehicle starts quickly in the ISG on state, or a clutch burning phenomenon, which is caused by excessive slip of the clutch, can be prevented.

[0050] The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.