Electronic control unit and method for compensating torque steering

Abstract

Electronic control unit (100) for compensating a torque steering, which electronic control unit (100) comprises: a drive torque calculation unit (110) that calculates a drive shaft drive torque value using engine operation information and transmission operation information; a torque steering degree calculation unit (130) that calculates the actual drive torque value of a vehicle based on the drive shaft drive torque value and calculates a torque steering degree by using the actual drive torque value; a compensation current calculation unit (140) that calculates a torque steering compensation current value that compensates for the torque steering using the torque steering degree; and a motor drive control unit (150) that calculates a basic control current value using a steering angle and a steering torque value, calculates the final control current value by adding the torque steering compensation current value to the basic control current value, and generates a control current according to the final control current value to supply the control current value to an electric motor (160) characterized by a skid determination unit (120) that determines whether a skid of the vehicle is occurring using behavior information about the vehicle including a front wheel rotation speed and a rear wheel rotation speed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to an electronic control unit according to the preamble of claim 1 and a method for compensating torque steer according to the preamble of claim 10. 2. Description of the state of the art

[0002] In general, the phenomenon in which the body of a vehicle leans to one side as a result of a difference between the driving forces of the left and right wheels when the vehicle starts abruptly is called a torque steer phenomenon.

[0003] The causes of torque steer include the difference between the lengths of the left and right drive shafts and the difference between the bending angles of the left and right drive shafts.

[0004] The method for solving torque steer includes a method of adding an intermediate shaft to a short drive shaft to equalize the drive shaft lengths and bending angles, and also includes a method of compensating for torque steer by using a power steering system.

[0005] Among them, the conventional method for compensating torque steer using a power steering system includes estimating the degree of torque steer by using an engine speed, an engine torque, an accelerator pedal opening degree, and the speed of the vehicle by an electronic control unit (ECU) of a power steering system, and supplying a compensating current proportional to the estimated torque steer to an electric motor.

[0006] In the above-mentioned conventional method, the torque steering degree is estimated by using indirect information on torque steering such as an engine speed, an engine torque, an accelerator operation degree, and the speed of the vehicle, and since direct information on torque steering such as the slipping degrees of the left and right wheels of the vehicle is not used, a torque steering degree that may vary according to a change in the slipping degrees of the wheels of the vehicle cannot be accurately detected.

[0007] Accordingly, when torque steer is compensated in an electronic control unit of a power steering system according to the conventional method, the torque steer occurring cannot actually be adequately reduced.

[0008] From the generic DE 10 2005 045 243 A1 a device for compensating for skew effects on a motor vehicle is known, in which a correction signal, which compensates for an asymmetrical bending behavior of drive shafts leading to the vehicle wheels, is calculated from a variable which represents the drive torque of the vehicle and is superimposed on the control signal of the steering. SUMMARY OF THE INVENTION

[0009] Against this background, the present invention provides an electronic control unit and method of a motor-driven power steering system that calculates the actual drive torque value applied during driving of a vehicle, taking into account the slipping degrees of the wheels of the vehicle, and generates an auxiliary steering force for compensating the torque steer.

[0010] According to one aspect of the present invention, there is provided an electronic control unit for compensating torque steer, which electronic control unit includes: a drive torque calculation unit that calculates a torque value for driving a drive shaft using engine operation information and transmission operation information; a torque steer degree calculation unit that calculates the actual drive torque value of a vehicle based on the torque value for driving the drive shaft and calculates a torque steer degree using the actual drive torque value; a compensation current calculation unit that calculates a torque steer compensation current value that compensates for torque steer using the torque steer degree;and a motor drive control unit that calculates a basic control current value using a steering angle and a steering torque value, calculates the final control current value by adding the torque steering compensation current value to the basic control current value, and generates a control current according to the final control current value to supply the control current value to an electric motor; further, a skid determination unit that determines whether a skid of the vehicle is occurring using behavior information about the vehicle including a front wheel rotation speed and a rear wheel rotation speed.

[0011] According to another aspect of the present invention, there is provided a method for compensating for torque steering in an electronic control unit of a motor-driven power steering system, including: a drive shaft drive torque calculation step of calculating a drive torque value for a drive shaft using engine operation information including an engine torque value and an engine speed value, and transmission operation information including a torque conversion speed value and a gear ratio; a skid determination step of determining whether a vehicle skid is occurring using vehicle behavior information including one or more of a front wheel rotation speed, a rear wheel rotation speed, and a longitudinal acceleration value;An actual drive torque value calculation step of, if it is determined in the slip determination step that slippage does not occur in the vehicle, setting a slip index to a predetermined value; and, if it is determined in the slip determination step that slippage does occur in the vehicle, calculating the slip index and calculating an actual drive torque value of the vehicle using the drive shaft drive torque value and the slip index; A compensation current calculation step of calculating a torque steering degree using the actual drive torque value, and calculating a torque steering compensation current value for compensating for the torque steering using the torque steering degree;and a torque steering compensation step of calculating a final control current value by adding the torque steering compensation current value to a basic control current value calculated using a steering angle and a steering torque value, and generating a current value according to the final control current value to supply the control current to an electric motor.;

[0012] As described above, according to the present invention, since an electronic control unit of a motor-driven power steering system calculates the actual drive torque value consumed during running of a vehicle in consideration of the slipping degrees of the wheels of a vehicle and generates a control current for compensating for torque steer occurring in the vehicle by the actual drive torque value, torque steer that may vary according to a change in a slipping degree of the vehicle can be appropriately compensated. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a block diagram schematically illustrating a configuration of an electric control unit according to an embodiment of the present invention; Fig. 2 is a view schematically illustrating a connecting structure of a drive shaft in a front-wheel drive vehicle; Fig. 3 is a flowchart illustrating an overall process of compensating for torque steering by the electronic control unit according to the embodiment of the present invention; Fig. 4 is a flowchart illustrating a process of calculating a drive shaft drive torque value by the electronic control unit according to the embodiment of the present invention; Fig. 5 and Fig. 6 are flowcharts illustrating a process of determining whether slippage occurs by the electronic control unit according to the embodiment of the present invention; Fig. 7 is a flowchart illustrating a process of calculating an actual drive torque value by the electronic device according to the embodiment of the present invention; and Fig. 8 and Fig. 9 are flowcharts illustrating a process of calculating a torque steering compensation current value by the electronic control unit according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the exemplary drawings. In describing the elements of the present invention, terms "first," "second," "A," "B," "(a)," "(b)," and the like may be used. These terms are used merely to distinguish one structural element from other structural elements, and a property, order, sequence, and the like of a corresponding structural element are not limited by the term. It should be noted that where the description states that one component is "connected," "coupled," or "joined" to another component, a third component may be "connected," "coupled," and "joined" between the first and second components, although the first component may be directly connected, coupled, or joined to the second component.

[0015] Fig. 1 is a block diagram schematically illustrating a configuration of an electronic control unit according to an embodiment of the present invention.

[0016] An electronic control unit 100 according to an embodiment of the present invention, which is an electronic control unit 100 of a motor-driven power steering system installed in a vehicle, includes a drive torque calculation unit 110, a slip determination unit 120, a torque steering degree calculation unit 130, a compensation current calculation unit 140, and a motor drive control unit 150.

[0017] The drive torque calculation unit 110 calculates a drive shaft drive torque value using engine operation information and transmission operation information. Here, the engine operation information includes the engine torque value and the engine speed value received from the engine module (not shown), and the transmission operation information includes a torque conversion speed value and a gear ratio received from a transmission module (not shown).

[0018] The drive torque calculation unit 110 calculates a speed ratio by dividing the torque converter speed value by the engine speed value as shown in Equation 1, extracts a torque converter efficiency according to the speed ratio in a previously stored torque converter efficiency map, and extracts a torque converter output torque ratio according to the speed ratio in a previously stored output torque ratio map. Speed ratio=torque converter speed valueMachine speed value

[0019] Thereafter, the drive torque calculation unit 110 calculates a torque converter output torque value by multiplying the torque converter efficiency, the torque converter output torque ratio, and the engine torque value together, as shown in Equation 2. Torque converter output torque value = torque converter efficiency × torque converter output torque ratio × engine torque value

[0020] The input torque calculation unit 110 calculates a transmission output torque value by multiplying the torque converter output torque value and the tooth ratio as shown in Equation 3, and calculates a drive shaft input torque value by multiplying the tooth ratio of a final reduction gear and a transmission output torque value as shown in Equation 4. Here, the drive shaft input torque value refers to a torque value transmitted from an operating machine to a drive shaft. Transmission output torque value = torque converter output torque value × tooth ratio Drive shaft input torque value = tooth ratio of a final reduction gear ×gearbox output torque value

[0021] The electronic control unit 100 according to the embodiment of the present invention may include a skid determination unit 120 if necessary. For example, the skid determination unit 120 determines whether a skid of the vehicle is occurring by using behavior information of the vehicle. Here, the skid determination unit 120 may set a skid index, which corresponds to a sliding index of the vehicle's wheels, to a specific value when it is determined that a skid is not occurring in the vehicle.

[0022] For example, the torque steering degree calculation unit 130 may calculate a torque steering degree using the drive shaft drive torque value. If the slip determination unit 120 is omitted, the torque steering degree calculation unit 130 may calculate the torque steering degree using the aforementioned specific value and the drive shaft drive torque value.

[0023] As another example, it is necessary to determine whether a vehicle skid is occurring and calculate a torque steering degree by using a different skid index according to a skid angle to calculate a more accurate torque steering degree. Accordingly, the electronic control unit 100 according to the present invention may further include a skid determination unit 120, and the skid determination unit 120 may determine whether a vehicle skid is occurring and also determine the skid angle. Accordingly, when it is determined that a skid is occurring in the vehicle, the torque steering degree calculation unit 130 may further calculate a skid index and calculate a more accurate torque steering degree.

[0024] According to the present invention, when an electronic stability control unit is not installed in the vehicle, the skid determination unit 120 uses a front wheel rotation speed and a rear wheel rotation speed received from a speed sensor (not illustrated) as behavior information of the vehicle. When an electronic stability control unit is installed in the vehicle, the skid determination unit 120 may use a longitudinal acceleration value of the vehicle received from a longitudinal acceleration sensor (not illustrated) as behavior information of the vehicle. Here, the front wheel rotation speed is an average value of the rotation speeds of the left and right front wheels, and the rear wheel rotation speed is an average value of the rotation speeds of the left and right rear wheels.

[0025] When the skid determination unit 120 uses the front wheel rotation speed and the rear wheel rotation speed as behavior information of the vehicle, the skid determination unit 120 compares the absolute value of a value obtained by subtracting the front wheel rotation speed from the rear wheel rotation speed with a first reference value, as shown in Equation 5. |Rear wheel rotation speed−Front wheel rotation speed| ≤First reference value

[0026] When the absolute value of Equation 5 is less than or equal to the first reference value, it is determined that skidding does not occur in the vehicle, and when the absolute value of Equation 5 is greater than the first reference value, it is determined that skidding does occur in the vehicle. That is, when the absolute value of Equation 5 is greater than the first reference value, it means that serious front wheel skidding occurs, and when the absolute value of Equation 5 is less than or equal to the first reference value, it means that extremely slight front wheel skidding occurs or no skidding occurs.

[0027] When the behavior information of the vehicle is used as the longitudinal acceleration value of the vehicle, the skid determination unit 120 extracts a general longitudinal acceleration value corresponding to the drive shaft drive torque value from a previously stored longitudinal acceleration map, and compares the absolute value of a value obtained by subtracting the general longitudinal acceleration value from the longitudinal acceleration value with the second reference value, as shown in Equation 6. Here, the longitudinal acceleration map is a data map including the drive shaft drive torque values and the longitudinal acceleration values corresponding to the drive shaft drive torque values when the drive shaft drive torque values are fully utilized while the vehicle is traveling. |Longitudinal acceleration value−General longitudinal acceleration value| ≤Second reference value

[0028] If the absolute value of Equation 6 is less than or equal to the second reference value, it is determined that skidding is not occurring in the vehicle, and if the absolute value of Equation 6 is greater than the second reference value, it is determined that skidding is occurring in the vehicle. In other words, if the absolute value of Equation 6 is greater than the second reference value, it means that the drive shaft drive torque value is not fully used for driving the vehicle due to skidding occurring in one or more of the front wheels and the rear wheels of the vehicle, and if the absolute value of Equation 6 is less than or equal to the second reference value, it means that the drive shaft drive torque value is fully used for driving the vehicle because skidding is not occurring in one or more of the front wheels and the rear wheels of the vehicle.

[0029] When the skid determination unit 120 determines that skid is occurring in the vehicle, the torque steering degree calculation unit 130 calculates a skid index, calculates the actual drive torque value of the vehicle using the drive shaft drive torque value and the calculated skid index, and calculates the torque steering degree using the actual drive torque value. Here, the specific value may be 1, and the range of the skid index calculated by the torque steering degree calculation unit 130 may be equal to or greater than 0 and less than 1.

[0030] A detailed description of this is given below.

[0031] When the skid determination unit 120 determines by Equation 5 that a skid occurs in the vehicle, the torque steering degree calculation unit 130 calculates a skid index by dividing the rear wheel rotation speed by a value obtained by subtracting the first reference value from the front wheel rotation speed, as shown in Equation 7, and calculates an actual drive torque value by multiplying the skid index calculated in Equation 9 and the drive shaft drive torque value. Slip index = rear wheel rotation value, front wheel rotation speed = first reference value

[0032] When the skid determination unit 120 determines by Equation 6 that a skid occurs in the vehicle, the torque steering degree calculation unit calculates a skid index by dividing the longitudinal acceleration value by a value obtained by subtracting the second reference value from the general longitudinal acceleration value, as shown in Equation 8, and calculates the actual drive torque value by multiplying the skid index calculated in Equation 9 and the drive shaft drive torque value. Slip index = Longitudinal acceleration value General longitudinal acceleration value − Second reference value Actual drive torque value = slip index × drive shaft drive torque value

[0033] When the skid determination unit 120 determines through Equation 5 or 6 that skid is not occurring in the vehicle, the torque steering degree calculation unit 130 calculates the actual drive torque value by multiplying a skid index set to a specific value by the skid determination unit 120 and the drive shaft drive torque value. Here, when the specific value is 1, the drive shaft drive torque value becomes the actual drive torque value.

[0034] The torque steering degree calculation unit 130 calculates a torque steering degree by using the actual drive torque value calculated as described above.

[0035] Here, when a vehicle height sensor (not shown) is mounted on the vehicle, the torque steering degree calculation unit 130 calculates a short-axis drive shaft bending angle θ shortand a longitudinal axis drive shaft bending angle θ long , as in Fig. 2 and Equation 10, using the vehicle height, the length of a short-axis drive shaft, and the length of a long-axis drive shaft. Here, a denotes the height of a front-wheel-side connecting part of the drive shaft from the ground, and b denotes the height of a transmission-side connecting part of the drive shaft from the bottom surface of the vehicle body. Drive shaft bending angle = sin 1 [vehicle height − (a + b) drive shaft length]

[0036] The torque steering degree calculation unit 130 calculates a short-axis drive shaft side coupling torque and a long-axis drive shaft side coupling torque as shown in Equation 11 by using the calculated drive shaft bending angle, and calculates a torque steering degree by a value obtained by subtracting a long-axis drive shaft side coupling torque Mz long from a short-axis drive shaft coupling torque Mz short is obtained as shown in equation 12. Coupling torque (Mz) = Actual drive torque value × (tanθ2) Torque steering ratio−Mzshort−Mzlong

[0037] When a vehicle height sensor (not shown) is not mounted on the vehicle, the torque steering degree calculation unit 130 extracts a torque steering degree corresponding to an actual drive torque value from a previously stored torque steering degree map. In other words, a torque steering degree corresponding to the actual drive torque value calculated by Equation 9 is extracted from a torque steering degree data map obtained by measuring the actual drive torque values and a plurality of torque steering degrees corresponding to the actual drive torque values through actual vehicle tests.

[0038] The compensation current calculation unit 140 calculates a torque steering compensation current value for compensating torque steering using the torque steering degree calculated by the torque steering degree calculation unit 130.

[0039] Specifically, the compensation current calculation unit 140 calculates a torque steering compensation current value by dividing the torque steering degree by a value obtained by multiplying a motor torque constant of an electric motor and a tooth number ratio included in the transmission operation information, as shown in Equation 13. Compensation current=torque steering degree, motor torque constant×tooth number ratio

[0040] A motor drive control unit 150 calculates a basic control current value using a steering angle and a steering torque value, calculates a final control current value by adding the torque steering compensation current value calculated by the compensation current calculation unit 140 to the basic control current value, and generates a control current according to the final control current value to supply the control current to the electric motor 160.

[0041] The electric motor 160, which has received the control current from the motor drive control unit 150, generates an auxiliary steering force to compensate for torque steering.

[0042] In this way, according to the present invention, since the electronic control unit 100 calculates an actual drive torque value taking into account a degree of slippage occurring in the wheels of the vehicle and calculates a torque steer compensation current value for compensating the torque steer using the actual drive torque value, the torque steer, which may vary according to a change in the degree of slippage of the wheels of the vehicle, can be appropriately compensated.

[0043] A process of compensating for torque steering in the electronic control unit 100 of the motor-driven power steering system will be described below.

[0044] Fig. 3 is a flowchart illustrating an overall process of compensating for torque steering by the electronic control unit 100 according to the embodiment of the present invention.

[0045] The electronic control unit 100 calculates a drive shaft input torque value using engine operation information including an engine torque value and an engine speed value, and transmission operation information including a torque converter speed value and a gear ratio (S310).

[0046] The electronic control unit 100 determines whether a skid of the vehicle occurs using behavior information of the vehicle including one or more of the front wheel rotation speed, the rear wheel rotation speed, and the longitudinal acceleration value (S320).

[0047] When it is determined in step S320 that slippage does not occur in the vehicle, a slippage index is set to a specific value, and an actual drive torque value is calculated using the slippage index set to the specific value and the drive shaft drive torque value (S330, S340, and S350).

[0048] If it is determined in step S320 that slippage occurs in the vehicle, a slip index is calculated, and an actual drive torque value of the vehicle is calculated using the calculated slip index and the drive shaft drive torque value (S360).

[0049] The electronic control unit 100 calculates a torque steering degree using the actual drive torque value, and calculates a torque steering compensation current value for compensating for torque steering using the torque steering degree (S370).

[0050] Thereafter, the electronic control unit 100 calculates a final control current value by adding the torque steering compensation current value to a basic control current value calculated using the steering angle and the steering torque value, and generates a control current according to the final control current value to supply the control current to the electric motor 160 (S380).

[0051] A detailed process for steps S310, S320, S360 and S370 is as follows.

[0052] Fig. 4 is a flowchart illustrating a process of calculating a drive shaft driving torque value by the electronic device according to the embodiment of the present invention.

[0053] In step S310, the electronic control unit 100 calculates a speed ratio by dividing a torque converter speed value by an engine speed value, and extracts a torque converter efficiency and a torque converter output torque ratio according to the speed ratio (S410 and S420).

[0054] Thereafter, the electronic control unit 100 calculates a torque converter output torque value by multiplying the torque converter efficiency, the torque converter output torque ratio, and the engine torque value together, and calculates a transmission output torque value by multiplying the torque converter output torque value and the tooth number ratio (S430 and S440).

[0055] The electronic control unit 100 calculates a drive shaft drive torque value by multiplying the transmission output torque value calculated in step S440 and a final reduction gear tooth number ratio of the last reduction gear (S450).

[0056] The Fig. 5 and Fig. 6 are flowcharts illustrating a process of determining whether a skid is occurring by the electronic control unit according to the embodiment of the present invention.

[0057] When an electronic stability control unit 100 is not mounted on the vehicle, the electronic control unit 100 compares the absolute value of a value obtained by subtracting the front wheel rotation speed from the rear wheel rotation speed as shown in Fig. 5 in step S320, with the first reference value (S510).

[0058] If the absolute value in step S510 is less than or equal to the first reference value, it is determined that slippage does not occur in the vehicle, and if the absolute value in step S510 is greater than the first reference value, it is determined that slippage occurs in the vehicle (S520 and S530).

[0059] When an electronic stability control unit is mounted on the vehicle, the electronic control unit 100 extracts a general longitudinal acceleration value according to the drive shaft drive torque value in step S320 from the previously stored longitudinal acceleration map as shown in Fig. 6, and compares the absolute value of a value obtained by subtracting the general longitudinal acceleration value from the longitudinal acceleration value with the second reference value (S610).

[0060] If the absolute value in step S610 is less than or equal to the second reference value, it is determined that slippage does not occur in the vehicle, and if the absolute value in step S610 is greater than the second reference value, it is determined that slippage occurs in the vehicle (S620 and S630).

[0061] Fig. 7 is a flowchart illustrating a process of calculating a slip index and an actual drive torque value by the electronic device according to the embodiment of the present invention.

[0062] If an electronic stability control unit 100 is not mounted on the vehicle, in step S360, the electronic control unit 100 divides the rear wheel rotation speed by a value obtained by subtracting the first reference value from the front wheel rotation speed to calculate a slip index, and if an electronic stability control unit is mounted on the vehicle, the electronic control unit 100 divides the second reference value by a general longitudinal acceleration value extracted from a previously stored longitudinal acceleration map according to the drive shaft drive torque value to calculate a slip index (S710).

[0063] The electronic control unit 100 multiplies the slip index calculated in step S710 and the drive shaft drive torque value to calculate the actual drive torque value (S720).

[0064] The Fig. 8 and Fig. 9 are flowcharts illustrating a process of calculating a torque steering compensation current value by the electronic control unit according to the embodiment of the present invention.

[0065] When a vehicle height sensor (not illustrated) is mounted on the vehicle, the electronic control unit 100 calculates a short-axis drive shaft bending angle and a long-axis drive shaft bending angle using the height of the vehicle, the length of the short-axis drive shaft, and the length of the long-axis drive shaft, as shown in Fig. 8 is illustrated (S810).

[0066] Thereafter, the electronic control unit 100 calculates a short-axis drive shaft side coupling torque and a long-axis drive shaft side coupling torque using the actual drive torque value, the short-axis drive shaft bending angle, and the long-axis drive shaft bending angle, and calculates a torque steering degree by subtracting the long-axis drive shaft side coupling torque from the short-axis drive shaft side coupling torque (S820 and S830).

[0067] The electronic control unit 100 divides the torque steering degree calculated in step S830 by a value obtained by multiplying the motor torque constant of the electric motor and a tooth number ratio to calculate the torque steering compensation current value (S840).

[0068] When a vehicle height sensor (not shown) is not mounted on the vehicle, the electronic control unit 100 extracts a torque steering degree corresponding to the actual drive torque value from a previously stored torque steering degree map and divides the torque steering degree by a value obtained by multiplying the motor torque constant and the tooth number ratio to calculate the torque steering compensation current value, as shown in Fig. 9 is illustrated (S910 and S920).

Claims

[1] Electronic control unit (100) for compensating a torque steering, which electronic control unit (100) comprises: a drive torque calculation unit (110) that calculates a drive shaft drive torque value using engine operation information and transmission operation information; a torque steering degree calculation unit (130) that calculates the actual drive torque value of a vehicle based on the drive shaft drive torque value and calculates a torque steering degree by using the actual drive torque value; a compensation current calculation unit (140) that calculates a torque steering compensation current value that compensates for the torque steering using the torque steering degree; and a motor drive control unit (150) that calculates a basic control current value using a steering angle and a steering torque value, calculates the final control current value by adding the torque steering compensation current value to the basic control current value, and generates a control current according to the final control current value to supply the control current value to an electric motor (160) characterized by a skid determination unit (120) that determines whether a skid of the vehicle is occurring using behavior information about the vehicle including a front wheel rotation speed and a rear wheel rotation speed. [2] The electronic control unit (100) of claim 1, wherein the engine operating information includes an engine torque value and an engine speed value, and the transmission operating information includes a torque converter speed value and a gear ratio. [3] The electronic control unit (100) according to claim 1, wherein the skid determining unit (120) determines that skid does not occur in the vehicle when the absolute value of a value obtained by subtracting the front wheel rotation speed from the rear wheel rotation speed is less than or equal to a first reference value, and determines that skid occurs in the vehicle when the absolute value is greater than the first reference value. [4] The electronic control unit (100) according to claim 1 or 3, wherein the torque steering degree calculation unit (130) calculates a slip index and calculates the actual drive torque value of the vehicle using the slip index and the drive shaft drive torque value when it is determined that a slip occurs in the vehicle. [5] The electronic control unit (100) according to claim 4, wherein the torque steering degree calculation unit (130) calculates the slip index by dividing the rear wheel rotation speed by a value obtained by subtracting a first reference value from the front wheel rotation speed, and calculates the actual drive torque value by multiplying the slip index and the drive shaft drive torque value. [6] The electronic control unit (100) according to any one of claims 1 to 5, wherein the behavior information includes a longitudinal acceleration value of the vehicle, and the skid determination unit (120) extracts a general longitudinal acceleration value according to the drive shaft drive torque value from a previously stored longitudinal acceleration map, determines that skid does not occur in the vehicle when the absolute value of a value obtained by subtracting the general longitudinal acceleration value from the longitudinal acceleration value is less than or equal to a second reference value, and determines that skid occurs in the vehicle when the absolute value is greater than the second reference value. [7] The electronic control unit (100) according to claim 6, wherein the torque steering degree calculation unit (130) calculates the slip index by dividing the longitudinal acceleration value by a value obtained by subtracting the second reference value from the general longitudinal acceleration value, and calculates the actual drive torque value by multiplying the slip index and the drive shaft drive torque value. [8] The electronic control unit (100) according to any one of claims 1 to 7, wherein the torque steering degree calculation unit (130) calculates the torque steering degree based on a short-axis drive shaft bending angle (θ short ) and a long-axis drive shaft bending angle (θ long ), which are calculated using the height value of the vehicle, the length of a short-axle drive shaft and the length of a long-axle drive shaft. [9] The electronic control unit (100) according to any one of claims 1 to 8, wherein the compensation current calculation unit (140) calculates the torque steering compensation current value by dividing the torque steering degree by a value obtained by multiplying a motor torque constant of the electric motor (160) and a tooth number ratio included in the transmission operation information. [10] A method for compensating for torque steering in an electronic control unit (100) of a motor-driven power steering system, comprising: a drive shaft drive torque calculation step of calculating a drive shaft drive torque value using engine operation information including an engine torque value and an engine speed value, and transmission operation information, a compensation current calculation step of calculating a torque steering degree using the actual drive torque value, and calculating a torque steering compensation current value for compensating the torque steering using the torque steering degree; and a torque steering compensation step of calculating a final control current value by adding the torque steering compensation current value to a basic control current value calculated using a steering angle and a steering torque value, and generating a current value according to the final control current value to supply the control current to an electric motor (160), characterized by that the transmission information includes a torque converter speed value and a gear ratio; and the following additional steps are included: a skid determining step of determining whether a skid of a vehicle occurs using behavior information of the vehicle including one or more of a front wheel rotation speed, a rear wheel rotation speed, and a longitudinal acceleration value; an actual drive torque value calculation step of, when it is determined in the slip determination step that slippage does not occur in the vehicle, setting a slip index to a specific value, and when it is determined in the slip determination step that slippage does occur in the vehicle, calculating the slip index and calculating an actual drive torque value of the vehicle using the drive shaft drive torque value and the slip index. [11] The method of claim 10, wherein the compensation current calculation step comprises: a step of calculating a short-axis drive shaft bending angle (θ short ) and a long-axis drive shaft bending angle (θ long ) using the height value of the vehicle, the length of a short-axle drive shaft and the length of a long-axle drive shaft; a step of calculating a short-axis drive shaft-side coupling torque (Mz short ) and a long-axis drive shaft coupling torque (Mz long ) using the actual drive torque value, short-axis drive shaft bending angle (θ short ) and the long axis drive shaft bending angle (θ long ); a step of calculating the torque steering ratio by subtracting the long-axis drive shaft side coupling torque (Mz long ) from the short-axis drive shaft coupling torque (Mz short ); and a step of calculating the torque steering compensation current value by dividing the torque steering degree by a value obtained by multiplying the motor torque constant of the electric motor (160) and the tooth number ratio. [12] A method according to claim 10 or 11, wherein the compensation current calculation step comprises: a step of extracting the torque steering degree corresponding to the actual drive torque value from a previously stored torque steering degree map; and a step of calculating the torque steering compensation current value by dividing the torque steering degree by a value obtained by multiplying a motor torque constant of the electric motor (160) and the tooth number ratio.

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