Apparatus and method for electric vehicle to depart from uneven roads

Abstract

The invention relates to an apparatus and a method for an electric vehicle to depart from uneven roads. The apparatus includes a maximum traction confirmation portion configured to find a steering angle that generates a maximum traction by applying a driving torque while rotating a steering wheel. The maximum traction force confirmation portion is further configured to confirm a maximum wheel torque that can be applied after the steering wheel is rotated to a steering angle at which the maximum traction force is generated. The apparatus further includes an axle load calculation section configured to repeatedly calculate axle loads applied to front wheels and rear wheels of the vehicle on which various pitching motions are performed. The apparatus also includes a departure controller configured to receive information from the maximum traction confirmation portion and the axle load calculation portion, and control departure of the vehicle.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to Korean Patent Application No. 10-2023-0146388 filed on October 30, 2023, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a device and a method for an electric vehicle to escape from an uneven driving road surface. Background Art

[0004] Recently, the number of people who enjoy off-road driving on surfaces such as sand, mud, and gravel has increased. In addition, in many overseas countries where off-road roads are a major part of the country, interest in off-road vehicles has also increased, and vehicle orders have increased.

[0005] On off-road surfaces, wheel slip may occur frequently and the wheels may be in a trapped state where the vehicle may be unable to move due to the resistance of the road. In such an environment, when improperly disengaged, the vehicle's wheels may become stuck in the road (sand, etc.) so that the wheels may be buried and there may be no way to disengage except towing.

[0006] Most off-road vehicles can be designed for four-wheel drive, and both the front and rear wheels can be used for driving. When a four-wheel drive vehicle is driven off-road, both the front and rear wheels may dig into the ground and become stuck, which can exacerbate the problem. Summary of the invention

[0007] One aspect of the present invention is to provide a device and method that can help an electric vehicle traveling off-road escape even when its wheels cannot move due to road resistance.

[0008] One aspect of the present invention is to provide a device and method that can help an electric vehicle traveling off-road get out of trouble by implementing a disengagement system in the vehicle's system to provide maximum traction without the driver's trial and error when the vehicle's wheels are unable to move due to road resistance.

[0009] According to an embodiment of the present invention, an apparatus for an electric vehicle to disengage from an uneven driving road surface includes a maximum traction force confirmation unit configured to find a steering angle that generates maximum traction force by applying a driving torque when turning a steering wheel. The maximum traction force confirmation unit is also configured to confirm the maximum wheel torque that can be applied after turning the steering wheel to the steering angle that generates the maximum traction force. The apparatus also includes an axle load calculation unit configured to repeatedly calculate the axle loads applied to the front and rear wheels of the vehicle in which various pitching motions are implemented. The apparatus also includes a departure controller configured to receive information from the maximum traction force confirmation unit and the axle load calculation unit, and to control the disengagement of the vehicle.

[0010] The maximum wheel torque confirmed by the maximum traction force confirming unit may include a maximum front wheel torque, which is a maximum wheel torque at which the front wheels do not experience wheel slip, and a maximum rear wheel torque, which is a maximum wheel torque at which the rear wheels do not experience wheel slip.

[0011] The drive-off controller commands the vehicle to break away when the axle load calculated by the axle load calculation unit is greater than a predetermined value in a case where the steering wheel of the vehicle is turned to a steering angle generating a maximum traction force.

[0012] The predetermined value may be selected from a value of 1.3 to 1.8 times the weight of the vehicle.

[0013] The drive-off controller may command the vehicle to disengage when the axle load calculated by the axle load calculation unit is at a maximum value in a case where the steering wheel of the vehicle is turned to a steering angle generating a maximum traction force.

[0014] The axle load calculation unit may include a pitching motion implementation unit configured to implement a pitching motion so that the vehicle moves back and forth.

[0015] The pitching motion implementing unit may implement the pitching motion by alternately and repeatedly applying positive torque and reverse torque of different magnitudes to the front wheel motor and the rear wheel motor of the vehicle while changing the application time (or application frequency).

[0016] The pitching motion implementing portion may implement the pitching motion by applying a maximum front wheel torque to a front wheel motor of the vehicle in a forward direction and applying a maximum rear wheel torque to a rear wheel motor of the vehicle in a rearward direction.

[0017] The pitching motion implementing portion may implement the pitching motion by changing an application time (or an application frequency) of the maximum front wheel torque and the maximum rear wheel torque applied to the front wheel motor and the rear wheel motor of the vehicle.

[0018] When performing the pitching motion, the front and rear wheels of the vehicle may be braked while the steering wheel of the vehicle is turned to a steering angle that generates maximum traction.

[0019] The departure controller may release the brakes on the front wheels and the rear wheels when commanding the vehicle to depart, and may command the front wheels and the rear wheels to be applied with a maximum front wheel torque and a maximum rear wheel torque, respectively, in a forward direction of the vehicle.

[0020] The departure controller may release the brakes on the front and rear wheels when commanding the vehicle to depart. The departure controller may also command the front and rear wheels to be applied with a maximum wheel torque in a forward direction of the vehicle without causing wheel slip, the maximum wheel torque being calculated by a predetermined value or a maximum value of the axle load calculated by the axle load calculation unit.

[0021] The method for an electric vehicle to disengage from an uneven driving surface includes a maximum traction confirmation operation, in which a steering angle generating maximum traction is found by applying a driving torque while turning a steering wheel. The method also includes: in the maximum traction confirmation operation, after turning the steering wheel to the steering angle generating maximum traction, confirming the maximum wheel torque that can be applied. The method also includes an axle load calculation operation, in which various pitching movements are implemented and the axle loads applied to the front and rear wheels of the vehicle are repeatedly calculated. The method also includes a departure control operation, in which a command is issued whether to execute the vehicle's departure based on information confirmed or calculated in the maximum traction confirmation operation and the axle load calculation operation.

[0022] Confirming the maximum wheel torque in the maximum traction confirmation operation may include confirming a maximum front wheel torque that is a maximum wheel torque at which the front wheels do not slip, and confirming a maximum rear wheel torque that is a maximum wheel torque at which the rear wheels do not slip.

[0023] The method may further include, in the departure control operation, instructing the vehicle to depart when the axle load calculated in the axle load calculation operation is greater than a predetermined value or a maximum value while the steering wheel of the vehicle is turned to a steering angle generating maximum traction.

[0024] Implementing various pitching motions may include applying brakes to the front and rear wheels of the vehicle. Implementing various pitching motions may also include implementing pitching motions by alternately and repeatedly applying front wheel disengagement wheel torque and rear wheel disengagement wheel torque to the front wheel motor and the rear wheel motor, respectively.

[0025] Implementing the various pitching movements may include implementing the pitching movements by changing the application time or application frequency of the maximum front wheel torque and the maximum rear wheel torque applied to the front wheel motors and the rear wheel motors of the vehicle.

[0026] The method may further include: releasing the brakes of the front and rear wheels when the vehicle is commanded to disengage in the departure control operation. The method may further include: applying a maximum front wheel torque and a maximum rear wheel torque to the front and rear wheels, respectively, in a forward direction of the vehicle in the departure control operation.

[0027] The method may further include: in the drive-off control operation, turning off the system control when the vehicle reaches a determined vehicle speed after the vehicle leaves the uneven driving surface.

[0028] The method for an electric vehicle to get off an uneven driving road surface according to the embodiment may be stored in a computer-readable storage medium in which there is a program for executing the method on a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other aspects, features and advantages of the present invention will be more clearly understood from the following detailed description presented in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a schematic diagram showing a device for an electric vehicle to escape from an uneven driving road surface according to an embodiment of the present invention;

[0031] Figure 2 is a schematic diagram showing a change in the contact area between the wheel of an electric vehicle and the ground according to the rotation of the steering wheel according to an embodiment of the present invention;

[0032] Figure 3 is the maximum wheel torque according to Figure 2 A reference map for determining a state of a steering angle of the steering wheel that generates a maximum traction force according to a change in a contact area of ​​the steering wheel during rotation of the steering wheel;

[0033] Figure 4 It is shown in Figure 3 A reference diagram of a process of confirming the maximum wheel torque without wheel slip at the steering angle where the maximum traction force is confirmed;

[0034] FIG. 5A to FIG. 5D is a reference diagram showing implementation of a pitching motion of an electric vehicle according to an embodiment of the present invention;

[0035] Figure 6 and Figure 7 It shows confirmation Figure 5D A reference diagram of a state in which the axle load of the electric vehicle performing the pitching motion is a maximum value or a target value;

[0036] Figure 8 is a reference diagram illustrating a method for calculating an axle load of an electric vehicle according to an embodiment of the present invention;

[0037] Fig. 9is a schematic diagram showing a method for an electric vehicle to escape from an uneven driving road surface according to an embodiment of the present invention;

[0038] Figures 10 to 14 is a schematic diagram illustrating a method for an electric vehicle to escape from an uneven driving road surface according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings.

[0040] Various embodiments are described with reference to the accompanying drawings. However, this may not necessarily limit the scope of the present invention to a specific embodiment form. On the contrary, modifications, equivalents and replacement forms included in the disclosed concept and technical scope of the present invention may be adopted. Throughout the present invention, similar reference numerals are used for similar elements.

[0041] In the embodiment, the terms "first", "second", etc. can be used to distinguish one element from another element, and may not limit the order and / or importance or other related to the elements. In some cases, the first element can be called the second element, and similarly, the second element can be called the first element, without departing from the scope of rights in the embodiment.

[0042] Embodiments can be implemented in various ways and are not limited to the embodiments described herein. Unless the expression has a significantly different meaning in the context, the expression used as a singular also includes the expression of the plural. The terms "comprise", "include", "configured to", etc. in the specification are used to indicate the presence of features, numbers, steps, operations, elements, parts or combinations thereof. These terms do not exclude the possibility of combining or adding one or more features, numbers, steps, operations, elements, parts or combinations thereof.

[0043] Unless otherwise defined, all terms (including technical or scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. Terms defined in commonly used dictionaries should be interpreted as having the same meaning as the contextual meaning of the relevant field. These terms should not be interpreted as having an ideal or overly formal meaning unless explicitly defined as having such a meaning in the present invention.

[0044] In an embodiment, a vehicle may refer to various vehicles that move a transport object (e.g., a person, an animal, or goods) from a starting point to a destination. The vehicle is not limited to vehicles that travel on roads or tracks. When components, devices, elements, etc. of the present invention are described as having a purpose or performing an operation, function, etc., the components, devices, elements, etc. should be considered as "configured to" meet the purpose or perform the operation or function in this article. As a part of a device, each of the components, devices, elements, etc. can be implemented as a processor and a memory (e.g., a non-volatile computer-readable medium) respectively, or included in a processor and a memory.

[0045] Figure 1 is a schematic diagram showing an apparatus for an electric vehicle to escape from an uneven driving road surface according to an embodiment.

[0046] refer to Figure 1 , the apparatus 100 for disengaging an electric vehicle from an uneven driving surface in the embodiment can assist in the electric disengagement of the vehicle by confirming the maximum traction state in the vehicle system without the need for trial and error by the driver.

[0047] When an off-road vehicle is stuck on an uneven driving surface and cannot move, in order to ensure maximum traction, the axle load can be increased by turning the steering wheel to try to disengage or leave the uneven driving surface, or by increasing the vertical force by loading the vehicle with cargo. In an embodiment, in this process, the vehicle can be assisted to disengage by ensuring the optimal position of the steering wheel and the maximum axle load of the vehicle.

[0048] The device 100 for an electric vehicle to escape from an uneven driving road surface in the embodiment may include a maximum traction force confirmation unit 110 , an axle load calculation unit 120 , and a driving-off controller 130 .

[0049] Although the controller is not shown in the drawings, in the embodiment, a controller for controlling the device 100 for an electric vehicle to escape from an uneven driving road surface and a method S100 for an electric vehicle to escape from an uneven driving road surface may be provided. The overall control may be performed by the controller. For example, the controller may be linked or connected to the device 100 for an electric vehicle to escape from an uneven driving road surface, and may be linked or connected to the maximum traction confirmation unit 110, the axle load calculation unit 120, and the departure controller 130, and may participate in the control of the components.

[0050] The maximum traction confirmation unit 110 can confirm the maximum torque that can be applied to the motor of the electric vehicle without wheel slippage, and the electric vehicle may be unable to move due to being stuck on an uneven driving road. In other words, it is considered that the maximum wheel torque can be changed based on the change in the contact area between the wheel (tire) and the ground. The optimal position can be found by turning the steering wheel of the electric vehicle. The maximum wheel torque can be applied. In addition, once the optimal position (steering angle) of the steering wheel is confirmed, the maximum wheel torque that can be applied when the steering wheel is turned to the corresponding steering angle can be found.

[0051] In other words, the maximum traction force confirmation unit 110 may find the steering angle that generates the maximum traction force by applying the driving torque when turning the steering wheel. The maximum traction force confirmation unit 110 may confirm the maximum wheel torque that can be applied after turning the steering wheel to the steering angle that generates the maximum traction force. In other words, the maximum traction force confirmation unit 110 may include a portion 111 for confirming the steering angle that generates the maximum traction force and a portion 115 for confirming the maximum wheel torque.

[0052] refer to Figure 2 , when the electric vehicle in the embodiment is stuck on an uneven driving road and cannot move, the contact area C between the wheel W (tire) and the ground G can be changed according to the rotation angle of the steering wheel. When the contact area C between the wheel W (tire) and the ground G is large, the friction force can be increased, so that the torque that can be applied to the wheel can be increased. On the contrary, when the contact area C is small, the friction force can be reduced, so that the torque that can be applied to the wheel can be relatively reduced.

[0053] exist Figure 2 In the accompanying drawings, for example, when the steering wheel is turned +60 degrees, the maximum contact area C between the wheel W (tire) and the ground G can be ensured, and the corresponding position can correspond to the steering angle that generates the maximum traction. This is just an example, the steering wheel can be turned to the maximum angle in the clockwise direction and the counterclockwise direction, and the steering angle that generates the maximum traction can be confirmed.

[0054] refer to Figure 3 When the electric vehicle in the implementation scheme is stuck on an uneven driving road and cannot move, the steering wheel can be turned to a maximum angle in a clockwise direction and a counterclockwise direction, and the steering angle that generates the maximum traction can be confirmed.

[0055] By turning the steering wheel, torque can be applied to the front wheels (front wheel motors) connected to the steering wheel while changing the contact area between the wheels and the ground. Based on the change in contact area, the wheel slip rate of the front wheels can be continuously changed. Therefore, the wheel torque that can be generated according to the position of the steering wheel (steering angle) can be continuously changed. The steering angle (θ) that generates the maximum wheel torque can be confirmed. The speed of the steering wheel and the applied torque can be changed (for example, the rotation of the steering wheel can be 30 degrees / second, and the applied torque can be 10% of the maximum value of the front wheel motor torque).

[0056] refer to Figure 4 , the maximum wheel torque that can be applied without wheel slip can be confirmed by turning to the confirmed steering angle that generates the maximum traction. When the steering wheel is fixed at the steering angle (θ) that generates the maximum traction and applies the maximum wheel torque, and the vehicle remains stationary without the wheel slipping due to friction and reaching the critical torque, the wheel slip can increase rapidly, the torque value can decrease, and the torque value immediately before the wheel slip occurs can correspond to the maximum wheel torque.

[0057] The reference can be calculated using various sensors installed in the vehicle (e.g., a speed sensor, a rotation sensor, an acceleration sensor, and an angular velocity sensor) and various algorithms provided in the vehicle. Figure 3 and Figure 4 The values ​​of the wheel torque and wheel slip ratio described above are not limited to any specific example.

[0058] The steering wheel may be fixed at a steering angle (θ) that generates the maximum wheel torque. At this position, torque may be applied to the front wheel motor to increase linearly in the forward direction (D gear), and the maximum front wheel motor torque Tmf without wheel slip may be confirmed. Since wheel slip does not occur, the torque applied to the wheel may be practically the same as the torque applied to the motor except for accidental factors.

[0059] In addition, the steering wheel can be fixed at a steering angle (θ) that produces maximum wheel torque. At this position, torque can be applied to the rear wheel motor to increase linearly in the backward direction (R gear), and the maximum rear wheel motor torque Tmr without wheel slip can be confirmed. Since wheel slip does not occur, the torque applied to the wheel can actually be the same as the torque applied to the motor, except for accidental factors. In addition, since the rear wheels are not connected to the steering wheel, regardless of whether the torque applied to the rear wheels is in the forward direction or the backward direction, the magnitude of the torque that does not cause wheel slip can actually be no different (the magnitude of the torque can be roughly almost the same).

[0060] The axle load calculation unit 120 may repeatedly calculate the axle load applied to the front and rear axles of the vehicle while applying a pitching motion to the vehicle. As the axle load increases, the maximum torque that can be applied to the wheels also increases.

[0061] In other words, referring to the following [Equation 1], the driveline torque (T M ×FGR) may not be greater than the wheel slip torque (μ×W×R) (ie, the maximum torque that can be transmitted to the road), and wheel slip may occur when the powertrain torque is greater than the wheel slip torque.

[0062] [Equation 1]

[0063] T M ×FGR≤μ×W×R

[0064] (Here, Tm is the motor torque, FGR is the reduction ratio, μ is the friction coefficient, W is the axle load, and R is the radius of the wheel)

[0065] Here, the axle load W may be proportional to the magnitude of the maximum torque that can be transmitted to the road (ground). Therefore, it can be pointed out that as the axle load increases, the driving force that can be transmitted to the ground without wheel slippage may increase.

[0066] Therefore, in an embodiment, the axle loads of the front and rear axles of the vehicle can be changed by applying a pitching motion to the vehicle. When the maximum axle load of the sum of the axle loads of the front and rear axles of the vehicle is formed, the vehicle can be disengaged.

[0067] Figure 5A The state before the pitching motion is applied is shown. FIG. 5B to FIG. 5D The state of the axle load applied to the front and rear wheels after the pitching motion is applied to the vehicle is shown. The length of the arrows on the front and rear wheels corresponds to the magnitude of the axle load, and the more pitching motion is applied, the more the axle load may increase. In addition, when the pitching motion is applied, the vehicle may rock forward and backward.

[0068] As an example of implementing the pitching motion, 1) the steering wheel may be fixed at a steering angle (θ) generating a maximum wheel torque, and brakes may be applied to the front and rear wheels, 2) a torque Tm1 may be applied to the front wheels in a forward direction for a predetermined period of time T1, so that a squat motion may be generated, 3) while reducing the torque applied to the front wheels, a torque Tm2 may be applied to the rear wheels in a backward direction for a predetermined period of time T2, so that a dive motion may be generated, 4) the pitching motion may be implemented by repeatedly performing the operations in 2) and 3). In the process, Tm1 and Tm2 may be changed, and T1 and T2 may also be changed.

[0069] In the embodiment, Tm1 and Tm2 may correspond to the maximum front wheel torque or the maximum rear wheel torque confirmed by the maximum traction force confirming unit 110. In addition, T1 and T2 may be the same or different.

[0070] refer to Figure 6 and Figure 7 , with the steering wheel fixed at a steering angle that generates maximum traction and brakes applied to the front and rear wheels, changes in the axle loads of the front and rear wheels that occur when wheel torque is applied alternately to the front and rear wheels can be confirmed. Figure 6 An example is shown in which the maximum front wheel torque Tmf and the maximum rear wheel torque Tmr confirmed by the maximum traction force confirmation section 110 can be applied to the front wheels and the rear wheels. Figure 7 An example is shown in which the torque applied to the front and rear wheels can vary over time. Figure 7 In the example (the implementation scheme is not limited thereto), referring to the maximum front wheel torque Tmf and the maximum rear wheel torque Tmr confirmed by the maximum traction force confirmation unit 110, a torque value within a predetermined range (for example, a value greater than or less than 10% to 30% of the above value) can be changed and applied to the front and rear wheels.

[0071] exist Figure 6 and Figure 7 In either case, the axle load applied to the front and rear wheels may become maximum or may exceed a predetermined value depending on the pitch motion, and in this case, the vehicle's detachment may be performed.

[0072] [Equation 2]

[0073]

[0074] [Equation 3]

[0075]

[0076] [Equation 4]

[0077] F z =F z,f +F z,r

[0078] (In equations 2, 3, and 4, F z is the total axle load, F z,f is the axle load of the front wheel, F z,r is the axle load of the rear wheel, m b is the weight of the vehicle, l r is the distance from the center of gravity to the rear axle, l f is the distance from the center of gravity to the front axle, g is the acceleration due to gravity, h CG is the height of the center of gravity, ba x is the longitudinal acceleration of the vehicle)

[0079] exist Figure 8 In the example, the center of gravity (COG) can be the center of gravity, ba y It could be the lateral acceleration of the vehicle.

[0080] refer to Figure 8 And using the above equations 2, 3, and 4, the total axle load of the vehicle that changes based on the pitching motion can be repeatedly calculated. In addition, the calculated total axle load of the vehicle can be transmitted to the departure controller 130. There may be a state in which the axle load applied to the front and rear wheels (i.e., the total axle load (F z )) becomes a maximum or greater than a predetermined value (for example, a value selected from 1.3 to 1.8 times the weight of the vehicle, preferably 1.5 times the weight of the vehicle). In this state, the departure controller 130 receiving the information can command the vehicle to leave.

[0081] The axle load calculation unit 120 may include a pitching motion implementation unit, which implements the pitching motion so that the vehicle can move back and forth. In addition, the pitching motion implementation unit can implement the pitching motion by alternately and repeatedly applying different sizes of positive torque and reverse torque to the front wheel motor and rear wheel motor of the vehicle, while changing the application time (or application frequency). In addition, the pitching motion implementation unit can implement the pitching motion by alternately applying the maximum front wheel torque to the front wheel motor of the vehicle in the forward direction, and applying the maximum rear wheel torque to the rear wheel motor of the vehicle in the backward direction. In addition, the pitching motion implementation unit can implement the pitching motion by changing the application time (or application frequency) of the maximum front wheel torque and the maximum rear wheel torque applied to the front wheel motor and rear wheel motor of the vehicle. In addition, in the process of implementing the pitching motion, when the steering wheel of the vehicle is turned to the steering angle generating the maximum traction and the front and rear wheels of the vehicle are braked, the pitching motion implementation unit can implement the pitching motion.

[0082] The departure controller 130 may receive information from the maximum traction force confirmation unit 110 and the axle load calculation unit 130, and may control the vehicle's departure based on the received information. That is, the departure controller 130 may command the vehicle to depart based on the optimal front wheel torque and the optimal rear wheel torque confirmed in the pitch motion when the steering wheel is turned to the optimal steering angle.

[0083] In an embodiment, when the axle load calculated by the axle load calculation unit is the maximum value and the steering wheel of the vehicle is turned to the steering angle that generates the maximum traction, the departure controller 130 can command the vehicle to depart. When a pitching motion is applied to the vehicle, the total axle load (the sum of the axle loads of the front wheels and the rear wheels) can increase or decrease, and the vehicle can be commanded to depart at the moment when the maximum axle load value is calculated.

[0084] In addition, in another embodiment, when the axle load calculated by the axle load calculation unit is greater than a predetermined value and the steering wheel of the vehicle is turned to a steering angle that generates maximum traction, the departure controller 130 may command the vehicle to depart. Here, the predetermined value may be predetermined and may be a value selected from 1.3 to 1.8 times the weight of the vehicle, and a value of 1.5 times the weight of the vehicle is desirable.

[0085] When the drive-off controller 130 commands the vehicle to disengage, torque in the forward direction may be applied to both the front and rear wheels.

[0086] In this case, in an embodiment, when the vehicle is commanded to disengage, the brakes of the front and rear wheels may be released, and the maximum front wheel torque and the maximum rear wheel torque confirmed by the maximum traction force confirmation unit 110 may be applied to the front and rear wheels in the forward direction of the vehicle.

[0087] In addition, in another embodiment, when the vehicle is commanded to disengage, the brakes of the front and rear wheels are released, and a torque value calculated by the maximum value Wmax of the axle load calculated by the axle load calculation unit 120 or a predetermined value (W_1.5) may be applied to the front and rear wheels. Here, specifically, the maximum value Wmax of the axle load may include the front wheel axle load (W_1.5) when the axle load is maximum. max,f ) and rear wheel axle load (W max,r Specifically, the predetermined value (W_1.5) may include the front wheel axle load (W 1.5,f ) and rear wheel axle load (W 1.5,r ).

[0088] In other words, the maximum wheel torque that does not cause wheel slip, calculated by the maximum value or the predetermined value of the axle load calculated by the axle load calculation section 120, may be applied in the forward direction of the vehicle.

[0089] In other words, referring to [Equation 1], [Equation 2], and [Equation 3], the maximum value of the powertrain torque may be proportional to the axle load of the vehicle. Therefore, the maximum value of the powertrain torque may be calculated by using the maximum value of the axle load (W) by the following [Equation 5] max,f and W max,r ) can be calculated, or it can be calculated by using the predetermined value (W 1.5,f and W 1.5,r ) to calculate.

[0090] [Equation 5]

[0091] T m,f ×FGR=μ×W max,f ×R

[0092] T m,r ×FGR=μ×W max,r ×R

[0093] [Equation 6]

[0094] T m,f ×FGR=μ×W 1.5,f ×R

[0095] T m,r ×FGR=μ×W 1.5,r ×R

[0096] After the vehicle leaves the uneven driving surface, the departure controller 130 can command the system control to be turned off at a certain speed of the vehicle. In other words, after the vehicle leaves the uneven driving surface, the departure controller 130 can control the operation of the device for the electric vehicle to leave the uneven driving surface to be turned off at, for example, 3kph.

[0097] In the following description, a method (S100) for an electric vehicle to escape from an uneven driving road surface is described. The method can be implemented using at least a portion of the above-mentioned device 100 for an electric vehicle to escape from an uneven driving road surface.

[0098] Fig. 9 is a schematic diagram showing a method for an electric vehicle to escape from an uneven driving road surface according to an embodiment, Figures 10 to 14 is a schematic diagram illustrating a method for an electric vehicle to escape from an uneven driving road surface according to an embodiment.

[0099] refer to Fig. 9 The method (S100) for an electric vehicle to disengage from an uneven driving surface in the embodiment may be a disengagement method performed in a device, which can help the vehicle to disengage electrically by confirming the maximum traction state in the vehicle system without the need for trial and error by the driver.

[0100] The method ( S100 ) for an electric vehicle to escape from an uneven driving road in the embodiment may include a maximum traction force confirmation operation ( S110 ), an axle load calculation operation ( S120 or S120 a ), and a drive-off control operation ( S130 or S130 a ).

[0101] The controller is not shown in the drawings, but in the embodiment, a controller for controlling the device 100 for an electric vehicle to disengage from an uneven driving road surface and a method for an electric vehicle to disengage from an uneven driving road surface (S100) may be provided, and the overall control may be performed by the controller. For example, the controller may participate in controlling the method for an electric vehicle to disengage from an uneven driving road surface (S100), specifically controlling the traction confirmation operation (S110), the axle load calculation operation (S120 or S120a), and / or the departure control operation (S130 or S130a). The controller may be linked with the maximum traction confirmation unit 110, the axle load calculation unit 120, and the departure controller 130 related to these controls, and may participate in the control components.

[0102] In the maximum traction confirmation operation (S110), the maximum torque that can be applied to the motor of the electric vehicle without causing wheel slip can be confirmed, and the electric vehicle is stuck on an uneven driving road and cannot move. In other words, considering that the maximum wheel torque can be changed according to the change in the contact area between the wheel (tire) and the ground, the optimal position can be found by turning the steering wheel of the electric vehicle, and the maximum wheel torque can be applied. In addition, once the optimal position (steering angle) of the steering wheel is confirmed, the maximum wheel torque that can be applied when the steering wheel is turned to the corresponding steering angle can be found.

[0103] In other words, the maximum traction confirmation operation (S110) may include applying a driving torque while turning the steering wheel to find a steering angle that generates maximum traction. The maximum traction confirmation operation (S110) may also include confirming a maximum wheel torque that may be applied after turning the steering wheel to the steering angle that generates maximum traction.

[0104] refer to Fig.10 When the electric vehicle is stuck on an uneven driving road and cannot move, the method for the electric vehicle to escape from an uneven driving road (S100) in the embodiment may be performed. The method for the electric vehicle to escape from an uneven driving road (S100) may be performed by the above-mentioned device 100 for the electric vehicle to escape from an uneven driving road, and each individual operation may be performed by the maximum traction confirmation unit 110, the axle load calculation unit 120, and the departure controller 130.

[0105] The maximum traction confirmation operation (S110) in the embodiment can be divided into an operation of confirming the steering angle (θ) that generates the maximum wheel torque and an operation of confirming the maximum wheel torque that can be applied at the steering angle (θ) without wheel slip. The maximum traction confirmation operation (S110) can be performed by the maximum traction confirmation unit 110 (S111). First, in the former case, when the electric vehicle is stuck on an uneven driving road and cannot move, the steering wheel can be turned to the maximum angle in the clockwise and counterclockwise directions, and the steering angle that generates the maximum traction can be confirmed (S112 and S113).

[0106] By turning the steering wheel, torque can be applied to the front wheels (front wheel motors) connected to the steering wheel while changing the contact area between the wheels and the ground. Based on the change in the contact area, the wheel slip rate of the front wheels can be continuously changed. Therefore, the wheel torque that can be generated based on the position of the steering wheel (steering angle) can be continuously changed. Among the magnitude of the torque, the steering angle (θ) that generates the maximum wheel torque can be confirmed (S114). The speed of the steering wheel and the applied torque can be changed (for example, the rotation of the steering wheel is 30 degrees / second, and the applied torque is 10% of the maximum value of the front wheel motor torque).

[0107] In the following description, in the latter case, the maximum wheel torque that can be applied without wheel slip can be confirmed by turning the steering wheel to the steering angle that generates the maximum traction force that is confirmed. When the steering wheel is fixed at the steering angle (θ) that generates the maximum traction force and the torque is applied, the vehicle can remain stationary without wheel slip due to friction. When the critical torque is reached, the wheel slip can increase rapidly, the torque value can decrease, and the torque value immediately before the wheel slip occurs can correspond to the maximum wheel torque. In this case, the maximum wheel torques of the front and rear wheels can be confirmed respectively.

[0108] The steering wheel can be fixed at a steering angle (θ) that generates the maximum wheel torque. At this position, torque can be applied to the front wheel motor so as to increase linearly in the forward direction (D gear), and the maximum front wheel motor torque Tmf that does not cause wheel slip can be confirmed. Since wheel slip does not occur, the torque applied to the wheel can be actually the same as the torque applied to the motor except for accidental factors.

[0109] In addition, the steering wheel can be fixed at a steering angle (θ) that produces maximum wheel torque. At this position, torque can be applied to the rear wheel motor to increase linearly in the backward direction (R gear), and the maximum rear wheel motor torque Tmr that does not cause wheel slip can be confirmed (S115). Since wheel slip does not occur, the torque applied to the wheel can actually be the same as the torque applied to the motor, except for accidental factors. In addition, since the rear wheels are not connected to the steering wheel, the magnitude of the torque that does not cause wheel slip can be no different regardless of whether the torque applied to the rear wheels is in the forward direction or the backward direction (in fact, the magnitude of the torque can be roughly almost the same).

[0110] The axle load calculation operation (S120) may include repeatedly calculating the axle load applied to the front and rear wheels of the vehicle while applying a pitching motion to the vehicle. As the axle load increases, the maximum torque that can be applied to the wheel also increases (see [Equation 1] and related description). The axle load calculation operation (S120) may be performed by the axle load calculation unit 120.

[0111] Therefore, in an embodiment, the axle loads of the front and rear axles of the vehicle can be changed by applying a pitching motion to the vehicle. When a maximum axle load is formed (the maximum axle load is the sum of the axle loads of the front and rear axles of the vehicle), the vehicle can be disengaged.

[0112] refer to Fig.11 As an example of implementing the pitching motion, 1) the steering wheel may be fixed at a steering angle (θ) that produces a maximum wheel torque, and brakes may be applied to the front and rear wheels, 2) a squat motion may be generated by applying the maximum front wheel torque confirmed in the maximum traction confirmation operation (S110) to the front wheels in a forward direction within a predetermined time period T1, 3) a nodding motion may be generated by applying the maximum rear wheel torque confirmed in the maximum traction confirmation operation (S110) to the rear wheels in a rearward direction within a predetermined time period T2, while reducing the torque applied to the front wheels, 4) the pitching motion may be implemented by repeatedly performing the above operations 2) and 3), in which process T1 and T2 may also be changed, and T1 and T2 may be the same or different.

[0113] In addition, in the departure control operation (S130 or S130a) to be described later, the axle load (ie, the total axle load (F z )), when the total axle load (F z ) reaches its maximum value, the vehicle is commanded to disengage.

[0114] In an embodiment, as the pitching motion continues, the pitch and bouncing applied to the vehicle may increase, and after passing the peak value, the pitch and bouncing may no longer increase, and an inflection point may occur, and accordingly, the total axle load (Fz ) no longer increases, it can be considered as the total axle load (F z ) and the process of confirming the value can be performed in operation S126. Therefore, when the total axle load (F z ) is no longer greater than the previously calculated total axle load, a subsequent operation, namely, a departure control operation (S130 or S130a), can be performed.

[0115] refer to Fig.12 As an example of implementing a pitching motion, 1) the steering wheel may be fixed at a steering angle (θ) that generates a maximum wheel torque, and brakes may be applied to the front and rear wheels, 2) a squat motion may be generated by applying a torque Tm1 to the front wheels in a forward direction within a predetermined time period T1, 3) a nodding motion may be generated by applying a torque Tm2 to the rear wheels in a backward direction within a predetermined time period T2 while reducing the torque applied to the front wheels, 4) a pitching motion may be implemented by repeatedly performing the above operations 2) and 3). In this process, Tm1 and Tm2 may be maintained or changed, and T1 and T2 may also be maintained or changed. In addition, in an embodiment, Tm1 and Tm2 may correspond to the maximum front wheel torque or the maximum rear wheel torque confirmed in the maximum traction confirmation operation (S110). In addition, T1 and T2 may be the same or different.

[0116] In the departure control operation (S130 or S130a) described later, the total axle load (F z ) value is greater than a predetermined value, thereby commanding the vehicle to disengage when the axle load applied to the front and rear wheels exceeds a predetermined value (for example, a value selected from 1.3 times to 1.8 times the weight of the vehicle, with a desired value of 1.5 times the weight of the vehicle).

[0117] In another embodiment, as the pitching motion continues, it is considered that the pitch and roll applied to the vehicle may increase and decrease or may increase again, that is, the total axle load (F z ) can be changed continuously, and the total axle load (F z ) value is greater than a predetermined value, and it can be confirmed in operation S126a. Therefore, when the total axle load (F z ) exceeds a predetermined value, it can be controlled to perform a subsequent operation, namely, a departure control operation (S130 or S130a).

[0118] refer to Fig.11 and Fig.12 , when the steering wheel is fixed at a steering angle generating maximum traction and braking is applied to the front and rear wheels, changes in axle loads of the front and rear wheels that may occur when wheel torque is alternately applied to the front and rear wheels can be confirmed.

[0119] Fig.11 An example is shown in which a predetermined amount of wheel torque is applied to the front and rear wheels, that is, the maximum front wheel torque Tmf and the maximum rear wheel torque Tmr confirmed in the maximum traction force confirmation operation ( S110 ) are applied to the front and rear wheels. Fig.12 An example of maintaining or changing the torque applied to the front and rear wheels over time is shown. Fig.12 In the example of , although the implementation scheme is not limited thereto, a torque or torque value within a predetermined range (e.g., 10% to 30% greater or less than the above value) can be applied to the front and rear wheels while maintaining or changing the value by referring to the maximum front wheel torque Tmf and the maximum rear wheel torque Tmr confirmed in the maximum traction confirmation operation (S110).

[0120] exist Fig.11 and Fig.12 In either method, the axle load applied to the front and rear wheels may become maximum or may exceed a predetermined value depending on the pitch motion, and in this case, the vehicle's detachment may be performed.

[0121] refer to Figure 8 And the total axle load of the vehicle that changes based on the pitching motion can be repeatedly calculated using the above equations 2, 3 and 4. In addition, the calculated total axle load of the vehicle can be used for the departure control operation (S130 or S130a).

[0122] The axle load calculation operation (S120) may include implementing a pitching motion, wherein the pitching motion may be implemented so that the vehicle can move back and forth (S121, S121a). In addition, the pitching motion may be implemented by alternately and repeatedly applying different magnitudes of positive torque and reverse torque to the front wheel motor and the rear wheel motor of the vehicle while changing the application time (or application frequency). In addition, the pitching motion may be implemented by alternately applying the maximum front wheel torque to the front wheel motor of the vehicle in the forward direction and applying the maximum rear wheel torque to the rear wheel motor of the vehicle in the backward direction. In addition, the pitching motion (S124, S125, S126, S127) can be implemented by changing the application time (or application frequency) of the maximum front wheel torque applied to the front wheel motor of the vehicle and the maximum rear wheel torque applied to the rear wheel motor of the vehicle, S125 and S126 are operated by equations 2, 3 and 4, and the maximum front wheel torque and the maximum rear wheel torque are calculated by iteration (S124a, S125a, S126a, S127a), S125a and S126a are operated by equations 2, 3 and 4, and the maximum front wheel torque and the maximum rear wheel torque are calculated based on the vehicle weight × 1.5. In addition, the pitching motion can be implemented when the steering wheel of the vehicle is turned to the steering angle (S123, S123a) that generates the maximum traction and the front and rear wheels of the vehicle are braked (S122, S122a).

[0123] The departure control operation (S130 or S130a) may control the vehicle to depart based on the information confirmed in the maximum traction confirmation operation (S110) and the axle load calculation operation (S120 or S120a). In other words, the departure control operation (S130 or S130a) may command the vehicle to depart by the optimal front wheel torque and the optimal rear wheel torque confirmed in the pitch motion when the steering wheel is turned to the optimal steering angle. The departure control operation (S130 or S130a) may be performed by the departure controller 130.

[0124] refer to Fig.13 and Fig.14 The driving-off control operation (S130 or S130a) in the embodiment may be performed under the axle load (i.e., the total axle load (F z )) becomes a maximum value or is greater than a predetermined value (for example, a value selected from 1.3 to 1.8 times the weight of the vehicle, preferably a value of 1.5 times the weight of the vehicle) (S131 and S131a), the vehicle is commanded to disengage. In addition, when the vehicle is commanded to disengage in the departure control operation (S130 or S130a), the brakes of the front and rear wheels may be released, and torque in the forward direction may be applied to both the front and rear wheels (S132).

[0125] However, in this case, Fig.13The illustrated driving-off control operation (S130) is merely an embodiment. When the vehicle is commanded to disengage, the brakes of the front and rear wheels may be released, and a torque value calculated by the maximum value Wmax of the axle load calculated by the axle load calculation unit 120 or a predetermined value (W_1.5) may be applied to the front and rear wheels (see Equations 5 and 6).

[0126] also, Fig.14 The illustrated departure control operation (S130a) may be another embodiment. When the vehicle is commanded to depart, the brakes of the front and rear wheels may be released, and the maximum front wheel torque and the maximum rear wheel torque confirmed by the maximum traction confirmation operation (S110) may be applied to the front and rear wheels in the forward direction of the vehicle.

[0127] After the vehicle leaves the uneven driving surface, the departure control operation (S130) can be controlled to turn off the system control when the vehicle reaches a certain speed. In other words, after the vehicle leaves the uneven driving surface, the operation of the device for electric vehicle to leave the uneven driving surface can be controlled to be turned off at, for example, 3kph.

[0128] The method according to the embodiment can be implemented in the form of program instructions, which can be executed by various computer devices and written to computer-readable media. The computer-readable medium can include program instructions, data files, data structures, etc. alone or in combination. The program instructions written to the computer-readable medium can be specially designed and configured for the embodiment, or can be known and available to those skilled in the art.

[0129] Examples of computer-readable media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. Examples of program instructions may include machine language codes created by a compiler, and high-level language codes that can be executed by a computer using an interpreter, etc. The above-mentioned hardware devices may be configured to operate together with at least one software module to perform the operations described in the embodiments, and vice versa.

[0130] The device 100 for an electric vehicle to escape from an uneven driving road surface in the embodiment may include a storage unit. The storage unit may be a recording medium suitable for the device 100 for an electric vehicle to escape from an uneven driving road surface, for example, a magnetic medium such as a hard disk, a floppy disk, and a magnetic tape, an optical medium such as a compact disk read-only memory (CD-ROM) and a digital video disk (DVD), a magneto-optical medium such as an optical floppy disk, or a semiconductor memory such as a flash memory, an erasable programmable ROM (EPROM), or an SSD manufactured based on a memory.

[0131] The embodiment may be implemented by a non-volatile memory (not shown) configured to store data related to an algorithm configured to control the operation of various components of the vehicle or software instructions to reproduce the algorithm. The embodiment may be implemented by a processor (not shown) configured to perform the operations described above or below using data stored in a corresponding memory. Here, the memory and the processor may be implemented as separate chips. Alternatively, the memory and the processor may be implemented as a single chip integrated with each other. The processor may be in the form of one or more processors.

[0132] The components of the device 100 for an electric vehicle to disengage from an uneven driving road surface can be connected in a wired manner or wirelessly, and information can be exchanged using a network provided in the vehicle. The method S100 for an electric vehicle to disengage from an uneven driving road surface can also use a network provided in the vehicle to exchange information in a wired manner or wirelessly. For example, data can be exchanged using a network communication device provided in the vehicle, such as Ethernet, media oriented system transport (MOST), Flexray, controller area network (CAN), local interconnect network (LIN), Internet, LTE, 5G, Wi-Fi, Bluetooth, near field communication (NFC), Zigbee, radio frequency (RF), etc.

[0133] According to the aforementioned embodiment, when the wheels of the electric vehicle traveling off-road cannot move due to road resistance, the device and method can easily perform disengagement in this environment.

[0134] Furthermore, by implementing a disengagement system in a vehicle system to achieve maximum traction, the apparatus and method may easily perform vehicle disengagement without trial and error by the driver.

[0135] While embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations may be made without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A device for an electric vehicle to escape from an uneven road surface, the device comprising: The maximum traction force confirmation unit is configured as follows: Finding the steering angle that generates the most traction by applying drive torque while turning the steering wheel; After turning the steering wheel to the steering angle that generates maximum traction, confirm the maximum wheel torque that can be applied; an axle load calculation unit configured to repeatedly calculate the axle loads applied to the front wheels and the rear wheels of the vehicle that performs various pitching motions; as well as The drive-off controller is configured to receive information from the maximum traction force confirmation unit and the axle load calculation unit, and control the vehicle's drive-off.

2. The device for an electric vehicle to escape from an uneven driving road according to claim 1, wherein: The maximum wheel torque confirmed by the maximum traction confirmation unit includes: Maximum front wheel torque, which is the maximum wheel torque at which the front wheels do not experience wheel slip, and Maximum rear wheel torque, which is the maximum wheel torque at which no wheel slip occurs on the rear wheels.

3. The device for an electric vehicle to escape from an uneven driving road according to claim 1, wherein: The drive-off controller is further configured to command the vehicle to disengage when the axle load calculated by the axle load calculation unit is greater than a predetermined value when the steering wheel of the vehicle is turned to a steering angle that generates maximum traction.

4. The device for an electric vehicle to escape from an uneven driving road according to claim 3, wherein: The predetermined value is selected from a value of 1.3 to 1.8 times the weight of the vehicle.

5. The device for an electric vehicle to escape from an uneven driving road according to claim 1, wherein: The drive-off controller is further configured to command the vehicle to disengage when the axle load calculated by the axle load calculation unit is a maximum value in a case where the steering wheel of the vehicle is turned to a steering angle that generates a maximum traction force.

6. The device for an electric vehicle to escape from an uneven driving road according to claim 1, wherein: The axle load calculation unit includes a pitching motion implementation unit configured to implement a pitching motion so that the vehicle moves back and forth.

7. The device for an electric vehicle to escape from an uneven driving road according to claim 6, wherein: The pitch motion implementing unit implements the pitch motion by alternately and repeatedly applying positive torque and reverse torque of different magnitudes to the front wheel motor and the rear wheel motor of the vehicle while changing the application time or the application frequency.

8. The device for an electric vehicle to escape from an uneven driving road according to claim 7, wherein: The pitching motion implementing portion implements the pitching motion by applying a maximum front wheel torque to a front wheel motor of the vehicle in a forward direction and applying a maximum rear wheel torque to a rear wheel motor of the vehicle in a rearward direction.

9. The device for an electric vehicle to escape from an uneven driving road according to claim 8, wherein: The pitching motion implementing section implements the pitching motion by changing the application time or application frequency of the maximum front wheel torque and the maximum rear wheel torque applied to the front wheel motor and the rear wheel motor of the vehicle.

10. The device for an electric vehicle to escape from an uneven driving road according to claim 6, wherein: When the pitching motion is implemented, the front and rear wheels of the vehicle are braked with the steering wheel of the vehicle turned to a steering angle that generates maximum traction.

11. The device for an electric vehicle to escape from an uneven driving road according to claim 2, wherein: The departure controller is further configured as follows: When the vehicle is commanded to disengage, the front and rear wheel brakes are released; The front wheels and the rear wheels are commanded to be applied with a maximum front wheel torque and a maximum rear wheel torque, respectively, in a forward direction of the vehicle.

12. The device for an electric vehicle to escape from an uneven driving road according to claim 2, wherein: The departure controller is further configured as follows: When the vehicle is commanded to disengage, the front and rear wheel brakes are released; The front and rear wheels are commanded to be applied with a maximum wheel torque in a forward direction of the vehicle without causing wheel slip, the maximum wheel torque being calculated by a predetermined value or a maximum value of the axle loads calculated by the axle load calculation section.

13. A method for an electric vehicle to escape from an uneven driving road surface, the method comprising a maximum traction confirmation operation, an axle load calculation operation and a drive-off control operation, During the maximum traction confirmation operation: Finding the steering angle that generates the most traction by applying drive torque while turning the steering wheel; After turning the steering wheel to the steering angle that generates maximum traction, confirm the maximum wheel torque that can be applied; During the axle load calculation operation: Implementing various pitching motions and repeatedly calculating the axle loads applied to the front and rear wheels of the vehicle; During departure control operation: Whether to execute the disengagement of the vehicle is commanded based on the information confirmed or calculated in the maximum traction force confirmation operation and the axle load calculation operation.

14. The method according to claim 13, wherein: Confirming the maximum wheel torque during the maximum traction confirmation operation includes: Determine the maximum front wheel torque, which is the maximum wheel torque without wheel slip on the front wheels; The maximum rear wheel torque is determined, which is the maximum wheel torque at which no wheel slip occurs on the rear wheels.

15. The method according to claim 13, further comprising: During departure control operation: In a case where the steering wheel of the vehicle is turned to a steering angle that generates a maximum traction force, when the axle load calculated in the axle load calculation operation is greater than a predetermined value or a maximum value, the vehicle is commanded to disengage.

16. The method according to claim 14, wherein: Implement various pitching movements including: Apply brakes to the front and rear wheels of the vehicle; The pitching motion is implemented by alternately and repeatedly applying the front wheel disengagement wheel torque and the rear wheel disengagement wheel torque to the front wheel motor and the rear wheel motor, respectively.

17. The method according to claim 16, wherein: Implementing various pitching movements further includes: The pitching motion is implemented by changing the application time or application frequency of the maximum front wheel torque and the maximum rear wheel torque applied to the front wheel motors and the rear wheel motors of the vehicle.

18. The method according to claim 17, further comprising: During departure control operation: When the vehicle is commanded to disengage, the front and rear wheel brakes are released; The maximum front wheel torque and the maximum rear wheel torque are applied to the front wheels and the rear wheels, respectively, in the forward direction of the vehicle.

19. The method according to claim 18, further comprising: During departure control operation: The system control is turned off when the vehicle reaches a determined speed after leaving the uneven driving surface.

20. A non-volatile computer-readable storage medium having recorded therein a program for executing a method for an electric vehicle to escape from an uneven driving road surface, the method for an electric vehicle to escape from an uneven driving road surface comprising a maximum traction force confirmation operation, an axle load calculation operation, and a drive-off control operation, During the maximum traction confirmation operation: Finding the steering angle that generates the most traction by applying drive torque while turning the steering wheel; After turning the steering wheel to the steering angle that generates maximum traction, confirm the maximum wheel torque that can be applied; During the axle load calculation operation: Implementing various pitching motions and repeatedly calculating the axle loads applied to the front and rear wheels of the vehicle; During departure control operation: Whether to execute the disengagement of the vehicle is commanded based on the information confirmed or calculated in the maximum traction force confirmation operation and the axle load calculation operation.

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