KR102602922B1 - Creep torque control method of electric vehicles - Google Patents

Abstract

The present invention improves the creep driving feeling and prevents deterioration of braking performance by varying the creep torque reduction speed according to the strength of braking and road conditions. In the present invention, the creep torque demand according to the braking force in the creep driving mode is secured; When braking force is applied during creep driving, the creep torque descent rate is calculated based on the braking force, braking force change rate, and creep torque demand; Calculating creep torque by reflecting the creep torque decline rate in the creep torque demand; A creep torque control method for an electric vehicle is introduced, characterized in that creep driving of the vehicle is controlled by driving a motor using the calculated creep torque.

Description

CREEP TORQUE CONTROL METHOD OF ELECTRIC VEHICLES}

The present invention relates to a creep torque control method for an electric vehicle that improves the creep driving feeling and prevents deterioration of braking performance by varying the creep torque reduction speed according to the strength of braking and road conditions.

In the case of electric vehicles driven using electric motors, unlike engine vehicles, there is no idle torque, so separate torque control is required for creep driving.

When braking force is applied during creep driving in an electric vehicle, the creep torque acts adversely as a resistance component to the braking force of the braking device, resulting in unnecessary fuel efficiency loss. Therefore, as shown in FIG. 1, control is performed to reduce creep torque according to the degree of braking (braking force or brake pedal operation amount).

However, in the existing creep torque control, when mild braking (braking force BF1↔BF2) is repeated, frequent reduction and increase in creep torque are repeated as shown in FIG. 2, resulting in excessive acceleration and deceleration compared to the braking intention, resulting in a decrease in the creep driving feeling. There was.

However, this problem can be alleviated by increasing the BF1/BF2 value, but in this case, the reduction of creep torque compared to braking is delayed, leading to increased braking resistance and loss of fuel efficiency.

The matters described as background technology above are only for the purpose of improving understanding of the background of the present invention, and should not be taken as acknowledgment that they correspond to prior art already known to those skilled in the art.

KR 10-1535020 B

The present invention was developed to solve the problems described above, and the creep torque reduction speed is varied according to the strength of braking and road conditions to improve the creep driving feeling and prevent the braking performance from being deteriorated during creep driving. The purpose is to provide a torque control method.

The configuration of the present invention for achieving the above object includes: securing, by a controller, a creep torque demand according to braking force in a creep driving mode; When a braking force is applied during creep driving, the controller calculates a creep torque descent rate based on the braking force, the braking force change rate, and the creep torque demand; A step of the controller calculating creep torque by reflecting the creep torque decline rate in the creep torque demand amount; and controlling, by the controller, the creep driving of the vehicle by driving the motor based on the calculated creep torque.

The creep torque drop rate can be calculated by setting the creep torque drop rate control parameter based on the braking force change rate and reflecting this in the following equation (1).

.........(One)

L: Creep torque fall rate

CT: Creep torque requirement

BF1: Braking force reference point where creep torque reduction begins

BF2: Braking force reference point at which reduction of creep torque ends

: Braking force change rate

p: Creep torque fall rate control parameter

The creep torque descent rate control parameter can be set as a function of the braking force change rate and road slope.

The creep torque drop rate control parameter may be set in proportion to the braking force change rate.

The creep torque descent rate control parameter may be set to decrease as the uphill slope increases in the case of an uphill slope, and may be set to increase as the downhill slope increases in the case of a downhill slope.

The amount of change in the creep torque descent rate control parameter on the downhill slope according to the change in the braking force change rate may be set to be greater than the amount of change in the creep torque descent rate control parameter on the uphill slope.

The creep torque can be calculated using equation (2) below.

T = CT + L * t................................................(2)

T: Cryptotalk

CT: Creep torque requirement

L: Creep torque fall rate

t : time

When reducing creep torque due to braking, the rate of creep torque decline can be limited so that it does not exceed in the negative direction.

The creep torque reduction speed is controlled so that the smaller the braking force change rate is, the slower the creep torque reduction rate is. The greater the braking force change rate, the faster the creep torque reduction rate can be controlled.

In the present invention, a method for controlling creep torque of an electric vehicle includes the steps of: determining, by a controller, whether the vehicle has entered a creep driving mode; When entering the creep driving mode, the controller calculates a creep torque demand for maintaining the creep driving speed and a creep torque demand required to be reduced according to braking force; A step of the controller determining whether braking force is applied; Calculating, by the controller, a creep torque descent rate control parameter as a function of the braking force change rate and road slope when the braking force exceeds the applied braking force reference value at which creep torque reduction begins; Calculating, by the controller, a creep torque falling rate based on the relationship between the calculated creep torque falling rate control parameter, braking force, braking force change rate, and creep torque demand; Calculating creep torque, by the controller, by adding the calculated creep torque decline rate multiplied by time and the creep torque demand amount; and a step of controlling, by the controller, the creep driving of the vehicle by providing a command value of the calculated creep torque to the motor.

Through the above-mentioned problem solving means, the present invention slows the creep torque reduction speed in the case of mild braking with a small braking force change rate during creep driving, thereby preventing excessive deceleration compared to the braking intention, thereby improving the creep driving feeling. , In the case of rough braking with a large rate of change in braking force, the creep torque reduction speed is increased, so that the braking resistance component is removed according to the intention of braking, which has the effect of preventing the braking performance from being deteriorated during creep driving.

In addition, in the case of a downhill slope, the creep torque reduction rate is controlled to be reduced faster than on flat ground, thereby preventing the braking performance from deteriorating by quickly removing the braking resistance component, and in the case of an uphill slope, the creep torque reduction speed is slower than on flat ground. By controlling it to reduce it, the braking resistance component is maintained to improve riding comfort, which has the effect of improving the creep driving feeling.

1 is a diagram showing the relationship between creep torque increasing and decreasing according to braking force.
Figure 2 is a diagram for explaining the repetition of acceleration and deceleration as creep torque is repeatedly reduced and increased.
Figure 3 is a diagram illustrating a creep torque control system applied to the present invention.
Figure 4 is a diagram showing a comparison between the acceleration (a) of a vehicle to which the creep torque descent rate of the present invention is not applied and the acceleration (a') of a vehicle to which the creep torque descent rate of the present invention is applied.
Figure 5 is a diagram showing the creep torque descent rate control parameters set according to the braking force change rate and road slope in the present invention.
Figure 6 is a diagram for explaining the difference in the amount of change in the creep torque descent rate control parameter according to the change in road slope and braking force change rate in the present invention.
Figure 7 is a flowchart sequentially explaining the creep torque control process according to the present invention.
Figure 8 is a diagram comparing the creep torque behavior to which the present invention is applied and the existing creep torque behavior.
Figure 9 is a diagram comparing the behavior of creep torque on a downhill slope and on flat land when the present invention is applied.

A preferred embodiment of the present invention will be described in detail with the accompanying drawings as follows.

The creep torque control method of an electric vehicle according to the present invention includes the steps of: a controller (CLR) securing a creep torque demand according to braking force in a creep driving mode; When a braking force is applied during creep driving, the controller (CLR) calculates a creep torque descent rate based on the braking force, the braking force change rate, and the creep torque demand; A controller (CLR) calculating creep torque by reflecting the creep torque decline rate in the creep torque demand; and controlling, by the controller (CLR), the creep driving of the vehicle by driving the motor 9 based on the calculated creep torque.

Control of the creep torque is achieved through the creep torque control system shown in FIG. 3. The creep torque control system includes a creep torque demand calculation unit 1, a creep torque decline rate calculation unit 3, and a creep torque control system. It is composed of a controller (CLR) including a calculation unit (5), an operability filter (7), and a motor (9).

If explained in detail with reference to FIG. 3, the creep torque demand calculation unit 1 of the controller (CLR) calculates the creep torque demand according to the braking force in the creep driving mode, for example, to maintain the creep driving speed constant. The creep torque demand can be calculated, and when braking force is applied, the creep torque demand decreases, making it possible to calculate the creep torque demand reflecting the braking force.

In addition, when braking force is applied during creep driving, the creep torque descent rate calculation unit 3 of the controller (CLR) calculates the creep torque descent rate based on the braking force, braking force change rate, and creep torque demand.

For example, the rate of change in braking force can be obtained by removing noise (e.g., low-pass filter) from the differential value of the braking force. When the braking force exceeds the reference value at which the reduction of the creep torque begins, the rate of change of the braking force is calculated based on the above factors. The creep torque decline rate is calculated.

In addition, the creep torque calculation unit 5 of the controller (CLR) calculates the creep torque by reflecting the creep torque decline rate in the creep torque demand amount.

Then, the motor 9 is driven by the creep torque calculated by the creep torque calculation unit 5 to control the creep driving of the vehicle.

In addition, a low-pass filter type drivability filter 7 may be provided between the controller (CLR) and the motor 9 to provide a smooth ride, and the creep torque signal is transmitted through the drivability filter 7. It is then applied to the motor 9 to control the driving of the motor 9.

That is, according to the above configuration, in the case of mild braking where the rate of change in braking force is small during creep driving, the creep torque reduction speed is slowed to prevent excessive deceleration compared to the braking intention, thereby improving the creep driving feeling.

On the other hand, in the case of rough braking with a large rate of change in braking force, the creep torque reduction speed is increased, so that the braking resistance component is removed according to the braking intention, thereby preventing the braking performance from being deteriorated during creep driving.

In addition, the creep torque drop rate can be calculated by setting the creep torque drop rate control parameter (p) based on the braking force change rate and reflecting this in Equation (1) below.

..........(One)

L: Creep torque fall rate

CT: Creep torque requirement

BF1: Braking force reference point where creep torque reduction begins

BF2: Braking force reference point at which reduction of creep torque ends

: Braking force change rate

p: Creep torque fall rate control parameter

At this time, the creep torque drop rate control parameter (p) can be set in proportion to the braking force change rate and can be set to a value between 0 and 1.

That is, Figure 4 shows a comparison between the acceleration (a) of a vehicle to which the creep torque descent rate of the present invention is not applied and the acceleration (a') of a vehicle to which the creep torque descent rate is applied. The accelerations a and a' are as follows. It can be described as formula (1-1) and formula (1-2).

......(1-1)

.....(1-2)

M: vehicle weight

θ: road slope

A: Reducer gear ratio ÷ tire diameter

T: Cryptotalk

BF: Braking power

In addition, the purpose of applying the creep torque drop rate in the present invention is to control the acceleration to be greater (smaller deceleration) than the existing theoretical acceleration a in the case of mild braking, and to control the acceleration to occur at the level a in the case of rough braking. It can be said to be controlled. Therefore, the present invention can set the design goal as a' ≥ a, d(a')/dt ≥ d(a)/dt, and compare the time derivatives of a and a' to use the following equation (1-3) It can be organized as follows.

.............(1-3)

In the above equation (1-3), the creep torque drop rate can be related to the braking force change rate, d(BF)/dt, so the creep torque drop rate control parameter (p) can be set as a control variable. In other words, the creep torque drop rate control parameter (p) is set closer to the maximum value of 1 as the braking force change rate increases (rough braking), and as the braking force change rate becomes smaller (mild braking), it is set closer to the minimum value of 0, using the formula ( 1) It can be organized as follows.

Meanwhile, in the present invention, the creep torque descent rate control parameter (p) can be set as a function of the braking force change rate and road slope. The road slope can be calculated using vehicle acceleration sensor values and vehicle speed information.

At this time, the creep torque drop rate control parameter (p) can be set in proportion to the braking force change rate and can be set to a value between 0 and 1.

In addition, the creep torque descent rate control parameter (p) is set to become smaller as the uphill slope increases in the case of an uphill slope, and in the case of a downhill slope, the creep torque descent rate control parameter (p) is set to become smaller as the downhill slope increases. (p) is set large.

Additionally, the amount of change in the creep torque descent rate control parameter (p) on the downhill slope according to the change in the braking force change rate may be set to be greater than the amount of change in the creep torque descent rate control parameter (p) on the uphill slope.

To explain, the creep torque descent rate control parameter (p) can be set as a plurality of lines (or relational equations) according to the braking force change rate and road slope, as shown in FIG. 5. That is, the creep torque drop rate control parameter (p) can be set closer to the maximum value of 1 as the braking force change rate increases, and closer to the minimum value of 0 as the braking force change rate decreases.

In addition, when the road is sloped downhill as shown in Figure 6, the acceleration of the vehicle itself increases, so the creep torque descent rate control parameter (p) is designed to be sensitive to changes (p1 ~ 1) according to the increase in the braking force change rate. If the slope is uphill, the vehicle's acceleration itself decreases, so on the contrary, it is designed to be insensitive.

In addition, the creep torque calculated by the creep torque calculation unit 5 of the present invention can be calculated using the following equation (2).

T = CT + L * t................................................(2)

T: Cryptotalk

CT: Creep torque requirement

L: Creep torque fall rate

t : time

In other words, the creep torque is calculated by adding the previously calculated creep torque descent rate multiplied by time (a negative value) to the creep torque demand. From the moment the braking force is applied and the braking force becomes BF1 or more, the creep torque is calculated using the above formula ( It is calculated by 2).

Hereinafter, the creep torque control process according to the present invention will be described with reference to FIG. 7.

While the vehicle is driving, signals reflecting the vehicle's driving condition are input to the controller (CLR). First, the acceleration sensor and vehicle speed signals are input to calculate the road slope (S10).

Then, the braking force is differentiated to calculate the braking force change rate (S20).

Next, it is determined whether the vehicle has entered the creep driving mode (S30), and if the determination results indicate that the vehicle has entered the creep driving mode, the creep torque demand is calculated (S40). The creep torque demand at this time is the torque demand to maintain the creep driving speed in a state where no braking force is applied.

Additionally, assuming a state in which braking force is applied, the creep torque demand reduced according to the braking force is also calculated (S50).

Afterwards, it is determined whether the braking force is applied (S60), and as a result of the judgment, if the braking force is applied and exceeds BF1, which is the standard value at which creep torque reduction begins, the creep torque descent rate control parameter (p) is adjusted as a function of the braking force change rate and road slope. It is calculated (S70).

Next, the creep torque fall rate is calculated using equation (1), which is organized in the relationship between the calculated creep torque fall rate control parameter (p), braking force, braking force change rate, and creep torque demand (S80). At this time, when the creep torque is reduced due to the braking, the creep torque decline rate is limited so that it does not exceed in the negative direction.

Then, the calculated creep torque decline rate multiplied by time is added to the creep torque demand to calculate creep torque (S90).

Next, the calculated creep torque command value is passed through the drivability filter 7 (S100) and then provided to the motor 9 (S110), so that the creep torque of the vehicle can be controlled by driving the motor 9. do.

Figure 8 is a diagram comparing the creep torque behavior according to the application of the present invention and the existing creep torque behavior without the application of the present invention. The braking situation on the left is relatively rough braking behavior, and the braking situation on the right is This is the result of relatively mild braking behavior.

In the case of the braking situation on the left, the creep torque reduction speed at the beginning of braking appears to be alleviated compared to the existing method, but after reaching the braking force and braking force rate that can be recognized as rough braking, creep occurs. Since the torque drop rate limit value is reduced, it can be seen that the creep torque is quickly reduced at a similar rate as before.

In the case of the braking situation on the right, in the existing method, the creep torque is already reduced to 0 at the time (t) when the application of the braking force ends, but in the case of the present invention, the braking force and braking force change rate that can be recognized as mild braking (Brake Force Rate), the creep torque descent rate limit value is maintained relatively high, so the creep torque is reduced slowly, and it can be seen that the creep torque still shows a large value even at the same time (t).

Figure 9 is a diagram comparing the behavior of creep torque on downhill slope and flat ground. Although it is a mild braking situation, since it is a -10% downhill slope, the creep torque descent rate is set relatively higher than on flat ground, and the creep torque is reduced quickly. You can check it.

In this way, in the case of mild braking where the rate of change in braking force is small during creep driving, the present invention slows the creep torque reduction speed to prevent excessive deceleration compared to the braking intention, thereby improving the creep driving feeling.

On the other hand, in the case of rough braking with a large rate of change in braking force, the creep torque reduction speed is increased, so that the braking resistance component is removed according to the braking intention, thereby preventing the braking performance from being deteriorated during creep driving.

In addition, in the case of a downhill slope, the creep torque reduction rate is controlled to be reduced faster than on level ground even with mild braking, thereby preventing the braking performance from being deteriorated by quickly removing the braking resistance component.

On the other hand, in the case of an uphill slope, the creep torque reduction rate is controlled to be reduced more slowly than on level ground even with rough braking, thereby improving riding comfort by maintaining the braking resistance component, thereby improving the creep driving feeling.

Meanwhile, although the present invention has been described in detail only with respect to the above-mentioned specific examples, it is clear to those skilled in the art that various changes and modifications are possible within the technical scope of the present invention, and it is natural that such changes and modifications fall within the scope of the appended patent claims. .

1: Creep talk demand calculation unit
3: Creep torque decline rate calculation unit
5: Cryptocurrency calculation unit
7: Driveability filter
9: motor
CLR: Controller

Claims (10)

A step of the controller securing a creep torque demand according to braking force in a creep driving mode;
When a braking force is applied during creep driving, the controller calculates a creep torque descent rate based on the braking force, the braking force change rate, and the creep torque demand;
A step of the controller calculating creep torque by reflecting the creep torque decline rate in the creep torque demand amount; and
A controller controls creep driving of the vehicle by driving a motor based on the calculated creep torque,
A creep torque control method for an electric vehicle, characterized in that the creep torque drop rate is calculated by setting a creep torque drop rate control parameter (p) based on the braking force change rate and reflecting this in the following equation (1).
.........(One)
L: Creep torque fall rate
CT: Creep torque requirement
BF1: Braking force reference point where creep torque reduction begins
BF2: Braking force reference point at which creep torque reduction ends
: Braking force change rate
p: Creep torque fall rate control parameter delete In claim 1,
A creep torque control method for an electric vehicle, wherein the creep torque descent rate control parameter is set as a function of the braking force change rate and road slope. In claim 3,
A creep torque control method for an electric vehicle, wherein the creep torque descent rate control parameter is set in proportion to the braking force change rate. In claim 3,
The creep torque descent rate control parameter is set to decrease as the uphill slope increases in the case of an uphill slope, and is set to increase as the downhill slope increases in the case of a downhill slope. A creep torque control method for an electric vehicle, characterized in that. In claim 5,
A creep torque control method for an electric vehicle, wherein the amount of change in the creep torque descent rate control parameter on the downhill slope according to the change in the braking force change rate is set to be larger than the change in the creep torque descent rate control parameter on the uphill slope. A step of the controller securing a creep torque demand according to braking force in a creep driving mode;
When a braking force is applied during creep driving, the controller calculates a creep torque descent rate based on the braking force, the braking force change rate, and the creep torque demand;
A step of the controller calculating creep torque by reflecting the creep torque decline rate in the creep torque demand amount; and
A controller controls creep driving of the vehicle by driving a motor based on the calculated creep torque,
A creep torque control method for an electric vehicle, characterized in that the creep torque is calculated by the following equation (2).
T = CT + L * t................................................(2)
T: Cryptotalk
CT: Creep torque requirement
L: Creep torque fall rate
t : time In claim 1,
A creep torque control method for an electric vehicle, characterized in that when reducing creep torque due to braking, the rate of creep torque decline is limited so that it does not exceed in the negative direction. In claim 1,
The creep torque reduction speed is controlled so that the smaller the braking force change rate is, the slower the creep torque reduction rate is.
A creep torque control method for an electric vehicle, characterized in that the creep torque reduction rate is controlled so that the greater the braking force change rate, the faster the creep torque reduction rate. As a method of controlling creep torque of an electric vehicle,
A controller determining whether the vehicle has entered a creep driving mode;
When entering the creep driving mode, the controller calculates a creep torque demand for maintaining the creep driving speed and a creep torque demand required to be reduced according to braking force;
A step of the controller determining whether braking force is applied;
Calculating, by the controller, a creep torque descent rate control parameter as a function of the braking force change rate and road slope when the braking force exceeds the applied braking force reference value at which creep torque reduction begins;
Calculating, by the controller, a creep torque falling rate based on the relationship between the calculated creep torque falling rate control parameter, braking force, braking force change rate, and creep torque demand;
Calculating creep torque, by the controller, by adding the calculated creep torque decline rate multiplied by time and the creep torque demand amount; and
A method of controlling creep torque of an electric vehicle comprising: controlling creep driving of the vehicle by providing a command value of the calculated creep torque to the motor, by a controller.

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