Traction control method for electric bicycle

Abstract

The present invention relates to a traction control method for an electric bicycle, comprising the following steps: S1, collecting the wheel speed of a driving wheel at time t1; S2, collecting the wheel speed of the driving wheel again at time t2; S3, calculating the wheel speed change rate of the driving wheel in the (t2-t1) time period; S4, intervening or not intervening in traction control according to the wheel speed change rate of the driving wheel. The present invention relies on a control algorithm to achieve a traditional traction control effect using existing conditions without adding any components. When the driving wheel slips, the motor electronic control quickly intervenes, and the slip is quickly curbed by reducing the output power or even generating electronic braking, thereby increasing driving safety and having strong applicability.

Description

Technical Field

[0001] The invention relates to the technical field of electric bicycles, in particular to a low-cost traction control method for electric bicycles. Background Art

[0002] The traction control of traditional electric bicycles is generally achieved by installing a speed sensor on the front and rear wheels to collect the wheel speeds of the front and rear wheels respectively, and then using a six-axis sensor to determine whether the drive wheel is slipping.

[0003] However, because speed sensors, and even six-axis sensors, need to be installed on both the front and rear wheels, the biggest problem with this control method in the increasingly competitive electric bicycle market is its high cost and limited applicability. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a traction control method for an electric bicycle, which can achieve the same traction control effect without adding additional sensors.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for controlling the traction force of an electric bicycle, comprising the following steps:

[0006] S1, collecting the driving wheel speed at time t1;

[0007] S2, collecting the driving wheel speed again at time t2;

[0008] S3, calculating the wheel speed change rate of the driving wheel in the time period (t2-t1);

[0009] S4: Intervention or non-intervention of traction control according to the wheel speed change rate of the driving wheels.

[0010] Furthermore, in order to achieve the purpose of low cost, the present invention does not need to obtain the driving wheel speed by installing a speed sensor. The driving wheel speed described in the present invention can be obtained by the output signal of the internal position sensor of the motor, or by electronically sampling the back electromotive force of the internal coil of the motor.

[0011] Furthermore, in step S4 of the present invention, the wheel speed change rate of the driving wheel includes the wheel speed change rate of the driving wheel in a starting acceleration state and the wheel speed change rate of the driving wheel in a non-starting acceleration state.

[0012] Furthermore, in step S4 of the present invention, in the starting acceleration state, the following steps are included:

[0013] S41, comparing the wheel speed change rate of the driving wheel with a set threshold value, if it is greater than the set threshold value, determining whether the driving wheel is idling, if so, traction control does not intervene; if not, executing the next step;

[0014] S42: Determine whether the driving wheel is in a starting slip state. If so, traction control intervenes; if not, traction control does not intervene.

[0015] Furthermore, in step S4 of the present invention, in a non-starting acceleration state, if the wheel speed change rate of the driving wheel is greater than a set threshold, the traction control intervenes; if not, the traction control does not intervene.

[0016] Furthermore, the traction control intervention method described in the present invention is to reduce the electronic control output power or the motor enters the braking mode, so as to prevent the motor speed from further sudden changes.

[0017] Furthermore, the present invention determines whether the driving wheel is in an idling or slipping state by calculating the slope K of the actual current and the speed at a certain time point within a set time period. I and K V , the state of the driving wheel is obtained by comparing the slope.

[0018] Furthermore, the threshold value of the present invention is set as follows: Where Δt is the sampling time interval, N x is the output torque of the motor at a certain speed, F3 is the air thrust generated at this wind speed measured by the wind tunnel at the corresponding vehicle speed, m is the total mass of the vehicle and its load, and r is the outer radius of the drive wheel.

[0019] The beneficial effect of the present invention is that it solves the defects existing in the background technology, relies on the control algorithm and utilizes the existing conditions to achieve the traditional traction control effect without adding any devices. When the driving wheel slips, the motor and electronic control quickly intervene to quickly curb the slipping phenomenon by reducing the output power or even generating electronic braking, thereby increasing driving safety and having strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a method principle block diagram of an embodiment of the present invention;

[0021] Figure 2 is a comparison diagram of the motor speed and the electronic control output current in the idling and starting slipping states of the embodiment of the present invention;

[0022] Figure 3 is a force decomposition diagram of a simplified mass model according to an embodiment of the present invention;

[0023] Figure 41 is a graph showing the load characteristic curve of a motor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will now be described in further detail in conjunction with the accompanying drawings and preferred embodiments. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0025] like Figure 1 The traction control method of an electric bicycle shown in the figure first determines whether the driving state is a starting acceleration state or a non-starting acceleration state.

[0026] In the starting acceleration state, the following steps are included:

[0027] S1, collecting the driving wheel speed;

[0028] S2, collecting the driving wheel speed again after a delay;

[0029] S3, calculating the wheel speed change rate of the driving wheel during this period;

[0030] S4. Determine whether the drive wheel is idling. If so, traction control will not intervene. If not, determine whether the drive wheel is in a slipping state at the start. If so, traction control will intervene to reduce the electronic control output power, or even put the motor into braking mode to prevent further sudden changes in the motor speed. If not, traction control will not intervene.

[0031] In the non-starting acceleration state, steps S1 to S3 are the same. In step S4, if the wheel speed change rate of the driving wheel is greater than the set threshold, the traction control intervenes, thereby reducing the electronic control output power, and even allowing the motor to enter the braking mode to prevent further sudden changes in the motor speed; if not, the traction control does not intervene.

[0032] The following is a further detailed description based on the principle.

[0033] The driving wheel speed of the present invention can be known by the real-time rotation speed of the motor through the output signal of the internal position sensor of the motor or the back electromotive force of the internal coil of the motor sampled by the electronic control.

[0034] For the determined vehicle model, its rated voltage, rated speed, outer wheel diameter and vehicle weight are all determined. In actual application, considering that the maximum driving wheel speed change that can be generated when the vehicle lands is: headwind + downhill + light driver (30kg can be preset), the maximum slope of ordinary roads is usually 10%. If a level 5 headwind wind is preset, it is extremely rare to meet the above three conditions at the same time.

[0035] Since the driving wheels are idling, the vehicle acceleration will be > a during the startup phase.TH ,Therefore, it is necessary to determine whether the vehicle is in a normal idling state or slipping.

[0036] The method of judging Figure 2 As shown,

[0037] First, let's look at the starting slip curve. There are two turning points in the starting slip curve, T1 and T4.

[0038] At time 0-T1, the current rises rapidly to I1 (I1≤electronic control current limit value, and>I3). The driving wheel tire is in a static friction state at time 0. Due to the slight gap in the mechanical transmission structure and the rotational deformation of the tire, even if the vehicle does not move, the electronic control may detect the relative speed between the motor stator and rotor, indicating that a small amount of movement has occurred, or a small amount of rolling friction occurs in the tire at this time, so that the motor rotates. This is the existence of n1 at time T1;

[0039] At time T1-T4, the tire changes from static friction (or rolling friction) to sliding friction, the tire grip decreases rapidly, the electronic control output load current decreases, the motor speed increases rapidly, and the vehicle acceleration is calculated to be > a TH , and finally stabilized at time T4. Due to the existence of sliding friction, the final stable current I2> idling stable current I4, the stable speed n2 is less than n4, and finally formed Figure 2 The starting slip curve.

[0040] Looking at the idling curve again, there are two turning points in the idling curve, T2 and T3;

[0041] At time 0 to T2, due to the rotational inertia formed by the motor rotor + tire, the electronic control needs to output part of the load current, and the speed rises rapidly to n3 (n3 is not necessarily greater than n2, depending on the working conditions, n2 may be large or small, but regardless of the size, it does not affect the state judgment).

[0042] At time T2-T3, when the speed reaches time T2, the motor back electromotive force increases, the output current decreases, and the speed slope decreases slightly compared to time 0-T2, and finally the speed stabilizes at time T3.

[0043] When the car is in an idling state, such as the idling curve, in the time period from 0 to T2, the corresponding current and speed curves are set, and the slopes of the two curves at a certain time point in this time period are set as K I1 and K V1 Since the mass and rated power of the driving wheels have been designed when the vehicle is designed, K I1 and K V1It can be obtained through testing, and the slope of the curve from 0 to T2 can be written into the electronic control or other calculation unit in advance.

[0044] Then, the slope K of the actual current and speed at a certain time point between 0 and T1 can be obtained by sampling I2 and K V2 Determine whether it is idling or not. The characteristic of non-idling is that K I1 <K I2 And K V2 >K V1 ,

[0045] In the state where idling has been eliminated during the time period from 0 to T1, the next step is to determine whether the vehicle acceleration is greater than a during the time period from T1 to T4. TH , it can be determined that the drive wheel has slipped.

[0046] For any time, a at any speed TH , calculated as follows:

[0047] like Figure 3 As shown in the figure, the box is a simple mass model of the whole vehicle + driver, where o is the center of gravity of the model. The model is on a slope, the weight of the whole vehicle is m1kg, and the weight of the driver is m2kg. A plane coordinate system is established with the center of gravity o as the origin, the x-axis is parallel to the slope, and the y-axis is perpendicular to the slope. The maximum slope of a general road is i=10 (i.e.: length L / height H=10), and the corresponding slope angle tangent value tanθ=10, and θ≈5.71° is derived.

[0048] The gravity generated by the center of gravity is G=mg, where g is the acceleration due to gravity and can be approximately taken as 10m / S 2 , m=m1+m2, the component force generated by gravity in the slope direction is: F1=sinθ*G=sin5.71*10*(m1+m2), and F1≈(m1+m2)N; to prevent the traction protection from being triggered by mistake, m2 should be as small as possible. For example, the driver's weight is generally not less than 30kg, so 30kg can be taken.

[0049] The motor can be measured under rated conditions by a dynamometer to obtain a dynamometer curve of speed and output torque. Figure 4 As shown, this curve combined with voltage compensation is written into the traction control system, and the vehicle will know the output torque N of the motor at any speed. x The unit is Newton meter. If the outer radius of the motor tire is r meters, then the corresponding torque that the motor can generate at a certain speed is obtained. ox.

[0050] Since the maximum wind speed of level 5 is 10.7m / S, the air thrust F3 generated at this wind speed can be measured through the wind tunnel at any vehicle speed.

[0051] when

[0052] Through wind tunnel experiments, the air thrust of the vehicle from 0 to the maximum rated speed V at the maximum wind speed of level 5 is made into F3-V x The curve is written into the traction control system.

[0053] In summary, the thrust of the vehicle at any vehicle speed can be obtained Then, according to the acceleration formula F=ma, the vehicle acceleration threshold at any speed is obtained. After simplification

[0054] In addition, the acceleration formula defines a = ΔV / Δt, where ΔV can be calculated by sampling the driving wheel speed twice, and Δt can be the manually set speed sampling time interval. Under this condition, the driving wheel speed n is sampled. t1 , since the outer radius of the tire is known, it can be set to r. At this time, the vehicle speed V t1 =2πrn t1 , sample the driving wheel speed n after a delay of Δt t2 , at this time the vehicle speed V t2 =2πrn t1 At this time, the average acceleration of the vehicle within the Δt time is Now we need to judge whether a and a TH The result can be used as a basis for triggering traction control. Even in actual applications, when encountering more demanding conditions, such as encountering a 10-level gale and a steep downhill slope, the measured vehicle acceleration is greater than a TH , accidentally triggering the traction control system, the result is also slowing down when going downhill, which is also helpful for driving safety.

[0055] Except for artificial idling, the acceleration of the vehicle measured at any speed will not be greater than a TH If it is greater than, it means that the drive wheel is slipping and the traction protection should be triggered to prevent further slipping.

[0056] The above description only describes the specific implementation mode of the present invention. Various examples do not limit the essential content of the present invention. After reading the description, ordinary technicians in the relevant technical field can modify or deform the specific implementation modes described above without departing from the essence and scope of the invention.

Claims

1. A method for controlling traction of an electric bicycle, characterized in that: The following steps are included: S1, collecting the driving wheel speed at time t1; S2, collecting the driving wheel speed again at time t2; S3, calculating the wheel speed change rate of the driving wheel in the time period (t2-t1); S4, intervening or not intervening traction control according to the wheel speed change rate of the driving wheel; In the step S4, the wheel speed change rate of the driving wheel includes the wheel speed change rate of the driving wheel in the starting acceleration state and the wheel speed change rate of the driving wheel in the non-starting acceleration state; In the step S4, in the starting acceleration state, The following steps are included: S41, comparing the wheel speed change rate of the driving wheel with a set threshold value, if it is greater than the set threshold value, determining whether the driving wheel is idling, if so, traction control does not intervene; if not, executing the next step; S42, determining whether the driving wheel is in a starting slip state, if so, the traction control is intervened; if not, the traction control is not intervened; The method for judging whether the driving wheel is in idling or slipping state is to calculate the slope K of the actual current and the speed at a certain time point within the set time period. I and K V , the state of the driving wheel is obtained by comparing the slopes; The threshold is set as follows: a TH =Δt*[1+(N X / r+ F3) / m], where Δt is the sampling time interval, N X is the output torque of the motor at a certain speed, F3 is the air thrust generated at this wind speed measured by the wind tunnel at the corresponding vehicle speed, m is the total mass of the vehicle and its load, and r is the outer radius of the drive wheel.

2. The electric bicycle traction control method according to claim 1, characterized in that: The driving wheel speed is obtained by outputting a signal from a position sensor inside the motor, or by electronically sampling the back electromotive force of a coil inside the motor.

3. The electric bicycle traction control method according to claim 1, characterized in that: In the step S4, in the non-starting acceleration state, if the wheel speed change rate of the driving wheel is greater than a set threshold, the traction control intervenes; if not, the traction control does not intervene.

4. The electric bicycle traction control method according to claim 1 or 3, characterized in that: The traction control intervention method is to reduce the electronic control output power or the motor enters the braking mode.

Images