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Analysis of the shaking of new energy vehicles

Analysis of the shaking of new energy vehicles

Analysis of the shaking of new energy vehicles

1 With the development of modern industry, countries all over the world demand more and more energy. In recent years, the research and development of electric vehicles as a new generation of environmentally friendly vehicles has now received more and more attention from many countries. As an important part of the electric vehicle power system, the current application of the engine is to replace the traditional piston internal combustion engine with a new switched reluctance motor. Therefore, its research is also one of the cutting-edge hotspots in electric vehicle technology. The new switched reluctance motor has high efficiency, good starting performance, low cost, simple structure, wide speed range, can work under constant power state and constant torque state, and is suitable for the performance requirements of the automobile's power system. Its main disadvantage is: the torque will fluctuate within a certain range, it will cause vibration, easy to produce noise, and then reduce the comfort and smoothness of the vehicle. Sufficient attention and research should be paid to the problem of vehicle vibration caused by electric motors.
 
2 Establishment of electric vehicle vibration model
 
For the research on the vibration of electric vehicles, it is very important to establish a vibration model of the system. According to the actual structure of electric vehicles and the focus of the research questions, for electric vehicles as shown in 1, make the following assumptions:
 
(1) The mass distribution of the entire vehicle is symmetrical, and the structure of the vehicle is also symmetrical. The road surface has the same excitation on the left and right wheels of the vehicle, that is, the lateral angular vibration of the vehicle is not considered, and the entire vehicle system is regarded as a vertical vertical plane. Vibration system.
 
(2) Simplify the wheel to a spring without considering the mass, without considering the damping effect.
 
(3) Regardless of the various orders of vibration generated by the elasticity of the body and frame, the body and frame are regarded as rigid bodies.
 
(4) The non-suspended distributed masses of the front and rear axles and the car body are replaced by concentrated masses.
 
(5) The damping force and elastic force of the shock absorber of the wheel and the frame are a linear function of speed and displacement respectively, that is, the entire vehicle vibration system is regarded as a complete linear system.
 
Therefore, the five-degree-of-freedom vibration model of an electric vehicle is as shown, and the parameters in the model are as follows:
 
m equivalent mass of the body; m 1 equivalent mass of the front axle (including the mass of the motor); m 2 equivalent mass of the rear axle; m 3 equivalent mass of the human body and the seat; J body around the center of gravity of the body Moment of inertia; x 0 the displacement of the center of gravity of the vehicle body in the vertical direction; θ the angular displacement of the front and rear pitch of the vehicle body; x1 the vertical displacement of the front axle unsuspended mass; x 2 the vertical displacement of the rear axle unsuspended mass; x 3 Displacement of the human body and seat in the vertical direction; xp Displacement of the body under the seat in the vertical direction; k 1 stiffness coefficient of the front suspension; k 2 stiffness coefficient of the rear suspension; k 3 stiffness coefficient of the seat ; K 4 front wheel stiffness coefficient; k 5 rear wheel stiffness coefficient; c 1 damping coefficient of the front suspension shock absorber; c 2 damping coefficient of the rear suspension shock absorber; c 3 damping coefficient of the seat; l front and rear axles L 1 The horizontal distance from the front axle to the center of gravity of the body; l 2 The horizontal distance from the rear axle to the center of gravity of the body; l 3 The horizontal distance from under the seat to the center of gravity of the body; F(t) SR drive motor excitation.
 
3 Electric vehicle vibration simulation According to the system dynamics model established above, the differential equation of motion in matrix form can be obtained as M x + Cx + Kx = F. In the formula, each matrix and column vector drive the rotor and stator cores of the motor It is completely superposed by silicon steel sheets. The teeth and slots are evenly distributed on the inner circumference of the rotor core and the outer circumference of the stator core. The teeth are salient poles. This structure is also called double salient pole structure. Several types of windings are installed on each salient pole of the stator core. The windings on the two salient poles on the inner circumference of the stator are connected in series to form a group, and the rotor core is not equipped with concentrated windings.
 
Due to the non-linearity and saturation of the magnetic circuit, and the on-off characteristics of the circuit, generally according to the task to be studied, the electromagnetic energy in the motor (the part of the energy converted into mechanical energy in the motor) or the inductance characteristic curve is first segmented, and then Linearize again. After simplification, the electromagnetic torque Te is Te = 1 2 Ki 2, where i is the motor phase winding current, and K is the change rate of the winding inductance to the position angle. For the drive motor, the vibration and noise produced by it are the result of the combined action of the radial force and the tangential force between the rotor and the stator. According to the actual working conditions of the motor, its electromagnetic torque is fluctuating. Therefore, the relationship between tangential force and time is shown in 3, and the specific expression is F n = T e R,
 
n T≤t≤(n + 7 20) T 0,
 
(N + 7 20) T <t ≤ (n + 1) T (n = 0, 1, 2, ...) where R is the inner radius of the motor stator, and the period is T = 1 f = 60 / aN r, a is Motor speed, N r is the number of rotor poles, t is the acting time of the exciting force in one cycle.
 
4 The relationship between radial force and time
 
Due to the saturation and nonlinearity of the magnetic circuit of SRM, it is very difficult to accurately express the radial force. Starting from qualitative analysis, the following assumptions can be made:
 
① The magnetic circuit is linear; ② The radial force is concentrated on the stator poles, and the phase current is assumed to be constant. Considering that the tangential force and the radial force have the same period of action, as shown in 4, the relationship between the radial force and time can be expressed as F n = i 2 L min + aπK 30 (t-n T) 2 b 2 + (aπK 30)2 7 T 20-(t-n T)2,
 
n T ≤ t ≤ (n + 7 20) T 0, (n + 7 20) T <t ≤ (n + 1) T, (n = 0, 1, 2, ...) In the above formula, short air gap length b = R-r, r is the rotor radius; L min is the small inductance of the winding; i is the winding current.
 
Since the vehicle vibration system responds to the excitation of the motor () in the vertical direction, according to the principle of force synthesis and decomposition, the resultant force of the excitation source on the system in the vertical direction is F n = T e R cos aπ30 t-i 2 L min + aπK 30 (t-n T) 2 b 2 + (aπK 30) 2 7 T 20-(t-n T) 2 sin aπ30 t,
 
n T≤t≤(n + 7 20) T 0,
 
(N + 7 20) T <t ≤ (n + 1) T, (n = 0, 1, 2, ...) This force is the vertical excitation force of the SR drive motor vibration system.
 
Among them is the rate of change of winding inductance to position angle.
 
For the electric vehicle shown in 1, a set of specific parameters are given below and then simulated.
 
m = 1354.
 
5kg, m 1 = 80kg, m 2 = 68.5kg, m 3 = 102kg, J = 64.30kg m 2, c 1 = 600N s/ m, c 2 = 550N s/ m, c 3 = 400N s/ m, k 1 = 18000N/m, k 2 = 16997N/m, k 3 = 5200N/m, k 4 = 118000N/m, k 5 = 118000N/m, l 1=1.
 
11m; l 2 = 1.
 
30m; l 3 = 0.
 
20m; the inner radius of the stator R=0.
 
05m; motor () speed a = 1500r/min; rotor pole number N r = 6; short air gap length b = 0.
 
001m; winding current i = 1 A; the rate of change of winding inductance to position angle K = 82.
 
5; Small winding inductance L min = 4.
 
95 H.
 
The New mark -β method is applied to this vehicle system, and β=1/4 and δ=1/2. After programming through Matlab software, the displacement x of the equivalent mass m 3 of the human body and the seat can be obtained after running. 3 response as shown, speed x 3 response as shown. It can be seen through calculation that the radial force of the motor is the main excitation force that causes the vibration of the vehicle body and the human body-seat.
 
4 Conclusion
 
When studying the vibration problem of electric vehicles with SRM as the driving source, we should first start from the whole vehicle system, boldly simplify it, and make reasonable assumptions, using the drive motor as the excitation source, so as to establish a system vibration model, and then obtain the vibration differential. Equations, and then further analyze the steady-state response of the body, the human body and the seat, and the response results will serve as an important basis for vehicle design. From the perspective of frequency domain, the harmonic frequency of the exciting force should be avoided as far as possible to be close to the natural frequency of the stator, and the output frequency of the motor vibration and the natural frequency of the car must be avoided to be close to each other. Only in this way can the resonance phenomenon of the whole vehicle be avoided. Therefore, we must comprehensively consider as much as possible, and consider its impact on the vibration excitation of the entire vehicle while suppressing the vibration of the drive motor itself, so as to improve the ride comfort and comfort of the electric vehicle.

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