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1 With the development of modern industry, the demand for energy in countries around the world is increasing. In recent years, research and development as a new generation of environmentally-friendly cars, electric vehicles, has become more and more important in many countries. As the most important component of the electric vehicle powertrain system, the most widely used engine is the replacement of the traditional piston-type internal combustion engine with a new type of switched reluctance motor. Therefore, its research is also one of the hot spots in the field of electric vehicle technology. The new type of switched reluctance motor has high efficiency, good start-up performance, low cost, simple structure and wide range of speed regulation. It can work in constant power state and constant torque state and is suitable for the performance requirements of the automotive power system. Its main disadvantage is that the torque will fluctuate within a certain range, it will cause vibration, and it is easy to produce noise, which in turn will reduce the comfort and the peace of the vehicle. Motor-induced vehicle vibration problems should be given enough attention and research.
2 Establishment of vibration model for electric vehicles
For the study of the vibration problem of electric vehicles, it is very important to establish a system vibration model. According to the actual structure of the electric vehicle and the focus of the research problem, the following assumptions are made for electric vehicles as shown in Fig. 1.
(1) The vehicle mass distribution is symmetrical, the structure of the car is also symmetrical, and the road surface has the same incentive for the left and right wheels of the car. That is, regardless of the transverse vibration of the car, the entire car system is considered as a vertically oriented surface. Vibration system.
(2) Simplify the wheel to a massless spring without considering the damping effect.
(3) Regardless of the vibrations generated by the elasticity of the body and the frame, the body and the frame are regarded as rigid bodies.
(4) The unsuspended masses of the front and rear axles and the body are respectively replaced by concentrated masses.
(5) The damping and elastic forces of the shock absorbers of the wheel and frame are respectively a function of speed and displacement, that is, the entire vehicle vibration system is considered as a complete linear system.
As a result, the five-degree-of-freedom vibration model for an electric vehicle is shown as follows. The parameters in the model are as follows:
m - The equivalent mass of the body; m 1 - - The equivalent mass of the front axle (including the mass of the motor); m 2 - - The equivalent mass of the rear axle; m 3 - - Body and seat The equivalent mass of the chair; J--The moment of inertia of the body around the center of gravity of the body; x 0--The displacement of the body's center of gravity in the vertical direction; θ--The angular displacement of the body in front and rear pitch; The displacement of the unsprung mass in the vertical direction; the displacement of the unsprung mass of the rear axle in the vertical direction; the displacement of the body and the seat in the vertical direction; and the xp--seat below the seat The displacement of the body in the vertical direction; k 1 - - the stiffness coefficient of the front suspension; k 2 - - the stiffness coefficient of the rear suspension; k 3 - - the stiffness coefficient of the seat; k 4 - - front wheel Stiffness coefficient; k 5 - - Stiffness coefficient of rear wheel; c 1 - - Damping coefficient of front suspension shock absorber; c 2 - - Damping coefficient of rear suspension shock absorber; c 3 - Seat The damping coefficient; l - - horizontal distance between the front and rear axles; l 1 - - the horizontal distance from the front axle to the body center of gravity; l 2 - - rear axle to the car The horizontal distance of the center of gravity; l 3 --- the horizontal distance from the seat to the center of gravity of the body; F (t) --- SR drive motor excitation.
3 Vibration Simulation of Electric Vehicle According to the dynamic model of the system established above, the differential equation expressed as a matrix can be obtained as the core of rotor and stator of each matrix and column vector driving motor in M ​​x + Cx + Kx = F type. It is composed entirely of silicon steel sheets. The teeth and grooves are evenly distributed on the inner circumference of the rotor core and the outer circumference of the stator core. The teeth are also salient poles. This structure is also called double salient pole structure. Each of the salient poles of the stator core is provided with several kinds of windings, and the windings on the two salient poles on the inner circumference of the stator are connected in series to form a group, and the upper concentrated windings are not installed on the rotor core.
Due to the non-linearity and saturation of the magnetic circuit and the switchability of the circuit, it is generally necessary to first segment the electromagnetic energy (that part of the energy converted into mechanical energy in the motor) or the inductance characteristic of the motor according to the task to be studied. Then linearize. After simplification, the electromagnetic torque T e is Te = 1 2 Ki 2, where i is the phase winding current of the motor and K is the rate of change of the inductance of the winding relative to the position angle. For a drive motor, the vibration and noise generated by the drive motor are the result of a combination of radial and tangential forces between the rotor and the stator. According to the actual work of the motor, its electromagnetic torque has fluctuations. Therefore, the relationship between tangential force and time is shown in Fig. 3. The specific expression is F n = T e R.
n T≤t≤( n + 7 20) T 0,
( n + 7 20) Relationship between T 4 Radial Force and Time
Due to the saturation and nonlinearity of the magnetic circuit of the SRM, the accurate analytical expression of its radial force is very difficult. Starting from the qualitative analysis, the following assumptions can be made:
1 magnetic circuit is linear; 2 radial force concentrated on the stator pole, and assume that the phase current is constant. Considering that the tangential force and the radial force have the same period of action, as shown in FIG. 4 , the relation of the radial force that can be changed with time is 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 Since the whole vehicle vibration system responds to the excitation of the motor () in the vertical direction, the excitation source pair is based on the principle of force synthesis and decomposition. The resultant force of the system in the vertical direction is F n = T e R cos aπ 30 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 where is the rate of change of the position of the winding inductance pair.
For an electric vehicle such as shown in 1 below, a set of specific parameters is given and then a simulation calculation is performed.
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; stator inner radius R = 0.
05m; motor () speed a = 1500r/min; rotor pole number Nr = 6; minimum air gap length b = 0.
001m; Winding current i = 1 A; rate of change of winding inductance versus position angle K = 82.
5; The minimum inductance of the winding Lmin = 4.
95 H.
Apply the New mark-β method to this vehicle system, and take β = 1 / 4 and δ = 1/2. After programming by Matlab software, the displacement of the equivalent mass m 3 of the human body and the seat can be obtained after running. 3 Response As shown, the speed x 3 response is as shown. It can be seen from the 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 driven by SRM, we must first proceed from the vehicle system, boldly simplify it, and reasonably assume that the drive motor is used as the excitation source to establish the system vibration model, and then obtain the vibration differentiation. Equations, and then further analysis of the body and body and seat steady-state response, the response results will be an important basis for vehicle design. From the frequency domain point of view, the harmonic frequency of excitation force should be avoided as close as possible to the natural frequency of the stator, and the output frequency of the motor vibration and the natural frequency of the vehicle must be kept close to each other. Only in this way can the resonance phenomenon of the entire vehicle be avoided. Therefore, it must be considered as comprehensively as possible, to minimize the vibration of the drive motor itself, consider its impact on the vehicle vibration excitation, thereby improving the smoothness and comfort of the electric vehicle.
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