How to solve the problem of car: Introduction to sensorless anti-pinch window regulator (I)

Nowadays, the lifting and lowering (closing and opening) of the door and window glass of many cars has abandoned the manual lifting method of the crank handle, and generally uses a button-type electric lifting method, that is, it is controlled by an electric glass lifter, which is what we often call "electric window".

The electric window system is mainly composed of windows, window lifters, window motors, and related electronic circuit modules and switches. The windows and window lifters are mainly mechanical structures, which will not be introduced here. All window systems are equipped with two sets of control switches. One set is installed in the middle of the driver's side door, which is the main switch. The driver controls the lifting and lowering of each window. The other set is installed in the middle of each door, which is a sub-switch and is operated by the passengers. The operation of the switch can complete the manual lifting and lowering of the window. Many high-end cars also have automatic lifting functions.

The quality of the window motor is directly related to the normal operation of the electric glass lifter. It has the characteristics of small size, light weight, high protection level, low noise, low electromagnetic interference, and reliable operation. At present, most of the window motors on domestic cars still use relay control or mechanical and electronic combination control using limit switches. Since the mid-1990s, the control technology of electric glass lifters has developed rapidly, and the electronic module control form has been widely used in batch installation and has safety protection functions.

At present, most of the domestic and foreign companies install Hall sensors on the window motors to determine the position of the window glass by judging the motor speed. Here I would like to introduce the sensorless window anti-pinch method. First, we analyze some characteristics of the motor itself, and then analyze the anti-pinch solution.

Brief Analysis of DC Motor Starting Process

The window motor uses a permanent magnet DC electric motor, whose magnetic field is generated by a permanent magnet, and its magnetic flux Φ=Φ N=constant. If the influence of the armature reaction is ignored, the equivalent circuit diagram is shown in Figure 1. In the figure, La represents the sum of the inductance of the armature winding and the external inductance, which is called the armature circuit inductance; Ra is the resistance of the armature circuit, Ea is the induced electromotive force of the armature winding; Φ N is the residual magnetic flux of the permanent magnet to the outside, and Eb and Rb are the open circuit voltage and internal resistance of the battery respectively, which are unchanged in the simulated battery-motor system.

Figure 1: DC motor equivalent circuit

In the figure, La represents the sum of the inductance of the armature winding and the external inductance, which is called the armature circuit inductance; Ra is the resistance of the armature circuit, Ea is the induced electromotive force of the armature winding: Φ is the external magnetic flux of the permanent magnet, Eb and Rb are the open circuit voltage and internal resistance of the battery respectively.

Assume that the static load torque of the motor is ML, which is equal to a constant. Before starting, the circuit is in a steady state, that is, at t=0-, the armature current +Ia(0-)=0. When the circuit is connected, the armature current I2 cannot change suddenly due to the inductance La in the armature circuit. That is, at t=O+, Ia(O+)=Ia(O-)=0, so when the armature voltage is just applied, the armature current is zero.

When t is greater than or equal to, the armature current increases from zero, and the electromagnetic torque M (M=CmΦIa) also increases from zero. Before the electromagnetic torque increases to equal the static load torque (M=Ml), the motor does not rotate. Only when the electromagnetic torque M is greater than the static load torque M., the motor can accelerate. We divide the entire transition process into two stages, which are analyzed below.