SBAA545 August   2022 DRV5013 , DRV5013-Q1 , TMAG5110 , TMAG5110-Q1 , TMAG5111 , TMAG5111-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Window Regulator Description and Example
    1. 2.1 Design Requirements
    2. 2.2 Mechanical Chain - Window Lever
  5. 3Hall Devices and Magnet for Motor Monitoring
  6. 4Analysis and Results
  7. 5Summary
  8. 6References

2.2 Mechanical Chain - Window Lever

A comprehensive treatment of mechanical behavior is beyond the scope of this paper. However, understanding the impact of the salient mechanical specifications on the magnet, Hall sensor and motor, and also knowing the device pairings and design margins is necessary. By using a model of the mechanical assembly (gear train coupled with the window lever), we will determine the motor speed needed to support the window open and close velocity and the resolution (accuracy) of the window position. We will also determine the Hall sensor bandwidth needed to meet the mechanical requirements.

The first stage of the mechanical chain is the window lever. In this approach, the window movement is symmetric about the lever gear x-axis. As an example, assuming an arm length of 12 in ( 304.8 mm), calculate the angle of rotation. The end of the arm travels in an arc and the angle for half the window vertical travel distance is found using Equation 1.

Equation 1. lever terminal angle = arcsin ( Full Wndow Displacement 2 lever length ) = arcsin ( 457 mm 2 304 mm ) = 48°

The movement of the window regulator can be surprisingly linear, in spite of the nonlinear functions in the lever equation. The plot in Figure 2-3 shows the near-linear window movement - from the example regulator - versus the number of gear rotations.

Figure 2-3 Window Movement
Figure 2-4 Window States

For the purposes of the developing example based on a window regulator for a popular car model, assume the mechanical requirements of the regulator are equivalent to a 120 tooth spur gear to be used on the arm. Based on the angles calculated in Section 2.2, only a fraction of the total spur is needed for the geared window lever. In other words, the lever gear does not make a full 360 degree rotation, so the gear does not need a full complement of 120 teeth . Recall Equation 1 is for a rotation equivalent to half of the total window movement, which defines the partial rotation of the lever gear. Now the minimum number of window lever gear teeth, NGL, can be calculated.

Equation 2. 2 × 48° 360° = N GL teeth 120 teeth
Equation 3. N GL = 120° × 2 × 48° 360° = 32 teeth

The next step is to consider individual points in the gear train and then create an overall model. The gear model - coupled with the window open and close time - helps develop an understanding of the speed requirements for the motor and, in turn, the magnet selection and the Hall sensors.

The individual points in the gear train use the gear parameters in the developing example. The 32-tooth lever gear interfaces with a 7 tooth pinion gear. The number of pinion gear rotations that occur as the lever arm raises or lowers the window is found using Equation 4.

Equation 4. pinion rotations = ( lever gear teeth pinion teeth pinion rotation ) = ( 32 teeth 7 teeth rotation ) = 4.57 rotations

The pinion shares the same axle as a worm wheel gear - which is internal to the motor module - and therefore the worm wheel gear rotates at the same speed as the pinion gear.

Equation 5. pinion rotations = worm wheel rotations

The worm wheel gear is driven by a worm gear that is on the motor shaft. Worm gears are considered 1 tooth gears, which means 1 tooth is used per motor shaft rotation. Benefits of the worm gear are that the gear trades speed for torque, which implies a powered motor is unnecessary to keep a window in position or prevent someone from trying to pull down the window.

Equation 6. worm gear rotations = ( worm wheel rotations × worm wheel teeth worm gear teeth ) = 4.57 rotations × 80 teeth 1 tooth = 365.7 rotations
Equation 7. worm gear rotations = motor shaft revolutions

Thus far, the points in the gear train have been detailed. Now the total gear ratio (from the motor to the lever gear) can be calculated, which allows the motor speed to be determined. Beginning at the motor and then moving along the mechanical path formed by the worm gear, worm wheel gear, pinion gear and finally the geared lever:

Equation 8. R R E G = ( N G L N PG ) × ( N WW N WG )

where

  • NGL = Number of teeth on the geared lever
  • NPG = Number of teeth on the external pinion gear of the motor module
  • NWW = Number of (internal) worm wheel gear teeth
  • NWG = Number of (internal) worm gear teeth driving the worm wheel = 1

A "revolution" of the geared lever (with NGL teeth) represents the window going from fully closed to fully open, or vice-versa as shown in Figure 2-4. As a result, the total gear ratio RREG is interpreted as the number of motor revolutions needed to open or close the window.

The motor speed needed to support a window going from fully closed to fully open or vice-versa is found using Equation 9.

Equation 9. S M = R R E G T WIN

where

  • TWIN = period of window open or close

The ongoing example is developed further in the Analysis and Results section.