# Study on Inertia Load Resistance Analysis Method of Light Truck Door Latch
## 3 Theoretical Calculation of Inertia Load Resistance of Light Truck Door Latch
### Calculation of Force of Light Truck Door Latch Outside Handle  
According to the movement of each part, they are divided into moving parts and rotating parts, and Formulas (2) and (3) can be obtained by analyzing the force conditions of the parts.  
\[\sum F_{i}=0 \tag{2}\]  
\[\sum F_{i}L_{i}=M \tag{3}\]  
The three-dimensional model of the light truck door latch system outside handle structure is shown in Figure 7.  
The force of the outside handle is shown in Figure 8. \(\mathrm{O_{H}}\) is the handle rotation center, \(\mathrm{F_{HI}}\) is the handle inertial force, and \(\mathrm{F_{HI}}\) is the thrust of the counterweight mechanism on the handle.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Name**} & **Wire** & **Mean Coil** & **Total Number** & **Material** & **Arm Length 1** & **Arm Length 2** \\  & **Diameter/mm** & **Diameter/mm** & **of Coils** & & **/mm** & **/mm** \\ \hline Outside handle torsion spring & 1.7 & 11.5 & 8.25 & 65 Mn & 12 & 12 \\ Opening connect arm torsion spring & 1.2 & 12 & 5.4 & 65 Mn & 23 & 5.6 \\ Lock return torsion spring & 0.8 & 7 & 3.55 & 65 Mn & 16.3 & 6.1 \\ Pawl torsion spring & 1.2 & 10.8 & 4.25 & 65 Mn & 17 & 8.4 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Torsion spring parameter table.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Name**} & **Preload Torque/(N\(\cdot\)mm)** & \
\begin{tabular}{c} **Inertia Load Resistance** \\ **Calculation Torque/(N\(\cdot\)mm)** \\ \end{tabular} &
\begin{tabular}{c} **Torque When Fully** \\ **Disengaged/(N\(\cdot\)mm)** \\ \end{tabular} \\ \hline Outside handle torsion spring/\(\mathrm{M_{0}}\) & \(-\) & \(-\) & 341.92 \\ Outside open torsion spring/\(\mathrm{M_{1}}\) & 113.79 & 130.04 & 146.30 \\ Lock back torsion spring/\(\mathrm{M_{2}}\) & 32.00 & \(-\) & \(-\) \\ Pawl torsion spring/\(\mathrm{M_{3}}\) & 124.80 & 139.55 & 154.30 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Torsion of torsion spring.  
Figure 7: Outside handle structure. (1) Handle, (2) counterweight, (3) counterweight mechanism, (4) outside handle torsion spring, (5) lever.  
The force of the counterweight mechanism of the outside handle is shown in Figure 9. \(\mathrm{O}_{\mathrm{CW}}\) is the rotation center of the counterweight mechanism, \(F_{\mathrm{CW}}\) is the inertial force of the counterweight block, and \(F_{pull}\) is the pulling force of the counterweight mechanism by the lever, and the inertial force of the counterweight mechanism itself can be ignored.  
The parameters of the parts involved in the theoretical calculation are shown in Table 3.  
Figure 8: Schematic diagram of handle force.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Volume/mm3** & **Density (kg/m3)** & **Mass/g** \\ \hline Outside handle & - & - & 139 \\ Outside handle & - & 7860 & 70 \\ counterweight & & & \\ Outside open toggle arm & 2355 & 1370 & - \\ Opening connect arm & 540 & 7850 & - \\ Pawl connect arm & 2817.5 & 1370 & - \\ Pawl & 970 & 7850 & - \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parts parameters.  
Figure 9: Schematic diagram of counterweight mechanism.  
The size parameters of the outside handle are shown in Table 4.  
The calculation formula can be obtained as follows:  
\[\left(\begin{array}{cc}F_{HI}&F_{H1}&F_{CW}&F_{Pull}\end{array}\right)\left( \begin{array}{cc}L_{HI}&0\\ L_{H1}&-L_{H1}\arcmin\arcmin\arcmin\arcmin\arcmin\arcmin\arcmin\arcmin\arcmin\arcmin \\ 0&L_{CW}\\ 0&L_{Pull}\end{array}\right)=\left(\begin{array}{cc}0&M_{0}\end{array}\right) \tag{4}\]  
Obtained: \(F_{Pull}=22.08\) N.