*2.2. Power Measuring Principle*

2.2.1. Parameter Symbol Definition

Variable symbols are defined as follows:


*k*—the transmission ratio the hydraulic pump and the engine

#### 2.2.2. Measuring Principle Analysis

According to the machine power roadmap of the maize silage harvester, the power sources of key operation parts include both mechanical drive and hydraulic drive.

For mechanically-driven working parts, the operating power can be acquired by measuring the rotational speed and rotating torque. For rotation torque measurement, the principle of torsion resistance strain gauge is used, and the strain gauge is attached to the rotating elastic shaft to form a strain bridge detection circuit, which outputs a frequency signal proportional to the torsion value, and thus the working torque is obtained. For rotation speed measurement, a speed sensor is mounted on the fixed part of the torque sensor, and an encoder with multiple detection positions is installed on the rotating part of the torque sensor. When the encoder rotates with the working shaft, the sensor outputs a series of speed pulse signals, and the working speed is measured. According to the definition of mechanical torque, the torque can be calculated by Formula (1).

$$T\_r = FR \tag{1}$$

The relationship between linear speed and rotational speed is shown as follows:

$$
v\_r = \frac{n\_r}{60} 2\pi R\tag{2}$$

The power consumption of the mechanical rotating parts is then given as follows:

$$P\_r = \frac{1}{1000} Fv\_r = \frac{1}{1000} \times \frac{T\_\mathbf{r}}{R} \times \frac{n\_\mathbf{r}}{60} \times 2\pi R = \frac{n\_\mathbf{r} T\_\mathbf{r}}{9549.3} \tag{3}$$

For hydraulic-driven working parts, the operating power can be obtained by the differential pressure between the outlet and inlet and the hydraulic flow of the hydraulic pump, and the power of the hydraulic parts is calculated as follows.

$$P\_h = \frac{(p\_o - p\_i)}{60} q = \frac{n\_0 k V\_0 \eta\_v}{60} (p\_o - p\_i) \tag{4}$$
