Keywords

1 Introduction

The current energy crisis and increasingly stringent emission regulations have made electric technologies the best way to improve the economy of construction machinery [1,2,3,4,5]. Some of the electric products of construction machinery were developed by domestic and foreign construction machinery groups [6,7,8,9,10], but the research and application in bulldozers are still relatively small. In this paper, the parameter matching of drive motors are carried out, and the effectiveness of parameter matching is especially analyzed.

2 Structure and Parameters of Electric Bulldozers

Figure 1 is a schematic diagram of the structure of an electric bulldozer. The dual motor independent drive bulldozer eliminates the horizontal mechanical connection between the drive wheels on both sides. By controlling the motor drive systems on both sides separately, the battery energy is converted into mechanical energy to drive the track. In addition, a separate motor drives the transfer box to distribute power to various pumps. Tables 1 and 2 show the parameters and of electric bulldozers respectively.

Fig. 1
A block diagram for the dual motor independent drive bulldozer configuration is as follows. Battery connected to the motor controller and motors 1 and 2. Both motors are connected to side transmission tracks.

Dual motor independent drive bulldozer configuration scheme

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Table 1 The parameters of electric bulldozers
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Table 2 The performance parameters of electric bulldozers
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3 Motor Matching Calculation

3.1 Motor Speed Matching

Considering the safe working speed of the drive motor, the maximum speed of the bulldozer drive motor is taken to be 3000 rpm. The side drive can be calculated from Eqs. (1) and (2).

$$ n_{\max } = \frac{{u_{\max } i}}{0.377r} $$
(1)
$$ i = i_{0} *i_{1} $$
(2)

In the above equation, \(r\) is the radius of the driving wheel 0.4553 m; \(i\) is the side transmission ratio; \(\mu_{\max }\) is the maximum driving speed of the bulldozer 10km/h; \(n_{\max }\) is the maximum working speed of the motor 3000rpm.This gives a calculated sidetrack ratio of 88. Since the speed of bulldozer in horizontal ground operation is generally 2~6km/h, the average driving speed of 4km/h is selected as the basis for matching the rated speed of the drive motor, and the rated speed of the motor is obtained by the calculation of Eq. (3).

$$ n_{e} = \frac{{u_{e} i}}{0.377r} $$
(3)

3.2 Matching of Torque

The calculated working condition of bulldozer operating resistance is the maximum working condition of operating resistance during normal bulldozing, i.e., the bulldozer is traveling at a constant speed on the horizontal road surface, the shovel blade operates at the maximum depth of cutting, the largest pile of soil is formed in front of the shovel blade, and the end of the cutting is about to lift the shovel blade at the instant of the end of the shovel blade. At this time, the unilateral track resistance \(R\) consists of two parts: the rolling resistance and the operating resistance. The unilateral track rolling resistance \(F_{f}\) is half of the rolling resistance of the whole vehicle, which is

$$ F_{f} = \frac{fG}{2} $$
(4)

where \(f\) is the rolling resistance coefficient, taken as 0.1, and \(G\) is the weight. Bulldozer operating resistance \(F_{T}\) mainly includes: tangential cutting resistance \(F_{1}\), push resistance of accumulated soil in front of the shovel blade \(F_{2}\), friction resistance between the blade and the soil \(F_{3}\) and the horizontal component of the friction resistance of the soil debris as it rises along the shovel blade \(F_{4}\). One-side track operating resistance is half that of the whole vehicle.

$$ F_{T} = \frac{{(F_{1} + F_{2} + F_{3} + F_{4} )}}{2} $$
(5)
  1. (1)

    Tangential cutting resistance \(F_{1}\)

    $$ F_{1} = 10^{6} B_{1} h_{p} k_{b} $$
    (6)

where \(B_{1}\) is the width of the shovel 3.4 m; \(h_{p}\) is the depth of cut of the bulldozer shovel 0.2 m; and \(k_{b}\) is the cutting specific resistance 0.15 MPa.

  1. (2)

    Pushover resistance of soil accumulated in front of the shovel blade \(F_{2}\)

    $$ F_{2} = G_{t} \mu_{1} \cos \alpha = \frac{{V\gamma \mu_{1} \cos \alpha }}{{k_{s} }} $$
    (7)
    $$ V = \frac{{B_{1} (H - h_{p} )^{2} k_{m} }}{{2\tan \alpha_{0} }} $$
    (8)

where, \(G_{t}\) is the gravity of the soil pile in front of the bulldozer plate (N); \(V\) is the volume of the soil pile in front of the bulldozer plate (m3); \(k_{s}\) is the loosening coefficient of the soil, which is generally taken as 1.06; \(k_{m}\) is the filling coefficient of the soil, which is generally taken as 1.0; \(H\) is the height of the shovel blade of 1.2 m; \(\mu_{1}\) is the friction coefficient between the soil and the soil, which is taken as 1.0; \(\gamma\) is the gravitational degree of the soil (N/m3), which is taken as 17,700; \(\alpha\) is the slope (°), calculated according to 0°; \(\alpha_{0}\) is the natural slope angle of soil (°),which is taken as 28°.

  1. (3)

    Blade-soil friction resistance \(F_{3}\)

    $$ F_{3} = 10^{3} B_{1} X\mu_{2} k_{y} $$
    (9)

where, \(k_{y}\) is the specific resistance (MPa) of the cutting edge pressed into the soil after the cutting edge is worn, taken as 0.6; \(X\) is the grounding length (m) of the cutting edge after the cutting edge is worn, taken as 0.01; \(\mu_{2}\) is the coefficient of friction between soil and steel, taken as 0.5.

  1. (4)

    Horizontal component of the frictional resistance of the soil chip as it rises along the shovel blade \(F_{4}\)

    $$ F_{4} = G_{t} \mu_{2} (\cos \delta )^{2} \cos \alpha $$
    (10)

where, \(\delta\) is the cutting angle (°) of the push shovel, taken as 25°.

Then there is unilateral track resistance.

$$ R = F_{f} + F_{T} $$
(11)

Unilateral track torque:

$$ T = Rr $$
(12)

Unilateral motor torque:

$$ T_{motor} = \frac{Rr}{{i\eta }} $$
(13)

where \(\eta\) is the motor-to-track transmission efficiency. By calculating the corresponding unilateral track resistance under different cutting depths.

Figure 2 is curve of resistance moment of unilateral motor changing with cutting depth. Therefore, the corresponding resistance moment of 800N·m when the cutting depth is 200mm is taken as the basis for matching the torque of the motor.

Fig. 2
A line graph of resistance moment versus cutting depth plots a rising line with some of the following estimated values. (0.05, 655), (0.10, 700), (0.15, 750), and (0.20, 790).

Curve of resistance moment of unilateral motor changing with cutting depth

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4 Motor Power Matching

Since torque, speed and power have the following relationship,

$$ T = 9549\frac{p}{n} $$
(14)

Where is \(n = 1200r/\min\)，\(T = 800N \cdot m\). The matched motor power is \(p = 100kW\).

5 Power Battery Parameter Matching

5.1 Power Battery Parameter Matching Calculation

The selection of power battery should ensure the requirements of bulldozer power and its range. This paper will take the grader 10km/h driving range of 80km as the design goal to match the parameters of its power battery. Considering the capacity consumed by the pure electric drive bulldozer operating device, set the drive motor power accounted for 85% of the power of the vehicle, then the discharge power of the power battery is

$$ P_{b} = \frac{{nP_{e} }}{0.85}\frac{2 \times 100}{{0.85}} = 235kW $$
(15)

Where \(P_{b}\) is the power battery discharge power, kW; n is the number of motors, which is taken as 2; and \(P_{e}\) is the individual motor power, kW, which is taken as 100kW.

6 Conclusion

In this paper, based on the working conditions of the electric drive bulldozer, the drive motor and side transmission parameters are matched, the peak torque of the drive motor is \(800N \cdot m\), the peak power is 100 kW, the maximum rotational speed is 3000 rpm, the rated rotational speed is 1200 rpm, and the side transmission ratio is 88, discharge power of the power battery is 235kW.