EXTENDED-RANGE FULL-ELECTRIC LOW-SPEED TRACTOR

Abstract

Disclosed is an extended-range full-electric low-speed tractor, which includes a system control unit, a battery pack, a frequency conversion driver, a bidirectional DC-DC converter, a generating set and a drive system. The generating set is capable of working in an intermittent mode. The generating set will be started when the power of the battery pack is lower than a preset working range; once the generating set begins to work, the generating set will be running under a condition of “the most economic fuel consumption” and provide stable output at constant speed and constant power, so as to make sure that the generating set is not overloaded, emits no black smoke and has highest energy efficiency. It has advantages of low energy consumption, low pollution and long life of the generating set.

Claims

1. An extended-range full-electric low-speed tractor, wherein comprises a system control unit, a battery pack, a frequency conversion driver, a bidirectional DC-DC converter, a generating set and a drive system, the generating set comprising an engine and a generator connected to the engine, the frequency conversion driver comprising an AC/DC converter and a DC/AC bidirectional converter; wherein the generating set is connected to the AC/DC converter and then divided to two branch circuits, one being connected to the bidirectional DC-DC converter and the battery set in sequence via a DC bus and the other one being connected to the DC/AC bidirectional converter; the battery pack, the bidirectional DC-DC converter, the generating set and the frequency conversion driver are all signal controlled by the system control unit; the DC/AC bidirectional converter is connected to a load; a charging-discharging power of the battery set is greater than or equal to a power of the drive system; the drive system comprises a drive motor, a gearbox, a drive axle and a drive wheel, all of which are connected in sequence; and the DC/AC bidirectional converter is connected to the drive motor.

2. The extended-range full-electric low-speed tractor according to claim 1, wherein the tractor further comprises an auxiliary power supply connected to the DC bus.

3. The extended-range full-electric low-speed tractor according to claim 1, wherein the tractor further comprises a 24V DC power supply connected to the DC bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a functional block diagram according to an embodiment of the present invention; and

[0013] FIG. 2 is a universal characteristics curve of a diesel engine.

DESCRIPTION OF THE REFERENCE NUMBER IN THE FIGURES

[0014] System control unit 1; battery pack 2; auxiliary power supply 3; 24V DC power supply 4; frequency conversion driver 5; generating set 6; bidirectional DC-DC converter 7; drive motor 8; gearbox 9; drive axle 10; and drive wheel 11.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

[0015] For understanding the objective, the technical content and the advantages of the present invention more sufficiently, some embodiments of the present invention will be described as follows, by way of example only, with reference to the accompanying drawings. The embodiments disclosed below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description.

[0016] Referring to FIG. 1, the extended-range full-electric low-speed tractor of the present invention is mainly used at cargo terminals, factories and so on. The tractor includes a system control unit 1, a battery pack 2, a frequency conversion driver 5, a bidirectional DC-DC converter 7, a generating set 6 and a drive system. The generating set 6 includes an engine and a generator connected to the engine. The frequency conversion driver 5 includes an AC/DC converter and a DC/AC bidirectional converter. The generating set 6 is connected to the AC/DC converter and then divided to two branch circuits, one is connected to the bidirectional DC-DC converter 7 and the battery set 2 in sequence via a DC bus and the other one being connected to the DC/AC bidirectional converter. The battery pack 2, the bidirectional DC-DC converter 7, the generating set 6 and the frequency conversion driver 5 are all connected to and signal controlled by the system control unit 1. The DC/AC bidirectional converter is connected to a load. The battery set 2 has a charging-discharging power which is greater than or equal to a power of the drive system. The drive system includes a drive motor 8, a gearbox 9 connected to the drive motor 8, a drive axle 10 connected to the gearbox 9 and a drive wheel 11 connected to the drive axle 10, that is, all of which are connected in sequence. The DC/AC bidirectional converter is connected to the drive motor 8.

[0017] In this preferred embodiment, the extended-range full-electric low-speed tractor further includes an auxiliary power supply 3 and a 24V DC power supply 4 both connected to the DC bus. The auxiliary power supply 3 is provided to supply power to the auxiliary devices in the tractor, such as air conditioner, air pump, electric power steering system and so on. The 24V DC power supply is provided to supply power to the lighting devices, the generating set 6 and so on.

[0018] According to the extended-range full-electric low-speed tractor of the present invention, the generating set 6 is capable of working in an intermittent mode. The generating set 6 will be started when the power of the battery pack 2 is lower than a preset working range; once the generating set 6 begins to work, the generating set 6 will be running under a condition of “the best economical fuel consumption” and provide stable output at constant speed and constant power, so as to make sure that the generating set 6 is not overloaded, emits no black smoke and has highest energy efficiency. When working, the power outputted by the generating set 6 is firstly used to satisfy the need of the drive system of the tractor and the surplus power is provided for charging the battery pack 2. The generating set 6 will be shut off when the power of the battery pack 2 reaches a preset high value. During the whole working course, the actual working time of the generating set 6 is shorter than the total operating time of the tractor. The actual working time of the generating set 6 is shorter when the power thereof is greater. Because the generating set 6 is controlled to output power in a condition of “the best economical fuel consumption”, the actual energy consumption of the system of the present invention has little to do with the power of the generating set 6. The total energy consumption depends on the characteristics of the selected generating set 6. Additionally, the present invention has advantages of low energy consumption, low pollution and long life of the generating set 6. The components, the connection relationship thereof and the innovation of the system control software are all included within the scope of protection of the invention.

[0019] The selection of specific parameters and the energy control of the system will be described as follows:

[0020] Determine the voltage of the DC bus and select the voltage grade of the battery pack 2 and then set the working range thereof, according to the working voltage range of the frequency conversion driver 5. The system control unit adjusts the input and output voltages of the battery pack 2 by means of the bidirectional DC-DC converter 7, and finally controls the charging and discharging current, so as to make the frequency conversion driver 5 be stable and ensure energy balance of the system. The auxiliary power supply 3 and the 24V DC power supply 4 are designed according to the voltage grade of the DC bus.

[0021] The generating set 6 is a power source for the whole tractor, thus how to design, control and manage the power of the generating set 6 is the key point of the system of the present invention. FIG. 2 illustrates a universal characteristics curve of a diesel engine. As shown in FIG. 2, when the rotational speed is about 1250 rpm and the output is 60-80 kW, the diesel engine has best specific fuel consumption 207 g/kWh, which is called “the most economic fuel consumption zone”. Suppose the diesel engine shown in FIG. 2 is selected to be used in the present invention, the working speed is set to 1250 rpm, and then corresponding generator is selected to match with the engine according to the working speed thereof, so as to make sure that the generating set 6 has maximum efficiency and the output voltage thereof can match with the voltage of the DC bus when the working speed is 1250 rpm. The generating set 6 is controlled to work in the “the most economic fuel consumption zone” so that the energy efficiency can reach a maximum value. The generating set 6 is set to work in three states: idle speed, full speed of 1250 rpm and stop state. During the whole working course of the tractor, the generator is running intermittently.

[0022] When the power of the battery pack 2 is within the preset range, the generating set 6 will be in a stop state, all of the power that the tractor required is supplied by the battery pack 2, and the power outputted by the battery pack 2 can match the need of the whole tractor under the control of the system control unit 1. When the power of the battery pack is reduced to the preset low value, the system control unit 1 will control the generating set 6 to work as follows: start up idle speed full speed; after entering normal working state, the generating set 6 will supply power to the whole tractor in a state of “the most economic fuel consumption” with constant speed and constant power, and the surplus power is used for charging the battery pack 2. The battery pack 2 serves as supplementary power supply for the whole tractor when the energy is insufficient. When the power of the battery pack 2 is increased to a preset high value, the system control unit 1 will control the generating set 6 to work as follows: full speed idle speed shut off, thus the power that the whole tractor needed is supplied by the battery pack 2. The whole tractor is driven by the drive motor 8, the starting torque of the tractor is enough, the motor brake takes precedence when braking, and the regenerative braking power will be recycled back into the battery pack 2. The pneumatic braking system and the motor braking system will both play roles at the same time when braking in an emergency, thus it can lead to a better safety performance compared with the traditional tractor.

[0023] Above descriptions of embodiments are provided for further illustrating the technical content of the present invention, so as to facilitate understanding and it should be understood that the invention is not to be limited to the disclosed embodiments. Any technique extension and recreation according to the present invention should be included within the scope of protection of the invention.