JPH09168207A - Electric automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the main battery potential from leaking out to the body frame of car by connecting the body frame electrically with an axle through a brush and a spring and connecting the axle electrically with a conductive tire through a wheel. SOLUTION: A spring 821 is connected electrically with an axle 812 and a brush 822 is held by a conductive brush holder 823 secured to the lower end part of a suspension 814. Body frame 100 of car is connected electrically with the brush 822 by means of a connecting wire 824 through the brush holder 823. Contact face 810a between a conductive tire 810 and a wheel 813 is widened and a metal conductor 810b is connected electrically with the wheel 813. The wheel 813 is coupled with the axle 812 through a bolt 813a and connected electrically therewith. According to the structure, the body frame 100 has a potential identical to that of the earth 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric vehicle driven by a battery as a power source, and more particularly to an electric vehicle characterized by grounding means of a vehicle body frame.

[0002]

2. Description of the Related Art FIG. 2 shows a known power train of an electric vehicle which uses a battery as a power source and drives a vehicle by an AC electric motor via an inverter. In the figure, reference numeral 1 is a main battery, which is configured by connecting a required number of unit batteries 10 in series. An inverter 4 drives an AC motor 5 for driving the vehicle. Reference numeral 3 is a protective fuse, which is used as necessary. A main switch 2 is for electrically connecting or disconnecting the main battery 1 and the inverter 4. Reference numeral 20 is a connection box in which the main switch 2 and the protective fuse 3 are housed together.

The shaft of the AC electric motor 5 is connected to the differential device 7 via the speed reducer 6 and drives the tires 81 and 82. As the AC motor 5, an induction motor that is excellent in price, performance, and maintainability is often used. In the figure,
Reference numerals 21, 22, 51 are connection lines.

FIG. 3 shows an electric system of the entire electric vehicle and shows electric equipment including the power train shown in FIG. The same components as those in FIG. 2 are designated by the same reference numerals.

In FIG. 3, reference numeral 401 is an auxiliary battery, and 402
Is a charger for charging the auxiliary battery 401 from the main battery 1, and a DC-DC converter is generally used for this charger 402. 403 is an air conditioner inverter, and 404 is a variable speed power source for driving power steering.
An inverter is generally used for 04. Reference numeral 405 is a charger for charging the main battery 1 from an AC power supply 406 (for example, an outlet) outside the vehicle, and 407 is a charger outside the vehicle for charging the main battery 1 via a connection line 408.

In an electric vehicle, many electric devices are connected to the main battery 1 as shown in FIG. A device electrically connected to the main battery 1 (main circuit device) is installed on a vehicle body frame in a state where a frame of the device and a conductive portion are electrically insulated, and each device is connected by an insulated wire. . FIG. 4 shows this state, and the same parts as those in FIGS. 2 and 3 are indicated by the same numbers. In FIG. 4, 21, 22, 51
Is a connection wire as an insulated electric wire that connects the respective devices 1, 20, 4, 5 and is safe even if a person touches the vehicle body.

Among the main circuit devices of an electric vehicle, there is a device composed of a power converter using a semiconductor switch. FIG. 5 shows a configuration of an inverter 4 which is an example thereof. 41 and 42 are transistors, 43 and 44 are diodes, and the transistors 41 and 43 and the transistors 42 and 44 form a semiconductor switch. . Reference numeral 45 is a DC smoothing capacitor. In such a power converter, the potential of the conductive portion with respect to the vehicle body changes due to the switching of the transistors 41 and 42.

FIG. 6 shows changes in the potential of the AC terminal A of the inverter 4. The potential of the terminal A varies with the magnitude of the main battery voltage Eb as the transistors 41 and 42 are turned on and off. In addition, the speed of this change depends on the transistor 4
Determined by the switching speed of 1,42, approximately several thousand
V / μs is reached.

The electrical insulator between the conductive portion of the main circuit device and the vehicle body frame acts as a capacitor. In particular, the winding insulator serves as a capacitor between the winding of the AC motor 5 and the iron core. As mentioned above, when the potential of the conductive part fluctuates at high frequency, the above electrical insulator acts as a capacitor,
A high frequency current will flow through the electrical insulator and the body frame.

Here, FIG. 7 shows how the above high-frequency current flows in the drive circuit of the electric vehicle. In the figure, Cm is an equivalent capacitor of a winding insulator of the AC motor 5, Ci is an equivalent capacitor of an insulator between the inverter 4 and the vehicle body frame, and Cb is a capacitor between the main battery 1 and the vehicle body frame. Each equivalent capacitor is shown as an insulator. Currents icm, ici, icb as shown in the figure flow through these capacitors due to potential fluctuations at the AC terminals of the inverter 4.

On the other hand, as shown in FIG.
00 is grounded to the ground 9 via an axle bearing 811, an axle 812, a wheel 813, and a tire 81.
The axle 812 is suspended on the vehicle body frame 100 via a suspension device 814. In the conventional electric vehicle, the bearing 811 and the tire 81 do not have sufficient conductivity, so that the body frame 100 does not become completely equal to the ground potential. On the other hand, the potential of the person who touches the vehicle body is almost the ground potential.

Here, FIG. 8 is equivalently expressed with reference to the ground potential, as shown in FIG. In the figure, Re is an equivalent insulation resistance between the body frame 100 and the ground 9, C
e is the equivalent capacitor, Rb is the main circuit conductor and body frame 1
00 is an equivalent insulation resistance, and Cb is an equivalent capacitor. Also, eb (+) and eb (-) are the ground potentials of the main circuit conductors, which are voltages generated by the main battery voltage, but their values differ depending on the wiring, the arrangement of devices, and the insulating structure.

FIG. 9 shows an electrical state between the (-) pole conductor of the main battery 1, the vehicle body frame 100 and the ground 9, and the (+) pole conductor is also represented in the same manner. . The same applies to the conductors of other main circuit devices connected to the main battery 1 shown in FIG. 3 and the body frame 100 and the ground 9.

[0014]

In the above-described conventional electric system of an electric vehicle, the electrical states of the conductive portion of the main circuit device and the body frame 100 and the ground 9 are represented as shown in FIG. Ground potential edc, eac of frame 100
Are as in Equation 1 and Equation 2, respectively.

[0015]

[Equation 1] edc = Edc · Re / (Rb + Re)

[0016]

[Equation 2] eac≈Eac · Cb / (Cb + Ce)

Formula 1 shows the case where the equipment is operated by direct current, and Edc is the ground potential of the conductive portion. Further, Equation 2 is a case where the operation of the device is an AC operation, and Eac is similarly the ground potential of the conductive portion.

In general, Re <Rb, Ce> Cb, but from Formula 1 and Formula 2, the main battery potential slightly leaks to the body frame 100 in the conventional electric vehicle. Even if the leakage potential is at a level that is not dangerous to the human body, it is not preferable for users of electric vehicles, and there is a problem to make it zero as in the case of conventional engine vehicles.

[0019]

The present invention has been made in order to solve the above-mentioned problems, and the ground potential of the vehicle body frame is made zero as follows. (1) A slip ring and a brush are attached to the axle, and the body frame and the axle are electrically connected via the slip ring and the brush. (2) The tire is a conductive tire. (3) The wheel and the tire electrically connected to the axle are electrically connected.

That is, in the present invention, (1) the vehicle body frame and the axle are electrically at the same potential by the slip ring and the brush attached to the axle. (2) The axle has the same potential as the wheel and the conductive tire. (3) From (1) and (2), the body frame has the same potential as the tire, and the tire has the same potential as the ground.
The body frame has the same potential as the ground, and the ground potential of the body frame becomes zero.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a main part showing an embodiment of the present invention, and the same components as those in FIG. 8 are given the same numbers.

In FIG. 1, reference numeral 821 denotes a slip ring fixed to the axle 812, which is also electrically excellently connected to the axle 812. 822 is a slip ring 821
The brush 822 is held by a brush holder 823 fixed to the lower end of the suspension device 814. The brush holder 823 is made of a conductive material. Reference numeral 824 is a connection line that electrically connects the body frame 100 and the brush 822 via the brush holder 823.

Further, in this embodiment, the tire 810 is made conductive by means such as embedding a sheet-shaped metal conductor 810b inside the tire 810. The contact surface 810a between the tire 810 and the wheel 813
The metal conductor 810b to the wheel 81.
By electrically connecting the tires 810 and the wheels 813 to each other, the tires 810 and the wheels 813 are electrically connected well.

Further, by connecting the wheel 813 and the axle 812 with a bolt 813a, the wheel 813 is
And the axle 812 are electrically connected well. Of course, a part of the metal conductor 810b in the tire 810 needs to contact the ground 9 and the wheel 813. Further, the vehicle body frame 100 to which each device is attached has a structure such that the whole body has the same potential.

Due to the structure as described above, the body frame 100 includes the connecting wire 824, the brush holder 823, and the brush 8.
22, slip ring 821, axle 812, wheel 8
13. Since the vehicle body frame 100 is grounded to the ground 9 through the conductive tire 810, the body frame 100 has the same potential as the ground 9.
Therefore, no leak potential is generated in the body frame 10, and the danger to the human body can be eliminated. In addition,
In order to make the tire 810 conductive, means such as embedding a sheet-shaped metal conductor in the tire and forming the tire with conductive rubber mixed with metal powder can be considered.

[0026]

As described above, according to the present invention, the vehicle body frame on which various devices connected to the main battery are installed and the axle are electrically connected via the brush and the slip ring, and the axle is electrically conductive. The vehicle body frame can always be kept at the same electric potential as the ground because the tires are electrically connected via the wheels. As a result, the vehicle body is always kept at the same potential as the human and the ground potential, so that a safe electric vehicle for the user can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of an embodiment of the present invention.

FIG. 2 is a diagram showing a power train of an electric vehicle.

FIG. 3 is a diagram illustrating an electric system of an electric vehicle.

FIG. 4 is a diagram showing a connection of electric devices that constitute a power train of an electric vehicle.

FIG. 5 is a configuration diagram of a known inverter.

FIG. 6 is an operation explanatory diagram of a known inverter.

FIG. 7 is a diagram showing a leakage current of an electric device forming a power train of an electric vehicle.

FIG. 8 is a cross-sectional view showing a main part of a known electric vehicle.

FIG. 9 is a diagram showing an electrical state between a main circuit conductor of a known electric vehicle, a vehicle body, and ground.

[Explanation of symbols]

 1 Main Battery 2 Main Switch 3 Protective Fuse 4 Inverter 5 AC Motor 6 Reducer 7 Differential Device 9 Earth 10 Unit Battery 20 Junction Box 21, 22, 51, 408, 824 Connection Line 41, 42 Transistor 43, 44 Diode 45 DC Smoothing capacitor 100 Body frame 401 Auxiliary battery 402,405,407 Charger 403 Air conditioner inverter 404 Power steering variable speed power supply 406 AC power supply 810 Tire 810a Contact surface 810b Metal conductor 811 Bearing 812 Axle 813 Wheel 813a Bolt 814 Suspension device 821 Slip ring 822 brush 823 brush holder

Claims (2)

[Claims] 1. An electric vehicle in which an electric device using a main battery as a power source is installed on a vehicle body frame, comprising a slip ring attached to an axle and a brush in contact with the slip ring, wherein the vehicle body frame is provided with the brush. And an electric vehicle electrically connected to an axle via a slip ring, and electrically connecting the axle to a conductive tire via a wheel. 2. The electric vehicle according to claim 1, wherein the conductive tire is formed by embedding a sheet-shaped metal conductor inside the tire.