JPH04360615A - Electric lawn mower - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an electric lawn mower, particularly a lawn mower driven by a DC motor, so that when the power switch is turned off, the blades of the lawn mower stop rapidly. The invention relates to electric lawn mowers.

0002

BACKGROUND OF THE INVENTION Current lawn mowers come in two types: engine type and electric type. Mechanical friction type brakes are often used as the blade stopping brake for engine type lawn mowers. A DC motor type lawn mower whose rotational speed can be easily controlled is a DC motor 1 and a DC motor that has a constant rotational speed or a constant terminal voltage using PWM control, etc., as shown in FIGS. 6 and 7. DC motor 1 is controlled according to the load condition.
It is composed of an electric circuit in which a controller 2 that controls the output of the controller 2 and a switch 3 that supplies DC power are connected in series.

[0003] In the figure, reference numeral 4 indicates a diode for freewheeling.

0004

SUMMARY OF THE INVENTION In order to prevent danger or emergencies, it is desirable that the blades of a lawn mower stop rapidly when the switch 3 is turned off. For this reason, some foreign countries have laws regulating this. For example, Canada's CSA standard states that ``the blades or impellers of lawn mowers, snow movers, shredder buckers, or similar equipment must be operated for 10 seconds (if the controls are on the handle) or 7 seconds after being turned off. (if the control is outside the operating range) rotation shall be stopped from the maximum speed specified by the manufacturer."

By the way, the lawn mowers with the electric circuits shown in FIGS. 6 and 7 are not equipped with a braking device, so even if the switch 3 is turned off, as shown in the experimental results shown in FIG. DC motor 1 does not stop. The experimental conditions in Figure 8 are:
The controller 2 controls the DC motor 1 to rotate at 4,500 rpm when no load is applied and at 3,000 rpm when the blade is attached.
The motor rotation stop time when the switch 3 is turned off during normal operation with the blade attached is measured by measuring the motor terminal voltage.

As can be seen from the figure, the blade stops,
That is, it takes 8 seconds to stop the DC motor 1. A self-stop lawn mower without a braking device, as shown in Figures 6 and 7, is not desirable, and using a mechanical brake, which is used in engine-powered lawn mowers, would result in a large and expensive device. There is a drawback.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks, and provides an electric lawn mower that uses an electric brake with a small and inexpensive electronic circuit and complies with the above-mentioned standards. It is an object.

[0008]

[Means for Solving the Problems] FIGS. 1 and 2 are basic configuration diagrams of the present invention. The configuration of the DC motor 1, controller 2, switch 3, and diode 4 is the same as the conventional one in FIGS. 6 and 7, and a braking circuit 5 is connected between the switch 3 and the ground, and A diode 6 that is reverse biased when switch 3 is on and forward biased when switch 3 is off is connected to controller 2.
are connected in parallel.

The braking circuit 5 includes, for example, a transistor M.
It includes a switching element 7 such as an OS-type FET transistor, GTO, or SCR, a brake signal circuit 8 that controls the switching element 7, and a resistor 9 that protects the switching element 7. When the switch 3 is turned off, the switching element 7 is turned off, and a brake signal is generated that keeps the switching element 7 on at least until the rotation of the DC motor 1 stops.

Note that when the switching element 7 has a large capacity, the resistor 9 may be omitted.

[0011]

[Operation] When switch 3 is on, switching element 7
is off, no current flows through the braking circuit 5, and the diode 6 is reverse biased, which is the same as the conventional operation shown in FIGS. 6 and 7.

When the switch 3 is turned off, the DC motor 1 operates as a generator. At this time, a brake signal that turns on the switching element 7 is generated from the brake signal circuit 8. Therefore, current due to the electromotive force generated in the DC motor 1 flows through the braking circuit 5 and the diode 6, and the DC motor 1 is rapidly braked.

[0013]

[Embodiment] FIG. 3 shows the configuration of an embodiment of the present invention.
Reference numerals 1 to 6 and 9 correspond to those in FIGS. 1 and 2. 11 is a MOS type FET transistor, 12 is R
-S latch circuit, 13 is an inverter, 14 is a diode, 15 is a capacitor, and 16 to 21 are resistors.

The braking circuit 5 includes FET transistors 11, R
-S latch circuit 12, inverter 13, diode 14
, a capacitor 15, and resistors 9, 16 to 21. A 36V DC battery drive source is used as the DC power source, and a voltage of 36V DC is applied to the DC motor 1 rated at 36V DC via the switch 3.

A controller 2 is connected between the DC motor 1 and ground, and the controller 2 controls the rotation of the DC motor 1. A diode 6 whose anode is connected to the DC motor 1 side and whose cathode is connected to the ground side is connected in parallel with the controller 2.

[0016] The controller 2 has a voltage from DC36V to DC12V.
It is also designed to create a voltage of V. FIG. 4 shows the configuration of an embodiment of the controller, and reference numerals 1 to 4 correspond to those in FIG.

Reference numeral 22 represents a variable resistor, 23 represents a transistor, and 24 represents a diode. The variable resistor 22 divides the DC 36V proportionally when the switch 3 is turned on and outputs the DC voltage.
A voltage of 12V is generated, and the transistor 23 is controlled by a PWM control signal (not shown) or the like to control the rotation of the DC motor 1.

Further, the diode 24 is for protecting the transistor 23, and when the diode 24 is built into the controller 2, the diode 6 shown in FIGS. 1 to 3 is not required. The capacitor 15 is instantly charged with a DC 12V voltage generated from the controller 2 via the diode 14 and the resistor 17. The voltage charged in this capacitor 15 serves as a power source for the R-S latch circuit 12 and inverter 13 when the switch 3 is turned off.
The R-S latch circuit 12 and the inverter 13 are of the CMOS type, which consumes less power, and the FET transistor 11, which has a large input resistance and therefore consumes less power, is used as a switching element. This allows the capacitance of the capacitor 15 to be reduced. Therefore, even after the switch 3 is turned off, the brake signal that turns on the FET transistor 11 can be easily maintained at least until the rotation of the DC motor 1 stops.

Next, the operation of FIG. 3 will be explained. When the switch 3 is on, the DC motor 1 rotates under switching control of the transistor 23 in the controller 2. At this time, the DC 12V voltage generated from the controller 2 is instantaneously applied to the capacitor 15 via the diode 14 and resistor 17.
to charge.

Further, the set terminal of the R-S latch circuit 12 is connected to the resistor 1 to connect the DC 36V voltage applied to the DC motor 1.
DC12V H signal divided proportionally between 8 and 19 is input,
The reset terminal is connected to the DC created by controller 2.
Since the 12V H signal is input, the H signal is output to the output terminal Q of the R-S latch circuit 12. This H signal is converted into an L signal by an inverter 13, and an L brake signal is supplied to the gate of the FET transistor 11. In other words, the FET transistor 11 is maintained in an off state.

On the other hand, when the switch 3 is turned from on to off, the DC power to the DC motor 1 and controller 2 is
The 36V voltage supply is cut off. However, the capacitor 15 is charged with a voltage of DC 12V, and this charging voltage becomes the power source for the R-S latch circuit 12 and the inverter 13. Then, this charging voltage is discharged through the resistor 16, but until the rotation of the DC motor 1 stops, the R-S
The resistance value of the resistor 16 is selected so as to maintain a voltage sufficient to drive the latch circuit 12 and the inverter 13 sufficiently.

Therefore, when the switch 3 is turned from on to off, the L signal is input to the set terminal of the R-S latch circuit 12, and the capacitor 1 is input to the reset terminal.
Since the H signal which is the charging voltage of 5 is input, the L signal is output to the output terminal Q of the R-S latch circuit 12. This L signal is converted into an H signal by an inverter 13, and an H signal brake signal is supplied to the gate of the FET transistor 11. That is, the FET transistor 11 is turned on.

When the FET transistor 11 is turned on, the electromotive force generated in the DC motor 1, which operates as a generator, causes current to flow through the resistor 9, FET transistor 11, and diode 6 or 24 as a closed circuit. It operates in the direction of rapidly stopping the rotation of the motor 1.

FIG. 5 shows the experimental results of the present invention. The experimental conditions were that the DC motor 1 and controller 2 were the same as those in FIG. That's what I did. As is clear from FIG. 5, it can be seen that the DC motor 1, that is, the lawn mower blade, stops within 3 seconds.

The embodiment shown in FIG. 3 has the following effects. CMOS type is used for the R-S latch circuit 12 and inverter 13, and MO is used as the switching element.
An S-type FET transistor 11 is used to reduce power consumption. This allows the capacitance of the capacitor 15 to be small, so even after the switch 3 is turned off, the FE
The brake signal that turns on the T transistor 11 can be easily maintained.

By using the R-S latch circuit 12, the on/off of the switch 3 and the signal from the controller 2, that is, the signal input to the set terminal and reset terminal of the R-S latch circuit 12, can be skillfully utilized. FET
Since the transistor 11 is controlled, the brake circuit 5 can be configured with a small number of electronic circuit components.

Since the capacitor 15 is instantly charged by the diode 14 and the resistor 17,
Even if the switch 3 is repeatedly turned on and off, the brake circuit 5 operates normally. Since power is supplied to the controller 2 via the switch 3 without being directly connected to the DC power battery, there is no need to use a relay to supply power to the controller 2 and the braking circuit 5. It is possible to secure cost and space savings.

Originally, this type of device is generally configured to turn on the main switch to enable the control circuit, and then start and stop the motor using something like a motor start switch or an accelerator. However, with such a configuration, even if the motor is stopped, there is a risk that the main switch may be forgotten to be turned off and the battery may be discharged.

In contrast, in the embodiment of the present invention, a time constant circuit consisting of a capacitor 15, resistors 16 and 17, and a diode 14 is provided in order to prevent the power supply voltage of the braking circuit 5 from disappearing after the switch 3 is turned off. In addition, since the configuration is such that only one switch 3 is used to start and stop the DC motor 1 and to supply power to the braking circuit 5, there is no risk of unnecessary discharge of the battery as described above. .

[0030]

As explained above, according to the present invention, the blades of the lawn mower rapidly stop after the power is turned off, and a lawn mower that complies with regulations can be put into practical use.

[Brief explanation of drawings]

FIG. 1 shows a basic configuration diagram of the present invention.

FIG. 2 shows a basic configuration diagram of the present invention.

FIG. 3 shows the configuration of an embodiment of the present invention.

FIG. 4 shows the configuration of an embodiment of the controller.

FIG. 5 is a diagram showing the results of an experiment on stopping the motor of the present invention.

FIG. 6 is a conventional configuration diagram.

FIG. 7 is a conventional configuration diagram.

FIG. 8 is a diagram showing the results of a conventional motor stop experiment.

[Explanation of symbols]

1 DC motor 2 Controller 3 Switch 4 Diode 5 Braking circuit 6 Diode 7 Switching element 8 Brake signal circuit 9 Resistance 11 FET transistor 12 R-S latch circuit 13 Inverter 14 Diode 15 Capacitor

Claims (1)

[Claims] [Claim 1] A DC motor (1
) and a controller (2) that controls the DC motor (1).
and a switch (3) for turning the power on and off, when the switch (3) is on, there is no conduction, and when the switch (3) is off, at least the DC motor (1) is turned off. A braking circuit (5) that maintains continuity until rotation stops is connected in parallel to the controller (2), and is biased in the opposite direction when the switch (3) is on, and is biased in the opposite direction when the switch (3) is off. a forward biased diode (6) and a switch (3);
When the DC motor (1) is turned off, a current based on the electromotive force generated in the DC motor (1) is caused to flow through a closed circuit between the braking circuit (5) and the diode (6), thereby applying rotational braking to the DC motor (1). An electric lawn mower characterized by: