The present invention relates to an engine-powered tool such as a chainsaw or a grass cutter, and particularly relates to an engine-powered tool started by driving a starter motor by use of a small-sized battery.
For small-sized power tools such as a chainsaw and a grass cutter, a small-sized engine has been widely used as a power source.
The engine as used in the engine-powered tool 101 is small-sized and lightweight and can generate large output, and also allows a work for long hours with the supply of fuel. To start the engine, a manual starter is used, and various ideas have been suggested to improve startability. For example, Patent Literature 1 suggests an engine-powered tool in which a battery and a starter motor are incorporated and startability is improved by the starter motor.
PTL 1: Japanese Patent No. 3400191
In the engine-powered tool of Patent Literature 1, if a battery having a size sufficient for driving the starter motor is mounted, portability of the engine-powered tool is degraded. To address this, it seems effective to mount a small-sized battery with a low battery voltage. However, since a large current is required for driving the starter motor, the starting current at the time of starting the motor puts a large load on the battery, and the life of the battery may be shortened. Moreover, at the time of low temperatures, the battery voltage is significantly lowered due to this starting current, and there is a possibility that the starter motor cannot be rotated.
An object of the present invention is to provide a lightweight, inexpensive engine-powered tool equipped with a battery and a starter motor.
Another object of the present invention is to provide an engine-powered tool capable of decreasing the size of a battery to be mounted by devising the control at the time of starting a starter motor.
Still another object of the present invention is to provide an engine-powered tool capable of driving a starter motor even with a battery whose voltage has been lowered.
Typical ones of features of the present invention disclosed in the present application are described as follows.
An embodiment of the present invention is an engine-powered tool to be driven by an engine, and the engine-powered tool includes: a starter motor driven by electric power supplied from a battery to start the engine; start control means driven by the electric power from the battery to control rotation of the starter motor; and a switching element provided in series to a power supply circuit from the battery to the starter motor, opening and closing of the switching element being controlled by the start control means. In this engine-powered tool, when the starter motor is to be started, the start control means performs PWM control on the switching element so as to gradually increase a duty ratio. Also, the engine-powered tool further includes: switch means for operating the engine, and when the switch means is turned ON, electric power is supplied from the battery to the start control means, and power supply to the starter motor is controlled by the start control means.
In the engine-powered tool, when the starter motor is to be started, the start control means performs PWM control on the switching element so as to gradually increase the duty ratio. Thus, so-called soft start of the starter motor can be performed, thereby suppressing an excessive starting current.
The above and other objects and novel characteristics of the present invention will be apparent from the following description of the specification and the accompanying drawings.
An engine-powered tool 1 according to an embodiment of the present invention is described below based on the drawings. Note that, in the drawings described below, identical portions are denoted by the same reference numeral and repetitive description thereof is omitted. Also, in the description in this specification, directions of front, back, left, right, up, and down are defined as those indicated in the drawings.
To a front side (output side) of the crank shaft 13, one end of a drive shaft (not shown) via a centrifugal clutch 29 is coupled via a clutch shaft 32. On a magneto rotor 22 to which the centrifugal clutch 29 is attached, a fin for cooling the engine is integrally formed. The centrifugal clutch 29 is a publicly-known centrifugal clutch in which a rocker 30a is connected to a clutch drum 30b by a centrifugal force when the number of revolutions of the crank shaft 13 reaches a predetermined number or larger. The clutch shaft 32 is rotatably held by a bearing 33 retained in a housing 34.
The engine-powered tool includes two systems of a starter motor 106 and a recoil starter 40 as a starting device. The starter motor 106 rotates by electric power supplied via an electric power line 52, and a pinion 57 provided on a rotation shaft 106a is rotated to rotate a gear 49. The gear 49 is rotatably held by a bearing 48 to the crank shaft 13. When the gear 49 rotates at high speed, a one-way clutch 50 attached on a part of the gear 49 protrudes in a radially outer direction by a centrifugal force to make close contact with a first drum 51 to rotate the first drum 51, thereby rotating the crank shaft 13. In the recoil starter 40, when a starter rope 42 wound around a reel 41 is rotated at high speed by a starter handle 36 (see
A battery holder unit 39 is separately provided from, for example, two grip parts 3 (see
Inside the battery 80, for example, three lithium-ion battery cells (not shown) of a 14500 size are accommodated. The battery 80 has a rear end (on a lower side in the drawing) shaped so as to cover an opening 39a at a lower end of the battery holder unit 39. At the other end of an insertion space of the battery 80 continued from the opening 39a, a terminal base 85 is provided, and a plurality of terminals 84 are provided so as to extend from the terminal base 85 toward the opening 39a. At a front end (on an upper side in the drawing) of the battery 80, a plurality of terminals 83 are provided, and since the terminals 83 are brought into contact with the terminals 84 formed on a battery holder unit 39 side when the battery 80 is inserted into the battery holder unit 39, electric power of the battery 80 is supplied via the terminals 84 to the control circuit 102 described further below.
The microcomputer 118 is driven with a constant voltage supplied by the regulator 116, and has a plurality of A/D conversion ports to which an output signal from the thermistor 119 indicating the temperature of the engine, a terminal voltage of the resistor 124 for detecting an open or close state of the starter switch 125, signals from the resistors 112 and 114 indicating the voltage of the battery 80, and an output signal from the rotation detection coil 105 are inputted. An engine rotation signal is detected by converting a magnetic flux from a magnet attached to the engine 10 into a voltage by the rotation detection coil 105 and inputting the resultant voltage to the micro-computer 118. The microcomputer 118 performs a predetermined logical operation from these input values, and sends gate signals of the FETs 117, 121, and 122, thereby controlling the conduction or non-conduction between the source and the drain of the FETs 117, 121, and 122.
The FET 121 serves as a switch for rotating the starter motor 106. By an instruction from the microcomputer 118 (supply of gate signal), the source and the drain of the FET 121 become in a conduction state, and a DC current from the battery 80 is supplied to the starter motor 106 made up of a DC motor. The microcomputer 118 detects the number of revolutions of the engine 10 from an output value of the rotation detection coil 105, and when the engine is started by the starter motor 106, the source and the drain of the FET 121 is closed to stop the rotation of the starter motor 106.
The FET 122 serves as a switch for opening the solenoid valve 104. By an instruction from the microcomputer 118 (supply of gate signal), the source and the drain of the FET 122 become in a conduction state to open the solenoid valve 104. The solenoid valve 104 is provided near the carburetor 35 and the insulator 19, and by opening the solenoid valve 104 at the time of starting, an enriched fuel is supplied to the intake air port of the engine 10, and the startability can be improved.
Next, a series of operations of the engine-powered tool 1 is described with reference to a flowchart of
When a predetermined voltage is inputted to a power supply terminal of the microcomputer 118, the microcomputer 118 is started (step 203). Next, the microcomputer 118 supplies a gate signal to turn the FET 117 ON (achieves conduction between the source and the drain), thereby keeping the ON state of the FET 107 even after the switch 110 is released (step 204).
Next, the microcomputer 118 measures a battery voltage (step 205). In the engine-powered tool 1, the battery 80 has a rated voltage of 10.8 V from three lithium-ion batteries each having a rated voltage of 3.6 V connected in series. The battery voltage is measured by smoothing a voltage divided by the resistors 111 and 112 by the capacitor 113 and inputting the resultant voltage to an A/D conversion input terminal of the microcomputer 118. Here, it is determined whether the battery voltage is, for example, 3.0 V or lower per cell, that is, whether the battery voltage is 9.0 V or lower in total because the three batteries are provided in this case (step 205). If the detected battery voltage is 9.0 V or lower, it is determined that the batteries are in a discharge state, and the procedure goes to step 214, where the FET 117 is turned OFF and the power supply of the control circuit 102 is shut down. On the other hand, if the detected battery voltage is higher than 9.0 V, the procedure goes to step 206.
Next, at step 206, it is determined whether the starter switch 125 has been pressed (turned ON). Here, if the starter switch 125 still remains in an OFF state, the microcomputer 118 waits until the starter switch 125 is turned ON. When the starter switch 125 is turned ON, the microcomputer 118 supplies a predetermined DC current to the starter motor 106 while performing PWM (Pulse Width Modulation) control on the FET 121, thereby soft-starting the starter motor 106 (step 207). Here, soft start means that the rotation of the starter motor 106 is moderately started while restricting the starting current of the starter motor 106 to suppress an excessive current flowing at the time of starting.
Control of the microcomputer 118 at this soft start is described with reference to
Referring back to
The solenoid valve 104 is controlled so as to be opened only for a short time interval and then immediately closed. For example, this opening is made once per rotation of the crank shaft 13. Next, at step 211, the microcomputer 118 determines whether the number of times of opening and closing of the solenoid valve 104 has reached 10. Here, if the number of times of opening and closing of the solenoid valve 104 has not reached 10, the procedure returns to step 209, steps 209 to 211 are repeated, and the procedure goes to step 212 when the number of times has reached 10. The reason why the processes at steps 209 to 211 are skipped when the temperature of the engine 10 is 20 deg C. or higher at step 208 is that additional injection of the fuel by the solenoid valve 104 is not necessary if the temperature is 20 deg C. or higher. Note that it is determined at step 211 whether the number of times of opening and closing has reached 10, but the number of times is not limited to 10, and can be set as appropriate in accordance with the characteristics of the engine and others.
At step 212, the microcomputer 118 detects whether the engine 10 has started, that is, whether the engine 10 is rotating. This can be determined based on whether an engine rotation signal from the rotation detection coil 105 is periodically detected by the microcomputer 118. If the engine 10 is rotating at step 212, the procedure goes to step 214. If the engine 10 is not rotating, the procedure goes to step 213 where a count value of the number of times of ON of the solenoid valve 104 is reset, and then returns to step 209. At step 214, the microcomputer 118 turns the FET 117 OFF, thereby shutting down the power supply of the control circuit 102 by itself to end the start control of the engine 10.
As described above, the engine-powered tool 1 is configured such that when the switch means is turned ON, the start control means controls the switching element to start the engine, and when the engine has started, the start control means turns its own power off. Since the power is supplied from the battery to the start control means when the switch means is turned ON and the power supply to the starter motor is controlled by the start control means, the start control means can be operated when needed. When the switch means is turned ON, the start control means controls the switching element to start the engine, and when the engine has started, the start control means turns its own power off. Therefore, wasteful power consumption can be prevented by the start control device.
The switching element is, for example, a FET (Field Effect Transistor), and since the source and the drain of the FET are connected in series to a power supply circuit from the battery to the starter motor and the gate of the FET is connected to a microcomputer included in the start control means, PWM control can be performed with high accuracy by use of the microcomputer. The battery is a removable lithium-ion secondary battery, and the start control means monitors the battery voltage of the lithium-ion secondary battery and keeps the switching element in an OFF state when the battery voltage is low, thereby controlling so that the start by the starter motor is not attempted. Therefore, an excessive discharge of the battery can be prevented, and the life of the battery can be prolonged.
The engine-powered tool 1 includes temperature detecting means for measuring a temperature of the engine and electrically-operated choke means for enriching an intake fuel to the engine, and since the start control means activates the choke means in accordance with the temperature detected by the temperature detecting means, auto-choke means can be achieved, and the worker is free from a choke operation. Accordingly, the engine-powered tool 1 with enhanced usability can be provided.
The engine-powered tool 1 includes revolution detecting means for detecting the number of revolutions of the engine, and since the start control means stops the starter motor by determining the completion of a start operation of the engine by use of an output from the revolution detecting means, the starter motor can be appropriately driven for an appropriate period, and an efficient start operation can be performed without wastefully consuming the battery. Since the start control means monitors the temperature of the engine and the voltage of the battery, and changes a ratio and time for increasing a duty ratio of the PWM control in accordance with the temperature and the voltage, an engine-powered tool capable of performing a stable start operation hardly affected by the state of the battery, outside air temperature, and others can be realized.
As described above, in the engine-powered tool 1, when the engine is to be started by the starter motor, the PWM control is performed by use of the switching effect of the FETs, thereby performing the soft start in which the duty ratio of electric power to be supplied to the starter motor is gradually increased. For this reason, the starting current at the time of starting the starter motor is suppressed, and therefore, the starter motor can be driven by use of a small-sized lithium-ion battery with a low battery voltage. Also, since control is made so that the time for soft start is changed in accordance with the ambient temperature and battery voltage, operation defects of the control circuit and the solenoid valve due to a voltage drop caused by the starting current at the time of low temperatures can be effectively prevented, and the engine-powered tool can be stably operated.
In the foregoing, the present invention has been described based on the embodiment. However, the present invention is not limited to the foregoing embodiment and various modifications and alterations can be made within the scope of the present invention. For example, a grass cutter is taken as an example in the description of the engine-powered tool, but the present invention can be applied not only to the grass cutter but also to another engine-powered tool configured to drive a working tool by taking an engine as a driving source, such as a cutter, a chainsaw, or a lawn mower.
The present invention is applied to an engine-powered tool that drives a working tool such as a rotary blade by using an engine as a power source.
Number | Date | Country | Kind |
---|---|---|---|
2012-011597 | Jan 2012 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2013/000333 | 1/23/2013 | WO | 00 | 7/23/2014 |