Patent Description:
Conventionally, lawn mowers and grass cutters are used for mowing lawn and grass. Among these work machines, machines are known which include a cutting blade arranged in the horizontal direction, in which the cutting blade is rotated by a driving source, with an engine or an electric motor being used as the driving source of the cutting blade. For example, in a walk-behind grass cutter disclosed in Patent Literature <NUM>, an electric motor <NUM> is used as the driving source of front and rear wheels and a cutting blade that rotates around the axial center thereof in the vertical direction.

The aforementioned walk-behind grass cutter includes a cutting-blade-system power transmission path <NUM> composed of a transmission shaft <NUM> connected to an output shaft <NUM> of the electric motor <NUM> via a coupling <NUM>, and a cutting blade clutch <NUM> that transmits motive power from the transmission shaft <NUM> to a cutting blade drive shaft <NUM> in an engageable/disengageable manner (see <FIG> of Patent Literature <NUM>). According to this configuration, when the cutting blade clutch <NUM> is engaged during mowing, rotation of the output shaft <NUM> of the electric motor <NUM> is transmitted to a cutting blade <NUM> via the cutting blade clutch <NUM>, and the cutting blade <NUM> is rotationally driven.

Further electric work machines are known from <CIT> and <CIT>.

In a case where an electric motor is used as a driving source, as in the walk-behind grass cutter described in Patent Literature <NUM>, enabling operation for an extended period with one charging of the battery is a problem. In such a case, it is difficult to mount a large battery in a work machine in which the machine body is moved while the operator is walking, as in the case of a walk-behind grass cutter, and consequently there is a need to reduce electric power consumption in order to enable operation for an extended period.

The present invention solves the conventional problem described above, and an object of the present invention is to provide an electric work machine with cutting blade that can enable operation for an extended period without making the battery a large size.

To achieve the above object, an electric work machine in accordance with claim <NUM> is suggested.

According to the electric work machine with cutting blade of the present invention, since an abrupt increase in current at a moment at which the clutch is engaged can be eliminated and electric power consumption can be reduced, operation for an extended period can be enabled without making the battery a large size.

The advantageous effects of the present invention are as described above, and since an abrupt increase in current at a moment at which the clutch is engaged can be eliminated and electric power consumption can be reduced, operation for an extended period can be enabled without making the battery a large size.

Hereunder, one embodiment of the present invention will be described with reference to the drawings. <FIG> is an external perspective view of an electric work machine with cutting blade <NUM> (hereinafter, referred to simply as "work machine <NUM>") relating to one embodiment of the present invention. <FIG> is a perspective view illustrating the inside of a motor box <NUM>. <FIG> is a perspective view of the work machine <NUM> when viewed from a handle side. <FIG> is a perspective view of the work machine <NUM> as viewed from the underside.

Although in the present embodiment the work machine <NUM> is described using an example of a walk-behind lawn mower, as will be described later, the present invention relates to control of an electric motor that rotationally drives a cutting blade via a clutch, and it suffices that the object for application of this control has a similar cutting blade rotation mechanism as the work machine <NUM>, and for example the object for application of this control may be a riding lawn mower or a grass cutter.

First, a general outline of the work machine <NUM> will be described with reference to <FIG>. In <FIG>, front wheels <NUM> are attached to the front of the motor box <NUM>, and rear wheels <NUM> are attached to the rear. As illustrated in <FIG>, an electric motor <NUM> is mounted inside the motor box <NUM>. The rear wheels <NUM> and a cutting blade <NUM> (see <FIG>) are rotationally driven by the electric motor <NUM>. In <FIG>, a battery <NUM> which is a power source for the electric motor <NUM> is mounted at the rear of the motor box <NUM>.

A housing deck <NUM> is provided below the motor box <NUM>, and a grass bag <NUM> is attached to the rear of the housing deck <NUM>. As illustrated in <FIG>, the cutting blade <NUM> is arranged inside the housing deck <NUM>. As will be described in detail later, rotation of the electric motor <NUM> is transmitted to the cutting blade <NUM> via a clutch <NUM> (see <FIG>), whereby the cutting blade <NUM> rotates. A disk with fins <NUM> rotates integrally with the rotation of the cutting blade <NUM>, and a flow of air is generated from the housing deck <NUM> to the grass bag <NUM>. As a result, grass cut by the rotation of the cutting blade <NUM> is sent to the grass bag <NUM> through an outlet <NUM>, and thereby collected in the grass bag <NUM>.

The work machine <NUM> is a machine that is used by an operator while walking. In <FIG>, operating rods <NUM> are attached to the machine body, and an operation handle <NUM>, a clutch lever <NUM> (operation means for the clutch), and a shift lever <NUM> are attached to an end of the operating rods <NUM>. Further, a frame <NUM> is arranged so as to extend between the pair of operating rods <NUM>, and a display <NUM> that displays the rotation speed or the like of the electric motor <NUM> is fixed to the frame <NUM>. As illustrated in <FIG>, a main switch <NUM> is attached to the display <NUM>, and the main power source can be turned on by rotating the main switch <NUM>.

In <FIG>, in a state in which the main power source has been turned on, the electric motor <NUM> can be started by sliding the shift lever <NUM> (in the arrow "a" direction), and the speed of rotation of the electric motor <NUM> can be gradually increased. An operation lever <NUM> is attached in the vicinity of the operation handle <NUM>, and by operation of the operation lever <NUM> in a state in which the electric motor <NUM> is rotating, the rear wheels <NUM> are driven and the work machine <NUM> moves forward.

Even if the electric motor <NUM> is rotating, rotational driving of the cutting blade <NUM> is stopped unless the clutch lever <NUM> is operated, and when lawn mowing is to be performed, it is necessary to operate the clutch <NUM> (see <FIG>) using the clutch lever <NUM> to switch from a state in which the clutch <NUM> is disengaged in which motive power of the electric motor <NUM> is not transmitted to the cutting blade <NUM> to a state in which the clutch <NUM> is engaged in which motive power of the electric motor <NUM> is transmitted to the cutting blade <NUM>.

Hereunder, operation of the clutch <NUM> will be described while referring to <FIG>. <FIG> is a cross-sectional view illustrating the structure of the clutch <NUM> that is arranged inside the housing deck <NUM>. <FIG> and <FIG> are enlarged views of the clutch <NUM>. <FIG> illustrates a state in which the clutch <NUM> is disengaged, and <FIG> illustrates a state in which the clutch <NUM> is engaged.

As illustrated in <FIG>, the clutch <NUM> is arranged inside the housing deck <NUM>, and a motor shaft <NUM> of the electric motor <NUM> (see <FIG>) that is arranged on the upper side of the housing deck <NUM> is connected to a drive disk <NUM>. The motor shaft <NUM> and the drive disk <NUM> are connected by a key (not illustrated), and the drive disk <NUM> also rotates integrally with the rotation of the motor shaft <NUM>.

In <FIG>, a brake disc support plate <NUM> is attached to the motor shaft <NUM> via an upper-side bearing <NUM>. An annular brake disc <NUM> is attached to the brake disc support plate <NUM> so as to be movable in the vertical direction. In this configuration, even if the motor shaft <NUM> rotates, because the upper-side bearing <NUM> is interposed between the motor shaft <NUM> and the brake disc support plate <NUM>, the brake disc support plate <NUM> and the brake disc <NUM> that is integrated with the brake disc support plate <NUM> do not rotate.

The cutting blade <NUM> is fixed to the lower side of a blade holder <NUM>, and a lower-side bearing <NUM> is interposed between the blade holder <NUM> and the drive disk <NUM>. A friction plate <NUM> is connected to the upper side of the blade holder <NUM> in a turn-stopping fashion so as to be vertically slidable, and when the friction plate <NUM> rotates, the blade holder <NUM> and the cutting blade <NUM> rotate integrally with the friction plate <NUM>.

A spring <NUM> is interposed between the blade holder <NUM> and the friction plate <NUM>, and the friction plate <NUM> slides in the vertical direction as the spring <NUM> expands and contracts. In the state illustrated in <FIG>, the friction plate <NUM> is pressed by the brake disc <NUM> and caused to slide downward, and the spring <NUM> is contracted. Therefore, the friction plate <NUM> is separated from the drive disk <NUM>. This state is a state in which the clutch <NUM> is disengaged, and even if the drive disk <NUM> rotates integrally with rotation of the motor shaft <NUM>, the rotation of the drive disk <NUM> is not transmitted to the friction plate <NUM>, and the cutting blade <NUM> does not rotate either.

In contrast, the state illustrated in <FIG> is a state in which the pressing of the friction plate <NUM> by the brake disc <NUM> has been released, and as a result the spring <NUM> extends and the friction plate <NUM> presses the drive disc <NUM> due to the repulsive force of the spring <NUM>. This state is a state in which the clutch <NUM> is engaged, and thus rotation of the drive disk <NUM> is transmitted to the friction plate <NUM>, and the cutting blade <NUM> rotates to enable lawn mowing.

The work machine <NUM> includes a switching mechanism (not illustrated) that switches between a state in which the brake disc <NUM> is pushed down to the lower side to disengage the clutch <NUM> (state in <FIG>), and a state in which the disengaged state of the clutch <NUM> has been released and the clutch <NUM> is engaged (state in <FIG>). This switching mechanism is operated by operating the clutch lever <NUM> (see <FIG>).

In <FIG>, when the clutch lever <NUM> is tilted to the front side in a state in which an operation button <NUM> at the upper portion of the clutch lever <NUM> is pressed, the switching mechanism is activated and the state in which the brake disc <NUM> is pushed down to the lower side is released, the friction plate <NUM> presses the drive disk <NUM> as illustrated in <FIG>, and the clutch <NUM> enters an engaged state and the cutting blade <NUM> rotates. The cutting blade <NUM> rotates as long as the state in which the operation button <NUM> is pressed and the clutch lever <NUM> is tilted to the front side is maintained, but when the operator's hand separates from the clutch lever <NUM>, the clutch lever <NUM> returns to its original state, and the clutch <NUM> enters a disengaged state and rotation of the cutting blade <NUM> stops.

The work machine <NUM> has built-in controller <NUM> (a computer) for controlling the operation of the electric motor <NUM>. The control of the electric motor <NUM> by the controller <NUM> is described below. <FIG> is a block diagram illustrating control of the electric motor <NUM> by the controller <NUM>, <FIG> is an external perspective view illustrating the vicinity of the clutch lever <NUM> and a clutch operation detection sensor <NUM>, and <FIG> a flowchart illustrating a process from starting operation until ending operation.

In <FIG>, a signal from the clutch operation detection sensor <NUM> is input to the controller <NUM>, and the controller <NUM> controls the operation of the electric motor <NUM> in response to this signal. As illustrated in <FIG>, the clutch operation detection sensor <NUM> is provided below the clutch lever <NUM>. The clutch operation detection sensor <NUM> includes a detection button <NUM>, and in the state illustrated in <FIG> (state in which the clutch lever <NUM> is not operated), the detection button <NUM> is pressed by a pressing plate <NUM> that is fixed to the clutch lever <NUM>.

In <FIG>, by pressing the operation button <NUM> (arrow b direction) and tilting the clutch lever <NUM> forward (arrow c direction), the state in which the clutch <NUM> is disengaged is released, and the clutch <NUM> enters an engaged state from the disengaged state. Since the pressing plate <NUM> moves in a direction away from the detection button <NUM> integrally with the movement of the clutch lever <NUM>, the detection button <NUM> that had been pressed by the pressing plate <NUM> rises upward, and the signal value that is output from the clutch operation detection sensor <NUM> changes.

That is, by setting the positional relationship between the clutch operation detection sensor <NUM> and the pressing plate <NUM> so that the detection button <NUM> rises upward when the state in which the clutch <NUM> is disengaged is released, the signal value of the clutch operation detection sensor <NUM> when the state changes becomes a signal value indicating that the disengaged state of the clutch <NUM> has been released, and it is thus possible for the controller <NUM> to recognize the release of state in which the clutch <NUM> is disengaged.

Hereunder, operations from the start of operation of the work machine <NUM> to the end of operation thereof are described while referring to <FIG>. In <FIG>, when starting operation (step <NUM>), the main power source is turned on (step <NUM>) by rotating the main switch <NUM> (see <FIG>). By sliding the shift lever <NUM> (see <FIG>) in this state, the electric motor <NUM> is started (step <NUM>), and the electric motor <NUM> rotates (step <NUM>). In this state, in <FIG>, by operating the operation lever <NUM>, the rear wheels <NUM> are driven and the work machine <NUM> moves forward.

On the other hand, as long as the clutch lever <NUM> (see <FIG>) is not operated, the clutch <NUM> is in a disengaged state and the cutting blade <NUM> does not rotate, and in order to cause the cutting blade <NUM> to rotate it is necessary to release the state in which the clutch <NUM> is disengaged by operating the clutch lever <NUM> to engage the clutch <NUM>. As described above, in <FIG>, a signal from the clutch operation detection sensor <NUM> is input to the controller <NUM>, and the controller <NUM> can recognize the release of the disengaged state of the clutch <NUM>. Upon recognizing the release of the state in which the clutch <NUM> is disengaged (step <NUM> in <FIG>), the controller <NUM> stops the energization of the electric motor <NUM> (stops the rotational driving) during a period from the time of recognizing the release until a prescribed time period elapses (step <NUM> in <FIG>).

This control is control that stops energization of the electric motor <NUM> during a period that includes the moment at which the clutch <NUM> is engaged, and it suffices that the period of stopping energization of the electric motor <NUM> includes the moment at which the clutch <NUM> is engaged. Although in the present embodiment the rotation of the electric motor <NUM> stops during a period from when the disengaged state of the clutch <NUM> is released until a prescribed time period elapses, since a period from release of the disengaged state of the clutch <NUM> until the clutch <NUM> is engaged is a momentary period, even if the prescribed time period is a very small time period of about <NUM> seconds, the moment at which the clutch <NUM> is engaged will be included in the period in which rotation of the electric motor <NUM> is stopped.

Whilst the prescribed time period for which rotation of the electric motor <NUM> is stopped is not particularly limited, for example the prescribed time period is within the range of <NUM> to <NUM> second. After the prescribed time period elapses, the controller <NUM> restarts the electric motor <NUM> (step <NUM>), and the electric motor <NUM> rotates once more (step <NUM>). In this state, the clutch <NUM> is in an engaged state, and the cutting blade <NUM> rotates due to the rotation of the electric motor <NUM>.

Thereafter, rotation of the electric motor <NUM> continues even when a state is entered in which the clutch <NUM> is disengaged, and when the state in which the clutch <NUM> is disengaged is released, although rotation of the electric motor <NUM> stops for a prescribed time period, after the prescribed time period elapses the electric motor <NUM> is restarted and thus the rotation of the electric motor <NUM> resumes (step <NUM> to step <NUM>). When the work is finished, the main power source is turned off (step <NUM>), and operation is ended (step <NUM>).

As a result of repeated experiments conducted by the inventors of the present application in order to achieve a reduction in the electric power consumption, the operation control of the electric motor <NUM> when the clutch <NUM> is operated as described above has been derived based on the finding that a change in the current at the moment at which the clutch <NUM> is engaged is large. Hereunder, the present invention is described more specifically while referring to measurement results obtained with respect to a Comparative Example and an Example.

In the Comparative Example, although the basic structural configuration of the work machine is the same as the work machine <NUM> according to the above embodiment, the Comparative Example has a configuration so that control that stops energization of the electric motor <NUM> (hereinafter, referred to as "energization stopping control") is not executed during a period from when the disengaged state of the clutch <NUM> is released until a prescribed time period elapses. That is, rotation of the electric motor <NUM> continues irrespective of the operation of the clutch <NUM>. The Example is configured so that energization stopping control is added to the configuration of the Comparative Example. With respect to the Comparative Example and the Example, a voltage measuring probe and a current measuring probe were connected thereto, and voltage values and current values were measured chronologically using a data logger.

For the Comparative Example and the Example, the period of one cycle was set to <NUM> seconds, with an engaged state of the clutch <NUM> being set to <NUM> seconds, and a disengaged state of the clutch <NUM> being set to <NUM> second. <FIG> illustrates waveforms of a current I and a voltage V of the electric motor <NUM> with respect to the Comparative Example. The abscissa axis represents the elapsed time t (s), and the ordinates axis is used to represent both the current I (A) and the voltage V (V) (the same applies with respect to <FIG>).

In <FIG> that relates to the Comparative Example, during a period T1 after the start of measurement, the clutch <NUM> is in an engaged state and the cutting blade <NUM> is rotating. During a period T2 (period of <NUM> second) that follows the period T1, the clutch <NUM> is in a disengaged state, and although rotation of the electric motor <NUM> continues, rotation of the cutting blade <NUM> is stopped. In the period T2, the voltage V is rising and the current I is falling. In a period T3 (period of <NUM> seconds) that follows the period T2, the clutch <NUM> is in an engaged state. At the beginning of the period T3, the voltage V drops (A part) and the current I rises sharply (B part). It is considered that this is because the load increased suddenly due to the clutch <NUM> being engaged. Thereafter, the current I falls and eventually stabilizes (C part).

In <FIG> that relates to the Example, although the waveforms of the current and voltage in the period T1 and the period T2 are the same as in <FIG> relating to the Comparative Example, the waveforms in the period T3 differ significantly between <FIG> and <FIG>. In <FIG>, the current value falls to the vicinity of zero at the beginning of the period T3 (D part). This is because energization stopping control was executed, and energization of the electric motor <NUM> was stopped. It is surmised that the reason the current value did not become completely zero was because of energization of the sensors and the characteristics of the three-phase motor. The energization stop time was set to <NUM> seconds, and upon <NUM> seconds elapsing from the time that energization of the electric motor <NUM> was stopped, the electric motor <NUM> restarted and simultaneously the cutting blade <NUM> also rotated. After restarting, the current rises as a whole (E part), and thereafter falls (F part), and eventually stabilizes (G part).

Comparing <FIG> relating to the Comparative Example and <FIG> relating to the Example, since the abrupt increase in current in the period T3 in <FIG> relating to the Comparative Example is not observed in <FIG> relating to the Example, a reduction in electric power consumption is expected in the Example in comparison to the Comparative Example. In order to confirm the electric power consumption reduction effect, the operating time from when the battery was fully charged until the electric motor <NUM> stopped due to battery discharge was measured for each of the Comparative Example and the Example. Similarly to the above experiment, one cycle was set to <NUM> seconds, with an engaged state of the clutch <NUM> being set to <NUM> seconds, and a disengaged state of the clutch <NUM> being set to <NUM> second. The results of the experiment are shown in Table <NUM> below.

According to the results shown in Table <NUM>, while the number of cycles in the Comparative Example was <NUM>, the number of cycles in the Example was <NUM>, which showed that the number of cycles in the Example increased by <NUM>% (the operating time increased by <NUM>%) compared to the Comparative Example, and thus the effect of reducing the electric power consumption could be confirmed. According to this result, it can be understood that an abrupt increase in current at the moment at which the clutch <NUM> is engaged is a major factor that increases the electric power consumption. On the other hand, when the electric motor <NUM> is restarted as in the Example, even though a large load is applied at the time of restarting, the electric power consumption is reduced compared to the Comparative Example. This is because an electric motor has a characteristic of generating a large torque when starting, and it is considered that restarting of the electric motor <NUM> is not a factor that greatly increases the electric power consumption.

Therefore, according to the present invention, since an abrupt increase in the current at a moment at which the clutch <NUM> is engaged can be eliminated and electric power consumption can be reduced, operation for an extended period can be enabled without making the battery a large size.

Further, since the effect of reducing the electric power consumption is obtained by suppressing an abrupt increase in the current at a moment at which the clutch <NUM> is engaged, the effect of reducing the electric power consumption increases as the frequency of engaging and disengaging the clutch <NUM> increases. In this regard, since a walk-behind lawn mower as illustrated in <FIG> is used in a narrow area, the frequency of engaging and disengaging the clutch <NUM> is high, and hence electric power consumption can be reduced more effectively.

Whilst an embodiment of the present invention has been described above, the above embodiment is an example and may be appropriately modified. For example, although in the above embodiment the clutch lever <NUM> is used as operation means for operating the clutch <NUM>, as long as the clutch <NUM> can be operated, the operation means is not limited to a lever structure.

Furthermore, although in the above embodiment the detection of release of a state in which the clutch <NUM> is disengaged is detection that is based on a change in a signal value that is output from the clutch operation detection sensor <NUM> as a result of operation of the clutch lever <NUM>, it suffices that the release of a state in which the clutch <NUM> is disengaged can be detected, and another method may be adopted as the detection method.

Claim 1:
An electric work machine (<NUM>) with cutting blade, comprising:
a cutting blade (<NUM>);
an electric motor (<NUM>) that rotationally drives the cutting blade (<NUM>);
a clutch (<NUM>) configured to engage and disengage motive power between the electric motor (<NUM>) and the cutting blade (<NUM>);
operation means (<NUM>) configured for operating the clutch (<NUM>) such as to switch between a state in which the clutch (<NUM>) is disengaged and motive power of the electric motor (<NUM>) is not transmitted to the cutting blade (<NUM>) and a state in which the clutch (<NUM>) is engaged and motive power of the electric motor (<NUM>) is transmitted to the cutting blade (<NUM>);
a sensor (<NUM>) configured to detect movement of the operation means (<NUM>); and
a controller (<NUM>) configured to control operation of the electric motor (<NUM>) and recognise release of the w state in which the clutch (<NUM>) is disengaged based on a signal from the sensor (<NUM>),
wherein the controller (<NUM>) is configured to stop rotation of the electric motor (<NUM>) during a period that includes a moment at which the clutch (<NUM>) is engaged by stopping energization of the electric motor (<NUM>) after the state, in which the clutch (<NUM>) is disengaged is released, and restarting the electric motor (<NUM>) after a prescribed time period elapses after stopping the energization.