Portable power supply incorporating a generator driven by an engine

A portable power supply includes an engine-driven generator that generates a first AC power. A rectifier rectifies the first AC power to a first DC power. A DC/DC converter converts a second DC power from a storage unit to a third DC power. A controller selectively enables one or both of the rectifier and the DC/DC converter to provide one or both of the first DC power and the third DC power to the input of an inverter. The inverter converts the DC power at its input to a second AC power. Alternatively, the power supply advantageously includes a second generator and a second rectifier. The outputs of the two rectifiers are summed and the sum of the two outputs is provided as an input the inverter to extend the range over which a constant second AC power can be provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a portable power supply. More particularly, the present invention relates to a portable power supply that incorporates a generator driven by an engine.

2. Description of the Related Art

Portable power supplies, such as electrical generators that incorporate a generator driven by an engine, are popular for many uses. In an exemplary portable power supply, the engine-driven generator generates a first AC power. The portable power supply includes a rectifier that rectifies the first AC power to produce a DC power. The portable power supply includes an inverter that converts the DC power to a second AC power. The second AC power has a quality that is superior to the quality of the first AC power directly from the generator.

Although a portable power supply having an engine-driven generator is quite convenient and useful, the engine can produce noise that bothers an operator of the power supply or that bothers persons around the power supply. In addition, the power that the engine-driven generator supplies has a magnitude that depends on a magnitude of the output from the engine. Accordingly, portable engine-driven generators may only be able to provide power to relatively small loads.

SUMMARY OF THE INVENTION

Features of the present invention improve conventional engine-driven generators in portable power supplies, and, in particular, enable an improved generator to operate quietly and to provide power to relatively large loads.

Exemplary applications and configurations of the improved engine-driven generator are discussed below. It should be noted that the following discussion relates to several distinct features of the present invention, and not all of the features need to be present in any single embodiment of the present invention. Thus, some of the features may be used with other features in some applications while other applications will only reflect one of the features. Moreover, the features, aspects and advantages can be applied to portable engine-driven generators in the narrow sense, but can be also applied to other power supplies, as will become apparent to those of ordinary skill in the art.

Accordingly, one aspect of the invention involves a power supply that comprises an internal combustion engine. The engine drives a generator that generates a first AC power. A rectifier rectifies the first AC power to produce a first DC power. An inverter converts the first DC power to a second AC power. An electrical energy storage device accumulates electrical energy to supply a second DC power. A DC-to-DC converter converts the second DC power to a third DC power. The third DC power is selectively provided as an additional input to the inverter. When the third DC power is provided as an input to the inverter, the inverter converts the third DC power to the second AC power. A controller controls at least the rectifier and the DC/DC converter. The controller selectively enables one of the rectifier and the DC/DC converter to provide either the first DC power or the third DC power as the input power to the inverter. The controller also selectively enables both the rectifier and the DC/DC converter to provide both the first DC power and the third DC power as input powers to the inverter.

Preferably, the controller monitors the second AC power and enables the rectifier and the DC/DC converter to provide the first and third DC powers to the inverter when the second AC power is greater than a preset magnitude. In particular embodiments, the controller monitors the current of the second AC power. For example, the controller monitors an increase rate of the current and enables the rectifier and the DC/DC converter to provide the first and third DC powers to the inverter when the increase rate of the current is greater than a preset increase rate. The controller may additionally monitor a voltage of the first DC power and enable the rectifier and the DC/DC converter to provide the first and third DC powers when the current is greater than a preset magnitude and the voltage is less than a preset voltage.

Also preferably, the power supply may additionally comprise a switch to select either a first control mode or a second control mode. When the switch is positioned in the first control mode, one of the rectifier and the DC/DC converter provides one of the first and third DC powers, respectively, to the inverter. When the switch is positioned in the second control mode, both of the rectifier and the DC/DC converter provide respective DC powers to the inverter. The power supply advantageously comprises a second switch to select either the rectifier or the DC/DC converter under the first control mode.

In certain preferred embodiments, the power supply additionally comprises a switch to select either a first engine operating mode or second engine operating mode. The controller monitors the second AC power and controls the engine such that an engine speed changes along with a change of the second AC power when the switch is positioned in the first engine operating mode, and controls the engine such that the engine speed is generally constant when the switch is positioned in the second engine operating mode. Preferably, the controller incorporates at least one control map of engine speed versus current of the second AC power. The controller monitors the current of the second AC power and controls the engine speed in accordance with a change of the current using the said control map.

In alternative preferred embodiments, the generator or the engine incorporates a charge coil that charges the electrical storage device. The electrical storage device advantageously includes a battery. Alternatively, the electrical storage device advantageously includes a double-layered capacitor.

In certain alternative preferred embodiments, the power supply additionally comprises at least a second generator. Each generator generates a respective first AC power, and the AC powers are different in magnitude with respect to each other. The power supply additionally comprises at least a second rectifier, wherein each rectifier receives a respective one of the first AC powers and produces a respective rectified DC power at a respective rectifier output. The rectifier outputs are connected in series to provide the first DC power as a sum of the respective rectified DC powers.

In particular embodiments, the power supply additionally comprises a housing at least enclosing the engine and the generator. A temperature sensor detects a temperature inside of the housing. The controller controls a speed of the engine based upon an output signal of the temperature sensor such that the controller increases engine speed when the temperature increases.

In accordance with another aspect of the present invention, a control method is provided for a power supply. The control method comprises monitoring an AC power from an inverter, determining whether the AC power exceeds a preset magnitude, and enabling a rectifier and a converter to cause both the rectifier and the converter to output respective DC powers to the input of the inverter when the AC power from the inverter exceeds the preset magnitude.

In preferred embodiments of the control method, the method additionally comprises determining whether a switch is placed in a first position corresponding to a first control mode or placed in a second position corresponding to a second control mode. The method enables one of the rectifier and the DC/DC converter to provide respective DC power to the inverter if the switch is placed in the first position. The method enables the rectifier and the DC/DC converter to provide respective DC powers to the inverter if the switch is placed in the second position.

In certain preferred embodiments, the rectifier rectifies a second AC power generated by a generator driven by an engine, and the method further comprises determining whether a second switch is placed in a first position corresponding to a first engine operating mode or the second switch is placed in a second position corresponding to a second engine operating mode. The method controls the engine such that an engine speed changes along with a change of the first AC power if the second switch is placed in the first position. The method controls the engine such that the engine speed is generally constant if the second switch is placed in the second position.

In accordance with another aspect of the present invention, an engine-driven power supply comprises an engine that operates at a variable engine speed and that produces a power output. A first generator coupled to the power output of the engine generates a first AC voltage that has a first magnitude characteristic in response to variations in the engine speed. A second generator coupled to the power output of the engine generates a second AC voltage that has a second magnitude characteristic in response to variations in the engine speed. A first rectifier has an input that receives the first AC voltage and has an output that provides a first DC voltage. A second rectifier has an input that receives the second AC voltage and has an output that provides a second DC voltage. The output of the second rectifier connected in series with the output of the first rectifier to superimpose the first DC voltage and the second DC to provide a composite DC voltage having a composite magnitude characteristic in response to engine speed. A DC-to-AC conversion unit has an input that receives the composite DC voltage and has an output that generates an AC output voltage responsive to the magnitude of the composite DC voltage.

In accordance with particularly preferred embodiments, the power supply further comprises a voltage stabilization circuit that stabilizes at least the first DC voltage such that the composite DC voltage increases only to a selected magnitude as the engine speed increases to a selected engine speed, and such that the composite DC voltage does not increase as the engine speed increases above the selected engine speed. The power supply further comprises a filter circuit coupled to the output of the DC-to-AC conversion unit. The filter circuit reduces harmonic components from the third AC voltage. The filter circuit generates a control voltage responsive to the third AC voltage. A control circuit is coupled to receive the control voltage from the filter circuit. The control circuit controls the voltage stabilization circuit in response to the control voltage. In particularly preferred embodiments, the first AC voltage generated by the first generator is greater than the second AC voltage generated by the second generator, and the voltage stabilization circuit stabilizes the first DC voltage provided by the first rectifier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overall Structure of Engine-Driven Generator

An overall structure of an engine-driven generator10that can be used with various features, aspects and advantages of the present invention is illustrated in FIG.1. The illustrated engine-driven generator10generally comprises an internal combustion engine12. The engine12can comprise one or more cylinders that form combustion chambers. The combustion chambers and cylinders may have any orientation (e.g., in-line, V configuration, opposed, vertical or horizontal). The engine12can operate in accordance with any combustion principle (e.g., four-cycle, two-cycle, rotary, or the like).

The engine12preferably comprises an air intake system, a fuel supply system, an ignition system and an exhaust system. A plenum chamber14draws air into the intake system. The plenum chamber14advantageously smoothes the air and reduces intake noise. A carburetor16is included as a portion of the intake system and as a portion of the fuel supply system. The air is introduced into combustion chambers of the engine12through the carburetor16. The carburetor16incorporates a throttle valve that regulates an amount of the air. For example, the amount of air introduced to the combustion chamber changes in response to a position of the throttle valve (e.g., an opening degree thereof). Fuel is drawn into the intake system at the carburetor14, and an amount of fuel also is regulated by the carburetor16so as to be generally in proportion to the air amount. Preferably, a stepping motor18proximate to the carburetor16actuates the throttle valve. The air and the fuel are mixed together within the combustion chambers to form an air/fuel charge. Normally, a greater opening degree of the throttle valve results in a greater air/fuel charge and a higher engine speed.

The air/fuel charge is fired by the ignition system at a proper time, and the engine12produces power when the air/fuel charge burns in the combustion chambers. The power rotates an output shaft or crankshaft of the engine12. Burnt charges (e.g., exhaust gases) are routed to an external location of the engine12through the exhaust system.

An AC generator22is positioned proximate to the engine12to be driven by the engine12. A shaft of the generator22is coupled with the output shaft of the engine12and rotates when the engine output shaft rotates to cause the AC generator22to generate AC power. The AC power produced by the AC generator22varies with engine speed.

A power converting unit26is electrically coupled to the generator22to convert the AC power from the generator22to a high quality AC power. The illustrated power converting unit26incorporates a controller28to control an output of the power converting unit26. The controller28also controls the stepping motor18coupled to the throttle valve. In some arrangements, the controller28is not located in the power converting unit26.

In the illustrated arrangement, the engine-driven generator10also comprises an electrical energy storage unit (electrical energy accumulator)32and a DC-to-DC converter34. The energy storage unit32preferably comprises a plurality of batteries35that are connected in series to provide a DC voltage that is the sum of the DC voltages of the batteries35.

The DC/DC converter34comprises an inverter (e.g., a DC-to-AC or DC/AC converter) and a rectifier to boost the DC voltage from the energy storage unit32to a higher DC voltage. The illustrated DC/DC converter34is electrically coupled to the power converting unit26.

The controller28coordinates the use of the output of the generator22and the output of the DC/DC converter34in addition to controlling the output of the power converting unit26. Preferably, the controller28comprises at least a central processing unit (CPU) and a memory or storage. As schematically illustrated in FIG.1andFIG. 2, first switch36, a second switch38and a third switch40are electrically connected to the power converting unit26. The first switch36is a normal/economy mode selection switch. The second switch38is a normal/power-up mode selection switch. The third switch40is a source selection switch. An operator is able to manually operate the switches36,38,40to provide command signals to the controller28to coordinate the two power sources in accordance with the functions described below.

The power converting unit26preferably produces AC power as its output. A load device44is coupled to the output of the power converting unit26to receive and use the AC power.

As shown inFIG. 2, the generator22preferably is a three-phase AC generator that comprises three generator coils48located at a stator of the generator22. A rotor rotates with when the engine output shaft rotates. When the rotor is rotated by the engine12, the generator coils48generate three AC currents that are phased at 120 degrees with respect to each other. The generated AC currents are supplied to the power converting unit26via respective power lines50. The three current phases from the generator22comprise a first AC power.

The illustrated generator22also includes a controller activating coil52that supplies activating power to the controller28via a line54whenever the generator22is driven by the engine12. The controller28advantageously includes a built-in rectifier (not shown) to rectify the activating power from the coil52to provide DC power for the controller. The energy storage unit32also can supply the activating power to the controller28via a line55when the generator22is not being driven by the engine12.

The generator22preferably includes a charge coil56that supplies a charging current to the energy storage unit32via a power line58. In the illustrated arrangement, only a half cycle of the charging current is supplied to the energy storage unit32. Alternatively, a full-wave rectifier can be interposed in the power line58to apply the full cycle of the charging current (e.g., apply full-wave power) from the charge coil56to the energy storage unit32. Also, the charge coil can be included in a generator located in the engine12that primarily generates power for engine components such as the ignition system.

The power converting unit26preferably comprises a full-wave rectifier62, an electrolytic capacitor64, an inverter or DC/AC converter66, a harmonics filter68, a current sensor70and a voltage sensor72. The illustrated power converting unit26also includes the controller28.

The full-wave rectifier62preferably is a mixed bridge circuit that comprises diodes and thyristers. The rectifier62can advantageously incorporate a voltage stabilization circuit (discussed below). The power lines50from the generator coils48are connected to input terminals of the rectifier62. The full-wave rectifier62rectifies the AC power from the coils48of the generator22to convert the AC power to DC power.

A power line74connects an output terminal of the rectifier62to an anode of the electrolytic capacitor64. A ground line76connects a ground terminal of the rectifier62to a cathode of the electrolytic capacitor64. Rather than the illustrated direct connection, the ground terminal of the rectifier62and the cathode of the electrolytic capacitor64can be advantageously interconnected by connecting each element to a common ground. The electrolytic capacitor64smoothes the output of the rectifier62.

The power line74further connects the anode of the electrolytic capacitor64to an input terminal of the inverter66. The ground line76connects the cathode of the electrolytic capacitor64to a ground terminal of the inverter66. Alternatively, the ground terminal of the inverter66may be connected to the common ground.

A DC voltage of the output power from the rectifier62is detected or monitored by the voltage sensor72and is provided to the controller28via a line78. Preferably, the voltage across the electrolytic capacitor64is detected by the voltage sensor72as the DC voltage.

The inverter66converts the DC power from the rectifier62to a second AC power. The converted second AC power is superior in quality than the AC power generated by the generator22. For example, the converted AC power can have any frequency. Unlike the frequency of the first AC power from the generator22, the frequency of the second AC power does not depend upon the speed of the engine12and can be maintained at a substantially constant value.

Two power lines80,82extend from output terminals of the inverter66and are connected to the input terminals of the harmonics filter68. The harmonics filter68preferably is a filter circuit that comprises an inductance coil84positioned in one of the power lines80,82and that comprises a capacitor86positioned between the power lines80,82. The illustrated inductance coil84is positioned in the power line80. A proper inductance of the coil and a proper capacitance of the capacitor86are selected to remove higher harmonics from the AC power. A load device can be coupled to output terminals88,90of the filter68, which also are output terminals of the power converting unit26. The AC power converted by the inverter66is supplied to the load device from the output terminals88,90after the higher harmonics are removed.

The current sensor70preferably is positioned in the power line82to detect or monitor an AC output current from the inverter82. The output current also is a load current. A rated current of this load current in the illustrated arrangement is 23 amperes, for example. The detected AC current is delivered to the controller28via a line94and is used in several controls described below. An output DC voltage also is detected or monitored by a voltage sensor95and is provided to the controller28via line96. Preferably, a voltage across the capacitor86is detected by the voltage sensor95as the output voltage and is used in feedback controls of the inverter66such that the output voltage is kept in a preset range around a desired voltage. This feedback control is provided from the controller28to the inverter66via a line98.

As shown inFIG. 4, the illustrated energy storage unit32comprises a plurality of batteries (e.g., six batteries)35connected in series. An anode terminal of the energy storage unit32is connected to an input terminal of the DC/DC converter34via a power line100. A cathode terminal of the energy storage unit32and a ground terminal of the DC/DC converter34are grounded. Each battery35preferably supplies twelve volts. Thus, the energy storage unit32advantageously supplies a total of 72 volts. As described above, the DC/DC converter34advantageously boosts the voltage to, for example, 100 volts, 120 volts or 250 volts. Because the illustrated batteries35supply a total of 72 volts, an input current required by the DC/DC converter34can be small. Thus, a heat loss at the input side of the DC/DC converter34is small. Connecting the batteries35in series to produce a greater input voltage to the DC/DC converter34permits the use of a compact, lightweight, inexpensive DC/DC converter34.

Alternatively, one or more commercially available double-layered capacitors can replace the batteries35in the energy storage unit32. The double-layered capacitors use an electrical double-layer phenomenon to provide relatively large capacitances in a low volume enclosure. The double-layer capacitors can be charged quickly by running the engine12for a short duration. Thus, the electrical double-layered capacitors are particularly suitable for the energy storage unit32if the energy storage unit32is used frequently to provide power to the inverter66. For example, when the engine-driven generator10is used in an environment where low noise is desired, continuous power can be provided by occasionally running the engine12to recharge the double-layered capacitors quickly. After the double-layered capacitors are charged, the engine12is stopped, and the input power to the inverter66is provided only by the double-layered capacitors until the double-layered capacitors need to be charged again.

In the illustrated arrangement, an output power terminal of the DC/DC converter34is connected to the power line74through a diode104that permits a current flow from the DC/DC converter34to the power line74but prevents a current flow from the power line74to the DC/DC converter34. A ground line106connects the DC/DC converter34to the ground line76. If the DC/DC converter34is grounded to the same common ground as the rectifier62and the inverter66, the ground line106is not necessary. As thus described, the DC output of the DC/DC converter34is electrically connected to the input of the inverter66in parallel with the DC output of the rectifier62.

The DC/DC converter34selectively supplies the DC power thereof to the inverter66under control of the controller28. The controller28controls the DC/DC converter34via a line110. The inverter66thus can receive either the first DC output from the rectifier62or the second DC output from the DC/DC converter34. Alternatively, the converter66can receive the output from the rectifier62and the output from the DC/DC converter34. In the illustrated arrangement, the second switch38and the third switch40are manipulated by the operator to control the selection of which DC output to provide to the DC/DC converter34.

As shown inFIG. 3, the controller28comprises AND gates114,116,118. The AND gate114has two input terminals that are both coupled to an ON terminal of the normal/power-up mode selection switch38. Each of the AND gates116,118also has two input terminals. A first input terminal of each AND gate116,118is coupled to an OFF terminal of the normal/power-up mode selection switch38. A second input terminal of the AND gate116is coupled to an energy storage unit-DC/DC converter selection terminal of the source selection switch40. The second input terminal of the AND gate118is coupled to an engine-generator selection terminal of the source selection switch40.

The controller28additionally comprises an engine-generator side control section122and an energy storage unit-DC/DC converter side control section124. The engine-generator side control section122controls the operation of the engine12and enables the output from the rectifier62to be provided as an input to the inverter66. The control signals are provided to the engine12and to the rectifier62via a line126(which may represent a plurality of control lines).

The energy storage unit-DC/DC converter side control section124enables the output from the DC/DC converter34to be provided as an input to the inverter66. An output terminal of the AND gate14is connected to both the engine-generator side control section122and the energy storage unit-DC/DC converter side control section124. An output terminal of the AND gate116is connected to the energy storage unit-DC/DC converter side control section124. An output terminal of the AND gate118is connected to the engine-generator side control section122.

When the normal/power-up mode selection switch38is turned on, both the engine-generator side control section122and the energy storage unit-DC/DC converter side control section124are enabled through the AND gate114. Thus, both the output power of the rectifier62and the output power of the DC/DC converter34are supplied to the inverter66. On the other hand, when the normal/power-up mode selection switch38is turned off and the energy storage unit-DC/DC converter selection terminal of the source selection switch40is selected, only the energy storage unit-DC/DC converter side control section124is enabled and only the output power of the DC/DC converter34is supplied to the inverter66. At this time, the engine12does not operate because the engine-generator side control section122is not enabled. For example, the ignition system cannot fire the air/fuel charge unless the engine-generator side control section122is enabled. When the normal/power-up mode selection switch38is turned off and the rectifier selection terminal of the source selection switch40is selected, the engine-generator side control section122is enabled and only the output power of the rectifier62is supplied to the inverter66.

As shown inFIG. 8, the controller28is able to automatically supply both the output power of the rectifier62and the output power of the DC/DC converter34to the inverter66even when the second switch38is turned under some conditions. For example, if the AC output current (load current) detected by the current sensor70is greater than 20 amperes and the DC voltage detected by the voltage sensor72is less than 190 volts, the controller28determines that a large load device (e.g., a device requiring substantial power) is connected to the output terminals88,90. The storage unit-DC/DC converter side control section124activates the DC/DC converter34to add the DC output power of the DC/DC converter34to the DC output power of the rectifier62.

The reference current of 20 amperes is an exemplary current. Other reference currents (e.g., 19 amperes or 21 amperes) can be used. Also, the reference voltage of 190 volts is an exemplary voltage. Other reference voltages (e.g., 170 volts) can be used.

If the load current becomes approximately twice as large as the rated current, the controller28determines that the load current has suddenly increased. The controller28determines this state by calculating a rate of increase of the load current. Under this condition, the energy storage unit-DC/DC converter side control section124also activates the DC/DC converter34to add the output power of the DC/DC converter34to the output power of the rectifier62.

As shown inFIG. 9, the illustrated throttle valve of the engine12is initially set in a preset position when the engine12starts under the control of engine-generator side control section122in accordance with a control program ofFIG. 9, and the inverter66starts outputting in this state.

The method ofFIG. 9starts and proceeds to a step S1. At the step S1, the engine-generator side control section122controls the stepping motor18to open the throttle valve such that the engine speed increases toward a speed of 1,500 rpm. The method then proceeds to a step S2to determine whether the engine speed is equal to or greater than 1,500 rpm. The engine speed is calculated by an engine speed calculation section128, described below with reference to FIG.5. If the determination at the step S2is negative (e.g., the engine speed is less than 1,500 rpm), the method returns to the step S2and repeats the step S2. If the determination at the step S2is affirmative (e.g., the engine speed is at least 1,500 rpm), the method proceeds to a step S3. At the step S3, the control section122sets the engine speed 2,800 rpm. Then, the method proceeds to a step S4, and the control section122sets an output start time to 0.5 seconds with a timer. After the start time (0.5 seconds) elapses, the inverter66starts outputting the AC power.

As shown inFIG. 5, the illustrated controller28additionally comprises a current/engine speed map storage section130, a throttle valve control amount calculation section132, and a motor driver section136.

The current/engine speed map storage section130is substantially part of the memory and stores a control map comprising an AC output current (load current) versus an engine speed. The relationship stored in the map is illustrated in FIG.6. The map involves two characteristics A and B. If the characteristic A is selected, the engine speed generally changes as the AC output current changes. On the other hand, if the characteristic B is selected, the engine speed is fixed at least in a range less than the rated current.

The operator can select either the characteristic A or the characteristic B with the normal/economy mode selection switch36. For example, when the normal/economy mode selection switch36is turned on, the characteristic A is selected. Also, when the normal/economy mode selection switch36is turned off, the characteristic B is selected. As shown inFIG. 7, the fuel consumption A1associated with the characteristic A is less than the fuel consumption B2associated with the characteristics B. Accordingly, the operation using the characteristic A is economical. In addition, the engine noise occurring when the engine is operated in accordance with the characteristic A is less than when the engine is operated in accordance with the characteristic B. On the other hand, the characteristic B is suitable for certain load devices such as, for example, an electric grinder, because the load current of such kinds of load devices changes quite often and the stable engine speed is convenient with the engine-driven generator10.

The throttle valve control amount calculation section132calculates a control amount of the throttle valve opening based upon the selection of the characteristic A or the characteristic B with the selected characteristic. The control amount is determined such that an actual engine speed approaches the preset engine speed with the characteristic A or with the characteristic B by increasing or decreasing the opening degree of the throttle valve and thereby increasing or decreasing the engine speed. The actual engine speed can be calculated by the engine speed calculation section132. An output shaft (crankshaft) rotation sensor140is provided at a location proximate to the output shaft of the engine12. The engine speed calculation section128calculates the actual engine speed using a signal from the output shaft rotation sensor140. The motor driver section136then actuates the stepping motor18based upon the control amount calculated by the throttle valve control amount calculation section132. Accordingly, the engine speed changes or is fixed along the characteristic A or the characteristic B, respectively. Preferably, a fixed engine speed is 3,600 rpm.

FIG. 10illustrates an exemplary control program that defines a method for setting the engine speed versus the AC output current (load current). The engine speed setting method starts and proceeds to a step S11. At the step S11, the controller28determines whether an engine start timer for low temperature has been set to zero. Preferably, a temperature sensor (not shown) is provided to detect a temperature proximate to the engine-driven generator10. The controller28previously determines whether the temperature is greater than a preset temperature such as, for example, 0 degrees Celsius (0° C.) in another control program. If the temperature is equal to or less than the preset temperature, the start timer is not set at zero. Rather, the start timer is set to several minutes. On the other hand, if the temperature is greater than the preset temperature, the start timer is set at zero.

If the controller28determines at the step S11that the start time is not zero (i.e., the method makes a negative (N) determination in the step S11), the method proceeds to a step S12. At the step S12, the controller28sets the engine speed to, for example, 3,800 rpm. The motor driver section136of the controller28thus actuates the stepping motor18to force the engine12to operate at the engine speed of 3,800 rpm for several minutes to warm up the engine12. The inverter66starts outputting power corresponding to this engine speed, and the method returns to the step S11.

If the controller28determines at the step S11that the low temperature timer is set at zero minutes (i.e., the method makes a positive (Y) determination at the step S11), the method proceeds to a step S13where the controller28calculates the engine speed using the characteristic A of the control map shown in FIG.6. The method then proceeds to a step S15.

At the step S15, the method determines whether the normal/economy mode selection switch36has been turned on. If the determination is affirmative (i.e., the normal/economy mode switch36is on), the motor driver section136of the controller28controls the stepping motor18such that the engine12operates at the engine speed set at the step S14. The inverter66starts outputting power corresponding to this engine speed, and the method returns to the step S11.

If the determination in the step S15is negative (i.e., the normal/economy mode switch36is not on), the controller28sets the engine speed generally at 3,600 rpm unless the engine speed has been set equal to or greater than 3,600 rpm at the step S14. The motor driver section136actuates the stepping motor18to force the engine12to operate at the engine speed of 3,600 rpm. The inverter66starts outputting corresponding to the engine speed. Meanwhile, the engine speed setting method starts again.

Alternatively, the engine12advantageously incorporates a throttle position sensor to sense an actual throttle valve opening. In this alternative, a throttle valve opening degree replaces the engine speed as illustrated in parenthesis in FIG.6. The engine speed calculation section128and the output shaft rotation sensor140are not necessary in this alternative control; however, it should be noted that the engine speed can completely correspond to the throttle valve opening degree.

Operation Modes of Engine-driven Generator

The illustrated engine-driven generator10operates in the following modes.

(1) Normal Power Mode

Normally, the operator sets the normal/power-up mode selection switch38off to select the power-up mode. The operator also selects the engine-generator side using the source selection switch40. The engine-generator side control section122is enabled via the AND gate118and activates the engine12. In the normal power mode, the engine12is controlled for economy operation or non-economy operation in accordance with the state of the normal/economy mode selection switch36.

(a) Economy Operation

If the operator needs a constant output (or economy operation), the operator turns the normal/economy mode selection switch36off to select the economy operation. The engine12thus operates at a constant engine speed (e.g., approximately 3,600 rpm) in accordance with the characteristic B of FIG.6. The generator22also generates a constant AC power corresponding to the constant engine speed, and the power converting unit26outputs the constant AC power.

If the operator needs a variable output (or non-economy operation), the operator turns the normal/economy mode selection switch36on to select non-economy operation. The engine12thus operates at various engine speeds in response to the AC output current (load current) sensed by the current sensor70. The generator22generates an AC power corresponding to the engine speed, and the power converting unit26outputs the variable AC power.

(2) Quiet Operation Mode

If the operator wants to select quiet operation of the engine-driven generator10, the operator sets the normal/power-up mode selection switch38off and selects the storage unit-DC/DC converter side using the source selection switch40. The energy storage unit-DC/DC converter side control section124is enabled via the AND gate116and stops the engine operation so that the engine12is no longer rotating and no power is generated. The energy storage unit-DC/DC converter side control section124controls the DC/DC converter34to output the DC power to the inverter66. The power converting unit26thus outputs an AC power corresponding to the DC power. Because the engine12does not operate in this mode, the engine-driven generator10can provide the required power output under quiet conditions.

If the operator wants to use a load device that requires a relatively large power that can exceed the rated current, the operator sets the normal/power-up mode selection switch38on. Both the engine-generator side control section122and the energy storage unit-DC/DC converter side control section124are enabled via the AND gate114. Thus, the engine12operates to drive the generator22. The output from the generator22, rectified by the rectifier62, and the output from the DC/DC converter34are both supplied to the inverter66. The power converting unit26outputs the full power to the load device. Preferably, the engine12operates at various engine speeds in response to the load current sensed by the current sensor70regardless of whether the normal/economy mode selection switch36is turned on or is turned off.

The illustrated engine-driven generator10automatically operates in the power-up mode under some conditions, such as, for example, when the controller28determines that the load device requires power that causes the load current to exceed the rated current or determines that the load current suddenly increased. The controller28determines that the load device requires such an amount of power using the relationship shown in FIG.8. For example, if the load current is greater than 20 amperes and the DC voltage from the rectifier62is less than 190 volts, the controller28determines that the load device requires a large amount of power. The controller28also determines that the load current suddenly increases by calculating the rate of increase of the load current sensed by the current sensor70.

In this automatic power-up mode, both the engine-generator side control section122and the energy storage unit-DC/DC converter side control section124are enabled through the AND gate114. The outputs from the rectifier62and the DC/DC converter34are both supplied to the inverter66. The power converting unit26outputs the full power to the load device. Preferably, the engine12operates at various engine speeds in response to the load current sensed by the current sensor70regardless of whether the normal/economy mode selection switch36is turned on or is turned off

The operation modes described above are exemplary modes. Other operation modes can be added. Alternatively, the operation modes can be modified. For example, the controller28can automatically add the power from the DC/DC converter34to the power from the rectifier62for a predetermined period of time whenever a load device requires a large amount of power immediately after the load device is switched. The controller28performs this function without using the sensed signals from either the current sensor70or the voltage sensor72. An example of a load device is an electric pump. Preferably, a load device selection button is provided, and the operator can push the load device selection button when such a load device (e.g., the pump) is connected.

As described above for the illustrated arrangement, the operator can select, for example, between a quiet operation mode with the energy storage unit being the sole source of output power or a more powerful operation mode in which both the generator and the energy storage unit provide the output power. The latter selection advantageously allows a relatively large load device to be connected to the engine-driven generator. In addition, if the latter selection is made, the engine-driven generator can quickly provide necessary power even though a relatively large load device abruptly requires a large power and the engine cannot follow the requirement. The illustrated arrangement can be used for a large number of applications in addition to the applications described herein.

Modified Engine-driven Generator

FIGS. 11-14illustrate a modified engine-driven generator148configured in accordance with another embodiment of the present invention. The same components and members that have been already described above are not described again. The same reference numerals that have been assigned to those components and members in the previous figures are assigned to like components inFIGS. 11-14. The energy storage unit32, the DC/DC converter34and the second and third switches38,40are not shown inFIGS. 11 and 12and may not be required for certain embodiments of the engine-driven generator148.

In the illustrated arrangement, the engine-driven generator148incorporates two generators22L,22S. Each generator22L,22S has a similar construction to the generator22described above, and the two generators22L,22S are similar to each other; however, the generator22L can generate more power than the generator22S because relatively larger generator coils48are provided in the generator22L than in the generator22S.

As shown inFIG. 12, the outputs of the generators22L,22S are connected as inputs to a rectifier assembly150. The rectifier assembly150comprises two full-wave rectifiers152,154and a voltage stabilization circuit156. The rectifier152comprises diodes158and thyristers160and is connected to the voltage stabilization circuit156through the thyristers160. The rectifier62ofFIG. 2is substantially the same as the rectifier152and can incorporate the same voltage stabilization circuit156. The generator22L is connected to the rectifier152. The generator22S is connected to the rectifier154. The rectifiers152,154are connected in series with one another such that the voltage generated by the rectifier152is added to the voltage generated by the rectifier154to produce an output voltage from the rectifier assembly150that is equal to the sum of the voltage generated by the rectifier152and the voltage generated by the rectifier154.

The output voltage from rectifier assembly150is provided as an input to the inverter66. An electrolytic capacitor64is connected across the output terminals of the rectifier assembly150. The inverter66comprises metal-oxide semiconductor (MOS) transistors164. The illustrated inverter ofFIG. 12incorporates the current sensor70therein. The inverter66is connected to a harmonics filter68such that the outputs of the inverter66can be supplied to load devices at the output terminals88,90. The harmonics filter68removes harmonics in the output power from the inverter66. Also, a voltage across a capacitor in the harmonics filter68is sensed, as described below, to stabilize the output power.

The controller28controls the inverter66and also controls the rectifier assembly150and the DC/DC converter (not illustrated in FIG.12). The second and third switches38,40(FIGS. 1-3) can be included in the controls as well as the first switch36. The controller28in this arrangement may advantageously have the same structure as described above and as illustrated inFIGS. 3 and 5, and may perform the same control operations as described above and illustrated inFIGS. 6-10.

As shown inFIG. 13, a DC voltage from the rectifier152changes in accordance with a characteristic C (solid line) in response to the engine speed unless the voltage stabilization circuit156is provided. In accordance with the characteristic C, a voltage at an engine speed of 6,000 rpm is fairly large (e.g., greater than 200 volts). The voltage stabilization circuit156is provided to cause the DC voltage from the rectifier152to change in accordance with a characteristic C1so that, for example, the voltage from the rectifier160at the engine speed of 6,000 rpm is 89 volts. A DC voltage from the rectifier154changes in accordance with a characteristic D in response to the engine speed. For example, a voltage from the rectifier154at an engine speed of 6,000 rpm is 125 volts. Since the rectifier152and the rectifier154are connected in series, the DC voltage having the characteristic C1and the DC voltage having the characteristic D are added together, and the sum of the two voltages changes in accordance with the characteristic E. In particular, the DC voltage according to the characteristic E generally increases to 204 volts as the engine speed increases toward approximately 2,500 rpm. After the engine speed reaches approximately 2,500 rpm, the DC voltage is generally maintained at this voltage, e.g., 204 volts, until the engine speed increase to approximately 6,000 rpm. Thus, the range of the DC voltage with the characteristic E between the engine speed of 2,500 rpm and the engine speed of 6,000 rpm is maintained approximately constant.

As shown inFIG. 14, if the same sized generators are provided, the DC voltage that is stabilized by the voltage stabilization circuit156could quickly go down to zero volts at 4,000 rpm, for example, as illustrated by a characteristic F, although another DC voltage that is not stabilized can continue to increase beyond 200 volts in the range over 4,000 rpm as illustrated by a characteristic G. Accordingly, an added characteristic H can be constant in a relatively short range between the engine speed of 2,500 rpm and the engine speed of 4,000 rpm. At engine speeds greater than 4,000 rpm, the DC voltage having the characteristic H increases in accordance with the characteristics G. That is, the DC voltage having the characteristic H cannot be normally controlled over 4,000 rpm.

As thus described, in the preferred embodiment, the generators22L,22S in the illustrated arrangement have different sizes (e.g., power generating capacities). In particular, the generator22L is larger than the generator22S. The DC voltage can be kept at 204 volts between the engine speeds 2,500 rpm and 6,000 rpm. Because the DC voltage of 204 volts can produce an effective AC voltage of 120 volts without the sine wave form thereof distorted, the engine-driven generator in this arrangement can provide a superior output in such a relatively long range of the engine speed.

Because the DC voltage does not exceed 204 volts in this arrangement, the voltage capacity of electrical components of the engine-driven generator does not need to be large.

Also, the illustrated rectifier assembly150only needs one voltage stabilization circuit156for the rectifier152. The rectifier154does not require a voltage stabilization circuit. Thus, the engine-driven generator148in this arrangement can have a simple structure.

In addition to other advantages, a constant voltage can be obtained for a greater range without requiring any switching mechanisms that switch from one generator to another generator or that switch from one generator component to another generator component. No excessive or sudden changes in the voltage characteristic and no electrical noises caused by switching are generated by the illustrated arrangement.

More than two generators can be used in the engine-driven generator148. Also, additional voltage stabilization circuits (preferably less than the number of generators) can be provided in the engine-driven generator.

Alternative Embodiment of Modified Engine-driven Generator

A modified engine-driven generator178configured in accordance with a further embodiment of the present invention is described below with reference toFIGS. 15-19. The same components and members that have been already described above are not described again. The same reference numerals that have been assigned to those components and members in the previous figures are assigned to like components inFIGS. 15-19. The energy storage unit32, the DC/DC converter34and the second and third switches38,40are not shown inFIGS. 15 and 16and may not be required for certain embodiments of the engine-driven generator178.

In the illustrated arrangement, a noise-suppressing housing180surrounds the engine12, the generator22and other engine/generator components. The engine-driven generators10,148described above can also have such a housing. The housing180effectively inhibits engine noise and generator noise from disturbing the operator or persons who are around the engine-driven generator178.

On the other hand, however, the heat produced by the engine12and the generator22can stay in a space182defined by the housing180. The temperature of air in the space182thus increases when the engine12operates. The high temperature of the air can affect the operations of the engine and the generator. Particularly, the efficiency for generating power can deteriorate as the internal resistances of the components increase with increased temperature. That is, the current sensor70detects the output current decreasing because of the increased resistances.

Under the increased temperature condition, if the voltage sensor95were not provided in the foregoing engine-driven generator10, for example, the controller28could determine that the load device does not need a high power because the current sensor70indicates that the output current decreases. The controller28thus actuates the stepping motor18to decrease the throttle valve opening degree such that the engine speed decreases. Then, the output voltage decreases further until the engine-driven generator can no longer supply sufficient voltage to the load device.

However, the foregoing engine-driven generator10is provided with the voltage sensor95and can properly inform the controller28that the load device still need the high power and the controller28can normally control the inverter28.

The engine-driven generator178in this modified arrangement includes another technique to improve the heat problem without the voltage sensor. However, it should be noted that the engine-driven generator178can still be provided with the voltage sensor for the improvement of the heat problem or other purposes.

The engine-driven generator178incorporates a temperature sensor unit186that detects a temperature of the air in the space182, preferably, an air temperature in the power converting unit26. The temperature sensor unit186is connected to the controller28through a proper interface to send a temperature signal to the controller28, preferably, the throttle valve calculation section132(FIG. 17) thereof through a signal line188. The temperature sensor unit186comprises a temperature sensor such as, for example, a thermistor190.

The engine speed calculation section128in this modified arrangement is located out of the controller28as an engine speed calculation unit as shown in FIG.17. However, the engine speed calculation unit is the same as the foregoing engine speed calculation section128. The output shaft rotation sensor140is omitted in FIG.17.

As shown inFIG. 18, the illustrated temperature sensor unit186has a characteristic I and outputs a voltage that generally changes in proportion to a temperature in the power converting unit26. For instance, the voltage at the temperature 25° C. is approximately 2.3 volt, the voltage at the temperature 70° C. is approximately 4.0 volt and the voltage at the temperature 90° C. is approximately 5.0 volt.

As shown inFIG. 19, the controller28operates in accordance with a control map that comprises engine speed versus an AC output current (load current). The illustrated controller28controls the inverter66using at least two characteristics J and K, although additional characteristics can be included. The characteristic J and the characteristic K are similar to each other, and the engine speed generally increases when the AC output current increases; however, the engine speed controlled in accordance with the characteristic K is higher than the engine speed controlled in accordance with the characteristic J.

In this embodiment, the controller28determines that the temperature is normal if the sensed temperature is less than 90° C. and selects the characteristic J. Also, the controller28determines that the temperature is abnormally high if the sensed temperature is equal to or greater than 90° C. and selects the characteristic K. The controller28controls the stepping motor18such that the engine speed changes in accordance with either the characteristic J or the characteristic K. Because the engine speed controlled in accordance with the characteristic K is higher than the engine speed controlled in accordance with the characteristic J, the generator22generates a higher power under the abnormal temperature condition than under the normal temperature condition. Thus, the engine-driven generator178can provide a proper power even under the high temperature condition without using any voltage sensor.

Similar to the engine-driven generator10, the engine12in this arrangement can alternatively incorporate a throttle position sensor to sense an actual throttle valve opening. As shown in parentheses inFIG. 19, the throttle valve opening degree can replace the engine speed. It should be noted, however, the engine speed can completely correspond to the throttle valve opening degree.

The illustrated temperature sensor unit186detects the air temperature in the space182. Generally, the temperature inside of the housing180does not depend on location and is generally equal at any locations. The temperature sensor unit186thus can be placed at any position in the space182and can even detect a temperature of generator components such as, for example, a temperature of the generator coils48.

The controller28does not necessarily require the control map and can calculate an engine speed that is added to a basic engine speed.

Decompression Mechanism of Engine

With reference toFIGS. 20-26, the engine12preferably incorporates a decompression mechanism200.

Typically, the illustrated engine12is manually started by the operator with a recoil starter unit. The recoil starter unit comprises a starter rope that is normally coiled by force of a bias mechanism such as, for example, a spring unit. One end of the rope is coupled with the output shaft (crankshaft) of the engine12, while another end of the rope extends outwardly and a knob is attached thereto. When the operator quickly pulls the knob, the rope drives the output shaft of the engine12and the engine12starts accordingly.

The starting operation of the engine12with the recoil starter unit can be somewhat difficult for some people to accomplish because it may require a large amount of force to start the engine. The difficulty is related to the construction of the engine12. The engine12has a combustion chamber defined by a piston and the force that the operator applies to the rope must be sufficient to move the piston against the repulsion force generated within the combustion chamber that occurs as the gases therein are compressed. The difficulty of performing the starting operation increases as the volume of the combustion chamber increases.

The decompression mechanism200is provided to reduce the repulsion force. For instance, the decompression mechanism can lift either one of an intake or exhaust valve or both of them to decompress the combustion chamber during the starting operation.

With reference toFIGS. 20 and 21, the engine12is preferably a single cylinder, four cycle engine. A cylinder block202defines a cylinder bore204. A piston206is reciprocally disposed within the cylinder bore204. The cylinder block202also defines an intake port208and an exhaust port (not shown) opposite to the piston206. The cylinder bore204communicates with both the intake port208and the exhaust port. An intake valve210and an exhaust valve extend through the intake port208and the exhaust port, respectively. The cylinder block202, the piston206, the intake valve210and the exhaust valve together form a combustion chamber212. The intake valve210and the exhaust valve selectively connect the intake port208and the exhaust port, respectively, with the combustion chamber212.

Bias springs213normally urge the intake valve210and the exhaust valve toward the respective closed position. At the closed position, the intake valve210or the exhaust valve closes the intake port208or the exhaust port, respectively, relative to the combustion chamber212and thus the intake port208or the exhaust port does not communicate with the combustion chamber212. At an open position, the intake valve210or the exhaust valve opens the intake port208or the exhaust port, respectively, toward the combustion chamber212and thus the intake port208or the exhaust port communicates with the combustion chamber212.

The illustrated cylinder block202defines a plurality of fins214extending outwardly from an outer surface of the cylinder block202to radiate heat.

A crankcase member216is coupled with the cylinder block202to form a crankcase chamber218therebetween. The cylinder block202and the crankcase member216together form an engine block219. A crankshaft220is supported at bearing portions of the crankcase member216for rotation by bearings221. The crankshaft220forms the output shaft of the engine12. The crankshaft220is connected with the piston206by a connecting rod222such that the crankshaft220rotates when the piston206reciprocates within the cylinder bore204.

The intake port208and the intake valve210form part of the air intake system through which the air is drawn to the combustion chamber212. The throttle valve is disposed in the intake system to regulate the air amount. The carburetor is also provided at a portion of the intake system to supply the fuel into the intake system as described above. The air and the fuel can enter the combustion chamber212when the intake valve210connects the intake port208with the combustion chamber212. The air/fuel charge is thus formed within the combustion chamber212. Other types of charge formers (e.g., direct or port injection fuel injectors) can also be used.

The ignition system has an ignition plug226that ignites the air/fuel charge within the combustion chamber212. The air/fuel charge burns and the volume thereof abruptly expands to move the piston206toward the crankcase chamber218. The reciprocal movement of the piston206rotates the crankshaft220through the connecting rod222. The burnt charge, i.e., the exhaust gases, are routed to the external location through the exhaust system that comprises the exhaust valve and the exhaust port.

The engine12incorporates a valve actuation mechanism230. The mechanism230comprises a drive gear232, a driven gear234, a cam236, intake and exhaust cam followers238,240, intake and exhaust push rods242,244and intake and exhaust rocker arms246,248.

The drive gear232is disposed next to one of the bearings221and is coupled to the crankshaft220for rotation with the crankshaft220. The driven gear234has a peripheral section250(FIGS. 22-24) where gear teeth extend outwardly. The gear teeth mesh with gear teeth of the drive gear232. The driven gear234has an outer diameter that is twice as large as the outer diameter of the drive gear232. Additionally, the number of gear teeth of the driven gear234is twice the number of the gear teeth of the drive gear232.

With reference back toFIGS. 20,21, a portion of the cylinder block202is partly nested in the crankcase member216. An outer surface of the cylinder block202and an inner surface of the crankcase member216together define a space252. The driven gear234is positioned in this space252. Also, the outer surface of the cylinder block202and the inner surface of the crankcase member216together define a lower support that supports a center shaft254of the driven gear234. The driven gear234is rotatable about the center shaft254. Alternatively, the center shaft254can rotate together with the driven gear234relative to the cylinder block202and the crankcase member216.

The illustrated cam236has a generally oval shape and is unitarily formed on the driven gear234as a cam section of the driven gear234. The center shaft254extends through a generally center portion of the cam section236. The cam section236defines a side surface256and a cam lobe258extends from the side surface256. The cam lobe258moves around the center shaft254clockwise as indicated by the arrow260ofFIG. 20when the cam section236rotates.

The intake and exhaust cam followers238,240are generally V-shaped members. The outer surface of the cylinder block202and the inner surface of the crankcase member216together define an upper support that supports a cam follower shaft264. The cam followers238,240are swingable about the shaft264at one end of the V-shape. That is, each lower end266of the cam followers238,240abuts on a side surface256of the cam section236and each cam follower238,240swings about the shaft264when the cam section236rotates and the cam lobe258meets the lower end266of the cam follower238,240.

Another end of the V-shape of the intake cam follower238holds a lower end of the intake push rod242. Also, another end of the V-shape of the exhaust cam follower240holds a lower end of the exhaust push rod244. Upper ends of the intake and exhaust push rods242,244are each coupled with a first end of the intake and exhaust rocker arms246,248, respectively, such that the upper ends thereof are not rigidly affixed to the rocker arms246,248but can push respective first ends of the rocker arms246,248upwardly. The rocker arms246,248are swingably supported atop the cylinder block202by rocker arm shafts269. Each rocker arm246,248has a second end that is coupled with the top of the intake valve210and the exhaust valve respectively. The respective rocker arms246,248swing about the rocker arm shafts269when the push rods242,244push the first end thereof The second ends of the rocker arms246,248then push the respective top ends of the intake valve210and the exhaust valve when the rocker arms246,248swing. The rocker arms246,248preferably are covered by a cylinder head cover268.

The drive gear232rotates together with the crankshaft220. The drive gear232drives the driven gear234. The driven gear234rotates once when the driven gear232and the crankshaft220rotate twice. The cam section236rotates as a portion of the driven gear234. The cam lobe258lifts the intake cam follower238first and then lifts the exhaust cam follower240. The intake push rod242and then the exhaust push rod244push the respective rocker arms246,248in this sequence. Then, the respective rocker arms246,248, one after another, push the intake valve210and the exhaust valve against the bias force of the springs213. The intake valve210and the exhaust valve thus move to each open position (connecting position) to allow the air and fuel to enter the combustion chamber212. The rocker arms246,248, the push rods242,244and the cam followers238,240return to their initial positions when the cam lobe258has passed over the cam followers238,240. The intake valve210and the exhaust valve thus return to their closed position (disconnecting position) to inhibit the air and fuel from entering the combustion chamber212. The intake valve210and the exhaust valve move to each open position once every two rotations of the crankshaft220.

With continued reference toFIGS. 20 and 21and additional reference toFIGS. 22-26, the decompression mechanism200is further described below.

The driven gear234has a boss270defined at the center thereof The illustrated boss270is rotatably mounted on the center shaft254. A circular recess272is coaxially defined around the boss270. In other words, an intermediate section274comprising the circular recess272is defined between the boss270and the peripheral section250. The intermediate section274is generally flat and, as best seen inFIG. 24, a wall thickness of the center area274is thinner than the thickness of the boss270and the thickness of the peripheral area250. The cam section236is generally formed on the side of the driven gear234opposite the recess272, which is defined by the intermediate section274and the peripheral section250. The intermediate section274extends beyond the cam section236to the peripheral section250.

A portion of the intermediate section274protrudes to form a pivot pin278extending toward a portion of the inner surface of the crankcase member216. The pivot pin278is disposed near the boss270and is offset from a center axis of the driven gear234. While the pivot pin278is integral with the intermediate section274in the illustrated embodiment, the pivot pin278can be formed separately and then assembled with the intermediate section.

A portion of the side surface256of the cam section236, which is located next to the pivot pin278, is partially and slightly recessed toward the pivot pin278to form an arcuate recess280. The arcuate recess280has a curvature that preferably forms a semicircular arc. The arcuate recess280is coaxially formed around the pivot pin278and has an outer diameter that is larger than the outer diameter of the pivot pin278.

The arcuate recess280constitutes a portion of a slot284that is defined in the intermediate section274. In other words, the arcuate recess280forms one side of the slot284. Another side of the slot284, opposite the arcuate recess280, also preferably is arcuately configured and is coaxially formed around the pivot pin278. With reference toFIG. 22, a portion of the side surface256of the cam section236can be seen through the slot284.

A decompression lever288is journaled on the pivot pin278for pivotal movement. The decompression lever288is thus located on a side of the intermediate section274that is opposite to the cam section236. With reference toFIGS. 25 and 26, the decompression lever288is generally configured as a hook-shape and is thinner than the depth D of the recess272. The lever288comprises a lifter section290and a weight section292. An opening294is defined adjacent to the lifter section290. The pivot pin278extends through the opening294.

The weight section292extends opposite the lifter section290and defines the major part by mass of the hook configuration. An outer surface of the weight section292preferably has a curvature that corresponds to the peripheral section250of the driven gear234.

The lifter section290is bent generally normal to the weight section292. The lifter section290has an arcuate surface296that faces the arcuate recess280of the cam section236. The arcuate surface296has a curvature that preferably forms a semicircular arc. An inner diameter of the arcuate surface296is slightly larger than the outer diameter of arcuate recess280. Also, the slot284is formed larger than the lifter section290. Thus, the lifter section290is movable along the cam section236within the slot284when the decompression lever288pivots about the pivot pin278. The lifter section290always leans upon the side surface256of the cam section236wherever the lifter section290is positioned.

The intermediate section274preferably defines ribs298that support the decompression lever288. The illustrated ribs298are arcuate and are generally coaxially formed around the pivot pin278. A side surface300(FIG. 24) of the decompression lever288can lean against the ribs298as the decompression lever288slidably moves over the ribs298.

The illustrated decompression lever288preferably is made of a flat sheet metal. An original lever member, which has the lifter section290extending straight relative to the weight section292, is punched out from the sheet metal. The opening294is simultaneously made in the punching process. The original lever member is then pressed so that the lifter section290is bent from a portion of the original lever. Afterwards, at least the arcuate surface296is finished in a machining process to form the desired curvature. Another surface of the lifter section290opposite to the arcuate surface296can be shaped arcuately, if necessary. Alternatively, the decompression lever288can be produced by sintering, forging, casting, machining or other conventional methods.

A bias spring302urges the decompression lever288toward an initial position. The initial position is defined by the bias spring302urging the weight section292of the decompression lever288against an abutment portion299that extends from the intermediate section274into the circular recess272. The solid lines ofFIG. 23, which illustrate the bias spring302, show that the lever288is in the initial position. In this initial position, the decompression lever288is generally positioned about the boss270of the driven gear234.

The bias spring302is preferably a coil spring. A coiled portion303of the bias spring302is disposed in a circular groove304(FIG. 24) that is formed adjacent to the pivot pin278and coaxially with the pivot pin278. The groove304has a larger diameter than the pivot pin278. The bias spring302also has two straight extending end portions306,308. An embankment310extends generally radially from the boss270adjacent to the pivot pin278and the slot284. A groove312extending from the circular groove304is defined along the embankment310and generally between the embankment310and the slot284. The end portion306of the spring302is positioned in the groove312such that the end portion306acts against the embankment310. The other end portion308is bent and is hooked on an engagement surface314of the decompression lever288which is located next to the lifter section290. Thus, the spring302normally biases the decompression lever288in the initial position.

A cover member318preferably covers the decompression mechanism200. The illustrated cover member318is generally circular and flat. The cover member318has a diameter slightly smaller than the diameter of the recess272. Preferably, the driven gear234defines flanges273that extend from the periphery section250to the intermediate section274and hold corresponding portions of the cover member318. Also, the driven gear234preferably defines three openings320at locations between the intermediate section274and the periphery section250such that steps322are formed at outer edges of the openings320in the periphery section250. The cover member318has three hooks324that are inserted into the respective openings320. A distal end of each hook324engages each step322. The cover member318is thus affixed to the driven gear234.

The cover member318preferably abuts a terminal end328of the boss270and a terminal end330of the pivot pin278. Accordingly, the decompression lever288and the bias spring302are inhibited from slipping off of the pivot pin278and slipping out of the grooves304,312, respectively. On the other hand, the cover member318is preferably spaced apart from the decompression lever288so as to allow the lever288to move freely.

The cover member318preferably defines an arcuate slot334(FIG. 23) that generally extends to the side of one of the ribs298. The hooked end of the bias spring302can thus move in the slot334when the decompression lever288pivots.

The decompression lever288rests in the initial position, illustrated by the actual line of FIG.23and also illustrated inFIG. 24, because the bias spring302urges the lever288to this position. The weight section292is generally positioned opposite the pivot pin278relative to the boss270. The lifter section290of the decompression lever288protrudes from the side surface256of the cam section236in this position as shown in FIG.20. In other words, the thickness of the lifter section290acts to add thickness to a part of the cam section236, i.e., it increases the cam profile. In the illustrated arrangement, the lifter section290preferably extends from a specific portion of the cam section236such that the lifter section290follows the cam section lobe258with a slight delay when the cam section236rotates.

The operator pulls the rope of the recoil starter unit. The drive gear232rotates together with the crankshaft220and drives the driven gear234. The decompression lever288remains in the initial position because the rotational speed of the driven gear234under this condition is relatively slow and does not generate any centrifugal force that will cause the lever288to move. The cam section236, which is unitarily formed with the driven gear234, rotates and the lifter section290attached to the cam section236lifts the cam section followers238,240. The intake valve210and the exhaust valve are thus opened through the valve actuation mechanism230and the combustion chamber212is decompressed. More specifically, because the lifter section290is attached at the specific portion of the cam section236as described above, the intake valve210can stay open for a time after the normal end timing of the intake stroke of the engine12has passed. Similarly, the exhaust valve can stay open for a time after the normal end timing of the exhaust stroke of the engine12has passed. Accordingly, the operator can more easily operate the recoil unit.

The engine12then starts operating. The drive gear234, together with the crankshaft220, rotates at a higher speed and drives the driven gear234. The driven gear234also rotates at a higher speed. The resultant centrifugal force on the weight section288throws the weight section288toward the peripheral area250thereby rotating the decompression lever288about the pivot pin278, as is indicated by the phantom line of the lever288of FIG.23. The lifter section290is now retracted into the recess280and under the cam section236so that it no longer protrudes beyond the cam surface256and lifts the cam followers238,240. Accordingly, the valve actuation mechanism230actuates the intake valve210and the exhaust valve at normal times and for normal durations.

As thus described, the illustrated decompression lever288has a simple configuration and is generally flat such that the thickness thereof is generally equal at every portion. The lever288can thus be made from a sheet metal to reduce the manufacturing cost of the decompression mechanism200in comparison to prior decompression devices.

The lift section290leans on the arcuate recess280of the cam section236in the decompression operation. In other words, the cam section236supports the lifter section290when the lifter section290lifts the cam followers238,240. Thus, the lifter section290and the lever288will experience less wear by the repeated collisions with the cam followers238,240and can have a long life. Accordingly, the decompression lever288, particularly the lifter section290thereof, can be thinner and the lever288can be lighter.

In addition, the pivot pin278does not need to support the lifter section290because the cam section supports the lifter section290. Accordingly, with the present embodiment the size of the pivot pin278can be reduced.

In some arrangements, for example, the lifter section may lift either the intake cam follower or the exhaust cam follower. Additionally, two lifter sections can be formed on a single decompression lever. Also, two decompression levers can be provided to separately lift the respective cam followers.