Patent Application
20090278509
This disclosure relates to a battery charging and isolation system. In particular, this disclosure relates to a battery charging and isolation circuit for a small internal-combustion engine configured to power lawn and gardening equipment, which has a starter motor, a battery, and control circuitry.
Some internal-combustion engines, such as small two-cycle engines used to power lawn and gardening equipment may be started by either electrically using a starter motor and a battery, or by using a mechanical device, such as a recoil mechanism. Some engines may include both starting systems. More sophisticated engines have a fuel-injection system, which is typically controlled by control circuitry. Rotation of the engine turns a magneto assembly, which supplies a high-voltage signal to the spark plugs. The high-voltage signal is typically stepped-down and filtered to provide a conditioned supply voltage to the circuitry.
However, if the control circuitry fails or the conditioned supply voltage is interrupted or otherwise degraded, the engine will not run, typically due to failure of the fuel injection system. The battery that supplies power to the starter motor has a finite life and eventually must be replaced. Such batteries tend to fail on occasion due to the harsh environment in which the devices are used. If the battery does fail, in known systems, such a failure typically interrupts, short-circuits, or otherwise degrades the conditioned supply voltage, thus causing engine failure, even though the other components of the system may be functioning properly. A need exists for effectively removing or isolating a drained or short-circuited battery from the other electrical components of the engine system so that the engine can still be started mechanically.
According to one specific embodiment, a control system is adapted to control an internal combustion engine, which has a battery for electric start operation and a mechanical starter for manual start operation. The control system includes a transformer configured to generate a high voltage output for providing a spark, and a power regulation circuit having an input adapted to receive the high voltage output and generate a low voltage supply. A battery charging circuit includes a switching element adapted to receive the low voltage supply and operatively couple the low voltage supply to the battery to charge the battery. The battery charging circuit includes disconnecting circuitry operatively coupled to the switching element so that if a voltage level of the battery falls below a predetermined value, the disconnecting circuitry turns off the transistor to electrically disconnect the battery from the low voltage supply to inhibit charging. The mechanical starter is configured to start the engine if the battery is insufficiently charged or otherwise unable to electrically start the engine.
According to another embodiment, the control system further includes an ignition circuit configured to generate a high-voltage output for providing a spark, a power conditioning circuit configured to convert the high-voltage output to a low voltage supply, and a voltage regulation circuit having an input adapted to receive the low voltage supply, which provides a regulated component supply voltage. An electronic control unit is adapted to receive the regulated component supply voltage and controls the functioning of the engine. A battery charging circuit includes an electronic switching element adapted to receive the low voltage supply and operatively couple the battery to the low voltage supply to charge the battery. The battery charging circuit includes disconnecting circuitry operatively coupled to a gate of the electronic switching element, so that if a voltage level of the battery falls below a predetermined value, the disconnecting circuitry turns off the electronic switching element to electrically disconnect the battery from the low voltage supply and isolate an output of the power conditioning circuit from the battery. The mechanical starter is then used to start the engine if the battery is electrically disconnected, insufficiently charged, or defective.
According to a further embodiment, a battery isolation circuit is used with a power conditioning circuit for an internal combustion engine, where the engine has an electric starter powered by a battery and a mechanical starter. The battery isolation circuit includes a transistor adapted to receive a low voltage supply from the power conditioning circuit and operatively couple the low voltage supply to the battery to charge the battery when the transistor is turned on. Disconnecting circuitry is operatively coupled to a gate of the transistor and to the low voltage supply, so that if a voltage level of the battery falls below a predetermined threshold value of the disconnecting circuitry, the disconnecting circuitry turns off the transistor to electrically disconnect the battery from the low voltage supply to prevent charging. The mechanical starter is used to start the engine if the battery has insufficient capacity.
The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and function of the various elements of this invention are better understood by the following description. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. The embodiments described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings.
The engine system 100 includes a starter motor 110 to start the engine 104, a starter motor battery 116 to power the starter motor 110, and an electric starting circuit 120 to control the starter motor. An ignition circuit 130 provides a high-voltage output via a high-voltage transformer coil 136 of a high voltage transformer 138 to supply a spark to the spark plugs. The high-voltage transformer coil 136 is inductively coupled to a power generation coil 144 of a power generation circuit 150, which may step-down and rectify the high voltage output to generate a reduced rectified supply voltage 148 at about an 18 volt level in one specific embodiment. The 18 volt supply voltage or supply voltage 148 may have spike or pulse-like waveform because it is derived from transformer coils having currents induced by rotating magnet components.
In the illustrated embodiment, a voltage regulator circuit 160 receives the supply voltage 148, and further conditions and filters the signal to provide a 12 volt component supply voltage or component voltage 152, which powers the various electrical components of the engine system 100. For example, the voltage regulator circuit 160 supplies the component voltage 152 to an electronic control unit 170, which in turn, controls a fuel injection system 180. The supply voltage 148 is also supplied to a battery/charging isolation circuit 186, which trickle-charges the starter motor battery 116. Of course, the power generation circuit 150 may be configured to provide any suitable voltage level so long as this level is equal to or greater than the voltage rating of the starter motor battery 116 so that trickle-charging may be performed.
The internal-combustion engine 104 of the illustrated embodiment is a conventional gasoline engine having a dual-mode starting mechanism. In that regard, the engine 104 has a conventional recoil starter 192, which is configured to rotate the engine flywheel when pulled or cranked by the user so as to start the engine 104. In addition to the recoil starter 192, the engine 104 includes the electric starter motor 110 to start the engine. Thus, the user may start the engine 104 either manually using the recoil starter 192 or electrically using the starter motor 110.
Because the above-described circuits are coupled to an internal-combustion engine 104, which may be adapted for outdoor use or use in challenging environments, such components may be subjected to harsh conditions. Such harsh conditions may include extremes of temperature, precipitation and moisture, shock and vibration, and other conditions that may damage the components or circuitry. Such harsh conditions may also damage the starter motor battery 116 or may cause a short circuit or open circuit somewhere in the engine system 100.
Although sufficiently harsh conditions may damage one or more critical components so that the engine 104 will fail to operate, neither the starter motor battery 116 nor the starter motor 110 is such a critical component. That is, failure of the starter motor battery 116 or the starter motor 110 should not disable the engine 104 because the second system, namely the manual recoil starter 192, may be used to start the engine. Furthermore, once the engine 104 has been started, the power generation circuit 150 generates the electricity necessary to power the electrical components. In addition to possible battery damage caused by misuse or harsh conditions, in some circumstances, the battery 116 may become drained or otherwise fail, as such batteries have a finite useful lifetime. For example, the battery 116 may no longer accept or retain a charge when it reaches the end of its useful life.
In contrast, the electronic control unit 170 and fuel injection system 180 are critical components, and the engine 104 will not run if these components are disabled or otherwise damaged. For example, the electronic control unit 170 or the fuel injection system 180 may become disabled if they do not receive the appropriate voltage levels from the voltage regulation circuit 160, which is dependent on the supply voltage 148 generated by the power generation circuit 150.
Because the starter motor battery 116 is trickle-charged by the supply voltage 148, and the electronic control unit 170 indirectly receives power based on the supply voltage 148 (via the voltage regulation circuit 160), a short-circuit or battery failure may cause failure or interruption of the 18 volt supply voltage 148, thus disabling the engine 104. Accordingly, the battery charge/isolation circuit 186 is configured to isolate the starter motor battery 116 from both the power generation circuit 150 and the voltage regulation circuit 160, and/or other components of the system should the battery become drained or short-circuited, or otherwise interfere with the supply voltage 148.
A positive terminal 202 of the starter motor battery 116, such as a 12 volt rechargeable battery, is coupled to the starter motor 110 through the electric starting circuit 120 to provide power to the starter motor, while a negative terminal 210 of the battery is connected to ground. Any suitable battery and/or voltage range may be used, depending on the operating characteristics of the starter motor and the voltage rating of the components of the various circuits.
In the illustrated embodiment, the supply voltage 148 is coupled to a source terminal of a MOS transistor 216. The MOS transistor 216 may be a P-channel enhancement mode vertical DMOS FET, such as part no. ZVP3306A, available from Zetex Semiconductors. Any suitable switching element or transistor may be used. The positive terminal of the battery 202 is operatively coupled to the drain terminal of the MOS transistor 216 through a blocking diode 220. The blocking diode 220 may prevent current flow from the battery to the MOS transistor 216. A bias resistor 224, such as a 470 ohm resistor, couples the source and gate terminals of the MOS transistor 216. The gate terminal of the transistor 216 is further coupled to ground through a Zener diode 230. The battery 116 may be trickle-charged by the supply voltage 148 through the MOS transistor 216.
If the battery voltage falls below the Zener breakdown threshold (about 12 volts in the illustrated embodiment), or if the battery 116 or the starter motor 110 becomes short-circuited to ground, the voltage level at the cathode of the Zener diode 230 will fall below the Zener threshold level. This occurs because the source terminal of the MOS transistor 216 will tend to be pulled down toward the battery potential through the conducting MOS transistor 216. In one embodiment, the threshold value of the Zener diode 230 is about 12 volts. In another embodiment, the threshold value of the Zener diode 230 is between about 9 volts and about 12 volts. Any suitable Zener threshold value may be used, which may be based on the voltage rating of the battery 116. For example, the Zener diode 230 may be selected to have a threshold value somewhat less than the voltage rating of the battery, for example between about 1 volt and about 5 volts lower than the maximum battery voltage.
The voltage at the gate of the MOS transistor 216 is fixed by the Zener diode 230 at its breakdown voltage. If the supply voltage 148 at the source of the MOS transistor 216 should drop enough to cause the Vgs of the device to be insufficient to keep it turned on, the MOS transistor 216 will turn off. In so doing, the battery 116 is disconnected from the supply voltage 148, thus protecting the voltage regulator circuit 160, the electronic control unit 170, and the fuel injection system 180.
Once the MOS transistor 216 turns off, the supply voltage 148 may then rise to full voltage. However, this may turn the MOS transistor 216 on again. Thus, the MOS transistor 216 may cycle on and off. The duty cycle of such a waveform may be about 20 milliseconds depending on the RC time constants inherent in the circuit and the battery charging characteristics of the battery 116. The cycling of the MOS transistor 216 during battery charging may induce ripple or spikes in the supply voltage 148, but such ripple does not adversely affect the voltage regulator circuit 160, which continues to provide a component voltage 152 to the electronic control unit 170.
During the “on” cycle of the MOS transistor 216, the battery 116 may be trickle-charged. Of course, if the battery 116 experiences a hard failure, or if the starter motor 110 is short-circuited to ground, the MOS transistor 216 will remain off to prevent interference with the supply voltage 148. Accordingly, the various components of the engine system 100 can function properly, including the electronic control unit 170 and the fuel injection system 180, even though the battery 116 or electric start capability is not operational. In this event, the user may start the engine manually using the recoil system 192.
A transistor 430 is controlled via its base terminal by the electronic control unit 170 (ECU 170) (see
The voltage regulation circuit 160 receives the supply voltage 148 from the power generation circuit 150 and provides regulated electrical power for the various electronic components and circuits that control the engine 104. For example, the voltage regulation circuit 160 provides the component voltage 152 at about a 12 volt level to the electronic control unit 170, which controls many of the electrical functions of the engine 104, including the fuel injection system 180. In the illustrated embodiment, the voltage regulation circuit 160 includes a bipolar transistor 550 having a base terminal 556 coupled to a Zener diode 560. The Zener diode 560 in one embodiment has a breakdown threshold voltage of about 13 volts so that the output of the transistor 550 at an emitter terminal 560 is about 12 volts, which is the component voltage 152 of the above illustrated embodiment. Depending upon system configuration and the various component voltage requirements, any suitable voltage level of the component voltage 152 may be used.
The power generation circuit 150 and voltage regulation circuit 160 need not be in separate circuits and may be combined. Such a combined power generation or power conditioning circuit may provide the appropriate voltage levels to the circuitry of the engine system 100.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.
