Apparatus for protecting bicycle electrical components

An electrical control apparatus comprises a current sensor and a current inhibiting circuit that inhibits current flow between first and second terminals of a bicycle dynamo when current sensed by the current sensor is below a selected value.

BACKGROUND OF THE INVENTION

The present invention is directed to bicycles and, more particularly, to an apparatus for protecting electrical components associated with the bicycle.

Many electrical devices are available for use with bicycles. For example, lighting systems comprising a headlight, a taillight and other lighting elements often are used for night riding. Such lighting systems and other electrical equipment usually receive operating power from a battery or a dynamo. When a dynamo is used for the power supply, the voltage generated by the dynamo usually is proportional to the bicycle speed (wheel RPM). At high speeds, the generated voltage can sometimes exceed 100 V, so some kind of protection device is needed to prevent excessive voltage from being applied to the electrical components. Japanese Unexamined Patent Application (Kokai) No. 2204-88812 discloses a voltage protection device in the form of a bypass circuit comprising a Zener diode disposed between the dynamo and the load. When the voltage generated by the dynamo is over a certain threshold, current flows through the Zener diode so that the voltage applied to lamps and to other electrical equipment is limited to no more than a selected voltage level.

While the use of a bypass circuit such as a Zener diode can provide overvoltage protection for the electrical components, bypass circuits can produce some undesirable side effects. For example, the electrical current consumed by the electrical devices creates rotational resistance in the dynamo, and such rotational resistance adds to the pedaling effort required by the cyclist. Some dynamos, such as block dynamos, are activated only when needed to power the electrical equipment. Accordingly, those dynamos do not create pedaling resistance when the electrical equipment is not in use.

On the other hand, internal hub dynamos are built integrally with the wheel hub and always rotate together with the wheel.FIG. 1is a schematic block diagram of a bicycle electrical component system that employs an internal hub dynamo and an overvoltage protection circuit. As shown therein, an overvoltage protection circuit3comprising a Zener diode is connected to the dynamo2of a wheel hub dynamo unit1. Electrical components powered by such dynamos are turned on manually or automatically independently of rotation of the wheel. Electrical power is consumed by headlight4and taillight5whenever they are turned on, thus causing rotational resistance in rotation of the wheel hub. When headlight4and taillight5are turned off, overvoltage protection circuit3consumes all of the power that was consumed by headlight4and taillight5when those lighting elements were turned on. Thus, dynamo2always generates power and creates rotational resistance, thus resulting in unnecessary pedaling burden on the rider.

SUMMARY OF THE INVENTION

The present invention is directed to various features of a device for protecting bicycle electrical components. In one embodiment, an electrical control apparatus comprises a current sensor and a current inhibiting circuit that inhibits current flow between first and second terminals of a bicycle dynamo when current sensed by the current sensor is below a selected value. Additional inventive features will become apparent from the description below, and such features alone or in combination with the above features may form the basis of further inventions as recited in the claims and their equivalents.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 2is a schematic block diagram of an embodiment of a bicycle electrical control apparatus with an inventive protective device. In this embodiment, an internal wheel hub dynamo8provides operating power to a lamp system9. Lamp system9may comprise a headlight, a taillight, other lighting elements, an auto light circuit for turning selected lighting elements on and off in response to ambient light, and other electronic components. Further circuit elements are provided to provide overvoltage protection and for controlling rotational resistance of dynamo8when lamp system9is turned off.

More specifically, a current sensor10detects current flow through lamp system9, a voltage amplifying circuit11amplifies a voltage produced by current sensor10, a determination circuit12determines whether or not current detected by current sensor10is below a selected value, a voltage clamping circuit14provides overvoltage protection for lamp system9, and a current inhibiting circuit in the form of a switching circuit13inhibits current flow through voltage clamping circuit14in response to signals from determination circuit12. In general, current flows through lamp system9when the auto light circuit within lamp system9turns on the various lighting elements. Little or no current flows through lamp system9when the auto light circuit within lamp system9turns off the lighting elements or when the lighting elements within lamp system9are nonfunctional, such as when the lighting elements are broken. When current sensor10senses current flow through lamp system9, and when determination circuit12determines that current sensed by current sensor10is above a selected value, then determination circuit12switches on switching circuit13, and current flows through voltage clamping circuit14when required to prevent excessive voltage from being applied to lamp system9. When determination circuit12determines that current sensed by current sensor10is below the selected value, then determination circuit12switches off switching circuit13. When that happens, no current flows through voltage clamping circuit14between the two output terminals of dynamo8, and rotational resistance in dynamo8caused by current consumption is eliminated.

FIG. 3is a schematic diagram of a specific embodiment of the circuit represented inFIG. 2. In this embodiment, a diode D2and a capacitor C2are connected in series between a Dynamo In1terminal (an output terminal from dynamo8) and a Dynamo In2terminal (another output terminal from dynamo8). A positive terminal of capacitor C2is connected to a cathode terminal of diode D2and to a node between a collector terminal of a transistor Q4and a terminal of a resistor R12. The other terminal of resistor R12is connected to a node between a base terminal of transistor Q4, a positive terminal of a capacitor C4, and a cathode terminal of a Zener diode D7. The other terminals of capacitor C4and Zener diode D7are connected to the Dynamo In2terminal. A positive terminal of a capacitor C3is connected to an emitter terminal of transistor Q4, and the other terminal of capacitor C3is connected to the dynamo In2terminal. Transistor Q4and Zener diode D7stabilize the voltage of capacitor C2to (D7Zener voltage)—(Q4base-emitter voltage drop). This stabilized voltage is used as the power source for the remaining circuit components.

Current sensor10comprises a resistor R20that is connected between the Dynamo In2terminal and a Dynamo Out2terminal connected to lamp system9. Thus, a voltage drop occurs across resistor R20when current flows from the Dynamo In2terminal through lamp system9, whereas a voltage drop does not occur across resistor R20when the lighting elements within lamp system9are turned off (or are nonfunctional) and no current flows through lamp system9. The voltage drop across resistor R20is amplified by voltage amplifier11, and this amplified voltage drop is used by determination circuit12to determine whether or not to turn on switching circuit13.

Voltage amplifier11comprises an operational amplifier (op amp) U17; resistors R10, R14, R16, and R17connected as shown to a non-inverting input terminal of op amp U17; and resistors R22and R23connected as shown to an inverting input terminal of op amp U17. Determination circuit12basically comprises an npn transistor Q5having a base terminal connected to an output terminal of op amp U17through a resistor R18, and a pnp transistor Q6having a base terminal connected to a collector terminal or transistor Q5through a resistor R15. Resistors R8and R21receive a positive power supply signal and are respectively connected to the base terminal of transistor Q6and to an emitter terminal of transistor Q5. A Zener diode D8is connected between the emitter terminal of transistor Q5and the Dynamo In2terminal. A resistor R9and diode D6are serially connected to a collector terminal of transistor Q6, wherein the cathode terminal of diode D6provides signals to combined switching circuit13and voltage clamping circuit14.

A combined switching circuit13and voltage clamping circuit14are disposed between the Dynamo In1terminal and the Dynamo In2terminal, wherein the Dynamo In1terminal is common with a Dynamo Out1terminal connected to lamp system9. Switching circuit13and clamping circuit14together generally comprise an npn transistor Q1having a base terminal connected to the cathode terminal of diode D6in determination circuit12through a resistor R3, a pnp transistor Q2having a base terminal connected to a collector terminal of transistor Q1through a resistor R6, and two serially connected field-effect (FET) (e.g., PMOS) transistors M1and M2connected between the Dynamo In1terminal and the Dynamo In2terminal. Gate terminals of transistors M1and M2are connected to a node between a resistor R1and a collector terminal of transistor Q2, wherein the other terminal of resistor R1is connected to a node between the source/drain terminals of transistors M1and M2. A resistor R2is connected to the base terminal of transistor Q1and to a node between the source/drain terminals of transistors M1and M2, and a capacitor C1is connected to a node between resistor R3and the cathode terminal of diode D6in determination circuit12and to a node between the source/drain terminals of transistors M1and M2. The emitter of transistor Q1also is connected to a node between the source/drain terminals of transistors M1and M2, whereas the emitter of transistor Q2is connected to a node between cathode terminals of diodes D3and D4. A resistor R5is connected between the base and emitter terminals of transistor Q2. Anode terminals of diodes D3and D4are connected to respective anode terminals of Zener diodes D1and D5, wherein the cathode terminal of Zener diode D1is connected to the Dynamo In1terminal, and the cathode terminal of diode D5is connected to the Dynamo IN2terminal. Diodes D1, D3, D4and D5form part of a bypass circuit BP that includes switching circuit13and voltage clamping circuit14and functions in a manner discussed below.

The system operates in the following manner when lamp system9is turned on. During positive half-cycles of dynamo8at the Dynamo In1terminal when the bicycle is traveling at low speed, capacitor C2charges and smoothes the voltage via the half-wave rectification performed by diode D2. At the same time, current flows from the Dynamo In1terminal through the Dynamo Out1terminal and to lamp system9. Capacitor C2provides voltage and current to the collector of transistor Q4, and the stabilized voltage is supplied to op amp U17, etc., as the power source of the circuit elements. Since the lighting elements in lamp system9are on, current flows through resistor R20, and positive voltage is produced at the Dynamo Out2terminal of resistor R20relative to the Dynamo In2terminal of resistor R20, assuming a standard ground. However, because of the inverting amplification of op amp U17, the output voltage of op amp U17tends to be low, and transistors Q5and Q6in determination circuit remain off. As a result, transistors Q1and Q2in switching circuit13and voltage clamping circuit14remain off, the gate voltage at transistors M1and M2is zero volts, and no voltage clamping occurs.

During positive half-cycles of dynamo8at the Dynamo In1terminal when the bicycle is traveling at high speed, the circuit operates in the same manner. Voltage clamping still will not occur regardless of whether or not the Zener diodes D1and D5break down, since transistors Q1and Q2are off and the gate voltage at transistors M1and M2is 0 V.

During positive half cycles of dynamo8at the Dynamo In2terminal when the bicycle is traveling at low speed, current input from the Dynamo In2terminal passes through resistor R20and is supplied by the Dynamo Out2terminal to lamp system9. A negative voltage drop is produced at the Dynamo Out2terminal of resistor R20relative to the Dynamo In2terminal of resistor R20, assuming a standard ground, and this voltage drop is amplified by op amp U17. When the voltage level at the output terminal of op amp U17is greater than (D8Zener voltage)+(Q5base-emitter voltage drop), transistor Q5turns on, thus turning on transistor Q6. At this time, the current flows as follows: Q6emitter→Q6collector→R9→D6→C1→M1source→M1drain→Dynamo Out1terminal. The charged capacitor C1turns on transistors Q1and Q2. However, at low speeds, the voltage is not sufficient to cause diodes D1and D5to break down, so no voltage clamping occurs at this time.

During positive half-cycles of dynamo8at the Dynamo In2terminal when the bicycle is traveling at high speed, transistors Q1and Q2are turned on in the same manner as noted above. When the voltage exceeds the Zener voltage of Zener diode D5, Zener diode D5breaks down, current passes through transistor Q2, and the gate voltage of transistors M1and M2increases. When the drain-source potential difference of transistor M2is greater than (D5Zener voltage+D4forward drop voltage+M2gate ON voltage), then an increase in the source gate voltage of transistor M2results in a drop in the drain-source resistance of transistor M2with a concomitant attenuation in the drain-source potential difference of transistor M2. On the other hand, when the drain-source potential difference of transistor M2is less than (D5Zener voltage+D4forward drop voltage+M2gate ON voltage), then a decrease in the source gate voltage of transistor M2results in an increase in the drain-source resistance of transistor M2with a concomitant increase in the drain-source potential difference of transistor M2. As a result, equilibrium is reached, with the drain-source potential difference of transistor M2equal to (D5Zener voltage+D4forward drop voltage+M2gate ON voltage). The difference in potential between the Dynamo IN1terminal and Dynamo IN2terminal is thus clipped to no more than (D5Zener voltage+D4forward drop voltage+M2gate ON voltage+M1parasitic diode drop voltage).

Once capacitor C1is charged as noted above, transistors Q1and Q2are turned on. Thus, during the next half cycle with a positive Dynamo In1terminal, transistor Q1remains on because of the charged capacitor C1, despite the positive voltage at the Dynamo In1terminal. This time, the difference in potential between the Dynamo In1terminal and the Dynamo In2terminal is clamped no more than (D1Zener voltage+D3forward drop voltage+M1gate ON voltage+M2parasitic diode drop voltage).

Because virtually all of the power is consumed by transistors M1and M2during the clamping operation, inexpensive and compact small-signal diodes can be used for Zener diodes D1and D5to determine the clamping voltage.

When the lighting elements in lamp system9are turned off, or when the lighting elements malfunction and draw no current, no current input from the Dynamo In2terminal passes through resistor R20(which forms the voltage sensor). Accordingly, the voltage drop across resistor R20is minute (theoretically zero), and transistors Q5and Q6(which form the determination circuit12) are turned off. No current charges capacitor C1, and the potential of capacitor C1drops. Eventually, transistors Q1and Q2turn off, the gate voltage at transistors M1and M2returns to zero, and the clamping operation ceases. With virtually no current flowing through switching and voltage clamping circuits13and14, and hence between the Dynamo In1and Dynamo In2terminals, the rotational resistance of dynamo8caused by such current flow does not increase.

While the above is a description of various embodiments of inventive features, further modifications may be employed without departing from the spirit and scope of the present invention. For example, while a lighting system was used as an example of electrical equipment powered by dynamo8, the teachings herein can be applied to many other types of electrical equipment. The size, shape, location or orientation of the various components may be changed as desired. Components that are shown directly connected or contacting each other may have intermediate structures disposed between them. The functions of one element may be performed by two, and vice versa. The structures and functions of one embodiment may be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature that is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the scope of the invention should not be limited by the specific structures disclosed or the apparent initial focus or emphasis on a particular structure or feature.