WO2009041969A1

WO2009041969A1 - Low-voltage battery protection methods and apparatus

Info

Publication number: WO2009041969A1
Application number: PCT/US2007/079643
Authority: WO
Inventors: Christopher D. Snyder; John T. Strug
Original assignee: Mack Trucks, Inc.
Priority date: 2007-09-27
Filing date: 2007-09-27
Publication date: 2009-04-02

Abstract

A low-voltage battery protect circuit preferably uses two latching relays, one a low-current relay and the other a high-current relay. A voltage pulse controls the state of the low-current relay, and the low-current relay controls the state of the high-current relay. An electronic control unit (ECU) transitions from time to time between a low-current sleep state and a reduced-current monitoring state, and in the reduced-current state, the ECU monitors the battery voltage and sends a pulse to the low-current relay if the voltage has crossed a settable threshold. Discontinuously monitoring the battery voltage in this way minimizes the battery discharge rate.

Description

INTERNATIONAL PATENT APPLICATION by

CHRISTOPHER D. SNYDER and JOHN T. STRUG for

LOW-VOLTAGE BATTERY PROTECTION METHODS AND APPARATUS

BACKGROUND

This invention relates to vehicles, such as over-the-highway trucks, having electrically powered equipment that can be operated while the vehicle's engine is not operating.

An over-the-highway truck, such as Class 8 trucks used in long-haul commerce, may be equipped with a cab having a sleeper compartment. The truck's driver can use the sleeper compartment to rest during travel over long distances. The truck may also be equipped with various driver convenience equipment, such as a heating/cooling system for the sleeper compartment, refrigerator, television, radio, microwave oven, etc.

Such convenience equipment is usually electrically powered and can create an excessive drain on the vehicle's battery when operated while the vehicle's engine is not running. While the engine is not running, the vehicle's alternator or other engine-driven electrical generator is not running, and thus the electrical loads presented by the convenience equipment are completely supplied by the vehicle's battery. While the engine is running, the alternator charges the vehicle's battery and supplies sufficient current so that the drain on the battery is minimal.

It is important for the vehicle's battery always to have at least the energy needed start the engine. Thus, it is desirable to disconnect the electrical loads presented by the convenience equipment when the battery voltage becomes too low, so that the remaining energy in the battery can be used to start the engine. Many devices have been developed that open the connection between a vehicle's battery and a load when the battery voltage drops below a threshold. Such battery protection devices typically use a voltage sensing circuit and a latching relay to disconnect the load from the battery.

U.S. Patent No. 4,412,267 to Hansen discloses an alarm and a protection circuit having an under-voltage sensor that trips a latching relay, which in turn opens a main relay to cut the load off from the battery. The latching relay must be reset manually, and requires two separate circuits to activate the contact-open coil and the contact-close coil. Voltage and time thresholds are set by fixed component values in an analog circuit that continuously monitors the battery's voltage, and so contributes to discharging the battery.

U.S. Patent No. 4,493,001 to Sheldrake discloses a battery protection circuit having a latching relay that controls the connection between the battery and load. A programmable uni-junction transistor monitors battery voltage. If the voltage drops below a threshold, several transistors are momentarily biassed into conduction, which energizes the relay coil and disconnects the vehicle's entire electrical system from the battery. This analog circuit monitors the battery voltage with a threshold set by fixed components and provides a latching-relay-open control circuit and a latching-relay-close control circuit. The analog circuit also contributes to discharging the battery.

U.S. Patent No. 5,321 ,389 to Meister includes a latching relay for opening the contacts between the battery and all of the vehicle's electrical loads, including the starter, when the battery voltage drops. An analog circuit continuously monitors the battery voltage, which contributes to discharging the battery. The latching relay must be reset manually before the vehicle can be restarted, and uses two separate relay-open and relay-closed coil control circuits.

U.S. Patent No. 5,327,068 to Lendrum et al. describes a battery charge monitor and a latching relay having separate relay-contact-open and relay-contact-close control circuits. A signal is required on either circuit to open or close the relay contacts. A voltage comparator monitors the battery voltage, and a potentiometer adjusts the battery voltage thresholds. This analog circuit provides a continuous battery voltage monitor, which contributes to discharging the battery.

U.S. Patent Application Publication No. 2005/0119821 by Malone et al. discloses a device having an Electronic Control Unit (ECU) that continuously monitors the vehicle battery's charge and a single latching relay that is triggered by the ECU to open the circuit between the battery and electrical loads when the voltage drops. The single latching relay is held latched by a continuous current, which with the continuous voltage monitor, contributes to discharging the battery when the engine is not running. An oil pressure switch determines whether the engine is running. The single latching relay needs two relay coils, one to open the relay contacts and one to close the relay contacts, with two associated control circuits, one for each contact.

A Battery Guard 200 brochure by lntelletec describes a battery protection device using an ECU to monitor battery charge and a latching relay that is pulsed to cut off the load from the battery. The brochure states that a voltage pulse is used to disconnect the electrical loads and that the user must manually press a reset switch to reconnect the electrical loads so the engine can be restarted.

The devices described above have drawbacks, not the least of which are that they contribute to discharging the vehicle's battery, that they use a single latching relay and complex and less reliable analog control circuits, and that they are difficult or inconvenient to reset.

SUMMARY

This invention provides a protection for a battery, for example a battery in a vehicle, by disconnecting non-essential electrical loads, such as driver convenience equipment.

In accordance with aspects of this invention, there is provided a protection circuit for a battery. The protection circuit includes a first latching relay having a first fixed contact, a second fixed contact, a common contact, and a coil having first and second terminals. The first fixed contact and the first terminal are connected to ground, the second fixed contact is connected to the battery, and the first latching relay changes state in response to a voltage pulse applied to its coil.

The protection circuit also includes a second latching relay having first and second contacts and a coil having first and second terminals. The first terminal is connected to ground, and the second latching relay changes state in response to a reversal of polarity across its coil.

The protection circuit also includes a capacitor having first and second terminals, a first terminal of the capacitor being connected to the common contact of the first latching relay and the second of the capacitor being connected to the second terminal of the coil of the second latching relay; and an ECU connected to the second terminal of the coil of the first latching relay. The ECU determines whether the voltage of the battery has crossed a threshold, and if the battery voltage has crossed the threshold, the ECU supplies the voltage pulse to the coil of the first latching relay. Thus, the capacitor is charged by the battery and contacts of the second latching relay are closed when the second fixed contact and the common contact of the first latching relay are closed; and in response to the voltage pulse, the first latching relay disconnects the battery from the capacitor and connects the second terminal of the capacitor to ground, thereby reversing the polarity of the coil of the second latching relay.

In accordance with further aspects of this invention, there is provided a method of protecting a battery that includes the steps of (a) starting a timer to determine a time period; (b) upon lapse of the time period, comparing a voltage of the battery to a settable threshold; (c) if the battery voltage exceeds the threshold, repeating steps (a), (b), and (c); and (d) if the battery voltage does not exceed the threshold, changing a state of a first latching relay, thereby causing a capacitor to discharge and change a polarity of a coil of a second latching relay, the second latching relay disconnecting an electrical load from the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of this invention will be understood by reading this description in conjunction with the drawings, in which:

FIG. 1 is a diagram of a battery disconnect circuit in a vehicle; and

FIG. 2 is a flow chart of a method of protecting a battery voltage.

DETAILED DESCRIPTION

As described in more detail below, a low-voltage battery protect circuit preferably uses two latching relays, one a low-current relay and the other a high-current relay. A voltage pulse on a single circuit from an ECU controls the state of the low-current relay, and the low-current relay controls the state of the high-current relay. With the vehicle's engine switched off, the ECU transitions from time to time between a low-current sleep state and a reduced-current monitoring state, and in the reduced-current state, the ECU monitors the battery voltage. Discontinuously monitoring the battery voltage in this way minimizes the battery discharge rate.

FIG. 1 is a schematic diagram of a battery protection circuit 100 that is in accordance with this invention. The circuit 100, which may be conveniently packaged in a chassis or suitable module, includes a first latching relay RLY1 and a second latching relay RLY2, a capacitor C1 , and an ECU. An over-current protection device, such as a fuse or circuit breaker (not shown in FIG. 1 ) may also be provided. As depicted in FIG. 1 , a terminal of the coil of the relay RLY1 is connected to ground GND, and the other terminal of the coil is connected to the ECU'S control output Ctrl. Also as depicted in FIG. 1 , a terminal of the coil of the relay RLY2 is connected to ground, and the other terminal of the coil of the relay RLY2 is connected to a terminal of the capacitor C1.

The first latching relay RLY1 changes its state, i.e., changes its contacts from closed to open or vice versa, in response to a voltage pulse to its coil. The contacts are depicted as neither closed nor open in FIG. 1 , and one fixed contact is shown connected to ground, another fixed contact is shown connected to the battery Vbatt, and a common contact is shown connected to a terminal of the capacitor C1. (The other terminal of the capacitor C1 is connected to a terminal of the coil of the second relay RLY2.) As described in more detail below, the state of the first latching relay RLY1 (and thereby the state of the second relay RLY2) is controlled by the ECU, and because the relay RLY1 contacts need supply only the current required by the coil of relay RLY2, the relay RLY1 can be a low-current relay, i.e., its contacts need not carry very high currents.

The second latching relay RLY2 changes its state in response to a reversal of polarity across its coil, and the second latching relay RLY2 is a high-current relay in that it supplies or blocks current to the electrical loads presented by the vehicle's convenience equipment and other devices as desired. The latching relays RLY1 , RLY2 do not draw current in either of their states, and so they do not contribute to discharging the battery if the engine is not running. A feedback signal Fbk that indicates the state of the relay RLY2 is conveniently taken from the loads and provided to the ECU, which can also use the feedback signal for measuring the battery voltage Vbatt. It will be appreciated that such a feedback signal may be provided from other points in the circuit 100.

In a first state of the circuit 100, the contacts of the relay RLY1 are closed between the battery Vbatt and the capacitor C1 , charging the capacitor C1. This activates the coil of relay RLY2, connecting the electrical loads to the battery Vbatt. If the ECU determines that the battery voltage has crossed an adjustable threshold, e.g., the battery voltage is too low, the ECU provides a voltage pulse to the coil of the relay RLY1 , changing the state of the circuit 100 to a second state. In response to the pulse, the relay RLY1 changes its state, disconnecting the voltage Vbatt from the capacitor C1 and connecting the capacitor C1 to ground. As capacitor C1 is charged, it discharges when it is thus connected to ground, and the current that flows while the capacitor C1 is discharging reverses the polarity of the coil of the relay RLY2, changing the state of the relay RLY2. When the relay RLY2 changes state, the loads are disconnected from the battery Vbatt, and the disconnection is indicated to the ECU by the feedback signal Fbk.

As described above, the ECU protects the battery voltage by monitoring the battery voltage Vbatt and effectively disconnecting non-essential electrical loads if the battery voltage becomes too low. The threshold for determining a low voltage may be adjustable, for example by suitably changing a programmable value used by the ECU. A typical automotive ECU, such as the ECU in a class-8 truck, can be configured by programming to protect the battery voltage only with the vehicle's ignition switched on, only with the ignition switched off, or with the ignition switched on or off. With the ignition switched off, the ECU preferably alternates between a sleep state, providing minimal functionality to minimize its current draw, and a "drowsy", or reduced, state, providing limited functionality and a somewhat higher current draw. In the drowsy state, the ECU monitors the battery voltage, and the monitoring time is preferably minimized to minimize the ECU'S current draw. By transitioning between the sleep and drowsy states when the vehicle's ignition is switched off, or more generally when the vehicle's electrical generation is off, the ECU'S current draw and its contribution to battery drain can be minimized.

FIG. 2 is a flow chart of a method of protecting the battery voltage that can be implemented by a suitable software program stored in a memory in the ECU. If the ECU determines that the ignition is switched on or the engine is running (No in step 202), the ECU operates in an awake, or fully operational, state, in which the contacts of the relay RLY2 are closed and the loads connected to the battery (step 204). The ECU can know that the ignition switch is on by a suitable signal from the switch, which may be provided to the ECU at an Ign/Eng terminal as depicted in FIG. 1 , or by monitoring suitable messages on an electronic data bus in the vehicle. The ECU can know that the engine is running by, for example, monitoring messages on an electronic data bus in the vehicle that show the engine speed, and if the engine speed is above a threshold, the engine is considered as running.

If the ECU determines that the ignition is switched off or the engine is not running (Yes in step 202), the ECU operates in the sleep state, and in step 206, the ECU sets an internal timer, which for a programmable ECU can be a software timer. Upon expiration of the time period counted by the timer (Yes in step 208), the ECU enters its drowsy state, in which the ECU compares the battery voltage to a threshold (step 210), such as a load-disconnect threshold, which may be programmable. If the ECU determines that the battery voltage exceeds the threshold (Yes in step 212), the ECU starts the timer and enters its sleep state; when the timer expires again, the ECU again enters its drowsy state to determine whether the battery voltage exceeds the threshold. The ECU'S transitioning between its sleep and drowsy states continues until either the battery voltage does not exceed the threshold or the ignition is switched on. It will be appreciated that these operations may also be disabled if desired, for example, during long-term vehicle storage or the like.

If in its drowsy state the ECU determines that the battery voltage does not exceed the threshold (No in step 212), the ECU may monitor the battery voltage for a period of time to ensure that this is not merely due to noise or another transient condition and then activate an alarm (step 214), such as an audible or visible signal, to alert the driver that the circuit 100 is about to disconnect electrical loads. The driver, who may be asleep in a sleeper compartment in the vehicle, may then start the engine (Yes in step 216), which rouses the ECU to its awake state and cancels the load-disconnect process, or the driver may allow the electrical loads to be disconnected. If the driver takes no action and the battery voltage remains below the disconnect threshold and the alarm has been activated (No in step 216), the ECU in its drowsy state sends a voltage pulse to the coil of the latching relay RLY1 (step 218). Relay RLY1 changes state, causing latching relay RLY2 to change state, disconnecting the electrical loads of convenience equipment and similar non-essential equipment as described above. In this way, the energy in the battery needed to start the engine is protected and preserved.

The circuit 100 and disconnected loads can be readily reset. After the ECU in its drowsy state causes the loads to be disconnected, the ECU enters the sleep state and remains in the sleep state preferably but not necessarily without further action until the ignition is switched on (step 220). When the ignition is switched on and the ECU is in its awake state, the disconnected electrical loads are reconnected in the course of normal operation of the vehicle. After the loads are reconnected and the ignition is switched off, the ECU initializes and starts its sleep timer for the monitoring process described above.

It will be understood that the ECU can also protect the battery voltage if the ignition is switched on and the engine is not running. In this case, the ECU is operating in its awake state, and so the sleep timer and transitions between the sleep and drowsy states are not needed. On the other hand, the ECU'S current draw is also not limited in this case. With the ignition switched on and engine not running, battery energy must still be maintained so the engine can be started, and so the ECU monitors the battery voltage and activates the alarm if the battery voltage does not exceed the threshold as described above. If the battery voltage remains below the threshold and the alarm has been activated for a time period, which may be predetermined, the electrical loads are disconnected and remain disconnected until the engine is started or the ignition is switched off and back on.

Unlike prior battery-monitoring devices, the pair of latching relays of the circuit 100 are reset automatically by the ECU, which controls the states of the relays. Also unlike prior devices that require two control circuits, one to latch connected and one to latch disconnected, the device described above has only one control circuit that controls the states of the device. The first latching relay RLY1 uses a single circuit to control one relay coil (of relay RLY2) and a voltage pulse to change its state. The ECU monitors the battery voltage and elapsed time, and transitions periodically between a low-current sleep state and a reduced-current drowsy state, thereby minimizing current draw and battery discharge rate. The threshold and timer parameters can be readily programmed and changed as desired in software with a suitable interface tool, enabling easy adjustment in the field by eliminating the need to change or adjust hardware components soldered to a circuit board.

It is currently believed to be preferable that only non-essential electrical loads are disconnected so the vehicle engine can be started without requiring the battery protect circuit to be reset. Essential electrical loads, such as the starter, do not draw current from the battery when they are not operational and so they need not be disconnected. Thus, the vehicle engine can be started without resetting the circuit 100 and without any special action by the driver.

It is expected that this invention can be implemented in a wide variety of vehicles, including for example over-the-highway trucks. It will be appreciated that procedures described above are carried out repetitively as necessary. To facilitate understanding, many aspects of the invention are described in terms of sequences of actions that can be performed by, for example, elements of a programmable computer system. It will be recognized that various actions could be performed by specialized circuits (e.g., discrete logic gates interconnected to perform a specialized function or application-specific integrated circuits), by program instructions executed by one or more processors, or by a combination of both. Many vehicles can easily carry out the computations and determinations described here with their programmable processors and application- specific integrated circuits.

Moreover, the invention described here can additionally be considered to be embodied entirely within any form of computer-readable storage medium having stored therein an appropriate set of instructions for use by or in connection with an instruction- execution system, apparatus, or device, such as a computer-based system, processor- containing system, or other system that can fetch instructions from a medium and execute the instructions. As used here, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction-execution system, apparatus, or device. The computer-readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non-exhaustive list) of the computer-readable medium include an electrical connection having one or more wires, a portable computer diskette, a RAM, a ROM, an erasable programmable read-only memory (EPROM or Flash memory), and an optical fiber.

Thus, the invention may be embodied in many different forms, not all of which are described above, and all such forms are contemplated to be within the scope of the invention. For each of the various aspects of the invention, any such form may be referred to as "logic configured to" perform a described action, or alternatively as "logic that" performs a described action.

It is emphasized that the terms "comprises" and "comprising", when used in this application, specify the presence of stated features, integers, steps, or components and do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

The particular embodiments described above are merely illustrative and should not be considered restrictive in any way. The scope of the invention is determined by the following claims, and all variations and equivalents that fall within the range of the claims are intended to be embraced therein.

Claims

CLAIMS:

1. A protection circuit for a battery, comprising: a first latching relay having a first fixed contact, a second fixed contact, a common contact, and a coil having first and second terminals, wherein the first fixed contact and the first terminal are connected to ground, the second fixed contact is connected to the battery, and the first latching relay changes state in response to a voltage pulse applied to its coil; a second latching relay having first and second contacts and a coil having first and second terminals, wherein the first terminal is connected to ground, and the second latching relay changes state in response to a reversal of polarity across its coil; a capacitor having first and second terminals, a first terminal of the capacitor being connected to the common contact of the first latching relay and the second of the capacitor being connected to the second terminal of the coil of the second latching relay; and an Electronic Control Unit (ECU) connected to the second terminal of the coil of the first latching relay, wherein the ECU determines whether a voltage of the battery has crossed a threshold, and if the battery voltage has crossed the threshold, the ECU supplies the voltage pulse to the coil of the first latching relay; whereby the capacitor is charged by the battery and contacts of the second latching relay are closed when the second fixed contact and the common contact of the first latching relay are closed; and in response to the voltage pulse, the first latching relay disconnects the battery from the capacitor and connects the second terminal of the capacitor to ground, thereby reversing the polarity of the coil of the second latching relay.

2. The circuit of claim 1 , wherein the second latching relay is a high-current relay that supplies or blocks battery current to an electrical load.

3. The circuit of claim 2, wherein the electrical load is presented by a vehicle's convenience equipment that is blocked from battery current when the second latching relay changes state in response to the voltage pulse applied to the coil of the first latching relay.

4. The circuit of claim 1 , wherein the ECU is programmed to supply the voltage pulse only with a vehicle's ignition switched on, only with the ignition switched off, or with the ignition switched on or off.

5. The circuit of claim 1 , wherein the ECU is programmed to transition between a sleep state and a drowsy state when the ignition is switched off

6. The circuit of claim 5, wherein in the drowsy state, the ECU monitors a voltage of the battery, and transitions between the sleep and drowsy states are based on an elapsed time period determined by the ECU.

7. A method of protecting a battery, comprising the steps of:

(a) starting a timer to determine a time period;

(b) upon lapse of the time period, comparing a voltage of the battery to a settable threshold;

(c) if the battery voltage exceeds the threshold, repeating steps (a), (b), and (c); and

(d) if the battery voltage does not exceed the threshold, changing a state of a first latching relay, thereby causing a capacitor to discharge and change a polarity of a coil of a second latching relay, the second latching relay disconnecting an electrical load from the battery.

8. The method of claim 7, wherein step (d) includes monitoring the battery voltage for a period of time.

9. The method of claim 7, further comprising the step of activating an alarm if the battery voltage does not exceed the threshold.

10. The method of claim 9, wherein the alarm is an audible or visible signal.

11. The method of claim 7, wherein the state of the first latching relay is not changed if a vehicle engine is started.

12. The method of claim 7, wherein the state of the first latching relay is changed in response to a voltage pulse applied to a coil of the first latching relay.

13. The method of claim 7, wherein whether steps (a) - (d) are performed is based on whether a vehicle ignition is ignition switched on or a vehicle engine is running.

14. The method of claim 13, wherein whether the vehicle engine is running is determined based on messages on an electronic data bus of the vehicle.