AU2021101405A4 - A circuit and method for vehicle alternator operation detection - Google Patents

Abstract

Described is a detection circuit for use with an electrical system. The detection circuit comprises a processing section and an input section that is arranged to receive an electrical signal from the electrical system and to provide the processing section with an input signal. The processing section is arranged to process the input signal and determine whether the input signal meets a predefined criterion. The processing section is arranged to effect a change to a load in the electrical system. 1/10 100 120 [T7 102 112 114 110 - - 108 FIGURE 1A

Description

1/10 100

120

[T7

102

112 114

110 - - 108

FIGURE 1A

A CIRCUIT AND METHOD FOR VEHICLE ALTERNATOR OPERATION DETECTION

Field

[0001] This specification relates generally to the field of detection circuits for electrical systems and has particular application to electrical systems used in motor vehicles.

Background

[0002] Many electrical systems employ a battery as a store of electrical charge and use a charging device for charging the battery to thereby prevent the battery from running "flat". By way of example, electrical systems in motor vehicles typically employ a mechanically driven alternator that is electrically connected to the battery for charging the battery. The alternator is driven by the vehicle's motor and the resultant mechanical rotation of the alternator produces an electrical current necessary to charge the battery. In a motor vehicle the engine typically drives the alternator via a belt or series of belts. When the alternator is not operating, for example as a consequence of the motor not running, the battery will not be charged and therefore it is important that current drawn from the battery be limited while the engine and alternator are not operating.

[0003] Fitting DC to DC chargers into modern applications can be difficult and fraught with frustration. Part of the problem is that many modern vehicles have variable voltage alternators, meaning that the voltage sensing function of some types of DC to DC chargers do not always work. It can be very challenging to find a suitable and close ignition source to enable accessories to turn on with the engine. The process of probing around wiring looms can be difficult, fiddly, and there is always the danger that the circuit that is tapped into could damage the engine control unit.

[0004] Some prior art has overcome this by introducing specific versions of chargers designed to work with variable voltage alternators. They do this by taking an ignition source and turning the charger on with the ignition. However, this is not a useful solution when you have a DC to DC charger located in a caravan or trailer because the user has to run an ignition source wire from the vehicle, through a plug and into the trailer or caravan.

[0005] One example of such a challenging situation is where a user needs to fit an emergency beacon at the rear of a road train and wire it to come on automatically when the engine is running. Where there is already power to the rear of the rig, the user would typically have to run a very long length of cable (eg 50m or more) from a suitable ignition source in the prime mover, through multiple trailers each with their own set of plugs to turn the beacon on and off.

[0006] Piggy-back fuses have been used for years, but without a thorough understanding of the vehicle's circuits, it could lead to all sorts of repercussions. Finding a suitable ignition source can be particularly difficult in modem vehicles. It is time consuming and expensive, and it can be disastrous as errors through backprobing or loading sensitive circuits in modern CAN bus vehicles can cause critical damage to sensitive equipment and computers. A few products have been developed to try and solve this problem, but these have been expensive and difficult to fit.

[0007] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

Summary

[0008] It would be advantageous to be able to detect whether the engine of a vehicle is operational (driving the alternator) and based on this detection control whether an electrical load is connected or disconnected to the battery.

[0009] Described herein is a device that acts as an alternator sensing switch that monitors electrical waveforms and can sense when an alternator is operating, and therefore indicate that the vehicle's engine is running. This intelligence allows a simple switch to power all manner of electrical accessories in most types of vehicles without interfering with the original equipment wiring. All that is required for the device to operate is a battery current source. The sensing device of the present invention can achieve the required ignition feed to operate the DC to DC charger, without a signal wire that needs to run from the vehicle through a plug and into a trailer.

[0010] In one embodiment of a detection circuit for use with an electrical system, the embodiment of the detection circuit comprises:

- a processing section; and

- an input section that is arranged to receive an electrical signal from the electrical system and to provide the processing section with an input signal,

- wherein the processing section is arranged to process the input signal and determine whether the input signal meets a predefined criterion, the processing section being further arranged to effect a change to a load in the electrical system.

[0011] This particular embodiment of the detection circuit is advantageous because the ability to effect the change to the load can be used in response to detecting if a motor vehicle engine is on and running. Detection of whether the vehicle engine is on and running is done by virtue of the processing section processing the input signal and determining whether the input signal meets a predefined criterion. In a motor vehicle when the engine is on and running the operation of the alternator will cause the resultant electric signal to correspond to a typical AC signal signature that represents an operational engine and alternator.

[0012] In some embodiments there is provided a device for sensing and switching that comprises the abovementioned detection circuit together with a switching arrangement configured to effect the change to the load based on whether the input signa meets the predefined criterion.

[0013] In the particular embodiment of the detection circuit the predefined criterion comprises the input signal having a characteristic that is related to a charging device providing a charging current to a battery.

[0014] The advantage of this characteristic is that it can facilitate detection of whether the charging device is operating.

[0015] In the particular embodiment of the detection circuit the characteristic comprises a voltage level that periodically changes with respect to time.

[0016] An advantage of using a characteristic in the form of a voltage level that periodically changes with respect to time is that it lends itself to detecting the operational status of a mechanical charging device such as an alternator that is used in a motor vehicle.

[0017] In the particular embodiment of the detection circuit the voltage has a frequency that is related to a mechanical characteristic of the charging device. This would typically be a frequency that is related to the rate of rotation of the alternator.

[0018] In this particular embodiment of the detection circuit the charging device is an alternator. The advantage of using an alternator is that the particular embodiment of the detection circuit is well suited to use in a motor vehicle.

[0019] In the particular embodiment of the detection circuit the input section comprises an amplifier circuit having a predefined passband frequency response. An advantage of using the amplifier with a predefined passband frequency response is that it allows filtering out of noise that may otherwise result in false positives or positive falses when it comes to detecting the operational status of the device for charging the battery

[0020] In the particular embodiment of the detection circuit the amplifier circuit is arranged to receive the electrical signal and output the input signal to the processing section.

[0021] In the particular embodiment of the detection circuit the processing section comprises:

- an analogue to digital converter for converting the input signal to a digital signal;

- a digital low pass filter for filtering the digital signal to create a filtered input signal; and

- a processor arranged to process the filtered input signal to thereby determine whether the input signal meets the predefined criterion.

[0022] An advantage of the above is that it allows modern digital signal processing techniques to be employed for efficient and cost effective processing.

[0023] In the particular embodiment of the detection circuit the processor is arranged to process the input signal and/or the filtered input signal according to a digital peak detector algorithm comprising:

- compare a current sample of the filtered input signal to a previous sample of the filtered input signal;

- if the current sample is greater than the previous sample, store the current sample to thereby represent a peak value signal, otherwise store the previous sample to thereby represent a peak value signal;

- compare the peak value signal to a predefined threshold value to thereby determine whether the input signal meets the predefined criterion; and

- reset the peak value signal periodically.

[0024] An advantage of using the above described digital peak detector algorithm is that it provides an efficient and novel methodology for analysing signals in the time domain.

[0025] In the particular embodiment of the detection circuit the processing section is arranged to effect the change to the load in the electrical system by operating a switching arrangement, for example a solid state relay, a MOSFET, or other suitable electronic switch, to thereby selectively connect or disconnect the load to or from the battery. An advantage that follows the ability to operate the solid state relay is that it provides a relatively simple mechanism for connecting or disconnecting the load from the battery.

[0026] In another embodiment there is provided a motor vehicle comprising the detection circuit as described above.

[0027] In a particular embodiment of a method for use with a detection circuit comprising a processing section and an input section, the input section is arranged to receive an electrical signal from an electrical system and to provide the processing section with an input signal, the method comprises:

- the processing section processing the input signal and determining whether the input signal meets a predefined criterion; and

- the processing section effecting a change to a load in the electrical system.

[0028] In the particular embodiment of the method the predefined criterion comprises the input signal having a characteristic that is related to a charging device providing a charging current to a battery.

[0029] In the particular embodiment of the method the characteristic comprises a voltage level that periodically changes with respect to time.

[0030] In the particular embodiment of the method the voltage has a frequency that is related to a mechanical characteristic of the charging device.

[0031] In the particular embodiment of the method the charging device is an alternator.

[0032] In the particular embodiment of the method the input section comprises an amplifier circuit having a predefined passband frequency response.

[0033] In the particular embodiment of the method the amplifier circuit is arranged to receive the electrical signal and output the input signal for the processing section.

[0034] In the particular embodiment of the method the processing section further comprises:

- an analogue to digital converter for converting the input signal to a digital signal; and

- a digital low pass filter for filtering the digital signal to create a filtered input signal; and

wherein the method further comprises the step of the processor processing the filtered input signal to thereby determine whether the input signal meets the predefined criterion.

[0035] In a particular embodiment of the method it further comprises the step of the processor processing the filtered input signal according to a digital peak detector algorithm comprising:

- the processor comparing a current sample of the filtered input signal to a previous sample of the filtered input signal;

- if the current sample is greater than the previous sample, store the current sample to thereby represent a peak value signal, otherwise store the previous sample to thereby represent a peak value signal;

- the processor comparing the peak value signal to a predefined threshold value to thereby determine whether the input signal meets the predefined criterion; and

- the processor resetting the peak value signal periodically.

[0036] In a particular embodiment of the method it further comprises the step of the processing section effecting the change to the load in the electrical system by operating a solid state relay to thereby selectively connect or disconnect the load to or from the battery.

[0037] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Brief Description of Drawings

[0038] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings in which:

[0039] Figure 1A provides a block diagram of an electrical system comprising an embodiment of a detection circuit;

[0040] Figure lB is a schematic representation of operational modes of a sensing and switching device forming part of the system illustrated in figure 1A;

[0041] Figure 2 provides a detailed schematic diagram of an input section of the detection circuit illustrated in figure 1A;

[0042] Figure 3 illustrates the gain and passband frequency response of the input section shown in figure 2;

[0043] Figure 4 illustrates a schematic diagram of the input section shown in figure 1A;

[0044] Figure 5 shows a signal that is present in the electrical system of figure 1A;

[0045] Figure 6 shows another signal that is present in the electrical system of figure 1A;

[0046] Figure 7 shows a schematic diagram of the processor section of the detection circuit shown in figure 1A;

[0047] Figure 8 provides a schematic diagram of a switching mechanism used in the electric system shown in figure 1A; and

[0048] Figure 9 shows a flow chart of a method performed by the electrical system of figure 1A.

Detailed Description

[0049] Figure 1A illustrates a block diagram of an electrical system 100 that incorporates an embodiment of a detection circuit 102. The electrical system 100 also comprises a store of electrical current in the form of a battery 104. The system also comprises a device for charging the battery in the form of an alternator 106 an electrical switch 108 and a load 110. This description of the electrical system 100 is given in the context of a motor vehicle electrical system so the battery 104 and alternator 106 are typical of those found in a motor vehicle. While the description is given in the context of a motor vehicle, persons skilled in the art will appreciate that the detection circuit 102 has application in a range of electrical systems and not just automotive electrical systems examples of which can include secondary batteries and accessories fed from such batteries such as portable fridges, microwave ovens, pumps, fans etc. The load 110 in the system 100 is a simplistic representation of all the electrical components typically found in a motor vehicle. As persons skilled in the art will readily appreciate the load 110 in a motor vehicle would include, by way of example only, components such as headlights, radio, window wipers, electric windows, an alarm system, a horn and any other components of the motor vehicle that require a source of DC current, which is provided by the battery 104.

[0050] A significant component of the electrical system 100 is the detection circuit 102. The detection circuit 102 is described in more detail in the following paragraphs of this section of the specification. The primary purpose of the detection circuit 102 is to determine whether the engine of the motor vehicle is on and running and the vehicle's alternator 106 is also operating and if the motor and alternator 106 are not operating the switch 108 is operated to electrically disconnect the load 110 from the battery 104. An advantage of disconnecting the load 110 from the battery 104 in the event the vehicle's engine and alternator 106 are not running is that it can prevent complete discharge of the battery 104 which results in an inability to start the motor vehicle.

[0051] As shown in figure 1A, the detection circuit 102 is made up of two main components: an input section 112 and a processing section 114. The input section 112 provides analogue preconditioning in the form of amplification and filtering of an input signal. A more detailed schematic diagram of the input section 112 is provided in figure 2. Referring to figure 2, the main components of the input section comprises operational amplifiers (identified as "Ul" and "U2" in figure 2) in the form of an LT1001, which can be sourced from companies such as Linear Technology. In addition to the operational amplifiers the input section 112 as shown in figure 2 also comprises several resistors and capacitors. The resistors and capacitors provide a desired passband frequency response for the input signal. In this embodiment the passband frequency response is a 40dB/dec slope with approximate 1.9kHz and 5.8kHz 3dB points and FO = 3.5kHz with 46dB gain. The gain and passband frequency response of the input section shown in figure 2 is illustrated in figure 3. The skilled person will understand that the frequency and gain characteristics of the curves illustrated in figure 3 can vary (for example by 10% or 20%) and still provide a useful result.

[0052] Figure 4 provides a further schematic diagram of the input section 112 shown in figure 1A. Figure 4 shows the precision operational amplifier LT1001. Referring to figure 4, the input to the bandpass filter amplifier is on C4 and the output is across C12 and both of these signals are referenced to pin 4 of the operational amplifier. Pin 4 receives an electrical signal from the electrical system 100 and pins 6 and 7 provide the processing section 114 with an input signal.

[0053] As described previously, the detection circuit 102 is arranged to detect whether the vehicle's engine and alternator 106 are running. While discussed in further detail in the following sections of this specification, the detection circuit 102 receives an electrical signal from the electrical system 100 and outputs an input signal that is further processed by the processing section 114. In some embodiments, the DC voltage from the alternator is obtained by direct galvanic connection via a resistive divider and the AC signal is via capacitive coupling to the filter (not illustrated in these figures).

[0054] To receive the electrical signal from the electrical system 100 the input section 112 is connected to the positive side of the electrical system 100. Figure 5 and figure 6 illustrate the input signal that is supplied to the processing section 112 when the alternator 106 is functional or off, respectively. Figure 5 shows the input signal in the scenario where the alternator 106 is not operating (which may be due to a non-functional alternator 106) and figure 6 shows the input signal with the alternator 106 in a normal operating state in which it is supplying a charging current to the battery 104.

[0055] As described earlier, the processing section 114 processes the input signal supplied by the input section 112 to detect whether the alternator 106 is operating within the required electrical specifications. If the processing section 114 determines that the input signal supplied from the input section 112 resembles the signal depicted in figure 5 then the processing section 114 will activate the switch 108 to disconnect the load 110 from the battery 104 and thereby prevent the battery 104 from being discharged or damaged. Alternatively, if the processing section 114 detects that the input signal resembles the signal depicted in figure 6 then the processing section 114 will either take no action to activate the switch 108 or alternatively if the load 110 is currently disconnected from the battery 104 the processing section 114 will activate the switch 108 to cause the load 110 to be re-connected to the battery 104.

[0056] In this exemplary embodiment, the processing section 114 is in the form of a microcontroller, for example a low cost ST7FLITE29F2M6 microcontroller, which is available from STMicroelectronics. It is an 8-bit microcontroller with 8k Flash memory, 384 bytes of RAM and 256 byte EPROM and runs at1MHz. A detailed schematic diagram of the processor section 114 is shown in figure 7. The output signal provided by the input section 112 is in an analogue form (which can be seen in figures 5 and 6). The analogue input signal is supplied to the processing section 114, and is converted to a digital signal using an analogue to digital converter circuit. In this embodiment the analogue to digital converter is a 10 bit, successive-approximation-register (SAR) with sample and hold running at about 100kHz and is internal to the microcontroller.

[0057] Once the digitally converted input signal (as described above) is provided to the processing section 114 (or more specifically the previously described microcontroller), the processing section 114 uses a time domain processing technique to process the digitised input signal to determine whether the alternator 106 is in an operational state. Firstly, the processing section 114 employs a digital low pass filter to produce a filtered digital signal which is implemented as a running average of a few (for example five) samples (of the filtered digital signal) with a delay between each of the five samples. The delay is selected based on characteristics of the input signal, and can be for example 0.01 seconds. This digitally filtered signal is then subjected to a digital peak detector algorithm which involves:

[0058] Comparing a current sample of the digitally filtered signal to a previously sampled of the digitally filtered signal. The processing section uses a 0.05 sample rate for sampling the digitally filtered input signal to obtain the first and second samples.

[0059] Once the processing section 114 has obtained the current and previous samples of the digitally filtered signal the processing section 114 will store the highest sample as a representation of the peak value of the digitally filtered input signal.

[0060] At this stage the processing section 114 then compares the peak value (as stored in the previous step) to a predefined criterion (threshold value) to determine whether the alternator 106 is operational. In this particular embodiment the threshold value is approximately 120mV.

[0061] The final step at this point is the stored value described in step 2 above is periodically reset every 0.5 seconds.

[0062] It is noted that all of the above described steps are performed by the microcontroller circuit (shown in figure 7) of the processing section 114. The above steps would be contained in the EPROM and executed using the RAM of the described microcontroller.

[0063] The processing section 114 will cause the switching arrangement (shown in figure 8) to create either an open or closed electrical circuit resulting in the load 110 either being connected to or disconnected from the battery 104. In some embodiments the switching arrangement may be in the form of a (e.g., 36 volt and 0.006 ohm) solid state relay . In this embodiment the switching arrangement is an Infineon BTS50055-ITMA high current power switch. The processing section 114 (or more specifically the microcontroller depicted in figure 7) will operate the switching arrangement 800 of figure 8 in response to performing the previously mentioned steps to detect whether the alternator 106 is operating or not operating. While the alternator 106 is not operating the switching arrangement of figure 8 will be in an open position, which electrically isolates the load 110 from the battery 104. When the alternator 106 is operating properly the switching arrangement of figure 8 will be in a closed position, which electrically connects the load 110 to the battery 104.

[0064] Figure lB illustrates the operational modes of a sensing and switching device 120 which includes the detection circuit 102 (with the input section 112 and the processing section 114), and the switch 108. The sensing and switching device 120 has a 3 wire connection consisting of battery (pin 3), earth (pin 1) and signal wires (pin 2). In some embodiments two additional pins are provided for a manual override mode, pin 4 and pin 5 (the "remote on/off"pin).

[0065] The device 120 has three main modes of implementation:

[0066] The basic mode 122: pins 3 and 1 are wired to the positive and negative power source, and pin 2 to the device to be powered whilst the engine is running.

[0067] The Voltage Sensing mode 124: when the user wants to power equipment through voltage sensing rather than alternator sensing. This mode will turn on over 13.OV and turn off when voltage drops below 12.5V. To use the device behind a voltage converter, or even on a pre-1960's vehicle with a generator, this mode can work where the alternator sensing mode might not. To turn the Voltage Sensing mode on, pin 4 is connected to negative pin 1.

[0068] The manual override mode 126: this mode works in conjunction with alternator sensing technology to allow the user to manually switch an accessory off while the engine is still running. In the example of an oversized rig with a warning beacon wired up to the device, when the trailer is disconnected, the driver may not need the beacon to be operating. By wiring pin 4 to a positive source and pin 5 through an isolating switch to pin 3, the operator can use the switch to manually turn the accessory off.

[0069] The previous description of the electrical system 100 shown in figure 1A has described various steps performed by the detection circuit 102 and these steps are shown in the flow chart 900 in figure 9.

[0070] The method 900 for use with the detection circuit 102 may be understood with reference to figure 9. The detection circuit 102 comprises the processing section 114 and the input section 112 , and the input section is arranged to receive an electrical signal from the electrical system 100 and to provide the processing section 114 with an input signal. In some embodiments the input section comprises an amplifier circuit having a predefined passband frequency response. In some embodiments the amplifier circuit is arranged to receive the electrical signal and output the input signal for the processing section.

[0071] At 902 the processing section processes the input signal and determines whether the input signal meets a predefined criterion, for example whether the signal has a characteristic that is related to a charging device (like an alternator) providing a charging current to a battery. The signal characteristic can be a voltage level that periodically changes with respect to time, and/or a frequency of the voltage that is related to a mechanical characteristic of the charging device. At 904 the processing section effects the change to the load in the electrical system, in one embodiment by operating a switch 906 (or causing the operation, i.e. closing/opening, of the switch), for example a solid state relay or other high power switch, to thereby selectively connect or disconnect the load to or from the battery.

[0072] In some embodiments the processing section 114 comprises an analogue to digital converter for converting the input signal to a digital signal, and a digital low pass filter for filtering the digital signal to create a filtered input signal. In these embodiments, step 902 further includes the processor processing the filtered input signal to thereby determine whether the input signal meets the predefined criterion. The filtered input signal is processed according to a digital peak detector algorithm 910 wherein the processor compares 912 a current sample of the filtered input signal to a previous sample of the filtered input signal. If the current sample is greater than the previous sample, the current sample is stored 914 to thereby represent a peak value signal (otherwise the previous sample is stored to thereby represent a peak value signal). The processor then compares 916 the peak value signal to a predefined threshold value to thereby determine whether the input signal meets the predefined criterion. The processor resets the peak value signal periodically (for example every 0.5 seconds).

[0073] The invention described herein provides a simple, easy, safe and cheap way to fit electrical accessories to modern vehicles. The sensing and switching device provides a simple solution to the issue of running an ignition source to a DC to DC charger on a smart alternator equipped vehicle. The device makes fitting a DC to DC charger easy and streamlines the fitting of electrical accessories to all types of vehicles. Furthermore, the electronics are sensitive and dependable enough that it can be fitted at the rear of almost any type of trailer or caravan and provide a reliable ignition source signal without the need to run metres of additional cable.

[0074] Taking into account the cost of labour, materials and risk, the cost of installing the device of the present invention could be as low as 10% of the alternative option. Probing, long searches, drilling holes and running lengths of cable can be eliminated with this device.

[0075] It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

Claims (5)

CLAIMS:

1. A detection circuit for use with an electrical system, the detection circuit comprising:

- a processing section; and

- an input section that is arranged to receive an electrical signal from the electrical system and to provide the processing section with an input signal,

- wherein the processing section is arranged to process the input signal and determine whether the input signal meets a predefined criterion, the processing section being further arranged to effect a change to a load in the electrical system.

2. The detection circuit as claimed in claim 1, wherein the predefined criterion comprises the input signal having a characteristic that is related to a charging device providing a charging current to a battery, and

wherein the characteristic comprises at least one of:

a voltage level that periodically changes with respect to time, and

a frequency of the voltage that is related to an electro-mechanical characteristic of the charging device.

3. The detection circuit as claimed in claim 1 or claim 2, wherein the processing section is arranged to prepare the input signal for peak detection, and to process the prepared input signal according to a digital peak detector algorithm comprising:

- compare a current sample of the input signal to a previous sample of the input signal;

- if the current sample is greater than the previous sample, store the current sample to thereby represent a peak value signal, otherwise store the previous sample to thereby represent a peak value signal;

- compare the peak value signal to a predefined threshold value to thereby determine whether the input signal meets the predefined criterion; and

- reset the peak value signal periodically.

4. A method for use with a detection circuit comprising a processing section and an input section, the input section is arranged to receive an electrical signal from an electrical system having a battery and to provide the processing section with an input signal, the method comprising:

- the processing section processing the input signal and determining whether the input signal meets a predefined criterion; and

- the processing section effecting a change to a load in the electrical system.

5. The method as claimed in claim 4 further comprising:

the processing section effecting the change to the load in the electrical system by operating a switching arrangement to thereby selectively connect or disconnect the load to or from the battery.