JPS59159013A - Running distance meter for automobile - Google Patents

Abstract

PURPOSE:To display an accurate running distance and to obtain a long life, by providing an input and output circuits, which write running distance data into a non-volatile memory based on the output of a judging circuit, which detects the cutoff state of a power source for circuit parts, and providing a reserved power source, which makes it possible to write the data after the cutoff of the power source. CONSTITUTION:When power is supplied from a power source, the running distance is counted by a counter 4 in correspondence with running, and displayed on a display device 7. The distance is sequentially written in an RAM in an input and output circuit 5 as the running distance data. When a key switch 9 is opened and the power source is cut off, the voltage drop due to the cutoff of the power source is detected by a judging circuit 11. The judged result is transmitted to the input and output circuit 5. The input and output circuits 5 write the running distance data held in the RAM into a non- volatile memory 8. A large capacity capacitor 13 is in a charge state at a voltage level of a battery 10 through a diode 12. Therefore, the voltage is supplied even after the cutoff of the power source so that the writing operation for a short time can be effected in the judging circuit 11, the input and output circuit 5, and the non-volatile circuit 8. The capacitor 13 functions as a temporary reserved power source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic automobile odometer, and more particularly to a writing device for a nonvolatile memory that can retain mileage data even when the power is cut off.

Traditionally, it has been widely used as an automobile odometer.
There is a so-called mechanical totalizer that arranges multiple digits of character wheels and sequentially increments the amount of rotation transmitted by a wire cable from a gear transmission to display a distance in °C.

However, in recent years, electronic display devices with improved information processing capabilities using microcomputers have come to be substituted for automobile instruments such as speed hands, making it possible to constantly maintain the distance traveled from the past while driving. Even with the distance needle, which needs to be added cumulatively each time, the design balance with other gauges or the elimination of wire cables improves credibility.

There is a desire for a shift to electronic displays that require improved durability.

In response to these demands, pulse motor-type totalizers have been adopted, and although wire cables have been eliminated and noise has been prevented and durability has been improved, they still have problems with design balance and visibility. As a result, pure electronic distance meters that use non-volatile memory that can retain data even when the power is turned off are beginning to be adopted in some vehicles.

In particular, in recent years, nonvolatile memory has been commercialized as a memory element that can withstand regular use in terms of reliability and cost, and there is a tendency for it to be rapidly used as a memory element for automobile odometers in the future.

Figure 1 shows mileage data stored in non-volatile memory.
This explains a one-stop odometer that reads out this value and cumulatively adds a new input value.The repetitive pulse with a frequency proportional to the traveling speed output from the middle distance sensor 1 in the figure is
It is integrated by a counter 4 which is a counting circuit via a waveform shaping circuit 22 and a evaporation period 3.
The data is sequentially transferred and held in the RAM (random accelerator memory) in the input/output circuit 5 as mileage data. This mileage data is also transferred to a display drive circuit 6 and displayed on a digital display 7, which may be, for example, a fluorescent display tube. usually,
Writing of mileage data and data from the RAM in the input/output circuit 5 to the non-volatile memory 8 is performed every time the mileage increases by a certain amount, and when power is supplied (key switch 9 is closed) The mileage data accumulated by the counter 4 is sequentially transferred and held in the RAM in the input/output circuit 5, and the mileage data is written to the nonvolatile memory 8 every time the mileage increases by a certain amount.

Therefore, when the power is turned off (switch 9 is open), the mileage data up to that point is always held in the nonvolatile memory 8, and when the power is turned on again, the mileage data in the nonvolatile memory 8 is stored in the input/output circuit 5. The data is transferred to the internal RAM, and further transferred to the counter 4, where the newly inputted mileage is cumulatively added using the previously read mileage as an initial value.

However, nonvolatile memories generally have a limit to the number of times they can be rewritten, and frequent rewriting causes deterioration of the elements, resulting in a shortened lifespan.

In the above-described method of rewriting the nonvolatile memory 8 every time the distance traveled increases by a certain amount, for example, 10
If you rewrite the mileage data every 0m, it will be 100,000km.
It requires rewriting 10 times before it can run. However,
The current rewritable cycle of non-volatile memory is 1♂~
There are only about 1 mileage, and when using it as an odometer, the rewriting cycle must be set within the above-mentioned rewritable cycle range.

However, the rewrite cycle that allows rewriting up to 10,000 km is limited to every 10,000 m increase in travel distance, and the data is stored in the RAM of the counter 4 or the input/output circuit 5 by opening the key switch 9. When the current mileage is erased, the newly accumulated mileage is invalidated using the latest rewritten mileage data as the initial value, and when the power is turned on again, the mileage data held in the nonvolatile memory 8 is read out. Even if you cumulatively add new mileage using this as the initial value, the maximum is 1.
This has the problem of an error of nearly 0°000 m, making it useless as an odometer for automobiles, which are becoming more durable.

The present invention was made in view of the above circumstances, and it is an object of the present invention to provide an electronic automobile odometer that can accurately display the distance traveled and has a long service life.

In order to achieve the above object, the present invention includes a determination circuit that detects a state in which power is cut off to a circuit section, and an input/output circuit that writes mileage data into a nonvolatile memory based on the output of this determination circuit. The present invention is characterized in that each of the circuits is provided with a backup power supply capable of supplying voltage for at least a period of time to enable a write operation after the power is cut off.

Embodiments of the present invention will be described in detail below based on the accompanying drawings.

In FIG. 2, the circuit configuration for accumulatively adding and displaying the mileage is the same as that of the conventional device in FIG.
A speed signal detected by a distance sensor 1 that outputs repetitive pulses with a frequency proportional to the traveling speed is integrated by a counter 4 via a waveform shaping circuit 2 and a frequency divider 3 to become traveling distance data, which is stored in an input/output circuit 5. Sequentially transferred and held in RAM. The distance traveled is also displayed on the display 7 via the display drive circuit 6. 8 is a non-volatile memory.

Here, a determination circuit 11 for determining a rewrite cycle according to the present invention is connected to an on-vehicle battery 10 as a main power source via a key switch 9, and detects a voltage drop due to power cutoff (opening of the key switch 9). Then, the determination result is given to the input/output circuit 5, and the mileage data can be written from the RAM in the input/output circuit 5 to the nonvolatile memory 8 when the power is cut off. In this case as well, when the power is turned on, the mileage data held in the non-volatile memory 8 is input and output!
735, and is further transferred to the counter 4, where a new mileage distance is cumulatively added using this as an initial value. Further, the anode side of a backflow prevention diode 12 is connected to the battery 10 via the key switch 9, and the cathode side of this diode 12 is connected to the determination circuit 11. Input/output circuit 5. It is connected to each power supply terminal of the nonvolatile memory 8 and one end of the large capacity capacitor 13. This capacitor 13 has one end grounded and is used as a backup power source for the circuit section.

To explain its function in the above configuration, first, when power is supplied, the mileage is accumulated by the counter 4 and displayed on the display 7 in accordance with the running, and is sequentially written to the RAM in the input/output circuit 5 as mileage data. It will be done.

When the power is cut off by opening the key switch 9, the determination circuit 11 detects a voltage drop due to the power cutoff, and transmits the determination result to the input/output circuit 5. The input/output circuit 5 writes the mileage data held in the RAM into the nonvolatile memory 8. Here, the capacitor h1 capacitor 13 is the diode 1
Since the battery 10 is in a charging state through the voltage level of the battery 10 through the power supply circuit 11.2, the determination circuit 11. A voltage is supplied to the input/output circuit 5 and the nonvolatile memory 8 to perform a short-time write operation, and the capacitor 13 transfers the mileage data held in the temporary memory 8 to the RAM. It is given to the counter 4 as an initial value for newly cumulatively adding the distance traveled along with subsequent travel.

Therefore, the mileage data is rewritten in the non-volatile memory 8 only when the key switch 9 is released, and the rewriting cycle can be extended over a long period of time, such as several times per driving opportunity, compared to the conventional frequent rewriting. It is possible to prevent early deterioration of the element and extend the life of the nonvolatile memory 8.Furthermore, the mileage data written to the nonvolatile memory 8 is transferred from the counter 4 to the R in the input/output circuit 5.
Since this is the latest data that is transferred and held in the AM sequentially (for example, every 100 m), when the power is turned on again, it is transferred to the counter 4 again to obtain an accurate mileage as the initial value for cumulatively adding up the new mileage. This makes it possible to provide a highly reliable mileage needle that can withstand long-term use.

Further, FIG. 3 shows another practical example of the present invention, in which the determination circuit 11. A configuration is provided in which the determination inputs of the input/output circuit 5 and the nonvolatile memory 11 are connected to a power supply line 14 directly connected to the battery 1o.

In this case as well, the integration operation when power is supplied is calculated by the counter 4, and is sequentially transferred and held in the RAM in the input/output circuit 5 as travel distance data.

When the power is cut off by opening the key switch 9, the counter 4
Although the contents of are erased, since power is directly supplied to the RAM in the input/output circuit 5 through the power supply line 14,
The latest mileage data when the key switch 9 is opened remains held in this RAM.

Therefore, when the power is turned on again, the latest mileage data held in the RAM in the input/output circuit 5 is transferred to the counter 4, and the counter 4 uses this data as an initial value to cumulatively add the newly input mileage. , is sequentially transferred and held in the RAM in the input/output circuit 5, and the distance traveled is displayed on the display 7.

In this embodiment, rewriting of the mileage data to the nonvolatile memory 8 is not executed unless the power supply from the power line 14 is cut off.

In other words, unless the power supply from the power line 14 is cut off, the latest mileage data will be stored in the RAM in the input/output circuit 5.
Because the data is stored in the memory, the mileage data will not be lost during normal use, and the mileage can always be displayed as an accurate value.

However, there is no guarantee that the power supply voltage from the in-vehicle battery 10 to the circuit section is always stably provided, and the battery 1
In rare cases, a momentary disconnection phenomenon may occur due to poor electrical contact due to the connection condition with 0 or the fitting condition of the connecting cover for routing, and also the sudden disconnection phenomenon due to disconnection when replacing the battery or sudden discharge of the battery 10. There is a fear that such a voltage drop will make it impossible to supply power to the circuit, and that the mileage data held in the RAM in the counter 4 and the input/output circuit 5 will be lost.

In this embodiment, the determination circuit 11 detects the above-mentioned power cut-off state in which power cannot be supplied from the battery 10, and only at this time the mileage data held in the RAM in the input/output circuit 5 is transferred to the non-volatile memory 8. It is characterized by writing to.

That is, if the power supply through the power line 14 is cut off when the key switch 9 is closed or opened, for example, assuming that the battery 10 is being replaced, the power supply to the counter 4 will be cut off. Although the mileage data accumulated up to that point will be lost, the determination circuit 11. Since voltage is continuously supplied to the input/output circuit 5 and the nonvolatile memory 8 by the large capacity capacitor 13 as a backup power source, the latest running data stored in the input/output circuit 5 is sequentially transferred and held from the counter 4 to the RAM in the input/output circuit 5. The distance data is written to the nonvolatile memory 8 based on the judgment output detected by the judgment circuit 11,
When the battery 10 is connected again, this data is read out and transferred to the RAM in the input/output circuit 5 or to the counter 4, thereby making it possible to always display an accurate accumulated distance traveled.

Therefore, the mileage data is rewritten to the non-volatile memory 8 only when the power supply from the battery 10 is completely cut off, so the number of data rewrites can be kept to an extremely small number. It becomes possible to further promote life extension.

Note that the above embodiment describes a connection configuration in which power is supplied to the counting circuit unit for accumulating mileage only when the key switch 9 is closed.
A connection configuration that enables integration even when the battery is opened and adds the mileage even when driving down a slope or coasting, that is, a similar writing operation can be performed even when the circuit section is directly connected to the battery 10. Nor.

As described above, according to the present invention, the power interruption 11
A determination circuit that detects the J1 state, an input/output circuit that writes to the nonvolatile memory based on this determination output, and a backup power supply that supplies voltage for a period of time (so that the writing operation can continue even when the power is cut off) are provided. This allows excellent effects such as being able to display accurate mileage without exceeding the rewritable cycle of the non-volatile memory, even if the mileage data km has been traveled only when the power is cut off. be.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional automobile odometer using non-volatile memory, Fig. 2 is a block diagram showing one embodiment of the present invention, and Fig. 3 is a block diagram showing another embodiment of the present invention. It is a diagram. 1: Distance sensor 4: Counter 5: Input/output circuit 7: Display 8: Nonvolatile memory 9: Key isochi 10: Vehicle battery as main power source

Claims (1)

[Claims] A distance sensor that outputs repetitive pulses with a frequency proportional to the running speed, a counting circuit that adds up the distance traveled using the output of this distance sensor, and a non-volatile memory that can retain the mileage data accumulated by this counting circuit even after the power is turned off. In the distance meter, the distance meter has a determination circuit that detects a state in which power is cut off to the circuit section, an input/output circuit that writes the mileage data accumulated by the counting circuit into a nonvolatile memory based on the determination output of this determination circuit, and a power supply cutoff circuit. 1. An automobile odometer comprising a standby power source capable of supplying voltage to the circuit section for a period of time to enable writing to a non-volatile memory even when there is no state.