Automotive electronic control unit

Generally, the current threshold value is set as a fixed value. Therefore, even in a case where an abnormality occurs in the load and the resistance value is small, when the power supply voltage applied to the load is low, the current value is also low, and falls below the threshold value, and there is a possibility that the overcurrent is not detected. In the present invention, by providing a second detection means that detects a load abnormality by calculating the resistance value of the load from information of the power supply voltage applied to the load, in addition to a first detection means that detects an overcurrent state that indicates the load abnormality using only current value information, it is possible to detect an overcurrent indicating an abnormality of the load even when the power supply voltage applied to the load is low.

TECHNICAL FIELD

The present invention relates to an in-vehicle electronic control device for the purpose of improving the accuracy of detecting an abnormality of a load driven by the in-vehicle electronic control device.

BACKGROUND ART

Vehicles include various sensors to control the engine. The information from these sensors is input to the in-vehicle electronic control device (ECU) and used to control the engine. For example, an O2 sensor detects the concentration of oxygen in the exhaust gas. The mixture ratio (air-fuel ratio) of fuel and air is controlled by this oxygen concentration information. If the O2 sensor does not operate properly, proper combustion will not occur, and the concentration of carbon monoxide and nitrogen oxides in the exhaust gas will increase, which may have a significant effect on the catalyst that purifies the exhaust gas. The ECU is required to detect an abnormality of the sensor at an early stage and urge the user to take measures such as repair.

The O2 sensor is activated by heating to an appropriate temperature to detect the oxygen concentration. Therefore, a heater is provided inside the sensor. However, in the case of a battery short where the battery voltage is applied to both ends of the heater, no current flows through the heater and the sensor cannot be heated. The ECU detects an overcurrent due to a battery short, makes notification of the occurrence of an abnormality, and performs processing such as stopping the drive of the heater.

In this way, detecting the abnormality such as load battery shorts is one of the major roles of ECUs.

When the resistance value drops due to deterioration of the external element, which is the load, or when the power supply contact (battery short circuit) occurs due to damage to the connection cable, an excessive current flows through the ECU. The ECU uses this as an overcurrent to detect load abnormalities.

The ECU detects the current value that drives the load, and detects it as an overcurrent when the current value exceeds the threshold value. Generally, this current threshold value is set as a fixed value.

PTL 1 discloses a technique of conventionally detecting only the current flowing through a load and detecting an overcurrent. The overcurrent is detected based on a fixed threshold value, and the overcurrent is detected as a current exceeding this threshold value.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The current value flowing through the load is determined by the applied power supply voltage, the resistance value of the load, the resistance value of the connection cable, the resistance values of the wiring in the ECU and the drive element, and the like. However, in general, resistance values other than the resistance value of the load are designed to be sufficiently smaller than the resistance value of the load. The conditions in which the current value is lowered include a case where the power supply voltage applied to the load is low and a case where the resistance value of the load increases. Therefore, even in a case where an abnormality occurs in the load and the resistance value is small, when the power supply voltage applied to the load is low, the current value is also low, and falls below the threshold value, and there is a possibility that the overcurrent is not detected.

In vehicles, the power supply voltage is not fixed and may be low. As a result, the current value may be low. Even when the current value is abnormal as a load, it is not detected as an overcurrent when it falls below the threshold value, so that it is not possible to detect the value as an abnormality.

An object of the present invention is to detect an overcurrent indicating an abnormality of a load even when the power supply voltage applied to the load is low.

Solution to Problem

To solve the above problems, in the in-vehicle electronic control device according to the present invention, by providing a second detection means that detects a load abnormality by calculating the resistance value of the load using information of the power supply voltage applied to the load, in addition to a first detection means that detects an overcurrent state that indicates the load abnormality using only current value information, it is possible to detect an overcurrent indicating an abnormality of the load even when the power supply voltage applied to the load is low.

Further, in the present invention, by providing a means for switching the threshold value for detecting an overcurrent stepwise according to the power supply voltage applied to the load, it is possible to detect an overcurrent indicating an abnormality of the load even when the power supply voltage applied to the load is low.

Advantageous Effects of Invention

According to the present invention, it is possible to detect an overcurrent indicating an abnormality of the load even when the power supply voltage applied to the load is lower than that in the related art by adding a new second detection means to the existing first detection means. When the second detection means is executed by the program of the arithmetic device, it can be realized with the existing circuit configuration.

Further, according to the present invention, since the overcurrent detection is performed by only the existing first detection means when the power supply voltage applied to the load is high, it is possible to reduce the processing burden when the second detection means is executed by the program of the arithmetic device.

Further, according to the present invention, since the threshold value for detecting an overcurrent can be switched stepwise according to the power supply voltage applied to the load, it is possible to reduce the burden on the second detection means when it is realized by a slight change in the existing first detection means or the program of the arithmetic device.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings. In addition, each embodiment can be combined.

First Embodiment

In order to drive a load3, a battery2as a load power supply is connected to the load3.

An ECU1includes a drive element103that drives the load3, a current detection resistor104that detects the current flowing through the load3, an integrated circuit102, and an arithmetic device101.

The drive element103drives the load3by a control signal203from the integrated circuit102.

The current detection resistor104acquires a voltage value proportional to the current flowing through the load3. The acquired voltage value is input to the integrated circuit102as load current value information204.

The arithmetic device101performs an operation that drives the load3by using an input signal such as that from a sensor connected to the ECU1. The integrated circuit102outputs the control signal203to the drive element103in response to a control command from the arithmetic device101. The integrated circuit102includes a first diagnostic unit that diagnoses an overcurrent when the load current value information204exceeds the current threshold value. This detection method is a conventionally known method, and is used here as the first detection means. Further, the current threshold value is generally set as a fixed value.

The current threshold value of the integrated circuit102is set as a fixed value as described above, but there is a range of possible values due to individual differences due to manufacturing variations and environmental factors such as temperature.

As shown inFIG.2, there are an individual having a maximum current threshold value401and an individual having a minimum current threshold value402.

In the related art, the overcurrent diagnosis has been performed at a voltage value where a current value301exceeds the maximum current threshold value401. In recent years, there has been an increasing demand for the overcurrent diagnosis at low voltage, and the overcurrent diagnosis at a voltage where the current value301is lower than the maximum current threshold value401is required. In this case, as shown inFIG.2, a new problem that the overcurrent diagnosis can be performed for an individual whose current threshold value is the minimum current threshold value402, but the overcurrent diagnosis cannot be performed for an individual whose current threshold value is the maximum current threshold value401has been found.

Therefore, in the embodiment, in order to detect the load abnormality, the second detection means is implemented in addition to the first detection means.

Next, the second detection means will be described.

The arithmetic device101communicates with the integrated circuit102through a communication line201, and acquires current value information204, flowing through the load3, input to the integrated circuit102. The power supply voltage applied to the load3is input to the arithmetic device101via an analog-to-digital converter (not shown) as load power supply voltage value information202.

When the arithmetic device101determines that the power supply voltage applied to the load is low based on the load power supply voltage value information202applied to the load3, a second detection means that detects a load abnormality is performed by calculating the resistance value of the load from the current value information204flowing through the load3and the load power supply voltage value information202applied to the load3.

The resistance value of the load is simply acquired by dividing the load power supply voltage value information202by the current value information204. To be precise, it is acquired by subtracting the resistance value of the connection cable of the load and the ECU, the wiring in the ECU, the resistance value of the drive element, etc. from the resistance value acquired simply.

For example, suppose that when the normal load is 10 ohms and does not fall below 9 ohms even when the initial variation and temperature characteristics are taken into consideration, the result of 2 ohms or less is reliably detected as a load abnormality. Considering the error of the load power supply voltage value information202and the current value information204, it can be realized by incorporating, in the arithmetic device101, a process of determining that the load is abnormal when the calculation result by the arithmetic device101is 3 ohms or less.

In the case of this example, when the resistance value at which it is determined that the load is abnormal is set to a value close to 9 ohms, it is easier to catch an abnormal sign before a complete battery short, and there is a possibility that load deterioration can be detected at an early stage.

On the contrary, when the resistance value is set to a value close to 2 ohms, it is easy to detect only when a truly abnormal state occurs, and the possibility of a false notification in which the result is detected as abnormal even though the load is normal can be reduced.

When the resistance threshold value is set to an intermediate value that is a compromise between the two, it is possible to catch an abnormal sign while reducing a false notification.

In the embodiment, the current detection resistor104is used as a current detection means for acquiring the current value information204. It is also possible to detect the current by building the drive element103into the integrated circuit102, and configuring a current mirror circuit.

Further, in the embodiment, while the communication line201with the integrated circuit102is used as a means for the arithmetic device101to acquire the current value information204, for example, it is also possible for the integrated circuit102to output the current value information204as amplified voltage information, and for the arithmetic device101to capture the information using an analog-to-digital converter.

The arithmetic device101is generally composed of a microcomputer, but can also be realized by an FPGA, a DSP, an ASIC, or the like.

Further, in the embodiment, while a low-side circuit is used in which the load3is connected to the power supply, and the drive element103sucks a current, the same effect can be acquired in a high-side circuit in which the load3is grounded, and the drive element103discharges a current.

In the embodiment, at a voltage when the current at the time of load resistance abnormality exceeds the maximum threshold value current value, only the first detection means that detects an abnormality in the integrated circuit based on the load current is used. In the embodiment, at a voltage, when the current at the time of load resistance abnormality is equal to or less than the maximum threshold value current value, in which abnormality may not be detected by the first detection means, both the second detection means that detects an abnormality by the resistance value acquired by the arithmetic device101based on the load power supply voltage information and the current value information input to the arithmetic device101, and the adopt first detection means are used to determine that the load is abnormal when either one is determined to be abnormal. According to the embodiment, since the load abnormality detection is performed without using the arithmetic device101in the area where the integrated circuit102can detect the abnormality, the arithmetic load of the arithmetic device101can be reduced, and in the low voltage region where load abnormalities cannot be detected by the integrated circuit102alone, the load resistance is calculated by the arithmetic device101to detect the load abnormality, so that it is possible to detect the load abnormality even in the low voltage region. After detecting the abnormality, the ECU1notifies the outside of the ECU1of the occurrence of the abnormality with a warning light or an alarm sound to perform a process such as stopping the driving of the load3.

Second Embodiment

Hereinafter, the second embodiment of the present invention will be described with reference toFIG.3. The description of the same configuration as the first embodiment will be omitted.

As described in the first embodiment, the first detection means has a maximum current threshold value401and a minimum current threshold value402shown inFIG.2. In the first embodiment, these two values are constant values (fixed values) regardless of the power supply voltage V applied to the load3. On the other hand, in the embodiment, as shown inFIG.3, it has a maximum current threshold value501and a minimum current threshold value502that are proportional to the power supply voltage V applied to the load3.

Here, since the minimum current threshold value502is set to a value larger than a current value302that can be taken when the load resistance is normal, and changes in the same manner as the current value302at the time of normality in proportion to the power supply voltage V applied to the load3, it is not detected as an overcurrent.

Further, since the maximum current threshold value501is set to a value smaller than the current value301that can be taken when the load resistance is abnormal, and changes in the same way as the current value301at the time of abnormality in proportion to the power supply voltage V applied to the load3, it can be detected as an overcurrent.

The maximum current threshold value501and the minimum current threshold value502can be defined as resistance values. As described in the first embodiment, it is simply acquired by dividing the load power supply voltage value information202by the current value information204. Using a microcomputer, it is possible to perform calculation in real time and diagnose whether the load3is abnormal or normal.

Third Embodiment

Hereinafter, the third embodiment will be described with reference toFIG.4.

FIG.4shows a simplification of the setting of the maximum current threshold value501and the minimum current threshold value502shown inFIG.3. A maximum current threshold value601and a minimum current threshold value602shown here have three steps of values with respect to the power supply voltage V applied to the load3.

The maximum current threshold value601and the minimum current threshold value602do not need to be calculated in real time by the load power supply voltage value information202and the current value information204, but may be set in advance as three current threshold values for the load power supply voltage value information202. In a case of realizing by a microcomputer, the processing load due to the calculation is not increased, and it can be achieved by inputting the load power supply voltage information202to the integrated circuit102and increasing the number of current threshold values from one to three.

In the embodiment, while the power supply voltage V applied to the load3has a three-step threshold value, it doesn't need to have the three-step threshold value. In some cases, two steps are enough, or on the contrary, it is possible to support a wide range of power supply voltages by setting the number of steps to 4 or more.

REFERENCE SIGNS LIST

1in-vehicle electronic control device2battery3load101arithmetic device102integrated circuit103drive element104current detection resistor201arithmetic device-integrated circuit communication line202load power supply voltage value information203drive element control signal line204load current value information301voltage-current straight line when load resistance is abnormal302voltage-current straight line when load resistance is normal401maximum current threshold value of first embodiment402minimum current threshold value of first embodiment501maximum current threshold value of second embodiment (straight line)502minimum current threshold value of second embodiment (straight line)601maximum current threshold value of second embodiment (3 steps)602minimum current threshold value of second embodiment (3 steps)