Patent Application
20180281708
This application claims foreign priority benefits under 35 U.S.C. § 119(a)-(d) to Application GB 1705341.4 filed Apr. 3, 2017, which is hereby incorporated by reference in its entirety.
This disclosure relates to improvements in or relating to oil temperature sensors configured to identify absence of oil from an intended location.
It is common practice to measure a temperature of oil in a vehicle engine. This is typically achieved through provision of a thermistor
In addition, considerable damage to the engine may occur if, for some reason, oil is absent from the system. It is therefore also known to provide an oil level sensor, which identifies a level of oil, and is configured to alert a driver if the level falls below a predetermined acceptable level. Oil level is measured through provision of a hot wire immersion type sensor, which requires a precise and relatively expensive constant current supply in an engine control module.
It is against this background that the present disclosure has arisen.
According to the present disclosure, there is provided a device to detect engine oil levels and temperatures. The device comprising: a thermistor; an unregulated, or voltage-only regulated, power supply configured to provide a non-continuous high current to the thermistor for a predetermined time in order to induce self-heating of the thermistor; a ADC configured to read voltage across the thermistor before and after heating of the thermistor; a processor configured to calculate a change in temperature of the thermistor on the basis of a change in voltage measured by the ADC and thereby to deduce an engine oil level and temperature.
In this context the term “high current” refers to currents that are sufficient to cause self-heating of the thermistor. This is in excess of lower currents that would typically be used to determine a value of resistance. A typical, temperature sensor thermistor may be read at a current of 500 μA with self-heating achieved at 10 mA. Specific current levels required for measurement and self-heating will vary based on a resistance range of the thermistor.
The use of an unregulated power supply is counter-intuitive, but it offers an opportunity for considerable efficiency improvements. Existing oil level sensing is typically achieved through use of a current regulated power supply. A current regulated supply is not typically available within the vehicle and must be added at extra cost. However, the use of a thermistor to measure both temperature and level using an unregulated, or regulated voltage, supply enables a reduction in cost.
The device may further comprise a storage device configured to store acceptable operating parameters and an alarm system configured to be triggered when a deduced engine oil level and/or temperature falls outside acceptable operating parameters.
The device may further comprise a voltage divider configured to separate the thermistor from the ADC.
The device may further comprise a control switch, which may be a p-channel metal-oxide semiconductor (PMOS). The control switch enables the device to be activated for a predetermined period of non-continuous operation. This provides a fixed burst of energy to the thermistor that will undergo self-heating. Depending on a specific heat capacity of fluid in which the thermistor is sitting, more or less of heat from the thermistor will be transferred into the surrounding fluid. The extent of heat transfer between the thermistor and oil will be significantly greater than if the thermistor is surrounded by air.
If the thermistor is surrounded by air, then the change in temperature of the thermistor as a result of heating facilitated by provision of power from the power supply will be much greater than if the thermistor is submerged in oil into which it can easily transfer heat. This change in thermistor temperature is determined by measuring the thermistor resistance at a beginning and end of a heating cycle.
Above a maximum acceptable change in temperature resulting from the self-heating, the device deduces that the thermistor is no longer surrounded by oil and therefore oil is at an unacceptably low level. An alarm can therefore be raised.
The temperature of the oil can be measured by connecting the power supply to the thermistor so that no significant self-heating occurs. This is done by applying power for a short period e.g. 5 μs and can be repeated to determine changes in temperature over time. This can be performed independently of a measuring level, if desired.
The device may further comprise a resistor in series with the switch to protect the switch.
The device may further comprise a reference voltage for a microcontroller unit (MCU). Some MCUs require a regulated voltage and the provision of a VREF provides for this.
The disclosure will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:
As required, detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the disclosure that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.
Like reference numerals have been used throughout the figures where common elements exist in different embodiments.
There are various common features, present in all embodiments. A device 10 is initiated using a switch 12 and comprises a thermistor 20, a power supply 30, an Analogue to Digital (ADC) converter 40 and voltage divider 44, 45, a processor (MCU) 50. The processor, or microcontroller 50 and the ADC 40 may be packaged together as indicated by the enclosing dashed line. These are 5V devices.
The thermistor 20 is a temperature-dependent resistance, which is positioned in a location that should, under normal operating conditions, be submerged in oil. The thermistor 20 has an exponential resistance function with temperature. As a result, within an automotive application, where temperatures may range from a cold start −40° C. to an engine operating temperature in the region of 150° C., the resistance may range from 800 kΩ at −40° C. to 530Ω at 150° C.
The power supply 30 is a battery that is of known, but uncontrolled voltage, VBAT, which may typically be a 12V supply. The use of a battery without current stabilization provides a considerable simplification on systems typically deployed. This power supply does not constitute a regulated current source as it lacks the required stabilization. The voltage is known, but is not necessarily constant.
The device 10 is activated using a switch 12 which, when activated, enables the power supply 30 to provide a short burst of power comprising a predetermined quantum of energy. The switch 12 is a PMOS in the illustrated embodiments. However, it will be understood that any suitable control switch could be substituted. When the device 10 is activated, current from the battery 30, VBAT is provided to the thermistor 20 through either resistor R1 or R2, and the ADC 40 reads the voltage across the thermistor 20. The resistance of the thermistor 20 is dependent on the temperature and therefore a measurement effectively provides a reading of the temperature of the thermistor 20.
The ADC 40 converts an analogue response of the thermistor 20 to provide a digital output indicative of a change in resistance of the thermistor 20 as a result of the self-heating induced by the provision of power from the power supply 30.
The processor or microcontroller unit (MCU) 50 then translates a digital response from the ADC 40 into oil temperature and level information. The MCU 50 also includes a memory, which store predetermined acceptable ranges for the oil level and temperature. If the MCU 50 determines that the oil temperature or oil level is outside the predetermined acceptable range, the MCU 50 provides this determination to an alert system. The alert system may provide an audible alarm to notify a driver or the alert may take the form of a visual warning, which may be displayed on a dashboard, on an infotainment system.
The ADC 40 is able to measure an unregulated voltage using a voltage divider comprising a resistor R4, 44 and R5, 45. In the illustrated embodiments R4, 44 is 16 kΩ and R5, 45 is 4 kΩ thereby providing a 4:1 ratio between resistors R4, 44 and R5, 45. This exact ratio is not required. Instead, the resistors R4, 44 and R5, 45 should permit the unregulated supply voltage to be reduced to a voltage level compatible with an ADC range that would commonly be 0-5V. Commonly this would be ratios in a region of 4:1. A provision of the voltage divider enables voltage of the power source 30 to be measured. The ability to measure voltage of the power source 30 obviates a need for voltage to be fixed and known as it can be measured dynamically.
In the embodiments illustrated in
In the embodiments illustrated in
When only one resistor, selected from between R1, 41 and R2, 42, is present, a resistance of that resistor R1, 41, R2, 42 is selected to ensure that voltage across the thermistor 20 remains within the 0-5V operational envelope of the ADC 40 and MCU 50 for all reasonable temperature values of the oil.
As illustrated in the embodiments shown in
An example of a heating duration could be as follows: If 10 mJ is to be delivered to the thermistor 20, which is at −1° C. and therefore 100 kΩ, when the switch 12 is closed to activate the device 10, VBAT of 12V flows, providing a current of 120 μA and a power of 1.44 mW. This therefore requires 7 s of heating to provide the 10 mJ.
If the thermistor 20 is at 100° C. and therefore 2.08 kΩ, a current of 4.65 mA and a power of 45 mW is provided. The heating time is therefore 0.22 s.
The embodiment illustrated in
The embodiment illustrated in
The embodiment illustrated in
The embodiment illustrated in
The embodiment illustrated in
The embodiment illustrated in
The embodiment illustrated in
It will further be appreciated by those skilled in the art that although the disclosure has been described by way of example with reference to several embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the disclosure as defined in the appended claims.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1705341.4 | Apr 2017 | GB | national |
