Heater control system based on slope of supply current

A heater control system includes a heater driver, a current sensor, a slope calculator, and a mode selector. The heater driver is configured to control current to a heater. The current sensor is configured to sense current supplied to the heater. The slope calculator is configured to calculate a slope of the current supplied to the heater. The mode selector is configured to adjust current supplied to the heater by the heated driver based on the slope of the current.

FIELD

The present disclosure relates to heater control systems and more particularly to heater control systems without temperature sensors.

BACKGROUND

When an occupant enters a vehicle after the vehicle is off for an extended period in a cold ambient environment, the temperature of exposed interior surfaces of the vehicle are at or near ambient temperature. When the occupant enters the vehicle after a long soak at low ambient temperatures, the interior surfaces may initially feel uncomfortable. Heaters are used to heat some of the exposed interior surfaces of the vehicle that are in contact with the occupants of the vehicle. For example, heaters may be used to heat seats and/or a steering wheel of the vehicle. When turned on, the heaters rapidly heat the exposed interior surfaces to a comfortable temperature without overheating the surfaces.

Control systems of heaters for seats and steering wheels may include one or more temperature sensors to sense the temperature of the exposed surfaces. The temperature sensors may include negative temperature coefficient (NTC) temperature sensors. Each temperature sensor tracks a local temperature of a portion of the seat or steering wheel. A controller receives the sensed temperature of the temperature sensor, estimates a temperature of the corresponding surface and adjusts power output to the corresponding heater.

Some manufacturers use heater control systems that do not use temperature sensors. For example, these heater control systems may determine a temperature of an exposed interior surface by calculating the resistance of the heater wire during heating based upon an instantaneous resistance, a thermal coefficient of the heating wire, and a reference resistance of the heater at a known temperature (e.g. during manufacture or at vehicle start using a temperature sensor). However, some manufacturers may refuse to provide a known temperature reference.

Some heater control systems attempt to determine heater wire temperature based on current supplied to the heater. This approach can be used if the resistance of the heater wire can be determined accurately. However, this approach does not work in systems with relatively high resistance tolerance ranges (such as +1-10%). In systems with relatively high resistance tolerance ranges, a reference resistance may be used to increase accuracy. However, using the reference resistance is relatively complex and costly.

SUMMARY

A heater control system is provided and includes a heater driver, a current sensor, a slope calculator, and a mode selector. The heater driver is configured to control current to a heater. The current sensor is configured to sense current supplied to the heater. The slope calculator is configured to calculate a slope of the current supplied to the heater. The mode selector is configured to adjust current supplied to the heater by the heated driver based on the slope of the current.

In other features, the heater driver is configured to use pulse width modulation (PWM) having a duty cycle, and wherein the mode selector is configured to adjust the duty cycle of the heater based on the slope of the current.

In other features, the mode selector is configured to define slope ranges, select one of the slope ranges based on the slope of the current, and adjust the current supplied by the heater based on the selected one of the slope ranges.

In other features, the heater control system further includes a low pass filter arranged between the current sensor and the slope calculator.

In other features, the mode selector is configured to receive a battery voltage value and adjust the current supplied to the heater based on the battery voltage value.

In other features, the mode selector includes N modes, where N is an integer greater than two, and where each of the N modes corresponds to a distinct current slope range.

In other features, the mode selector is configured to decrease a duty cycle of the heater driver as the slope of the current decreases.

In other features, the heater control system further includes a timer configured to reset when the heater is turned on, where the mode selector is configured to select a predetermined duty cycle for the heater after the timer reaches a predetermined period.

In other features, the mode selector includes a first mode, a second mode and a third mode. The first mode is selected when the slope of the current is in a first current slope range. The mode selector selects a first duty cycle when the slope of the current is in the first current slope range. The second mode is selected when the slope of the current is in a second current slope range. The mode selector selects a second duty cycle when the slope of the current is in the second current slope range. The third mode is selected when the slope of the current is in a third current slope range. The mode selector selects a third duty cycle when the slope of the current is in the third current slope range. The first current slope range is greater than the second current slope range. The second current slope range is greater than the third current slope range. The first duty cycle is greater than the second duty cycle. The second duty cycle is greater than the third duty cycle.

In other features, a system is provided and includes the heater control system, the heater, and a seat including the heater.

In other features, a system is provided and includes the heater control system, the heater, and a steering wheel including the heater.

In other features, a heater control system is provided and includes a heater driver, a current sensor, a slope calculator, and a temperature estimator. The heater driver configured to supply current to a heater. The current sensor is configured to sense current supplied to the heater. The slope calculator is configured to calculate a slope of the current supplied to the heater. The temperature estimator is configured to estimate a temperature of a heated surface based on the slope of the current. The heater driver is configured to receive a temperature setpoint and the estimated temperature of the heated surface.

In other features, the heater driver is configured to use pulse width modulation (PWM) having a duty cycle, and wherein the heater driver is configured to adjust the duty cycle of the heater based on a difference between the temperature setpoint and the estimated temperature of the heated surface.

In other features, the heater control system further includes a low pass filter arranged between the current sensor and the slope calculator.

In other features, the heater driver is configured to receive a battery voltage value and adjust the current supplied to the heater further based on the battery voltage value.

In other features, the heater driver is configured to decrease a duty cycle of the heater driver as the slope of the current decreases.

In other features, a system is provided and includes the heater control system, the heater, and a seat including the heater.

In other features, a system is provided and includes the heater control system, the heater, and a steering wheel including the heater.

DETAILED DESCRIPTION

While the foregoing disclosure relates to seat heaters and/or steering wheels, the systems and methods described herein can be used for other heaters in other locations. The present disclosure relates to a heater control system that senses a slope of current supplied to the heater and estimates a temperature of a surface that is being heated based thereon. In other examples, the slope of the current supplied to the heater is used to determine when to switch a heater driver from a high or variable duty cycle mode to initiate fast heating of an interior surface to a predetermined or fixed duty cycle mode to maintain a target temperature range without causing discomfort to the occupant.

The heater control system does not require a temperature sensor or a reference resistance. As a result, the temperature sensor, connection wiring, and at least two terminals of a heater connector can be eliminated, which reduces cost. Eliminating components such as the temperature sensor and wiring also tends to increase reliability. In other words, accurate control of the temperature of the seat surface can be accomplished at a lower cost without the temperature sensor or the reference resistance.

Due to a positive temperature coefficient (PTC) effect of the heater wire, the current supplied to the heater tends to drop as the heater wire self-heats. The PTC effect leads to a non-constant, exponential decrease in current as the temperature of the heater wire increases. In other words, the rate-of-change or slope of current d reduces proportionally as wire temperature increases. There is a fixed correlation based on the particular seat and heater design that are used. By monitoring the slope of the current, the wire temperature and seat surface temperature can be estimated accurately.

The current level may also depend on the voltage received from the battery. For example, after starting the vehicle after a long soak, the voltage of the battery may be lower. Therefore in some examples, different scaling factors or adjustments may be used based on where the battery voltage lies relative to a nominal battery voltage and/or a plurality of voltage ranges. The self-heating rate of the wire is primarily affected by heat transfer to surrounding components, and should not vary significantly with resistance tolerances of the finished goods.

In some examples, the slope of the current is monitored after the heater is turned on to determine when the heater is approaching a target operating temperature. When the slope indicates that the target operating temperature is reached, the controller switches to a predetermined or fixed duty cycle to maintain the desired temperature. In other words, a duty cycle that accurately maintains the desired seat surface temperature is calibrated for the seat. The systems and methods described herein eliminate the temperature sensor and related components from the heater control system while maintaining accurate temperature control of the heated surface.

Referring now toFIG.1, a heater controller10includes a heater driver20. In some examples, the heater driver20generates pulse width modulated (PWM) signals having a variable duty cycle (DC) that are output to a heater40(e.g. for a seat, a steering wheel or other heated surface). As can be appreciated, higher DC values may be used when the surface to be heated is cool/cold to reduce the time required to heat the surface. As the temperature of the heater wire and the interior surface increases, lower DC values may be used to prevent discomfort due to overheating.

A current sensor30is arranged between the heater driver20and the heater40to sense current Irawsupplied to the heater40. In some examples, a low-pass filter50is used to filter the current Irawto reduce noise and to generate a filtered current Ifiltered.

A slope calculator54receives the filtered current Ifiltered, calculates a slope of the filtered current Ifilteredduring a predetermined period and outputs a current slope Islope. A temperature estimator60estimates a temperature of a heated surface based on the current slope Islope. For example only, the temperature estimator60includes a lookup table or a formula that determines the estimated temperature Testbased on the current slope Islope.

In some examples, the temperature estimator60indexes the lookup table using the current slope Islope. In some examples, the temperature estimator60determines the estimated temperature Testfurther based on the voltage of the battery Vbatt. For example, the temperature estimator60compares the voltage of the battery Vbattto the nominal battery voltage and/or two or more voltage ranges and selects one of a plurality of lookup tables or formulas or adjusts a formula based on the comparison. Then, the temperature estimator60access the selected lookup table, uses the selected formula or adjusts the formula based on the current slope Islope. The heater driver20receives the temperature setpoint Tsetand the estimated temperature Testand sets the DC based thereon. In some examples, the DC is set based on a difference between the temperature setpoint Tsetand the estimated temperature Test.

Referring now toFIG.2A, a heater controller100is shown to include a heater driver120. In some examples, the heater driver120generates PWM signals having a variable duty cycle (DC) that are output to a heater140(e.g. for a seat, a steering wheel or other exposed interior surface of a vehicle). As can be appreciated, higher DC values may be used when the surface to be heated is cool/cold to quickly heat the surface. As the temperature of the heater wire and the interior surface increases, lower DC values may be used.

A current sensor130is arranged between the heater driver120and the heater140to sense current Irawsupplied to the heater140. In some examples, a low-pass filter150is used to filter the current Irawto reduce noise and to generate a filtered current Ifiltered.

A slope calculator154receives the filtered current Ifiltered, calculates a slope of the filtered current Ifilteredand outputs a current slope Islope. A heating mode selector160selects a heating mode based on the current slope Islope. In some examples, the heating mode selector160compares the current slope Islopeto one of a plurality of slope ranges and selects a mode of the heater based thereon. In other words, the heating mode selector160selects different heating control parameters based on the current slope Islope. In some examples, the heating mode selector160selects one of a plurality of DC values for the heater driver120based on the current slope Islope.

In some examples, the heating mode selector160includes a lookup table or a formula that outputs a desired DC based on the current slope Islope. In some examples, the heating mode selector160indexes the lookup table using the current slope Islope. In some examples, the heating mode selector160selects one of a plurality of heating modes based on the current slope Islopeas will be described further below. The heating mode selector160may select a lookup table or formula or adjust a formula based on the voltage of the battery Vbatt.

Referring now toFIG.2B, another heater controller170is shown. The heater controller170further includes a timer180that is reset when the heater transitions to an on state. In some examples, the heating mode selector160transitions to an open loop mode where the DC of the heater driver120is set to a predetermined or fixed DC after a predetermined period of operation to maintain a selected heater setting as determined by the timer180.

Referring now toFIGS.3A and3B, a graph is shown illustrating current supplied to a heater and a temperature of a heater wire. InFIG.3B, the current is sampled over time and the current slope Islopeis calculated during a predetermined period. InFIG.3B, a steep slope value typically occurs when the heater is initially turned on after a long soak at low ambient temperatures. When the heater wire and the interior surface are cold, the current supplied to the heater140is relatively high and decreases rapidly due to self-heating of the heater wire. At this point, the current slope is in a first or high slope range. The heating mode selector160can set a relatively high DC value to heat the surface quickly without causing discomfort to the occupant when the target slope range is reached.

As the wire self-heats, the current continues to decrease and the slope of the current decreases from the high slope range to lower slope values corresponding to a second or middle slope range. The heating mode selector160can reduce the DC value to heat the surface less quickly to avoid causing discomfort to the occupant. As the wire heats further, the current further decreases and starts to stabilize. The slope values of the current decreases to a target slope range. In some examples, a target or fixed duty cycle is used when in the target slope range.

When using the heater control system inFIG.2A, the target duty cycle is reached when the current slope Islopereaches the target slope range (independent of time). When using the heater control system inFIG.2B, the target duty cycle is reached when the current slope Islopereaches the target slope range or the predetermined period of the timer expires (whichever occurs first).

Referring now toFIG.4, a flowchart of a method300for controlling a heater based on current slope is shown. At210, the method determines whether the heater is on. If210is true, the method continues at214and optionally determines battery voltage. At226, the method measures the current supplied to the heater. In some examples, low pass filtering is used to reduce noise in the measured current. At230, the method determines the slope of the current. At238, the method estimates the temperature of the heated surface based on the current and optionally based on the voltage of the battery. In some examples, the heater driver sets the DC based on the temperature setpoint and the estimated temperature. In other examples, the heater driver sets the DC based on a difference between the temperature setpoint and the estimated temperature at242.

Referring now toFIG.5, a flowchart of a method300for controlling a heater based on current slope is shown. At310, the method determines whether the heater is on. If310is true, the method continues at314and optionally determines battery voltage. At318, the method optionally selects a voltage range corresponding to the battery voltage. At322, the method optionally selects or adjusts a current slope lookup table or formula based on the selected voltage range of the battery voltage.

At326, the method measures the current supplied to the heater. In some examples, low pass filtering is used to reduce noise. At330, the method determines the slope of the current. At340, the method determines whether the current slope is in a first slope range. If340is true, then the heater is operated using a first set of heater parameters at344. For example, the first set of heater parameters may set the DC of the heater driver to a first value or a first range of DC values.

If340is false, the method determines whether the current slope is in a second slope range at350. If340is true, then the heater is operated using a second set of heater parameters at354. For example, the second set of heater parameters may set the DC of the heater driver to a second value or a second range of DC values. In some examples, the second value or DC range is less than the first value or DC range.

If350is false, then the heater is operated using a third set of heater parameters at360. For example, the third set of heater parameters may set the DC of the heater driver to fixed DC value or a third range of DC values. In some examples, the third value or DC range is less than the first value or DC range and the second value or DC range. While three different modes are shown, additional or fewer modes can be used.