METHOD AND SYSTEM FOR LOW LEVEL DETECTION

Abstract

Methods and systems for evaluating the operation of an electric vehicle's cooling system are described. In one example, a superheat temperature at a compressor inlet can be generated using only a temperature sensor and a pressure sensor. This superheat temperature can be compared to a threshold superheat temperature to assess whether the amount of refrigerant in the cooling system is as expected.

Description

FIELD OF TECHNOLOGY

[0001] The present description relates to methods and a system for diagnosing the operation of a vehicle's cooling system. The methods and system may be particularly useful for vehicles that incorporate refrigerant-based cooling. GENERAL STATE OF THE ART

[0002] A vehicle may include a cooling system. The cooling system may cool a passenger compartment and a battery that provides power to propel a vehicle. In particular, the cooling system may include refrigerant, and the refrigerant may be used to cool the battery and the passenger compartment. The refrigerant may be compressed and condensed into a liquid before being expanded in a cooling device or an evaporator. The cooling device may cool liquid coolant, and the liquid coolant may be circulated within the battery, thereby cooling the battery. The evaporator may cool air that is passed over the evaporator and returned to the passenger compartment. Thus, a cooling system may use refrigerant as a medium for cooling a liquid and a gas.

[0003] It should be understood that the foregoing summary is provided to introduce, in simplified form, a selection of concepts that are described in more detail in the detailed description. It is not intended to identify important or significant features of the claimed subject matter, the scope of which is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that overcome any of the disadvantages recited above or in any part of this disclosure. SUMMARY

[0004] The present description relates to diagnosing the operation of a cooling system of a vehicle. The cooling system may provide cooling to a traction battery and a passenger compartment or passenger cell of a vehicle. In one example, the cooling system may include a refrigerant to move heat from a first location to a second location. The cooling system may be part of an electric vehicle, as described in Fig. 1. Alternatively, the cooling system may be part of a hybrid vehicle or a fuel cell vehicle. The cooling system may be as shown in Fig. 2 or configured in a different arrangement. The cooling system may use refrigerant as the cooling medium. The cooling system may be configured as shown in Fig. 3 to diagnose the cooling system. A method for operating the cooling system is shown in Fig. 4 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The advantages described in this document will be more fully appreciated by reading an example of an example, referred to in this document as the detailed description, when considered alone or with reference to the drawings, in which: Fig. 1 is a schematic diagram of a non-restrictive electric vehicle; Fig. 2 shows a vehicle cooling system that can cool a battery and a passenger compartment of a vehicle; Fig. 3 shows an exemplary operating sequence according to the method of Fig. 4 and the system Fig. 1 and Fig. 2; and Fig. 4 shows a flowchart of an exemplary method for diagnosing a cooling system of a vehicle. DETAILED DESCRIPTION

[0006] A vehicle may include a cooling system based on a refrigerant (e.g., R410A) to cool passenger compartments and components of a vehicle. The cooling system may be configured as a heat pump, which can interchange the functionality of heat exchangers in the heat pump during varying operating conditions. The vehicle's cooling system may provide cooling to different compartments of a vehicle and devices within the vehicle simultaneously. For example, the cooling system may simultaneously cool a traction battery and a passenger compartment of a vehicle. The cooling system may adjust a speed of a refrigerant compressor or refrigerant pump and positions of one or more valves (e.g., expansion valves) to provide different levels of cooling capacity to the devices and passenger compartments of the vehicle.However, if refrigerant is lost from the refrigeration system, compressor lubrication may be reduced and the compressor may be compromised. One way to determine whether or not refrigerant has been lost from the refrigeration system is to monitor the pressure at an inlet side of a compressor and at an outlet side of the compressor. However, measuring the refrigerant pressure at a compressor inlet and outlet can only respond to large refrigerant losses. Consequently, there may be fewer opportunities to implement corrective actions before potentially more significant mitigation techniques must be applied to reduce the possibility of compressor degradation. Therefore, it may be desirable to provide a means of detecting smaller refrigerant losses from a refrigeration system.

[0007] The inventors herein have recognized the above-mentioned disadvantage and developed a method for operating a cooling system of a vehicle, comprising: generating an estimate of a superheat temperature of a refrigerant according to a pressure at an inlet side of a compressor and a temperature at the inlet side of the compressor; and shutting down the compressor in response to the estimate of the superheat temperature of the refrigerant exceeding a superheat threshold temperature.

[0008] By estimating a superheat temperature at a compressor inlet and comparing the superheat temperature to a threshold superheat temperature, it may be possible to determine whether a cooling system has lost small or large amounts of refrigerant, allowing less significant mitigation measures to be taken before more significant mitigation measures are implemented. These less significant mitigation measures may allow the vehicle's cooling to be maintained for a period of time, allowing a vehicle user to plan for vehicle service. Furthermore, these mitigation measures may reduce the possibility of compressor degradation.

[0009] The present description can provide several advantages. In particular, the approach can reduce the possibility of compressor degradation. Furthermore, the approach can provide a higher level of confidence for detecting refrigerant loss in a refrigeration system. Additionally, the approach can be implemented at cold or warm ambient temperatures and regardless of whether a heat pump is operating in cooling or heating mode.

[0010] The above advantages, as well as other advantages and features of the present description, will be readily apparent from the following detailed description when read alone or in conjunction with the accompanying drawings.

[0011] With reference to Fig. 1, a non-limiting exemplary vehicle propulsion system 100 for a vehicle 121 is shown. A front portion of the vehicle 121 is indicated at 110 and a rear portion of the vehicle 121 is indicated at 111. The vehicle propulsion system 100 includes at least two power sources, including a front electric machine 125 and a rear electric machine 126. However, in other examples, the vehicle 121 may include only one electric machine. The electric machines 125 and 126 may consume or generate electrical power depending on their operating mode. Throughout the description of Fig. 1, mechanical connections between different components are illustrated as solid lines, while electrical connections between different components are illustrated as dashed lines.

[0012] The vehicle propulsion system 100 includes a front axle 133 and a rear axle 122. In some examples, the rear axle may include two half-shafts, for example, a first half-shaft 122a and a second half-shaft 122b. Likewise, the front axle 133 may include a first half-shaft 133a and a second half-shaft 133b. The vehicle propulsion system 100 further includes front wheels 130 and rear wheels 131. In this example, the front wheels 130 may be selectively driven via the electric machine 125. The rear wheels 131 may be driven via the electric machine 126.

[0013] The rear axle 122 is coupled to the electric machine 126. A rear drive unit 136 may transfer power from the electric machine 126 to the axle 122, resulting in rotation of the drive wheels 131. The rear drive unit 136 may include a set of small gears 175 and a large gear 177 coupled to the electric machine 126 via an output shaft 126a of the rear electric machine 126. The small gear 175 may be engaged via fully closing a clutch 176 of the small gears. The large gear 178 may be engaged via fully closing a clutch of a large gear 178. The high gear clutch 178 and the low gear clutch 176 may be opened and closed via commands received from the rear drive unit 136 via a CAN 299.Alternatively, high gear clutch 178 and low gear clutch 176 may be opened and closed via digital outputs or pulse widths provided via control system 14. Rear drive unit 136 may include a differential 128 so that torque may be provided to axle 122a and axle 122b. In some examples, an electrically controlled differential clutch (not shown) may be included in rear drive unit 136.

[0014] The front axle 133 is coupled to the electric machine 125. A front drive unit 137 can transfer power from the electric machine 125 to the axle 133, resulting in rotation of the drive wheels 130. The front drive unit 137 can include a set of small gears 170 and a large gear 173 coupled to the electric machine 125 via an output shaft 125a of the front electric machine 125. The set of small gears 170 can be engaged via a full closure of a clutch of the small gears 171. The large gear 173 can be engaged via a full closure of a clutch of a large gear 174. The clutch of the large gear 174 and the clutch of the small gears 171 can be opened and closed via commands received by the front drive unit 137 via the CAN 299.Alternatively, the clutch of large gear 174 and the clutch of small gears 171 may be opened and closed via digital outputs or pulse widths provided via control system 14. The front-wheel drive unit 137 may include a differential 127 so that torque may be provided to axle 133a and axle 133b. In some examples, an electrically controlled differential clutch (not shown) may be included in the front-wheel drive unit 137.

[0015] The electric machines 125 and 126 may receive electrical power from an onboard electrical energy storage device 132 (e.g., a traction battery or a battery that provides power for a vehicle's motive power). Furthermore, the electric machines 125 and 126 may provide a generator function to convert the vehicle's kinetic energy into electrical energy, which electrical energy may be stored in the electrical energy storage device 132 for later use by the electric machine 125 and / or the electric machine 126. A first inverter system controller (ISCI) 134 may convert alternating current (AC) generated by the rear electric machine 126 to direct current (DC) for storage in the electrical energy storage device 132, and vice versa.A second inverter system controller (ISC2) 147 can convert alternating current generated by the front electric machine 125 into direct current for storage in the electrical energy storage device 132, and vice versa.

[0016] The electrical energy storage device 132 may be a battery, a capacitor, an inductor, or other electrical energy storage device.

[0017] In some examples, the electrical energy storage device 132 may be configured to store electrical energy that may be supplied to other electrical loads onboard the vehicle (other than the electric motor), including the interior heating and air conditioning systems, engine starting, headlights, interior audio and video systems, etc.

[0018] The control system 14 may communicate with one or more of the electric machine 125, the electric machine 126, the energy storage device 132, etc. The control system 14 may receive sensory feedback information from one or more of the electric machine 125, the electric machine 126, the energy storage device 132, etc. Further, in response to this sensory feedback, the control system 14 may send control signals to one or more of the electric machine 125, the electric machine 126, the energy storage device 132, etc. The control system 14 may receive an indication regarding a vehicle operator-requested output of the vehicle propulsion system from a human vehicle operator 102 or an autonomous controller. For example, the control system 14 may receive sensory feedback from a pedal position sensor 194 that communicates with a pedal 192.Pedal 192 may schematically refer to a power pedal. Likewise, control system 14 may receive an indication of operator-requested vehicle braking via a human operator 102 or an autonomous controller. For example, control system 14 may receive sensory feedback from a pedal position sensor 157 that communicates with a brake pedal 156.

[0019] The energy storage device 132 may temporarily receive electrical energy from a power source, such as a fixed electrical grid (not shown), that is external to the vehicle (e.g., not part of the vehicle). As a non-limiting example, the vehicle propulsion system 100 may be configured as a plug-in electric vehicle (EV), whereby electrical energy may be supplied to the energy storage device 132 via the electrical grid (not shown).

[0020] The electrical energy storage device 132 includes an electrical energy storage device controller 139 and a power distribution module 138. The electrical energy storage device controller 139 can provide charge balancing between energy storage elements (e.g., battery cells) and communication with other vehicle controllers (e.g., controller 12). The power distribution module 138 controls the flow of power into and out of the electrical energy storage device 132.

[0021] One or more wheel speed sensors (WSS) 195 may be coupled to one or more wheels of the vehicle propulsion system 100. The wheel speed sensors may detect the rotational speed of each wheel. One such example of a WSS may include a permanent magnet sensor.

[0022] The controller 12 may comprise a portion of a control system 14. In some examples, the controller 12 may be a single controller of the vehicle. The control system 14 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). As one example, the sensors 16 may include tire pressure sensor(s) (not shown), wheel speed sensor(s) 195, etc. In some examples, sensors associated with the electric machine 125, the electric machine 126, the wheel speed sensor 195, etc. may communicate information regarding various operating states of the electric machines to the controller 12. The controller 12 includes non-volatile memory (e.g.,Read-only memory) 165, a random access memory 166, digital inputs / outputs 168 and a microcontroller 167.

[0023] The vehicle propulsion system 100 may also include an on-board navigation system 17 (e.g., a global positioning system) on an instrument panel 19 with which a vehicle operator can interact. The navigation system 17 may include one or more location sensors to assist in estimating a location (e.g., geographic coordinates) of the vehicle. For example, the on-board navigation system 17 may receive signals from GPS satellites 33 and determine the geographic location of the vehicle based on the signal. In some examples, the geographic location coordinates may be communicated to the controller 12. The navigation system may also divide a driving route into an actual total number of segments so that vehicle operation within the segments can be predicted. The navigation system 17 may communicate data from the driving route to the controller 12.

[0024] The instrument panel 19 may further include a display system 18 configured to display information to the vehicle operator. The display system 18 may include, as a non-limiting example, a touchscreen or a human-machine interface (HMI) display that allows the vehicle operator to view graphical information as well as input commands. In some examples, the display system 18 may be wirelessly connected to the internet (not shown) via a controller (e.g., 12). In some examples, the vehicle operator may communicate with a website or a software application (app) via the display system 18.

[0025] The instrument panel 19 may further include a vehicle operator interface 15 through which the vehicle operator can adjust the operating state of the vehicle. Specifically, the operator interface 15 may be configured to initiate and / or terminate operation of the vehicle powertrain (e.g., the electric machine 125 and the electric machine 126) based on a vehicle operator input. Various examples of the vehicle operator ignition interface 15 may include interfaces that require a physical device, such as an active key that can be inserted into the vehicle operator interface 15 to start the electric machines 125 and 126 and turn on the vehicle, or removed to turn off the electric machines 125 and 126 and turn off the vehicle. Other examples may include a passive key communicatively coupled to the vehicle operator interface 15.The passive key may be configured as an electronic remote key or a smart key that does not need to be inserted into or removed from the interface 15 to operate the vehicle's electric machines 125 and 126. Instead, the passive key may need to be inside or near the vehicle (e.g., within a threshold distance of the vehicle). Still other examples may additionally or optionally utilize a start / stop button manually pressed by the vehicle operator to start or stop the electric machines 125 and 126 and to turn the vehicle on or off.In other examples, a remote start of the electric machine may be initiated by a remote computing device (not shown), for example, a mobile phone or a smartphone-based system, where a user's mobile phone sends data to a server and the server communicates with the controller 12 to start the engine.

[0026] With reference to Fig. 2 is a schematic representation of a vehicle 10 with a non-restrictive cooling system 200. Solid flow direction arrows (e.g., 204) represent conduits and show coolant and refrigerant flow directions in the cooling system 200 when the cooling system 200 is operated in a cooling mode. The vehicle 10 may have any suitable powertrain and may include one or more electric machines (e.g., 125 as shown in Fig. 1) that can be used to propel the vehicle 10 and / or power vehicle components. Alternatively, the vehicle may be a hybrid vehicle. The vehicle 10 may include a passenger compartment 250 and a cooling system 200. Devices and fluid channels or conduits are shown in Fig. 2 as solid lines. Electrical connections are shown in Fig. 2 shown as dashed lines.

[0027] The cooling system 200 includes a coolant circuit 260 in which cooled coolant can circulate, as indicated by the coolant flow arrows (e.g., 201). The coolant circuit 260 includes an electrical energy storage device 132, other devices 202 (e.g., power converters, etc.) that can be cooled by coolant cooled via a cooling device 206 (e.g., a gas-liquid heat exchanger), a coolant pump 218, the cooling device 206, and a coolant temperature sensor 233. Coolant cooled via the cooling device can cool the electrical energy storage device 132 and other devices 202. The coolant pump 218 can circulate coolant in the coolant circuit 260.

[0028] The cooling system 200 also includes a refrigerant circuit 262 in which refrigerant can circulate, as indicated by refrigerant flow arrows (e.g., 203). The refrigerant circuit 262 includes the cooling device 206, an evaporator 208, an electrically driven compressor 214, integrated temperature and pressure sensors 230, a pressure sensor 244, a water-cooled condenser 216, an outdoor heat exchanger 212, a first expansion valve 232, and a second expansion valve 234. Refrigerant compressed by the electrically driven compressor 214 can be condensed and cooled by the water-cooled condenser and the outdoor heat exchanger 212 before the refrigerant is expanded at the first expansion valve 232 or the second expansion valve 234. The expanded refrigerant can cool the liquid coolant in the cooling device 206.Furthermore, the expanded refrigerant may cool air in the passenger compartment 250 via the evaporator 208. An evaporator sensor 242 may provide an indication of a temperature at fins of the evaporator 208. Air is cooled by flowing air over the fins.

[0029] A controller 12 (e.g., a vehicle system controller) may adjust a speed of the electrically driven compressor 214 by controlling a flow of electrical power to the electrically driven compressor 214. Integrated temperature and pressure sensors 230 may provide the controller 12 with refrigerant temperatures at an inlet side 214a of the electrically driven compressor 214. Integrated temperature and pressure sensors 230 are positioned downstream of the chiller 206 and upstream of the electrically driven compressor 214 according to the direction of refrigerant flow. A pressure sensor 244 may provide a second controller 220 with an indication of refrigerant pressure at an outlet side 214b of the electrically driven compressor 214. The controller 12 may also adjust positions of the first expansion valve 232 and the second expansion valve 234 via electrical power controlled by the controller 12.

[0030] The second controller 220 may adjust a position of vehicle grille shutters 222 and a speed of a cooling fan 224 via electrical power controlled by the second controller 220. For example, the second controller 220 may increase an opening degree of the vehicle grille shutters 222 and increase a speed of the cooling fan 224 as the refrigerant pressure at the outlet side of the electrically driven compressor 214 increases.

[0031] The system from Fig. 1 and Fig. 2 provides a vehicle system comprising: a refrigeration system including a compressor, an evaporator, a chiller, an outdoor heat exchanger, and a water-cooled condenser; and a controller including executable instructions stored in non-transitory memory that cause the controller to adjust a speed of the compressor in response to a superheat temperature of a refrigerant being greater than a superheat temperature threshold. In a first example, the vehicle system further includes additional executable instructions stored in non-transitory memory that cause the controller to estimate the superheat temperature of the refrigerant according to a temperature and a pressure of the refrigerant.In a second example, which may include the first example, the vehicle system includes where adjusting the speed of the compressor includes setting the compressor speed to a zero speed. In a third example, which may include one or both of the first and second examples, the vehicle system further includes additional executable instructions stored in non-transitory memory that cause the controller to reduce a speed of the compressor in response to the superheat temperature of the refrigerant being greater than the superheat temperature threshold.In a fourth example, which may include one or more of the first through third examples, the vehicle system further comprises additional executable instructions stored in non-transitory memory that cause the controller to count an actual total number of executable instruction loops executed when the refrigerant superheat temperature is greater than the superheat temperature threshold. In a fifth example, which may include one or more of the first through fourth examples, the vehicle system includes the controller adjusting the speed of the compressor after a predetermined amount of time has elapsed since a last time the refrigerant superheat temperature changed from less than the superheat temperature threshold to greater than or equal to the superheat temperature threshold.In a sixth example, which may include one or more of the first through fifth examples, the vehicle system includes where the superheat temperature is based only on a temperature and pressure upstream of the compressor and downstream of the chiller.

[0032] With reference now to Fig. 3 is an exemplary expected operating sequence of the cooling system according to the method of Fig. 4. The curves from Fig. 3 are timed to match. The sequence of Fig. 3 can be accessed via the system Fig. 1 and Fig. 2 in conjunction with the procedure from Fig. 4. The vertical lines at times t0-t2 represent points of interest in the curves.

[0033] The first course from above in Fig. Figure 3 is a plot of a cooling system diagnostic status over time. The vertical axis represents the cooling system diagnostic status, and the cooling system diagnostic status is inactive when curve 302 is at a lower level near the horizontal axis. The cooling system diagnostic status is active when curve 302 is at a higher level near the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the figure to the right side of the figure. Curve 302 represents the cooling system diagnostic status.

[0034] The second course from the top in Fig. Figure 3 is a graph of compressor speed over time. The vertical axis represents the compressor speed, and the compressor speed increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the figure to the right side of the figure. The horizontal line 350 represents a threshold compressor speed. Line 304 represents the compressor speed.

[0035] The third course from the top in Fig. Figure 3 is a graph of a superheat temperature value for refrigerant in the cooling system. The superheat temperature value can be expressed as the present refrigerant temperature minus a boiling point temperature of the refrigerant when the refrigerant is in a liquid state. The superheat temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the figure to the right side of the figure. The horizontal line 352 represents a threshold superheat temperature value. Line 306 represents the superheat temperature value for the refrigerant in the cooling system.

[0036] The fourth course from the top in Fig. Figure 3 is a graph of a timer value over time. The vertical axis represents the timer value, and the timer value increases in the direction of the vertical axis arrow. The horizontal axis represents time, and time increases from the left side of the figure to the right side of the figure. Line 308 represents the timer value. Horizontal line 354 represents a threshold time period.

[0037] At time t0, the compressor diagnostics are not enabled and the compressor speed is above the threshold compressor speed of 350. The superheat temperature for refrigerant in the cooling system is greater than the superheat temperature threshold and the timer value is zero because the diagnostics have not started since then.

[0038] At time t1, the cooling system diagnostics are enabled. The cooling system diagnostics can be enabled during predetermined conditions (e.g., the vehicle has been operated for a threshold period of time, the cooling system has been turned on for a threshold period of time, etc.). Because the compressor speed is greater than the threshold compressor speed and the refrigerant superheat temperature is greater than the superheat temperature threshold, the compressor speed is commanded to a lower speed shortly after time t1. The timer is not enabled.

[0039] At time t2, the refrigeration system diagnostics are still active and the compressor speed falls below the compressor threshold speed. This causes the timer to begin accumulating time. The superheat temperature remains above the threshold superheat temperature even though the compressor speed has been reduced. This may indicate that there may be less refrigerant in the refrigeration system than expected and / or desired.

[0040] At time t3, the timer value exceeds the timer threshold, but the superheat temperature is still above the superheat temperature threshold, which may indicate a low refrigerant level (charge). Therefore, the diagnostic is terminated. In this example, the compressor speed is reduced to zero speed to reduce the possibility of compressor degradation. Additionally, other mitigation actions may be taken in response to the superheat temperature value being greater than the superheat temperature threshold. The timer stops counting, and the superheat value begins to decrease after the compressor speed is reduced.

[0041] In this way, a diagnostic can determine whether or not a refrigeration system may be compromised. Specifically, a superheat temperature greater than a threshold temperature may indicate that there is less refrigerant in the refrigerant circuit than desired. If a low refrigerant level is detected, the electrically driven compressor can be shut down to reduce the possibility of electrically driven compressor degradation.

[0042] With reference now to Fig. 4 shows a method for operating a cooling system of a vehicle. The method of Fig. 4 can be implemented as executable instructions stored in a non-transitory memory in the system of Fig. 1 and Fig. 2. Furthermore, sections of the procedure may be Fig. 4 actions that are carried out in the physical world by a controller.

[0043] At 402, method 400 judges whether or not there is no indication of an existing cooling system degradation (e.g., no electric air conditioning (eAC) degradation) and no pressure sensor and temperature sensor (PTS) degradation. If there is no cooling system degradation and no pressure and temperature sensor degradation, the answer is yes, and method 400 proceeds to 404. Otherwise, the answer is no, and method 400 proceeds to 440. The timer and counter values ​​mentioned below may be reset to zero upon entering the diagnostic or upon completion of the diagnostic.

[0044] At 440, method 400 operates the air conditioning (AC) system or heat pump according to baseline or normal operation. For example, method 400 may adjust the compressor speed according to the cooling load and independent of the refrigerant superheat temperature. Method 400 proceeds to exit.

[0045] At 404, method 400 determines the commanded speed for the AC compressor. In one example, method 400 may command and adjust the AC compressor speed according to a difference between a requested passenger compartment temperature and an actual or measured passenger compartment temperature. Furthermore, the compressor speed may also be commanded and adjusted according to a difference between a requested traction battery temperature and an actual traction battery temperature. Method 400 proceeds to 406 after the electrically driven compressor speed is commanded and adjusted according to a base electrically driven compressor speed control routine.

[0046] At 406, method 400 judges whether or not the speed of the electrically driven compressor is greater than a first threshold speed for the electrically driven compressor. In one example, the first threshold speed for the electrically driven compressor is based on empirically determined data collected while varying ambient temperature, compressor speed, refrigerant charge, etc. If method 400 judges that the current speed of the electrically driven compressor is greater than the first compressor speed threshold, the answer is yes and method 400 proceeds to 408. Otherwise, the answer is no and method 400 proceeds to 420.

[0047] At 408, method 400 judges whether the refrigerant superheat temperature is less than a first superheat temperature threshold. If so, the answer is yes, and method 400 proceeds to 410. Otherwise, the answer is no, and method 400 proceeds to 430. In one example, the refrigerant superheat temperature may be determined using the following equation: Superheat=f(compintemp,compinpress)−refboiltmp where superheat is the estimated superheat temperature of the refrigerant, f is a function that returns a temperature based on empirically determined values ​​of the electrically driven compressor inlet temperature and the electrically driven compressor inlet pressure, and refboiltmp is the boiling temperature of the refrigerant from a liquid phase to a gas phase. By considering both the refrigerant temperature at the compressor inlet and the refrigerant pressure at the compressor inlet, the superheat temperature estimation can be improved. The first superheat temperature threshold is based on empirically determined data collected when varying the refrigerant charge, varying the compressor speed, and varying the ambient air temperature.

[0048] At 410, method 400 judges whether or not the refrigerant superheat temperature is less than a first superheat temperature threshold minus a hysteresis temperature Hyst. If so, the answer is yes, and method 400 proceeds to 412. Otherwise, the answer is no, and method 400 returns to 404.

[0049] At 412, method 400 decrements a counter and returns to 404. The counter may be embodied as instructions stored in non-transitory memory, and the counter is used as a basis for reducing a possibility of compressor degradation. The threshold counter value at 420 may be selected to reduce the influence of noise factors in the system and lower the risk of system degradation. Method 400 returns to 404.

[0050] At 430, method 400 increments the counter and proceeds to 432. At 432, method 400 reduces a speed of the compressor to a predetermined speed (speed2). The predetermined speed may be a compressor speed that causes an expected superheat temperature when the amount of refrigerant in the refrigeration system is greater than a threshold amount (e.g., sufficient not to be considered low). Method 400 returns to 406.

[0051] At 420, method 400 judges whether or not the refrigerant superheat temperature is greater than a second superheat temperature threshold. If so, the answer is yes, and method 400 proceeds to 422. Otherwise, the answer is no, and method 400 returns to 404.

[0052] At 422, method 400 maintains the speed of the electrically driven compressor to be less than the first threshold speed. Method 400 proceeds to 424.

[0053] At 424, method 400 increments a timer (timer2) and allows a cumulative time to increase. Method 400 proceeds to 426.

[0054] At 426, method 400 judges whether the value of the timer (timer2) is greater than a threshold time period. If so, the answer is yes, and method 400 proceeds to 468. Otherwise, the answer is no, and method 400 returns to 420.

[0055] At 428, method 400 may indicate that the refrigerant level (the refrigerant charge) is low, and method 400 may perform mitigation actions. The low charge indication may be displayed via a human-machine interface. The mitigation actions may include, but are not limited to, setting the electrically driven compressor speed to zero (turning off the compressor), reducing loads on the refrigeration system, such as closing one or more expansion valves and limiting vehicle torque to reduce the load on the refrigeration equipment, etc. Method 400 proceeds to exit.

[0056] In this way, the method 400 can detect low refrigerant levels without using a temperature and / or pressure upstream of a compressor in a refrigerant circuit. Furthermore, the method 400 can take mitigating actions when a low refrigerant level is detected, so that the likelihood of compressor degradation can be reduced.

[0057] The procedure from Fig. 4 provides a method of operating a cooling system of a vehicle, comprising: generating an estimate of a superheat temperature of a refrigerant according to a pressure at an inlet side of a compressor and a temperature at the inlet side of the compressor; and shutting down the compressor in response to the estimate of the superheat temperature of the refrigerant exceeding a superheat threshold temperature. In a first example, the method may include shutting down the compressor when the estimate of the superheat temperature of the refrigerant exceeds the superheat threshold temperature for a predetermined period of time. In a second example, which may include the first example, the method includes where the superheat threshold temperature is based on an ambient temperature and a speed of the compressor.In a third example, which may include one or both of the first and second examples, the method includes where the superheat temperature is a current temperature of the refrigerant minus a boiling temperature of the refrigerant in a liquid state. In a fourth example, which may include one or more of the first to third examples, the method includes where the estimate of the superheat temperature is determined without a pressure downstream of the compressor and upstream of an expansion valve. In a fifth example, which may include one or more of the first to fourth examples, the method includes where the temperature and pressure are downstream of a chiller and upstream of the compressor.In a sixth example, which may include one or more of the first through fifth examples, the method further comprises commanding the compressor to a speed based on a temperature difference. In a seventh example, which may include one or more of the first through sixth examples, the method includes where the temperature difference is a difference between a requested cabin temperature and a measured cabin temperature.

[0058] The procedure from Fig. 4 further provides a method of operating a cooling system of a vehicle, comprising: adjusting a speed of a compressor in response to a user-requested temperature; generating an estimate of a superheat temperature of a refrigerant according to a pressure at an inlet side of a compressor and a temperature at the inlet side of the compressor; reducing the speed of the compressor to a reduced speed in response to the superheat temperature of the refrigerant being greater than a superheat threshold temperature; generating the estimate of the superheat temperature of the refrigerant according to the pressure at the inlet side of the compressor and the temperature at the inlet side of the compressor; and shutting down the compressor in response to the compressor being at the reduced speed and the estimate of the superheat temperature of the refrigerant exceeding the superheat threshold temperature.In a first example, the method includes where shutting down the compressor includes reducing the speed of the compressor to zero. In a second example, which may include the first example, the method further includes providing an indication of a loss of refrigerant in response to the superheat temperature of the refrigerant exceeding the superheat threshold temperature. In a third example, which may include one or both of the first and second examples, the method further includes cooling a battery and a passenger compartment of the vehicle via the cooling system while generating the estimate of the superheat temperature of the refrigerant. In a fourth example, which may include one or more of the first through third examples, the method includes where the battery is a traction battery.

[0059] The average person skilled in the art will understand that the Fig.4 may represent one or more of any number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Accordingly, various illustrated steps or functions may be performed in the illustrated sequence, in parallel, or in some cases omitted. Likewise, the processing order is not required to achieve the objectives, features, and advantages described herein, but is provided for ease of illustration and description. Although not expressly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be performed repeatedly depending on the particular strategy employed.Furthermore, the methods described in this document may be a combination of actions performed by a controller in the physical world and instructions within the controller. At least portions of the control methods and routines disclosed in this document may be stored as executable instructions in non-transitory memory and executed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware.

[0060] This concludes the description. If read by a person skilled in the art, many changes and modifications would become apparent without departing from the spirit and scope of the description. For example, the systems and methods described in this document can be applied to all-electric vehicles and vehicles that include an internal combustion engine and an electric motor for propulsion.

Claims

[1] A method for operating a cooling system of a vehicle, comprising: Generating an estimate of a superheat temperature of a refrigerant according to a pressure at an inlet side of a compressor and a temperature at the inlet side of the compressor; and Shutdown of the compressor in response to the refrigerant superheat temperature estimate exceeding a superheat threshold temperature. [2] The method of claim 1, wherein the compressor is shut down when the estimate of the superheat temperature of the refrigerant exceeds the superheat threshold temperature for a predetermined period of time. [3] The method of claim 2, wherein the superheat threshold temperature is based on an ambient temperature and a speed of the compressor. [4] The method of claim 3, wherein the superheat temperature is a current temperature of the refrigerant minus a boiling temperature of the refrigerant in a liquid state. [5] The method of claim 1, wherein the superheat temperature estimate is determined without a pressure downstream of the compressor and upstream of an expansion valve. [6] The method of claim 1, wherein the temperature and pressure are downstream of a cooler and upstream of the compressor. [7] The method of claim 1, further comprising commanding the compressor to a speed based on a temperature difference. [8] The method of claim 7, wherein the temperature difference is a difference between a requested passenger compartment temperature and a measured passenger compartment temperature. [9] Vehicle system comprising: a refrigeration system including a compressor, an evaporator, a chiller, an outdoor heat exchanger, and a water-cooled condenser; and a controller including executable instructions stored in non-transitory memory that cause the controller to adjust a speed of the compressor in response to a superheat temperature of a refrigerant being greater than a superheat temperature threshold. [10] The vehicle system of claim 9, further comprising additional executable instructions stored in non-transitory memory that cause the controller to estimate the superheat temperature of the refrigerant according to a temperature and a pressure of the refrigerant. [11] The vehicle system of claim 9, wherein adjusting the speed of the compressor includes adjusting the speed of the compressor to a speed of zero. [12] The vehicle system of claim 9, further comprising additional executable instructions stored in non-transitory memory that cause the controller to reduce the speed of the compressor in response to the superheat temperature of the refrigerant being greater than the superheat temperature threshold. [13] The vehicle system of claim 9, further comprising additional executable instructions stored in non-transitory memory that cause the controller to count an actual total number of executable instruction loops executed when the refrigerant superheat temperature is greater than the superheat temperature threshold. [14] The vehicle system of claim 9, wherein the controller adjusts the speed of the compressor after a predetermined period of time has elapsed since a last time at which the superheat temperature of the refrigerant changed from less than the superheat temperature threshold to greater than or equal to the superheat temperature threshold. [15] The vehicle system of claim 9, wherein the superheat temperature is based only on a temperature and pressure upstream of the compressor and downstream of the cooler.

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