GB2581483A

GB2581483A - Energy storage and release in an electric vehicle

Info

Publication number: GB2581483A
Application number: GB1902117.9A
Authority: GB
Inventors: Maughan Ryan; Alexakis Atanasios
Original assignee: Avid Technology Ltd
Current assignee: Avid Technology Ltd
Priority date: 2019-02-15
Filing date: 2019-02-15
Publication date: 2020-08-26
Also published as: GB201902117D0

Abstract

An energy storage system for an electric vehicle (EV) having plural components including a battery, an electric machine and an inverter, at least one of the components requiring cooling and a cooling system. The cooling system has: a liquid coolant circuit 10; a pump 12; a coolant-carrying conduit 11a delivering coolant to each component 18 requiring cooling; and a refrigeration circuit 2 having a compressor 5 and an evaporator 4. The evaporator and a heat exchange element 13 of the coolant circuit are both situated in a heat exchanger 1. A controller, a plurality of parameter sensors and at least some of the components are connected to a communications network. The parameter sensors include a battery charge status sensor and an electric machine torque sensor. The controller controls electricity flow between; the electric machine, the battery, and other electricity-consuming components, according to pre-programmed priorities. The controller operates the refrigeration circuit compressor and the coolant circuit pump when it senses that: the battery is fully-charged; and the torque on the electric machine is negative, to sub-cool the liquid coolant below a normal operating temperature. The system releases energy stored in the sub-cooled liquid coolant when the controller senses that torque on the electric machine is positive, the compressor operating at a reduced speed.

Description

Energy Storage and Release in an Electric Vehicle

Field of the Invention

The invention is concerned with storing energy in a vehicle having a battery in an energy storage medium other than the battery, and is useful with any vehicle having an energy recovery system.

Background of the Invention

It is becoming more common for vehicles to include an energy recovery system the function of which is to convert excess kinetic energy into stored energy that can be used to propel the vehicle when additional energy is required.

Typically, such a vehicle includes a crank assisted generation unit which in one mode generates electricity, which is stored in a battery, when the vehicle is decelerating and in another mode provides energy from the battery to the vehicle's drive train to assist in propulsion of the vehicle.

Situations may arise where the driving conditions for the vehicle would indicate that energy should be stored to the battery, but the battery may be incapable of accepting further charge. For example, the vehicles batteries may be fully charged as a result of the vehicle having being connected to a charger, yet the first terrain encountered by the vehicle may be a descending road. Were the battery not fully charged, as the potential energy of the vehicle is converted to kinetic energy, some of the potential energy could be converted to stored energy in the battery. However, if the battery is full this is not possible and the energy is wasted.

It would be desirable to store energy in other systems in the vehicle, so that such stored energy may be used at a time when otherwise an alternative energy source would be required to power a function of the vehicle.

Most vehicles include liquid coolant circuits. Electric or hybrid electric vehicles have more complex cooling requirements than traditional internal combustion engine driven vehicles. For example, whereas internal combustion engines would typically use refrigerated coolants only for cabin air conditioning, electric vehicles require refrigerated coolant for cooling electric motors, electric generators, inverters, batteries and other components.

It has also been observed that the greatest requirement for cooling of the electrical components of an electric vehicle can occur when there is the greatest need for energy to propel the vehicle, that is during maximum acceleration. In fact, certain electric vehicles have a special mode for maximum acceleration which involves sub-cooling certain components prior to the acceleration event so that a greater proportion of the energy may be used for propulsion. This is because under maximum acceleration the cooling systems of such known vehicles are not capable of removing heat from components such as electric motors rapidly enough to maintain the vehicle within its operating temperature parameters. Furthermore, the cooling system requires energy that could otherwise be used to accelerate the vehicle.

It would be desirable to provide an energy storage system for a vehicle having an energy recovery system in which the energy is stored in an alternative form to electrical charge in a battery.

It would also be desirable to provide an energy storage system for a vehicle which allows the maximum amount of energy possible to be available for accelerating the vehicle.

Summary of the Invention

According to the invention there is provided an energy storage system for an electric vehicle, the vehicle having a plurality of components including a battery, an electric machine and an inverter, at least one of the plurality of components requiring cooling and a cooling system, the cooling system comprising a liquid coolant circuit charged with liquid coolant, the liquid coolant having a normal operating temperature, the cooling system including a pump and a coolant carrying conduit, the conduit delivering coolant to the or each component requiring cooling, and a refrigeration circuit, wherein the refrigeration circuit includes a compressor and an evaporator, and wherein the evaporator and a heat exchange element of the coolant circuit are both situated in a heat exchanger, the energy storage system further comprising: a plurality of parameter sensors including at least a battery charge status sensor and an electric machine torque sensor; a communications network; and a controller, wherein the controller, the parameter sensors and at least some of the plurality of components are connected to the communications network; and wherein the controller is configured to control the flow of electricity between the electric machine, the battery, and other electricity consuming components of the said plurality of components according to pre-programmed priorities and wherein the controller is configured to cause the compressor of the refrigeration circuit and the pump of the coolant circuit to operate when the controller senses that the battery is fully charged and the torque on the electric machine is negative to sub-cool the liquid coolant below the normal liquid coolant operating temperature.

Advantageously, the pre-programmed priorities include turning off the compressor when the liquid coolant is cooled to 10C.

The pre-programmed priorities may include operating the compressor of the refrigeration circuit when the liquid coolant temperature exceeds 50C when the battery is not fully charged.

The liquid coolant circuit may include a vehicle cabin heat exchange conduit and a fan configured to force air over the vehicle cabin heat exchange conduit.

The at least one pump of the liquid coolant circuit may include a pump associated with the vehicle cabin heat exchange conduit.

The controller may be configured to control the speed of the pump and/or fan according to a required vehicle cabin temperature and the liquid coolant temperature.

The liquid coolant circuit may include a phase change heat storage medium.

Preferably, the phase change heat storage medium is situated down stream of the vehicle cabin heat exchange conduit and upstream of the heat exchange element of the cooling circuit.

Advantageously, the liquid coolant circuit includes a bypass valve providing a fluid flow path in parallel with the heat exchange element of the liquid cooling circuit.

Preferably, the coolant carrying conduit includes one or more a temperature controlled valves, each temperature controlled valve associated with a respective one of the plurality of components requiring cooling.

The energy storage system may be further configured to release energy stored in the sub-cooled liquid coolant when the controller senses that torque on the electric machine is positive, the controller causing the compressor to operate at a reduced speed.

Advantageously, the controller causes the at least one pump to operate at a reduced speed.

Preferably, the controller causes one or more fans of the cooling system to operate at reduced speed.

Brief Description of the Drawings

In the Drawings, which illustrate preferred embodiments of the invention and which are by way of example: Figure 1 is a schematic representation of a vehicle cooling system according to the invention; and Figure 2 is a block diagram of an electronic control circuit of the vehicle cooling system illustrated in Figure 1.

Detailed Description of the Preferred Embodiments

Referring now to Figure 1 the coolant system comprises a heat exchanger 1 which is connected to a refrigerant circuit 2 and a liquid coolant circuit 10.

The refrigerant circuit 2 includes a condenser 3, an evaporator 4, a compressor 5, an expansion valve 6 and a fan 7 for blowing air over the evaporator 4 cooling the air, the cooled air passing over the heat exchange conduit 13 of the refrigerant circuit 2.

The liquid coolant circuit 10 comprises a conduit lla that connects to one side of a pump 12. A conduit llb is connected to the other side of the pump 12 and an input end of a heat exchange conduit 13 that is situated in the heat exchanger 1. A conduit 11c is connected to the output end of the heat exchange conduit 13.

The conduit 11c connects to the conduit lla at branch b, forming a continuous loop. The conduit 11c continues and connects to one end of a cabin heat exchanger 19. A conduit 11d is connected to the other end of the cabin heat exchanger 14 and returns to connect to the conduit 11b. A phase change material heat store 22 is located in the conduit 11d.

The conduit lla delivers coolant to a fan 14 (which is arranged to blow air over the conduit lla to deliver cooled air to a component requiring cooling), a motor 15, an inverter 16, a battery 17 and another component 18 requiring cooling. Coolant fluid (typically a water, ethylene glycol mix) is pumped around the conduits 11a, 11b, 11c and through heat exchange conduit 13 by the pump 12.

A valve 20 is provided in parallel with the heat exchange conduit 13 between the conduits llb and 11c. In this way, fluid may be allowed to pass from conduit llb to conduit 11c without cooling in heat exchange conduit 13. A valve may also be provided to shut off flow of fluid through the heat exchange conduit 13. The valve 20 may be closed until the components that normally require cooling have reached their normal operating temperature.

The part of the coolant circuit that delivers cool air to the cabin includes a pump 25 which controls the flow of coolant through the part of conduit 11c downstream of branch b via the heat exchange conduit 19 and conduit 11d back to conduit 11 b upstream of heat exchange conduit 13. A fan 21 draws ambient air over the heat exchange conduit 19 to cool the vehicle cabin.

In use, coolant in the heat exchange conduit 13 is cooled by the refrigerant circuit 1. The pump 12 circulates coolant through the conduits 11a, 11b, 11c. As the coolant passes the devices requiring cooling (the motor 15, inverter 16, battery 17, etc) the temperature of the coolant increases removing heat from the devices requiring cooling. Coolant downstream of the pump 12 requires cooling, which occurs in heat exchanger 1 as the coolant passes through the heat exchange conduit 13.

If the passenger cabin requires cooling the pump 25 is engaged. Coolant fluid is drawn through the conduit 11c down stream of branch b. The degree of cabin cooling may be controlled by either or both of controlling the pump 25 and controlling the fan 21. As the warmed coolant fluid returns to the inlet side of heat exchange conduit 13 it passes through the phase change material 22 which absorbs heat energy from the coolant and cools the coolant entering the heat exchanger conduit 13, so that the load on the refrigeration circuit 2 is reduced.

The phase change material provides a source of stored heat energy which may be used when required. For example, heat energy stored in the phase change material 22 may be used to heat the cabin by operating the pump 25 when the compressor 5 is inactive. With the valve 20 closed, as shown in Figure 1 and pump 12 inactive, liquid coolant flows only around the conduits 11c, 11d and through the heat exchange conduit 13. Coolant returning through the phase change material 22 picks up heat energy, increasing in temperature. The heat energy in the coolant is drawn into the cabin by fan 21.

The heat in the phase change material 22 may also be used to pre-condition the components that are normally cooled by the coolant carried in conduit 11a-11d to raise them to their normal operating temperatures. If pump 12 is operated at the same time as pump 25 with the compressors inactive, coolant returning through the phase change material 22 picks up heat energy, increasing in temperature. The operation fo the pump 12, 15 to extract heat stored in phase change material 22 is commanded via the controller 50 as described in greater detail below.

The system illustrated in Figure 1 may be used to store and release energy. Energy is stored by sub-cooling the coolant flowing through the conduits 11a-11d, which is achieved by operating the refrigeration circuit when there is a surplus of electrical energy and the cooling needs of the devices requiring cooling are met by the coolant flowing at is optimum temperature and flow rates.

In order to use the coolant in the cooling circuit 10 as an energy store a controller is required to control the operation of the cooling circuit 10 and the refrigeration circuit 2. A controller and its associated inputs and outputs are illustrated in Figure 2.

Referring now to Figure 2 a controller 50 receives inputs in the form of electron signals from many sensors. The sensors measure parameters that are relevant to the temperature and flow of the coolant in the coolant circuit 10, the sensor 51 measuring coolant temperature.

Sensors 52, 53, 54, 55 and 56 are temperature sensors. They sense the temperature of the inverter 16, the motor 15, the battery 17, the device 18 and the air moved by fan 14 respectively The controller 50 compares the signal from each of the sensors 52 to 56 and compares them with corresponding threshold values that are indicative of a temperature at which cooling is required. When the temperature of one of the sensors 52 to 56 indicates a cooling requirement the controller 50 sends a signal to adjust the speed of the pump 12. Alternatively, each of the motor 15, inverter 16, battery 17 and device 18 may be provided with a motorised valve allowing for the selective flow of coolant from the conduit 11a to any one of the components 14 to 18. When so equipped, the controller 50 sends a signal to the respective motorised valve to open or close the same depending on the signal received from the temperature sensor 52 to 56 and the speed of the pump 12 is adjusted when a cooling demand is indicated by any one of the sensors 52-56.

The controller 50 also receives input signals from an electric motor torque sensor 60 and battery charge sensor 62. The signal from the electric motor torque sensor 60 tells the controller 50 whether the vehicle is accelerating or decelerating. If the sensor 60 indicates a negative torque then the vehicle is decelerating and electric charge is being generated. The signal from the battery charge sensor indicates to the controller 50 whether the battery is capable of receiving further charge. If electric charge is being generated and the battery is incapable of storing additional charge, the controller sends a signal to operate the refrigeration circuit 10.

When the vehicle is generating electrical charge but its battery is fully charged the controller 50 sends a signal to the compressors and pump 12, causing them to operate. It is possible to program the controller 50 in a number of different ways, each of which results sub-cooling of the coolant flowing in the conduits lla -11. For example, both the refrigeration circuit 2 and the liquid coolant circuit 10 may be operated, thereby utilising the electrical charge generated by the vehicle whilst it is decelerating, until each coolant consuming device is at its optimum temperature. Where coolant consuming devices are provided with a shut off valve, when the device is at its optimum temperature the shut off valve may be closed, which may result in coolant flowing around the coolant circuit 10 without cooling the devices that need cooling. In such a circumstance the coolant would become colder, that is sub-cooled. If the coolant reaches a lower threshold temperature, the pump 12 and the compressors may be switched off or its speed may be reduced to avoid further cooling of the coolant. The compressor 5 may be operated at a reduced speed in order to maintain the coolant at the lower threshold temperature. Typically, a car type vehicle would charged with 10 litres of coolant. A glycol based coolant such as 50/50 water/ethylene glycol (WEG) may store 3.5 kJ energy/degree C/kg. Hence, it can be seen that by sub-cooling from 50C to 20C, a typical car type vehicle can store 300kJ of energy.

The controller 50 may be configured such that some or all of the components that are cooled by the coolant circuit may also be sub-cooled to a lower threshold temperature, which may be the same as the lower threshold temperature of the coolant or a higher temperature. In such an arrangement, a shut-off valve is provided for some or all of the components around which coolant is circulated. The extent to which the or each valve is open is controlled electronically by a signal from the controller 50 in accordance with temperatures sensed by sensors 52 to 56.

The coolant in conduit 11d for the cabin air conditioning may be sub-cooled by the operation of pump 25. Of course, it is desirable to maintain the cabin temperature at that set by the cabin occupant. The cabin temperature can be maintained whilst the coolant is sub-cooled by reducing the speed of fan 21.

Another control configuration allows increased amounts of energy to be made available for acceleration. Pumps, compressors and fans of the cooling system have energy requirements. Such loads are often known as parasitic loads. These parasitic loads have most impact on vehicle performance when the demand for acceleration is greatest. More energy can be made available for acceleration by reducing parasitic loads during acceleration which is achieved by releasing heat energy stored in the sub-cooled coolant and/or components. lithe signal from the torque sensor is positive (indicating acceleration) and the signal from the coolant temperature sensor 51 indicates that the coolant has been sub-cooled and is lower than a threshold temperature, for example below 40C, the controller reduces the speed of and may switch off the compressor 5. Cooling of the coolant is either reduced or stopped, reducing the energy demand from the compressor, meaning that more energy is available for acceleration. Additional energy can be saved by reducing the speed of the coolant pumps 12, 15 and/or the fans used to distributed heat. The cooling requirements fo the components are still met, even with the coolant flowing more slowly. The coolant increases in temperature from its sub-cooled state to a normal operating temperature, for example 45C. When the coolant reaches the normal optimum temperature the speed of the compressor is changed. The speed of the pumps and fans may also be changed when the normal operating temperature is reached. In this situation the controller 50 operates the cooling system to maintain the coolant at or around the optimum temperature.

In essence, the invention provides for surplus energy to be stored during acceleration in the coolant and for the stored energy to be released during acceleration.

Claims

Claims 1. An energy storage system for an electric vehicle, the vehicle having a plurality of components including a battery, an electric machine and an inverter, at least one of the plurality of components requiring cooling and a cooling system, the cooling system comprising a liquid coolant circuit charged with liquid coolant, the liquid coolant having a normal operating temperature, the cooling system including a pump and a coolant carrying conduit, the conduit delivering coolant to the or each component requiring cooling, and a refrigeration circuit, wherein the refrigeration circuit includes a compressor and an evaporator, and wherein the evaporator and a heat exchange element of the coolant circuit are both situated in a heat exchanger, the energy storage system further comprising: a plurality of parameter sensors including at least a battery charge status sensor and an electric machine torque sensor; a communications network; and a controller, wherein the controller, the parameter sensors and at least some of the plurality of components are connected to the communications network; and wherein the controller is configured to control the flow of electricity between the electric machine, the battery, and other electricity consuming components of the said plurality of components according to preprogrammed priorities and wherein the controller is configured to cause the compressor of the refrigeration circuit and the pump of the coolant circuit to operate when the controller senses that the battery is fully charged and the torque on the electric machine is negative to sub-cool the liquid coolant below the normal liquid coolant operating temperature.
2. An energy storage system according to Claim 1, wherein the pre-programmed priorities include turning off the compressor when the liquid coolant is cooled to 10C.
3. An energy storage system according to Claim 1 or 2, wherein the pre-programmed priorities include operating the compressor of the refrigeration circuit when the liquid coolant temperature exceeds 50C when the battery is not fully charged.
4. An energy storage system according to any preceding claim, wherein the liquid coolant circuit includes a vehicle cabin heat exchange conduit and a fan configured to force air over the vehicle cabin heat exchange conduit.
5. An energy storage system according to Claim 5, wherein the at least one pump of the liquid coolant circuit includes a pump associated with the vehicle cabin heat exchange conduit.
6. An energy storage system according to Claim 5, wherein the controller is configured to control the speed of the pump and/or fan according to a required vehicle cabin temperature and the liquid coolant temperature.
7. An energy storage system according to any preceding claim, wherein the liquid coolant circuit includes a phase change heat storage medium.
8. An energy storage system according to Claim 6, wherein the phase change heat storage medium is situated down stream of the vehicle cabin heat exchange conduit and upstream of the heat exchange element of the cooling circuit.
9. An energy storage system according to any preceding claim, wherein the liquid coolant circuit includes a bypass valve providing a fluid flow path in parallel with the heat exchange element of the liquid cooling circuit.
10. An energy storage system according to any preceding claim, wherein the coolant carrying conduit includes one or more a temperature controlled valves, each temperature controlled valve associated with a respective one of the plurality of components requiring cooling.
11. An energy storage system according to any preceding claim, wherein the system is further configured to release energy stored in the sub-cooled liquid coolant when the controller senses that torque on the electric machine is positive, the controller causing the compressor to operate at a reduced speed.
12. An energy storage system according to Claim 11, wherein the controller causes the at least one pump to operate at a reduced speed.
13. An energy storage system according to Claim 11 or 12, wherein the controller causes one or more fans of the cooling system to operate at reduced speed.