Claims:
1. A HVAC system for controlling vehicle cabin temperature comprising:
a blower (11);
an evaporator (12);
a by-pass duct (41) provided parallel to the evaporator (12), wherein the by-pass duct (41) is configured to be optionally opened by using a by-pass valve (40) to selectively divert a stream of air flow (400b) from the total airflow (400), through said by-pass duct (41);
a heater (13) configured for optionally operating and selectively heating the air flow (400a) coming from the evaporator (12) and supplying the hot air flow (400d) to vehicle cabin (36); and
a blend/temperature door (14) configured to control the flow of air (400c) through the heater (13).

2. A HVAC system for controlling vehicle cabin temperature as claimed in claim 1, wherein the air flow (400b) from the by-pass duct (41) is configured to be mixed with the conditioned air (400a) exiting the evaporator (12) and the said mixture of air (400d) is configured to be supplied to the vehicle cabin (36).

3. A HVAC system for controlling vehicle cabin temperature as claimed in claim 1, wherein the by-pass valve (40) is configured to divert 0% to 90% of the total air flow (400) leaving the blower (11), to pass through the by-pass duct (41).

4. A HVAC system for controlling vehicle cabin temperature as claimed in claim 1, wherein the by-pass valve (40) is configured to allow 10% to 100% of the total air flow (400) leaving the blower (11), to pass through the evaporator (12).

5. A HVAC system for controlling vehicle cabin temperature as claimed in claim 1, wherein a climate control module (30) is configured to control the by-pass valve (40) based on set temperature received from a control panel or a temperature knob (33), outside air temperature received from an outside air temperature sensor (32) and in-cabin temperature received from an in-cabin temperature sensor (35).

6. A HVAC system for controlling vehicle cabin temperature as claimed in claim 5, wherein the climate control module (30) is configured to control the degree of opening of the by-pass valve (40) based on set temperature or temperature knob position and in-cabin temperature.

7. A HVAC system for controlling vehicle cabin temperature as claimed in claim 5, wherein the climate control module (30) is configured to open the by-pass valve (40) on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C.

8. A HVAC system for controlling vehicle cabin temperature as claimed in claim 7, wherein the climate control module (30) is configured to close the blend/temperature door (14) and to switch off the heater (13) on opening the by-pass valve (40).

9. A HVAC system for controlling vehicle cabin temperature as claimed in claim 7, wherein the climate control module (30) is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode upon detection of relative humidity of the outside air being more than 80%.

10. A HVAC system for controlling vehicle cabin temperature as claimed in claim 5, wherein the climate control module (30) is configured to close the by-pass valve (40) on detection of the in-cabin temperature being greater than the set temperature.

11. A HVAC system for controlling vehicle cabin temperature as claimed in claim 5, wherein the climate control module (30) is configured to close the by-pass valve (40), open the blend/temperature door (14) and switch on the heater (13), on detection of the outside air temperature greater than the set temperature and the difference between the set temperature and in-cabin temperature is greater than 8°C.

12. A method for controlling HVAC system comprising,
receiving signals by a climate control module (30), from various sensors like an outside air temperature sensor (32), an in-cabin temperature sensor (35) and outside humidity sensor (31) and a control panel or a temperature knob (33);
processing the received signals by the climate control module (30), to control flow of air through a by-pass duct (41) and an evaporator (12), by operation of a by-pass valve (40);
opening the by-pass valve (40), by a climate control module (30), to selectively divert a stream of air flow (400b) from the total airflow (400), through said by-pass duct (41), on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C; and
mixing the air flow (400b) from the by-pass duct (41) with the conditioned air (400a) exiting the evaporator (12) for supplying the mixture of air (400d) to the vehicle cabin (36).

13. A method for controlling HVAC system as claimed in claim 12, wherein the climate control module (30) is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode on detection of relative humidity of the outside air being more than 80%.
, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

Title of invention:
A HVAC SYSTEM FOR CONTROLLING CABIN TEMPERATURE USING A BY-PASS VALVE AND ITS METHOD THEREOF

Applicant:
Tata Motors Limited
A company Incorporated in India under the Companies Act, 1956
Having address:
Bombay House, 24 Homi Mody Street,
Hutatma Chowk, Mumbai 400001,
Maharashtra, India

The following specification particularly describes the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
[001] The present subject matter described herein, in general relates to a HVAC system for a vehicle. More particularly the subject matter relates to a HVAC system with a by-pass valve for controlling the vehicle cabin temperature.

BACKGROUND OF THE INVENTION
[002] In a conventional vehicle, a HVAC system is used to control the climate inside the vehicle cabin by achieving and maintaining desired cabin temperature. In case of manually operated HVAC system, user operates a temperature knob and a compressor switch in order to get desired conditioned air. Moreover, a fully automatic temperature control (FATC) takes inputs from the user and various sensors to automatically maintain desired temperature conditions.
[003] Figure 1 shows a schematic arrangement of conventional HVAC system. The HVAC system (10), in general consists of a blower (11) to draw air from outside atmosphere in a fresh-air inlet mode or from vehicle cabin in recirculation mode. The air from the blower (11) then passes over an evaporator/cooling coil (12) and gets cooled due to heat exchange with cold refrigerant inside the evaporator/cooling coil (12). This air from the evaporator (12) is then either directly sent to vehicle cabin or a part of this conditioned air is made to pass over a heater (13) by operating a blend/temperature door (14), based on the desired in-cabin temperature. As illustrated in Figure 1, when the temperature knob is near ‘max cool’ position or cabin cooling is required, the blend/temperature door (14) is completely closed and the conditioned air coming from the evaporator/cooling coil (12) is directly supplied to the vehicle cabin. Therefore, cabin temperature starts reducing to maintain thermal comfort to passengers inside the vehicle. The heater (13) is in switched off state when the blend/temperature door (14) is closed. This functioning of the HVAC system is controlled by a climate control module (CCM) and involves control of dampers or blend/temperature door, blower duty, compressor duty cycle, air inlet mode etc. For a cabin temperature control, there are different logics given in internal combustion engines and electric vehicles.
[004] However, when the user/occupant starts turning the temperature knob away from ‘max cool’ position towards hot side to increase cabin temperature in case of manual HVAC systems, or when cabin temperature falls below desired/set temperature in case of FATC system, the blend/temperature door (14) becomes operational. In this situation, as shown in Figure 2, the blend door opens partially or fully and some portion of air or entire flow of air leaving the evaporator/cooling coil flows over the heater. In case of fully opened blend/temperature door, entire flow of air from the evaporator is heated by the heater and then supplied to vehicle cabin. However, in case of partially opened blend/temperature door, two air steams of cold air bypassing the heater and warm air coming from the heater mixes together and supplied to the vehicle cabin to achieve required cabin temperature. As a result, the HVAC system compressor continues to operate even if cabin temperature requirement is low, rather than getting switched off to stop any further cooling down the cabin. In order to maintain a desirable temperature, the user/occupant put the heater as well as compressor in switch on state, resulting in higher electrical power consumption in electric vehicles (EVs).
[005] Further, at such condition of temperature blending in AC cooling cycle when AC compressor and heater both are operational, external heat is added in a cooling cycle due to heat exchange between air and heating medium inside the heater coil, which increases compressor load indirectly. The process of addition of external heat by the heater during temperature blending, needs to be addressed and eliminated.
[006] In modern EV’s, electrically operated Positive Temperature Coefficient (PTC) heater consumes substantial battery power which may adversely affect the vehicle mileage. Although the use of such electrical heater is necessary at extremely cold ambient conditions, the use of electrical heater can be reduced for certain air blending conditions. Hence, to eliminate aforesaid problem, a HVAC system needs to be developed to minimize the use of heater by use of readily available hot air.

OBJECTS OF THE INVENTION
[007] The principal object of the invention is to provide a HVAC system for controlling vehicle cabin temperature.
[008] Another object of the invention is to provide a HVAC system for controlling vehicle cabin temperature by providing a by-pass valve with a by-pass duct provided parallel to an evaporator of the HVAC system.
[009] Yet another object of the invention is to reduce power consumption by an electric heater in EVs at certain operating conditions of a HVAC system.
[0010] Yet another object of the invention is to reduce power consumption of AC compressor in cooling cycle of HVAC system.
[0011] Yet another object of the invention is to improve vehicle mileage of EVs by eliminating the use of heater for temperature blending in HVAC system.
[0012] Yet another object of the invention is to reduce parasitic load on a battery of a vehicle, by reducing electric heater operation during blending process of mixing cold and hot air to control cabin temperature set by the user.
[0013] Yet another object of the invention is to provide a method for controlling vehicle cabin temperature, by blending of unconditioned air (by-pass air) without using heater of any type.
[0014] Yet another object of the invention is to provide a method for controlling vehicle cabin temperature by restricting a HVAC system to operate in air recirculation mode, on detection of relative humidity of outside air above a pre-set value and by operating the HVAC system in fresh air inlet mode on detection of relative humidity of outside air below the pre-set value, during opened state of the by-pass valve.
[0015] Yet another object of the invention is to provide a method for controlling vehicle cabin temperature by selectively allowing a HVAC system to operate in fresh air inlet mode during closed state of the by-pass valve.

SUMMARY OF THE INVENTION
[0016] Before the present system is described, it is to be understood that this application is not limited to the particular machine or an apparatus, and methodologies described, as there can be multiple possible embodiments that are not expressly illustrated in the present disclosure. It is also to be understood that the terminologies used in the description is for the purpose of describing the particular version or embodiment only and is not intended to limit the scope of the present application. This summary is provided to introduce aspects related to a HVAC system for controlling cabin temperature using a by-pass valve and method thereof, and the aspects are further elaborated below in the detailed application description. This summary is not intended to identify essential features of the proposed subject matter nor is it intended for use in determining or limiting the scope of the proposed subject matter.
[0017] The present subject matter discloses a HVAC system and its method thereof, for controlling vehicle cabin temperature. The HVAC system comprises a HVAC module including a blower to draw air either from outside atmosphere or from vehicle cabin, an evaporator/cooling coil to cool the air coming from the blower, a heater to heat the conditioned air flowing over it, a blend/temperature door to control the air flowing over the heater and a by-pass valve with a by-pass duct configured parallel to the evaporator/cooling coil. The by-pass valve is configured to optionally divide the air flow coming from the blower, in two parallel flows through the evaporator and the by-pass duct. The HVAC system further comprises a climate control module (CCM) to control the operation of the by-pass valve based on the signals received from a control panel or a temperature knob, an outside air temperature (OAT) sensor, an in-cabin temperature sensor and an outside humidity sensor. The CCM is configured to vary degree of opening of the by-pass valve based on set temperature or temperature knob position and in-cabin temperature.

STATEMENT OF THE INVENTION
[0018] The present subject matter discloses a HVAC system for controlling vehicle cabin temperature comprising a blower, an evaporator, a by-pass duct provided parallel to the evaporator and a by-pass valve to optionally open the by-pass duct. The by-pass duct is optionally opened by using the by-pass valve to selectively divert a stream of air flow from the total airflow, through said by-pass duct. A heater is provided for optionally operating and selectively heating the air flow coming from the evaporator and supplying the hot air flow to vehicle cabin. A blend/temperature door is configured to control the flow of air through the heater. The air flow from the by-pass duct is configured to be mixed with the conditioned air exiting the evaporator and the said mixture of air is configured to be supplied to the vehicle cabin. The by-pass valve is configured to divert 0% to 90% of the total air flow leaving the blower, to pass through the by-pass duct. The by-pass valve is configured to allow 10% to 100% of the total air flow leaving the blower, to pass through the evaporator.
[0019] A climate control module is provided to control the by-pass valve based on set temperature received from a control panel or a temperature knob, outside air temperature received from an outside air temperature sensor and in-cabin temperature received from an in-cabin temperature sensor. The climate control module is configured to control the degree of opening of the by-pass valve based on set temperature or temperature knob position and in-cabin temperature. The climate control module is configured to open the by-pass valve on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C. The climate control module is configured to close the blend/temperature door and to switch off the heater on opening the by-pass valve. The climate control module is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode upon detection of relative humidity of the outside air being more than 80%. The climate control module is configured to close the by-pass valve on detection of the in-cabin temperature being greater than the set temperature. The climate control module is configured to close the by-pass valve, open the blend/temperature door and switch on the heater, on detection of the outside air temperature greater than the set temperature and the difference between the set temperature and in-cabin temperature is greater than 8°C. Also, the climate control module is configured to close the by-pass valve, open the blend/temperature door and switch on the heater, on detection of the outside air temperature lesser than the set temperature.
[0020] The present subject matter further discloses a method for controlling HVAC system comprising, (a):- receiving signals by a climate control module, from various sensors like an outside air temperature sensor, an in-cabin temperature sensor and outside humidity sensor and a control panel or a temperature knob; (b):- processing the received signals by the climate control module, to control flow of air through a by-pass duct and an evaporator, by operation of a by-pass valve; (c):- opening the by-pass valve, by a climate control module, to selectively divert a stream of air flow from the total airflow, through said by-pass duct, on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C; and (d):- mixing the air flow from the by-pass duct with the conditioned air exiting the evaporator for supplying the mixture of air to the vehicle cabin. The climate control module is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode on detection of relative humidity of the outside air being more than 80%.

BRIEF DESCRIPTION OF DRAWINGS
[0021] The foregoing summary, as well as the following detailed description of embodiment, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, there is shown in the present document example constructions of the disclosure, however, the disclosure is not limited to the specific methods and apparatus disclosed in the document and the drawings.
[0022] The detailed description is described with reference to the accompanying figure. The same numbers are used throughout the drawing to refer like features and components.
[0023] Figure 1 illustrates a schematic view of a conventional HVAC system (Prior art).
[0024] Figure 2 illustrates a schematic view of a conventional HVAC system during blending operation (Prior art).
[0025] Figure 3 illustrates a schematic view of HVAC system in accordance to the present disclosure.
[0026] Figure 4 illustrates a schematic view of a HVAC module of HVAC system with the by-pass valve, as per present invention.
[0027] Figure 5 illustrates a schematic view of the HVAC module of HVAC system in AC cooling cycle when the by-pass valve is closed, as per present invention.
[0028] Figure 6 illustrates a schematic view of the HVAC module of HVAC system when the by-pass valve is partially opened (25% opening), as per present invention.
[0029] Figure 7 illustrates a schematic view of the HVAC module of HVAC system when the by-pass valve is partially opened (50% opening), as per present invention.
[0030] Figure 8 illustrates a schematic view of the HVAC module of HVAC system when the by-pass valve is fully opened (100% opening), as per present invention.
[0031] Figure 9 illustrates a schematic view of the HVAC module of HVAC system in heating cycle when the by-pass valve is fully closed (0% opening), as per present invention.
[0032] Figure 10 illustrates a flowchart depicting the control of by-pass valve during temperature blending operation, as per present invention.
[0033] Figures depict various embodiments of the present disclosure for purpose of illustration only. Only skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION
[0034] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words “comprising”, “having”, and “including,” and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary, systems and methods are now described. The disclosed embodiments are merely exemplary of the disclosure, which may be embodied in various forms.
[0035] Various modification to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to another embodiment. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated but is to be accorded the widest scope consistent with the principles and features described herein.
[0036] The disclosure herein provides a HVAC system for controlling cabin temperature using a by-pass valve and method thereof. Figure 3 illustrates a schematic view of HVAC system according to present invention. The HVAC system comprises a climate control module (CCM) (30) configured to receive signals from an outside humidity sensor (31), an outside air temperature (OAT) sensor (32), a control panel/temperature knob (33) and an in-cabin temperature sensor (35), for controlling a HVAC module (37). The CCM (30) is further configured to control HVAC aggregates like blower speed, blower air inlet actuator (34) to change air inlet mode, air outlet mode, blend/temperature door position, compressor duty cycle and by-pass valve position, based on the signals received from aforementioned sensors. The CCM (30) has a calibrated program for operation of whole HVAC system for a cabin comfort.
[0037] Figure 4 shows a configuration of the HVAC module (37) of the HVAC system in accordance with the present invention. The HVAC module (37) comprises a blower (11) to draw air either from outside atmosphere in fresh air inlet mode or from vehicle cabin (36) in air recirculation mode, an evaporator/cooling coil (12) to cool the air (400) coming from the blower (11), a heater (13) to heat the air (400c) flowing over it, a blend/temperature door (14) to control the air flowing to the heater (13) and a by-pass valve (40) with a by-pass duct (41) configured parallel to the evaporator/cooling coil (12). The by-pass valve (40) is configured to be governed by the parameters like set temperature or temperature knob position, outside air temperature, temperature inside the vehicle cabin (36) etc. The by-pass valve (40) is designed in such a way that it optionally allows certain portion (400b) of total airflow (400) from the blower (11) to pass through the by-pass passage/duct (41) when the bypass valve (40) is in at least partially open condition. Remaining portion of air (400a) that does not pass through the by-pass valve (40), continues to pass over the evaporator/cooling coil (12). The portion of air flow (400b) passing through the by-pass duct/passage (41) depends on degree of opening of the by-pass valve (40), which is controlled by the CCM (30) based on set temperature or temperature knob position and in-cabin temperature. The relatively warm air (400b) from the by-pass duct (41) is configured to be mixed with the relatively cool conditioned air (400a) leaving the evaporator/cooling coil (12) after the evaporator/cooling coil (12), maintaining overall air flow constant and is supplied to vehicle cabin (36) without passing over the heater coil (13).
[0038] The present subject matter further discloses the operation of controlling the by-pass valve (40), by the CCM (30), when the OAT is greater than set temperature which is greater than in-cabin temperature and when the difference between set temperature and in-cabin temperature is less than or equal to a predefined limit (e.g., 8°C). The CCM (30) is further configured to determine the degree of opening of the by-pass valve (40) based on the in-cabin temperature and set temperature or temperature knob position. The HVAC system is configured to be operated in fresh air inlet mode for drawing air from outside atmosphere when the relative humidity of outside atmospheric air is below a pre-set value. The HVAC system is further configured to restrict the fresh air inlet and to recirculate the air from the vehicle cabin (36) when the relative humidity of the outside atmospheric air raises above the pre-set value, in order to avoid any condensation after mixing of cold and warm air streams at the evaporator (12) outlet and avoid splashing of water droplets in the vehicle cabin (36). The HVAC system is further configured to selectively allow fresh air inlet when the by-pass valve (40) is completely closed, irrespective of the relative humidity level in outside atmospheric air. In fresh air inlet mode, the CCM (30) actuates the blower air inlet actuator (34) to draw air from the outside atmosphere, whereas the blower (11) draws air from vehicle cabin (36) in the air recirculation mode. The HVAC system is further configured to close the blend/temperature door (14) and to switch off the heater (13) when the by-pass valve (40) is at least partially opened. The HVAC system is further configured to close the by-pass valve (40) when the set temperature is greater than OAT, to open the blend/temperature door (14) and to switch on the heater (13), when vehicle cabin (36) heating is required.
[0039] Figure 5 shows a configuration of the HVAC module (37) of the HVAC system in a pure cooling cycle according to present invention. In pure cooling cycle, both the blend/temperature door (14) and the bypass valve (40) are closed. Therefore, the air coming from the blower (11) passes over the evaporator/cooling coil (12) and gets cooled. This cold air from the evaporator/cooling coil (12) is directly supplied to vehicle cabin (36). The blower (11) draws air from either outside atmosphere in case of fresh air inlet mode or from vehicle cabin (36) in case of air recirculation mode.
[0040] Referring to Figures 6, 7 and 8, which show a configuration of the HVAC module (37) of the HVAC system in an air blending mode with various configurations of the by-pass valve (40) opening. The CCM (30) controls the degrees of opening of the by-pass valve (40) based on set temperature or temperature knob position and in-cabin temperature. The air flow (400) from the blower (11) is divided in to two streams, one stream of air (400b) flows through the by-pass valve (40) to the by-pass duct (41) and another stream of air (400a) passes over the evaporator/cooling coil (12). The relatively warm air (400b) from the by-pass duct (41) mixes with the cold air (400a) from the evaporator (12) and is then supplied to the cabin (36) to increase the in-cabin temperature without the use of the heater (13). During this operation, the blend/temperature door (14) is closed and the heater (13) is in switched off state. Therefore, the air (400d) being supplied to the vehicle cabin (36) is mixture of warm air stream (400b) flowing through the by-pass duct (41) and the cold air stream (400a) leaving the evaporator (12) (i.e., 400 = 400a + 400b = 400d). In an embodiment, the air flow (400b) through the by-pass valve (40) is varied from 0% to 70% of the entire air stream (400) leaving the blower (11). The by-pass valve (40) is designed and positioned in such a way that, even in fully opened state (i.e., 100% opened state), it will not allow deflection of the entire air stream (400) from the blower (11) to the by-pass duct (41). Hence, the air flow (400b) through the by-pass duct, can be varied from 0% to 70%, but is optimally used in the range of 0% to 30% of the air stream (400) leaving the blower (11). In other words, the by-pass valve (40) is configured to allow 30% to 100%, but is optimally used in the range of 70% to 100% of the air flow (400) leaving the blower (11), to pass through the evaporator (12). However, as per another embodiment, the air flow (400b) through the by-pass valve (40) can be varied based on the positioning of the by-pass valve (40) in the by-pass duct (41) from the blower (11) and size of the by-pass valve (40) and the by-pass duct (41). The CCM (30) is configured to allow the blower (11) to operate in fresh air inlet mode when the relative humidity of outside atmospheric air is below a pre-set limit (i.e., <80% or <90% etc.) and in recirculation mode when the relative humidity of the outside atmospheric air raises above the pre-set limit.
[0041] Figure 6 shows the state where the by-pass valve (40) is opened by 25%. In this position, 90% of the air flow (400) from the blower (11) passes through the evaporator/cooling coil (12) to cool said 90% air flow (i.e., 400a = 90% of 400). Remaining 10% air passes through the by-pass duct (41) without any conditioning (i.e., 400b = 10% of 400). When this 90% cooled air flow mixes with 10% warm air of the by-pass duct and supplied to the vehicle cabin (36) to slightly raise the in-cabin temperature without use of the heater (13).
[0042] Figure 7 shows the state where the by-pass valve (40) is opened by 50%. In this position, 80% of the air (400) from the blower (11) passes over the evaporator/cooling coil (12) to cool said 80% air flow (i.e., 400a = 80% of 400). Remaining 20% air passes through the by-pass duct (41) without any conditioning (i.e., 400b = 20% of 400). When this 80% cooled air flow mixes with 20% warm air of the by-pass duct and supplied to the vehicle cabin (36) to considerably raise the in-cabin temperature without use of the heater (13).
[0043] Figure 8 shows fully open i.e., 100% opened state of the by-pass valve (40). In this position, 70% of the air (400) from the blower (40) passes over the evaporator/cooling coil (12) to cool said 70% air flow (i.e., 400a = 70% of 400). Remaining 30% air passes through by-pass duct (41) without any conditioning (i.e., 400b = 30% of 400). When this 70% cooled air flow mixes with 30% warm air of the by-pass duct and supplied to the vehicle cabin (36) to raise the in-cabin temperature to a greater extent without use of the heater (13).
[0044] Figure 9 shows a configuration of the HVAC module (37) of the HVAC system in heating cycle in which blend/temperature door (14) is in fully opened state and entire air flow (400) from the blower, after flowing over the evaporator/cooling coil (12), passes over the heater (13) (i.e., 400 = 400a = 400c = 400d). In case of fully opened blend/temperature door (14), the warm air (400c) from the heater (13) is supplied to the vehicle cabin (36) to raise the in-cabin temperature. The heater (13) operates only if there is purely heating demand like in cold weather conditions or for windscreen demisting purpose. The by-pass valve (40) is in closed state in the heating cycle.
[0045] Figure 10 illustrates a flowchart for controlling the by-pass valve (40). The user sets a desired temperature using control panel or by turning a temperature knob (33). The CCM (30) receives the input signals from the control panel/temperature knob (33), OAT sensor (32), in-cabin temperature sensor (35) and outside humidity sensor (31). The CCM (30) operates the HVAC aggregates based on the aforementioned input signals, as follows,
a. If the set temperature is greater than the in-cabin temperature and the set temperature is less than or equal to the OAT and the difference between set temperature and in-cabin temperature is less than or equal to the predefined limit (e.g., 8°C) and the relative humidity of the outside atmospheric air is below a pre-set value, then the blower (11) is operated in the fresh air inlet mode, the by-pass valve (40) is opened, the blend/temperature door (14) is closed and the heater (13) is switched off. (Refer raw numbers 1 and 5 of Table 1)
b. If the set temperature is greater than the in-cabin temperature and the set temperature is less than or equal to OAT and the difference between set temperature and in-cabin temperature is less than or equal to the predefined limit (e.g., 8°C) and the relative humidity of the outside atmospheric air is above the pre-set value, then the blower (11) is operated in air recirculation mode, the by-pass valve (40) is opened, the blend/temperature door (14) is closed and the heater (13) is switched off. (Refer raw numbers 2 and 6 of Table 1)
c. If the set temperature is greater than the in-cabin temperature and the difference between set temperature and in-cabin temperature is greater than a predefined limit (e.g., 8°C), then the by-pass valve (40) is closed, blend/temperature door (14) is opened and heater (13) is turned on.
d. If the set temperature is greater than the in-cabin temperature and the set temperature is greater than OAT and the difference between set temperature and in-cabin temperature is less than or equal to the predefined limit, then the by-pass valve (40) is closed, blend/temperature door (14) is opened and heater (13) is turned on.
e. If the set temperature is less than or equal to the in-cabin temperature, then the by-pass valve (40) and blend/temperature door (14) are closed, and the heater is switched off, resulting in providing cold air from the evaporator (12) directly to the vehicle cabin (36). (Refer raw numbers 3 and 7 of Table 1)
[0046] Therefore CCM (30) opens the by-pass valve (40) for temperature blending purpose, only if following conditions are satisfied,
a. OAT > Set Temperature > In-cabin Temperature, and
b. (Set Temperature – In-cabin Temperature) = Predefined Value (e.g., 8°C).
[0047] In an exemplary embodiment, the HVAC system controls its aggregates based on the temperatures and relative humidity level as shown in table below.
Table 1
Sr. No. Set Temp. Cabin Temp. OAT Relative Humidity AC ON/OFF By-pass valve PTC heater Air inlet mode
1 X = X-1 = X < 80% ON ON OFF Fresh
2 X = X-1 = X > 80% ON ON OFF Recirculation
3 X = X = X ˜ ON OFF OFF Fresh/Recirculation
4 X = X =X ˜ OFF OFF ON Fresh/Recirculation
5 23 22 26 < 80% ON ON OFF Fresh
6 23 22 26 > 80% ON ON OFF Recirculation
7 23 25 26 ˜ ON OFF OFF Fresh/Recirculation
8 25 16 16 ˜ OFF OFF ON Fresh/Recirculation
[0048] Rows 1-5 of table 1 shows configurations of HVAC aggregates such as AC, by-pass valve (40), heater (13) and air inlet mode for the different values of set temperature, in-cabin temperature, outside air temperature and relative humidity of outside air. The variable ‘X’ denotes the set temperature value and the different situations are considered where the in-cabin temperature and outside air temperature are expressed in relation to the set temperature i.e., in terms of variable ‘X’. Further, rows 5-8 shows the similar configurations of the HVAC aggregates with the help of numerical values.
[0049] Accordingly, present invention discloses a HVAC system for controlling vehicle cabin temperature comprising a blower (11), an evaporator (12), a by-pass duct (41) provided parallel to the evaporator (12) and a by-pass valve (40) to optionally open the by-pass duct (41). The by-pass duct (41) is optionally opened by using the by-pass valve (40) to selectively divert a stream of air flow (400b) from the total airflow (400), through said by-pass duct (41). A heater (13) is provided for optionally operating and selectively heating the air flow (400a) coming from the evaporator (12) and supplying the hot air flow (400d) to vehicle cabin (36). A blend/temperature door (14) is configured to control the flow of air (400c) through the heater (13). The air flow (400b) from the by-pass duct (41) is configured to be mixed with the conditioned air (400a) exiting the evaporator (12) and the said mixture of air (400d) is configured to be supplied to the vehicle cabin (36). The by-pass valve (40) is configured to divert 0% to 90% of the total air flow (400) leaving the blower (11), to pass through the by-pass duct (41). The by-pass valve (40) is configured to allow 10% to 100% of the total air flow (400) leaving the blower (11), to pass through the evaporator (12).
[0050] Present invention further discloses a climate control module (30) configured to control the by-pass valve (40) based on set temperature received from a control panel or a temperature knob (33), outside air temperature received from an outside air temperature sensor (32) and in-cabin temperature received from an in-cabin temperature sensor (35). The climate control module (30) is configured to control the degree of opening of the by-pass valve (40) based on set temperature or temperature knob position and in-cabin temperature. The climate control module (30) is configured to open the by-pass valve (40) on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C. The climate control module (30) is configured to close the blend/temperature door (14) and to switch off the heater (13) on opening the by-pass valve (40). The climate control module (30) is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode upon detection of relative humidity of the outside air being more than 80%. The climate control module (30) is configured to close the by-pass valve (40) on detection of the in-cabin temperature being greater than the set temperature. The climate control module (30) is configured to close the by-pass valve (40), open the blend/temperature door (14) and switch on the heater (13), on detection of the outside air temperature greater than the set temperature and the difference between the set temperature and in-cabin temperature is greater than 8°C.
[0051] Present invention further discloses a method for controlling HVAC system comprising, (a):- receiving signals by a climate control module (30), from various sensors like an outside air temperature sensor (32), an in-cabin temperature sensor (35) and outside humidity sensor (31) and a control panel or a temperature knob (33); (b):- processing the received signals by the climate control module (30), to control flow of air through a by-pass duct (41) and an evaporator (12), by operation of a by-pass valve (40); (c):- opening the by-pass valve (40), by a climate control module (30), to selectively divert a stream of air flow (400b) from the total airflow (400), through said by-pass duct (41), on detection of the outside air temperature greater than the set temperature and the set temperature is greater than the in-cabin temperature with the difference between the set temperature and in-cabin temperature being less than or equal to 8°C; and (d):- mixing the air flow (400b) from the by-pass duct (41) with the conditioned air (400a) exiting the evaporator (12) for supplying the mixture of air (400d) to the vehicle cabin (36). The climate control module (30) is configured to operate the HVAC system in fresh air inlet mode on detection of relative humidity of outside air being less than 80% and to switch the system to air recirculation mode on detection of relative humidity of the outside air being more than 80%.
[0052] Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features.
[0053] Some embodiments provide a HVAC system for controlling vehicle cabin temperature.
[0054] Some embodiments provide a HVAC system for controlling vehicle cabin temperature by providing a by-pass valve with a by-pass duct provided parallel to an evaporator of the HVAC system.
[0055] Some embodiments provide a HVAC system for reducing power consumption by the electric heater in EVs at certain operating conditions of the HVAC system.
[0056] Some embodiments provide a HVAC system for reducing power consumption of AC compressor in cooling cycle of HVAC system.
[0057] Some embodiments provide a HVAC system for improving vehicle mileage of EVs by eliminating the use of heater for temperature blending in HVAC system.
[0058] Some embodiments provide a HVAC system for reducing parasitic load on battery of vehicle, by reducing the electric heater operation during the blending process of mixing cold and hot air to control cabin temperature set by the user.
[0059] Some embodiments provide a method for controlling vehicle cabin temperature by restricting a HVAC system to operate in air recirculation mode, on detection of relative humidity of outside air above a pre-set value and by operating the HVAC system in fresh air inlet mode on detection of relative humidity of outside air below the pre-set value, during opened state of the by-pass valve.
[0060] Some embodiments provide a method for controlling vehicle cabin temperature, by blending of unconditioned air (by-pass air) without using heater of any type.
[0061] Some embodiments provide a method for controlling vehicle cabin temperature by selectively allowing a HVAC system to operate in fresh air inlet mode during closed state of the by-pass valve.
[0062] Although implementations for a HVAC system for controlling vehicle cabin temperature have been described in language specific to structural features, it is to be understood that the appended claims are not necessarily limited to the specific features described. Rather, the specific features are disclosed as examples of implementation for a HVAC system.
[0063] Figures 1-9 are now described using the reference numbers stated in the below table.

Element Description Reference Numeral
Conventional HVAC system 10
A Blower 11
An evaporator/cooling coil 12
A heater 13
A blend door/temperature door 14
Climate Control Module (CCM) 30
Outside humidity sensor 31
Outside Air Temperature (OAT) sensor 32
Control panel/temperature Knob 33
Blower air inlet actuator 34
In-cabin temperature sensor 35
Vehicle Cabin 36
HVAC Module 37
A by-pass valve 40
A by-pass duct 41
Air stream leaving the blower 400
Air stream passing through the evaporator 400a
Air stream passing through the by-pass duct 400b
Air stream passing through the heater 400c
Air stream supplied to the vehicle cabin 400d