Running a PHEV in EV mode under cold conditions

Abstract

A plug-in hybrid electric vehicle has an internal combustion engine with a coolant outlet connected to a coolant inlet of a fuel operated heater and wherein a coolant outlet of the fuel operated heater is connected to a coolant inlet of an HVAC heater, a coolant outlet of the HVAC heater further being connected to a coolant inlet of the internal combustion engine. The vehicle also has a temperature sensor at the coolant outlet of the internal combustion engine and a temperature sensor at the coolant outlet of the fuel operated heater. The vehicle has a three way valve arranged between the coolant outlet of the HVAC heater and the coolant inlet of the internal combustion engine such that there is a connection between the coolant outlet of the HVAC heater and the coolant inlet of the fuel operated heater, the connection bypassing the internal combustion engine.

Claims

1. A plug-in hybrid electric vehicle comprising an internal combustion engine, a coolant outlet of the internal combustion engine being connected to a coolant inlet of a fuel operated heater and wherein a coolant outlet of the fuel operated heater is connected to a coolant inlet of an HVAC heater, a coolant outlet of the HVAC heater further being connected to a coolant inlet of the internal combustion engine, the vehicle further comprising a temperature sensor arranged at the coolant outlet of the internal combustion engine and a temperature sensor arranged at the coolant outlet of the fuel operated heater, wherein the vehicle further comprises a three way valve arranged between the coolant outlet of the HVAC heater and the coolant inlet of the internal combustion engine such that there is a connection between the coolant outlet of the HVAC heater and the coolant inlet of the fuel operated heater, the connection thus bypassing the internal combustion engine, wherein the three way valve is configured to, at electrical driving (EV or HEV) modes of the plug-in hybrid electric vehicle and upon at least one of the temperature sensor arranged at the coolant outlet of the internal combustion engine or the temperature sensor arranged at the coolant outlet of the fuel operated heater sensing a temperature less than or equal to a certain threshold temperature, close to direct coolant flow to bypass the internal combustion engine through the connection and thereafter, upon a certain operation time or upon the temperature sensor arranged at the coolant outlet of the fuel operated heater sensing a temperature less than a second certain threshold temperature, partially open to allow partial coolant volume flow through the valve to the internal combustion engine while at least some coolant flow through the connection remains.

2. The plug-in hybrid electric vehicle according to claim 1, wherein the vehicle further comprises an electrical pump upstream the coolant inlet of the fuel operated heater.

3. The plug-in hybrid electric vehicle according to claim 1, wherein the vehicle further comprises a mechanical pump upstream the coolant inlet of the internal combustion engine.

4. The plug-in hybrid electric vehicle according to claim 1, wherein the three way valve is an electromagnetic valve.

5. The plug-in hybrid electric vehicle according to claim 1, wherein the three way valve is a vacuum valve.

6. The plug-in hybrid electric vehicle according to claim 1, wherein the three way valve is an electric machine driven continuous coolant flow control valve.

7. A method for controlling an internal combustion-cabin heater coolant circuit for a plug-in hybrid electric vehicle, the vehicle comprising an internal combustion engine, a coolant outlet of the internal combustion engine being connected to a coolant inlet of a fuel operated heater and wherein a coolant outlet of the fuel operated heater is connected to a coolant inlet of an HVAC heater, a coolant outlet of the HVAC heater further being connected to a coolant inlet of the internal combustion engine, the vehicle further comprising a temperature sensor arranged at the coolant outlet of the internal combustion engine and a temperature sensor arranged at the coolant outlet of the fuel operated heater, the vehicle further comprising a three way valve arranged between the coolant outlet of the HVAC heater and the coolant inlet of the internal combustion engine such that there is a connection between the coolant outlet of the HVAC heater and the coolant inlet of the fuel operated heater, the connection thus bypassing the internal combustion engine, the circuit comprising an electrical pump, the vehicle further comprising a climate system control unit, an internal combustion engine control unit, and an ambient temperature sensor, the method comprising, monitoring the ambient temperature, if the vehicle is in electric drive and the ambient temperature is below or equal to 15 C. and above or equal to 0 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and the electrical pump and request closing of the valve to direct coolant flow through the connection to bypass the internal combustion engine, and thereafter, if a certain operation time has passed or if the coolant outlet temperature of the fuel operated heater is less than a temperature (Y) corresponding to a temperature which is less than a coolant outlet temperature of the fuel operated heater for which half power/capacity operation the fuel operated heater is to be requested, request partial opening of the valve to allow partial coolant volume flow through the valve to the internal combustion engine while at least some coolant flow through the connection remains, if the vehicle is in electric drive and the ambient temperature is below 0 C. and above 40 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the internal combustion engine and start of the fuel operated heater and start of the electrical pump where the valve control will be aimed to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility, if the vehicle is in electric drive and the ambient temperature is equal to or below 15 C. or above 8 C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of the fuel operated heater and start of the electrical pump and request closing of the valve to direct coolant flow through the connection to bypass the internal combustion engine, if the vehicle is in electric drive and the ambient temperature is equal to or below 15 C. or above 8 C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request start of the electrical pump but not the fuel operated heater and request opening of the valve, if the vehicle is in electric drive and the ambient temperature is below 0 C. and above 40 C. and the coolant outlet temperature of the fuel operated heater is higher than the temperature when the internal combustion engine is requested to start, request start of the fuel operated heater and electrical pump where the valve control will aim to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility, if the vehicle is in electric drive and the ambient temperature is below 0 C. and above 40 C. and the coolant outlet temperature of the fuel operated heater is lower than the temperature when the internal combustion engine is requested to start, request start of the internal combustion engine, start of the fuel operated heater, and start of the electrical pump where the valve control will aim to optimally fulfil the internal combustion engine and the climate system thermal targets considering the vehicle fuel consumption and its electrical drive feasibility, if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and start of the electrical pump and request opening of the valve, if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request opening of the valve but do not request start of either the fuel operated heater or the electrical pump, if the vehicle is in hybrid drive and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of fuel operated heater and start of electrical pump and request opening of the valve, if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request start of the fuel operated heater and start of the electrical pump and request opening of the valve, if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the internal combustion engine is higher than the coolant outlet temperature when the fuel operated heater is requested to start, request opening of the valve but do not request start of either the fuel operated heater or the electrical pump, if the vehicle is in an internal combustion engine driving mode and the ambient temperature is equal to or below 15 C. and above 40 C. and the coolant outlet temperature of the internal combustion engine is lower than the coolant outlet temperature when the fuel operated heater is requested to start, request start of fuel operated heater and start of electrical pump and request opening of the valve, if the vehicle is in a hybrid or an internal combustion engine driving mode and the ambient temperature is above or equal to 25 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump, if the vehicle is in a hybrid or an internal combustion engine driving mode and the ambient temperature is above or equal to 25 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine is higher than the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump, if the vehicle is in electrical drive and the ambient temperature is above or equal to 25 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine are equal to the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump, if the vehicle is in electrical drive and the ambient temperature is above or equal to 25 C. and the coolant outlet temperature of the fuel operated heater and the coolant outlet temperature of the internal combustion engine is higher than the ambient temperature, request closed valve and do not request start of either the fuel operated heater or the electrical pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be further disclosed with reference to the accompanying drawings in which FIG. 1 shows a simplified layout of the system according to the present invention.

DISCLOSURE OF PREFERRED EMBODIMENTS

(2) FIG. 1 shows an internal combustion engine 1, a coolant outlet 2 of the internal combustion engine 1 that is connected to a coolant inlet 3 of a fuel operated heater 4 and wherein a coolant outlet 5 of the fuel operated heater 4 is connected to a coolant inlet 6 of an HVAC heater 7, a coolant outlet 8 of the HVAC heater 7 further being connected to a coolant inlet 9 of the internal combustion engine 1. Also shown is a temperature sensor 10 arranged at the coolant outlet 2 of the internal combustion engine 1 and a temperature sensor 11 arranged at the coolant outlet 5 of the fuel operated heater 4.

(3) FIG. 1 further shows a three way valve 12 arranged between the coolant outlet 8 of the HVAC heater 7 and the coolant inlet 9 of the internal combustion engine 1 such that there is a connection 13 between the coolant outlet 8 of the HVAC heater 7 and the coolant inlet 3 of the fuel operated heater 4, the connection 13 thus bypassing the internal combustion engine 1. An electrical pump 14 will run when the short flow circuit is fully or partially used at all plug-in hybrid electric vehicles' (PHEV) driving modes or when the long flow circuit is used at electrical drive mode and a mechanical pump 15 will run when the internal combustion engine 1 is running.

(4) To make electrical drive feasible at and below 15 C. ambient temperature with fulfilled climate system and internal combustion engine (ICE) thermal targets (the latter to facilitate acceptable vehicle take-off performance at driving mode shift from electrical drive mode to an ICE-initiated one (e.g., HEV, ICE-drive or AWD)) as well as reduce and minimise the electrical power needed to fulfil the climate system thermal targets at and above 25 C. ambient temperature. the ICE-cabin heater coolant circuit is split into two by a valve that controls the coolant water flow through both and as a consequence the thermal power distribution to the ICE and the cabin heater, see FIG. 1, a modular valve control strategy that efficiently considers all the PHEV driving modes (i.e. EV-, HEV-, and ICE-drive-modes) and different thermal initial conditions, by optimally dealing with a simultaneous or an individual fulfilment of ICE's and climate system's thermal power needs/targets. This modular control strategy (where the control algorithm different modules can be reused, activated or deactivated at the different initial and operational conditions) reduces system solution complexity, decreases needed software variations, and improve robustness whereas paving the way for an efficient introduction of the whole system (i.e., hardware and software) to any other existing or future vehicle (e.g., EV-, HEV-, PHEV-, or ICE-drive-vehicle) with positive impact on product development, production, and production costs, a short time limited, power consumption efficient, and sparking-plugs durability accounted ICE's plugs pre-glow dependant on PHEV's electrical drive mode shift-arising information (e.g. gas pedal angle at overtaking or high voltage battery state of charge level close to sustaining) to an ICE-initiated one (e.g., HEV, ICE-drive or AWD) that considers ICE's thermal power needs related to vehicle take-off target at such PHEV-driving mode shift at cold climate at and below 15 C. ambient temperature until the coolant water temperature at ICE-side is at or above the ICE's thermal targets, and a climate control system's ICE-Start-control strategy where the ICE operates as an additional heater, to further extend EV-drive feasibility below 0 C. down to about 40 C. ambient temperature with fulfilled ICE's- and climate system-targets
have been developed and implemented to fulfil and extend electrical drive feasibility between 15 C. and about 40 C. ambient temperature as well as minimise climate system electrical power needs at and above 25 C. ambient temperature (which benefits both OEM and final customer) while fully extracting and utilizing the PHEV technologies full capacities.

(5) The following is a description of how the system is controlled under various conditions.

(6) ICold climate electrical drive climate system control strategy at cold start, i.e. 0 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out15 C.

(7) If 0 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out15 C. at electrical drive key-on then:

(8) 1request the fuel operated heater (FOH) start (including electrical water pump). 2request closed valve, i.e. coolant volume flow is limited to FOH-SFC () until =x [min] or T.sub.FOH-out=Y [ C.] (where Y<T.sub.FOH-half), then allow a partial coolant volume flow =v through the valve to ICE (while the FOH-short flow circuit (FOH-SFC) coolant volume flow remain v, i.e. total coolant volume flow is +v<V). Thereafter, at =X [min] or T.sub.FOH-out=T.sub.FOH-halfy [ C.], request open valve until T.sub.ICE-out=T.sub.ICE-target, then the valve control will allow a partial coolant volume flow =V to the ICE to maintain T.sub.ICE-out=T.sub.ICE-target while the reminder of the thermal power generated by FOH is used to approach and maintain climate comfort through the FOH-SFC volume flow () where the total coolant volume flow is +V. 3If T.sub.FOH-out=T.sub.FOH-halfy [ C.] then request open valve until T.sub.FOH-out=T.sub.FOH-half[ C.] where y=5 C. then allow a partial volume flow = again and so on for =[min]. Thereafter, T.sub.FOH-out will approach T.sub.FOH-half and the FOH will shift to operate at half-power/capacity. If T.sub.FOH-out=T.sub.FOH-full+y [ C.] then request closed valve until T.sub.FOH-out=T.sub.FOH-full+ [ C.] (where y=5 C.) then allow a partial volume flow = once again and so on for =x[min]. Thereafter, Thereafter, T.sub.FOH-out will approach T.sub.FOH-full and the FOH will shift to operate at full-power/capacity, and so on. The reason for that is to damp down any eventual quick fluctuation of the FOH operation between its full and half power/capacity which is harmful for it when dealing with durability. 4If T.sub.FOH-out=T.sub.FOH-offy [ C.] then request open valve to avoid FOH turn off during electrical vehicle drive below 15 C. ambient temperature. If, thereafter, T.sub.FOH-out approaches T.sub.FOH-out=T.sub.FOH-half [ C.] then follow I-3 above. 5A short time limited ICE-plugs pre-glow dependant on drive mode shift-arising information (e.g. gas pedal angle at overtaking or high voltage battery state of charge level close to sustaining) will be used to achieve a power consumption efficient and take-off acceptable PHEV-mode shift (from EV- to HEV-, ICE-, or AWD-drive mode) performance. This ICE-plugs pre-glow will be available until =X [min] or T.sub.ICE-outT.sub.ICE-target.
IICold climate, i.e. 8 C.T.sub.amb15 C., electrical drive climate system control strategy of a FOH-preconditioned or warm started vehicle, where T.sub.ICE-out<T.sub.ICE-FOH-on-req and T.sub.ICE-outT.sub.FOH-out<T.sub.FOH-off
If 8 C.T.sub.amb15 C. and T.sub.ICE-out<T.sub.ICE-FOH-on-req and T.sub.ICE-outT.sub.FOH-out<T.sub.FOH-off (e.g. after a timer start FOH-based preconditioning), at electrical drive key-on then request control strategy as at I above.
IIICold climate, i.e. 8 C.T.sub.amb15 C., electrical drive climate system control strategy of a FOH-preconditioned or warm started vehicle, where T.sub.ICE-out>T.sub.ICE-FOH-on-req and T.sub.FOH-outT.sub.ICE-out
If 8 C.T.sub.amb15 C. and T.sub.ICE-out>T.sub.ICE-FOH-on-req and T.sub.FOH-outT.sub.ICE-out (e.g. after a direct start (DS) FOH-based preconditioning), i.e. FOH is off, at electrical drive key-on then: 1request the electrical water pump to start 2FOH will remain off until T.sub.ICE-out=T.sub.ICE-FOH-on-req then it will turn on where the valve remain open until T.sub.FOH-out>T.sub.ICE-out+Y [ C.] and then it requested closed, i.e. coolant volume flow is limited to FOH-SFC (). 3IF T.sub.FOH-out approach T.sub.FOH-out=T.sub.FOH-halfy [ C.] then go to I-3 and 4 above. 4if T.sub.ICE-out approach T.sub.ICE-target the valve control will allow a partial coolant volume flow =V to ICE to maintain T.sub.ICE-out=T.sub.ICE-target while the reminder of the thermal power generated by FOH is used to approach and maintain climate comfort through the FOH-SFC volume flow (). 5No short time limited ICE-plugs pre-glow will be needed in this case.
IVCold climate electrical drive climate system control strategy at cold start, i.e. 40 C.<T.sub.amb=T.sub.ICE-out=T.sub.FOH-out<0 C.
If 40 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out0 C. at electrical drive key-on then: 1request both ICE and FOH (including electrical water pump) to turn on as well as open valve until T.sub.ICE-out approaches T.sub.ICE-ICE-off-req then turn off the ICE, i.e. allow electrical drive. 2at T.sub.ICE-outT.sub.ICE-FOH-on-req (where varies with T.sub.amb) the valve control will follow III-2 above (i.e. when T.sub.FOH-out>T.sub.ICE-out+Y [ C.] request closed valve) and otherwise (at T.sub.ICE-out>T.sub.ICE-FOH-on-reg the valve will be open. 3when T.sub.FOH-out approaches T.sub.FOH-ICE-on-reg turn on the ICE (i.e. electrical drive comes to an end) until T.sub.ICE-out approaches T.sub.ICE-ICE-off-reg then turn off the ICE once again and so on until the high voltage battery state of charge level achieve the sustaining one and the vehicle shifts to HEV-driving mode. The number of electrical drive interruptions by ICE-start depends, among other things, on T.sub.amb and vehicle speed.
VCold climate, i.e. 40 C.<T.sub.amb<0 C., electrical drive climate system control strategy at warm start, i.e. T.sub.FOH-out>T.sub.FOH-ICE-on-req
If 40 C.T.sub.amb<0 C. and T.sub.FOH-out>T.sub.FOH-ICE-on-req at electrical drive at electrical drive key-on then: 1the FOH will turn on (including electrical water pump) and the ICE will remain off (i.e. electrical drive is feasible) until T.sub.FOH-out=T.sub.FOH-ICE-on-req where the ICE will turn on (i.e. electrical drive comes to an end) until T.sub.ICE-out=T.sub.ICE-ICE-off-req where it (the ICE) will turn off (i.e. electrical drive is feasible once again) and so on until the high voltage battery state of charge level achieve the sustaining one and the vehicle shifts to HEV-driving mode. 2the valve control will follow IV-2 above. 3Again, the number of electrical drive interruptions by ICE-start depends on T.sub.amb and vehicle speed.
VICold climate, i.e. 40 C.<T.sub.amb<0 C., electrical drive climate system control strategy at warm start, i.e. T.sub.FOH-out<T.sub.FOH-ICE-on-req
If 40 C.T.sub.amb<0 C. and T.sub.FOH-out<T.sub.FOH-ICE-on-req at electrical drive at electrical drive key-on then: 1both ICE and FOH (including electrical water pump) will turn on (i.e. electrical drive is not feasible) until T.sub.ICE-out=T.sub.ICE-ICE-off-req where the ICE will turn off (i.e. electrical drive is feasible) until T.sub.FOH-out=T.sub.FOH-ICE-on-req where the ICE will turn on once again (i.e. electrical drive comes to an end) and so on until the high voltage battery state of charge level achieve the sustaining one and the vehicle shifts to HEV-driving mode. 2the valve control will follow IV-2 above. 3Again, the number of electrical drive interruptions by ICE-start depends on T.sub.amb and vehicle speed.
VIICold climate HEV (i.e. Hybrid-Sustaining)-drive climate system control strategy at cold start, i.e. 40 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out15 C.
If 40 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out15 C. at HEV (i.e. Hybrid-Sustaining)-drive key-on where the vehicle shifts between ICE- and electrical machine drive within a certain high voltage battery state of charge interval, then: 1request FOH-start (including electrical water pump) and open valve, i.e. coolant volume flow is V. 2when T.sub.FOH-out>T.sub.ICE-out+Y [ C.] then request closed valve, i.e. coolant volume flow is limited to FOH-SFC () until T.sub.FOH-out<T.sub.ICE-outY [ C.] then request open valve and so on until T.sub.FOH-out=T.sub.ICE-FOH-off-req then the FOH will turn off and the valve will remain open as at its default position. 3when T.sub.ICE-out=T.sub.ICE-FOH-on-req then the FOH will restart and the above mentioned control strategy at 2 will be re-performed.
VIIICold climate HEV (i.e. Hybrid-Sustaining)-drive, i.e. 40 C.<T.sub.amb<15 C., climate system control strategy at warm start where T.sub.ICE-out<T.sub.ICE-FOH-on-req or T.sub.ICE-out>T.sub.ICE-FOH-on-req and T.sub.FOH-outT.sub.ICE-out
If 40 C.T.sub.amb<15 C. and T.sub.ICE-out>T.sub.ICE-FOH-on-req at HEV (i.e. Hybrid-Sustaining)-drive key-on then the FOH will remain off until T.sub.ICE-out=T.sub.ICE-FOH-on-req where it will turn on (including electrical water pump) and the above mentioned control strategy at VII-2 and 3 will be performed.
If 40 C.T.sub.amb<15 C. and T.sub.ICE-out<T.sub.ICE-FOH-on-req at HEV (i.e. Hybrid-Sustaining)-drive key-on then the FOH will turn on (including electrical water pump) and the above mentioned control strategy at VII-2 and 3 will be performed.
IXCold climate ICE- and AWD-drive climate system control strategy at cold start, i.e. 40 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out15 C. or warm start, where T.sub.ICE-out<T.sub.ICE-FOH-on-req or T.sub.ICE-out>T.sub.ICE-FOH-on-req and T.sub.FOH-outT.sub.ICE-out
Operation is similar as at HEV-driving mode at VII and VIII with the exception of having ICE continuously running during the driving mode which further limits the needs of FOH as a supplementary heater.
XWarm climate HEV-, ICE- and AWD-drive climate system control strategy at cold start, i.e. 25 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out or warm start, where T.sub.ICE-outT.sub.FOH-out>T.sub.amb25 C.
If 25 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out or T.sub.ICE-outT.sub.FOH-out>T.sub.amb25 C. at PHEV drive mode where the ICE is on (e.g. HEV-, ICE- or AWD-drive) then request closed valve. The FOH and electrical pump will remain off and the ICE driven mechanical pump will circulate the coolant water within the ICE-part of the coolant circuit but not the short flow circuit, i.e. the cabin heater- and FOH-part of the coolant circuit.
XIWarm climate electrical drive climate system control strategy at cold start, i.e. 25 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out or warm start, where T.sub.ICE-outT.sub.FOH-out>T.sub.amb25 C.
If 25 C.T.sub.amb=T.sub.ICE-out=T.sub.FOH-out or T.sub.ICE-outT.sub.FOH-out>T.sub.amb25 C. at electrical drive then request closed valve while the FOH and electrical pump will remain off.
The foregoing is a disclosure of an example practicing the present invention. However, it is apparent that method incorporating modifications and variations will be obvious to one skilled in the art. Inasmuch as the foregoing disclosure is intended to enable one skilled in the art to practice the instant invention, it should not be construed to be limited thereby, but should be construed to include such modifications and variations as fall within the scope of the claims.

DEFINITIONS

(9) ICE Internal Combustion Engine FOH Fuel Operated Heater Operation time T.sub.amb Ambient temperature V Coolant water volume flow through the ICE coolant circuit at open valve Coolant water volume flow through the FOH's short flow circuit (FOH-SFC) at closed valve Partial coolant water volume flow through the valve to ICE where V, and ==V at open valve T.sub.FOH-out Coolant temperature after the FOH T.sub.ICE-out Coolant temperature after the ICE T.sub.HVAC-in Coolant temperature before cabin heater T.sub.HVAC-out Coolant temperature after cabin heater T.sub.FOH-off FOH's coolant temperature that requests FOH to turn-off T.sub.FOH-half FOH's coolant temperature that requests FOH to operate at half power/capacity T.sub.FOH-full FOH's coolant temperature that requests FOH to operate at full power/capacity while it is operating at half power/capacity T.sub.ICE-target ICE's coolant temperature that is required to approach an acceptable vehicle take-off performance at mode shift from electrical drive to an ICE initiated one T.sub.ICE-FOH-on-req ICE's coolant temperature that requests FOH to turn-on as an additional heater T.sub.ICE-FOH-off-req ICE's coolant temperature that requests FOH to turn-off as an additional heater T.sub.FOH-ICE-on-req FOH's coolant temperature that requests ICE to turn-on as an additional heater T.sub.ICE-ICE-off-req ICE's coolant temperature that requests ICE to turn-off as an additional heater