GB2454349A

GB2454349A - Heating hybrid vehicle engine oil

Info

Publication number: GB2454349A
Application number: GB0819832A
Authority: GB
Inventors: Ian Graham Pegg; Michael James Watts
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2007-10-30
Filing date: 2008-10-29
Publication date: 2009-05-06
Anticipated expiration: 2028-10-29
Also published as: DE102008037820A1; CN101424200A; GB0819832D0; CN101424200B; GB2454349B; GB0721262D0

Abstract

A method for heating the engine oil of a diesel engine 20 of a hybrid electric vehicle 5 having an electrical drive system 60 cooled by a liquid cooling circuit. The method comprises using heat which needs to be rejected from the cooling circuit of the electrical drive system 60 to heat the engine oil of the heat engine 20 by using a heat exchanger 70 through which the coolant and the engine oil are selectively caused to flow when regeneration of an exhaust aftertreatment device 50 is required. The method overcomes a problem with a hybrid vehicle having cold lubricant oil, especially when its diesel has only recently been restarted.

Description

A Method for Heating the Oil of an Engine This invention relates to hybrid electric vehicles having an internal combustion engine and an electric drive system.

The need to reduce fossil fuel consumption by and emissions from automobiles and other vehicles powered by an Internal Combustion Engine (ICE) is well known. Vehicles powered by electric motors attempt to address these needs.

However, electric vehicles have limited range, limited power capabilities and need substantial time to recharge their batteries. An alternative solution is to combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called Hybrid Electric Vehicles (HEV5) . An HEV can be arranged in a variety of configurations, some of which require an operator to select between electric and internal combustion operation and others in which the transition between internal combustion engine drive and electric drive is performed automatically.

The most common configurations are:-a/ Series Hybrid Electric Vehicle (SHEV) in which the internal combustion engine is connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels; b/ Parallel Hybrid Electrical Vehicle (PHEV) configuration has an internal combustion engine and an electric motor that together provide the necessary wheel torque to drive the vehicle. In the PHEV configuration, the electric motor can be used as a generator to charge the battery from the power produced by the ICE; and 206-2010GB2 c/ Parallel/Series Flybrid Electric Vehicle (PSHEV) because this has the characteristics of both the PHEV and the SHEV configurations and is typically known as a 5!vpowersplitn configuration. In the PSHEV, the internal combustion engine is mechanically coupled to two electric motors via a planetary gearset transaxie. A first electric motor, the generator, is connected to a sun gear, the internal combustion engine is connected to a carrier, a second electric motor in the form of a traction motor is connected to a ring (output) gear via additional gearing in a transaxle. Torque from the internal combustion engine powers the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery if a regenerative braking system is used.

The desirability of combinuing an internal combustion engine with an electric motor is clear, the fuel consumption and emissions from the internal combustion engine are reduced with no appreciable loss of vehicle performance or range.

It is a common feature of all hybrid electric vehicles that the internal combustion engine is stopped whenever possible in order to reduce emissions and fuel consumption and this has the disadvantage that the internal combustion engine is often running below its optimum operating temperature and in particular the oil temperature of the engine is often lower than desirable which increases friction within the engine and thus results in lower overall efficiency.

The cold running of the engine poses a particular problem in the case of a diesel engine because it is common practice for a Diesel engine to inject fuel late in the 206-2010GB2 combustion cycle in a process known as post injection in order to regenerate an exhaust aftertreatment device such as a diesel particulate trap, a NOx trap or a catalytic converter. This post injection of fuel is disadvantageous as it results in the transfer of fuel into the engine oil and the vo]..ume of fuel transferred to the oil tends to increase as the temperature of the oil is reduced.

It is therefore desirable to operate with the maximum possible safe oil temperature when regeneration of the aftertreatment device is required.

It is an object of this invention to provide a method and apparatus for heating the engine oil of an internal combustion engine of a hybrid electric vehicle in an efficient manner.

According to a first aspect of the invention there is provided a method for heating the engine oil of a diesel engine of a hybrid electric vehicle having an electric drive system with a cooling circuit including a heat exchanger arranged to transfer heat from coolant used to cool the electric drive system to the engine oil and the diesel engine has an exhaust aftertreatment device, the method comprising determining whether the temperature of the coolant is greater than the temperature of the engine oil, determining whether regeneration of the exhaust aftertreatment device is required and, if regeneration of the aftertreatment device is required and the temperature of the coolant is greater than the temperature of the engine oil, heating the engine oil prior to commencing regeneration of the exhaust aftertreatment device using the transfer of heat from the coolant to the engine oil.

Using the coolant to heat the engine oil may comprise flowing the coolant arid the engine oil through a common heat exchanger.

206-2010GB2 According to a second aspect of the invention there is provided a hybrid electric vehicle having a diesel engine lubricated by engine oil supplying exhaust gas to an aftertreatment device arid an electric drive system with a cooling circuit having a heat exchanger through which coolant used to cool the electric drive system is selectively passed and a valve conLrolled by a controller to control the flow of coolant through the heat exchanger wherein the heat exchanger is arranged to transfer heat between the coolant and the engine oil and the controller is operable to open the valve so as to allow coolant to flow through the heat exchanger so as to heat the engine oil when the temperature of the coolant is greater than the temperature of the engine oil and regeneration of the exhaust aftertreatment device is to take place.

The controller may be operable to allow coolant to flow through the heat exchanger so as to heat the engine oil prior to commencing regeneration of the aftertreatment device.

The heat exchanger may be a common heat exchanger and the both the coolant and the engine oil are caused to flow through it when regeneration of the aftertreatment device is to take place.

This has the advantage that separate control of the flow of coolant and engine oil through the heat exchanger can be used to control heating of the engine oil. This is not possible if, for example the heat exchanger is located in the oil sump and only coolant is flowed through it.

A second advantage of the invention is that the transfer of fuel into the engine oil can be reduced in the case of regeneration of an exhaust aftertreatment device connected to a diesel engine.

6-2 O1OGB2 The invention will now be described by way of example with reference to the accompanying drawing of which:-FIG.l is a schematic representation a Diesel Hybrid Electric Vehicle according to the invention; Fig.2A is a schematic representation of the cooling circuits associated with an internal combustion engine and electric drive system of the hybrid electric vehicle; Fig.2B is a modified cooling circuit for the electrical drive system; Fig.3 a flowchart showing a method for heating engine oil using coolant from an electric drive system; and Fig.4 is a flowchart showing a method of regenerating an exhaust aftertreatment device using oil heating according to the invention.

With reference to Figs.l and 2 there is shown a diesel hybrid electric vehicle 5 which in this case is of the Parallel/Series Hybrid Electric Vehicle (powersplit) configuration.

The vehicle 5 has a diesel engine 20, the exhaust flow from the diesel engine 20 is passed through an exhaust aftertreatment device, which in this case is a diesel particulate trap 50.

A pump 54 (not shown on Fig.l) is used to circulate the oil from a sump 21 through the oil lubrication circuit of the diesel engine 20 and an engine oil cooler circuit and return the oil to the sump 21.

6-2 O1OGB2 The oil pump 54 may be directly driven by the engine 20 or may be an electric oil pump in which case the oil flow through the diesel engine 20 is controllable by a controller 3 6.

The engine oil cooler circuit comprises the oil pump 54, a radiator 56 and a bypass valve 55 which may be thermostatically or electronically control ted to bypass the radiator 56 when the temperature of the engine oil is below a predetermined temperature so as to speed up heating of the engine oil.

The engine 20 also has a coolant circuit for cooling a cylinder block and cylinder head of the engine 20 comprising a coolant pump 52, a radiator 51 and a bypass valve 53 which may be thermostatically or electronically controlled to bypass the radiator 51 when the temperature of the engine coolant is below a predetermined temperature so as to speed up heating of the engine 20.

An electric drive system 60 which includes a traction motor 30 and may also include other components of the system used to provide electrical drive to the hybrid vehicle 5 such as a generator/motor 25, a battery control module 38 and a transmission control unit 40 has a cooling circuit comprising a radiator 61, a pump 62, a bypass valve 63, a liquid to liquid heat exchanger 70 and an electronically controlled valve 64.

The liquid coolant flowing through the electric drive cooling circuit may be water or oil or any other suitable i i quid.

The controller 36 is operable to receive a number of temperature inputs from sensors 71, 72 and 73 which provide signals indicative of the engine oil temperature, coolant 206-2010GB2 temperature upstream from heat exchanger 70 and downstream from the heat exchanger 70 respectively.

A Planetary Gear Set 26 mechanically couples a carrier gear to the diesel engine 20 via a One Way Clutch 44 and also mechanically couples a sun gear to the generator/motor 24 and a ring (output) gear to a traction motor 30.

The generator motor 24 is also mechanically connected to a brake 22 and is electrically linked to a battery 28.

The traction motor 30 is mechanically coupled to the ring gear of the planetary gear set 26 via a second gear set 32 and is electrically linked to the battery 28. The ring gear of the planetary gear set 26 is mechanically coupled to driven wheels 34 of the vehicle 5 via an output shaft 33.

The traction motor 30 can be used to augment the power from the diesel engine 20 to the drive wheels 34 on a parallel path through the second gear set 32.

Overall system control is performed by the controller 36 which is often referred to as a Vehicle System Controller.

The controller 36 operates all main vehicle components by connecting to each component controller and contains in this case a Powertrain Control Nodule (PCM) although the PCN could he housed in a separate unit.

The controller 36 is connected to the diesel engine 20 via a hardwire interface and is also connected to the battery control unat ("BCU") 38 and the transmission management unit (!!TMUcV) 40 through a Communication Network.

The battery control unit 38 is connected to the battery 28 via hardwire interface and the transmission management 206-20100B2 unit 40 controls the generator/motor 24 and the traction motor 30 via a hardwire interface.

The controller 36 determines when to run the diesel engine 20 in order to provide tractve effort for the vehicle 5 or in order to drive the generator/ motor 24 in oider to recharge the battery 28.

Operation of the hybrid electric vehicle 5 will now be ao described with particular reference to F'ig.2A.

The engine 20 is started and stopped when required by the controller 36 so as to minimise pollution and maximise fuel economy. As will be appreciated by those skilled in the art it is desirable to have the engine oil which is used to lubricate the engine 20 at or close to a preferred operating temperature which is in the region of 100°C in order to minimise friction within the engine 20.

Therefore in accordance with one embodiment of the invention, whenever the engine 20 is running, the controller 36 is operable to determine whether the engine oil is below its preferred operating temperature by using the signal received from the temperature sensor 71 and, if it is determined by the controller 36 that the engine oil temperature is below its preferred operating temperature, the controller 36 is then operable to determine whether the coolant used to cool the electric drive system can be used to heat the engine oil. That is to say, if the electric drive system coolant temperature is greater than the engine oil temperature the heat exchanger 70 can be used to speed up or assist with heating of the engine oil.

In such a case, which will normally exist just after start up from cold of the engine 20 or when the hybrid vehicle is operating in a city environment where the engine has not be used for some time, the controller 36 is 206-2010GB2 operable to cause the valve 64 to be opened so that coolant can flow through the heat exchanger 70 and heat the engine oil.

In a modification to the embodiment described above, the bypass valve 63 is also controlled by the controller 36 and is arranged to prevent the f]ow of coolant through the radiator 61 when heating of the engine oil is required unless the temperature of the coolant exceeds a predetermined maximum safe operating temperature as determined from the signal received from the temperature sensor 73 on the downstream side of the heat exchanger. The maximum safe operating temperature is a temperature above which boiling of the coolant would occur or if the coolant is oil based, deterioration or rapid ageing of the oil will occur.

In either case, during the period when heating of the engine oil by the heat exchanger 70 is occurring, the bypass valve 55 is also open so that substantially no engine oil passes through the radiator 56. The bypass valve 55 can be of a thermostatic type or can be controlled by the controller 36.

In a second embodiment of the invention the oil pump 54 is an electric oil pump and so the engine 20 does not have to be running to cause circulation of oil through the radiator 56 or the heat exchanger 70. In this case, provided the hybrid vehicle 5 is in use, it is possible to use the heat exchanger 70 as the primary cooler for the electric drive system 60 and circulate the electric drive system coolant through the heat exchanger 70. The engine oil is continuously circulated through the heat exchanger 70 even if the engine 20 is not running while the hybrid electric vehicle 5 is in use.

206-201 OGB2 -10 -This has the advantage that the circulating engine oil will keep the engine 20 warmer than it would otherwise be thereby reducing emissions upon start-up and ensuring that when the engine 20 is started the engine oil is already at a temperature well above normal ambient temperature such as for example and without limitation 75°C thereby reducing friction during initial running of the engine 20. In this case, the valve 64 will allow electric drive system coolant to flow through the heat exchanger 70 provided the temperature of the electric drive system coolant is greater than the temperature of the engine oil. If the cooling effect of the heat exchanger 70 is not sufficient to maintain the temperature of the electric drive system coolant below its preferred operating temperature then the controller 36 is operable to close the bypass valve 63 so that coolant flows through the radiator 61 or, if the bypass valve 63 is a thermostatic valve, the temperature of the coolant will automatically close the bypass valve 63 when the coolant temperature exceeds the preferred operating temperature.

In both of the above described embodiments the heat exchanger 70 is used to heat the engine oil so as to reduce friction in the engine 20 and/or reduce emissions upon engine start-up.

Fig.2B shows a cooling circuit for the electrical drive system that is intended as a direct replacement for the electrical drive system cooling circuit shown in Fig.2A.

In accordance with the invention the heat exchanger 70 is used to heat the engine oil when regeneration of the exhaust aftertreatment device 50 is required in order to reduce the volume of fuel transferred into the oil during regeneration.

206-2010GB2 -11 -It will be appreciated by those skilled in the art that in order to regenerate an exhaust aftertreatment device connected to a diesel engine it is common practice to use late or post injection of fuel in order to increase the temperature of the aftertreatment device and that this post injection of fuel often leads to the transfer of fuel into the engine oil. The transfer of fuel into the oil is disadvantageous because a high level of fuel dilution can cause serious engine wear. To avoid such oil dilution induced wear it is common to shorten the interval between engine servicing which is inconvenient to a user of the engine and will increase vehicle running costs.

To assist with oil heating for the purpose of is aftertreatinent regeneration it is desirable if the operating temperature of the electric drive system coolant is greater than the normal operating temperature of the engine oil.

During normal running of the engine 20 and normal operation of the electrical drive system 60 the engine oil is cooled if required by the radiator 56 and the electrical drive coolant is cooled by passing it through the radiator 61.

However, prior to commencing regeneration of the aftertreatment device 50 the controller 36 is operable to switch the flow of the coolant passing through the electrical drive system 60 so that it flows through the heat exchanger 70 and bypasses the radiator 61 provided the temperature of the coolant returning from the heat exchanger is below a maximum operating temperature for the coolant.

If the temperature is above the maximum operating temperature then the bypass valve 63 is closed and the coolant also flows through the radiator 61 before returning to the electrical drive system 60. This maximises the heat transferred to the engine oil from the electric drive system coolant while ensuring that the electrical drive system 60 does not overheat.

206-2010GB2 -12 -Heating of the engine oil prior to regeneration of the aftertreatment device is desirable because the higher the engine oil temperature the lower will be the volume of fuel transferred into the engine oil during regeneration of the exhaust attertreatment device 50.

W] th reference to Fig. 3 there is shown a method for heating engine oil using the systems described above.

The method begins at step 100 which is when the engine is started. The step may be referred to as a key on' step.

The method then advances to step 110 where it is determined whether heating of the engine oil is required.

Heating of the engine oil may be required for several reason but primarily if the temperature of the engine oil is low it is desirable to heat it.

If heating of the engine oil is not required because it is already at its normal working temperature, the method loops around step 110 until heating is required at which point the method advances to step 120.

At step 120 it is determined whether the temperature of the coolant flowing through the electrical drive system is greater than the temperature of the engine oil circulating through the diesel engine 20. If the temperature of the coolant is not greater than the temperature of the engine oil it can not be used to heat the engine oil and so the method terminates at step 160.

If the temperature of the coolant is greater than the temperature of the engine oil then the method advances to step 130.

206-2010GB2 -13 -At step 130, the controller 36 is operable to permit coolant from the eiectric drive system 60 to flow through the heat exchanger 70 so that it can heat the engine oil and advantageously the engine oil is continuously circulated through the engine 20 by an electric oil pump while the hybrid electric vehicle 5 is in use. Alternatively, if an engine driven oil pump is used, although the coolant is circulated through the heat exchanger it will have only a small heating effect on the engine oil until the engine 20 is started and oil is flowing through the engine 20 and the heat exchanger 70.

Then at step 140 it is determined whether engine oil heating is still required. For example, if the temperature is of the engine oil approaches the temperature of the coolant flowing to the heat exchanger 70 from the electrical drive system 60 then further heating of the engine oil by the coolant fiom the electrical drive system 60 is not possible and the controller 36 is operable to stop the flow of coolant from the electrical drive system 60 through the heat exchanger 70 as indicated by step 150. As an alternative example of when heating may no longer be required, if the operating temperature of the engine oil approaches its normal operating temperature heating will no longer be required and the controller 36 is operable to stop the flow of coolant from the electrical drive system 60 through the heat exchanger 70 as indicated by step 150. In either case, if continued heating is required at step 140 then the method returns to step 120.

After step 150 the method ends at step 160 although in practice it may revert to step 110 so that it operates continuously while the hybrid electric vehicle 5 is in use.

With particular reference to Figs.2B and 4 there is shown part of a regeneration method for an exhaust aftertreatment device for a diesel engine that uses the 206-2010GB2 -14 -electric system coolant to heat the engine oil prior to commencing regeneration of the aftertreatment device. The step 220 therefore corresponds generally to the step 130 shown in Fig. 3 and step 250 corresponds to step 150 shown on Fig.3 The method starts at step 200 which is when the engine is started. The step may be referred to as a key on' step.

The method then advances to step 210 where it is determined whether regeneration of the aftertreatment device is required. If regeneration is not required, the method loops around step 110 until regeneration is required at which point the method advances to step 220.

At step 220 the temperature of the oil circulating through the engine 20 is increased from its normal operating temperature range of 90 to 100°C to an elevated temperature in the range of 120 to 150°C by using the heat exchanger 70 to heat the engine oil as previously described with reference to Fig.3. That is to say, the step 110 shown on Fig.3, is in this case is a decision as to whether regeneration of the exhaust aftertreatment device 50 is required. Note that the temperature of the engine oil is increased before regeneration starts to ensure that it is at an elevated temperature when regeneration commences.

At step 230 it is determined using the oil temperature sensor 71 whether the temperature of the oil has reached a predetermined lower temperature limit, which in this case is 120°C and, if the predetermined temperature has been reached, the controller 36 is operable to either directly start post injection of fuel or send a signal to another control unit to start this process as indicated by step 230.

If the temperature has not reached the predetermined 206-2010GB2 -15 -temperature, regeneration is delayed until the engine oil temperature has risen sufficiently.

During the period of time during which regeneration of the aftcrtreatment device 50 is taking place the temperature of the oil is maintained at its elevated temperature which not only reduces the absorption of fuel by the oil but also causes fuel to be evaporated from any oil circulating through the system or being stored in a reservoir such as a sump.

When it is determined that the aftertreatment device has been regenerated, the post injection of fuel is terminated as indicated in step 240.

The temperature of the oil is however maintained at its elevated level for a predetermined period of time after regeneration has ceased in order to further evaporate fuel from the oil. This period may run from the time that post injection ends or may run from the time regeneration starts taking into account a predicted or expected time for regeneration.

As soon as the desired time period has elapsed, the method advances from step 240 to step 250. In step 250 the temperature of the oil is reduced to its normal operating range by, in this case, the closing the valve 64 under the control of the controller 36 so that coolant from the electrical drive system 60 not longer can flow through the heat exchanger 70.

The method then advances to step 260 where it is determined whether the engine 20 is still operating. If the engine 20 is still operating (Key-on =Yes) then the method returns to step 210 but if it is determined that it is not operating (Key-on =No) then it ends.

206-2010GB2 -16 -It will be appreciated that the described method is just one example of a method according to this invention and that the invention is not limited to the steps described or to the order in which such steps are executed.

It will also be appreciated that various cooling system arrangements could he devised to facilitate Iie transfer of heat from the electric drive system coolant to the engine oil and that a method according to this invention is not limited to the systems shown in Figs. 2A and 2B.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

Claims

-17 -Claims 1. A method for heating the engine oil of a diesel engine of a hybrid electric vehicle having an electric drive system with a cooling circuit including a heat exchanger arranged to transfer heat from coolant used to cool the electric drive system to the engine oil and the diesel engine has an exhaust aftertreatment device, the method comprising determining whether the temperature of the coolant is greater than the temperature of the engine oil, determining whether regeneration of the exhaust aftertreatment device is required and, if regeneration of the aftertreatment device is required and the temperature of the coolant is greater than the temperature of the engine oil, heating the engine oil prior to commencing regeneration of the exhaust aftertreatment device using the transfer of heat from the coolant to the engine oil.
2. A method as claimed in claim 1 wherein using the coolant to heat the engine oil comprises flowing the coolant and the engine oil through a common heat exchanger.
3. A hybrid electric vehicle having a diesel engine lubricated by engine oil supplying exhaust gas to an aftertreatment device and an electric drive system with a cooling circuit having a heat exchanger through which coolant used to cool the electric drive system is selectively passed and a valve controlled by a controller to control the flow of coolant through the heat exchanger wherein the heat exchanger is arranged to transfer heat between the coolant and the engine oil and the controller is operable to open the valve so as to allow coolant to flow through the heat exchanger so as to heat the engine oil when the temperature of the coolant is greater than the temperature of the engine oil and regeneration of the exhaust aftertreatment device is to take place.

-18 -
4. A hybrid electric vehicle as claimed in claim 3 wherein the controller is operable to allow coolant to flow through the heat exchanger so as to heat the engine oil prior to commencing regeneration of the aftertreatment device.
5. A hybrid electric vehicle as claimed in claim 3 or in claim 4 wherein the heat exchanger is a common heat exchanger and the both the coolant and the engine oil are caused to flow Lhrough it when regeneration of the aftertreatment device is to take place.
6. A method for heating the engine oil of an internal combustion engine of a hybrid electric vehicle substantially is as described herein with reference to Fig.4 of the accompanying drawing.
7. A hybrid electric vehicle substantially as described herein with reference to Figs.l to 2B of the accompanying drawing.