TECHNICAL FIELD The present invention relates to a hybrid electric vehicle comprising at least one electric motor and at least one combustion engine. The invention also relates to a hybrid electric drive arrangement and to a coupling device.

PRIOR ART

Electric vehicles comprising electric engines for propulsion of the vehicles are known in the art since mid 19th century. Electric vehicles experienced a peak in the beginning of the 20th century, after which they were outcompeted by the combustion engine, mostly due to the increased range provided by the higher energy density in fossil fuels. Combustion engines however have several drawbacks for example in terms of environmental impact, noise and low energy efficiency.

To overcome these problems hybrid vehicles have been developed, which comprises at least one combustion engine and at least one electric motor in the same vehicle for providing propulsion. Such hybrid vehicles combine the characteristics of both electric motor and fossil fuel combustion drive. Hence the vehicles have the advantages of higher efficiency and less noise from using the electric motor, and a longer available range from using the combustion engine. One problem with such hybrid vehicles however is that there is normally little space inside the vehicle so that it is difficult to fit both drive forms inside the vehicle. Another problem is to efficiently connect and combine both power sources into a transmission for providing propulsion to the same drive shaft or shafts. One example of a known type of hybrid vehicle is a series hybrid vehicle, in which the combustion engine drives a generator charging a battery pack, which in turn powers the electric motor. This type of vehicle however suffers from an extensive power loss inherent with the transformation of electricity into battery charge, and the subsequent transformation from battery charge into electricity for the electric motor. The efficiency benefit from this type of vehicle is therefore low. Another example of a known type of hybrid vehicle is a parallel hybrid vehicle, in which both the combustion engine and the electric motor are connected to the same drive shaft via one or more gears and differentials. In mild parallel hybrid type vehicles the combustion engine cannot be turned off, thus increasing environmental impact and noise. For full parallel hybrid vehicles one or more clutches is provided so that the vehicle can be driven by the combustion engine or the electric motor alone or in combination. Series- parallel hybrid vehicles combines the series connection with parallel connection, wherein a generator is connected with the output from the combustion engine, which charges a battery pack for the electric motor, and the outputs from the combustion engine and the electric motor are both connected to a gearbox, which in turn is connected with a differential and one or more drive shafts. These types of vehicles suffer from problems with low power or torque when using only one of the electric motor and the combustion engine. Furthermore, when connecting the combustion engine to provide propulsion while already driving with the electric motor, a shock is created by the difference in rotational speeds, which may damage the engine and also lead to discomforts when driving.

SUMMARY OF THE INVENTION

One objective of the present invention is to indicate a hybrid electric vehicle with an improved transmission and improved performance. According to one aspect of the invention this objective is achieved with the hybrid electric vehicle according to claim 1.

According to a second aspect of the invention this objective is also achieved with the coupling device according to claim 12.

According to a third aspect of the invention this objective is also achieved with the hybrid electric drive arrangement according to claim 15. The hybrid electric vehicle preferably comprises at least one combustion engine, at least one gearbox operably connected with the combustion engine, and at least one differential operably connected with the gearbox and further connected with a first and a second drive shaft for the purpose of propulsion of the vehicle. The hybrid electric vehicle preferably also comprises at least one electric motor arranged to provide propulsion for the vehicle in parallel with the combustion engine.

The invention comprises providing a coupling device arranged to connect an output shaft from the electric motor with an input shaft to the differential in a position after the gearbox of the combustion engine the torque and power generated from the electric motor is thus transferred to the differential directly and therefore with better efficiency. Preferably the coupling device is also arranged to connect the output shaft from the electric motor with the input shaft to the differential without any additional, intermediate gearboxes or planetary gears. Hence transmission losses in any gearboxes or planetary gears are avoided for the power originating from the electric motor, leading to better efficiency and performance for the transmission and for the vehicle. Hence the range of the vehicle, and also the speed regime in which the electric motor may be used, are both increased.

The vehicle is preferrably a parallel hybrid vehicle, wherein the combustion engine and the electric motor both are connected with, and arranged to provide power to, the input of the differential. Preferably the coupling device is designed and arranged to connect the electric motor to the differential so that there is an unchangeable gear ratio between the electric motor and the differential. Preferably the unchangeable gear ratio is 1 : 1. Preferably the coupling device is arranged to connect the electric motor to the differential without any intermediate gears. Preferably the coupling device is designed and arranged to connect the electric motor to the differential rigidly, so that the input shaft of the differential and the output shaft of the electric motor co-rotate, and preferably with the same speed. In one embodiment the input shaft to the differential may be formed from the same shaft as the output shaft from the gearbox, wherein the output shaft from the electric motor also co-rotates with the same rotational speed as the output shaft from the gearbox. Hence the drive arrangement is configured in a configuration of same speed between the electric motor and the output from the gearbox, meaning that the torques from the electric motor and the gearbox may be added together to give an increased acceleration for the vehicle.

According to one embodiment the electric motor is dimensioned so that it may act as the single power source for propulsion of the vehicle at least within a speed range of between 50-70 km/h for the vehicle. Preferably the hybrid electric vehicle is simultaneously arranged to enable driving in an ecologic drive mode, in which mode the combustion engine is shut off and the electric motor acts as the single power source. Preferably the vehicle is thus designed to enable the ecologic drive mode at least within the entire speed range of between 50-70 km/h. Since most traffic within cities is within the speed range of 50-70 km/h it is a huge advantage to be able to drive with only the electric drive at least in this situation. For prior art parallel hybrid electric vehicles the combustion engine normally needs to be turned on and utilised in order to be able to drive the vehicle in speeds in excess of 50 km/h and the electric motor can only be used alone in speeds below 50 km/h. Hence these prior art hybrid vehicles necessarily produce more exhaust gases during normal driving.

In a preferred embodiment the electric motor according to the invention and the hybrid vehicle are dimensioned and designed so that the electric motor may act as the single power source for propulsion of the vehicle at least within the entire speed range of between 50-70 km/h, preferably within the entire speed range of between 50-90 km/h, and even more preferably within the entire speed range of between 50- 1 10 km/h. Preferably the electric motor and the hybrid vehicle are dimensioned and designed so that the electric motor may act as the single power source for propulsion of the vehicle at least when driving the vehicle within the entire speed range of between 20- 1 10 km/h for the vehicle, even more preferably between 0- 120 km/h. Hence the combustion engine is only needed to be turned on when driving in excess of 120 km/h or when the battery power becomes low. Preferably the vehicle is a plug-in hybrid vehicle comprising a battery pack rechargeable with external power. Preferably the battery pack is dimensioned to enable driving with electric power only for at least 30 km in a drive cycle on flat ground, without wind and without accelerations or braking, and more preferably for at least 50 km.

Further advantages and features of the invention are described in the following detailed description.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

The invention is now to be described as a number of non-limiting examples of the invention with reference to the attached drawings.

Fig. 1 shows one example of a vehicle comprising a hybrid electric drive arrangement according to the invention.

Fig. 2 shows another example of a vehicle comprising a hybrid electric drive arrangement according to the invention.

Fig. 3 shows one example of a suitable position for mounting the electric motor relative the differential.

Fig. 4 shows another example of a suitable position for mounting the electric motor relative the differential. DETAILED DESCRIPTION

In figs. 1 and 2 two different examples of hybrid electric vehicles 1 according to the invention are shown. Since the examples are rather like each other both hybrid vehicles are described jointly and are given the same reference numbers, except for in the passages introducing the differences. In general, the hybrid electric vehicle in fig. 1 and 2 comprises a body 3, schematically depicted by the dotted line, forming the bulk of the vehicle and also including any other known components normally included in vehicles, but which are not described here.

The hybrid electric vehicle 1 according to the invention comprises a combustion engine 5, in this example in the form of an internal combustion engine, for converting fuel into mechanical energy. The vehicle further comprises a gearbox 7 operably connected with the combustion engine in order to receive mechanical power and torque from the combustion engine 5, and comprising one or more gears being capable of transforming the received torque and power into an output torque and power based on a gear ratio. The gearbox 7 comprises at least two different gears with different gear ratios, which two or more gears may be changed dependent on the present driving conditions, either automatically (preferred) or manually by a driver. Such gearboxes are also known in the art and are therefore not further described here.

The output from the gearbox 7 is connected with an input to a differential 9 in the vehicle, which differential in turn is connected with first 1 1 and second 13 drive shafts. The differential 9 is designed to transfer mechanical action to the drive shafts and to allow a difference in rotational speed between the two drive shafts depending on the distance travelled by two drive wheels 15, 17. Such differentials are also well known in the art and the differential is therefore not described any closer in this specification. The input and outputs mentioned above are normally formed by shafts mechanically and operably connecting the components, but other forms of connections are also possible. In this example the vehicle 1 comprises a transmission shaft 19 adapted to jointly form the output shaft from the gearbox 7 and the input shaft to the differential 9 as one integral shaft, and to accept power from the gearbox and transmit the power to the differential.

The hybrid electric vehicle 1 also comprises at least one electric motor 21 designed and arranged to provide propulsion for the vehicle 1. The hybrid electric vehicle further comprises a coupling device 23 arranged to connect an output from the electric motor 21 with an input to the differential 9 in a position after the gearbox 7. In this example the coupling device 23 is arranged to connect an output shaft 25 from the electric motor with an input shaft to the differential. Thus the advantages as previously stated in the general description can be achieved. In the example in fig. 1 the coupling device 23 is arranged to connect the electric motor 21 to the differential in a point in between the gearbox and the differential. In this example the coupling device is thus connected to the transmission shaft 19. In the example in fig. 2 however the differential 9 is equipped with a second input shaft 27 allowing for connection with the coupling device 23. Both these versions of the coupling device 23 however are considered to be connected to the differential after the gearbox. Hence the coupling device is arranged to connect the output shaft 25 from the electric motor with the input shaft to the differential 9 without an intermediate gearbox or planetary gear. The torque supplied by the electric motor is thus directly transmitted to the input of the differential without any intermediate gears and without a changeable gear ratio. The coupling device 23 itself is also devoid of any planetary gears so as to reduce transmission losses.

In the examples in figs. 1 and 2 the coupling device comprises a flexible element 29 forming a closed loop and arranged to run on two rounded, preferably circular, transmission members associated with each output and input shafts for transmission of power from the electric motor to the differential. In this example the flexible element 29 comprises a chain made of high-performance metal links for durability and strength, but in another example the flexible element could also comprise bands, such as of rubber or any other material, ribbons, lines or wires. The rounded transmission members may comprise wheels, pulleys, rollers, gears or similar connected with the respective shafts, or possibly the flexible element could run directly onto a surface designed for the flexible element formed on the respective shafts.

The chain drive allow for rigid transmission of the torque from the electric motor 21 to the differential 9 in the sense that any torque applied by, or on, one of the electric motor or the input shaft is directly transmitted to the other. Thus there is less transmission losses between the electric motor and the differential. The input shaft to the differential (19 or 27) and the output shaft 25 from the electric motor are further arranged to co-rotate. In this example the diameter of the transmission members are substantially equal, wherein the gear ratio for the transmission is 1: 1 so that the output and input shafts co-rotate with the same rotational speed. In another example however it is possible to introduce a gear ratio via the chain drive by using different diameters for the two transmission members. The use of a long flexible element formed into a closed loop, such as a chain drive, allows for positioning of the electric motor at a distance from the differential. This in turn allows for using a larger and more powerful electric motor than if positioning the electric motor directly between the gearbox and the differential. In the latter case the size of the electric motor which is possible to mount inside the vehicle is limited both in terms of its height, due to problems with ground clearance, and in terms of its width, due to that all three of the combustion engine, gearbox and motor need to be fitted in one row within the width of the vehicle. In this example the electric motor 21 is at least partly mounted in the same plane along the length of the vehicle as the differential 9, and so that the centre of the electric motor 21 is located above the centre of the differential 9. In figs. 1 and 2 this can be seen as the electric motor 21 is positioned directly above the differential. This means that the space available in the vehicle above the differential may be utilised more efficiently. Thus there are no problems with neither ground clearance nor with sufficient space available in the width direction of the vehicle. Alternative designs comprises that the electric motor, the differential and / or the gearbox may be mounted next to or adjacent to each other, possibly also so that they bear on each other, or, as yet a further alternative, they may be integrated with each other inside one and the same housing. In this example the gearbox is positioned adjacent with and slightly below the combustion engine, the electric motor is positioned adjacent with and slightly above the gearbox, and the coupling device is positioned adjacent to the gearbox and below the electric motor.

In this example the electric motor 21 is dimensioned so that it may act as the single power source for propulsion of the vehicle 1 at least within a speed range of between 50-70 km/h for the vehicle. This is at least in part possible due to the nature of the coupling device 23 and the possibility to position the electric motor where there is more space available so as to allow a larger electric motor. In this example the electric motor 21 is dimensioned so that it may act as the single power source for propulsion of the vehicle at least within the entire speed range of between 0- 120 km/h for the vehicle 1. For a standard personal automobile this may mean that the electric motor needs to have a maximum power output above or equal to 50 kW, preferably above or equal to 65 kW, and/ or have a minimum torque at standstill of above or equal to 300 Nm, preferably above or equal to 500 Nm. In this preferred example the electric motor has a maximum power of between 75- 100 kW.

The hybrid electric vehicle 1 is simultaneously arranged to enable driving in an ecologic drive mode, in which ecologic drive mode the combustion engine is shut off and the electric motor acts as the single power source. In this example the vehicle is designed to enable the ecologic drive mode at least within the entire speed range of between 0- 120 km/h. Hence the hybrid electric vehicle may be driven with electricity alone for almost all drive cycles. One exception is when driving at very high speeds, something which usually is done on motorways or highways, and thus normally entails driving a longer distance and thus demands switching to the combustion engine in any case. The vehicle 1 further comprises a battery pack 35 for storing power to the electric motor. The vehicle is in this example a plug-in hybrid vehicle, wherein the battery pack is rechargeable with power from an external power source via an electrical cable and connector. Preferably the battery pack 35 has an energy capacity allowing driving with electric power alone for at least 30 km, preferably for at least 40 km. For a standard personal automobile the battery is thus capable of storing at least 5 kWh, preferably at least 7 kWh. The estimation of the driving range is in this example performed under the conditions of driving on flat ground in 90 km/h, without any wind, and without accelerating or braking the vehicle.

In this example the combustion engine 5 is dimensioned so that it may act as the single power source for propulsion of the vehicle at least within a speed range of between 50- 120 km/h for the vehicle, preferably within a speed range of between 0- 150 km/h for the vehicle. For a standard personal automobile this may mean that the combustion engine needs to have a maximum power output above or equal to 75 kW, preferably above or equal to 100 kW. In this preferred example the electric motor has a power of 150 kW.

The hybrid electric vehicle 1 is further arranged to enable driving in an extended range drive mode, in which the combustion engine 5 acts as the primary power source while the vehicle allows temporary torque boosts from the electric motor 21 during accelerations at least within a speed range of between 50- 140 km/h.

The vehicle further comprises a clutch 37 arranged in connection with the gearbox 7 to allow decoupling of the mechanical action to or from the gearbox. Hence decoupling and shutting down of the combustion engine 5 is possible for example when driving in the ecological drive mode. The clutch is in this example arranged internally with, and at the output end of, the gearbox. Hence when driving with the electric motor 21 alone both the combustion engine and the gearbox can remain at rest by use of the clutch. The environmental impact from driving the vehicle can then be decreased. In another example the clutch could instead be arranged at the input end of the gearbox. The gears inside the gearbox are then running when driving with the electric motor alone. The clutch may also be provided as a separate component externally from the gearbox.

The hybrid electric vehicle further comprises a second electric motor 39 acting as a starter motor for the combustion engine. The starter motor 39 as such is thus not designed to provide power for propulsion of the vehicle. In case the main electric motor 21 alone propels the vehicle and the combustion engine 5 is off the transmission shaft is still turning. When connecting the combustion engine for power delivery and in case the electric motor is already supplying power to the differential, the vehicle is arranged to first start up the combustion engine by use of the starter motor, secondly automatically control the combustion engine to run at an adapted engine speed, and thirdly to automatically connect the clutch. By including a separate starter motor 39 it is thus possible to start the combustion engine without relying on being actuated by the main electric motor. The combustion engine can then be actuated so as to reach nearly the same rotational speeds for the respective sides of the clutch 37. Thus, when closing the clutch there will be less or no mechanical shocks in the gearbox 7 or in the combustion engine 5 due to different rotational speeds. In this example the adapted speed is such that in case the clutch is positioned after the gearbox, the rotational speed of the output shaft from the gearbox differs less than 10 % from the rotational speed of the input shaft of the differential. In case the clutch is positioned before the gearbox, the adapted speed is such that the output shaft from the combustion engine differs less than 10 % from the rotational speed of the input shaft of the gearbox.

In this example, since the coupling device 23 connects the electric motor to the transmission shaft rigidly, the rotor of the electric motor is rotating even when the vehicle is driven by the combustion engine alone. However, the power developed in the electric motor 21 is controllable so as to be small in comparison to the power needed to drive the vehicle. Furthermore, the electric motor 21 may also be used as a generator, wherein the battery pack 35 may be recharged by the current developed in the electric motor when driving with the combustion engine 5 alone. In another example however the vehicle may comprise a second clutch 37 connected with the electric motor and / or with the coupling device to allow controlled decoupling of the electric motor from the transmission.

In this example, since the coupling device 23 is rigid, the coupling device and the transmission are adapted to add the torques originating from the combustion engine and the electric motor respectively. Hence it is possible to use the electric motor as a temporary torque boost in order to gain additional acceleration. This is very advantageous for example when performing an overtake, which tends to be more dangerous the longer time it takes to perform. In another example the coupling device could instead comprise a mechanism adapted to allow addition of the rotational speeds originating from the combustion engine and the electric motor. Thus the available power is added so that the vehicle can be driven at higher total speeds. The coupling device may then also comprise a clutch connected with the electric motor to allow decoupling of the action from the electric motor. Alternatively the coupling device could comprise a free-wheel mechanism for the electric motor, which would allow the rotor of the electric motor to remain stationary when driving the vehicle with only the combustion engine. In fig. 3 and 4 side views of examples of a hybrid electric drive arrangements 41 according to the invention are shown. As for figs. 1 and 2, the hybrid electric drive arrangements 41 are rather like each other and therefore the arrangements are described simultaneously and with like reference numbers. The hybrid electric drive arrangements are also more or less corresponding with the vehicles 1 as shown in figs. 1 and 2, and the same reference numbers are therefore used and the features and advantages described for the vehicles are also applicable for the drive arrangements 41. In figs 3 and 4 the hybrid electric drive arrangement comprises an electric motor 21 and a coupling device 23. The hybrid electric drive arrangement 41 also comprises a differential 9 connected with a drive shaft 1 1 , 13. The coupling device 23 is adapted to connect an output shaft 25 from the electric motor with an input shaft (19 or 27) to the differential 9. In this example the coupling device 23 connects the electric motor to the input shaft close to the differential, and thus in a position after a gearbox 7 being connected to a combustion engine 5. As is better viewed in figs. 1 and 2, the electric motor 21 is arranged to be at least partly mounted in the same plane along the length of the vehicle as the differential. In figs. 3 and 4 the length direction of the vehicle extends to the left and right and in the plane of the paper sheet, while in figs. 1 and 2, the length of the vehicle extends inwardly into the paper sheet.

The electric motor 21 in the drive arrangement is furthermore positioned so that the centre of the electric motor is located above the centre of the differential 9. In fig. 3 the electric motor 21 is positioned right on top and directly above the differential 9. This is advantageous if there is less space in the lengthwise direction of the vehicle, but more space in the height direction. In fig. 4 the electric motor 21 is instead positioned slightly obliquely above the differential 9. This is advantageous if there is less space in the height direction of the vehicle, but more space in the lengthwise direction. Hence both examples allow for positioning and using of a larger and more powerful electric motor 21. The electric motor 21 is thus dimensioned so that it may act as the single power source at least within a speed range of between 50-70 km/h for the vehicle. In another example the electric motor 21 could also be positioned next to the differential 9 so that the undersides of the motor and the differential are at the same height. Since the motor is normally larger than the differential the centre of the motor would still be above the centre of the differential.

The invention is not limited to the examples and embodiments shown but may be varied freely within the framework of the following claims. In particular, the individual features of one example may be freely transferred to another example, and one or more features may be deleted, added or substituted without departing from the scope of the invention.