EP3030442A2

EP3030442A2 - Hybrid powertrain systems

Info

Publication number: EP3030442A2
Application number: EP14750797.4A
Authority: EP
Inventors: Ian Foley; Angelo Fanourakis
Original assignee: GKN Hybrid Power Ltd
Current assignee: GKN Hybrid Power Ltd
Priority date: 2013-08-06
Filing date: 2014-08-06
Publication date: 2016-06-15
Also published as: CN105579266A; GB201314083D0; GB2517142A; CN105579266B; WO2015019085A3; WO2015019085A2; GB2517142B

Abstract

A hybrid powertrain system for a vehicle (5) includes a hybrid powertrain motor-generator (140) which communicates with a mechanical flywheel unit (7), a vehicle battery or chemical/electrical energy store (15) and a control system (13) via a communication/energy pathway (9).

Description

Hybrid Powertrain Systems

The present inventive relates to hybrid powertrain systems for hybrid vehicles, such as heavy buses, especially vehicles of the type capable of storing kinetic energy, and to hybrid powertrain systems and kits and methods for converting non-hybrid vehicles into such hybrid vehicles.

Many omnibuses (buses) and public service vehicles (PSV) are configured to maximise the passenger space and ensure access to the powertrain for maintenance. For example DE2934314A discloses an arrangement whereby the internal combustion (IC) engine is positioned overhanging the rear axle and transverse to the vehicle centreline. An angled drive is utilised to take the output drive from the engine and in a forward direction via a propeller or drive shaft to the driven axle. Such a layout has become almost a standard in current bus or PSV design. GB2117335A shows a similar arrangement in Figure 2 thereof where the acute angle of the propeller shaft driving forwards to the rear axle can be clearly seen. Further, that figure demonstrates the requirement for the heavy overhanging IC engine and transmission to be appropriately supported and cross braced, to ensure the torque reaction of the drive train is fully resisted by the overhung chassis, specifically item 3a and 23 of Figure 2 thereof.

In DE2934314A and GB21 17335A there is no means to store the kinetic energy of the vehicle, resulting in poor fuel economy.

A light commercial goods vehicle hybrid drive arrangement can be seen in GB2467543A, wherein a belt drive arrangement is used to drive a motor-generator bolted to an axle assembly such that the drive is permanently engaged with the electric motor-generator.

Although such an arrangement may be appropriate for mild or low power assistance hybrid drive arrangements, for example less than 10 or 20 kW of hybrid electric motive power with a limited speed range in a light commercial vehicle with a gross vehicle weight under 3.5 tonnes, the arrangement is not suitable in a heavy vehicle such as a bus which may, even when unarticulated, have an unloaded weight of over 10 or 12 tonnes and a fully loaded gross weight of over 15 tonnes, e.g. with 80 passengers on board weighing approximately an additional 5 tonnes. The arrangement in GB2467543A places bending loads on the rear live axle body for which it may not have been originally designed, as well as lateral loads on the differential input shaft and bearing in order to keep the wheels of the hybrid drive parallel as the belt applies lateral loads to them. The arrangement is only suitable in a vehicle like a light commercial vehicle having the engine at the front of the vehicle and a longitudinally extending propshaft having its axis co-axial with the differential's input shaft such that, as shown in the patent, the propshaft can be directly bolted onto the hybrid wheel on the differential input shaft with the two wheels of the hybrid system kept next to one another with their axes of rotation parallel to one another. Also, the drive belt is only feasible at relatively low torque since it can only transmit and drive at a limited tension. Also, the two hybrid wheels are approximately the same size, set for speed ranges suitable for fast runabout light commercial vehicles but sub-optimal heavy vehicles operated at low average congested inner city speeds with many stops and starts. Also, the mounting of the motor-generator on the axle increases the unsprung weight of the vehicle which can be undesirable for passenger comfort and vehicle handling, and also undesirably shakes the motor-generator. The unsprung weight is also asymmetric which can cause different handling for the two sides of a vehicle. The present invention aims to alleviate at least to a certain extent at least one of the problems of the prior art. Alternatively, the present invention has the aim of providing a useful vehicle.

A first aspect of the invention provides a hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising: a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system being adapted to be substantially fixedly mounted relative to the main support. Advantageously, the hybrid drive system can easily be fitted or retro fitted to a main support or chassis of a vehicle in a fashion in which it is robustly secured, well able to resist torque loads and does not contribute to unsprung weight. Also, when the vehicle is suspended by air suspension, which the present inventors have discovered can be particularly sensitive to high or asymmetric unsprung weight, the unsprung weight can be limited and maintained laterally symmetrical.

The main support may comprise a chassis.

The ground-engaging drive wheel may comprise a rear wheel from which the chassis is suspended by a suspension. The hybrid drive system may be adapted to be mounted to the chassis between the final drive and an engine and/or gearbox mounted to the chassis behind the final drive.

The hybrid drive system may be adapted to be connected to the final drive by a drive or propshaft, the final drive having a live axle, the propshaft optionally being telescopable in length to accommodate movement of the live axle relative to the chassis. The propshaft may have an articulatable drive joint such as a CV or universal joint located at at least one end thereof.

The hybrid drive system may include a motor-generator. The motor-generator may form or be part of the energy receiver.

The motor-generator may be adapted to communicate with an energy store, such as an energy store including a mechanical flywheel. A further aspect of the invention provides a hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising: a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system including a clutch for selectively decoupling an energy path between the final drive and energy store. This advantageously provides for protection of the hybrid drive system when a vehicle to which it is fitted is driven faster than a particular speed. The system may include a control system, the control system being adapted to activate the clutch to decouple the energy path at above a predetermined speed.

The predetermined speed may be a velocity of a vehicle to which the system is mountable.

The predetermined speed may be 50 kph or higher.

The predetermined speed may be 80 kph or higher.

The control system may be adapted to activate the clutch to couple the energy path at below a second predetermined speed.

The second predetermined speed may be 80 kph or lower.

The second predetermined speed may be 50 kph or lower.

The hybrid drive system may have a motor-generator, the clutch being adapted to decouple the motor-generator from the final drive. Thus, the clutch may be used to prevent a shaft of the motor generator from rotating faster than desired.

The hybrid drive system may include a step up ratio drive set adapted to rotate a shaft of the motor-generator more than 50% faster than a propeller drive shaft leading towards the final drive from the hybrid drive system. In this way, when a heavy vehicle routed on a congested stop start route is stationary or at low speed, the motor- generator is able to generate significant electrical energy for storage and/or produce high motive torque and power in an efficient way, yet the clutch can also be used at higher speed to decouple the motor-generator to prevent it from over-speeding. A further aspect of the invention provides a hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising: a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system having a motor-generator and including a step up ratio drive set adapted to rotate a shaft of the motor-generator more than 50% faster than a propeller drive shaft leading towards the final drive from the hybrid drive system. This enables the motor-generator to generate significant electrical energy for storage and/or produce high motive torque and power in an efficient way.

A further aspect of the invention provides a hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the ground-engaging wheel being a rear wheel of the vehicle, the vehicle having an engine and/or gearbox mounted behind the rear axle, the hybrid powertrain system comprising:

a hybrid system having a drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid system being mountable behind the rear wheel between the rear wheel and the engine and/or gearbox. This advantageously allows positioning of the hybrid system in a free space normally taken up by a bus or other vehicle propshaft without intruding undesirably into occupant space.

The system may include a motor-generator.

The drive ratio between a shaft of the motor-generator and an output gear which is adapted to rotate with a propshaft leading to a final drive of a vehicle to which the system is mountable may be a fixed ratio.

Alternatively, the drive ratio between a shaft of the motor-generator and an output gear which is adapted to rotate with a propshaft leading to a final drive of a vehicle to which the system is mountable may be variable, for example by provision of a speed change gear, an epicyclic gear or a variator mechanism.

The system may include drive ratio componentry such that a step up ratio is provided between an input to the hybrid drive system leading from an engine and/or gear ratio change gearbox and an output from the hybrid drive system leading towards a final drive. The system may include drive ratio componentry such that a step down ratio is provided between an input to the hybrid drive system leading from an engine and/or gear ratio change gearbox and an output from the hybrid drive system leading towards a final drive.

A further aspect of the invention comprises a kit of parts for converting a powertrain to a converted hybrid powertrain, the powertrain having a propshaft having an input end leading from an engine and/or gear ratio change gearbox and an output end leading towards a final drive, for example being connected to a differential by an articulatable drive joint, such as a CV or universal joint, the kit comprising:

a system as set out in any preceding aspect hereof.

The kit may further include at least one mount for substantially fixedly securing the hybrid drive system of the system (or at least a casing or section thereof) to a chassis of a vehicle.

The kit may further include two drive shafts which together with the hybrid drive system are adapted to replace the propshaft with the hybrid drive system being located between the two drive shafts in the converted hybrid powertrain. The kit may include a motor-generator adapted to drivingly communicate into the hybrid powertrain at a location between the drive shafts. Each drive shaft may include an articulatable drive joint, such as a CV, universal or flexible joint, at at least one end thereof preferably at both ends. One of the drive shafts may be connectable to a differential of a live rear axle and may be telescopably length-adjustable to accommodate movement of the live axle.

A further aspect of the invention provides a motor land vehicle including apparatus as set out in any previous aspect hereof.

A vehicle may comprise a passenger bus.

The vehicle may have a gross vehicle weight over 3.5 tonnes. The vehicle may have a gross vehicle weight of over 10 tonnes, for example in the region of about 15 to 20 tonnes, such as about 18 or about 19 tonnes. A further aspect of the invention provides a method of converting a vehicle powertrain to a converted hybrid powertrain, the powertrain having a propshaft having an input end leading from an engine and/or gear ratio change gearbox and an output end leading towards a final drive, for example being connected to a differential by an articulatable joint, such as a CV or universal joint, the method comprising replacing the propshaft with (a) a hybrid drive system, (b) a first connection from the hybrid drive system which has an end to replace the input end of the propshaft and (c) a second connection from the hybrid system which has an end to replace the output end of the propshaft.

The method may include securing the hybrid drive system to a main support of the vehicle in a substantially rigid fashion. Said securing may be accomplished in an easily removable fashion, such as by screw bolts, instead of permanently such as by welding.

A further aspect of the invention provides method of converting a hybrid powertrain to a non-hybrid powertrain, the hybrid powertrain having previously been converted in accordance with the previous aspect hereof, the method comprising removing the hybrid drive system and the first and second connections and re-installing the propshaft or one substantially the same thereas. Advantageously, therefore, the vehicle can be converted back to no-hybrid form, for example if it is to be sold or re-routed on a long distance fast country route.

A further aspect of the invention provides a hybrid drive system, for wherein the existing transmission shaft of a vehicle may be removed and replaced with a removable kit of parts consisting at least a motor-generator, an over speed clutch and a speed change gearing system wherein the speed change gearing system allows the motor-generator to be driven or to drive at the more efficient speeds and the clutch is operated to prevent the motor-generator being damaged by excessive rotational speed.

A further aspect of the invention provides hybrid drive method wherein a transmission shaft of a vehicle may be removed and replaced with a removable kit of parts consisting at least a motor-generator, an over speed clutch and a reduction gearing system wherein the reduction gearing system allows the motor-generator to be driven or drive at the most efficient speed and the clutch is operated to prevent the motor- generator being damaged by excessive rotational speed, the motor-generator being operational during low speed stop start driving and the motor-generator being isolated from the drive train during high speed operation of the vehicle.

The low speed operation may be between zero and 80 kph or between zero and 50 kph.

The high speed operation mode may be between 50 kph and 120 kph or higher. The drive ratio between the motor-generator and the output gear may be a fixed ratio.

The drive ratio between the motor-generator and the output gear may alternatively be variable ether by a speed change gear, an epicyclic gear or a variator mechanism

The gear train may be such that a step up ratio is provided between the input and output.

Alternatively, the gear train may be such that a step down ratio is provided between the input and output. At least some preferred embodiments hereof enable good fuel efficiency, especially of vehicles with fuel-burning motive power engines, such as those burning diesel, hydrogen, petrol (octane-based) or other combustible fuels, especially heavy vehicles such as those like buses or PSVs with over 3.5 tonnes, over 7.5 tonnes or over 10 or 15 tonnes gross vehicle weight for example about 12.5 tonnes or about 17 to 18 tonnes gross weight. This is particularly so during multiple stop start operation and low maximum/average vehicle speeds for example as found in a city centre or otherwise congested omnibus route.

In some embodiments, the vehicle kerb weight may be over 3.5 tonnes, over 7 tonnes or over 12 tonnes. At least some preferred embodiments hereof enable a system which optimises or in some cases maximises the electric motor-generator's efficiency range.

At least some preferred embodiments hereof enable the protection of a hybrid power motor-generator from over-speed damage. At least some preferred embodiments hereof enable a system which is easily removable should the vehicle be, for example, taken off a city centre route and sold or used by an operator on long distance high speed routes where the hybrid system would be of a more limited or possibly negative advantage and possibly may be damaged by continued operation at high speed.

The present invention may be carried out in various ways and a number of preferred embodiment of systems in accordance with the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Fig 1 is a schematic representation of the transmission of an omnibus vehicle similar to that disclosed in the prior art;

Fig 2 is a schematic representation of the transmission in fig 1 modified by the application of a hybrid powertrain kit in accordance with a preferred embodiment of the present invention so as to be converted from a non-hybrid bus vehicle to a bus with a hybrid powertrain;

Fig 3 is a schematic enlarged representation of an over speed protection, speed reduction and geared hybrid drive system used in the apparatus of Fig 2;

Fig 4 shows a modified embodiment; and

Fig 5 shows the vehicle in which the apparatus of Figs 2 and 3 is installed.

As shown in Fig 5, a vehicle 5 in the form of a double decker bus has wheels 90, brakes 1 1 , an engine 10, and a hybrid powertrain motor-generator 140 which communicates with a mechanical flywheel (or mechanical energy store) unit 7, a vehicle battery or chemical/electrical energy store 15 and a control system 13 via a communication/energy pathway 9. The motor-generator may send electrical energy to and receive energy from the mechanical flywheel unit 7. The mechanical flywheel unit 7 may include means (not shown) including a further motor-generator for converting electrical energy into mechanical energy by way of spinning up a mechanical flywheel and for later converting the mechanical energy into electrical energy in order to provide electrical power to the motor-generator 140. The motor-generator 140 may comprise a single alternator unit in which the same winding are used for both motoring and generating modes or may in other embodiments be split so as to incorporate a motor and a separate generator.

The vehicle 5 has a kerb weight of about 12.5 tonnes and a gross vehicle weight of about 18 tonnes. In other embodiments, the vehicle may be heavier, for example about 36 or 40 tonnes when the vehicle is, for example a haulage truck, or even heavier, for example when the vehicle is in the form of a heavy construction vehicle.

As shown in Figs 2 and 5, the vehicle 5 has a conventional ladder-like chassis or support frame 71 which supports the vehicle bodywork 73 and occupant accommodation 75. Engine 10 is directly fastened to chassis 71 at mounts 77, 79 as is speed change gearbox 30 at mount 81. The chassis 71 is supported by left and right front wheel/front suspension units 83 and by conventional rear left and right suspension units 85 which are in turn supported by a live rear axle 35 of the vehicle 5 having a generally central differential 70, which may, for example, be of the crown wheel and pinion type and may or may not include limited slip componentry. In other embodiments, the differential need not be central but could, for example, be located approximately one third of the way along the rear axle from one rear wheel 90 to the other. The live rear axle 35 will normally have a conventional rigid tubular body including differential housing and supporting the respective wheel bearings, but may be replaced in other embodiments with an alternative, for example by having the differential 70 substantially fixedly mounted to or relative to the chassis 71 , in which case conventional wheel control components may be employed to control the axis of the rear wheels, for example De Dion tube with Watts linkage and/or Panhard rods, trailing arms, double wishbones etc.

Fig 1 shows the schematic of a type of drive arrangement for a conventional omnibus (bus) or PSV where the internal combustion (IC) engine 10, clutch 20 and speed change gearbox 30 are Overhung' in a cantilever fashion behind the "rear axle" 35 of the vehicle. This provides good space for passengers and or goods between the vehicle wheels and also provides for good access (from rear mounted doors) to service or maintain the IC engine. Figure 1 thus shows the conventional bus prior to conversion into vehicle 5. In this configuration, pre-conversion, an angle drive 40 is located at the output of the speed change gearbox to take the drive through an angle such that the propeller shaft 50 and universal or Hooke's joints 60 transmit the rotational torque to the rear drive axle differential 70 via half shafts 80 to the rear wheel 90 of the vehicle. As such a drive system arrangement is now effectively an industry standard the application of a hybrid drive system to such a transmission with minimum or negligible modification is of significant commercial and environmental benefit.

Fig 2 shows the same layout as found in Fig 1 with the addition of the hybrid drive unit 100. Propeller shaft 50 has now been replaced by two shorter drive shafts 52 and 55, with the two Hooke's joints or constant velocity joints 60 of the original system are retained.

If desired later on, the hybrid unit 100 along with the two short propeller shafts 52 and 55 can therefore advantageously be simply and easily removed and replaced by the original shaft 50 thereby returning the vehicle to its original state. Importantly, the proposed invention not only may be fitted to the vehicle with minimal alteration to the standard transmission but it can also be removed and the original drivetrain reinstated. This may be seen as a significant advantage should the vehicle suffer an unforeseen or complex problem with the hybrid drivetrain or the owner operator may wish to operate the vehicle on a route not advantageous to hybrid operation or even dispose of the vehicle and retain the hybrid system for use on another vehicle.

Fig 3 shows that the hybrid conversion unit 100 in greater detail comprises a casing 101 to which supporting members 103 are affixed. The supporting members are mounted to the chassis 71 , in this example with one supporting member 103 mounted to a longitudinal chassis member 105 and the other supporting members 103 to a cross brace 107. The supporting members 103 are not only used to support the mass of the unit 100 but serve as torque reaction members to prevent rotation of the unit 100 and support and isolate the transmission by suitable rubber mountings (not shown, included as part of members 103) from the chassis 71 (or body in other embodiments) to which they are fixed. The torque reaction members 103 shown in Figs 2 and 3 are by way of an example and may be modified to the individual vehicle as appropriate. In some embodiments, three or four or more supporting members may mount the unit 100 to the chassis 71 at different locations around a periphery of the unit 100. Advantageously, the casing 101 is substantially fixedly mounted to the chassis 71 and does not form part of the unsprung weight of the vehicle 5, such that occupant comfort and handling can be optimised. Further advantageously, drive shaft 55 is provided with a telescoping or splined joint 109 between the CV joints 1 11 , 113 allowing telescoping of the drive shaft 55. In this way, the live axle 35 with differential 70 may move relative to the casing 101 and chassis 71 as the suspension units 85 allow the wheels 90 to move up and down relative to the chassis 71 during use of the vehicle 5. Although, not entirely necessary in some embodiments, a similar telescoping or splined joint 1 15 may be used in the drive shaft 52 to limit stress on the supports 103, 79, 77, 81 by allowing a slight relative motion between the casing 101 and the relatively unitary and rigid power unit 1 17 made up by the engine 10, clutch 20, gearbox 30 and angle drive unit 40. The configuration described ensures that a substantially rigid and unitary main tube casing 37 of rear axle 35/differential 70 is not subject to stresses for which it may not have been designed and that undesirable lateral loadings are not applied to input shaft 39 of differential 70 or its bearing 41. Motor-generator 140 is not subjected to high acceleration incurred on bumps by the axle 35 and can if desired be housed in a dry area away from road or site pollutants and water spray.

Input/output shafts 52 and 55 are connected to a gear train 106, 11 1 , 120, 110, 105 having input/output gears 105 and 106, and intermediate input/output gears 1 10 and 11 1.

An intermediate gear 120, which is rotatingly fixed between gears 1 10 and 11 1 and is coaxial therewith, is engaged with an input/output motor-generator gear 125 which is rotatingly fixedly and releasably linked via a clutch 130 to the electric motor-generator 140.

The motor-generator 140 in this embodiment is rated as cable of motoring up to 120 kW and generating at up to this value or lower, although in other embodiments for heavy vehicles with over 3.5 tonnes gross vehicle weight, e.g. over 10 tonnes such about 18 to 20 tonnes, rated values in the region over 20kW, over 50kW, over 75 kW, over 100 kW or over 150 kW, such as 200 kW or 250 kW are envisaged, as are other values. In the present example, the engine 10 is able to delivery about 160kW (brake), such that the motor-generator 140 at 120kW is able to provide a boost of about 75%, the boost being generally in the region of 33 to 125%, or about 50 to 90% or about 65 to 85% in some other envisaged examples. Despite the very high power and torque which the motor-generator 140 is able to communicate with the shaft 55 and differential 70, with the stiff casing 101 mounted firmly at the support members 103 (albeit partly by heavy duty rubber components) to the strong chassis 71 , since a plane passing through the mounts 103 is substantially or generally perpendicular to the line between CV joint 1 11 closest to the differential 70 and CV joint 117 closest to the angle drive, the motor-generator hybrid unit 100 can easily counter the effects or torque during operation without undesirably stressing or twisting the support members 103, with the casing 101 generally staying stationary relative to the chassis 71.

In non-hybrid operation the internal combustion engine 10 drives the input shaft 52 to rotate the gear train 106, 1 11 , 120, 110 and 105. The gears 106, 1 11 , 120, 110 and 105 may be chosen to provide a 1 to 1 ratio between the input output shafts 52 and 55 or a step up or step down ratio may for example be desirable.

In Fig 3, gear 106 has the same number of teeth and general diameter of each of the gears 1 11 , 105, 1 10. Thus, shaft 52 and shaft 55 always rotate at the same speed. Gear 120 has five times as many teeth as and five times the general diameter of gear 125 such that gear 125 (and shaft 131 onto which gear 125 is rotationally fixed) rotate five times faster than gears 1 11 , 120, 1 10 and shafts 52,55. As desired, gear 106 may be made larger/smaller and gear 11 1 smaller/larger (with both rotating on the same axes as in Fig 3) to provide a step up. Gear 110, 105 may be similarly altered in a very simple way. Thus, the powertrain can easily be designed to optimise the efficiency, power and torque characteristics of the IC engine 10 and the motor-generator 140 for a particular envisaged bus routing or other vehicle activity, taking into account hills, expected speeds, amount of congestion and stop start frequency. Since the replacement of the propshaft 50 with the various components of the present embodiments provides for more torque to the rear axle 35 with the engine 10 and motor-generator 140 used together, the rotational speed of the engine 10 may be shifted down by for example 1 to 15%, typically 2 to 10%, about 2%, about 4% or about 6% being some examples. Thus, the engine 10 may itself be more economical and the loss of torque and/or power (at low speed from) the engine applied at the rear axle 35 may be made up by the motor-generator 140. In the non-hybrid operational mode a clutch 130 may be opened to disconnect the motor-generator drive gear 125 from the motor-generator 140. In this way the motor/ generator 140 cannot be damaged by running over its maximum operational speed should the vehicle be driven at for example continuous motorway road speed, for example over 80 kph or up to 100 kph or even higher speeds. When the vehicle 5 is decelerating, e.g. an over run condition, where the kinetic energy stored in the moving mass thereof is driving through the transmission in the opposite direction, the energy is transmitted or resisted by the engine 10 and lost.

In a hybrid state of the system with safe speed within an optimum range, such as below 80 kph, the clutch 130 may be closed to drive the motor-generator 140 which will load up the drive train and provide power to the motor-generator 140 to charge up a hybrid storage system via energy path 9. The gear drive train motor-generator gear 125 and the intermediate gear 120 may be chosen to provide for example a ratio of 2 to 1 or 4 to 1 or even higher such that on the over run (charging) the motor-generator 140 is rotated at sufficient speed to optimise charge rate even if the vehicle is only moving at a low speed for example 30kph or 50 kph or well below these speeds.

During a driving (motoring) mode the motor-generator may be operated at high speed to maximise the power efficiency through the reduction gearing to provide high power and high torque at low vehicle speed.

The energy storage system 7 is in the present embodiment in the form of an electrically driven high speed flywheel 7, although various other arrangements are considered including a super capacitor or a chemical battery storage device. In present example, the flywheel 7 has an accessible energy storage capacity of about 1.3MJ over a useable range of 18,000 to 36,000 RPM, enabling a power boost into the transmission of about 120KW for about 10 to 12 (or roughly 11) seconds. Thus, with the 18 tonne vehicle 5 stationary at a bus stop with the flywheel at 36,000RPM and the engine 10 off, the flywheel 7 and motor-generator 140 are able with such an approximately 11 -second boost able to accelerate the vehicle to roughly 40kph (about 10 to 12 m/s) along a horizontal road before the engine 10 needs to start. With the vehicle 5 at kerb weight of about 12.5 tonnes, the boost may accelerate the vehicle to about 50kph (about 12 to 14.5 m/s) in about 10 to 12 seconds before the engine 10 needs to start. Thus, in stop-start traffic generally below 50 (or 40 or 30) kph, starting actuations of the engine 10 can be minimised subject to the control system 13 keeping the flywheel between 18,000 and 36,000 RPM. The energy storage system 7 may have different capacities in other embodiments, such as about 0.5 to 3MJ, about 0.75 to 2MJ, some examples being in the range of 1 to 1.5MJ

The hybrid state thus includes an energy recovery mode wherein the kinetic energy stored in the mass of the vehicle 5 may be captured. Further the system may also act as a retarder slowing the vehicle 5 without the need to use friction brakes 1 1 of the vehicle 5 or at least partly to store energy in the store 7 while the friction brakes 11 are operated, such that the loss of energy as heat via the friction brakes 11 and/or by engine braking (friction in or resistance from) can be limited.

The hybrid unit 100 may be operated in several energy use modes. For example, in a hybrid assistance mode the storage system 7, under control of an electronic control system 18, powers the motor-generator 140 to drive through clutch 130 to reduction gear 125 onto the intermediate gear 120 to drive the vehicle 5 whilst at the same time power is provided via the shaft 52 from the internal combustion engine 10 to the output shaft 55. In this mode the omnibus can therefor advantageously benefit from stored energy to offset fuel consumption of the IC engine 10.

Further if the IC engine 10 is turned off (for example automatically by the control system 13 in response to signals from the mechanical flywheel unit 7 and/or the battery 15 indicating stored energy above a predetermined level and an indication of zero vehicle speed and/or hand brake or park brake selected) the vehicle 5 may be driven in a fully hybrid vehicle mode to accelerate the vehicle 5 or to move the vehicle for example in stop start traffic therefore minimising emissions and preventing unnecessary starting of the IC engine 10 with electrical energy being fed into the motor-generator 140 to accomplish this from the electrical store 15 or energy store 7. When the energy store 7 is a mechanical flywheel, energy may transmitted along energy path 9 to a rotor 141 of the motor-generator 140 to accomplish this. Further, should the electrical store 15 be undercharged and a predicted requirement for hybrid use is signalled by the control system 13, it is possible to operate the IC engine 10 to drive both the vehicle 5 and charge the storage system 7 at the same time. Also, the control system 13 may be arranged for electrical energy to be sent from an alternator (not shown) mounted to the engine 10 to the electrical store 15 and/or the storage system. The IC engine 10, which may for example be arranged as a reciprocating engine to combust diesel, LPG, petrol (octane), biofuels or other fuel in air, may be replaced in other embodiments by other forms of engine such as a gas turbine engine, external combustion engine (e.g. Stirling Cycle) or fuel cell such as a hydrogen fuel cell, or may be an engine incorporating more than one of these systems.

Instead of using gears in the hybrid unit 100, interconnected rollers or pulleys may be used instead. Use of a hydraulic interconnection system within the hybrid unit 100 is also envisaged as an alternative or in addition. For example, a torque converter could be used, for example between the motor-generator 140 and mechanically-connected parts of the powertrain.

Various modifications may be made to the described embodiments without departing from the scope of the invention as defined by the accompanying claims.

Claims

1. A hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising:

a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system being adapted to be substantially fixedly mounted relative to the main support.

2. A system as claimed in claim 1 in which the main support comprises a chassis.

3. A system as claimed in claim 2 in which the ground-engaging drive wheel comprises a rear wheel from which the chassis is suspended by a suspension.

4. A system as claimed in claim 2 or claim 3 in which the hybrid drive system is adapted to be mounted to the chassis between the final drive and an engine and/or gearbox mounted to the chassis behind the final drive.

5. A system as claimed in claim 2 or claim 3 or claim 4 in which the hybrid drive system is adapted to be connected to the final drive by a propshaft; the final drive optionally having a live axle, the propshaft being telescopable in length to accommodate movement of the live axle relative to the chassis.

6. A system as claimed in any preceding claim in which the energy receiver includes a motor-generator.

7. A system as claimed in claim 6 in which the motor-generator is adapted to communicate with an energy store, such as an energy store including a mechanical flywheel.

8. A hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising:

a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system including a clutch for selectively decoupling an energy path between the final drive and energy store.

9. A system as claimed in claim 8 which includes a control system, the control system being adapted to activate the clutch to decouple the energy path at above a predetermined speed.

10. A system as claimed in claim 9 in which the predetermined speed is a velocity of a vehicle to which the system is mountable.

11. A system as claimed in claim 10 in which the predetermined speed is 50 kph or higher.

12. A system as claimed in claim 10 in which the predetermined speed is 80 kph or higher.

13. A system as claimed in an y one of claim 9 to 12 in which the control system is adapted to activate the clutch to couple the energy path at below a second predetermined speed.

14. A system as claimed in claim 13 in which the second predetermined speed is 80 kph or lower.

15. A system as claimed in claim 13 in which the second predetermined speed is 50 kph or lower.

16. A system as claimed in any one of claims 8 to 15 in which the hybrid drive system has a motor-generator, the clutch being adapted to decouple the motor- generator from the final drive.

17. A system as claimed in claim 16 in which the hybrid drive system includes a step up ratio drive set adapted to rotate a shaft of the motor-generator more than 50% faster than a propeller drive shaft leading towards the final drive from the drive hybrid system.

18. A hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the hybrid powertrain system comprising:

a hybrid drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid drive system having a motor-generator and including a step up ratio drive set adapted to rotate a shaft of the motor-generator more than 50% faster than a propeller drive shaft leading towards the final drive from the hybrid drive system.

19. A hybrid powertrain system for a hybrid powertrain having an energy receiver for adapting kinetic energy for transmission to an energy store, the powertrain having an engine adapted to drive a ground-engaging drive wheel via a final drive, the vehicle having a main support for supporting occupant accommodation and/or bodywork thereof, the ground-engaging wheel being a rear wheel of the vehicle, the vehicle having an engine and/or gearbox mounted behind the rear axle, the hybrid powertrain system comprising:

a hybrid system having a drive system for drivingly communicating energy passing between a final drive of such vehicle and an energy store, the hybrid system being mountable behind the rear wheel between the rear wheel and the engine and/or gearbox.

20. A system as claimed in claim 18 or claim 19 which includes a motor-generator.

21. A system as claimed in any one of claims 6, 16 and 20 wherein the drive ratio between a shaft of the motor-generator and an output gear which is adapted to rotate with a propshaft leading to a final drive of a vehicle to which the system is mountable is a fixed ratio.

22. A system as claimed in any one of claims 6, 16 and 20 wherein the drive ratio between a shaft of the motor-generator and an output gear which is adapted to rotate with a propshaft leading to a final drive of a vehicle to which the system is mountable is variable for example by provision of a speed change gear, an epicyclic gear or a variator mechanism.

23. A system as claimed in any preceding claim which includes drive ratio componentry such that a step up ratio is provided between an input to the hybrid drive system leading from an engine and/or gear ratio change gearbox and an output from the hybrid drive system leading towards a final drive.

24. A system as claimed in any one of claims 1 to 22 which includes drive ratio componentry such that a step down ratio is provided between an input to the hybrid drive system leading from an engine and/or gear ratio change gearbox and an output from the hybrid drive system leading towards a final drive.

25. A kit of parts for converting a powertrain to a converted hybrid powertrain, the powertrain having a propshaft having an input end leading from an engine and/or gear ratio change gearbox and an output end leading towards a final drive, for example being connected to a differential by a CV or universal joint, the kit comprising:

a system as claimed in any preceding claim.

26. A kit as claimed in claim 25 which further includes at least one mount for substantially fixedly securing the hybrid drive system of the system to or relative to a chassis of a vehicle.

27. A kit as claimed in claims 25 or claim 26 which further includes two drive shafts which together with the hybrid drive system are adapted to replace the propshaft with the hybrid drive system being located between the two drive shafts in the converted hybrid powertrain.

28. A kit as claimed in claim 27 in which one of the drive shafts is connectable to a differential of a live rear axle and is telescopably length-adjustable to accommodate movement of the live axle.

29. A motor land vehicle including apparatus as claimed in any preceding claim.

30 A motor land vehicle as claimed in claim 29 which comprises a passenger bus.

31. A motor land vehicle as claimed in claim 29 or claim 30 which has a gross vehicle weight over 3.5 tonnes.

32. A motor vehicle as claimed in claim 29 or claim 30 which has a gross vehicle weight of over 10 tonnes, for example about 18 tonnes.

33. A method of converting a powertrain to a converted hybrid powertrain, the powertrain having a propshaft having an input end leading from an engine and/or gear ratio change gearbox and an output end leading towards a final drive, for example being connected to a differential by a CV or universal joint, the method comprising replacing the propshaft with (a) a hybrid drive system, (b) a first connection from the hybrid system which has an end to replace the input end of the propshaft and (c) a second connection from the hybrid system which has an end to replace the output end of the propshaft.

34. A method as claimed in claim 33 which includes securing the hybrid drive system to a main support of the vehicle in a substantially rigid fashion.

35. A method of converting a hybrid powertrain to a non-hybrid powertrain, the hybrid powertrain having previously been converted in accordance with claim 33 or claim 34, the method comprising removing the hybrid drive system and the first and second connections and re-installing the propshaft or one substantially the same thereas.

36. A hybrid powertrain system substantially as described herein with reference to Figures 1 to 3 and 5 of the accompanying drawings or as modified substantially as described herein with reference to Figure 4.

37. A kit of parts for converting a powertrain to a converted hybrid powertrain, the kit being substantially as described herein with reference to Figures 1 to 3 and 5 of the accompanying drawings or as modified substantially as described herein with reference to Figure 4.

38 A motor land vehicle substantially as described herein with reference to Figures 1 to 3 and 5 of the accompanying drawings or as modified substantially as described herein with reference to Figure 4.

39. A method of converting a powertrain to a converted hybrid powertrain, the method being substantially as described herein with reference to Figures 1 to 3 and 5 of the accompanying drawings or as modified substantially as described herein with reference to Figure 4.