ES2366156T3 - ELECTRICAL TRACTION. - Google Patents

Abstract

System presenting: a transmission train that includes an internal combustion engine ("ICE") coupled to a transmission input shaft (125) of a transmission (122), the transmission (122) presenting a power take-off port (124), and a transmission output shaft (129) connected to a differential; an electric motor (150); and a transfer device (140) that couples the electric motor (150) to the transmission (122) through the port (124), the system being configured to allow the electric motor (150) to selectively drive the train's output shaft of transmission for at least certain intervals in which the ICE is turned off.

Description

Related Requests

This document is a non-provisional application that claims the benefit of the priority date of US Provisional Application No. 60 / 774,732, by Warner Olan Harris, filed on 2/21/2006, entitled “Hybrid Electric Traction Power System for move tractors of class 7 and 8 by means of a drive motor connected to the power take-off (PTO) of the connection point of the tractor transmission PTO ”.

This document is also a continuation request in part that claims the benefit of the priority date of Warner Olan Harris US Patent Application No. 11 / 374.709, filed on 3/14/2006, entitled “Auxiliary System powered by fuel cell, and method for it ”.

This application also claims priority over US utility application No. 11 / 558,786, filed on 11/10/2006, entitled "Electric Traction."

Background

Field of the Invention

The present invention relates to a transmission train that includes an internal combustion engine ("ICE") coupled to a transmission having an opening, and, more particularly, refers to an electric motor and transfer device that couples the engine electric to the transmission through the opening, allowing the electric motor to selectively drive the transmission train for at least certain intervals in which the ICE is off.

Description of the related technique

Under certain circumstances, ICE-driven trucks are idling for long intervals and sporadically move. This may occur, for example, while waiting in ports and other time-scale areas. In addition, it can occur both for loading and for unloading loads and, also, for both the entry and exit of a time-scale zone. This use of ICEs is undesirable in some aspects. Fuel consumption and emissions of heat, noise and exhaust gases in these situations are very large in relation to the distances that the loads move. However, an economically feasible alternative has not been developed, particularly for loads driven by industrial tractor trailer trucks.

It is known, of course, the use of an electric motor in a relatively small hybrid electric vehicle ("HEV") to support an ICE or even to briefly replace the use of an ICE for traction, that is, to move the vehicle. There are, however, numerous obstacles to the use of electric motors, particularly for applications such as those described above for trucks. For example, truck loads in time-scale areas are potentially much greater than those handled by conventional HEVs.

US Patent No. 5,558,588 ("Schmidt"), while not dealing with all these matters, illustrates how an obstacle related to the transfer of rotating cargo has been treated in the context of HEVs. As Schmidt illustrates, a hybrid transmission for a HEV includes an electric traction motor and a planetary gear unit within the hybrid transmission housing to transfer rotation from the electric motor to the transmission output shaft, which can also be driven by the ICE. Even simply in relation to this single obstacle, Schmidt's teachings may be of limited utility for the problem described above in this document and similar problems. That is, to apply the Schmidt provision to drive a conventional ICE vehicle by an electric motor, the conventional transmission of the vehicle is replaced by the hybrid transmission. Since there are multiple trucks currently in service, this approach does not provide a practical transition to the use of electric motors for this service.

In another prior art arrangement that addresses sporadic and relatively slow movement, US Patent No. 6,269,713 ("Ohke") discloses the addition of a conventional power take-off device ("PTO") for a vehicle of passengers in order to take power from the vehicle's ICE for "slow progress". Ohke further discloses the addition of a hydraulic pump, a hydraulic motor and a secondary transmission coupled to the conventional transmission output shaft of the vehicle to return power from the PTO to move the vehicle in the slow forward mode. Although this provision does not require the replacement of the original vehicle transmission, it has other disadvantages, of which it is not the least that the ICE operates full-time to supply power to the PTO for slow forward. Power losses through the hydraulic pump, hydraulic motor and secondary transmission are also considerable.

Referring to Figure 1A of the prior art, details of a conventional PTO arrangement as shown in Ohke's patent are shown. A transmission 122 has a housing 127 defining a port 124, which is covered by a removable access plate 121. The crankshaft shaft 110 of the internal combustion engine ("ICE") is connected to the transmission input shaft 125 through of clutch 120. In other words, the ICE is coupled through the crankshaft shaft 110 to a transmission train that includes clutch 120 coupled to input 125 of transmission 122.

The transmission 122 has a transfer gear 130 coupled to the input shaft 125. As shown in Figure 1B of the prior art, a conventional power take-off ("PTO") 140, which is a type of transfer device, it has a housing 142 that defines an opening that corresponds to the port

124. The housing 142 is adapted to be screwed to the transmission housing 127 to align the housing 142 with the port 124 so that the gear 141 of the PTO 140 engages with the gear 130 of the transmission 122, as is conventional. This arrangement conventionally allows the power take-off from the crankshaft shaft 110 of the ICE through the PTO shaft 143.

US Patent No. 2,923,171 ("Jedrzykowski") also discloses the use of a PTO for very low speed operation. In the teachings of Jedrzykowski, the application is for a tractor and the low speed operation is referred to as "little by little movement". According to Jedrzykowski, the tractor clutch is disengaged for the mode of movement operation little by little and the PTO is used to transmit power to its drive shaft from an externally mounted electric motor. The electric motor is excited by a generator which, in turn, is driven by the tractor ICE. As in Ohke's teachings, Jedrzykowski's description only deals with a limited set of obstacles in relation to the present problem and also presents the disadvantage that the operation of the ICE ultimately supplies the power for the movement little by little, so that ICE must work full time.

Document US2003162631 describes a hybrid vehicle system that is provided with an internal combustion engine that drives a set of wheels and an electric motor connected to the other wheels through an active clutch system. A power take-off unit is provided to selectively provide torque from the internal combustion engine to the electric motor to operate the engine in a regenerative mode of operation. The active clutch system is selectively engaged and disengaged based on whether the vehicle is operating in an internal combustion engine operating mode, an electric motor operating mode, a combined internal combustion engine and electric motor operating mode , or a regenerative mode of operation.

Document US6484831 describes a hybrid vehicle that includes a power take-off assembly, which is selectively coupled to an induction motor by means of a clutch assembly and that selectively receives a part of the torque produced by the induction motor, effective for operating a Wide variety of utility type sets.

Document DE19528629 describes a hybrid transmission for a vehicle comprising an internal combustion engine, as a primary energy source, and an electric motor, as a secondary. In an operating regime, the internal combustion engine can be decoupled and only the engine can be used. In this regime, the engine speed is monitored and if it exceeds a certain threshold, automatic procedures are invoked to prevent a further increase. One procedure is to reduce the motor current. Other procedures are to switch the engine to a generator or brake mode, re-couple the internal combustion engine, activate a warning light to apply the brakes and activate the automatic braking.

Therefore, it should be appreciated that there is a need for a way to reduce fuel consumption and emissions of heat, noise and exhaust gases in connection with the use of ICEs when they are idling or when they move short distances or at relatively high speeds low. The need is especially pronounced for the transport of large loads by industrial tractor-trailer trucks, particularly in situations such as heavy traffic or in time-scale areas, in which the movement can be sporadic or relatively slow.

Summary of the invention

The invention is precisely defined in system claim 1 and method claim 14. The dependent claims indicate advantageous embodiments of the invention.

Brief description of the drawings

The above and other objectives, aspects and advantages will be better understood from the following detailed description of a preferred embodiment (s) of the invention with reference to the attached drawings. The same reference numbers are used throughout all figures to refer to similar components and features. In the drawings:

Figure 1A illustrates aspects of a prior art transmission train.

Figure 1B illustrates aspects of a prior art transmission train with a PTO.

Figure 2 illustrates certain components and certain aspects of assembly and engagement of an electric traction system for a vehicle, according to an embodiment of the present invention.

Figures 3A and 3B are block diagrams illustrating additional aspects of an electric traction system for a vehicle, according to an embodiment of the present invention.

Figure 4 an electrical schematic diagram illustrating certain control aspects of the electric traction system of Figure 3, according to an embodiment of the present invention.

Figure 5 illustrates certain aspects of an actuator and an articulation to a main engine clutch for the vehicle of Figure 3, according to an embodiment of the present invention.

Figure 6 illustrates a computer system in which at least aspects of control processes of the invention can be implemented, according to an embodiment of the present invention.

Detailed description of the preferred embodiments of the invention

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings illustrating embodiments in which the invention can be practiced. It should be understood that other embodiments may be used and changes may be made without departing from the scope of the present invention. The drawings and detailed description are not intended to limit the invention to the particular form disclosed. On the contrary, the intention is to contemplate all modifications, equivalents and alternatives that fall within the spirit and scope of the present invention as defined in the appended claims. The titles in this document are not intended to limit the content in any way.

Synopsis

According to an embodiment of the present invention, an electric traction system includes an electric motor (referred to herein also as an electric traction motor) to drive a transmission of conventional or original vehicle equipment for traction when the Vehicle is moving slowly, is often idling, or when noise or pollution is a concern. Otherwise, the main traction motor, an ICE, can be started and used normally. During normal operation of the vehicle on the highway or in the city, the electric traction motor can be operated in a second mode as a generator, which is driven by the main traction motor through the OEM transmission, to recharge the system batteries electric traction The system includes a hydrogen fuel cell that also generates electricity and thus reduces the size of the batteries required to run the system's electric traction motor.

A preferred application of the invention is for trucks for industrial use traveling at speeds below approximately 20 miles per hour (32 km / h). However, in various embodiments, the invention can be applied at higher speeds and for different vehicles. For example, in one application, trucks can be driven at least partially by an electric traction motor even at speeds greater than 20 miles per hour when they are near communities where noise or emissions pose a problem, such as a lot of traffic and in densely populated communities near ports, for example, where polluting fog and noise can be particularly problematic. There may be other reasons for at least partially driving a truck or other vehicle by an electric drive motor at speeds greater than 20 miles per hour according to an embodiment of the invention.

Referring now to Figure 2, according to the present invention, the electric traction motor 150 mounted on the chassis rails 156 of a truck is shown. The arrangement of Figure 2 is structurally different from a conventional HEV arrangement, in which a hybrid transmission houses an electric motor and a planetary gear unit that couples the electric motor shaft to the transmission output shaft to transfer rotation from the electric traction motor to the transmission output shaft, which is also driven by the ICE (not shown in Figure 2). The electric traction motor 150 in Figure 2 is external to the transmission housing 127 and is too heavy and large for the housing 127 to reliably support it, since the transmission housing 127 cannot reliably withstand all this cantilever weight In the illustrated embodiment of the invention, the brackets 154 are mounted on the chassis rail 156 of the truck by means of screw clamps 158. In turn, the motor 150 is screwed to the brackets 154 with sufficient margin to allow the transmission train Conventional, which includes transmission 122, moves freely with respect to chassis rail 156 and other components.

The motor 150 is controlled by the control system 160 and is powered by the battery 170, which is a type of power device. The battery 170, in turn, is powered by the hydrogen fuel cell 180, which is another type of feeding device. The engine 150 is provided to drive the transmission output shaft 129 through the gear 141 of the PTO 140 which engages with the gear 130 on an input shaft 125 of the transmission 122. That is, the gear 141 is for transfer rotation from the electric traction motor 150 to the drive shaft 129. The PTO 140 houses the gear 141 in a housing 142 independent of, and bolted removably to the transmission housing 127, so that the gear 141 is aligned to engage with gear 130 through port 124 of transmission case 127.

According to the illustrated embodiment, the electric traction motor 150 is preferably for driving the truck instead of the ICE of the truck, that is, with the ICE off. Therefore, for the electric traction motor 150 to drive the transmission input shaft 125 without rotating the ICE, which is connected to the crankshaft 110, it is desirable to disengage the crankshaft shaft 110 from the input shaft 125 at least Some modes of operation. Accordingly, a shutdown device (not shown in Figure 2) is provided that includes control logic (not shown in Figure 2) to de-excite the electric traction motor 150 in response to the crankshaft shaft 110 by gearing the input shaft of transmission 125, [CHECK THIS] as further described below in this document. A mechanical or electromechanical device (not shown in Figure 2) is also included to hold the clutch 120 in a position where the shaft 110 is disengaged from the shaft 125, thereby satisfying the logic.

Block diagrams

Referring now to Figure 3A, a block diagram of an electric traction system for a vehicle 300 is shown, according to an embodiment of the present invention. The vehicle 300 has a transmission train, which includes a conventional arrangement of the traction ICE 302 coupled to the crankshaft shaft 110, the clutch 120, the transmission input shaft 125, the transmission 122, the transmission output shaft 125 and differential 316. Differential 316 transfers the rotation of the crankshaft shaft 110 to the shafts 318 and, in turn, to the wheels 320. The vehicle 300 also has a conventional 12 VDC battery 310 to supply the conventional electrical system 308 for ignition, lights, etc.

The vehicle 300 includes the electric traction motor 150 to drive the transmission 122 through the PTO 140, as described above. The motor 150 is directly driven by an AC output of a motor controller (not shown in Figure 3A) of the control system 160, which is driven by 144 VDC batteries 170, which are recharged, in turn, by the hydrogen fuel cell 180. Hydrogen fuel cell 180 is fed by a compressed hydrogen container 314. In addition to charging the batteries 170 to supply power for the engine 150, the fuel cell 180 also charges the battery of 12 VDC 310 of the conventional tractor system.

In the illustrated embodiment of the invention, the electric motor 150 is of the alternating current type, so that it can be operated in reverse to generate electricity when the motor 302 is running and the clutch 120 gears the crankshaft shaft 110 with the shaft transmission input 125. When operating in this generation mode, the motor / generator 150 charges the batteries 170 through the control system 160.

The nominal horsepower characteristic of the engine 150 may vary from one embodiment of the invention to the next, depending on the load that needs to be supported and the speed and acceleration required. A fully loaded industrial trailer trailer truck can weigh around

80,000 pounds (36,388 kilograms). (Conventional electric vehicles of around 1800 pounds (816 kilograms) require an electric motor of approximately 50 hp to get and maintain 80 miles per hour (129 km / h) with electric power only). In one embodiment of the present invention, the electric motor 150 is of the direct current type, weighing approximately 180 pounds (81.6 kilograms), and has a nominal power characteristic of 40 hp continuously and 80 hp during Up to two minutes In another embodiment, the electric motor 150 is an alternating current motor with a characteristic of nominal power and at least somewhat similar weight. Obviously, the characteristic of nominal power in CV and its corresponding regime depends on the vehicle and the load.

The capacity in kWh of the batteries 170 may vary from one embodiment to the next, as well as the capacity in kW of the fuel cell 180 and the storage capacity of the container 314. In one embodiment, the batteries 170 have a capacity of 14 , 4 kWh, fuel cell 180 has a capacity of 15 kW, and container 314 has a storage capacity of 1 kg of hydrogen at 300 psi.

Referring now to Figure 3B together with Figure 3A, the vehicle 300 also includes subsystem 304 which includes the air conditioning, clutch, braking and steering subsystems. The refrigerant for cooling, ie air conditioning, of subsystem 304 is compressed by compressor 342 driven by ICE 302, as is conventional. The braking subsystem of subsystem 304 is controlled by air that is compressed by an air compressor 346 driven by ICE 302 and stored in reservoir 347, as is conventional for industrial trucks. The steering subsystem of the subsystem 304 is controlled by a hydraulic actuator (not shown) fed from the reservoir 355 forced by the hydraulic pump 354 driven by the main ICE 302, as is also conventional.

In addition to the conventional arrangement described above for the air conditioning, braking and steering subsystem 304, the illustrated embodiment of the present invention includes auxiliary controllers 306 controlled by control system 160 and powered by batteries 170 for air conditioning operation. , clutch, braking and steering when the ICE 302 is not running. In this electrical mode of operation, the air conditioning compressor 342 is directly driven by an auxiliary electric motor 344 controlled by the control system 160, as described in US patent application number 11 / 374,709 to which it has been made reference above. The auxiliary controllers 306 also include an auxiliary air compressor 348 coupled to the air reservoir 347 by means of a check valve 352, which prevents return flow, and driven by the auxiliary electric motor 350 to provide compressed air in the electrical mode of operation. controlled by the control system 160. The controllers 306 also include an auxiliary hydraulic fluid pump 356 coupled to the hydraulic fluid reservoir 355 by means of a check valve 360, which prevents return flow, and driven by the auxiliary electric motor 358, so that the pump 356 provides driving fluid for braking during the electrical operation of the vehicle 300 controlled by the control system 160.

Control system

Referring now to Figure 4 together with Figures 3A and 3B, a schematic diagram illustrating aspects of the control system 160 is shown to allow operation of a vehicle with an electric traction motor 150, according to an embodiment of the present invention. . System 160 includes a motor controller 406 to provide voltage to control the speed of motor 150. In one embodiment of the invention, motor controller 406 is a Cutler PMC1238. In another embodiment of the invention, the motor controller 406 is a Cutler PMC 1231C. More specifically, the motor controller 406 outputs a voltage to control the speed of the electric traction motor 150 in response to a demand signal. In the illustrated control system 160, an FTR sensor is mechanically, electrically or optically coupled to an accelerator pedal (not shown) of the vehicle so that the resistance or impedance of the FTR varies depending on the placement of the accelerator pedal by the driver , thereby providing a variable demand signal in response to which the output voltage of the motor 406 varies, thereby varying the voltage to the motor 150 so that the vehicle speed is modulated smoothly in response to the demand signal. variable. Varying the voltage may include varying any of, or any combination of, the frequency, the voltage level, or the voltage pulse widths. (The accelerator pedal is a conventional and well-known means of controlling the speed of rotation of an ICE and the resulting speed of a vehicle, such as that of the vehicle controlled by system 160.)

As mentioned above, the auxiliary electric motor 350 drives an auxiliary air compressor 348 to pressurize the air to operate a vehicle braking system, and the auxiliary electric motor 358 drives an auxiliary pump 356 to pressurize the hydraulic fluid to operate. a vehicle power steering system 300 when the vehicle is running through electric traction motor 150. As described hereinbelow, system 160 also includes various controls that provide logical interlocking functions, which receive signals from sensors 330, to ensure the safe operation of vehicle 300, which includes electric traction motor 150, auxiliary controllers 306 and HVAC components, clutch, braking and steering system 304.

VDE key switch

The conventional operation of the vehicle in relation to the switch 402, which is part of the electrical system 308 is described below. Wiring in the conventional 12 VDC electrical system of the vehicle 300, the system 160 features a vehicle diesel engine key switch conventional 402, which has several different positions, three of which are explicitly shown in Figure 4, that is, the "running", "off" and "accessory" positions. A driver conventionally inserts a key into the switch 402, the switch 402 being initially oriented in the "off" position. To start the vehicle, the driver then turns the key clockwise to an "on" position (not shown in Figure 4) to drive a starter motor that moves the crankshaft of the diesel engine of vehicle 302. Then, once the engine 302 maintains its operation by internal combustion, the driver releases the key in the switch 402, which spring backs up to the "running" position shown in Figure 4, a position that is conventionally between the " off ”and the“ start ”position and in which the switch will remain if it is not touched, that is, a position that does not have a spring recoil characteristic. To stop the diesel engine 302 of the vehicle, the driver can turn the key in the switch 402 turn counterclockwise to the "off" position, where the switch 402 will remain if it is not touched. Switch 402 also has an "accessory" position, as shown in Figure 4, which is conventionally to the left of the "off" position, to turn on accessories such as a radio. Conventionally, if the driver turns the key to the "accessory" position, the switch 402 will remain in this position if it is not touched.

VDE key switch logically interlocked with electric traction motor controller

Returning now to a description of an embodiment of the present invention, according to the system 160, the coils of the AC and V relays are wired to the accessory and "running" positions of the switch 402, respectively, so that when the switch 402 is in the "accessory" position the coil of the AC relay is excited and when the switch 402 is in the "running" position the coil of the relay V is excited with 12 VDC, which are supplied conventionally by the 12 VDC battery 310.

The system 160 also includes an auxiliary battery 170 that supplies a first auxiliary voltage for an electric traction system, which includes the electric traction motor / generator 150, with the supplied voltage of 144 VDC shown in Figure 4. (Although referred to as "144 VDC" it should be understood that the voltage supplied by the battery 170 may vary and that the control system 160 can function properly within a range of supply voltages. In one embodiment of the invention , the controller 406 will function properly with a supply voltage of only 84 VDC, for example.) An electronic traction system key switch 404 has a "running" position wired with the 12 VDC supply and in series with a contact normally closed V1 of the relay V mentioned above herein and the relay coil KR, as shown, so that when the switch 404 is in the "running" position, the "running" contacts of the switch 404. Therefore, if relay V is de-energized so that contacts V1 are created, relay coil KR is energized through the 12 VDC supply. Therefore, it should be understood that the relay V provides an interlock so that if the vehicle diesel engine switch 402 is in the "running" position, the relay coil KR is prevented from being excited. (Reference is also made to be deprecated in this document as being "disconnected"). But if the switch 402 of the diesel engine of vehicle 302 is not in the "running" position, the relay V is de-energized so that if the electronic traction system switch 404 is in the "running" position, the coil of KR relay will be excited (also referred to herein as being "connected").

System 160 also includes a wired MC relay coil in the 144 VDC supply in series with the normally open contacts AC1 of the AC relay mentioned above. Therefore, the AC relay provides another interlock. That is, if the switch 402 of the vehicle diesel engine 302 is in the "accessory" position, the relay coil AC is connected, which creates the contacts AC1, thereby connecting the relay MC. But if the switch 402 is not in the "accessory" position, the relay coil AC is disconnected, which breaks the contacts AC1, thereby disconnecting the relay MC.

The normally open MC1 contacts of the MC relay are wired to connect (ie, "create") 144 VDC to the main + terminal of the controller 406, as shown. Also, the parallel combination of the normally open contacts KR1 and KG1 of the relays KR and KG is wired in series with the contacts MC1 to create 144 VDC for a control power terminal CP of the controller 406 and the parallel combination of the Normally open contacts KR2 and KG2 of the KR and KG relays are connected in series with the variable resistance FTR and the input control terminals of the controller 406, as shown.

Therefore, the AC, V, KR, KG and MC relays act together to provide a control logic as further described below so that for the operation of the engine controller 406 the diesel engine switch of vehicle 402 must not be in the "running" position, but instead must be in the "accessory" position, while the electric traction switch 404 must be in the "running" position. That is, to excite the main + and -controller terminals 406, which is required, of course, to control the speed of the electric traction motor 150 via the FTR through the accelerator pedal, the MC1 contacts must be created. To create the MC1 contacts, the MC coil must be connected, of course. To do this, the switch 402 of the vehicle diesel engine 302 must be in the "accessory" position, which connects the AC coil, creating the AC1 contacts and connecting the MC coil.

Additionally, additional 420 shutdown devices are provided in series with the AC1 contacts and the MC coil. These devices 420 can prevent the connection of MC, thereby preventing the motor 150 from starting, or they can interrupt the path for the connection and maintenance of MC, thereby stopping the motor 150 once it is running. Shutdown devices 420 may operate in response to additional sensors 330 that generate shutdown signals indicating the operation of the ICE or a precursor of the operation of the ICE, such as a signal to start the ICE, a clutch position signal, a ICE rotation signal, an ICE ignition signal. However, all or some of the shutdown devices 420 can be overridden by means of override devices 425 for different modes of operation, such as to operate the electric motor 150 as a generator driven by the ICE 302 through the clutch 120, so that the canceled 420 shutdown devices do not stop the engine 150.

The excitation of the main + and - terminals of the controller 406 supplies a main power to the controller 406, but the controller 406 also requires control power for the CP terminal. With the MC1 contacts created, the 144 VDC supply is coupled to the CP terminal through a resistor R of 1000 ohm, 20 watts and this preloads the internal controls of the controller 406 coupled to the CP terminal. This preload is useful for providing a rapid response by the controller 406 for the action of the variable resistance FTR, but does not provide sufficient current to fully operate the controller 406.

In order for controller 406 to function fully, contacts KR1 or KG1 and KR2 or KG2 must be created to supply all power to controller 406, which of course requires that the relay coil KR or the relay coil KG be connected. For this, the diesel engine switch of vehicle 402 must not be in the "running" position, thereby ensuring that relay V remains disconnected and contacts V1 and V2 are created. Also, the electric traction switch 404 must be in the "running" position, which connects the relay coil KR through the created V1 contacts, or in the "generate" position, which connects the coil of KG relay through the V2 contacts created.

The "generate" position of the switch 404 is provided to allow the battery 170 to be charged by means of the ICE 302. That is, in a "generate" operating configuration of the electric traction system, the charging of the battery 170 is allowed. by ICE 302, which includes that transmission 122 engages with ICE 302 through clutch 120 to mechanically transfer power from ICE 302 to engine / generator 150 through clutch 120, so that the engine can be operated / generator 150 as generator.

Controls related to clutch operation

In addition to the controls described above, the system 160 has controls for engaging and disengaging the diesel engine clutch 120 of the main vehicle 302 when in the electric drive system operating mode.

With respect to the controls relating to the operation of the clutch 120, the system 160 includes a clutch actuator 412 mechanically connected with the clutch 120, as explained further in connection with Figure 5 below in the present document. Actuator 412 features a clutch pedal tread coil D and a clutch pedal release coil R. The excitation of the tread coil D causes actuator 412 to extend, thereby actuating the articulation coupled to a pedal of the conventional clutch of the vehicle towards a pedal pedal position in which the crankshaft shaft 110 is disengaged from the transmission input shaft 125. Conversely, the excitation of the release coil R causes the actuator 412 to retract, driving thereby the clutch pedal towards a released pedal position in which the clutch 120 gears the crankshaft shaft 110 with the transmission input shaft 125. Associated with the actuator 412 are the limit switches 416 CD and CR . The limit switch CD opens in response to the arrival of the actuator 412 to a fully extended position, while the limit switch CR opens in response to the arrival of the actuator 412 to a fully retracted position.

With the tread coil D and the release coil R de-energized, the actuator 412 remains in its last position, which tends to retain the clutch 120 trodden to the extent that the actuator 412 has finally operated the clutch pedal for its tread , if that is the case. However, neither the actuator 412 nor the mechanical joint connecting the actuator 412 to the clutch 120 prevents the clutch pedal from being additionally depressed manually if the pedal is not already fully depressed.

Referring now to Figure 5, the articulation of the actuator 412 with the clutch 120 is further illustrated. It should be noted that the illustration is generally indicative of a joint, but is schematic. That is, in figure 5 some mechanical details can be omitted or represented figuratively to more clearly represent particular characteristics and aspects of how the illustrated arrangement works.

In addition to representing the actuator 412 of the present invention and its associated articulation, Figure 5 also represents a conventional joint for the conventional clutch pedal 510 and the conventional clutch 120, as indicated below. To conventionally disengage clutch 120 a driver depresses the conventional clutch pedal 510 in the passenger compartment of the vehicle, thereby producing a disengagement movement 530. The clutch pedal 510 is on the clutch arm 514, which is rotatably fixed. to pivot point 512, so that the disengagement movement 530 transmits a disengagement movement 532 through the clutch arm 514 to the joint 520. The joint 520 has a distal end opposite the engagement of the joint 520 to the clutch arm 514 and rotatably connected 538 to joint 522, as shown. Also, the joint 520 is rotatably fixed to the pivot point.

513. Therefore, the joint 520 transmits a disengagement movement 532 to the articulation 522, producing a disengagement movement 534 in the articulation 522. The articulation 522 has a distal end opposite its coupling with the articulation 520 and rotatably connected to the clutch arm 524, which is rotatably coupled to a clutch 120 and engages with a clutch bearing (not shown) of the clutch 120. In this way the joint 520 transmits a disengagement movement 534 to the clutch arm 524, producing a disengagement movement 536 by the clutch arm 524, which causes the clutch release bearing 120 to disengage the clutch 120, thereby disengaging the crankshaft shaft 110 of the transmission input shaft 125.

According to the illustrated embodiment of the present invention, the actuator 412 and its associated joint are added to the conventional joint described in the preceding paragraph, as follows. Actuator 412 is rotatably secured at one end to the vehicle chassis at pivot point 516. An extendable / retractable shaft 542 of actuator 412 (shown in Figure 5 in its fully retracted position) at the other end of actuator 412 it is secured by the cup 540 to the connection 538 of the joint 520 and 522, so that the joints 520 and 522 have sufficient freedom of movement to allow conventional operation by the pedal 510, as described immediately before, but allowing even to the actuator shaft 542 412 which also transmits the disengagement movement 534 to the joint 522 via the drive shaft 542 towards its fully extended position.

By way of reiteration, the illustrated arrangement of Figure 5 allows conventional freedom of movement of the joints 520 and 522 for the conventional operation of the clutch pedal 510 of the clutch 120 without extending or retracting the shaft 542 of the actuator 412, which has been added to the conventional joint between the clutch 120 and the clutch pedal 510. That is, the cup 540 captures the coupling 538 loosely enough to allow for this conventional freedom of movement but tight enough so that the shaft 542 remain engaged with the coupling 538 throughout the entire conventional movement range of the clutch pedal 510 and the corresponding movement range of the coupling 538. Also, this maintained engagement allows the actuator 412 to provide an alternative means for disengaging and reengaging. of clutch 120. For disengagement, actuator 412 drives articulation 522 in a motion Disengagement 534 extending the shaft 542. Conventional clutch 120 includes a spring retraction mechanism or mechanisms (not explicitly shown in Figure 5) so that the clutch 120 is simply reengaged by simply retracting the shaft 542. That is, the clutch spring recoil mechanism 120 moves the clutch arm 524 to the re-engaged position so that the engagement of the cup 540 and the coupling 538 is maintained even if the shaft 542 is retracted.

The limit switches 416CR and 416CD mounted on the actuator 412 detect the position of the shaft 542, as further explained hereinbelow.

Referring again to Figure 4 together with Figures 3A and 3B, the system 160 includes a relay coil C wired to the 12 VDC supply of the battery 310 in series with the normally open contacts KR3 of the KR relay. Therefore, the relay coil C is connected in response to the connection by the relay coil KR creating the contacts KR3. As described above, the vehicle diesel engine switch 402 that is not in the "running" position disconnects the relay V, creating the normally closed contacts V1, which connects the relay coil KR if the system switch Electronic traction 404 is in the "running" position. Therefore, through the action of the KR and V relays, the relay C is connected in response to the fact that the vehicle diesel engine switch 402 is not in the "running" position and the electronic traction system switch 404 It is in the "running" position. That is, the creation of the KR3 contacts provides a signal indicating the initialization of an "electric traction" mode of operation, that is, a mode in which the movement, that is, the traction, of the vehicle 300 is driven by the electric motor 150.

Relay C has normally open contacts C1 in series with the tread coil D of the actuator 412 and the actuator limit switch 416 CD. Therefore, the contacts C1 are created in response to the connection by the relay C and this excites the tread coil D and causes the actuator 412 to move towards the fully extended position, provided that the clutch actuator 412 does not is fully extended so that the limit switch 416 CD is closed. Once the actuator 412 reaches the fully extended position, the limit switch 416 CD opens and the tread coil D of the actuator 412 disconnects in response.

Once the actuator 412 moves away from the fully retracted position, the actuator limit switch 416 CR is closed so that the release coil R of the actuator 412 can be excited to retract the actuator 412 when necessary. However, in response to the connection by relay C, the normally closed contacts C2 are broken so that the release coil R of 412 will not be energized. In this way, the relay C prevents the actuator 412 from retracting unless either i) the vehicle diesel engine switch 402 is in the "running" position, which connects the relay V that disconnects the relay KR , which, in turn, disconnects relay C, or if not ii) the electronic traction system switch 404 is in the “off” position, which disconnects the KR relay, which, in turn, disconnects the relay C. But in response to either the rotation of the vehicle diesel engine switch 402 to the "running" position or the rotation of the electronic traction system switch 404 to the "off" position, the relay C will be disconnected, which creates contacts C2 so that the release coil R of the actuator 412 will be excited in response through the contacts C2. This moves the actuator 412 to the retracted position until the limit switch 416 CR breaks when it detects that the actuator 412 is fully retracted.

Controls related to the operation of the braking and steering systems

In addition to the controls described above, the system 160 has controls to ensure the operation of the braking and steering components of the system 304 when in the mode of operation of the electric traction system.

As mentioned earlier, the conventional braking system for vehicle 300 includes an air reservoir 347 and a compressor 346 driven by internal combustion engine 302 to supply pressurized air to operate the brakes. The control system 160 provides a mechanism by which air pressure is supplied for braking even if the engine 302 is off. Specifically, the control system 160 provides a mechanism whereby if the air pressure for the conventional braking system of the vehicle falls below a certain predetermined limit, then if the driver depresses the conventional accelerator pedal of the vehicle, a Supplementary air compressor motor 350 to provide supplementary compressed air for the operation of the conventional vehicle brake system.

As also mentioned above, the conventional steering system for the vehicle 300 includes a hydraulic pump 354 driven by the internal combustion engine 302 to supply hydraulic fluid to operate the power direction of the vehicle 300. The control system 160 It also provides a mechanism by which the hydraulic fluid is pumped for steering even if the engine 302 is off. Specifically, the control system 160 provides a mechanism by which if the steering wheel of the vehicle is turned left or right beyond predetermined limits, then if the driver depresses the conventional accelerator pedal of the vehicle, a motor is started of supplementary hydraulic pump 358 to drive pump 356 to provide supplementary hydraulic fluid pressure for operation of the conventional steering system of the vehicle.

Specific details of controls 160 relating to the operation of the braking system are as follows. The FTLS 420 limit switch accelerator pedal can be operated to close its contacts in response to the detection that the driver has stepped on the conventional accelerator pedal of the vehicle. FTLS 420 is in series in the 12 VDC supply with a T relay, so that in response to the FTLS 420 contact, the T contact relay is connected. The connection by the relay T starts the demand for compressed air for the conventional vehicle braking system and hydraulic fluid for the conventional vehicle steering system, as follows.

According to the illustrated embodiment of control system 160 of the present invention, an air pressure switch 418 is coupled to the air supply reservoir 347. The switch 418 makes contact in response to the detection that the air pressure in the reservoir 347 has fallen below a predetermined limit, for example, 100 psi. The normally open contacts T1 of the relay T are in series in the 12 VDC supply with the air pressure switch 418. Also, the relay coil A is in series with T1 and with the switch 418.

Relay A is to initiate the demand for supplementary compressed air for the conventional vehicle braking system. That is, relay A has normally open contacts A1 in series in a 24 VDC supply with an auxiliary air compressor motor 350. Relay A is connected in response to contact of T1 and switch 418, creating contacts A1 and exciting the brake system auxiliary air compressor motor

350. In summary, in response to the driver's tread of the conventional accelerator pedal of the vehicle, if the air pressure drops below 100 psi, for example, the auxiliary air compressor motor 350 is turned on to provide more air for the operation of the conventional brake system of the vehicle.

Specific details of the controls 160 relating to the operation of the steering system are as follows. The normally open contacts T1 of relay T are also in series in the 12 VDC supply with the steering arm limit switches connected in parallel 414SRL and 414 SRR. Also, the relay coil S is in series with T1 and the switches connected in parallel 414SRL and 414 SRR, which are mounted on the conventional steering arm of the vehicle so that the switch 414SRL makes contact in response to the steering wheel rotation towards the left beyond a certain predetermined limit and switch 414 SRR makes contact in response to steering wheel rotation to the right beyond a certain predetermined limit.

The relay S is to initiate the demand for supplementary hydraulic fluid pressure for the conventional vehicle steering system. That is to say, the relay S has normally open contacts S1 in series in a 24 VDC supply with the auxiliary hydraulic pump motor of steering system 358. The relay S is connected in response to the contact of T1 and the switch 414SRL or 414 SRR, creating the contacts S1 and driving the supplementary hydraulic pump motor of steering system 358. In summary, in response to the tread by the driver of the conventional accelerator pedal of the vehicle, if the steering wheel of the vehicle is turned to the left or To the right beyond certain limits, the auxiliary hydraulic pump motor 358 is turned on to provide more hydraulic fluid pressure for the operation of the conventional steering system of the vehicle.

General remarks regarding controls

Note that in Figure 4 there are three different voltage systems, 12 VDC, which is a conventional ICE starter voltage system, 144 VDC and 24 VDC. Higher voltage systems are desirable to provide superior power delivery with a relatively lower current. It is advantageous for relays such as KR, KG, C, etc. provide a capacity of isolation of voltage and of cut of current, in addition to the logical function that realize. For example, it is desirable not to send voltages higher than 12 VDC to the interior of a vehicle.

Modifications and control variations

The description of the present embodiment has been presented for illustrative purposes, but is not intended to be exhaustive or to limit the invention to the manner disclosed. Many modifications and variations will be apparent to those skilled in the art. For example, the controls have been previously described herein in the context of relays with corresponding control related processes of the relay logic type. It should be appreciated that the same logical processes described above can be achieved with different combinations of relays. For example, with appropriate settings it is possible to essentially provide a logical process implemented or by a relay that is excited to initiate an action or a relay that is de-energized to initiate the action. The options may vary depending on various factors, including, for example, the complexity and mode of failure desired.

Likewise, what has been shown previously in this document as relays and relay logic can be implemented at least partially in the form of a built-in controller or other form of computer system that presents corresponding control-related processes of the computer program type. Such a computer system and control processes can be incorporated in the motor controller described above, for example. Additionally, discrete sensors 330 are shown herein to drive various dedicated relays. The signals provided by the sensors 330 may be available on an original equipment data bus supplied by the vehicle manufacturer for input to a control system computer 160.

Referring now to Figure 6, a computer system 600 is illustrated in which the processes relating to the control of the present invention can be implemented, according to an embodiment of the present invention. It should be understood that the term "computer system" is intended to encompass any device that presents a processor that executes instructions from a memory medium, regardless of whether it is referred to in terms of a built-in controller, microcontroller, personal computer system ( safe or not), or in some other terminology. The computer system 600 includes a processor or processors 615, a volatile memory 627, for example, RAM and a non-volatile memory 629. The memories 627 and 629 store program instructions (also known as "software program"), which can be executed 615 processors, to implement various embodiments of a software program according to the present invention. The processor or processors 615 and the memories 627 and 629 are interconnected by bus 640. An input / output adapter (not shown) is also connected to bus 640 to allow the exchange of information between processors 615 and other devices or assembly of circuits The system 600 is also adapted for at least the temporary connection of a keyboard 633, a pointing device 630, for example, a mouse, and a display device 637.

In the illustrated embodiment, nonvolatile memory 629 may include a disk for data storage and an operating system and computer applications. In other embodiments, nonvolatile memory 629 is not necessarily a disk. The operating system can even be programmed in a specialized integrated circuit physical support. Memory 629 also includes a ROM, which is not explicitly shown, and may include other devices, which are not explicitly shown, such as tapes.

The data storage can be performed by one or more processes of the computer system 600 and can include storage in a memory, such as memory 627 or 629, of the same computer system 600 in which the process is running or in a different computer system .

In addition, at least some of the processes related to the control of the present invention may be distributed in the form of a computer-readable medium of instructions executable by a processor to perform a method, that is, a process, as described above in This document. Such a computer-readable medium can have various forms. The present invention applies equally regardless of the particular type of signal carrier means used in practice to carry out the distribution. Examples of tangible computer readable media include recordable media such as a floppy disk, a hard disk drive, a RAM, and CD-ROM. Examples of transmission type media include digital and analog communications links.

Various embodiments implement the software or programs in various ways, including procedure-based techniques, component-based techniques, and / or object-oriented techniques, among others. Specific examples include XML, C, C ++, Java objects and commercial type libraries. Those skilled in the art will appreciate that the physical support depicted herein may vary depending on the implementation. The example shown is not intended to imply limitations in the architecture with respect to the present invention.

Many more modifications and variations will be apparent to those skilled in the art. For example, earlier in this document it has been described to vary the voltage to the electric motor, which allows to change the vehicle speed smoothly in response to a variable demand signal. In one embodiment of the present invention, the controls can be operated to strike the engine with the electric motor to move the vehicle in jerks, that is, simply to excite and de-excite the electric motor at low frequency. The motor controller can achieve these motor blows in response to an on-off demand signal.

Securing the APU in the vehicle

Referring again to Figure 3A, the fuel cell 180 may include other things in an auxiliary power unit ("APU") secured behind a passenger compartment of the vehicle 300 in a chassis of a tractor part thereof. The cabin is also mounted on the chassis. The APU includes a rectangular housing for the fuel cell 180 bolted to respective pneumatic springs located directly under four corners of the housing. The APU additionally includes a spreader to which the pneumatic springs are screwed. Also, two helical springs are connected to the spreader by means of respective ring bolts bolted to one side of the housing near respective corners, so that the connections of the helical springs in the spreader are located such that they keep the helical springs extended downwards. from the bottom of the accommodation and out. In addition to the helical springs that are held by the spreader so that they extend outwardly and downwardly from the bottom of the housing, the helical springs also stretch a little through the spreader, even though they are completely within their elastic limit. In this way, the springs are held in tension and tend to provide forces that oppose each other and keep the housing centered up and pushed down securely towards the pneumatic springs.

The pneumatic springs are interconnected by an air supply line that has a connection through a pressure regulator to connect the pneumatic springs to the conventional compressed air system included in the subsystem 304 for the brakes of the vehicle 300. Thus, After screwing the APU spreader to the chassis, the pneumatic springs can be inflated from the compressed air system, which increases the tension of the helical springs and thereby keeps the housing centered up and pushed down towards the pneumatic springs more safely. It is advantageous for the housing to be secured to the vehicle chassis 300 in this way without any rigid elements, or even piston-type shock absorbers, which can directly transfer shock and shock shocks from the chassis to the housing. Although shock absorbers tend, of course, to absorb shocks of this type in a single direction, they do not tend to prevent movement in some directions, so that they have a greater tendency to transfer forces from some directions that the provision described above. Conventional pneumatic springs are available that are suitable for the use described above, for example, of McMaster-Carr.

General remarks

It should be appreciated from the foregoing that the present invention provides numerous useful benefits, including the following:

A conventional PTO can be added to a conventional transmission through a conventional PTO port to serve as a transfer device in an unconventional way to power a vehicle transmission train from an electric traction motor powered by a device external power, even when the vehicle's ICE is off;

A hydrogen fuel cell in a suitable auxiliary power unit mounted in a vehicle as disclosed herein is durable enough and provides sufficient energy so that it can be provided as an external power device to move even a load. very considerable, such as a fully loaded tow tractor, over a considerable distance or for operation of considerable duration; Y

A battery can provide even more additional energy for instantaneous power demands and can be recharged at appropriate intervals of demand for low or non-electric operation either by the fuel cell or by the ICE through reverse operation of the electric traction motor ; Y

Auxiliary subsystems and controls, including clutch actuation, auxiliary air subsystems and auxiliary hydraulic fluid, are disclosed to allow operation of the electric traction motor coupled to the drive train without interfering with, or in opposition to, the ICE conventional, and to coordinate the safe operation of existing vehicle subsystems with the operating modes of the generator and electric traction motor.

By way of reiteration, the embodiments have been chosen and described to better explain the principles of the invention, the practical application, and to allow other experts in the art to understand the invention. Various other embodiments that present various modifications for a particular contemplated use may be suitable, but may be within the scope of the present invention.

Unless stated clearly and explicitly, the following claims are not intended to imply any particular sequence of actions. The inclusion of labels, such as a), b), c) etc., for parts of the claims does not in itself imply any particular sequence, but is simply to facilitate the reference to the parts.

Claims (18)

1. System presenting: a transmission train that includes an internal combustion engine ("ICE") coupled to a transmission input shaft (125) of a transmission (122), the transmission (122) having a power take-off port (124), and a transmission output shaft (129) connected to a differential; an electric motor (150); Y a transfer device (140) that couples the electric motor (150) to the transmission (122) through the port (124), the system being configured to allow the electric motor (150) to selectively drive the output shaft of the transmission train for at least certain intervals in which the ICE is off. 2. System according to claim 1, comprising: a power device for supplying power to the electric motor, wherein optionally the power device comprises a fuel cell (180); or the power device comprises a battery (170), the system being preferably configured to allow the battery to be charged by the ICE when the ICE is on; or the feeding device comprises: a battery (170); and a fuel cell (180) configured to charge the battery.

3.

System according to claim 1, wherein the transmission train includes a clutch (120) coupled to a transmission input, transferring the transfer device (140) the rotation of the electric motor (150) to the transmission input to move the vehicle; and wherein the system includes a power device (170, 180) electrically coupled to the electric motor to supply power for vehicle movement for at least certain intervals when the ICE is off; and controls (160) configured to selectively allow vehicle movement.

Four.

System according to claim 3 comprising: a motor controller (406), wherein the power device is electrically coupled to the electric motor through the motor controller.

5.

System according to claim 4, wherein the controls are electrically coupled to, and can be operated with, the electric motor controller (406) to drive the electric motor (150) in response to a demand signal, in which optionally The demand signal is a variable demand signal and the excitation of the electric motor includes a variable excitation so that the vehicle speed is modulated in response to the variable demand signal, in which more optionally the controls include: an accelerator; and a variable impedance device, in which the excitation of the electric motor includes a variable excitation and the demand signal includes a variable impedance signal from the variable impedance device, the impedance being varied in response to the accelerator.

6.

System according to claim 4, wherein the controls (160) are electrically coupled to, and can be operated with, the motor controller (406) to de-excite the electric motor in response to a shutdown signal, in which the signal off indicates the operation of the ICE or a precursor of the operation of the ICE; wherein optionally the shutdown signal includes a signal to start the ICE or the shutdown signal includes a clutch position signal, or the shutdown signal includes an ICE rotation signal, or the shutdown signal includes a signal from ICE ignition.

7.

System according to claim 4, wherein the controls (160) comprise: an actuator (412) configured to automatically move the clutch (120) to a position where the ICE is disengaged from the transmission input in response to a signal , in which the signal optionally indicates the initialization of a mode of operation in which the movement of the vehicle is driven by the electric motor (150).

8.

System according to claims 2 and 4, wherein the system is configured to allow the battery to be charged (170) by the ICE, wherein the configuration that allows the battery to be charged by the ICE includes transmission gearing with the ICE through the clutch to transfer power mechanically from the ICE to the engine through the clutch, so that the engine can be operated as a generator.

9.

System according to claim 4, wherein the vehicle includes an air compressor (342) driven by the ICE (302) to supply air to a reservoir for a vehicle braking subsystem, and wherein the electric traction system comprises : an auxiliary air compressor to supply air to the reservoir during at least certain times when the ICE is off; an electric auxiliary air motor for

operate the auxiliary air compressor; and an air pressure switch coupled to the reservoir to start the auxiliary air electric motor in response to a low air pressure; or wherein the vehicle includes a hydraulic fluid pump (354) driven by the ICE (302) to supply fluid to a vehicle steering subsystem, and in which the electric traction system comprises: an auxiliary hydraulic fluid pump to supply fluid to the power steering subsystem for at least certain times when the ICE is turned off; an electric auxiliary hydraulic fluid motor to drive the auxiliary hydraulic fluid pump; and at least one limit switch connected to the steering subsystem to start the auxiliary hydraulic fluid electric motor in response to a position of at least one component of the steering subsystem.

10.

System according to claim 1, wherein the transmission (122) has a housing defining a port

(124) to access the transmission input (125) and the transfer device (140) has a fixed housing to the transmission housing so that the transfer device engages with the transmission input (125) to transfer the electric motor rotation.

eleven.

System according to claim 1 or 10, wherein the motor (150) drives the transmission output shaft

(129) through a gear (141) of the transfer device (140) that engages with a gear (130) in the input shaft (125) of the transmission (122).

12.

System according to claim 11, wherein the transfer device (140) comprises a housing

(142) housing the gear (141), the carcass being independent of, and being screwably removable to, a transmission carcass (127), so that the gear (141) is aligned to engage with the gear (130) ) through the port (124) of the transmission housing (127).

13.

System according to claim 1, wherein the system comprises a clutch (120) between the ICE and the transmission input shaft (125); in which optionally in at least some operating modes the clutch (120) operates to disengage the crankshaft shaft (110) from the input shaft (125), so that the electric traction motor (150) drives the input shaft of transmission (125) without rotating the ICE.

14.

Method to control a traction system for a vehicle, including the system:

-

 a transmission train with an internal combustion engine "ICE" (302) coupled to a transmission having a power take-off port (124); Y

-

 a transfer device (140) that couples an electric motor (150) to the transmission through the port (124),

Understanding the method:

-

 allow the electric motor (150) to selectively drive the transmission train through the power take-off port (124) of the transmission to transfer the rotation of the electric motor (150) to the transmission inlet (125) to move the vehicle during at least certain intervals when the ICE (302) is off, supplying a power device (160, 170) power to the electric motor;

-

 allow the ICE (302) to drive the transmission input (125) and charge the power device (160), when the ICE is on.

fifteen.

Method according to claim 14, wherein the system comprises a clutch (120) between the internal combustion engine ("ICE") and the transmission input shaft (125).

16.

A method according to claim 15, wherein allowing the electric motor (150) to selectively drive the transmission train through the power take-off port (124) comprises transferring the rotation of the electric motor to the transmission input.

17.

Method according to claim 15, wherein the power source comprises a battery (160) and allowing the charging of the power device comprises allowing the battery to be charged by the ICE (302), the transmission being engaged to the ICE through the clutch (120) to transfer power mechanically from the ICE (302) to the electric motor (150) through the clutch so that the electric motor can be operated as a generator.

18.

Method according to claim 14, wherein the electric motor (150) is excited in response to a demand signal, wherein optionally the demand signal is a variable demand signal and the excitation of the electric motor includes a variable excitation of so that the vehicle speed is modulated in response to the variable demand signal.