Patent Description:
Although the invention will be described mainly with respect to semi-trailer vehicles and trucks, the invention is not restricted to this particular type of vehicle but may also be used in other types of vehicles.

A semitrailer vehicle normally comprises a tractor arranged to tow a trailer unit via a fifth wheel connection. In order to extend the cargo transport ability of the semitrailer vehicle, a dolly vehicle unit can be added to the vehicle combination, which allows for additional trailer units to be towed by the same tractor. A traditional dolly is an unpowered vehicle unit designed for connection to a tractor unit, truck or prime mover vehicle with strong traction power.

Dolly vehicles comprising on-board energy sources such as electric machines and dolly vehicles with one or more steered axles have recently been proposed. Such dolly vehicles can provide additional power to the vehicle combination, thus reducing the traction power requirements imposed on the prime mover vehicle. Electrified dolly vehicles may also reduce overall fuel consumption by the vehicle combination, since they provide a degree of hybridization to conventional diesel-engine powered tractors. Steered axle dolly vehicles may furthermore be used for improved steering of the vehicle combination, e.g., when negotiating sharp curves.

<CIT> relates to self-powered steerable dolly vehicles. Methods for controlling the dolly vehicles in order to, e.g., negotiate sharp turns, are disclosed. Methods for controlling propulsion and regenerative braking operations in dependence of an upcoming vehicle route to be travelled by the dolly vehicle are also discussed.

<CIT> relates to an electric vehicle propulsion system featuring two electric motors, each with their own output shaft and reduction gearbox. These motors can be selectively coupled, and their output shafts can also be connected by a third coupling system.

<CIT> relates to a multi-motor drive in which two electric motors which are assigned to a common output with a dual-stage gearbox are provided. An automatic controller controls the load distribution between the motors and the gearbox in order to ensure an optimum degree of efficiency of the drive.

<CIT> relates to a vehicle powertrain with two electric machines connected to separate input shafts of a transmission. The first torque path has one gear ratio, while the second has two selectable gear ratios.

<CIT> relates to an active converter dolly for tractor-trailers, designed to connect a first trailer to a second trailer. It includes a kinetic energy recovery device to convert mechanical motion into electrical energy for charging batteries or powering functionalities.

However, there is a need for further development and optimization of self-powered dolly vehicles in order to improve performance over a wide span of driving scenarios where self-powered dolly vehicles may be used to boost overall vehicle performance.

It is an object of the present invention to provide electrified dolly vehicle units with improved propulsion arrangements which allow higher performance over a wide range of vehicle speeds.

This object is at least in part achieved by a propulsion arrangement for a self-powered dolly vehicle unit being defined in claim <NUM>.

The propulsion arrangement comprises a first electric machine, a second electric machine, a gearbox, and an open differential for driving first and second wheels of a driven axle. The first and second electric machines are arranged in parallel and connected to the open differential via the gearbox at respective gear ratios. This arrangement with two motors arranged in parallel to power a driven axle via a gearbox and an open differential provides great flexibility for supporting both startability of a combination vehicle and also operation at higher vehicle speeds, such as for highway cruising.

The first electric machine is associated with a fixed gear ratio and the second electric machine is associated with a configurable gear ratio. By allowing for a change of gears of at least one of the electric machines, the propulsion arrangement can be further adapted to support both starting from stand-still and highway driving scenarios in an efficient manner, which is an advantage. For instance, the configurable gear ratio of the second electric machine can be made selectable between a second gear ratio and a third gear ratio. This allows for a design with a relatively low complexity control unit which controls the gearbox to switch gears for the second electric machine in dependence driving scenario.

The control unit is arranged to determine if the dolly vehicle unit is in a low speed range of operation or in a high speed range of operation, and it is configured to set the configurable gear ratio of the second electric machine in dependence of the low or high speed range of operation and to drive the wheels of the self-powered dolly vehicle unit by the motors, wherein a low speed range of operation entails a wheel rotational speed of less than <NUM> rpm and a high speed range of operation entails a wheel rotational speed of more than <NUM> rpm.

The control unit may for instance be arranged to set the configurable gear ratio of the second electric machine in dependence of an electric machine axle speed of the second electric machine.

The dolly vehicle unit speed can be measured with wheel speed sensors on the dolly, which means that the control of the dolly vehicle unit gears can advantageously be performed in a stand-alone manner independent from the control of the prime mover. However, additional advantages may be obtained if the control of the dolly vehicle unit is coordinated with that of the prime mover and also that of other vehicle units in the vehicle combination.

Advantageously, the first and second electric machines and the gearbox can be integrally formed as a single module. This single module simplifies dolly vehicle assembly.

According to aspects, the propulsion arrangement comprises an electrical energy source. The first and the second electric machines may then be configurable in a propulsion mode of operation where positive torque is generated and power from the energy source is consumed, and in a regenerative braking mode of operation where negative torque is generated and power is fed to the energy source, thereby replenishing the energy source. The gearbox may thus be used to optimize both propulsion and braking by selecting a suitable gear ratio for the operation at hand.

The above mentioned problems are further solved by the self-powered dolly vehicle unit defined in claim <NUM>, the method defined in claim <NUM> for operating a self-powered dolly vehicle unit, and the control unit defined in claim <NUM> and configured to perform the method.

Advantageous embodiments of the invention are laid down in the dependent claims.

<FIG> illustrates an example vehicle combination <NUM> for cargo transport. The vehicle combination <NUM> comprises a truck or towing vehicle <NUM>, i.e., a prime mover, configured to tow a first trailer unit <NUM> in a known manner, e.g., by a fifth wheel connection. To extend the cargo transport capability of the vehicle combination <NUM>, a dolly vehicle <NUM> can be connected to the rear of the first trailer <NUM> via a drawbar. This dolly vehicle can then tow a second trailer <NUM>, thus increasing the cargo transport capacity of the vehicle combination.

A dolly vehicle <NUM> is traditionally a passive vehicle comprising no driven or steerable axles, and with a relatively short wheelbase. It has recently been shown that self-powered steerable dolly vehicles may provide both increased fuel efficiency and maneuverability. This type of self-powered dolly vehicle comprises an on-board energy source, such as a battery, super-capacitor or a fuel cell stack, and at least one pair of driven wheels.

Increased fuel efficiency is for instance obtained if an electric machine arranged for regenerative braking along with a battery or super-capacitor is installed in the dolly vehicle. The vehicle combination then effectively becomes a hybrid electric vehicle, even if the towing vehicle only comprises a traditional diesel engine with no on-board electric hybridization. An example of this type of self-powered dolly vehicle will be discussed in more detail below in connection to, e.g., <FIG>.

Adding a self-powered dolly vehicle <NUM> to the vehicle combination <NUM> can also improve startability, since the dolly vehicle is then able to generate extra torque when bringing the vehicle combination into motion from a stand-still. Vehicle startability may be a limiting factor in the maximum load possible to carry, and a self-powered dolly vehicle may therefore contribute to an increased cargo capacity, which is an advantage.

Both the truck <NUM> and the self-powered steerable dolly vehicle <NUM> may comprise electric machines for propulsion and/or regenerative brakes for decelerating the vehicle unit while harvesting energy. The self-powered vehicle units also comprise respective energy sources. An energy source is normally a battery, super-capacitor, fuel cell or other device arranged to store electrical energy. However, an energy source may also comprise mechanical energy storage devices such as springs and compressed air tanks for pneumatic machines. Combinations of different types of energy sources can also be used. A traditional fuel tank for storing gasoline or diesel fuel can of course also be considered an energy source in this context. The present disclosure, however, focuses on propulsion arrangements based on electric machines powered by a battery.

<FIG> illustrates a driving scenario <NUM> where a vehicle combination comprising a dolly vehicle unit <NUM> is driving in a forward direction F on a relatively flat road <NUM>. If the dolly vehicle is self-powered, it can support the tractor <NUM> in generating propulsive force for cruising along the road at an even speed on the order of, say <NUM>/h or so. This driving scenario requires a relatively low amount of torque to be generated in comparison to the torque required for bringing a heavy vehicle into motion from stand-still. However, the torque needs to be generated at high axle speed, which may be a challenge for some electrical machines where the torque generating ability often declines with axle speeds.

Thus, it is desired to be able to generate large amounts of torque at low vehicle speeds for improved startability, and also to be able to generate a sufficient torque at higher engine speeds in order to support, e.g., highway cruising and the like. A purpose of the present disclosure is to provide propulsion arrangements for dolly vehicle units which are flexible enough to generate required torque levels over wide range of axle speeds, from stand-still up to cruising speeds.

<FIG> illustrate an example dolly vehicle unit <NUM> comprising rear wheels <NUM> and front wheels <NUM>, as well as a fifth wheel connection <NUM> and a drawbar <NUM>. The drawbar in <FIG> represents one example drawbar, and the drawbar in <FIG> represents another example drawbar which has additional supporting members for increased mechanical strength. The dolly vehicle <NUM> is self-powered by a propulsion arrangement which is schematically shown in <FIG>. The propulsion arrangement may, generally, power one or both axles on the dolly, although a single driven axle is shown in <FIG>.

The dolly vehicle unit <NUM> is arranged to be connected to a truck or towing trailer unit via the drawbar <NUM>. This connection is associated with a longitudinal force Fd. This force will be positive, i.e., an accelerating pull force acting on the dolly in case the vehicle combination is accelerating, and a negative force, i.e., a braking force, in case the vehicle combination is slowing down. A similar force Ff will be generated at the fifth wheel connection <NUM> in the longitudinal direction of the dolly.

The dolly may also comprise a control unit <NUM> configured to control various functions on the dolly, such as generated torque by the propulsion arrangement, braking, steering, and so on. This control unit will be discussed in more detail below in connection to <FIG>.

<FIG> schematically shows a propulsion arrangement <NUM> for a self-powered dolly vehicle unit <NUM>. The propulsion arrangement comprises a first electric machine <NUM>, a second electric machine <NUM> and a gearbox <NUM>. The gearbox output shaft <NUM> is connected to an open differential <NUM> which drives first and second wheels <NUM>, 310r of the driven axle <NUM> on the dolly vehicle unit <NUM>. Thus, the first and second electric machines are connected in parallel to the same drive axle <NUM> via the gearbox. Since the first <NUM> and second <NUM> electric machines are arranged in parallel and connected to the same drive axle, the torques generated by the two machines will sum up after accounting for respective gear ratios to generate a sum torque T and an axle rotational velocity V. The open differential allows for speed differences across the two wheels in a known manner. The primary function of the open differential is to split torque TI, Tr between the two wheels <NUM>, 310r.

The gearbox is arranged to connect the electric machines to the open differential <NUM> at respective gear ratios g1, g2, g3. These gear ratios are configured such as to improve startability performance while at the same time being able to deliver sufficient torque at higher axle speeds.

It is appreciated that the first electric machine <NUM> and the second electric machine <NUM> can be configured with equal torque vs machine axle speed characteristics, i.e., the first and the second electric machine can be the same type of electric machine. However, in some cases it may be beneficial to configure the second electric machine <NUM> to generate a larger axle torque compared to the first electric machine <NUM> in a low speed range extending from zero rpm to about <NUM> rpm. This way the second electric machine will mainly contribute to supporting startability, while the first electric machine mainly contributes to supporting higher speed driving.

The propulsion arrangement <NUM> also comprises a rechargeable electrical energy source <NUM>, such as a battery or a super-capacitor. The first and the second electric machines <NUM>, <NUM> can then be configurable in a propulsion mode of operation where positive torque is generated and power from the energy source is consumed, and in a regenerative braking mode of operation where negative torque is generated and power is fed to the energy source. Of course, the electrical machines <NUM>, <NUM> may also at least in part be powered by a fuel cell stack or the like.

<FIG> also shows service brakes <NUM>, 460r arranged to brake the wheels in case the regenerative braking capacity should prove insufficient.

<FIG> are graphs <NUM>, <NUM> of generated torque in Newton-meters (Nm) vs gearbox output shaft rotation speed in revolutions per minute (rpm). The torque curve of the first electric machine in graph <NUM> is shown as a dash-dotted curve <NUM>, while the torque curve of the second electric machine is shown as a dashed curve <NUM>. The sum of the two torques on the output shaft of the gearbox is illustrated in graph <NUM> as function of the same output shaft speed. Here, the solid line <NUM> shows torque generated during continuous drive while the dash-dotted line <NUM> shows generated torque during intermittent drive.

There is a first range of axle speeds <NUM> shown in <FIG> which may range from standstill, i.e., <NUM> rpm up to about <NUM>-<NUM> rpm. This range indicates torque generated during vehicle start from standstill and operation in low speed driving scenarios, such as maneuvering at low speeds at a cargo facility or the like. It is important to achieve high torque in this region to be able to, e.g., bring heavily loaded vehicles into motion, and to allow robust vehicle handling in uphill driving scenarios. There is also a second range of output shaft speeds <NUM> which may range from about <NUM> rpm or so and upwards to about <NUM> rpm. This high speed range indicates the torques which can be generated in driving scenarios such as highway cruising and the like, where a relatively high constant velocity is to be maintained but where less torque is required.

The first electric machine <NUM> is associated with a fixed gear ratio g1 and the second electric machine <NUM> is associated with a configurable gear ratio g2, g3. This provides great flexibility when it comes to optimizing performance over a wider range of vehicle speeds, such as from a standstill condition, i.e., vehicle startability, to highway cruising at higher speeds, e.g., on the order of <NUM>/h or so. To provide cruising capability, the fixed gear ratio g1 of the first electric machine <NUM> can be a first gear ratio g1 configured between <NUM>:<NUM> and <NUM>:<NUM>, and preferably about <NUM>:<NUM>. This way the first electric machine provides torque over a wide range of vehicle speeds, e.g., corresponding to a range of motor speeds from <NUM> rpm to about <NUM> rpm.

With reference to <FIG>, the maximum torque generated by the first electric machine <NUM> is indicated as <NUM>. This torque is maintained at a constant level up to a speed <NUM> where the torque starts to decline slowly up to some maximum speed <NUM>. It is noted that the rate of decline is not overly dramatic, hence a significant portion of the torque is generated also in the high speed range <NUM>.

The configurable gear ratio g2,g3 of the second electric machine <NUM> is optionally selectable between a second gear ratio g2 and a third gear ratio g3. The second gear ratio g2 can be chosen relatively low, such as between <NUM>:<NUM> and <NUM>:<NUM>, and preferably about <NUM>:<NUM>, i.e., similar to that of the first electric machine <NUM>. At this gear ratio, the second electric machine performs almost the same in terms of torque vs speed as the first electric machine. This means that the sum of the two electric machine torques provide sufficient torque for supporting vehicle motion up to relatively high vehicle speeds. The third gear ratio g3 is preferably selected at a higher value, e.g., between <NUM>:<NUM> and <NUM>:<NUM>, and preferably about <NUM>:<NUM>. This gear ratio implies a significantly higher generated torque at low speeds, as indicated by the dashed curve in <FIG>. The configurable gear ratio of the second electric machine can be manually or automatically switched at a suitable shaft speed <NUM>, e.g., at about <NUM> rpm or so.

It is appreciated that the gearbox <NUM> may be arranged to provide more than one gear for the first electric machine <NUM>, and more than two gears for the second electric machine <NUM>. This leads to a more complicated gearbox, but also provides further options for optimizing dolly vehicle propulsion and regenerative braking.

The propulsion arrangement <NUM> also comprises a control unit <NUM> arranged to set the configurable gear ratio g2, g3 of the second electric machine <NUM> in dependence of an electric machine axle speed of the second electric machine and/or in dependence of a vehicle speed of the dolly vehicle unit <NUM>. The vehicle speed of the dolly can be measured directly on the dolly wheels using wheel speed sensors. Thus, the control of the gears can be controlled independently from a control of the truck or towing vehicle <NUM>. However, additional benefits may be obtained if the prime mover is allowed to control the different motion support devices on the dolly vehicle unit.

The truck <NUM> (and possibly also on the trailers <NUM>, <NUM>) may comprise control units arranged to perform advanced vehicle motion management (VMM) functions. Such a function may, e.g., comprise global force generation to obtain some vehicle behavior, and coordination of motion support devices (MSDs) such as brakes and propulsion devices throughput the combination vehicle. Generally, the vehicle combination control may be arranged according to a layered functional architecture where some functions may be comprised in a traffic situation management (TSM) function layer and some other functions may be comprised in a VMM function layer. The TSM layer may plan vehicle operation with a time horizon of, e.g., <NUM> seconds. This time frame corresponds to, e.g., the time it takes for the vehicle <NUM> to negotiate a curve. The vehicle maneuvers planned and executed by the TSM function can be associated with acceleration profiles and curvature profiles. The TSM function layer continuously requests the desired acceleration profiles and curvature profiles from the VMM function layer.

The VMM function layer operates with a time horizon of about <NUM> second or so, and continuously transforms the acceleration profiles and curvature profiles into control commands for the various MSD functions on the vehicle, i.e., it among other things performs MSD coordination. One such MSD function may be the propulsion, braking, and steering functions of the dolly vehicle unit <NUM>. Thus, the dolly vehicle units disclosed herein may be arranged to be communicatively coupled to a main control unit of the vehicle combination <NUM>.

With reference again to <FIG>, the maximum torque <NUM> of the first electric machine <NUM> may be on the order of <NUM>, which remains constant up to a speed <NUM> of about <NUM> rpm. Torque is, however, delivered by the first electric machine <NUM> up to a maximum speed <NUM> of at least <NUM> rpm. The maximum torque <NUM> generated by the second electric machine <NUM> may be on the order of <NUM>. This maximum torque is maintained at a constant level up to a speed <NUM> of about <NUM> rpm where it starts to decline relatively fast.

When the torques of the first and the second electric machines are combined, the generated torque is at a high level <NUM> in the low speed range <NUM> for supporting startability and low speed maneuvering, and maintained at a reasonable level all the way up to the maximum speed <NUM>. A gearshift <NUM> may take place approximately at the speed <NUM> indicated in <FIG>, this speed may be on the order of <NUM> rpm.

<FIG> shows an example of a dolly vehicle propulsion module <NUM>, where the first and second electric machines <NUM>, <NUM> and the gearbox <NUM> have been integrally formed as a single module. The two electric machines <NUM>, <NUM> are arranged on either side of a longitudinal centrum line C of the module, where they interface with the gearbox <NUM>. An output shaft <NUM> of the gearbox can be seen extending in a direction aligned with the centrum line C. This integrally formed module conserves space and simplifies dolly vehicle unit assembly. This is an advantage since space is limited in the relatively small dolly vehicle unit.

<FIG> is a flow chart illustrating a method for operating a self-powered dolly vehicle unit <NUM>. The method comprises configuring S1 a propulsion arrangement <NUM> for the self-powered dolly vehicle unit <NUM> comprising a first electric machine <NUM>, a second electric machine <NUM>, a gearbox <NUM>, and an open differential <NUM> for driving first and second wheels <NUM>, 310r of a driven axle <NUM>, i.e., a propulsion arrangement according to the discussion above. The first <NUM> and second <NUM> electric machines are arranged in parallel and connected to the open differential <NUM> via the gearbox <NUM> at respective gear ratios g1, g2, g3. The first electric machine <NUM> is associated with a fixed gear ratio g1 and the second electric machine <NUM> is associated with a configurable gear ratio g2, g3. The method further comprises determining S2 if the dolly vehicle unit <NUM> is in a low speed range of operation <NUM> or in a high speed range of operation <NUM>, and setting S3 the configurable gear ratio g2, g3 of the second electric machine in dependence of the low or high speed range of operation. The determining of the speed range, i.e., whether the dolly vehicle is operating in the low speed range or in the high speed range can be based on wheel speed sensors and/or on axle speed sensors.

As mentioned in connection to <FIG>, longitudinal forces are generated at the drawbar <NUM> and at the fifth wheel connection <NUM>. The method may also comprise determining this longitudinal force Fd associated with the drawbar <NUM> of the dolly vehicle unit <NUM> and/or the longitudinal force Ff associated with the fifth wheel connection <NUM> of the dolly vehicle unit <NUM>, and controlling the electric machines <NUM>, <NUM> and/or the gearbox <NUM> in dependence of the longitudinal force Fd, Ff. The control unit <NUM> is thus able to act in a stand-alone manner to support the various operations by the vehicle combination <NUM>. If the vehicle is to be brought into motion from a stand-still, the control unit <NUM> can detect this by monitoring, e.g., wheel speed sensors and the longitudinal drawbar force. The control unit then selects the appropriate gear for the second electric machine <NUM> in order to generate the maximum torque <NUM>. As the speed of the vehicle combination increases, the control unit eventually switches gear of the second electric machine into a gear more suitable for supporting high speed driving.

<FIG> schematically illustrates, in terms of a number of functional units, the components of a control unit <NUM> according to embodiments of the discussions and methods disclosed herein. This control unit <NUM> may be comprised in the vehicle <NUM>, e.g., in the form of a vehicle motion management (VMM) function unit configured to perform force allocation and the like. Processing circuitry <NUM> is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium <NUM>. The processing circuitry <NUM> may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

Particularly, the processing circuitry <NUM> is configured to cause the control unit <NUM> to perform a set of operations, or steps, such as the methods discussed in connection to Figure <NUM>.

The control unit <NUM> may further comprise an interface <NUM> for communications with at least one external device, such as an electric machine or a gearbox.

Claim 1:
A propulsion arrangement (<NUM>) for a self-powered dolly vehicle unit (<NUM>), the propulsion arrangement comprising a first electric machine (<NUM>), a second electric machine (<NUM>), a gearbox (<NUM>), and an open differential (<NUM>) for driving first and second wheels (<NUM>, 310r) of a driven axle (<NUM>), wherein the first (<NUM>) and second (<NUM>) electric machines are arranged in parallel and connected to the open differential (<NUM>) via the gearbox (<NUM>) at respective gear ratios (g1, g2, g3), wherein the first electric machine (<NUM>) is associated with a fixed gear ratio (g1), and the second electric machine (<NUM>) is associated with a configurable gear ratio (g2, g3), characterised in that the propulsion arrangement (<NUM>) further comprises a control unit (<NUM>) arranged to determine if the dolly vehicle unit (<NUM>) is in a low speed range of operation or in a high speed range of operation, configured to set the configurable gear ratio (g2, g3) of the second electric machine in dependence of the low or high speed range of operation and configured to drive the wheels of the self-powered dolly vehicle unit by the motors, wherein a low speed range of operation entails a wheel rotational speed of less than <NUM> rpm and a high speed range of operation entails a wheel rotational speed in the range from <NUM> rpm to <NUM> rpm.