Patent Publication Number: US-2020298694-A1

Title: Bus with cooled in-wheel electric engines

Description:
TECHNICAL FIELD 
     The invention lies in the field of engine cooling. More precisely, the invention proposes a bus with driving wheels which comprises cooled electric engines. 
     BACKGROUND OF THE INVENTION 
     Electric buses are provided with electric engines. During propulsion phases and regenerative phases, the electric machines heat. This temperature elevation reduces the efficiency since the permanent magnet properties decrease. In addition, a high temperature may irremediably damage the permanent magnets and other electric devices. 
     In order to preserve the yield, an electric engine is generally provided with a cooling device. A cooling flow prevents excessive heat peaks, and allows a temperature control. Yet, this temperature control may turn out cumbersome when the corresponding vehicle runs in cities where speed is limited by law or by traffic jam. Then, the potential cooling flow is limited. Uphill slopes require more electric power which heat even more the electric engines. 
     Moreover, the positioning of the heat exchanger must comply with several requirements, notably in mass transportation vehicles such as buses. Indeed, the available place is reduced. In addition, the cost, the weight and the passenger comfort must be considered as well. On top of this, servicing and collisions with other vehicles also affect the way the heat exchangers are arranged close to seating and standing passengers. 
     The document DE 197 32 637 A1 discloses an omnibus comprising an electric engine with a cooling pipe where cooling water flows. 
     The document JP 2009 227130 A discloses a wheel with an in-wheel engine lubricated by an oil circuit. The oil flows through an oil cooler in the middle of the oil path. 
     The document US 2019/068028 A1 discloses a four-wheel vehicle equipped with a cooling mechanism. Each wheel is dotted with an electric engine cooled by an oil cooler. The oil coolers compose heat exchangers coupled to the radiator. 
     Technical Problem to be Solved 
     It is an objective of the invention to present a bus, which overcomes at least some of the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, it is provided a bus, notably an articulated bus with several units, the bus comprising: a passenger compartment adapted for at least fifty passengers, a wheel housing, a wheel disposed in the wheel housing and comprising an in-wheel electric engine, a cooling circuit in fluid flow communication with the in-wheel electric engine and comprising a heat exchanger outside the wheel housing. 
     Preferably, the cooling circuit comprises a first passage which is outside the in-wheel electric engine and which comprise a first inner width W 1 , the cooling circuit further comprising a second passage which is in the in-wheel electric engine and which comprise a second inner width W 2 , the first inner width W 1  representing at least 80% of the second inner width W 2 , optionally the first inner width W 1  is larger than the second inner width W 2 . 
     Preferably, the heat exchanger is transversally and/or vertically level with the wheel, respectively with the in-wheel electric engine, the bus further comprising a seat row above said heat exchanger, or a seat above the heat exchanger. 
     Preferably, the wheel housing comprises a tight wall and/or a protection bar between the wheel and the heat exchanger. 
     Preferably, the bus comprises an enclosure in which the heat exchanger is arranged, said enclosure being adjacent to the wheel housing and/or the passenger compartment, the bus is notably adapted such that the heat exchanger heats the passenger compartment. 
     Preferably, the wheel is a first wheel, the bus further comprising a second wheel identical to the first wheel and disposed in the wheel housing longitudinally at distance from the first wheel, the cooling medium being adapted for flowing through the in-wheel electric engine of said second wheel. 
     Preferably, the cooling circuit comprises a pump adapted for pressurizing a cooling liquid in the first wheel and in the second wheel, and/or a tank with a cooling liquid, such as a water glycol mix, the cooling liquid being intended to flow through the in-wheel electric engine in order to cool it. 
     Preferably, the bus comprises a suspension arm adapted to pivot with respect to the wheel housing and/or the passenger compartment, the cooling circuit comprising a tube, notably a resilient tube, joined to said suspension arm and being in fluid flow communication with the in-wheel electric engine. 
     Preferably, the suspension arm is an upper suspension arm, the cooling circuit comprising a pipe fixed to said tipper suspension arm, said pipe being stiffer than the resilient tube. 
     Preferably, the bus comprises a battery pack adapted for electrically powering the in-wheel electric engine, the cooling circuit comprising a cooling unit adapted fur cooling said battery pack, the wheel housing being disposed longitudinally between the battery pack and the heat exchanger. 
     Preferably, the in-wheel electric engine comprises a rotor and a stator, said stator comprising a diameter and a thickness TH along the rotation axis of the in-wheel electric engine. 
     Preferably, the stator is arranged in the rotor, the cooling circuit comprising an inner network through the stator in order to cool said stator. 
     Preferably, the wheel further comprises a disc brake with a brake disc, the distance D between the brake disc and the stator being larger than the width W of the stator. 
     Preferably, the bus comprises a frame and a movable wheel support on which the wheel is rotatably fixed, the wheel support is notably disposed between the brake disc and the in-wheel electric engine. 
     Preferably, transversally, the in-wheel electric engine comprises an inner face and an outer face, the cooling circuit comprising an inlet and an outlet on the inner face, the inlet and the outlet notably being arranged on the inner face, preferably in the upper half of the inner face. 
     Preferably, the wheel comprises a radial space between the in-wheel electric engine and the rim of the wheel, said radial space being radially larger than the outer radius of the in-wheel electric engine, possibly at least two times larger than the outer radius. 
     Preferably, the cooling circuit is a first cooling circuit, the wheel housing is a first wheel housing, the bus farther comprising additional wheel housings and additional cooling circuits which are identical to the first cooling circuit and which are each associated with one of the additional wheel housings, the additional cooling circuits notably being independent from one another. 
     Preferably, the cooling circuit comprises a first passage which is outside the in-wheel electric engine and which comprise a first inner width W 1 , the cooling circuit further comprising a second passage which is in the in-wheel electric engine and which comprise a second inner width W 2 , the first inner width W 1  being larger than the second inner width W 2 . 
     Preferably, the second inner width W 2  represents at least 4% of the outer diameter of the in-wheel electric engine. 
     Preferably, the heat exchanger is longitudinally aligned with the wheel. 
     Preferably, the heat exchanger is vertically level with the passenger compartment. 
     Preferably, the heat exchanger comprises a heat dissipation device. 
     Preferably, the wheel extends over the whole height of the heat exchanger. 
     Preferably, the pump and/or the tank are arranged in the enclosure. 
     Preferably, the heat exchanger is intended to be cooled by the bus environment. 
     Preferably, the heat exchanger is adapted for cooling a cooling medium flowing through the cooling circuit. 
     Preferably, the wheel comprises a rim with an inner space, the in-wheel electric engine being at least partially disposed in said inner space. 
     Preferably, the inner space comprises a first outer diameter which is larger than a second outer diameter of the in-wheel electric engine, preferably at least two times larger. 
     Preferably, the additional cooling circuits are separate and distinct. 
     Preferably, the wheel comprises an outer half and an inner half in which the in-wheel electric engine is arranged, the in-wheel electric engine being at distance from said outer half. 
     Preferably, the wheel support is a steering knuckle which is adapted for moving vertically and/or for pivoting about a vertical pivot axis. 
     Preferably, the cooling circuit comprises water, and is notably adapted to keep the water temperature under 100° C. 
     Preferably, the second wheel and the heat exchanger are aligned, and/or transversally overlapping. 
     Preferably, the cooling fluid is isolated from the bus environment by the cooling circuit. 
     Preferably, the cooling circuit comprise a first portion fixed to a suspension arm, and a second portion of reduced stiffness which comprise a lower stiffness than the first portion. 
     Preferably, the second portion is between the first portion and the engine. 
     Preferably, the first portion is at distance from the engine. 
     It is another aspect of the invention to provide a bus, notably an articulated bus with several units, the bus comprising: a passenger compartment adapted for at least fifty passengers, a seat row, notably a longitudinal seat row; a wheel disposed under the seat row and comprising an in-wheel electric engine, a cooling circuit in fluid flow communication with the in-wheel electric engine and comprising a heat exchanger under the seat row. 
     The passenger compartment is not an essential aspect of the invention. 
     It is another aspect of the invention to provide a cooling process of an in-wheel electric engine for a bus, the bus comprising: a capacity of at least fifty passengers notably defined by a passenger compartment, a wheel housing, a wheel with an in-wheel electric engine, a cooling circuit with a cooling liquid, a heat exchanger at distance from the wheel, a connection between the heat exchanger and the in-wheel electric engine, the cooling process comprising the steps: heating the in-wheel electric engine, and cooling the in-wheel electric engine by means of the cooling liquid, wherein the speed of the cooling liquid in the connection is similar to the speed of the cooling liquid in the in-wheel electric engine, the bus notably being in accordance the invention, and the bus comprises a seat over the cooling circuit. 
     The cooling liquid may generally be a fluid such as a gas. 
     Preferably, the speed of the cooling liquid in the connection represents from 50% to 150%, or from 80% to 120%, of the speed of the cooling liquid in the in-wheel electric engine. 
     Preferably, during step cooling the in-wheel electric engine, the passenger compartment is heated, and the pressure of the cooling fluid in the connection is similar to the pressure of the cooling fluid in the in-wheel electric engine. 
     Preferably, the heat exchanger is at distance and: or outside the wheel housing. 
     Preferably, the wheel is inside the wheel housing. 
     It is another aspect of the invention to provide a cooling process of an in-wheel electric engine for a bus, the bus comprising: a passenger compartment adapted for receiving at least fifty passengers, a wheel housing, a wheel and comprising an in-wheel electric engine, a cooling circuit with a cooling liquid, a heat exchanger at distance from the wheel, a connection between the heat exchanger and the in-wheel electric engine, the cooling process comprising the steps: heating the in-wheel electric engine, and cooling the in-wheel electric engine by means of the cooling liquid, wherein the flow speed of the cooling liquid in the connection represents from 40% to 200%, or from 50% to 150%, or from 80% to 120%, of the flow speed of the cooling liquid in the in-wheel electric engine, the bus notably being in accordance with the invention. 
     The heat exchanger is not an essential feature of the invention. It is another aspect of the invention to provide a cooling process, notably a temperature management process, of an in-wheel electric engine for a bus, the bus comprising: a passenger compartment adapted for receiving at least fifty passengers, a wheel housing, a wheel and comprising an in-wheel electric engine, a cooling circuit with a cooling liquid, the cooling process comprising the steps: heating the in-wheel electric engine, and cooling the in-wheel electric engine by means of the cooling liquid which is cooled outside the wheel and notably outside the wheel housing, the bus notably being in accordance with the invention. 
     The cooling liquid flow speed(s) may he an average flow speed, or a maximum flow speed. 
     It is another aspect of the invention to provide a use of a heat exchanger for heating the passenger compartment of a bus, wherein the bus comprises:
         a wheel housing,   a wheel disposed in the wheel housing and comprising an in-wheel electric engine,   a cooling circuit for with the in-wheel electric engine and comprising a heat exchanger;   an enclosure in heat exchange with the passenger compartment and in which the heat exchanger is disposed, the bus notably being in accordance with the invention,       

     It is another aspect of the invention to provide a use of a heat exchanger for heating a passenger compartment of a bus, wherein the bus comprises a wheel housing, a wheel in said wheel housing, an electric in-wheel engine in said wheel, a cooling circuit through the electric in-wheel engine, the heat exchanger being part of said cooling circuit, the bus notably being in accordance with the invention. 
     It is another aspect of the invention to provide a use of a heat exchanger for heating the passenger compartment of a bus, wherein the bus comprises:
         a wheel housing,   a wheel disposed in the wheel housing and comprising an in-wheel electric engine,   a cooling circuit thermally cooperating with the in-wheel electric engine and comprising a heat exchanger; and optionally   an enclosure in thermal communication with the passenger compartment and in which the heat exchanger is disposed, the bus notably being in accordance with the invention.       

     It is another aspect of the invention to provide a use of a heat exchanger for heating seat of a bus, wherein the bus comprises:
         a wheel housing,   a wheel disposed in the wheel housing and comprising an in-wheel electric engine,   a cooling circuit thermally cooperating with the in-wheel electric engine and comprising a heat exchanger thermally coupled to the seat;   the bus notably being in accordance with the invention.       

     Preferably, the bus further comprises an enclosure in which the heat exchanger is disposed and the set being above said enclosure. 
     Preferably the seat comprises a seat place row thermally coupled to the heat exchanger and/or above said enclosure. 
     The different aspects of the invention may be combined to each other. In addition, the preferable features of each aspect of the invention may be combined with the other aspects of the invention, unless the contrary is explicitly mentioned. 
     Technical Advantages of the Invention 
     The invention improves the flow control through the cooling circuit. It provides a position for the heat exchanger which is sufficiently remote from the hot source for a better cooling, but sufficiently close in order to shorten the lines so as to lower the pressure losses. 
     In addition, the pressure losses are further managed by specific diameter or width choices. These dimensions foster smooth flow in spite of the connection deformation, and of the vibrations generated by the contact between the wheel and the ground unevenness. 
     The invention addresses the technical problem of cooling a substantially small size in-wheel electric engine equipping a steering and driving wheel, where said wheel drives a bus which keeps a spacious passenger compartment with seat rows. Thus, the passenger capacity is preserved, and the ratio between seat places and standing places is optimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Several embodiments of the present invention are illustrated by way of figures, which do not limit the scope of the invention, wherein: 
         FIG. 1  provides a schematic illustration of a side view of a bus in accordance with a preferred embodiment of the invention; 
         FIG. 2  provides a schematic illustration of an aerial view of a portion of a bus frame in accordance with a preferred embodiment of the invention; 
         FIG. 3  provides a schematic illustration of a longitudinal view of a suspension assembly in accordance with a preferred embodiment of the invention; 
         FIG. 4  provides a schematic illustration of through cut of a wheel with a cooling circuit in accordance with a preferred embodiment of the invention; 
         FIG. 5  provides a schematic illustration of a transversal view of a wheel with a cooling circuit in accordance with a preferred embodiment of the invention; 
         FIG. 6  provides a schematic illustration of the interface between a connection and an engine of a cooling circuit in accordance with a preferred embodiment of the invention; 
         FIG. 7  provides a schematic illustration of a cooling process in accordance with a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This section describes the invention in further detail based on preferred embodiments and on the figures. Similar reference numbers will be used to describe similar or the same concepts throughout different embodiments of the invention. 
     It should be noted that features described for a specific embodiment described herein may be combined with the features of other embodiments unless the contrary is explicitly mentioned. Features commonly known in the art will not he explicitly mentioned for the sake of focusing on the features that are specific to the invention. For example, the bus in accordance with the invention is evidently controlled by a computer, even though such a computer is not explicitly referenced on the figures nor referenced in the description. 
     By way of convention, it may be defined that the word “longitudinal” refers to the longitudinal direction and may correspond to the main driving direction of the bus. It may be along the main central axis of the vehicle. The word “transversal” refers to the transversal direction and may be perpendicular to the longitudinal direction. It may be understood that the directions are not used in a strict meaning. Indeed, each direction used below may include a variation of at most 5°, or 2°, or 1°, with respect to a strict meaning. The skilled in the art will understood that a longitudinal pivot axis may be inclined with respect to the longitudinal direction of the bus and/or the horizontal direction. 
     In the following description and claims, the mentioned length(s), width(s), and thickness(es) may be average ones. 
     The radial direction is understood as perpendicularly to an associated wheel rotation axis. The radial direction is along the radius of a wheel. 
     The term “similar” used in relation with a value such as a size or flow, is understood as implying a variation of at most 50%; preferably 20%, more preferably 10%. 
     It should be noticed that the present drawings generally provide configurations where wheels are substantially parallel to the longitudinal direction. The steering angle is of 0°. The vehicle may drive along a straight trajectory. However, the skilled in the art will be able to adapt the following teaching to situations where the steering angle of the bus is changed. 
       FIG. 1  shows a vehicle for mass transportation in accordance with a preferred embodiment of the invention. The vehicle is partially represented. 
     The vehicle is adapted for transportation of passengers in cities and may transport about fifty, or one hundred passengers, for instance one hundred and twenty passengers. The vehicle may be a bus  2 , notably an electric bus  2 . The bus  2  may include electric driving engines and electric batteries (not represented) powering the electric driving engines. The bus  2  may be purely electric, in the meaning that it is only driven by electric power. The bus  2  may be combustion engine free. 
     The bus  2  may be an articulated bus. It may comprise a first unit  4  and a second unit  4  (partially represented). Each unit  4 , may form a body, and/or may form a rigid cart. Each unit  4  may be a trailer and/or a tractor. The units  4  may be similar or identical. These units  4  may be joined by a joint, for instance a hinged joint  6  enabling the units  4  to swivel with respect to each other. 
     In the current embodiment, only two units  4  are represented, however it is contemplated in the current invention that the electric bus  2  includes three, four, or more units  4 ; which are articulated. with respect to one another by hinged joint(s)  6 . Then, the passenger capacity may be of more than two hundred. Each unit  4  may be self-supporting. Thus, each unit  4  may move without the hinged joint  6 . 
     A bus formed of a single unit is also considered in the invention. 
     Each unit  4  may include several wheels  8  engaging the ground G. Pairs of symmetric wheels  8  may form axles, for instance four axles for each unit  4 . The axles and thus the wheels  8  may be distributed along the length of the bus  2 . At least one pair of wheels is formed of steered wheels. Optionally, each wheel  8  of the bus  2  or of at least one unit  4  are steered wheels and/or driving wheels. 
     The bus  2  may include a bus structure. The bus structure may distribute and/or support the weight of the bus, and load therein. The bus structure may include a roof  10 , and/or a passenger platform  12 , and/or side walls  14 . The side walls  14  may be outer walls. Two transversally opposite side walls  14  may go down from the roof  10  to the passenger platform  12 . They may form the bodywork of the bus  2 . They may mask the wheels  8 . The bodywork may be part of the bus structure. The side walls  14  may receive windows  16  and doors  17  for passengers. Optionally, doors  17  are arranged in one of the two side walls  14 , notably between windows  16 . 
     For instance; the side walls  14  may close the wheel housings  18 . Optionally, at least one or each wheel housing  18  may receive two longitudinally spaced wheels  8 . The wheel housings  18  may form downwardly open boxes. The wheel housings  18  may exhibit four faces in front of the wheels  8 . At least one or each wheel housing  18  may be adapted for blocking front, rear and top projections from the associated wheel. The wheel housings  18  may be longitudinally at distance from the ends of the units  4 . The wheel housings  18  may be arranged below the windows  16 . The door  17  may be disposed between two wheel housings  18  of the corresponding unit  4 . 
     Generally, the or each wheel housing  18  may be understood a space in which at least one wheel is arranged. The or each wheel housing  18  may be a wheel cavity. The or each wheel housing  18  may be a wheel guard. 
     Equipment may be provided on the roof  10 . For instance, the bus may comprise an air conditioning device  20 . The air conditioning device  20  may be adapted to cool air in the passenger compartment (behind the door  17 ). It may be adapted for keeping the temperature between 18° C. and 25° C. for the passenger comfort. This air conditioning device  20  may be reversible and may heat the passenger compartment during winter. It may comprise a compressible gas. 
     The bus  2  may comprise at least one battery pack  22 . The battery packs  22  may power electric engines driving the bus  2 . The battery packs  22  may power electric engines (not represented) which activate the wheels  8 . The electric engines may be in-wheel electric engines. For instance, each wheel housing  18  is associated with a battery pack  22 . The battery packs  22  may be independent. In the current example, each unit  4  may comprise four battery packs  22 . By way of illustration, the bus  2  includes eight battery packs  22  and eight wheel housings  18 . There may be sixteen wheels  8 , for instance each with an electric engine. The battery packs  22  may power other equipment of the bus  2 . 
     In order to cool the electric engines, notably the in-wheel electric engines, the bus  2  may comprise at least one cooling circuit  24 . The bus  2  may comprise one cooling circuit  24  for each of the wheel housings  18 , and thus for each of the wheel pairs. Each battery pack  22  may be associated with a cooling circuit  24 , Each cooling circuit  24  may be associated with one wheel housing  18 , and/or with at least one wheel  8 . Each cooling circuit  24  may cool one or two electric engines. At least one door  17  may be between two adjacent cooling circuit  24 . The cooling circuits  24  may be independent from each other. They may be separate and distinct. They may be at distance from each other in order to reduce the length of required pipes when considering the whole vehicle. 
     The current configuration reduces the thermal stress of the cooling circuits  24 , and improves the general reliability. The cost and the weight are considered as well. The or each cooling circuit  24  may comprise a closed loop, and/or vanes which arc easier to control. 
     The or each cooling circuit  24  may comprise a tank  26 . Each tank  26  may be a closed and tight vessel. Each tank  26  may be adapted for containing a cooling fluid, notably a cooling liquid. The cooling liquid may comprise water and glycol. The tank  26  may be adapted for resisting to the cooling fluid pressure. The cooling circuit may be adapted for avoiding contact between the cooling fluid and the bus environment. 
     The or each cooling circuit  24  may comprise a pump  28 . The pumps  28  may be adapted for sucking up the cooling fluid, and for injecting it through the corresponding, circuit  24 . The pumps  28  may inject the cooling fluid in the hydraulically connected electric engines in order to cool them. The cooling fluid pressure in the electric engines may be comprised between 0.5 bar and 2 bars. 
     The or each cooling circuit  24  may comprise a heat exchanger  30 . The heat exchanger(s)  30  may be heat dissipator(s). Each heat exchanger  30  may be adapted to cool down the cooling fluid flowing therethrough by means of the pump  28 . The heat exchangers  30  may be in thermal contact of the bus environment. The or each heat exchanger  30  may be separate and distinct from the air conditioning device  20 . The heat exchangers  30  may be adapted to cool the battery packs  22 , the tanks  26  and the electric engines. 
     The heat exchangers  30  may be vertically level with the passenger compartment. The heat exchangers  30  may be above the platform  12 . They may heat the passenger compartment. 
     At least one or each heat exchanger  30  may be at distance from the wheels  8 . They may be outside the wheel housings  18 . Thus, the heat exchangers  30  may be physically protected from projections propelled by the wheels  8 . 
     At least one or each heat exchanger  30  may be arranged in an enclosure. The enclosure may receive the connected pump  28  and the connected tank  26 . At least one or each enclosure may be adjacent to the corresponding wheel housing  18 . The enclosure and the associated wheel housing  18  may be in contact of each other. Thus, the length of pipe is reduced such that the pressure loss, the cost and the weight are optimized. The cooling circuits  24  are more reliable. The length of the pipes becomes important when their diameter increases. 
       FIG. 2  provides an aerial illustration of the frame  32  of a bus  2 , notably from a unit  4 , in accordance with a preferred embodiment of the invention. The longitudinal central axis L and the transversal direction T are represented. The longitudinal central axis L may correspond to the longitudinal direction L, and may be horizontal. 
     The bus  2  and/or the unit  4  may correspond to those as described in relation with  FIG. 1 . Two pairs or wheels  8  are disposed in the respective wheel housings  18 . The rotations axes  9  of the wheels  8  are represented. The wheel rotations axes  9  may correspond to the axles when the wheels  8  are aligned at each side. It may be understood that the wheels  8  comprise toe-in or toe-out. Thus, the term “aligned” may be understood in the meaning of the environment of the invention. 
     In each wheel housing  18 , the wheels  8  may form pairs. The wheel gap  8 G between the wheels  8  in the same wheel housing may be smaller than the transversal width  8 W of at least one wheel  8  or of each wheel  8 . The wheels  8  of each pair are adapted to run on the same wheel path. These wheels  8  may be transversally aligned. In each pair, the wheels  8  are longitudinally offset. The wheel gap  8 G may separate them longitudinally. The wheels  8  of each pair may be identical. 
     The frame  32  may comprise longitudinal beams  34  and transversal beams  36 . The platform  12  may be part of the frame  32 . The longitudinal beams  34  may delimit transversally the wheel housings  18 . Transversal bars  38  may delimit longitudinally the wheel housings  18 . Other beams  40  may also form the frame  32  and may delimit the wheel housing  18  and the frame  32 . The transversal bar  38  may be considered as a protection bar  38  between the wheels  8  and the heat exchanger  30 . 
     At least one or each wheel  8  may be a driving wheel. At least one or each wheel  8 , respectively driving wheel, may comprise an electric engine  42 . The electric engines  42  may generally be electric machines. The electric engines  42  may be in-wheel electric engines, or more generally in-wheel engines. The electric engines  42 , notably the in-wheel electric engines  42 , may be powered by the battery pack  22 . The cooling circuit  24  may comprising a cooling unit  22 C in at least one of the battery packs  22 . Each cooling unit  22 C may be adapted for cooling the corresponding battery pack  22 . The cooling units  22 C may be in thermal contact of the corresponding battery pack  22 , notably of the contained battery cells. 
     In the current example two battery packs  22  are represented, namely a left battery pack  22  and a right battery pack  22 . The combination of the battery packs  22  and of the electric engines  42 , notably the in-wheel electric engines  42 , allows to drive the bus  2 . These electric components may be adapted for driving the bus  2  at least at: 50 km/h or 100 km/h. These speeds may be reached with one hundred passengers in the passenger compartment  2 P of the bus. 
     At least one or each wheel  2  may be joined to the frame  32  by a suspension system  44 . At least one or each wheel is joined to the frame  32  by a dedicated suspension system  44 . The suspension systems  44  may be separate and distinct from each other. At least one or each suspension system  44  may comprise a steering module (not represented). 
     At least one or each suspension system  44  may comprise suspension arms  46 . The suspension arms may be designated as pivoting arms. The suspension arms  46  may be pivotably fixed to the frame  32 , for instance to longitudinal beams  40 . The suspension arms  46  may be pivoting links, notably swinging arms. The suspension arms  46  may pivot about horizontal pivot axis. At least one or each suspension arm  46  may pivot about longitudinal pivot axis  48 . The longitudinal pivot axes  48  may be parallel. 
     The wheel housings  18  may comprise plates  50 . The plates  52  may be vertical. They may be tight. They may be fixed to the transversal bars  38 . The plates  50  may close tightly the wheel housings  18 . They may form longitudinal end walls thereon. 
     The frame  32  may exhibit enclosures  52 . The plates  50  may be at the interface between the wheel housings  18  and the enclosures  52 . The enclosures  52  may be adjacent to the wheel housings  18 . At least one or each enclosure  52  may be adjacent to the passenger compartment  2 P. The enclosures  52  may be above the platform  12 . The position of the enclosures  52  with respect to the wheel housings  18  allows thermal cooperation. The enclosures  52 , more precisely the heat exchangers disposed therein, are cooled by the wheel housings  18  which raises when the bus drives due to the air flow forced by the wheels. 
     The current portion of the bus  2 , respectively of the unit  4 , exhibit two cooling circuits  24 , namely a left cooling circuit  24  and a right cooling circuit  24 . The left and the right cooling circuits  24  may be separated by the passenger compartment  2 P. They may be transversally distant. They may be hydraulically and/or thermally independent. 
     At least one cooling circuit  24  may comprise a tank  26  in the corresponding enclosure  52 , and/or a pump  28  in the corresponding enclosure  52 . At least one or each cooling circuit  24  may comprise a heat exchanger  30  in the enclosure  52 . As an option, the enclosure  52  may allow an air flow with the passenger compartment  2 P and/or with the bus environment. Thus, at least one or each heat exchanger  30  may provide calories to the bus environment and/or the passenger compartment  2 P. Thus, the passenger compartment  2 P may benefit from the calories generated by the electric engines  42 . A kind of synergy is achieved. 
     As apparent from the current figure, each wheel housings  18  separates the associated battery pack  22  and the associated enclosure  52 . It may increase heat exchange while allowing a height and a transversal width reduction of the enclosures  52 . 
     The integration of the cooling circuits  24  is performed in a narrow area. Indeed, the cooling circuits  24  may be below seats  56 . The seats  56  may form longitudinal rows. The seats  56  may be above the cooling circuits  24 . For instance, the tanks  26 , the pumps  28  and the heat exchangers  30  may be under the seats  56 . 
     Thus, the cooling circuits  24  may be disposed between the seats  56  and the platform  12 . Then the cooling system  54  and its cooling circuits  24  only require a reduced place in the bus since it is divided in smaller units which are individually easier to arrange in the bus  2 . At least one or the cooling circuits  24  are adapted for heating the seat(s)  56 . Then, the thermal management of the vehicle is improved. The thermal comfort of the seat(s) increases. 
     The cooling circuits  24  may comprise connections  58 , or lines. The connections  58  may form loops, notably closed loops. The pumps  28  may force the cooling liquid circulation in the associated loops. The cooling liquid may flow through the connections  58  in order to meet the battery packs  22 , the engines  42 , the heat exchangers  30 ; and thereby achieving temperature control. In addition, the connections  58  and the engines  42  may be configured such that the flow speeds in the connections  58  and the engines  42  are similar, and notably reduced. The differences of speeds may be of at most: 30%, or 20% or 10%. The considered speed may be average speeds. Accordingly, the cooling fluid speed remains homogeneous. Accelerations and slowdowns are controlled, notably at the interfaces of the engines  42 . The pressures losses are limited. In addition, the liquid speed in the connections  58  may he limited in order to limit the pressure tosses therein. 
       FIG. 3  provides a schematic illustration of a longitudinal view of a cooling system  24 , and of a suspension system  44  in a wheel housing  18 . The transversal direction T, the longitudinal direction L and the vertical direction V are provided. These directions (T, L, V) may be perpendicular to each other. 
     The bus  2  may correspond to those as described in relation with any one of  FIGS. 1 and 2 . 
     The suspension system  44  may be provided with a gas actuator  60  and a damper  62 . In addition or as an alternative, the gas actuator  60  forms a gas spring. Varying the gas pressure therein may allow to set its stiffness. This may be useful when the number of passengers varies in the passenger compartment  2 P. The damper  62 , also designated as shock absorber, may be adapted to absorb and dissipate energy when the wheel  8  meets a protrusion or a recess on/in the ground G, namely the road on which the bus  2  drives. 
     The suspension system  44  may comprise arms  46  or links. The suspension system  44  may comprise pivoting arms  46  also designated as pivoting links. The pivoting arms  46  may comprise an upper pivoting arm  64  and a lower pivoting arm  66 . The upper pivoting arm  64  and the lower pivoting arm  66  may pivot about longitudinal pivot axes  48 . Pivot joints  48 J may allow the pivoting motions of the pivoting arms ( 64 ;  66 ) about the longitudinal pivot axes  48 . These pivoting motions allow the wheel  8  to move between an upper position and a lower position. 
     The gas actuator  60  may be joined to the upper pivoting arm  64  whereas the damper  62  may be joined to the lower pivoting arm  66 . The damper  62  and the gas actuator  60  may be separate and distinct. They may be at distance from each other. 
     The lower pivoting arm  66  may be joined to the longitudinal beam  34  by means of the lower pivot joint  48 J. A transversal beam  36  is apparent. The rotation axis  9  of the wheel  8  may extend through the longitudinal beam  34 . The ground clearance GC between the platform  12  and the ground G is represented. An upper longitudinal beam  40  of the frame  32  may form an upper and outer end of the wheel housing  18 . 
     A wheel support  68  receives the wheel  8 . The wheel support  68  may comprise bearing about which the wheel  8  turns around its rotation axis  8 . The wheel support  68  may be joined to the upper pivoting arm  64  and the lower pivoting arm  66 . Thus, the outboard ends of these pivoting arms may be maintained at a fixed distance. joints, such as pivot joints or ball joints  68 J may attach the wheel support  68  to the upper pivoting arm  64  and to the lower pivoting arm  66 . The ball joints may allow rotation with respect to three directions. Then, the wheel support  68  may swivel about a vertical pivot axis  68 P in any angular orientation of the arms with respect to the frame  32 . 
     Accordingly, the wheel support  68  may be a steering knuckle. A steering actuator (not represented) may control the orientation of the steering knuckle about the vertical pivot axis  68 P. 
     A connection  68  of the cooling system  24  is apparent. The connection  68  may comprise a deformable portion. The connection  68  may comprise a tube  70 . The tube  70  may be a resilient tube  70  and/or an arcuate tube  70 . The tube  70  may form an arcuate line with curves in the cooling system  24 . The tube  70  may project from the electric engine  42 . The tube  70  may extend toward a pivoting arm, for instance the upper pivoting arm  64 . The tube  70  may extend along the upper ball joint  68 J attaching the upper pivoting arm  64  to the wheel support  68 . The tube  70  may be deformed in order to accommodate the motion of the engine  42  about the ball joints  68 J. 
     The connection  58  may comprise a pipe  72 , notably a stiff pipe. The pipe  72  may project from the tube  70 . The pipe  72  may be essentially straight. It may be rigidly fixed to the upper pivoting arm  64 . It may extend toward the pivot joint  48 J attaching the upper pivoting arm  64  to the wheel housing  18 . The pipe  72  may he stiffer than the rube  70 . The tube  70  may be more resilient than the pipe  72 . 
     As an option, the connection  58  may comprise an additional resilient tube  70 A joining the pipe  72  to the frame  32 . 
     As an option, the connection  68  comprise a single resilient tube projecting from the electric engine  42  to the pivot joint  48 J attaching the upper pivoting arm  64  to the wheel housing  18 . 
     The electric engine  42  may be an in-wheel electric engine  42 . The in-wheel electric engine  42  may be in the rim  8 R of the wheel  8 . The in-wheel electric engine  42  may be encircled by the tire  8 T received by the rim  8 R. The in-wheel electric engine  42  may comprise a portion outside the wheel  8 . It may comprise an inner face outside the wheel  8 , and notably outside the rim  8 R. 
     A heat exchanger  30  is represented with a dotted line. The eight of the heat exchanger  30  is smaller than that of the wheel housing  18 . The wheel housing  18  extends on the whole height and/or the whole width of the heat exchanger  30 . The wheel  8  may extends on the whole height of the heat exchanger  30 . Thus, the heat exchanger  30  is disposed in a narrow space. Its integration in the frame  32  requires a small place. The cooling system  24  is therefore compact. 
     The bus  2  comprises at least one seat  56 , for instance several seats forming one row. Each seat  56  may comprise a seat base  56 B and a back rest  56 R. The seat(s)  56 , notably the seat base(s)  56 B, may be above the cooling system  24 . The seat(s)  56 , notably the seat base(s)  56 B, may be above the connection  58 . The seat(s)  56 , notably the seat base(s)  56 B, may be above the tube(s)  70  and/or the pipe  72 . Accordingly, the available space for the connection  68  and its portion is delimited by the seat(s)  56 . Such an arrangement optimises the bus  2  compacity and respect a specific seat arrangement allowing to increase the number of seats  56  in the bus. Hence, the invention improves compacity. 
     The current figure only describes the cooling system  24  in relation with one wheel  8 . However, the wheel housing  18  may further receive another wheel  8 . Thus, the above description may be duplicated for said another wheel  8 . 
     In addition, the bus  2  may comprise another wheel housing which is symmetric to the above described one. A symmetric cooling system may be associated to the symmetric wheel housing  18  As an alternative, the ball joints  68 J may be replaced by pivot joints. 
       FIG. 4  provides a schematic illustration of a cut out of a wheel where a cooling system  24  according to the invention, spans. The bus  2  may correspond to those as described in relation with any one of  FIGS. 1 to 3 . 
     The transversal direction T, the longitudinal direction L and the vertical direction V are provided. These directions (T, L, V) may be perpendicular to each other. The rotation axis  9  of the wheel  8  may be along the transversal direction T, notably depending on the steering angle of the wheel support  68 , and of the configuration of the suspension system  44 . The position of the vertical pivot axis  68 P is provided. A longitudinal beam  34  is represented, whereas the pivoting arms are omitted for the sake of clarity. 
     The wheel support  68  may comprise a main body  68 M also designated as central body. The main body  68 M may be disposed in the wheel  8 , notably in the radial space  8 C delimited by the rim  8 R. The radial space  8 C may form an inner cavity in the rim  8 R. The radial space  8 C may have an annular shape. It may have a toroidal shape encircling the rotation axis  9 . In addition, the wheel support  68  may comprise an inner plate  74  to which the electric engine  42  is fixed. The inner plate  74  may be fixed to the main body  68 M by fixation means  74 F such as screws. The fixation means  74 F may project along, and notably over the electric engine  42 . 
     The electric engine  42  may comprise a rotor  42 R and a stator  42 S. The rotor  42 R may comprise permanent magnets (not represented). The stator  42 S may comprise magnetic coils. The electric engine  42  may be of radial type, with a radial magnetic air gap. Alternatively, it may be an axial one. 
     The rotor  42 R may be outside the stator  42 S. The rotor  42 R may encircle, and possibly encapsulate the stator  42 S. As an option, the stator  42 S may be fixed to the inner plate  74  at a location outside the rim  8 R, and more generally the wheel  8 . Fittings  58 F (only one represented) of the connection  58 , may form the inlet and the outlet of the electric engine  42 , and may cross the inner plate  74 . As an example, the fittings  58 F may be connected to the tube  70 . 
     The cooling circuit  24  may comprise an inner network  76  through the electric engine  42 . The cooling circuit  24 , respectively the inner network  76 , may comprise at least one loop in the electric engine  42 , notably in the stator  42 S. The inner network  76  may form a serpentine. The inner network  76  may allow a cooling fluid flow adapted for cooling the electric engine  42 . The inner network  76  may be formed in, and in thermal contact of the stator  42 S. The inner network  76  may be at distance from the rotor  42 R. The inner network  76  may be, at least partially in the radial space  8 C; and more generally in the wheel  8 . Thus, the inner network  76  may directly cool the stator  42 S, and may cool the magnetic coils heated by the electric power. Then, the temperature may be reduced during drive, and the maximum torque may be delivered continuously. 
     The wheel  8  may comprise a disc brake with a brake calliper and a brake disc  78 . The disc brake may be an emergency brake, or a safety brake. It may be activated mechanically. It may assist the electric engine  42  when it is used a power generator during braking. The brake disc  78  may be at distance from the electric engine  42 . The main body  58 M of the wheel support  58  may be arranged between them. The brake disc  78  may be in the wheel  8 . The thickness TH of the stator  42 S may be smaller than the distance D between the brake disc  78  and the stator  42 S. The thickness TH and the distance D may be measured transversally and/or along the rotation axis  9  or the wheel  8 . 
     Optionally, the thickness of the electric engine  42  is as thick or smaller than the distance D between the brake disc  78  and the electric engine  42 . 
     The arrangement of the brake disc  78  with respect to the electric engine  42 , respectively the stator  42 S, reduce the thermal effect of the brake disc  78  on the magnetic parts. Accordingly, the performances of the electric engine  42  are preserved. Its physical properties too. 
     The tube  70  may define a first passage with a first inner width in the cooling circuit  24 . The inner network  76  may define a second passage with a second inner width in the cooling circuit  24 . The first passage may be outside the in-wheel electric engine  42 . The first inner width may represent at least 80% of the second inner width. As an option, the first inner width is larger than the second inner width. The widths may be measured perpendicularly to the cooling flow through the corresponding segment. 
     The heat exchanger  30  is represented. Along the longitudinal direction, the heat exchanger  30  may be aligned with the wheel  8 . In addition, the heat exchanger  30  may be outside the wheel housing in which the wheel is arranged. 
       FIG. 5  provides a schematic illustration of a wheel  8  combined with a cooling system  24  of a bus  2  according to the invention. The bus  2  may correspond to those as described in relation with any one of  FIGS. 1 to 4 . 
     The transversal direction T, the longitudinal direction L and the vertical direction V are provided. These directions (T, L, V) may be perpendicular to each other, 
     The suspension system  44  is represented with the upper pivoting arm  64  and the lower pivoting arm  66 . The upper pivoting arm  64  and the lower pivoting arm  66  are joined by the wheel support  68 . The ball joints  68 J and the pivot joints  48 J at their transversal ends are represented. The later allows oscillations about the longitudinal pivot axis  48 . The fixation means  74 F of the wheel support  68  are represented. The fixation means  74 F may project from the main body  68 M winch is represented behind the engine  42 . 
     The rim  8 R of the wheel  8  defines a radial space  8 C in which the engine  42  is disposed. The radial space  8 C may have an annular shape around the rotation axis  9 . The engine  42  may be an in-wheel electric engine  42 . The in-wheel electric engine  42 , notably its rotor  42 R, may rotate about the rotation axis  9  of the wheel  8 . 
     The heat exchanger  30  may be at distance from the in-wheel electric engine  42 . The heat exchanger  30  may be at distance from the wheel  8 . The heat exchanger  30  may be outside the wheel housing  18 . The heat exchanger  30  may be in fluid flow communication with the in-wheel electric engine  42  by means of the connections  58 . The represented position of the heat exchanger  30  with respect to the wheel  8  may be purely illustrative in the current figure. 
     The connections  58  may comprise several lines entering or going out of the heat exchanger  30 . The connections  58  may comprise lines attached to the pivoting arms, for instance the upper pivoting arm  64 . As apparent from the current figure, the wheel  8  may transversally comprise an outer half, and an inner half in which the in-wheel electric engine  42  is arranged. The in-wheel electric engine  42  may be at distance from said outer half. 
     The cooling circuit  24  may comprise an inlet  24 I and an outlet  24 O in the in-wheel electric engine  42 . The inlet  24 I and an outlet  24 O may be at the interface between the connections  58  and the in-wheel electric engine  42 . They may be at the interface between the tube  70  and the inner network  76 . The inlet  24 I and an outlet  24 O may be disposed on the upper half of the engine  42 . They may be above the rotation axis  9 . Thereby, they are more protected against stone projections lifted from the ground G. 
     The inner network  76  may comprise passageways arranged radially. A radial passageway extends perpendicularly to the rotation axis  9 . The inner network  76  may comprise circular passageways, for instance around the rotation axis  9  of the wheel  8 . These passageways, and thus the inner network  76 , increase the contact surface between the stator  42 S and the cooling fluid. This surface increase allows a cooling fluid flow speed reduction in order to avoid pressure losses in the cooling circuit. Thus, the associated pump requires less energy. 
     The wheel  8  may comprise a radial space  8 C between the in-wheel electric engine  42  and the rim  8 R. The radial space  8 C may be radially larger than the outer radius  42 O of the in-wheel electric engine  42 , possibly at least two times larger than the outer radius  42 O. For instance, the radial thickness  8 TH of the radial space  8 C may be radially larger than the outer radius  42 O of the in-wheel electric engine  42 , possibly at least two times larger than the outer radius  42 O. 
     The cooling circuit  24  may comprise several tubes  70 . The tubes  70  may be arcuate tubes. They may have elbow portions. The tubes  70  may extend from the inlet  24 I and the outlet  24 O connected to the in-wheel electric engine  42 . The cooling circuit  24  may comprise pipes  72 . The pipes may be in contact of the tubes  70 . They may be one after the other. The pipes  72  may be fixed and secured to at least one pivoting arm ( 64 ;  66 ), notably the upper pivoting arm  64 . The tubes  70  may be more resilient than the pipes  72  in order to allow wheel motions about the vertical pivot axis  68 P. 
       FIG. 6  provides a schematic illustration of the interface between an engine  42 , notably an in-wheel electric engine  42 , and connections  58  of a cooling circuit  24 . The engine  42 , notably an in-wheel electric engine  42 , may correspond to those as described in relation with anyone of  FIGS. 1 . to  5 . The cooling circuit  24  may correspond to anyone of those as described in relation with  FIGS. 1 to 5 . 
     The, cooling circuit  24  may comprises a first passage  80  outside the in-wheel electric engine  42 . The first passage $ 0  may comprise a first inner width W 1 . The inner width W 1  may be an inner diameter. The cooling circuit  23  may further comprise a second passage  82  in the in-wheel electric engine  42 . The second passage  82  may comprise a second inner width W 2 , which may correspond to an inner diameter. The second passage  82  may correspond to the passageway. The second passage  82  may be in fluid flow communication with the inner network  76 . 
     The first passage  80  and the second passage  82  may have similar cross sections. The first inner width W 1  may represent at least 80% of the second inner width W 2 . As an option, the first inner width W 1  is larger than the second inner width W 2 . The ratio W 1 /W 2  may range from 0.8 to 1.50. Optionally the ratio W 1 /W 2  is equal to 1. These inner widths (W 1 ; W 2 ) may be similar. The first inner width W 1  and the second inner width W 2  may be measured at distance from the fitting  58 F. They may be measured where they are constant. They may be measured at the inlet  24 I or at the outlet  24 O of the cooling circuit  24 . 
     By way of an example, the first inner width W 1  measures about: 8 mm, or 10 mm, or 12 mm. The second inner width W 2  may represents at least; 2%, or 4%, or 6%, of the outer diameter of the in-wheel electric engine  42 . The outer diameter may he deduced from the outer radius  42 O as defined in  FIG. 5 . The outer diameter of the engine  42  may be at most: 30 cm, or 25 cm. Thus, the engine is substantially small in order to reduce unbalanced weight, and to increase track control and road holding. 
     The first passage  80  may be formed in a connection  58 , notably in a tube  70 . The tube  70  may be arcuate. Its centreline may draw a curve. The second passage  82  may be formed in the engine  42 , notably an in-wheel electric engine  42 . It may be formed in the stator  42 S. It may be at distance from the inner plate  74  of the wheel support. 
     The current arrangement ensures a smooth transition for the cooling fluid. In addition, it avoids pressure losses which negatively affects the engine temperature control. The size of the required pump may be reduced, and the pumping energy as well. 
     The invention considers an embodiment with the combination of the teachings of  FIGS. 1 to 6 . 
       FIG. 7  provides a schematic illustration of a cooling process of an in-wheel electric engine by means of a cooling circuit for a bus in accordance with a preferred embodiment of the invention. The bus, and notably the cooling circuit, may correspond to anyone of those as described in relation with  FIGS. 1 to 6 , or more generally above. 
     The cooling process may comprise the steps: 
     standby  100 ,
 
heating  102  the in-wheel electric engine, and
 
cooling  104  the in-wheel electric engine by means of the cooling liquid.
 
     During step standby  100 , the in-wheel electric engine may he free of electric power. It may be electrically disconnected from the battery pack. Similarly, the pump may be free of electric power, The cooling fluid may he stopped therein, 
     Steps heating  102  and cooling  104  may be performed simultaneously. After them, the bus, notably the electric engine and the battery pack may return to step standby  100 . 
     During step heating  102  and/or during step cooling  104 , the flow speed of the cooling fluid in the connection may be similar to the flow speed of the cooling fluid in the in-wheel electric engine. 
     During step heating  102  and/or during step cooling  104 , the flow speed of the cooling fluid in the connection may represent: from 50% to 150%, or from 80% to 120%, of the flow speed of the cooling fluid in the in-wheel electric engine. 
     The cooling fluid may be a cooling liquid. Its temperature may be kept below 100° C. 
     During step cooling  104  the in-wheel electric engine, the passenger compartment is heated, and the pressure of the cooling fluid in the connection may be similar to the pressure of the cooling fluid in the in-wheel electric engine.
 
During step heating  102  and/or during step cooling  104 , the pressure of the cooling liquid in the connection may represent: from 50% to 150%, or from 80% to 120%, of the pressure of the cooling liquid in the in-wheel electric engine. The pressure may be the static or the dynamic pressure.
 
     It should be understood that the detailed description of specific preferred embodiments is given by way of illustration only, since various changes and modifications within the scope of the invention will be apparent to the person skilled in the art. The scope of protection is defined by the following set of claims.