Multiple speed ratio transmission with integrated differential for vehicles

Abstract

Multiple speed ratio transmission for driving a pair of half-axles (1,2) of a vehicle, comprising: a primary assembly (100) for taking up a rotational movement from a primary shaft (M1) driven by a motor (M); a gearbox assembly (200) comprising a secondary shaft (214) rotationally driven by the primary assembly (100), a plurality of different secondary gears (220,221,222) mounted idle on the secondary shaft and configured to output to the gearbox assembly different transmission ratios, and at least one first and one second engaging element (218,224) rotating with the secondary shaft and axially slidable on the secondary shaft (214); an assembly (300) for operating the gearbox assembly, configured to axially move said engaging elements (218,224) so as to rotationally engage or disengage the secondary shaft (214) with / from one of the secondary gears (220,221,222) depending on a required transmission ratio; a differential assembly (400) designed to be arranged between the two half-axles (1,2) of the vehicle and to receive a rotational movement from one of the secondary gears for rotational driving of the half-axles; wherein the differential assembly comprises: a differential housing (430), designed to be coupled to the two half-axles; a first gear (410) for receiving the movement for the differential, directly meshing with one or more of the secondary gears (220,221,222) and rotationally coupled to the differential housing; a second gear (420) for receiving the movement for the differential, directly meshing with one or more of the secondary gears (220,221,222) not engaged with the first gear (410) of the differential assembly, rotationally coupled to the differential housing.

Description

[0001] MULTIPLE SPEED RATIO TRANSMISSION WITH INTEGRATED DIFFERENTIAL FOR VEHICLES

[0002] DESCRIPTION

[0003] The present invention relates to a multiple speed ratio transmission with integrated differential for vehicles, in particular electric propulsion vehicles.

[0004] It is known, in the technical sector of automative engineering, to use assemblies for transmission of the movement from the drive shaft to the halfaxles of the wheels, which comprise a gearbox normally of the multiplespeed type and a differential, the different functions of which are well-known.

[0005] In particular, the gearbox is commonly used in combustion engine motor vehicles in order to be able to vary within a wide range the speed of the vehicle, while keeping the internal combustion engine in an optimum operating range in terms of efficiency, driving torque or power.

[0006] The latest generation of vehicles includes electric propulsion vehicles which do not strictly need to have a multiple-speed gearbox, equipped with possible clutch, since the wide availability of torque at every speed and the fact that the engine is not required to “run idle” when the vehicle is stopped means that such vehicles may be equipped with a simple fixed-ratio reducer, consequently of the single-gear type, with one or more reduction stages, in order to simplify the kinematic chain, while reducing at the same time the costs of such a component.

[0007] The use of a fixed ratio, however, despite its constructional simplicity, has several drawbacks since, in order to be able to travel in more severe conditions, i.e. in order to overcome maximum gradients under maximum load, the vehicle requires the smallest possible ratio to avoid overheating or in any case overloading the engine; at the same time, the said ratio must also be able to ensure compliance with the specifications concerning the maximum required speed; this, in addition to requiring engines with a very wide operating range, inevitably results in major limitations in terms of efficiency in one of the two end operating ranges of the vehicle.

[0008] Since it is not particularly problematic to install electric motors which have a high peak power, the current solution to all of the above problems is to use motors which are much more powerful than actually needed, even for basic low-performance vehicles. This results in significantly higher production costs than strictly necessary and often sub-optimal electrical energy consumption.

[0009] It is also known that some electric vehicles are already equipped with a multiple ratio transmission; these include the Porsche Taycan and the Audi RS e-tron GT which feature a two-speed transmission based on an epicycloidal gear train, controlled through the use of two clutch packs. These engage and disengage as needed to select the appropriate gear ratio.

[0010] This solution, while valid in itself, has several drawbacks stemming from the fact that a single-stage epicycloidal gear train, for purely geometric reasons, offers a relatively limited range of gear ratios and to a certain extent limits the selection thereof depending on the size of the assembly. From a practical standpoint, this leads to a preference for a reasonable design simplicity by limiting the transmission to just two final gear ratios.

[0011] Examples of transmissions according to the prior art and the preamble of claim 1 are described in DE10 2019 125156, JP 625999 and WO 2018 / 184808.

[0012] The technical problem which is posed, therefore, is that providing a multiple speed ratio transmission for vehicles, in particular for electric propulsion vehicles, which is able to ensure a high performance of the vehicle and an optimum efficiency under different conditions of use, while being compact and reliable.

[0013] In connection with this problem it is also required that this transmission should have small number of component parts, be easy and inexpensive to produce and assemble and have a low final weight.

[0014] These results are obtained according to the present invention by a multiple speed ratio transmission according to the characteristic features of Claim 1 .

[0015] Further details may be obtained from the following description of a nonlimiting example of embodiment of the subject of the present invention provided with reference to the attached drawings in which:

[0016] Fioure 1 : shows a cross-section along a vertical plane of the transmission according to the present invention;

[0017] Fiqure 2 shows a cross-sectional view of the transmission shown in Fig.1 ;

[0018] Fiqure 3 is a diagram showing the cams formed on a desmodromic shaft;

[0019] Fiqure 4 is a diagram showing the power versus speed / energy consumption of a single-gear electric motor; and

[0020] Fiqure 5 is a diagram showing the power versus speed / energy consumption of the same electric motor with a multiple-gear transmission according to the present invention.

[0021] As shown in Fig. 1 , a preferred example of a multiple-ratio transmission according to the present invention is designed to transmit a rotational movement to a pair of half-axles 1 ,2 of a driving axle of a vehicle and for this purpose comprises a primary assembly 100 for taking up a rotational movement from a rotating shaft M1 of a motor M, in the example of the electric type.

[0022] The transmission is advantageously contained in a housing body, preferably formed by two half-casings 1 a, 1b which are joined together. During use, the housing body may be fixed, for example fastened to a fixed part of the vehicle, which in the example shown in Fig.1 is a base of the electric motor M.

[0023] The rotational movement taken up by the primary assembly 100 is transmitted to a gearbox assembly 200, which comprises a secondary shaft 214 rotationally driven by the primary assembly 100 and a plurality of different secondary gears 220, 221 , 222 mounted idle on the secondary shaft. A first engaging element 218 and a second engaging element 224, rotating together with the secondary shaft, are axially slidable on the secondary shaft 214 itself so that one or other of the secondary gears 220,221 ,222 is rotationally integral with the shaft 214.

[0024] An assembly 300 for controlling operation of the gearbox is configured to axially move said engaging elements 218,224 so as to rotationally engage or disengage the secondary shaft 214 with / from one of the secondary gears 220,221 ,222 depending on a required transmission ratio.

[0025] Depending on the secondary gear rotationally coupled to the secondary shaft 214, the gearbox assembly will output a rotational movement with a different transmission ratio.

[0026] A differential assembly 400 is interposed between the two half-shafts 1 ,2 of the vehicle and receives the rotational movement output from the gearbox assembly by the secondary gear 220,221 ,222 in each case rotationally coupled to the secondary shaft 214, for rotationally driving the said halfaxles.

[0027] In greater detail and with reference to the example of embodiment shown:

[0028] • The primary assembly 100 for taking up the movement comprises: a gear 107 rotationally supported on the first half-casing 1a by bearings 106,108. The gear 107 is rotated by the output shaft M1 of the electric motor M. The gear 107 rotationally drives a crown wheel 126.

[0029] • The gearbox 200 comprises:

[0030] - said secondary shaft 214 supported by bearings 219 and 227 respectively mounted on the first half-casing 1 a and the second half-casing 1 b. One end of the secondary shaft 214 is connected to the crown wheel 126 from which it receives the rotational movement;

[0031] - on the secondary shaft 214 there are mounted:

[0032] - three secondary gears 220,221 ,222 which are free to rotate on bushes 223,225 coaxially fitted on the said shaft;

[0033] - a first front engaging element 218 and a second front engaging element 224, the engaging elements being keyed and slidable axially on the shaft 214 and designed to integrally join rotationally with the shaft one of other of the secondary gears 220,221 ,222, depending on the required speed. In the preferred example, the first front engaging element 218 is arranged between one end of the secondary shaft 214 and the first secondary gear 220 and is axially movable along the secondary shaft between a position disengaged from said first gear 220 and a position engaged with said first gear 220. The second engaging element 224 is axially arranged between the second gear 221 and the third gear 222 and is movable axially along the shaft between a position engaged with the second gear 221 and a position engaged with the third gear 222, there also being defined an intermediate position for disengagement from both the gears, which may therefore be kept in the idle condition with respect to the secondary shaft. The secondary gears may for example be in the form of respective pinions with different diameters.

[0034] • The operating assembly 300 comprises:

[0035] - an actuator 310, for example composed of an electric motor 311 and a reducer 312, mounted on the second half-casing 1b and connected to:

[0036] - a desmodromic shaft 309 supported on bearings 313,317 respectively mounted on a respective one of the two half-casings 1a, 1b;

[0037] - forks 316 are mounted on the desmodromic shaft 309 axially movably upon command of the actuator for axial operation of the front engaging elements 218,224 for selecting the secondary gear 220,221 ,222 to be rotated depending on the transmission ratio of the required speed; - cams 314 (Fig. 3) formed on the desmodromic shaft 309 determine, during rotation of the shaft 309, the axial displacement of the forks and therefore of the front engaging elements for engaging or disengaging the speeds.

[0038] Preferably, the axial movement is transmitted to the forks 316 by the cams 314 located on the desmodromic shaft 309 by means of a roller wheel 333 and a pin 332 connected to a drive element 334 fixed to the fork by a pin.

[0039] In greater detail, preferably, in the recesses of the cams 314 formed on the desmodromic shaft 309, intended to drive the fork 316, the following are arranged: a central pin 332 integral with the fork and a freely rotatable roller wheel 333 located between the pin and the profile of the cam, so as to reduce the friction during rotation of the desmodromic shaft, in order to facilitate engagement of the speed.

[0040] In preferred embodiments, the actuator for driving the cam shaft 309 may be arranged coaxially with the shaft itself (Fig. 1 ) or in an axially offset position, with suitable means for transmission of the movement to the desmodromic shaft 309. Furthermore, the actuator may be housed inside the casing 1 a which supports it or on the outside thereof.

[0041] • The differential assembly 400 comprises:

[0042] - a differential housing 430 supported by means of the bearings 431 on the first and second casings 1 a,1 b;

[0043] - a first gear 410 with a double toothing 411 ,412 of different diameter, respectively meshing with either one of the two secondary gears 220,221 of the secondary shaft 214;

[0044] - a secondary gear 420 with a single toothing 421 , having a further different diameter, for meshing with the last gear 222 of the secondary shaft.

[0045] In preferred embodiments, the housing 430 of the differential comprises a first housing part 430a which supports a first half-axle 1 of the two half-axles and a second housing part 430b which supports the second half-axle 2 of the two half-axles, the two housing parts being assembled to form a single body. The first gear 410 of the differential is mounted on the first housing part 430a and the second gear 420 is mounted on the second housing part 430b.

[0046] Preferably, the first gear 410 and the second gear 420 of the differential assembly rotate coaxially with the axis of the two half-shafts 1 ,2 so that the transmission is extremely compact in the radial direction.

[0047] The differential assembly is therefore driven by one of the gears 410,411 ,420 rotationally integral with the differential housing 430.

[0048] The differential housing generally houses inside it a speed distribution assembly which, in the example shown, is of the type (per se conventional) comprising bevel wheels 413 and 423 keyed onto each half-axle 1 ,2.

[0049] According to a preferred embodiment, the two half-casings 1a, 1 b are configured so that, once joined together, the differential assembly 400 is contained inside the housing body, with the arrangement of said bearings 431 in between the half-casings 1a, 1 b and the housing 430 of the differential.

[0050] An electronic unit 500 with programmable software is envisaged for the control and operation of the drives and the moving parts.

[0051] With this configuration, an example of operation of the transmission according to the invention is as follows: when it is required to vary the transmission ratio (gear), the management software activates the actuator 310 which causes rotation of the desmodromic shaft 309 which, in turn, via the cams 311 , causes the axial displacement of the forks 316, thus displacing the engaging elements 318 and 324.

[0052] This movement may be controlled depending on the speed and the torque of the electric motor, the speed of the vehicle, the strength of the current which can be supplied by the battery, the possible selection of travel mode (sport, touring, economy, rain) and in particular the type of gear change (i.e. whether changing up with the gears from first to second or from second to third, or changing down from third to second or from second to first).

[0053] In the case of changing up from the first speed to the second speed, the software determines the stoppage time for the operating current of the electric motor M so as to reduce the torque of the secondary shaft 214 such that the engaging element 224 may disengage from the gear 222 and engage with the gear 221 .

[0054] In the case, instead, of changing down (for example from the second speed to the first speed), the operation becomes more complex because, in order to engage correctly the lower gear, it is required first of all to reduce the torque of the shaft 214, rotate the desmodromic shaft 309 so as to disengage the engaging element 224 of the second speed; once disengaged, it is required to supply again the motor M with current in order to accelerate again the shaft 214 and reach the speed which the gear 222 has at that moment, and then reduce again the torque of the shaft 214 so that the engaging element 224 may engage with the gear 222 of the first speed. In emergency conditions it may also be required to place the vehicle in the idle condition; therefore, in the management software it is envisaged finding the “neutral” position of the gears, which normally, but not necessarily, is arranged between the first speed and the second speed.

[0055] As can be seen from a comparison of the diagrams shown in Figs 4 and 5, with the transmission according to the invention, in particular in the case of electric vehicles, the power and torque curve of these motors may be fully exploited.

[0056] It is therefore clear how with the multiple speed ratio transmission according to the invention, the configuration of which determines the operation of the differential by means of direct coupling between secondary gears of secondary shaft of the gearbox and the gears for taking up the movement of the said differential, it is possible to use only two rotation axles, instead of the conventional three which comprise a further shaft between the secondary shaft and the differential. The configuration according to the invention therefore allows a reduction in weight and greater ease of assembly with savings in terms of the final costs of the transmission.

[0057] As a result of the housing of the primary, gearbox and operating assemblies, as well as the differential inside the two half-casings, the transmission is very compact with the further advantage of a reduction in the overall dimensions, allowing the easy use of and freedom of technical choice of a number of ratios which will be limited only by the maximum dimensions which the assembly must have during installation inside the motor unit.

[0058] A further advantage is the possibility of achieving more favourable transmission ratios through appropriate sizing of the secondary gears and movement input gears of the differential.

[0059] The description provided with reference to three gear ratios illustrates a number of - but not all - the examples of embodiment according to the invention, examples of embodiment with only two transmission ratios or with more than three transmission ratios being possible. It is considered, however, that three ratios may constitute an optimum compromise in terms of costs and benefits.

[0060] Although described in detail, it is also envisaged that the different ratios may be selected during travel, or when the vehicle is at a standstill, both via mechanical commands and by means of electronic actuation or by means of a servo mechanism of any type.

[0061] The choice of ratio to be used during travel may be determined by the driver as desired or controlled independently by the same vehicle (by means of algorithms or other data processing logic configured in the electronic control unit) so as to provide a so-called automatic gearbox.

[0062] Although described in connection with a number of embodiments and a number of preferred examples of implementation of the invention, it is understood that the scope of protection of the present patent is determined solely by the claims below.

Claims

CLAIMS1. Multiple speed ratio transmission for driving a pair of half-axles (1 ,2) of a vehicle, comprising:- a primary assembly (100) for taking up a rotational movement from a primary shaft (M1) configured to be driven by a motor (M);- a gearbox assembly (200) comprising a secondary shaft (214) rotationally driven by the primary assembly (100), a plurality of different secondary gears (220,221 ,222) mounted idle on the secondary shaft and configured to output to the gearbox assembly different transmission ratios, and at least one first and one second engaging element (218,224) rotating with the secondary shaft and axially slidable on the secondary shaft (214);- an assembly (300) for operating the gearbox assembly, configured to axially move said engaging elements (218,224) so as to rotationally engage or disengage the secondary shaft (214) with / from one of the secondary gears (220,221 ,222) depending on a required transmission ratio;- a differential assembly (400) designed to be arranged between the two half-axles (1 ,2) of the vehicle and to receive a rotational movement from one of the secondary gears for rotational driving of the half-axles; wherein the differential assembly comprises:- a differential housing (430), designed to be coupled to the two half-axles;- a first gear (410) for receiving the movement for the differential, directly meshing with one or more of the secondary gears (220,221 ,222) and rotationally coupled to the differential housing;- a second gear (420) for receiving the movement for the differential, directly meshing with one or more of the secondary gears (220,221 ,222) not engaged with the first gear (410) of the differential assembly, rotationally coupled to the differential housing, characterized in that the first gear (410) of the differential assembly has two toothings with a different diameter, each toothing meshing with a respective different secondary gear of the gearbox assembly.

2. Transmission according to Claim 1 , characterized in that the second gear (420) of the differential assembly has a toothing with a further different diameter meshing with a respective further different secondary gear (222) ofthe gearbox assembly.

3. Transmission according to one of the preceding claims, wherein the primary shaft is driven by an electric motor (M).

4. Transmission according to one of the preceding claims, wherein the housing (430) of the differential comprises a first housing part (430a) which supports a first half-axle (1) of the two half-axles and a second housing part (430b) which supports the second half-axle (2) of the two half-axles and wherein the first gear (410) is mounted on the first housing part and the second gear (420) is mounted on the second housing part.

5. Transmission according to one of the preceding claims, wherein the primary assembly (100), the gearbox assembly (200) and the differential assembly (400) are contained inside a housing body preferably formed by two half-casings (1a, 1 b) and designed to be attached to a fixed part of the vehicle.

6. Transmission according to one of the preceding claims, wherein the first gear (410) and the second gear (420) of the differential assembly rotate coaxially with the axis of the two half-axles (1 ,2).

7. Transmission according to one of the preceding claims, wherein the primary assembly (100) comprises a gear (107) supported by bearings (106;108) mounted on a first half-casing (1 a) and rotated by the output shaft (M1 ) of the motor (M) and a crown wheel (126) driven by said gear (107) and designed to transmit the movement to the secondary shaft (214) of the gearbox assembly.

8. Transmission according to one of the preceding claims, wherein said secondary gears (220,221 ,222) are mounted on bushes (223;225) which are coaxially fitted onto the secondary shaft and are idle with respect thereto.

9. Transmission according to one of the preceding claims, wherein the engaging elements of said gearbox assembly (200) are front engaging elements (218;224) axially slidable on the secondary shaft (214) between at least a position of engagement with a secondary gear and a position of disengagement from each secondary gear, corresponding to an idle condition.

10. Transmission according to one of the preceding claims, wherein the assembly (300) for operating the gearbox (200) comprises an electric actuator (310) connected to a desmodromic shaft (309) which has, mountedthereon, forks (316) which are axially movable depending on the rotation of the desmodromic shaft for displacement of the front engaging elements (218,224) for selecting the secondary gear (220,221 ,222) to be rotated depending on the required speed.

11. Transmission according to Claim 10, characterized in that cams (314) configured to perform the axial displacement of the forks and therefore of the front engaging elements during rotation of the desmodromic shaft (309) are formed on the desmodromic shaft.

12. Transmission according to one of the preceding claims, comprising an electronic unit (500) with programmable software designed to control and operate a gearbox operating unit.

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