Gearbox for Vehicle Electric Axle and Integrated Electric Axle

Technical Field

The present disclosure relates to the field of drive systems of vehicles, particularly to a gearbox of an electric axle (electrically-driven axle) for electric drive vehicles (for example, a battery electric vehicle or a fuel cell vehicle) and an integrated electric axle including the gearbox.

Background Art

The current electric drive vehicles are mostly configured with a central drive system on a drive axle (e.g., a rear axle), and a drive shaft (e.g., a rear shaft) for connecting two wheel shafts is housed in the drive axle. The central drive system may be a combination of one or two motors and a multi-speed gearbox (or transmission box), an output shaft of the gearbox being oriented perpendicular to the drive shaft and connected to the drive shaft via a long distance countershaft arranged coaxially with the output shaft of the gearbox. This drive system is heavy, occupying large space, and drive efficiency is low. Moreover, the countershaft and drive shaft perpendicular to each other also require a cardan shaft joint for connection.

For such a drive system, the center of gravity of the drive system including the gearbox is located further from the geometric center of the axle housing due to the long countershaft between the gearbox and the drive axle, which is detrimental to the performance of NVH of the vehicle.

Summary of the Invention

An object of the present disclosure is to resolve one or more of the above-described technical problems.

In one aspect, a gearbox for a vehicle electric axle is provided to provide a neutral position and at least one non-neutral gear shift position, wherein each of the at least one non-neutral gear shift position includes a gear drive gear and a gear driven gear engaged with each other, the gearbox including: an output shaft on which a gear driven gear for each non-neutral gear shift position is mounted and to which an output drive gear is fixedly attached, the gear driven gear for each non-neutral gear shift position being capable of being engaged to the output shaft and disengaged from the output shaft; a drive shaft configured such that two opposite ends in an axial direction are connected to wheel shafts of two wheels, respectively, an output driven gear that is rotatable independently from the drive shaft and engaged with the output drive gear being mounted on the drive shaft, and a drive gear being fixedly attached to the drive shaft, the output driven gear including a driven gear rotating synchronously therewith; and a first and a second balance shafts arranged on opposite sides in a radial direction of the drive shaft, the first and second balance shafts respectively including: a first and a second balance shaft input gears fixedly attached to a respective balance shaft and having the same outer diameter and number of teeth and simultaneously engaged with the driven gear; and a first and a second balance shaft output gears fixedly attached to a respective shaft and having the same outer diameter and number of teeth and simultaneously engaged with the drive gear.

In another aspect of the present application, an integrated electric axle for a vehicle is provided, including: an axle housing including two axle housing portions; two wheel shafts respectively housed within the two axle housing portions; and the gearbox for a vehicle electric axle mentioned above, a gearbox housing of the gearbox positioned between and connected with the two axle housing portions, and opposite ends of the drive shaft of the gearbox being respectively connected to the two wheel shafts.

In the gearbox for a vehicle electric axle of the present application, the opposite ends of the drive shaft in the axial direction are respectively connected to the two wheel shafts of the vehicle, two balance shafts are symmetrically arranged on the opposite sides in the radial direction, and the output driven gear of the gearbox transmits the rotational motion to the drive shaft via the transmission of the gears on the two balance shafts. The axial force on the drive shaft is balanced or counteracted to the maximum extent in the case where all gear meshing pairs are helical gear pairs. All shafts of the gearbox (including the input shaft, the main shaft, the output shaft, the drive shaft, and all balance shafts) are arranged in parallel with each other such that the volume of the gearbox and the occupied space required for the gearbox are reduced, and as a result, the drive system including a motor and the gearbox is arranged or mounted more flexibly on the drive axle. Due to the parallel arrangement of the shafts and the addition of two balance shafts near the drive shafts (two opposite sides), the center of gravity of the gearbox is closer to the geometric center of the axle housing of the drive axle, improving the performance of NVH of the vehicle. The gearbox of the present application does not limit the number of gear shift positions, and when the number of nonneutral gear shift positions is greater than 2 (e.g., four gear shift positions of an illustrated embodiment), the climbing ability of the vehicle can be greatly improved.

Brief Description of the Drawings

The above and other merits and advantages are readily understood when the present invention is understood in reference to the following detailed description in conjunction with the accompanying drawings. The drawings are for illustrative embodiments only, merely to illustrate the principles of the present application, are not exclusive and restrictive, and are not necessarily drawn to scale.

Fig. 1 is a schematic diagram of the drive principle of a gearbox of the present application.

Fig. 2 is a stereoscopic view of an exemplary structural embodiment capable of implementing the drive principle of Fig. 1.

Fig. 3 is a rear view of Fig. 2 illustrating the relative spatial arrangement of the respective shafts and gears.

Fig. 4 is a simplified schematic view of a gearbox constructed according to the present application mounted on a drive axle of a vehicle.

Description of Embodiments

The present application provides a gearbox for an electric axle, which may be applied to any vehicle using electrical energy as a power source, such as a battery electric vehicle (BEV) and a fuel cell electric vehicle (FCEV), and which is particularly advantageous for heavy commercial vehicles, such as heavy trucks.

The gearbox of the present application may be a gearbox (or transmission box) that is capable of providing a neutral position and only one or more non-neutral gear shift positions. The drawings will detail the drive principle of the gearbox of the present application by providing a gearbox with four non-neutral gear shift positions as an example.

Referring to Fig. 1 , the gearbox generally includes an input shaft 10, a main shaft 20, an output shaft 30, a drive shaft 40, and a first balance shaft 50 and a second balance shaft 60respectively arranged on two opposite sides in a radial direction of the drive shaft 40. The dashed box in Fig. 1 may be understood as illustrating a housing of a gearbox.

The input shaft 10 of the gearbox protrudes the housing of the gearbox, and is arranged coaxially with an output shaft of a motor EM (e.g., a synchronous or asynchronous AC motor, or a DC brushed or brushless motor, optionally including an inverter) and connected to the output shaft of the motor EM in any known manner in the art (e.g., a key connection), such that the output shaft of the motor EM transmits the rotational motion of the motor EM to the input shaft 10 of the gearbox.

The input shaft 10 is rotatably supported by the gearbox housing and an input shaft gear 12 is fixedly attached thereto. In some embodiments, the input shaft gear 12 may be a shaft gear integral with the input shaft 10 or a gear that is individually provided and assembled and fixed thereto.

Note that, herein, a gear "fixedly attached" to a shaft means that the gear and the shaft are attached or fixed together such that they cannot move relative to each other, especially cannot rotate relative to each other, or that the rotation of any one of the gear and the shaft causes the other to rotate synchronously. In addition, "fixed attachment" of one gear to one shaft herein may be achieved by any known manner in the art, including, but not limited to, integral formation of the gear with the shaft (i.e., making one piece), connection using fasteners, welding, splined connection, and the like. If a gear is described as "mounted" or "sleeved" on a shaft, it only means literally that the gear is mounted or sleeved on the shaft, and does not define the relative rotational freedom and the relative translational freedom between the gear and the shaft. A gear "independently rotationally mounted" on a shaft indicates that the gear is sleeved on the shaft in such a way that the gear can rotate independently from the shaft, and the rotation of one of the gear and the shaft does not cause the other to rotate. A gear “detachably mounted/sleeved” on a shaft refers to that the gear can be engaged to the shaft so that the two cannot rotate relative to each other and the gear can be disengaged from the shaft so that the two can rotate independently from each other. Other similar expressions are understood by reference to the definitions of these terms.

The main shaft 20 arranged in parallel with the input shaft 10 is rotatably supported by the gearbox housing, for example by means of two bearings. The main shaft 20 is fixedly attached with a first-speed drive gear 22, a second-speed drive gear 24, a third-speed drive gear 26, and a fourth-speed drive gear 28. The input shaft gear 12 of the input shaft 10 is always engaged with the fourth-speed drive gear 28 to drive the main shaft 20 to rotate, and the main shaft 20 in turn drives the other speed drive gears 22, 24, and 26 to rotate synchronously. The gears 22, 24, 26, and 28 each have a different outer diameter and/or different number of teeth. In the illustrated embodiment, the outer diameter and number of teeth of the four speed drive gears 22, 24, 26 and 28 are increasing gradually; however, the arrangement order or positional relationship of the four drive gears may differ from that of the illustration. Optionally, the one engaged with the input shaft gear 12 of the input shaft 10 may be any one of the four drive gears, not only the fourth-speed drive gear 28 illustrated. Optionally, the main shaft 20 may be provided with an additional gear that is fixedly attached for engaging the input shaft gear 12 of the input shaft 10 to transmit a rotational motion from the input shaft 10 to the main shaft 20.

In the illustrated embodiment, the four speed drive gears 22, 24, 26 and 28 (and optionally an additional gear) are all fixedly attached to the main shaft 20 and rotate synchronously with the main shaft20. These gears may be integrally formed, or may be individually formed and each fixedly attached to the main shaft 20, or adjacent two or three may be integrally formed as actually desired.

The output shaft 30 is arranged in parallel with the main shaft 20, and a first-speed driven gear 32, a second-speed driven gear 34, a third-speed driven gear 36, and a fourthspeed driven gear 38, which are engaged with the first-speed drive gear 22, the second- speed drive gear 24, the third-speed drive gear 26, and the fourth-speed drive gear 28 respectively, can be independently rotatably mounted on the output shaft. The four driven gears 32, 34, 36, and 38 also have different (outer diameters) and/or different numbers of teeth, corresponding to the four drive gears 22, 24, 26 and 28, respectively, thereby enabling the provision of four different transmission ratios for the gearbox. When the four drive gears 22, 24, 26, and 28 and the main shaft 20 rotate at the same speed due to the engagement of the drive gear 28 with the input shaft gear 12, the four driven gears 32, 34, 36, and 38 rotate in the same direction, but at different rotational speeds. In the illustrated embodiment, the rotational speeds of the driven gears 32, 34, 36, and 38 increase sequentially.

The four driven gears 32, 34, 36, and 38 on the output shaft 30 are merely sleeved on the output shaft 30, and have no engagement with the output shaft 30. Two gear shift devices (or members) 33 and 37 fixedly attached to the output shaft 30 are provided on the output shaft 30, so rotation of any one of the two gear shift devices 33 and 37 drives the other of the output shaft 30 and the two gear shift devices 33 and 37. The first gear shift device 33 is disposed between the first-speed driven gear 32 and the second-speed driven gear 34 and is configured to selectively engage any one of the first-speed driven gear 32 and the second- speed driven gear 34 to provide a first or second gear shift position, and the second gear shift device 37 is disposed between the third-speed driven gear 36 and the fourth-speed driven gear 38 and is configured to selectively engage any one of the third-speed driven gear 36 and the fourth-speed driven gear 38 to provide a third or fourth gear shift position. The first gear shift device 33 and the second gear shift device 37 are configured to be capable of providing a neutral position (as shown in Fig. 1 , where the two gear shift devices 33 and 37 are not engaged with any one of the four driven gears 32, 34, and 36, and the rotation of the four driven gears 32, 34, 36, and 38 does not result in rotation of the output shaft 30) and four non-neutral gear shift positions: a first non-neutral gear shift position, where, when the first gear shift device 33 is engaged with the first-speed driven gear 32 but not engaged with the second-speed driven gear 34, the output shaft 30 fixed together with the first gear shift device 33 has the same rotational speed with the first-speed driven gear 32; a second non- neutral gear shift position, where, when the first gear shift device 33 is engaged with the second-speed driven gear 34 but not engaged with the first-speed driven gear 32, the output shaft 30 fixed together with the first gear shift device 33 has the same rotational speed with the second-speed driven gear 34; a third non-neutral gear shift position, where, when the second gear shift device 37 is engaged with the third-speed driven gear 36 but not engaged with the fourth-speed driven gear 38, the output shaft 30 fixed together with the second gear shift device 37 has the same rotational speed with the third-speed driven gear 36; and a fourth non-neutral gear shift position, where, when the second gear shift device 37 is engaged with the fourth-speed driven gear 38 but not engaged with the third-speed driven gear 36, the output shaft 30 fixed together with the second gear shift device 37 has the same rotational speed with the fourth-speed driven gear 38. In this way, the output shaft 30 may have a zero rotational speed or a rotational speed corresponding to the engaged driven gear, depending on whether and which gear driven gear is engaged by the two gear shift devices 33 and 37. It will be understood by those skilled in the art that the number of gear shift devices or members is not limited to the two as illustrated. The gearbox of the present application may include only one gear shift device capable of not engaging with the four driven gears so as to provide a neutral position and selectively engaging with any one of the four driven gears to provide any non-neutral gear shift position, or may include three or four gear shift devices. The gear shift device may employ any possible mechanical structure, such as a pawl clutch, so long as the gearing function can be achieved and provide all of the required gear shift positions.

An output drive gear 39 is also fixedly attached to the output shaft 30, and thus the output drive gear 39 rotates with the output shaft 30. An output driven gear 49, which is engaged with the output drive gear 39, is independently rotatable sleeved on the drive shaft 40, and the output driven gear 49 is rotated by the output drive gear 39 without causing the drive shaft 40 to rotate.

The output driven gear 49 includes a driven gear 47 that is integrally formed and thus rotates synchronously about the drive shaft 40 together. As shown in the drawings, both the output driven gear 49 and the driven gear 47 are integrally formed on a central shaft 70, and the central shaft 70 is independently rotatably sleeved on the drive shaft 40. It is contemplated that the output driven gear 49 and the driven gear 47 may also be formed separately and secured together.

The first balance shaft 50 and the second balance shaft 60 are disposed on two opposite sides in a radial direction of the drive shaft 40, respectively, and are arranged radially symmetrically with respect to the axis of rotation of the drive shaft 40. The two opposite ends of the drive shaft 40 in the axial direction are used to connect two wheel shafts of the vehicle respectively, thereby driving the two wheels to rotate as the drive shaft 40 rotates.

The first balance shaft 50 and the second balance shaft 60 respectively include a first balance shaft input gear 57 and a second balance shaft input gear 67 fixedly attached to respective shafts, respectively, and the two are simultaneously meshed with the driven gear 47 from two opposite sides in the radial direction of the driven gear 47 and are simultaneously driven by the gear 47 to respectively drive the first balance shaft 50 and the second balance shaft 60 to rotate in opposite directions around their respective axes (e.g., when the driven gear 47 rotates clockwise as illustrated, the first balance shaft 50 and the second balance shaft 60 rotate clockwise and counterclockwise, respectively). The first balance shaft 50 and the second balance shaft 60 are also respectively provided with a first and a second balance shaft output gears 55 and 65 fixedly attached to respective shafts, so that the first and second balance shaft output gears 55 and 65 also rotate synchronously with the first and second balance shaft input gears 57 and 67, respectively. The parameters such as outer diameter and number of teeth of the first and second balance shaft input gears 57 and 67 are the same. As a result, the first and second balance shaft input gears 57 and 67 have the same rotational speed when simultaneously driven by the driven gear 47, and thus the first balance shaft 50 and the second balance shaft 60, as well as the first and second balance shaft output gears 55 and 65, also have the same rotational speed.

The drive shaft 40 is provided with a drive gear 45 fixedly attached thereto, and the drive gear 45 is simultaneously engaged with the first and second balance shaft input gears 57 and 67 at the same rotational speed and rotating in the same direction and is driven by both simultaneously to cause the drive shaft 40 to rotate. The first and second balance shaft output gears 55 and 65 have the same parameters of outer diameter, number of teeth, etc., so that both can rotate the drive gear 45 simultaneously. When the gear box described in detail above is in operation, the output shaft of the motor EM drives the input shaft 10 (along with the input shaft gear 12 thereon) to rotate. Due to the engagement of the input shaft gear 12 with the fourth-speed drive gear 28 on the main shaft 20, the main shaft 20 and the other three gear drive gears 22, 24, and 26 thereon rotate in a direction opposite the input shaft 10, with each of the drive gears 22, 24, 26 and 28 simultaneously causing the meshed driven gears 32, 34, 36 and 38 to rotate. Based on the actual engagement of the two gear shift devices with the driven gears, the output shaft 30 (along with the output drive gear 39) does not rotate (e.g., when the gearbox is in a neutral position as shown in Fig. 1) or rotates at the same speed as any one of the driven gears 32, 34, 36, and 38 (e.g., when the gearbox is in one of the first, second, third, and fourth gear shift positions). The output drive gear 39 drives the output driven gear 49 (along with the driven gear 47) to rotate, and the driven gear 47 drives the first and second balance shaft input gears 57 and 67, the respective balance shafts 50 and 60, and the first and second balance shaft output gears 55 and 65 to rotate. Ultimately, the first and second balance shaft output gears 55 and 65 engage from both sides and cause the drive gear 45 to rotate, and the drive gear 45 drives the drive shaft 40 and the two wheel shafts connected at both ends to rotate.

In the gearbox of Fig. 1 , each shaft (the input shaft 10, the main shaft 20, the output shaft 30, and the first and second balance shafts 50 and 60) is arranged parallel to the drive shaft 40 (i.e., drive shaft of a vehicle drive axle) connected to the wheel shaft, offset from each other in a direction perpendicular to their respective axis of rotation. The present gearbox has a more compact structure, a smaller overall dimension, and less space required than a gearbox in the prior art where an output shaft of the gearbox is perpendicular to the drive shaft of the drive axle.

In the gearbox of Fig. 1 , each meshing gear is a helical gear, and the shafts on which the gears are mounted are subjected to a greater axial force while transmitting torque, especially the drive shaft 40 that directly drives the wheel shaft of the vehicle. Comparing to other shafts of the gearbox (e.g., the input shaft 10), the drive shaft 40 has a lower rotational speed, a larger torque, and receives a larger axial force. In the illustrated structure, the drive gear 45 on the drive shaft 40 simultaneously engages on two opposite sides the first and second balance shaft output gears 55 and 65 rotating in opposite directions, and the helical engagement between the first and second balance shaft output gears 55 and 65 and the drive gear 45 causes the first and second balance shaft output gears 55 and 65 to apply axial forces of equal magnitude and in opposite directions to the drive gear 45 such that the axial forces on the drive shaft 40 are mostly cancelled. Thus, the illustrated arranged bi-balance shaft (50 plus 60) structure provides an advantage in reducing the axial force on the drive shaft 40.

The two balance shafts 50 and 60 are arranged proximate the drive shaft 40, playing the role of reducing the axial force described above. Moreover, comparing to a structure without these balance shafts, the center of gravity of the gearbox is located closer to the drive shaft 40 and thus closer to the geometric center of the drive axle, which improves the noise, vibration, and harshness (i.e., NVH) performance of the vehicle.

In the gearbox of Fig. 1 , the input shaft gear 12 of the input shaft 10 directly engages one of the gear drive gears (specifically the fourth-speed drive gear 28) on the main shaft 20. Compared to the gearbox structure in which an additional gear is separately provided on the main shaft 20 in addition to the four drive gears 22, 24, 26 and 28 for engaging the input shaft gear 12 to transmit rotational motion to the main shaft 20, the drive gear 28 provides both the function of transmitting the rotational motion onto the main shaft 20 and the function of the drive gear of one of the gear shift positions. Therefore, one gear meshing pair is reduced in the present gearbox, which makes the structure simpler and improves the transmission efficiency of the gearbox. Of course, those skilled in the art will understand that the technical solution of having an additional gear engaged with the input shaft gear 12 separately on the main shaft 20 and the technical solution of selecting any one of the other drive gears 22, 24, and 26 to engage with the input shaft gear 12 are also within the protection of the present application.

In the gearbox of Fig. 1 , the implementation of a plurality of gear shift positions is achieved by fixedly attaching each gear drive gear to the main shaft 20, mounting each gear driven gear detachably (independently rotatably) on the output shaft 30, and keeping each gear drive gear in mesh with the corresponding gear driven gear all the time. At this point, each gear drive gear may be integrally formed, or two or more thereof may be integrally formed, or may be individually formed and then fixedly attached to the main shaft 20 individually. The detachable mounting of each gear driven gear on the output shaft 30 may be achieved by two gear shift devices 33 and 37 as shown in Fig. 1. As explained previously, the present application does not limit the number of gear shift devices, the form of structures, and other details, as long as it is able to provide a neutral gear and all gear shift positions.

Fig. 2 illustrates an exemplary structural embodiment of a gearbox embodying the drive principle of Fig. 1 , wherein the gearbox housing is removed. Fig. 3 is a rear view of Fig. 2 showing very clearly the spatial positional relationship of each shaft and each gear. The input shaft 10, the main shaft 20, the output shaft 30, the drive shaft 40, and the first and second balance shafts 50 and 60, as well as each gear, are shown. It can also be seen from Fig. 2 that each shaft is hollow, which minimizes the weight of the gearbox. The reduced weight of the gearbox facilitates the flexibility of the entire gearbox to be arranged on a drive axle. For example, a gearbox with less weight, a smaller volume, and a smaller required mounting space may be mounted on either radial side of the drive shaft (i.e., the illustrated drive shaft 40) of the drive axle.

Fig. 4 is a schematic diagram of the gearbox of Fig. 2 mounted on a drive axle of a wheel. The gearbox of the present application may be applied to a vehicle with only one drive axle (e.g., in a drive form of 4x2, 6x2, or 8x2, etc.), and at this point, the drive shaft may be a front shaft (draw vehicle) or a rear shaft (thrust vehicle) of a vehicle, or may be any intermediate shaft for a vehicle including more than two shafts. The above-described gearbox of the present application may also be applied to a vehicle including two drive axles (e.g., in a drive form of 6x4 or 8x4, etc.).

The drive axle of the vehicle may include an elongated axle housing 200, and the axle housing 200 includes two portions 200a and 200b, between which a gearbox of the present application is located. The two portions 200a and 200b are connected to the gearbox housing 100 of the gearbox by fasteners. The gearbox housing 100 includes a motor housing portion 150. Due to the compact structure of the gearbox, the motor housing portion 150 may be provided as part of the gearbox housing 100, which is simplified in structure, less costly, and is advantageous in reducing the weight of the gearbox as compared to a structure in which a separate motor housing is provided and then connected to the gearbox housing.

The gearbox housing 100 and the axle housing 200 may be connected together with commonly used fasteners, such as bolts, for ease of construction and assembly. The interface structure of the gearbox housing 100 to the axle housing 200 is not affected by variations in the design, configuration, or structure of the parts and associated other systems or components (e.g., suspension, plate springs, axles, hubs, wheel brake components, etc.) positioned within the axle housing 200 (200a and 200b). In other words, the interface structure is not affected by variations in the internal structure of the axle housing 200. As a result, the gearbox of the present application has superior versatility.

The present application also relates to an integrated electric axle including the abovedescribed gearbox. The integrated electric axle includes an axle housing 200 consisting of two axle housing portions 200a and 200b, two wheel shafts (not shown in the drawings) for mounting wheels positioned within the two axle housing portions 200a and 200b, respectively, and the above-described gearbox. The gearbox housing 100 of the gearbox is located between and connected to both of the axle housing portions 200a and 200b, and two ends of the drive shaft 40 of the gearbox are respectively connected with the wheel shafts.

An exemplary embodiment of the present application is described in detail above with reference to the accompanying drawings; however, the present disclosure is not limited to the description of the foregoing embodiments, but may be modified within the scope of the present disclosure. The present disclosure may also vary in many ways, all of which are intended to be included within the scope of the present disclosure. Further, it should be understood that no single component is certainly necessary unless a component is expressly designated as essential.