The present invention relates to a axle assembly and to a vehicle comprising such an axle assembly. Such a vehicle may be an automated guided vehicle (AGV).

Axle assemblies may be provided with a plurality of sensors. For example, an Anti Braking System (ABS) nowadays typically comprises encoders that are contactless sensors providing a resolution of approximately 100 pulses per revolution, resulting in an accuracy of 3.6° per pulse. This is considered low resolution, and insufficient for many applications. For example, accurate positioning of an automated guided vehicle, which is also known as “inching”, will require a higher accuracy to accurately position the vehicle. During such “inching”, the vehicle is slowly moved over small distances to accurately position the vehicle. As most ABS sensors are induction based, a further problem arises. After all, induction based ABS sensor will fail to generate a measurement signal at low speeds, e.g. below 10 km/h, typically used for inching. During starting and stopping, the distance that is moved at a speed below the threshold speed required for the induction based sensor to accurately operate, is missed. This leads to an inaccuracy.

There is a need for an axle assembly comprising one or more than one sensor that is capable of providing accurate measurement data suitable for e.g. inching of an (autonomous) vehicle and/or for high precision steering thereof.

European patent application EP 0985910 Al, which is considered the closest prior art, is directed to a structure for fitting a rotary displacement sensor for determining a steering angle to a vehicle. The structure prevents application of a radial force to an input shaft and slack between a rotational shaft and an input shaft, thereby improving durability and detection sensitivity of the rotary displacement sensor. It discloses a base, a rotary part that is rotatable relative to the base, a bearing that is arranged between the base and the rotary part, an encoder that is fixed to the base, wherein the encoder has a rotatable shaft extending in a longitudinal direction and wherein the encoder comprises a connection to the rotary part. The structure disclosed in EP 0985910 Al is related to determining a steering angle displacement, e.g. for applications such as limiting pivoting of a rear axle of a forklift to prevent excessive inclination from centrifugal forces when turning. For such human operated vehicles having a driver, measuring the steering angle displacement at a limited accuracy suffices.

Accurate positioning of an automated guided vehicle (AGV) requires measurements of a steering angle displacement at a high accuracy. Moreover, inching of an autonomous vehicle also requires accurately determining a displacement of said vehicle by measuring a relative rotation of a wheel relative to a wheel bearing shaft in addition to measuring steering angle displacement. EP 0985910 A1 fails to disclose a structure configured to measure a displacement of a vehicle by measuring a relative rotation of a wheel relative to a wheel bearing shaft. Such a measurement is not only unnecessary for a human operated forklift, but it is also far more complex for a number of reasons.

First of all, the nature of rotation of a wheel relative to a wheel bearing shaft requires the use of wheel bearings that require lubrication. Conventionally, such wheel bearings are typically arranged in an enclosed lubrication compartment filled with oil or grease. Such a lubrication however conflicts with a structure as proposed in EP 0985910 A1 for measuring the steering angle displacement.

Secondly, a steering angle displacement is related to an angular displacement over a limited range back and forth, i.e. a rotation clockwise and counterclockwise. Instead, a relative rotation of a wheel relative to a wheel bearing shaft will normally comprise a very high number of revolutions, and is not restricted to a specific range, which increases the complexity of creating a connection between the base and the rotary part.

European patent applications EP 0 174422 A2, EP 2653 837 A1 and EP 0 178 694 A2 are acknowledged as further prior art.

An objective of the present invention is to provide an axle assembly that is improved relative to the prior art and wherein at least one of the above stated problems is obviated.

Said objective is achieved with the axle assembly according to claim 1 of the present invention, comprising:

- a base;

- a rotary part that is rotatable relative to the base;

- a bearing that is arranged between the base and the rotary part;

- an encoder that is fixed to the base;

- wherein the encoder has a rotatable shaft extending in a longitudinal direction;

- wherein the encoder comprises a connection to the rotary part;

- wherein the base is fixedly arranged on or integrated with a wheel bearing shaft ;

- wherein the rotary part is a wheel that is rotatable relative to the wheel bearing shaft;

- wherein the bearing that is arranged between the base and the rotary part is a wheel bearing; and

- wherein the encoder is a wheel encoder that is configured to measure a relative rotation of the wheel relative to the base that is related to a rotation of said wheel.

Instead of using a contactless induction based sensor, the axle assembly according to the invention is provided with an encoder having a rotatable shaft, wherein the encoder comprises a physical connection to the rotary part. Via said physical connection, a relative rotation of the rotary part relative to the base causes a rotation of the rotatable shaft of the encoder under all circumstances and at all speeds, including while driving at very low speeds well below 5 km/h.

According to a preferred embodiment of the invention, the encoder is a high resolution encoder having a resolution of at least 500 pulses per revolution, preferably having at least 750 pulses per revolution, more preferably having at least 1000 pulses per revolution, even more preferably having at least 1250 pulses per revolution, and most preferably having at least 1500 pulses per revolution. A resolution of 500 pulses per revolution results in an accuracy of 0,72° per revolution, whereas a resolution of 1000 pulses per revolution results in an accuracy of 0,36° per revolution. The high resolution encoder should ideally provide enough resolution for mm precise vehicle positioning. Taking into account a wheel radius of typically between 450 and 650 m a resolution of 1000 to 5000 pulses per revolution is preferred. By using a high resolution encoder, an accurate measurement of the relative rotation of the rotary part relative to the base causes is obtained.

According to a further preferred embodiment, the connection between the encoder and the rotary part is flexible. By using a flexible connection, the lifespan of the high resolution encoder may be significantly increased, resulting in a more reliable axle assembly. After all, a flexible connection may prevent that all relative movement, e.g. in axial, radial and angular directions or combinations thereof, is directly transferred for the rotary part to the base or vice versa. For example, over time the bearing that is arranged between the base and the rotary part will wear out to some extent. Wear of this bearing and loads on the axle assembly, and especially combinations thereof, may cause undesired but unavoidable relative movements between the rotary part and the base that would disadvantageously load the encoder.

According to an even further preferred embodiment, the connection is configured to allow one or more than one of:

- a radial displacement of the rotary part relative to the encoder in a radial direction that is directed transverse to the longitudinal direction defined by the rotatable shaft;

- an axial displacement of the rotary part relative to the encoder in an axial direction that is directed in the longitudinal direction defined by the rotatable shaft; and

- an angular displacement of the rotary part relative to the encoder in an angular direction around the longitudinal direction defined by the rotatable shaft.

Allowing a limited displacement already suffices to reduce the magnitude of potentially damaging loads on the encoder. Especially the angular displacement should be of a limited nature, such that it only prevents damage to the encoder, while not interfering with the measurement accuracy of the encoder. Because the rotatable shaft of the encoder will normally exhibit a limited resistance against rotation, the angular displacement of the connection will hardly ever be used. However, when a relative radial and axial displacement occur in combination, it may be advantageous to have some angular flexibility.

Although it is conceivable that the rotatable shaft of the encoder and the flexible connection are integrated in some embodiments, the flexible connection may comprise a flexible shaft coupling in other embodiments.

Preferred embodiments are the subject of the dependent claims.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, and in particular the aspects and features described in the attached dependent claims, may be made subject of divisional patent applications.

In the following description preferred embodiments of the present invention are further elucidated with reference to the drawing, in which:

Figure 1 is a side view of a vehicle comprising an axle assembly according to the invention;

Figures 2 and 3 are perspective views of a front axle assembly of the vehicle of

Figure 1;

Figure 4 is a detailed cross sectional view of the axle assembly;

Figure 5 is a detailed perspective view of the axle assembly;

Figures 6 and 7 show detailed perspective views of a wheel encoder arrangement;

Figures 8 and 9 show detailed perspective views of a steering encoder arrangement.

Figure 1 shows a vehicle 1, more in particular a so-called Terminal Tractor, that comprises an optional intermediate frame 3 that is pivotably attached to the vehicle chassis 2 thereof, and that comprises a connector 4 at the end of intermediate frame 3. The intermediate frame 3 can be lifted with a lift cylinder 6. The vehicle 1 of Figure 1 may be automated, while still allowing (or possibly even requiring) a driver to be seated in the drivers cabin 7. It is however explicitly mentioned that the invention may also be applied to fully automated guided vehicles (AGV’s) of different types and sizes, including driverless vehicles with or without a driver cabin.

The invention will now be elucidated on the basis of an axle assembly 8 of the front wheel hub 9 of the vehicle 1. This axle assembly 8 is shown in Figures 2 and 3, wherein the brake drums 22 are made transparent in Figure 3 to show the wheel bearing shafts 11.

The axle assembly 8 according to the invention comprises a base 12 and a rotary part 13 that is rotatable relative to the base 12. A bearing 14 that is arranged between the base 12 and the rotary part 13 facilitates this relative rotation between the rotary part 13 and the base 12. An encoder 15 is fixed to the base 12, and comprises a rotatable shaft 16 extending in a longitudinal direction L. The encoder 15 is a high resolution encoder and the encoder 15 is connected to the rotary part 13 via a connection 17.

The high resolution encoder 15 has a resolution of at least 500 pulses per revolution, preferably of at least 750 pulses per revolution, more preferably of at least 1000 pulses per revolution, even more preferably of at least 1250 pulses per revolution, and most preferably of at least 1500 pulses per revolution. The high resolution encoder 15 should ideally provide enough resolution for mm precise vehicle positioning. Taking into account a wheel radius of typically between 450 and 650 mm requires therefore a preferred resolution of 1000 to 5000 pulses per revolution.

In the axle assembly 8 as shown in the Figures, an assembly of base 12, rotary part 13, bearing 14, encoder 15 and connection 17 is applied for two applications (A and B in Figure 5). The first application is for measuring a relative rotation A of a wheel hub 9 relative to the wheel bearing shaft 11, as will be explained in more detail using Figures 4, 6 and 7. The second application is for measuring a relative rotation B of the base 12 relative to the rotary part 13 that is related to a steering angle displacement of the wheel hub 9 relative to an axle housing 18. This will be explained in more detail using Figures 4, 8 and 9.

In both applications of the shown axle assembly 8, the connection 17 between the encoder 15 and the rotary part 13 is preferably flexible. By using a flexible connection 17, the lifespan of the high resolution encoder 15 may be significantly increased, resulting in a more reliable axle assembly 8. The flexibility of the connection 17 reduces the loads on the high resolution encoder 15 that may be caused by wear of the bearing 14 that is arranged between the base 12 and the rotary part 13, by loads on the axle assembly 8, and especially by combinations thereof. As elucidated below, the bearing 14 may be a wheel bearing 19 or a knuckle bearing 20.

Although it is conceivable that the rotatable shaft 16 of the encoder 15 and the flexible connection 17 are integrated in some embodiments, the flexible connection 17 may comprise a flexible shaft coupling in other embodiments. Such a flexible shaft coupling may for example be a double loop coupling 34.

The connection 17 may be configured to allow one or more than one of:

- a radial displacement of the rotary part 13 relative to the encoder 15 in a radial direction RA that is directed transverse to the longitudinal direction L defined by the rotatable shaft 16;

- an axial displacement of the rotary part 13 relative to the encoder 15 in an axial direction AX that is directed in the longitudinal direction L defined by the rotatable shaft 16; and

- an angular displacement of the rotary part 13 relative to the encoder 15 in an angular direction AN around the longitudinal direction L defined by the rotatable shaft 16. The first application for measuring a relative rotation A of a wheel 9 relative to the wheel bearing shaft 11 is now explained in more detail using Figures 4, 6 and 7. In this first application, the base 12 is fixedly arranged on or integrated with the wheel bearing shaft 11, the rotary part 13 is a wheel 19 that is rotatable relative to the wheel bearing shaft 11, and the bearing 14 that is arranged between the base 12 and the rotary part 13 is a wheel 19. Although the wheel bearing shaft 11 may itself form a base 12, a wheel bearing nut 26 forms a base 12 in the shown embodiment. The wheel bearing nut 26 may comprise an internal screw thread 27 that allows it to be screwed onto an end 28 of the wheel bearing shaft 11. This end 28 is provided with an external screw thread.

Figures 5-7 show a wheel hub 10 having a wheel hub flange 21 that is configured to be connected to a wheel hub assembly 22 of a wheel 9. The encoder 15 is a wheel encoder 23 that is configured to measure a relative rotation of the wheel 9 relative to the base 12, i.e. the wheel bearing shaft 11, that is related to a rotation of said wheel 9.

The axle assembly 8 further comprises a wheel hub bushing assembly 35 that comprises a wheel hub bushing 36 configured to rotate with the rotary part 13 and a wheel hub flange 21 that is configured to engage with the connection 17 of the encoder 15, 23 to the rotary part 13. The wheel hub bushing 36 may be connectable to a wheel hub 37 of the rotary part 13. The wheel hub flange 21 is fixed to the wheel hub bushing 36, preferably via a screw thread 38, and thus rotates together with the rotary part 13. Via the wheel hub flange 21, the encoder 15, 23 may be connected to the rotary part 13.

In the axle assembly 8 shown in Figure 4, the connection 17 between the encoder 15, 23 and the rotary part 13 is arranged in a housing 39 having walls 40, 41 defined by the wheel bearing nut 26, that defines the base 12 to which the encoder 15, 23 is fixed, and the wheel hub bushing assembly 35, that is configured to rotate with the rotary part 13, respectively. Said housing 39 is sealed off from the wheel bearing by a sealing 42. The sealing 42 allows the wheel bearing 19 to be lubricated with grease or oil, while simulatenously the housing 39 may be dry, i.e. substantially free of any lubrication. The connection 17 is thus arranged in an air chamber enclosed in the housing 39, shielding the connection 17 from the outside environment and keeping it free from lubrication of the wheel bearing 19.

Sealing 42 is clamped between the wheel bearing nut 26 and the wheel bearing 19. The sealing 42 is clamped when the bearing nut 26 is screwed on the wheel bearing shaft 11 to thereby pre-tension the wheel bearing 19.

As can be best seen in Figure 4, the wheel bearing shaft 11 comprises a longitudinal though hole 24 that is configured to guide a cable 25 that is connected to the wheel encoder 15, 23. The wheel encoder 15, 23 is thus fixed relative to the wheel bearing shaft 11, while the wheel hub 10 that forms the rotary part 13 may rotate freely relative to the encoder 15. The cable 25 that is configured to transmit the measurement signal to a controller 29 is guided via the non-rotating wheel bearing shaft 11.

The second application for measuring a relative rotation B of the base 12 relative to the rotary part 13 that is related to a steering angle displacement of the wheel 9 relative to an axle housing 18 is now explained in more detail using Figures 4, 8 and 9. In this second application, the base 12 is rotatably arranged relative to an axle housing 18 and configured to rotate in relation to a steering angle displacement of a wheel 9 relative to said axle housing 18. The rotary part 13, that is rotatable relative to the base 12, is a bearing shaft 29 that is fixed relative to said axle housing 18, and the encoder 15 is configured to measure a relative rotation of the base 12 relative to the rotary part 13 that is related to the steering angle displacement. The encoder 15 is a steering encoder 30. The bearing shaft 29 is also known as knuckle bearing shaft.

From the perspective of the vehicle 1, the rotary part 13 is fixed and the base 12 rotates plus or minus 50° in relation to the steering angle displacement. However, form the perspective of the base 12, the rotary part 13 rotates. The limited rotation angle of plus or minus 50° allows the steering encoder 15, 30 to be arranged in the rotating base 12, because the flexibility of the cable 25 is able to provide enough freedom of movement.

The vehicle 1 of Figure 1 further comprises the controller 29 that is connected to the encoder(s) 15, 23, 30. The controller 29 is configured to control at least one of a drive 31 and a steering motor 32 of the vehicle 1. Using the high resolution data provided by the high resolution encoders 15, 23, 30, the controller 29 may control the drive 31 and steering motor 32 for automated “inching” of the vehicle 1, which may therefore be an automated guided vehicle (AGV).

Summarizing, the invention proposes an axle assembly 18, and vehicle 1 comprising such an axle assembly 18, having high resolution encoders 15. These high resolution encoders 15 may comprise a wheel encoder 23 and/or a steering encoder 30. According to the invention, the encoders 15, 23, 30 and connections 17 to the respective rotary part 13 are arranged in a very limited space available in an axle assembly 18. A wheel bearing nut 26 may be used to arrange the wheel encoder 15, 23 inside the boundaries of a conventional axle assembly. The steering encoder 15, 30 also had to be fitted in a limited space. Other components, such as brake cylinder 33, limit the available space.

Although they show preferred embodiments of the invention, the above described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. Furthermore, it is particularly noted that the skilled person can combine technical measures of the different embodiments. The scope of the invention is therefore defined solely by the following claims.