WO2010108519A1

WO2010108519A1 - Wheel end assembly of a vehicle and method for determining a braking torque

Info

Publication number: WO2010108519A1
Application number: PCT/EP2009/002256
Authority: WO
Inventors: Igor Dorrestijn
Original assignee: Ab Skf
Priority date: 2009-03-27
Filing date: 2009-03-27
Publication date: 2010-09-30

Abstract

The invention relates to a wheel end assembly (1) of a vehicle comprising a hub element (2), a brake rotor (3) and a sensor system (4, 5, 8) for determining a braking torque (MB) exerted on the brake rotor (3) during a brake operation, the hub element (2) comprising a radially extending wheel mounting flange (6) provided with means to enable the attachment of a vehicle wheel. To determine the braking torque on the wheel hub assembly in an easy and precise way, the invention is characterized in that the sensor system (4, 5, 8) comprises: a first rotary encoder (4) for determining a relative angular position between the hub element (2) and a fixed reference (7), the first encoder (4) comprising first encoding means (4') and a first sensor (4") arranged to detect the first encoding means (4') and produce a first signal (Φ₁); a second rotary encoder (5) for determining a relative angular position between the brake rotor (3) and a fixed reference (7), the second rotary encoder (5) comprising second encoding means (5') and a second sensor (5") arranged to detect the second encoding means (5') and produce a second signal (Φ₂), a processing unit (8) that is arranged to: receive the first and second signals (Φ₁, Φ₂), calculate a phase difference (ΔΦ₁) between the first signal (Φ₁) and the second signal (Φ₂), and determine the exerted braking torque (MB) from the calculated phase difference (ΔΦ₁). Furthermore, the invention relates to a method of determining a braking torque (M_B) exerted on a brake rotor.

Description

Wheel End Assembly of a Vehicle and Method for Determining a Braking Torque

Technical Field

The invention relates to a wheel end assembly of a vehicle comprising a hub element, a brake rotor and a sensor system for determining a braking torque exerted on the brake rotor during a brake operation, the hub element comprising a radially extending wheel mounting flange provided with means to enable the attachment of a vehicle wheel. Furthermore, the invention relates to a method for determining the braking torque of a wheel end assembly of a vehicle.

Background

A wheel end assembly of this kind is known from WO 02/08048 Al and from EP 1 589 328 Al. Here, the torque is detected which is exerted on a wheel end assembly during the braking operation. As a torque sensor a strain gauge is employed. This element delivers an electronic signal which corresponds to the deformation of a part of the hub assembly which in turn corresponds to the braking torque which is transmitted by the wheel hub assembly. Summary of the invention

In some cases the determination of the torque by the pre-known manner is not suitable or not precisely enough.

Thus, it is an o bj e c t of the invention to propose a design for a wheel end assembly of the kind mentioned above and a method for determining the torque exerted on the assembly during a braking process which can be easily established and which comes up with a high accuracy of measurement.

A s o l u t i o n according to the invention is characterized in that the sensor system, comprises:

a first rotary encoder for determining a relative angular position between the hub element and a fixed reference, the first encoder comprising first encoding means and a first sensor arranged to detect the first encoding means and produce a first signal;

a second rotary encoder for determining a relative angular position between the brake rotor and a fixed reference, the second rotary encoder comprising second encoding means and a second sensor arranged to detect the second encoding means and produce a second signal,

a processing unit that is arranged to:

receive the first and second signals, calculate a phase difference between the first signal and the second signal, and determine the exerted braking torque from the calculated phase difference.

The second rotary encoder can comprise more than one second sensor that is arranged to detect the second encoding means. By this, deformations of the whole wheel end arrangement during braking can be compensated. Suitably, the second rotary encoder comprises two second sensors arranged to detect diametrically opposite sides of the second encoding means.

The brake rotor can be a brake drum or a brake disc. In the latter case the second encoding means can be mounted to or provided on an inboard side face of the brake disc. This is a preferred location, because the one or more second sensors can then be mounted to an upright of the suspension system. Alternatively, the second encoding means can be mounted to or provided on a radially inner side of a hat section of the brake disc. Furthermore, the second encoding means can be mounted to or provided on an outer circumference of the brake disc.

The first encoding means can be mounted to or provided on a rotating part of a bearing arrangement that is in connection with the hub element.

The first encoding means can be mounted to or provided on the wheel mounting flange of the hub element.

In one embodiment, the hub element is a flanged ring of the bearing arrangement; i.e. a flanged inner ring adapted for inner ring rotation or a flanged outer ring adapted for outer ring rotation. In another embodiment, the hub element is a flanged hub on which the bearing arrangement is mounted. To equip the suggested wheel end assembly for determining a drive torque the assembly can be further provided with a third rotary encoder for determining a relative angular position between the hub element and a fixed reference, the third rotary encoder comprising third encoding means and a third sensor arranged to detect the third encoding means and produce a third sensor signal, wherein the third encoding means is arranged at a location on the hub element radially distal from the first encoding means. In this case, the processing unit can further be arranged to: receive the third signal, calculate a phase difference between the first signal and the third signal, and determine an exerted drive torque from the calculated phase difference.

At least one of the first, second and third encoding means can comprise an essentially regular pattern that is cast or machined into a surface on which the respective encoding means are provided. The pattern can comprises a missing increment that serves as a reference point. The pattern can be a plurality of rectangular or trapezoid teeth, grooves/recesses, or protrusions.

The first, second and third encoding means preferably comprise an equal number of detectable increments.

The method of determining a braking torque exerted on a brake rotor of a wheel end assembly comprises the steps of:

detecting a first signal indicative of a relative angular position between the hub element and a fixed reference;

detecting a second signal indicative of a relative angular position between the brake rotor and the fixed reference; calculating a phase difference between the first signal and the second signal; and

determining the exerted braking torque from the calculated phase difference.

At least one of the encoder means can be an encoder used for an ABS system of the wheel end assembly.

According to the invention a method for the measuring of the braking torque exerted on a brake disk as well as a method for the measuring of the drive torque exerted on the bearing spline is proposed. This is useful for applications like ABS, vehicle dynamics control systems, and general to aid load sensing performance of the wheel bearings.

In spite of the fact that magnetic encoders/sensors with teeth are preferred all kinds of encoders and sensors can be engaged.

A preferred embodiment of the proposed method minimizes errors due to machining tolerances, s. below.

Brief description of the drawing

The drawings show embodiments of the wheel hub arrangement according to the invention. Fig. 1 shows a cross sectional view of a wheel end arrangement according to a first embodiment of the invention,

Fig. 2, Fig. 3 and

Fig. 4 show schematically the information detected by a sensor which reads an encoding means,

Fig. 5 shows schematically the curve progression of the torque in the wheel hub assembly as the function of the determined phase difference between two signals,

Fig. 6a shows schematically a radial cross section through a wheel end arrangement with first and second encoder means and first and second sensors shown at a first possible location,

Fig. 6b shows schematically a radial cross section through a wheel end arrangement with first and second encoder means and first and second sensors shown at a second possible location,

Fig. 6c shows schematically a radial cross section through a wheel end arrangement with third encoder means and a third sensor shown at two different alternative locations,

Fig. 6d shows schematically a radial cross section through a wheel end arrangement with first, second and third encoder means and first, second, and third sensors shown at a possible location, Fig. 7 shows the signals emitted from an encoder means, similar to those according to Fig. 2, Fig. 3, and Fig. 4, schematically around a full turn of the encoder means, and

Fig. 8 shows a correction table as stored in a controlling unit, showing the precise start of the rectangular signal of each excitation element of the encoder means according to Fig. 7.

Detailed description of the invention

Fig. 1 shows an example of a wheel end assembly 1 with the most relevant parts only to understand the present invention. The wheel end assembly 1 comprises a hub element 2 with a radially extending wheel mounting flange 6 to which a vehicle wheel rim is mounted by means of bolts 15. In this example, the hub element 2 is a flanged bearing outer ring that is part of a bearing arrangement 12 for supporting the vehicle wheel relative to the vehicle suspension. The bolts 15 also fix a brake rotor 3 to the wheel mounting flange 6. The brake rotor - presently in the form of a brake disk - has a first radial section that is mounted against the flange 6 and a second radial section having an outer circumference 10, whereby the second radial section is engaged by brake pads (not shown) during a brake operation. The first and second radial sections are joined by an axial section 9, often referred to as a hat section or a rotor hat. In some embodiments, the brake rotor is integrally formed with the hub element.

The bearing arrangement 12 has two inner bearing rings and an outer bearing ring 11 (with two raceways) between which two rows of balls are arranged. The inner rings of the bearing arrangement 12 are stationary and connected with a stationary axis 16 which also carries a carrier element 7 forming a fixed reference. The fixed reference can also be a component of the vehicle suspension system.

When a brake caliper (not shown) brakes the brake rotor 3, a braking torque M_B is exerted on the wheel end assembly. To enable the wheel end assembly 1 to determine this braking torque M_B, the following features are provided:

The fixed reference 7 supports a first sensor 4" which is part of a first rotary encoder 4. The sensor 4" reads the signals from a first encoding means 4' which is arranged on the outer bearing ring 11, i.e. on the rotating bearing ring.

The fixed reference 7 also supports a second sensor 5" which is part of a second rotary encoder 5. The second sensor 5" reads the signal from a second encoding means 5 ' which is arranged on the hat section 9 of the brake rotor 3 at an axial inboard side of the rotor 3.

Furthermore, a processing unit 8 is arranged which is in electrical connection with the first and second sensor 4" and 5". Each sensor 4", 5" delivers a first signal Φi and a second signal Φ₂ respectively which correspond to the rotation angles of the parts which bear the first and second encoding means 4' and 5 ' respectively.

In the processing unit 8 both signals Φj and Φ₂ are evaluated. Reference is made to Figures 2 till 4. In Fig. 2 the signal coming from the first sensor 4" is shown. As the encoding means 4', 5' typically have a plurality of teeth or recesses being equidistantly arranged around the circumference, the detected information is a pattern as shown in Fig. 2. The same applies for the second sensor 5", which detected signal is shown in Fig. 3 for the wheel end assembly being without load, i. e. running without any torque transfer.

As can be seen both patterns are substantially identical but shifted relatively to each other by a phase difference ΔΦ₀. This phase difference can thus be observed when the wheel end assembly is running without any exerted torque.

If a braking torque M_B is exerted on the brake rotor, deformation occurs between the location of the outer bearing ring 11 and the brake rotor 3 where the second encoding means 5' are arranged. Consequently, an additional phase difference AO₁ is observed which is caused by the braking torque M_B only. This is shown in Fig. 4 for the signal of the sensor 5".

Between the phase difference AO₁ and the braking torque M_B exerted on the brake rotor 3 a specific function exists which is exemplarily shown in Fig. 5.

This graph can be obtained by a calibration test. Thus, when knowing the phase difference AO₁ it is possible to specifically say which braking torque

M_B is exerted on the wheel end assembly. All this is done in the processing unit 8 where the graph according to Fig. 5 is stored. Stored look-up tables may also be used.

Thus, when detecting the rotational movement of the two encoding means 4' and 5' by the two sensors 4", 5" the processing unit 8 can easily output the braking torque M_B.

As the brake caliper (not depicted) is arranged at one circumferential position of the brake rotor 3 a certain unsymmetrical deformation of the whole system takes place during braking. Due to this, a part of the phase difference ΔO] is caused by this effect of asymmetry and an incorrect torque value may be determined. This can be avoided by employing two second sensors 5" (not depicted). The two sensors read the same second encoding means 5', and are preferably arranged at diametrically opposite sides of the second encoding means. By generating the average of the signal of the two second sensors and by using this data in the processing unit 8 it is possible to eliminate the mentioned effect.

The wheel end assembly according to Fig. 1 is also equipped additionally with the possibility to determine the drive torque M_D which is exerted on the assembly. In this connection it should be mentioned that drive means for driving the wheel are not shown in Fig. 1 but are well known in the art. For the purpose of determining the drive torque a third rotary encoder 13 with third encoding means 13 ' is arranged on the hub element at a location radially distant from the first encoding means 4' i.e. the third encoding means 13' is arranged on the wheel mounting flange 6. Also, a third sensor 13" reading the third encoding means 13' is arranged.

In an analogous way as explained in connection with the determination of the braking torque M_B, the drive torque M_D is appraised. Thus, the rotation angle Φ₃ as detected by the third sensor 13" is fed into the processing unit 8. By determining the phase difference ΔΦ₂ between the two rotation angles Φj and Φ₃ of the hub element 2 at locations radially distant from each other, the drive torque M_D can be calculated.

It should also be noted that the phase difference between the angular position signal from the third encoder 13 and the angular position signal from the second encoder 5 can be used to determine the braking torque, assuming that the assembly has been calibrated to enable this In Fig. 6a till Fig. 6c some suitable locations for different rotary encoders are schematically shown.

In Fig. 6a, the hub element is a flanged bearing inner ring, whereby the first rotary encoder 4 detects the angular position of the inner ring. The second rotary encoder 5 is arranged at the hat section 9 of the brake rotor 3, whereby the second encoding means are arranged on an inboard face side of the brake rotor 3. By this arrangement a braking torque M_B can be detected.

Fig. 6b shows a modification of Fig. 6a. Here, the second rotary encoder 5 is arranged at the outer circumference 10 of the brake rotor 3.

In Fig. 6c a third rotary encoder 13 is shown at two alternative locations. The signal from the third rotary encoder can be used - as explained above - to determine the drive torque M_D acting on the hub element or the braking torque M_B acting on the brake rotor.

An arrangement for determining the brake torque as well as the drive torque is shown in Fig. 6d. Again the hub element 2 is a flanged bearing inner ring, which is adapted to be driven by a drive element (not shown). When a drive torque is exerted on the flanged inner ring, the part in connection with the drive element will be deformed (warped) relative to the wheel mounting flange 6. One encoder 4 is therefore arranged to detect the angular position of the inner ring 17 and another encoder 13 is arranged to detect the angular position of the wheel mounting flange 6, and drive torque M_D can be determined as previously explained. The assembly 1 further comprises an encoder 5 measuring the angular position of the brake disc 3, enabling braking torque M_B to be determined as previously explained. For obtaining a high precision of the determination of the torques exerted on the wheel end assembly the following method can be employed with reference to Fig. 7 and 8:

One of the teeth (or even more than one tooth) or recess respectively can be omitted from the encoding means 4', 5', and 13' respectively. In Fig. 7 the missing increment is denoted with 14. Thus, the signal detected by the sensors 4', 5', 13' looks like depicted in Fig. 7. At one circumferential position (corresponding to the missing increment 14) no signal is obtained. This can be used by the processing unit 8 to find an absolute position of the encoding means. I. e. the processing unit 8 then knows which specific tooth or recess of the encoding means delivers a signal. In the depicted example according to Fig. 7 the encoder has 47 teeth and one omission at the location 14.

The encoding means can be calibrated before use and a precise table according to Fig. 8 can be established and stored in the processing unit 8. In the table for each tooth (or recess) the exact angular position is recorded. Thus, the method as described above for the determination of the torque can be carried out by taking into account the precise location of the beginning of each tooth (or recess) according to the table.

By the explained proceedings, errors in the measurement of the torque, which are due to machining tolerances, can be minimized.

Thus, the described invention can again be summarized as follows:

The braking torque will warp the hat brake disk, causing a phase difference between the signals generated by a sensor detecting the rotational position of the brake rotor and a sensor detecting the rotational position of the hub element. Also, a drive torque exerted on a driven hub element, for example a flanged inner ring will warp the inner ring relative to the flange, thereby causing a similar phase difference between the signals generated by a sensor detecting the rotational position of the inner ring and a sensor detecting the rotational position of the flange.

To solve the problem of tolerances when one of the encoding means comprises the teeth / recesses, the encoding means can have one (or more) missing teeth / recesses. This enables the identification of the individual teeth / recess and allows the mapping of the phase difference per tooth / recess.

The teeth / ridges / recesses can be incorporated into the casting mold of e.g. a brake disc, removing the need for extra manufacturing steps. The recesses (holes) are suitably rectangular or trapezoid, to allow for radial misalignment.

The phase of the signals from different encoders should be as similar as possible.

The number of teeth / recesses of the different encoders are preferably equal, to facilitate the described calculation of the torques.

Reference Numerals:

1 Wheel end assembly

2 Hub element

3 Brake rotor -

4,5,8 Sensor system

4 First rotary encoder

4' First encoding means

4" First sensor

5 Second rotary encoder

5' Second encoding means

5" Second sensor

6 Wheel mounting flange

7 Fixed reference

8 Processing unit

9 Hat section

10 Outer circumference of brake disc

11 Rotating bearing ring

12 Bearing arrangement

13 Third rotary encoder

13' Third encoding means

13" Third sensor

14 Missing increment

15 Bolt

16 Axis

17 Inner ring M_B Braking torque

M_D Drive torque

ΔΦi Phase difference

ΔΦ₂ Phase difference

Φi First signal (rotation angle)

Φ₂ Second signal (rotation angle)

Φ₃ Third signal (rotation angle)

Claims

Patent Claims:

1. Wheel end assembly (1) of a vehicle comprising a hub element (2), a brake rotor (3) and a sensor system (4, 5, 8) for determining a braking torque (M_B) exerted on the brake rotor (3) during a brake operation, the hub element (2) comprising a radially extending wheel mounting flange

(6) provided with means to enable the attachment of a vehicle wheel,

characterized in that

the sensor system (4, 5, 8) comprises:

a first rotary encoder (4) for determining a relative angular position between the hub element (2) and a fixed reference (7), the first encoder (4) comprising first encoding means (4') and a first sensor (4") arranged to detect the first encoding means (4') and produce a first signal (Φi);

a second rotary encoder (5) for determining a relative angular position between the brake rotor (3) and a fixed reference (7), the second rotary encoder (5) comprising second encoding means (5') and a second sensor (5") arranged to detect the second encoding means (5') and produce a second signal (Φ₂),

a processing unit (8) that is arranged to: receive the first and second signals (Φ_\, Φ₂),

calculate a phase difference (ΔΦi) between the first signal (O₁) and the second signal (Φ₂), and

determine the exerted braking torque (M_B) from the calculated phase difference (ΔΦ,).

2. Wheel end assembly according to claim 1, characterized in that the second rotary encoder (5) comprises two second sensors (5") that are arranged to detect the second encoding means (5') at diametrically opposite sides of the second encoding means.

3. Wheel end assembly according to claim 1 or 2, characterized in that the brake rotor (3) is a brake drum.

4. Wheel end assembly according to claim 1 or 2, characterized in that the brake rotor (3) is a brake disc.

5. Wheel end assembly according to claim 4, characterized in that the second encoding means (5') is mounted to or provided on an inboard side face of the brake disc (3).

6. Wheel end assembly according to claim 4, characterized in that the second encoding means (5') is mounted to or provided on a radially inner side of a hat section (9) of the brake disc (3).

7. Wheel end assembly according to claim 4, characterized in that the second encoding means (5') is mounted to or provided on an outer circumference (10) of the brake disc (3).

8. Wheel end assembly according to any of claims 1 to 7, characterized in that the first encoding means (4') is mounted to or provided on a rotating part (11) of a bearing arrangement (12) that is in connection with the hub element (2).

9. Wheel end assembly according to any of claims 1 to 8, characterized in that the first encoding means (4') is mounted to or provided on the wheel mounting flange (6) of the hub element (2).

10. Wheel end assembly according to any of claims 1 to 9, characterized in that the assembly is further provided with a third rotary encoder (13) for determining a relative angular position between the hub element (2) and a fixed reference (7), the third rotary encoder (13) comprising third encoding means (13') and a third sensor (13 ") arranged to detect the third encoding means (13 ') and produce a third sensor signal (Φ₃), wherein the third encoding means (13) is arranged at a location on the hub element (2) radially distal from the first encoding means (4).

11. Wheel end assembly according to claim 10, characterized in that the processing unit (8) is further arranged to:

receive the third signal (Φ₃),

calculate a phase difference (ΔΦ₂) between the first signal (Φi) and the third signal (Φ₃), and

determine an exerted drive torque (M₀) from the calculated phase difference (ΔΦ₂).

12. Wheel end assembly according to any of claims 1 till 11, characterized in that at least one of the first (4'), second (5') and third (13') encoding means comprises an essentially regular pattern that is cast or machined into a surface on which the respective encoding means (4', 5', 13') are provided.

13. Wheel assembly according to claim 12, characterized in that the pattern comprises a missing increment (14) that serves as a reference point.

14. Wheel end assembly according to any of claims 1 to 13, characterized in that the first and second encoding means (4', 5') comprise an equal number of detectable increments.

15. Method of determining a braking torque (M_B) exerted on a brake rotor (3) of a wheel end assembly (1), the wheel end assembly comprising a hub element (2) with a radially extending wheel mounting flange (6) for the attachment of a vehicle wheel, the method comprising the steps of:

detecting a first signal (Φi) indicative of a relative angular position between the hub element (2) and a fixed reference (7);

detecting a second signal (Φ₂) indicative of a relative angular position between the brake rotor (3) and the fixed reference (7);

calculating a phase difference (ΔΦ,) between the first signal (Φ_t) and the second signal (Φ₂); and

determining the exerted braking torque (M₈) from the calculated phase difference (ΔΦ,).