DE102017120796B4 - Drivetrain with integrated torque sensing - Google Patents

Abstract

A drive train for torque transmission, particularly in a motor vehicle, comprising the following features: a shaft (110) for receiving a torque (M) to be transmitted, wherein the shaft (110) has an axially extending cavity (115) with an internal thread (117); at least one gear (120) that is rotationally fixedly mounted on the shaft (110) and has helical gearing (122) for outputting the torque (M) to be transmitted; a connecting element (130) having a base portion (132), a head portion (134), and an elastically deformable hollow portion (133) that is arranged between the base portion (132) and the head portion (134), wherein the head portion (134) couples to the at least one gear (120) and the base portion (132) has an external thread (137) to engage with the internal thread (117) of the shaft (110), and thus fixing an axial position of the at least one gear (120) on the shaft (110); and a strain sensor or force sensor (140) formed in the hollow portion (133) to detect an elastic strain of the hollow portion (133) as a result of an axial force (F) caused by the helical gearing (122) during torque transmission.

Description

The present invention relates to a drive train and in particular to a drive train with integrated torque sensing.

background

The increasing demands on functional safety, for example, in electric drives in vehicles, necessitate the reliable measurement of the transmitted torque in the electric drive. Various safety regulations often require the use of two different and independent measurement methods to reliably measure the torque. These functional safety requirements particularly affect vehicles in which the electric drive acts directly on the wheels, where incorrect torque distribution between the wheels can lead to loss of vehicle control.

In conventional systems, two different calculation models are used on two different processors in the vehicle's powertrain control unit. However, this is disadvantageous because two comprehensive characteristic maps must then be determined (e.g., to calibrate the corresponding calculation models), which entails considerable effort for determining the parameters. For example, the torque in the drivetrain is measured by measuring the motor current and speed, and a corresponding calculation model is used. A disadvantage of this method lies in the uncertainty in the model used. Disturbances have a significant influence on the result.

Conventional methods for measuring torques and corresponding structures are described, for example, in DE 10 2012 005 614 A1 , DE 10 2010 045 448 A1 , DE 11 2014 000 966 T5 , DE 1 498 691 A1 revealed.

Therefore, there is a need for further ways to determine the transmitted torque in a simple and reliable manner.

Summary

At least some of the above-mentioned problems are solved by a drive train according to claim 1 and a method according to claim 7. The dependent claims define further advantageous embodiments.

The present invention relates to a drive train for torque transmission, particularly in a motor vehicle. The drive train comprises: a shaft for receiving a torque to be transmitted, at least one gear that is rotationally fixedly mounted on the shaft and has helical gearing for outputting the torque to be transmitted, a connecting element with a base portion, a head portion, and an elastically deformable hollow portion arranged between the base portion and the head portion, and a strain sensor. The shaft has an axially extending cavity with an internal thread. The head portion couples to the at least one gear, and the base portion has an external thread for engaging the internal thread of the shaft and thus fixing an axial position of the at least one gear on the shaft. The strain sensor is formed in the hollow portion to detect (or measure) an elastic strain of the hollow portion due to an axial force caused by the helical gearing during torque transmission.

Optionally, the connecting element is a screw with a screw head and a screw shaft, wherein the head part is the screw head, the external thread is partially formed on the screw shaft and the elastically deformable hollow-shaped portion is formed in the screw shaft in a region in which the screw shaft has no external thread and comprises a thinned outer wall (e.g., to improve extensibility).

Optionally, the strain sensor comprises a plurality of strain gauges, which are optionally connected, for example, to form a bridge circuit, and/or a temperature sensor which measures a temperature in the hollow section via a change in resistance.

Optionally, the strain sensor is formed directly on an inner surface of the hollow section or is part of a sensor unit that can be inserted into the hollow section and locked there, in particular by projections formed in the hollow section. The strain sensor can be mounted in the hollow section in such a way that the strain sensor is subject to a preload (e.g., after assembly of the gear), so that during strain measurements, the preload is increased or decreased depending on the direction of the transmitted torque.

Optionally, the strain sensor comprises an evaluation unit designed to carry out a preliminary evaluation of the recorded strain values.

Optionally, the drive train further comprises a contacting unit designed to electrically contact the strain sensor to enable electrical supply to the strain sensor and/or measured value transmission. The contacting unit can electrically contact the strain sensor, in particular, via a sliding contact for a rotating contact pin. It is also possible to provide an inductive or capacitive contacting unit.

• - Ausüben eines zu übertragenden Drehmomentes auf eine Welle, auf der rotationsfest zumindest ein Zahnrad mit einer Schrägverzahnung zur Abgabe des zu übertragenden Drehmomentes ausgebildet ist, wobei das Zahnrad mit einem Verbindungselement axial auf der Welle fixiert ist;
• - Messen einer elastischen Dehnung des Verbindungselementes infolge einer durch die Schrägverzahnung verursachten axialen Kraft bei der Drehmomentübertragung.

The present invention also relates to a method for measuring a transmitted torque, particularly in a motor vehicle. The method comprises the steps:

• - exerting a torque to be transmitted on a shaft on which at least one gear with helical teeth is formed in a rotationally fixed manner for delivering the torque to be transmitted, wherein the gear is fixed axially on the shaft by a connecting element;
• - Measuring an elastic strain of the connecting element as a result of an axial force caused by the helical gearing during torque transmission.

Embodiments solve at least some of the above-mentioned technical problems by using an axial force-measuring screw or bolt, which is used directly in the electric drive to measure the axial force generated by the applied torque. The axial force is generated by the helical gearing during power transmission. This measuring principle is also used in the ConSenses force measuring screws from the DE 10 2012 005 614 A1 is used, with the force being measured by piezo elements.

• - Die Ermittlung des Drehmomentes ist grundlegend verschieden von den bisher verwendeten Berechnungsmodellen und eignet sich daher insbesondere auch für eine redundante Drehmomenterfassung.
• - Die Messstelle der Sensorik bietet außerdem den Vorteil, dass die Anzahl möglicher Störgrößen gering gehalten wird, was die Berechnung des Drehmomentes aus der Messgröße erheblich vereinfacht und die benötigte Rechenleistung deutlich reduziert.
• - Weiterhin ist die Ermittlung des Drehmomentes auf der Basis von Ausführungsbeispielen der vorliegenden Erfindung nur von einer geringen Anzahl von Parametern und Eigenschaften des Getriebes abhängig, wodurch Ausführungsbeispiele in einem breiten Spektrum von Anwendungen einsetzbar sind.
• - Die Berechnung des Drehmomentes aus der Axialkraft bietet ein hohes Maß an funktionaler Sicherheit in elektrischen Antrieben und erfüllt somit selbst anspruchsvolle Anforderungen.
• - Eine gleichzeitige Reduktion des Entwicklungsaufwandes wird erreicht (es braucht lediglich die Befestigungsschraube ersetzt werden).

Examples offer the following advantages:

• - The determination of the torque is fundamentally different from the calculation models used previously and is therefore particularly suitable for redundant torque measurement.
• - The measuring point of the sensor also offers the advantage that the number of possible disturbances is kept low, which considerably simplifies the calculation of the torque from the measured variable and significantly reduces the required computing power.
• - Furthermore, the determination of the torque based on embodiments of the present invention depends only on a small number of parameters and properties of the transmission, whereby embodiments can be used in a wide range of applications.
• - Calculating the torque from the axial force offers a high degree of functional safety in electric drives and thus meets even the most demanding requirements.
• - A simultaneous reduction in development effort is achieved (only the fastening screw needs to be replaced).

Short description of the characters

• 1 veranschaulicht die Kraftübertragung von einer sich drehenden Welle auf ein externes Zahnrad.
• 2 zeigt eine Drehmomenterfassung über eine Dehnungsmessung in einem hohlförmigen Abschnitt eines Verbindungselementes in dem Antriebsstrang gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.
• 3 zeigt weitere Details des Antriebsstrangs zur Drehmomentübertragung gemäß weiterer Ausführungsbeispiele.

The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the various embodiments, which, however, should not be construed as limiting the disclosure to the specific embodiments, but are for explanation and understanding only.

• 1 illustrates the transfer of power from a rotating shaft to an external gear.
• 2 shows a torque detection via a strain measurement in a hollow section of a connecting element in the drive train according to an embodiment of the present invention.
• 3 shows further details of the drive train for torque transmission according to further embodiments.

Detailed description

1 illustrates the transmission of torque from a rotatable shaft 110 with a gear 120 to an external gear 50. The gear 120 is fastened to the shaft 110 via a connecting element 130, wherein the connecting element 130 can in particular be a screw that is screwed into a cavity of the shaft 110 and axially fixes the gear 120. The gear 120 is also connected in a rotationally fixed manner to the shaft 110 via a corresponding spline connection or another positive connection. In response to a rotational movement of the shaft 110, the gear 120 therefore drives the external gear 50, so that the torque M is transmitted from the shaft 110 to the external gear 50. The external gear 50 can have external teeth as shown. However, it is also possible for the external gear 50 to represent internal teeth of a cylindrical cavity. The invention is not intended to be limited to the specific shape/design of the external gear.

Due to the helical toothing 122 of the gear 120, the transmitted torque M is proportional to an axial force F acting on the gear 120 due to the helical gearing 122. This axial force F is absorbed by the connecting element 130 (e.g., a screw), which fixes the axial position of the gear 120 on the shaft 110. Therefore, the acting axial force F can be measured by a strain measurement on the connecting element 130.

2 shows an embodiment of the present invention in which the strain measurement is carried out via a strain sensor 140, which is fixed in a hollow section 133 of the connecting element 130. The connecting element 130 also comprises a base section 132, on which the connecting element 130 has an external thread 137, which engages an internal thread of the shaft 110 (not shown in 2 ) to fix the connecting element 130 there. Finally, the connecting element 130 comprises the head part 134 to fix the gear 120 (see 1 ) in the axial position.

The hollow section 133 is designed such that it can expand upon axial fixing of the gear 120, wherein the expansion is proportional to the axially acting force F, which in turn is proportional to the transmitted torque M. For this purpose, the strain sensor 140 can be fixed axially relative to the connecting element 130, for example by projection elements 135, so that an expansion of the connecting element 130 also leads to an expansion of the strain sensor 140.

In the embodiment of the 2 The strain sensor 140 is designed, for example, as a unit which can be inserted into the hollow section 133, for example as an insertion element or slide element, and engages with the projections 135 via corresponding locking elements 144, so that after the sensor unit 140 has been inserted, no axial movement of the strain sensor 140 relative to the connecting element 130 is possible.

The 2 also shows further details of the strain sensor 140, which is designed as an insert element. For this purpose, a shaft portion with a rectangular cross-section is formed on the strain sensor 140, which also expands when the connecting element 130 expands. On the four outer surfaces of the rectangular shaft portion, three strain measuring elements 141, 142, 143 are formed, for example, which can be interconnected, for example, to form a bridge circuit. Furthermore, a temperature sensor 145 is formed on a further surface of the shaft portion, which is capable of measuring a temperature within the hollow section 133. Head portions are provided at both ends of the shaft portion, which engage with the projections 135 of the connecting element 130 via corresponding projections 144 in order to fix the axial position of the strain sensor 140.

Optionally, it is also possible for the strain gauges 141, 142, 143 to be attached directly to the inner wall of the hollow section 133 in order to directly measure the strains there. The strain sensor 140 or the strain gauges can advantageously comprise piezo elements to measure the strains. However, other measuring principles are also possible for measuring the axial force F.

The 3 shows a basic structure of the drive train according to an embodiment of the present invention. To measure the torque M transmitted in the electric drive train, an axial force-measuring sensor screw 130 is used as a connecting element for fastening and clamping the helical gear 120. The fastening is achieved by screwing the screw 130 into an axial thread 117 in an (elongated) cavity 115 in the shaft 110.

The components mounted on the shaft 110 are clamped against a shaft collar located behind the gear 120 or another axial stop surface, taking feasibility aspects into account, via the head support (head part) 134. The components mounted on the shaft include, for example, a centering disk 240, one or more spacer sleeves 230, and various bearings 250, 260. The torque transmission of the drive continues to occur via the splined shaft connection 124 or another positive shaft-hub connection. The non-rotatable connection used does not affect the torque transmission behavior, and there are no impairments to existing calculation models.

The gear 120 has helical teeth 122, with the tooth angles of the gear 120 being selected such that the axial forces F caused by the toothing and the applied torque M do not exceed the load-bearing capacity of the screw connection 130 during torque transmission. The axial force F generated during tooth engagement depends solely on the transmitted torque M and the geometry of the tooth engagement, of which only the torque M is variable during operation. This creates a very direct relationship between the axial force F and the torque M, which can be easily converted into a calculation model.

The resulting axial force F is introduced into the screw connection and thus into the sensor screw 130. The sensor 140 embedded in the sensor screw 130 enables this sensor screw to measure the axial forces F acting on it. The axial force F applied to the sensor screw 130 is composed of the preload force required to clamp and secure the components on the shaft 110 and the operating force, in this case the axial force F caused by the torque M. The sensor element 140 mounted in the shaft of the sensor screw 130 converts the elongation or compression of the sensor screw 130 caused by the axial force F into a measurement signal. The measurement signal of the sensor screw 130 can then be transmitted via a signal pickup 290 to a housing 200 or the non-rotating part of the system. In embodiments, the friction caused in the contact point is minimized by using a signal pickup 290 with the smallest possible diameter.

For signal acquisition, a measurement signal acquisition unit 150 with a contact pin 290 can be provided as a signal pickup, which provides frictional contact with the sensor unit 140. This electrical contact can also be used for the electrical supply, with a second contact being achieved via ground. Furthermore, it is possible to model sensor signals on the electrical flow path thus created in order to transmit them to an external evaluation unit. It is also possible for the signal pickup 290 to be designed as a pin, which establishes electrical contact with the strain sensor 140 via a ball bearing. It is also possible for the strain sensor 140 to offer a pin-like contact, which can be electrically contacted externally via a sliding contact or a ball bearing.

In addition to transmitting the unprocessed sensor signal, a signal evaluation unit can also be integrated into the sensor unit 140. The signal evaluation unit can, for example, comprise a microcontroller or an analog-to-digital converter, which are also housed in the screw 130. This also offers the advantage of meeting the functional safety requirements with regard to the calculation unit used, since the calculation of the torque M in the drive train is thus performed on an independent processor. In general, the signal transmission and the power supply of the sensor 140 can also be implemented via design-related, unique current paths without having to change the described measuring principle for torque measurement.

Thus, the present embodiments achieve a novel method for measuring torque, independent of previous calculation methods and clearly distinguishable from them. These embodiments can meet high functional safety requirements, especially in electric drive trains, with minimal effort.

The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention both individually and in any combination.

List of reference symbols

50

gear

110

Wave

115

Cavity in the shaft

117

Internal thread in the cavity

120

gear

122

Helical gear teeth

130

connecting element

132

Basic section

134

headboard

133

hollow section

135, 144

projections

137

External thread on the base section

140

Strain or force sensor

141, 142,...

strain gauges

145

Temperature sensor

150

Contacting unit

200

Housing

230

spacer sleeve

240

Centering disc

250, 260

warehouse

290

Signal pickup

M

transmitted torque

F

axial force acting during torque transmission

Claims (7)

Drive train for torque transmission, in particular in a motor vehicle, with the following Features: a shaft (110) for receiving a torque (M) to be transmitted, wherein the shaft (110) has an axially extending cavity (115) with an internal thread (117); at least one gear (120) which is rotationally fixedly mounted on the shaft (110) and has helical gearing (122) for outputting the torque (M) to be transmitted; a connecting element (130) having a base portion (132), a head portion (134), and an elastically deformable hollow portion (133) arranged between the base portion (132) and the head portion (134), wherein the head portion (134) couples to the at least one gear (120), and the base portion (132) has an external thread (137) for engaging with the internal thread (117) of the shaft (110) and thus fixing an axial position of the at least one gear (120) on the shaft (110); and a strain sensor or force sensor (140) formed in the hollow portion (133) for detecting an elastic strain of the hollow portion (133) as a result of an axial force (F) caused by the helical gearing (122) during torque transmission. Drivetrain according to Claim 1 , wherein the connecting element (130) is a screw with a screw head and a screw shaft, wherein the head part (134) is the screw head, the external thread (137) is partially formed on the screw shaft and the elastically deformable hollow section (133) is formed in the screw shaft in a region in which the screw shaft has no external thread (137) and comprises a thinned outer wall. Drivetrain according to Claim 1 or Claim 2 , wherein the strain sensor (140) comprises a plurality of strain gauges (141, 142, 143) which are connected to form a bridge circuit, and/or a temperature sensor (145) which measures a temperature in the hollow section (133) via a change in resistance. Drive train according to one of the preceding claims, wherein the strain sensor (140) is formed directly on an inner surface of the hollow section (133) or is part of a sensor unit that can be inserted into the hollow section (133) and locked there, in particular by projections (135) formed in the hollow section (133), and wherein the strain sensor (140) is fastened in the hollow section (133) in such a way that, after the gearwheel (120) has been axially fixed by the connecting element (130), the strain sensor (140) is subject to a preload, so that during strain measurements, the preload is increased or decreased depending on a direction of the transmitted torque (M). Drive train according to one of the preceding claims, wherein the strain sensor (140) comprises an evaluation unit which is designed to carry out a preliminary evaluation of the detected strain values. Drive train according to one of the preceding claims, further comprising: a contacting unit (150) configured to electrically contact the strain sensor (140) to enable electrical supply to the strain sensor (140) and/or measured value transmission, wherein the contacting unit (150) contacts the strain sensor (140), in particular via a sliding contact or a ball bearing for a rotating contact pin. A method for measuring a transmitted torque (M), particularly in a motor vehicle, comprising the following steps: Exerting a torque (M) to be transmitted to a shaft (110) on which at least one gear (120) with helical gearing (122) is formed in a rotationally fixed manner for delivering the torque (M) to be transmitted, wherein the gear (120) is axially fixed to the shaft (110) by a connecting element (130); Measuring an elastic strain of the connecting element (130) as a result of an axial force (F) caused by the helical gearing (122) during torque transmission.