DE102017120796A1 - Powertrain with integrated torque detection - Google Patents

Abstract

It is a powertrain for transmitting torque, especially in a motor vehicle disclosed. The drive train includes a shaft (110) for receiving a torque (M) to be transmitted, the shaft (110) having an axially extending cavity (115) with an internal thread (117). The drive train further comprises at least one toothed wheel (120) which is rotatably mounted on the shaft (110) and has a helical toothing (122) for outputting the torque (M) to be transmitted, a connecting element (130) and a strain or force sensor ( 140). The connecting element (130) comprises a base portion (132), a head portion (134) and an elastically deformable hollow-shaped portion (133) disposed between the base portion (132) and the head portion (134), wherein the head portion (134) the at least one gear (120) coupled and the base portion (132) has an external thread (137) to engage with the internal thread (117) of the shaft (110) and thus an axial position of the at least one gear (120) to fix the shaft (110). The strain sensor (140) is formed in the hollow portion (133) to measure an elastic strain of the hollow portion (133) due to an axial force (F) caused by the helical gear (122) in torque transmission.

Description

The present invention relates to a powertrain, and more particularly to a powertrain with integrated torque sensing.

background

The increasing demands on functional safety, for example in electric drives in vehicles, lead to the necessity that the transmitted torque is reliably detected in the electric drive. Various safety regulations often require the use of two different and independent measuring methods in order to reliably detect the torque. These functional safety requirements relate in particular to vehicles in which the electric drive acts directly on the wheels, where an incorrect torque distribution on the wheels can lead to the loss of vehicle control.

In conventional systems, two different calculation models are used on two different processors in the control unit of the vehicle drive. However, this is disadvantageous, because then two comprehensive maps are to be determined (for example, to calibrate the corresponding computational models), which involves a considerable effort for the determination of the parameters. For this purpose, for example, a measurement of the torque in the drive train via a measurement of the motor current and the speed made and again an associated calculation model used. A disadvantage of this method is the uncertainty in the model used. Disturbance variables have a considerable influence on the result.

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

Summary

At least part of the above 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 transmitting torque, in particular in a motor vehicle. The drive train comprises: a shaft for receiving a torque to be transmitted, at least one gear which is rotationally fixedly mounted on the shaft and has a helical toothing for delivering the torque to be transmitted, a connecting element having a base portion, a head portion and an elastically deformable hollow-shaped portion, which is arranged between the base portion and the head part, and a strain sensor. The shaft has an axially extending cavity with an internal thread. The head portion coupled to the at least one gear and the base portion has an external thread to engage with the internal thread of the shaft and thus to fix an axial position of the at least one gear on the shaft. The strain sensor is formed in the hollow-shaped portion to detect (or measure) an elastic strain of the hollow-shaped portion due to an axial force in the torque transmission caused by the helical gear.

Optionally, the connecting element is a screw having a screw head and a screw shaft, the head part being the screw head, the external thread partially formed on the screw shaft, and the elastically deformable hollow-shaped portion being formed in the screw shaft in a region where the screw shaft has no external thread and includes a thinned outer wall (eg to improve extensibility).

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

Optionally, the strain sensor is formed directly on an inner surface of the hollow portion or is part of a sensor unit which is insertable and lockable in the hollow portion, in particular by protrusions formed in the hollow portion. The strain sensor may be mounted in the hollow portion such that the strain sensor is biased (e.g., after assembly of the gear) such that upon strain measurements, the bias voltage is increased or decreased depending on a direction of the transmitted torque.

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

Optionally, the drive train further comprises a contacting unit, which is designed to contact the strain sensor electrically, in order to enable an electrical supply of the strain sensor and / or a measured value transmission. The contacting unit can make electrical contact with 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, in particular in a motor vehicle. The method comprises the steps:

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

Embodiments solve at least part of the above-mentioned technical problems by the use of an axial force-measuring screw or bolt, which is used in the electric drive directly for detecting the axial force occurring due to the applied torque. The axial force is generated by the helical toothing during power transmission. This measuring principle is also used in the calipers of ConSenses DE 10 2012 005 614 A1 used, wherein the force is 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).

Embodiments offer the following advantages:

• - The determination of the torque is fundamentally different from the previously used calculation models and is therefore particularly suitable for a redundant torque detection.
• - The measuring point of the sensor also offers the advantage that the number of possible disturbances is kept low, which greatly simplifies the calculation of the torque from the measured variable and significantly reduces the required computing power.
• Furthermore, the determination of the torque on the basis of 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.
• - The calculation of the torque from the axial force provides a high level of functional safety in electric drives and therefore meets even demanding requirements.
• - A simultaneous reduction of the development effort is achieved (it only needs to be replaced the fixing screw).

list of figures

• 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 different embodiments, which should not, however, be construed as limiting the disclosure to the specific embodiments, but for explanation and understanding only.

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

Detailed description

1 illustrates torque transmission from a rotatable shaft 110 with a gear 120 on an external gear 50 , The gear 120 is about a connecting element 130 on the shaft 110 fastened, wherein the connecting element 130 in particular, a screw may be in a cavity of the shaft 110 is screwed in and the gear 120 axially fixed. The gear 120 is also rotatable with the shaft 110 connected via corresponding wedge connection or another positive connection. On a rotary motion of the shaft 110 therefore drives the gear 120 the external gear 50 on, so the torque M from the wave 110 on the external gear 50 is transmitted. The external gear 50 may have an external toothing as shown. However, it is also possible that the external gear 50 represents an internal toothing of a cylindrical cavity. The invention should not be limited to the specific form / design of the external gear.

Due to the helical gearing 122 of the gear 120 is the transmitting torque M proportional to an axial force F on the gear 120 due to the helical gearing 122 acts. This axial force F is through the connecting element 130 (eg a screw), which is the axial position of the gear 120 on the wave 110 fixed, recorded. Therefore, the acting axial force F by a strain measurement on the connecting element 130 be measured.

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

The hollow section 133 is formed so that it is in the axial fixing of the gear 120 can stretch, the strain being proportional to the axial force F which in turn is proportional to the transmitted torque M , This can be done by the strain sensor 140 for example by projection elements 135 axially relative to the connecting element 130 be fixed, so that an elongation of the connecting element 130 also to an expansion of the strain sensor 140 leads.

In the embodiment of 2 is the strain sensor 140 exemplified as a unit, for example, as a male member or slide member in the hollow-shaped portion 133 can be inserted and via corresponding latching elements 144 with the projections 135 engages, so after inserting the sensor unit 140 no axial movement of the strain sensor 140 relative to the connecting element 130 is possible.

The 2 also shows more details of the strain sensor 140 which is designed as a plug-in element. For this purpose, a rectangular cross-section shaft part to the strain sensor 140 formed, which is at expansions of the connecting element 130 also stretches. On the four outer surfaces of the rectangular shaft part are exemplary three strain gauges 141 . 142 . 143 formed, which can be interconnected, for example, to a bridge circuit. In addition, a temperature sensor is on a further surface of the shaft part 145 formed, which is capable of a temperature within the hollow-shaped portion 133 to eat. At both ends of the shaft part each head parts are provided, which have corresponding projections 144 with the projections 135 of the connecting element 130 snap in to the axial position of the strain sensor 140 to fix.

Optionally, it is also possible that the strain gauges 141 . 142 . 143 directly on the inner wall of the hollow-shaped section 133 are fixed to directly detect the strains there. The strain sensor 140 or the strain gauges may advantageously comprise piezo elements to measure the strains. But there are also other measuring principles possible to the axial force F to eat.

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

Over the head rest (head part) 134 be on the wave 110 mounted components against one behind the gear 120 lying shaft collar or another axial abutment surface under consideration of feasibility aspects braced. The mounted on the shaft components include, for example, a centering 240 , one or more spacer sleeves 230 and different bearings 250 . 260 , The torque transmission of the drive continues to take place via the splined connection used 124 or another positive shaft-hub connection. Due to the non-rotatable connection, the behavior during torque transmission is not affected, there is no impairment of existing calculation models.

The gear 120 has a helical toothing 122 , where the tooth angles of the gear 120 are chosen so that by the gearing and the introduced torque M caused axial forces F For torque transmission, the load capacity of the screw connection 130 do not exceed. The axial force created during meshing F depends only on the transmitted torque M and the geometry of the meshing engagement, of which only the torque M is variable during operation. As a result, there is a very direct relationship between the axial force F and the torque M which can be converted into a calculation model by simple means.

The resulting axial force F is in the screw connection and thus in the sensor screw 130 initiated. By the in the sensor screw 130 embedded sensor 140 This sensor screw is capable of acting on them axial forces F to eat. The at the sensor screw 130 applied axial force F consists of the preload force that is used to tighten and secure the components on the shaft 110 is needed, and the operating force, in this case by the torque M caused axial force F , together. The in the shaft of the sensor screw 130 attached sensor element 140 converts by the axial force F resulting elongation or compression of the sensor screw 130 into a measuring signal. The measuring signal of the sensor screw 130 can now have a signal collector 290 to a housing 200 or the non-rotating part of the system. In embodiments, the use of a signal collector 290 minimize the friction caused in the contact point with the smallest possible diameter.

For signal acquisition, a measurement signal detection unit 150 with a contact pin 290 be provided as a signal pickup, which is a frictional contact to the sensor unit 140 provides. This electrical contact can also be used for the electrical supply, wherein a second contact is achieved via ground. In addition, it is possible to model sensor signals on the electrical flux path produced thereby in order to transmit them to an external evaluation unit. It is also possible that the signal collector 290 is formed as a pin, which via a ball bearing makes electrical contact with the strain sensor 140 manufactures. It is also possible that the strain sensor 140 offers a pin-like contact, which can be electrically contacted externally via a sliding contact or a ball bearing.

In addition to the transmission of the unprocessed sensor signal can also be a signal evaluation unit in the sensor unit 140 to get integrated. The signal evaluation unit may comprise, for example, a microcontroller or an analog-to-digital converter, which is also in the screw 130 be housed. This also has the advantage that the requirements for the functional safety with respect to the calculation unit used are met because 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 be realized by design-related unique current paths, without the described measuring principle for torque measurement would have to be changed.

Thus, embodiments achieve a novel, independent of the previous calculation method and clearly distinguishable method for measuring the torque in preferably electric drive trains. Embodiments can meet high demands on functional safety, especially in the electric drive train, with little effort.

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

LIST OF REFERENCE NUMBERS

110

wave

115

Cavity in the shaft

117

Internal thread in the cavity

120

gear

122

Helical toothing of the toothed wheel

130

connecting member

132

base portion

134

headboard

133

hollow section

137

External thread on the base section

140

Strain or force sensor

141, 142, ...

Strain gauges

145

temperature sensor

150

contacting unit

200

casing

230

spacer

240

centering

250, 260

camp

290

signal pickup

M

transmitted torque

F

axial force in torque transmission

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012005614 A1 [0013]

Claims (7)

Drive train for transmitting torque, in particular in a motor vehicle, having the following features: a shaft (110) for receiving a torque (M) to be transmitted, the shaft (110) having an axially extending cavity (115) with an internal thread (117); at least one toothed wheel (120) which is rotatably mounted on the shaft (110) and has a helical toothing (122) for outputting the torque (M) to be transmitted; a connector (130) having a base portion (132), a head portion (134) and an elastically deformable hollow portion (133) disposed between the base portion (132) and the head portion (134), the head portion (134) abutting the at least one gear (120) coupled and the base portion (132) has an external thread (137) to engage with the internal thread (117) of the shaft (110) and thus an axial position of the at least one gear (120) to fix 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) due to an axial force (F) caused by the helical gear (122) in the torque transmission. Drive train after Claim 1 wherein the connector (130) is a screw having a screw head and a screw shaft, the head member (134) being the screw head, the male screw (137) being partially formed on the screw shaft, and the elastically deformable hollow shaped portion (133) in the screw shaft a region is formed in which the screw shaft has no external thread (137) and a thinned outer wall comprises. Drive train after Claim 1 or Claim 2 wherein the strain gauge sensor (140) comprises a plurality of strain gauges (141, 142, 143) connected to a bridge circuit and / or a temperature sensor (145) which measures a temperature in the hollow section (133) via a resistance change. Drive train according to one of the preceding claims, wherein the strain sensor (140) is formed directly on an inner surface of the hollow portion (133) or is part of a sensor unit which is insertable and lockable in the hollow portion (133), in particular by protrusions (135) formed in the hollow portion (133) are formed, and wherein the strain sensor (140) is mounted in the hollow portion (133) such that the strain sensor (140) is biased upon axial fixation of the gear (120) by the connector (130) so that the strain in Dependence of a direction of the transmitted torque (M) is increased or decreased. Drive train according to one of the preceding claims, wherein the strain sensor (140) comprises an evaluation unit, which is designed to perform a pre-evaluation of the detected strain values. A powertrain according to any one of the preceding claims, further comprising: a contacting unit (150) which is designed to electrically contact the strain sensor (140) in order to enable an electrical supply of the strain sensor (140) and / or a 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. Method for measuring a transmitted torque (M), in particular in a motor vehicle, with the following steps: Exerting a torque to be transmitted (M) on a shaft (110) on which at least one gear (120) with a helical toothing (122) for discharging the torque to be transmitted (M) is formed, wherein the gear (120) with a Connecting element (130) is axially fixed on the shaft (110); Measuring an elastic elongation of the connecting element (130) as a result of an axial force (F) caused by the helical gearing (122) during the torque transmission.

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