Haldex coupling

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The Haldex coupling is an electronically controlled multi-plate coupling that was developed by the Swedish automotive supplier Haldex . It has been manufactured and sold by BorgWarner since 2011 . It is used in cars to set up an all-wheel drive .

construction

The axis close to the motor is permanently driven. The Haldex coupling is flanged directly to the housing of the axle differential gear remote from the engine and is driven by an additional shaft outlet of the gearbox. It consists of a hydraulically operated multi-disc clutch located in a closed housing between the cardan shaft and bevel gear of the axle drive , a hydraulic pump and a control valve in the bypass of the hydraulic oil flow. There is also a pressure relief valve and a control device for the control valve. All components such as pump and working cylinders, bypass and valves sit on one of the shafts and rotate with it.

Originally, the hydraulic pump was a piston pump that was driven by a cam disk on the input shaft and seated on the output shaft. This annular piston pump comes into operation automatically due to the differences in speed between the input and output shaft due to the cam disk.

Later, an independent pump was used and a pressure reservoir made it possible to couple without a speed difference.

Mode of action

The all-wheel drive, based on a Haldex coupling, automatically transfers engine power to the normally non-driven axle (usually the rear axle) without being influenced by the driver.

Depending on the electronic control of the Haldex coupling, a variable proportion of the engine power is transmitted to this axle. This is possible with the bypass valve, through which the pressure can be reduced. For example, if an axle spins, the annular piston pump is actuated by the cam disk and generates fluid pressure. This acts on the working piston, which presses the lamellae against each other. With full frictional connection in the disk pack, the input and output shafts (and thus the front and rear axle drives) are non-rotatably connected to one another. The torque is distributed to the drive wheels according to their grip. The contact pressure for the disk pack and thus the clutch torque is controlled by the control unit via the control valve.

The clutch therefore does not divide the torque equally between the axles like a differential gear . Rather, the coupling of the axles is more or less rigid and must therefore be canceled, especially when cornering. In its effect, it can therefore be understood more as a longitudinal lock of a differential gear. The steering behavior would deteriorate with coupled axles and there would be increased wear, since the rear axle runs further inside when cornering and therefore turns more slowly.

Thanks to the electronic control, an all-wheel drive based on the Haldex coupling is compatible with driver assistance systems such as the anti-lock braking system (ABS) and vehicle dynamics control (Electronic Stability Control, ESP). If necessary, the rear axle drive can be deactivated within 60 ms.

In order to be able to intervene even when the vehicle is at a standstill and before a speed difference between the axles, an independent pump with a pressure reservoir was later added to the system. As a result, all wheels can be accelerated from a standing start on difficult terrain.

The Haldex system replaced the viscous coupling , which was neither self-regulating nor controllable and therefore not compatible with driver assistance systems.

The Haldex system only provides full cross-country mobility in conjunction with limited slip differentials or automatic slip control - otherwise one wheel per axle could spin or lock.

Origins and versions

The developer of the Haldex principle is said to have been the SAAB employee Sigge Johannsson, his son Peter Johannsson later headed a department for all-wheel drive development for passenger cars at General Motors in a phase in which SAAB was still part of General Motors. In 2008, Peter Johannsson presented the all-wheel drive at SAAB with the designation XWD ("Cross Wheel Drive"). Since SAAB did not want to invest in the market-ready development of the Haldex system itself, the patent was sold to Haldex.

There are several generations of Haldex couplings (1 to 5, as of 2013, see web links). The torque of the Haldex couplings generation 1 to 3 is mainly controlled by the speed difference of the driven axles with the aim of maximizing traction.

Generation 4 has an electric oil pump with pressure accumulator and can be used to increase driving dynamics, e.g. B. to stabilize the vehicle without previous wheel slip before undesired driving situations occur. It is possible to engage the Haldex coupling when the vehicle is at a standstill to increase the starting acceleration. The clutch torque is independent of the shaft speed.

According to the manufacturer, generation 5 is easier, more compact and less complicated to integrate. With the help of an electro-hydraulic centrifugal bypass valve, the power is distributed between the front and rear wheels. An integrated electronic control unit calculates the data and ensures a preventive, immediate reaction with high torque accuracy. A separating clutch was added to decouple the entire secondary drive train in order to save fuel. Fifth generation Haldex clutches are installed in the Volkswagen Golf VII 4Motion, for example.

commitment

All-wheel drives controlled with Haldex clutches can be found in the following car models (extract from):

Individual evidence

  1. ↑ Saab - first development with all-wheel drive . In: ATZ Automobiltechnische Zeitschrift . 2008th edition. No. 04 . Franckh'sche Verlagshandlung, Stuttgart, p. 314 .
  2. ↑ BorgWarner Inc. (PDF; 61 kB) borgwarner.com. Archived from the original on December 24, 2013. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved March 26, 2013. @1@ 2Template: Webachiv / IABot / www.borgwarner.com
  3. ↑ press release . Volkswagen Media Service. Retrieved on March 26, 2013.  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (deadlink)@1@ 2Template: Dead Link / www.volkswagen-media-services.com  
  4. ↑ Car models with Haldex all-wheel drive, manufacturer's website : www.haldex.com ( Memento from September 15, 2008 in the Internet Archive )

Web links