Harvest boon

While its road-holding may not be quite up there with its sports-car namesake, the Claas Jaguar, one of the farming industry's top-selling forage harvesters, boasts some pretty impressive performance characteristics.

With a top road-speed of 40km/h, and, more significantly, a typical working speed of 16.8km/h, the Jaguar, which is used to produce silage, can harvest up to 400 tonnes of maize or grass an hour.

Key to this performance is a specially developed hydrostatic — or hydraulic — drive system developed by Linde Hydraulics.

A feature of Claas's foragers since 2000, this so-called hydrostatic propel drive system, which consists of a hydraulic drive-system coupled with an electronically controlled diesel engine, has been enhanced with a recent redesign.

One of the prime areas of improvement was in the 18-tonne vehicle's tractive force, an essential feature on the slopes and wet ground that form its typical working conditions.

According to

, use of its CED electronic control technology enables Claas to achieve a significant boost in tractive force without increasing energy consumption by changing the diesel power, pump, rotating speed or pressure.

Another key to increasing tractive force was the development of a switchable hydrostatic rear-wheel-drive system. According to Claas, this enables greater design freedom than the previous mechanical system, as the absence of a mechanical drive shaft has made it possible to enlarge the tank and locate it in a more favourable position.

Linde added that the existing pump capacity is sufficient to supply the rear axle. A HMV 135-02 variable motor with a displacement of 135cm3/rev is fitted, which is supplied with approximately one-third of the pump capacity during normal operation. This eliminates the need for a transfer gear-box and other components.

The two axles are not speed-linked: the torque is distributed by the control unit as required. The necessary data is generated from the system pressure and driving speed; the tractive force required can then be derived from these values.

If an axle should slip despite these measures, the control unit reduces the torque and redirects it to the axle with traction. This ensures the optimum utilisation of the tractive capacity of each axle, thus rendering an anti-slip control system unnecessary. The additional rear axle drive allows the four-wheel-drive Jaguar to achieve a maximum tractive force of 140kN.

Another innovation is the additional function of a hydraulic interaxle differential. The axles are no longer speed-linked, as speed-linked axles can damage the delicate subsoil when the harvester is turning. Now the hydraulics take into account the fact that the routes travelled by the front and rear axles are of different lengths during sharp cornering, and the subsoil is protected.

For road travel, little demand is placed on the diesel engine — it is only in the field that full power is required. For this reason, the drive system has been fitted with an overdrive function, which reduces the diesel-engine speed to 1550rpm. When the forage harvester reaches a slight incline, for example, the engine speed is automatically increased, thus ensuring that the driving speed remains constant.

The Jaguar model with the most powerful engine is especially efficient in transport mode: when driving on the road, only one of the two diesel engines is used. So the Jaguar travels at half-power and the CED controlling the hydrostatic drive is adjusted to match this setting.

As with its predecessors, the electronic control unit developed by Linde Hydraulics is linked to the diesel engine. The latest version features even more powerful processors to handle drive control. A second, independent, processor is responsible for safety monitoring. Furthermore, the storage capacity of the control unit has been increased.

This means control functions can achieve greater dynamics, safety and driving comfort. This eliminates the need to install additional hydraulic hardware components that make the machine more complex and more service-intensive.

One of the safety features that protects the driver and the diesel engine against overspeed is the automatic swashing of the pump to zero if the control signals are cut, which ensures the machine is stopped safely. In this case, the motor on the rear axle is swashed to zero, while the motor on the front axle is swashed back from 210cm3/rev to 55cm3/rev. This means that, in the event of a fault, the machine is thus gently brought to a halt.

In transport mode, the four-wheel drive is naturally switched off. In this case, the rear hydraulic motor is mechanically disengaged and locked. An end-position sensor monitors the lock.

The crop intake has also been fitted with a hydraulic drive. The feed system of the propel drive supplies a variable pump with 75cm3/rev and an HMF 75-02 or HMF 105-02 fixed-displacement motor. This allows the operator to enjoy the convenience of a hydraulically infinitely variable cutting length without the need for an additional feed circuit.

The quick-stop function for the intake is now also a hydraulic system: if stones or metal objects are detected, the intake can be stopped within approximately 65ms. The electrical signal is also used to stop the propel drive. The hydraulics only require around 50ms to perform the controlled shutdown of the intake function.

The stop-function of the main drive once work has finished is also quicker. Previously, the knife drum required approximately 90 seconds to run down. Now the drive is braked by the hydraulics within just a few seconds, after which the operator can access the cutting tools.

Another feature is the Tempomat function, which comes into its own during harvesting. The selected Tempomat speed can be saved in the CED control and then reselected after each turn.