Optimising the benefits of hydrostatic technology
The Jaguar forage harvesters from Claas are high-performance machines that can harvest up to 400 tonnes of maize or grass per hour. The latest generation of hydrostatic propel drive has undergone further optimisation: the machines set themselves apart from the rest of the field by a significant increase in tractive force and further improvements to operator comfort — thanks to the LinDrive® concept from Linde Hydraulics.

Claas has enjoyed global success with the forage harvesters in its Jaguar series: the company has built over 25,000 units since 1985, and the machines enjoy a global market share of around 50%. The bar had been set extremely high for the development of the next generation of machines, and the same was true for the drives.

Highly productive in the field, quick on the road
The combination of the electronically controlled diesel engine with electronic variable control of the hydraulic pump and hydraulic motor, first introduced in the year 2000, meets the need for a sizeable decrease in diesel engine speed. This in turn ensures lower fuel consumption and high productivity: the Jaguar Speedstar can achieve working speeds of up to 16.8 km/h even in first gear. This means that the driver has no need to change gear in the field and can draw on very high power reserves when the going gets tough — depending on the version, the diesel engines can achieve an output of up to 830 hp. In second gear, the Jaguar can hit 40 km/h on the road.

The search for improvement
So is there any room for improvement in the drive of this high-performance agricultural machine? That was the question facing the Claas development engineers and the engineers from Linde Hydraulics, which for more than 30 years has played a vital part in the further development of the hydrostatic propel drive, in its role as the development partner for hydraulic drive technology.

The overwhelming consensus is that the concept has also proved its worth in the current motor-pump arrangement. It uses a Linde Hydraulics HPV 105-02 variable pump with a delivery volume of 105 cm³/rev, which is connected to the diesel engine via a pump transfer gear-box. Because the propel drive is a safety-related component, the principle of providing the greatest possible safety has been applied. For this reason, the pump is equipped with E2 control: without a control signal, a fail-safe shut-down occurs by means of a proportional and a switching solenoid. The pump is swashed back in a controlled manner and the diesel engine is protected. The vehicle is subject to targeted braking until the machine is stationary. During this process, the electronically adjusted front-wheel-drive motors ensure that the Jaguar is gently brought to a halt. When no signal is received, they swash from the maximum displacement of 210 cm³/rev to the minimum displacement.

Customer requirement: more tractive force
One area for improvement identified by the designers was tractive force: the vehicles — which can weigh up to 18 tonnes — are intended to be able to work at harvest time even in the most unfavourable conditions. Tractive force is essential on slopes and especially on wet ground, and the Claas Jaguar has plenty to draw on.

The new model boasts a significant increase in tractive force — even though the diesel power, pump, rotating speed and pressure remain unchanged, so there is no increase in consumption. This is in line with the LinDrive® driving philosophy, which aims to achieve optimum utilisation of the installed power. Of course, the electronic control technology also played a key part in increasing the tractive force: the CED control from Linde Hydraulics was optimised to provide precise driving characteristics, impressive dynamics and absolute safety when driving on roads.

Switchable four-wheel drive: hydrostatic instead of mechanical
A key innovation — and one that plays a massive part in increasing the tractive force — is the switchable hydrostatic rear-wheel drive, which replaces the previous mechanical version. A large proportion of customers are choosing this option. For Claas, the benefit of this change is the greater design freedom it allows: since it is no longer necessary to include a mechanical drive shaft, it is possible to enlarge the tank and locate it in a more favourable position. Furthermore, the customer can have the Jaguar retrofitted with four-wheel drive: Doing so simply involves changing the rear axle and attaching the hydraulic and electric lines.

The existing pump capacity is sufficient to supply the rear axle as well. An HMV 135-02 variable motor with a displacement of 135 cm³/rev is fitted, which is supplied with approximately one third of the pump capacity during normal operation. This means it is possible to do without 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 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 140 kN: this should be more than a match even for extremely challenging terrain.

Additional function: hydraulic interaxle differential
Another innovation is the additional function of a hydraulic interaxle differential. The axles are now no longer speed-linked. This was another customer requirement, because speed-linked axles can damage the delicate subsoil when the harvester is turning. Forced tensioning leads to forced slippage and damages the turf. Now the hydraulics take into account that the routes travelled by the front and rear axles are of different lengths during sharp cornering, and the subsoil is protected. This function could also be implemented at low cost and without additional components.

Constant top speed under changing conditions
For road travel, there's very little demand placed on the diesel engine — it's 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 1550 rpm. 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.

Control unit: optimum safety
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. Dynamics, safety and driving comfort can thus to a great extent be achieved using control functions. This eliminates the need to install additional hydraulic hardware components that make the machine more complex and more service-intensive. Instead, you simply invest in processor capacity and achieve the key goals of the LinDrive philosophy — more dynamic handling, total reliability and high safety standards — through the intelligent linking and optimum control of existing components.

One of the safety features that not only protect the driver, but also protect the diesel engine against overspeed, is the fact that the pump automatically swashes to zero if the control signals are cut. This ensures that 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 210 cm³/rev to 55 cm³/rev. 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.

Extra convenience thanks to hydrostatic auxiliary drive
In the new Jaguar, the crop intake has also been fitted with a hydraulic drive.

The feed system of the propel drive supplies a variable pump with 75 ccm/rev and an HMF 75-02 or HMF 105-02 fixed displacement motor. This means that the operator can 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 65 ms. The electrical signal is also used to stop the propel drive. The hydraulics only require around. 50 ms 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 s 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 handy new feature is the Tempomat function, which really comes into its own during harvesting. The selected Tempomat speed can be saved in the CED control and then reselected after each turn.

Tyres: automatic adjustment
Another sign of the Claas Jaguar's impressive versatility and of how the hydrostatic propel drive adapts to the prevailing conditions is the response to changes in tyre pressure. When the driver adapts the tyre pressure to the ground conditions during harvesting, handling and driving speed naturally change as well. To prevent this, the change in tyre pressure is one of the parameters taken into account in the control unit. A short calibration drive in the field is all it takes for the Jaguar to achieve maximum working speed and normal handling.

LinDrive®: enhanced dynamics, enhanced comfort, enhanced safety
The extra functions that Linde Hydraulics and Claas have introduced into the new generation of Jaguar demonstrate the practical nature of the LinDrive® philosophy. The machine dynamics have been significantly improved, mainly thanks to the increase in tractive force, and handy new features such as the Tempomat take the strain off the operator. Improved safety is also achieved with a feature that has so far not been mentioned: the increased braking capacity when driving downhill. In addition, so many driving and operating functions are predictively controlled that back-up systems such as anti-slip control are not required.

What's more, all of the additional functions have been implemented without increasing the complexity of the drive system or creating additional maintenance work. It is therefore no surprise that the new Claas Jaguar meets the needs of the most demanding customers and that many buyers opt for the additional function of the switchable hydrostatic four-wheel drive.

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