Mobility Systems

Mobility Systems

Introduction

Horstman design and develop a wide range of suspension solutions for military vehicles for a world market. We have provided high performance suspension solutions for Lightweight Guns, Infantry Fighting Vehicles and Main Battle Tanks. We are a One-Stop shop for your military vehicle suspension and running gear needs.
	The diagram shows the running gear arrangement for AS90 SPG - A Hydrogas suspension system using nitrogen gas for the springs and hydraulics for the fluid damper.
	No other independent Company can offer such a wide choice of solutions ranging from hydropneumatic systems to hydraulic rotary dampers. What ever your suspension requirement, Horstman will be able to provide a proven suspension solution to meet your requirement.
The diagram shows the running gear arrangement for Warrior IFV - A torsion bar sprung vehicle fitted with integral (chassis) high performance hydraulic rotary dampers.

Hydrogas

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One of our most successful suspension solutions in terms of production quantities is the Hydrogas hydropneumatic suspension wheel station. Approximately 30,000 of these units have been manufactured around the world. The design was first used on FV 4030 MBT which later entered service as Challenger. Versions of the design have subsequently been used on AS90, K9 Thunder, Challenger 2 and derivative vehicles. The new British Army TERRIER engineer vehicle will also use a version of the Hydrogas suspension with suspension lockout.

The AS90 SPG and the Korean K9 Thunder SPG have a hydropneumatic suspension based on the Hydrogas design.

Each vehicle is fitted with twelve Hydrogas wheel stations that are totally independent. The loading per wheel station varies to a degree and this is compensated by adjusting the gas pressures to balance the wheel load. This is a significant advantage over a mechanical spring system where there is less flexibility.

Both vehicles have exceptional cross country ride performance as well as a highly stable weapon platform. Neither vehicle is fitted with mechanical stabilizers that would reduce the key into and out of action response times.

The Hydrogas proven technology can be readily adapted for new and retrofit vehicles. Hydrogas is external to the vehicle hull and therefore helps maximize on the internal payload volume. Hydrogas also offers a progressive suspension spring characteristic with a low rate around static for a compliant ride rising steeply at the bump position to avoid running out of suspension travel. The raising rate means that a simple bump stop can be fitted rather than a more complex hydraulic bump stop.

Different hull profiles can be accommodated including angles from 0 to 60 degrees. For vehicles where the space for the suspension is limited, then an In Arm Hydrogas unit is the best possible solution.

In Arm Hydrogas

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The In Arm Hydrogas suspension wheel station uses the proven technology from the Hydrogas range and optimized for minimal volume, low weight, high performance and low cost of ownership.

The In Arm unit shown has been developed for the UK FRES and US FCS family of vehicles in the 16 to 22 tonne weight range.

Typical Technical Specification

Static wheel loading	1.2 to 2.2 tonnes
Max Spring Force	4.5 x static wheel load
Wheel travel	up to 450 mm
Damping Ratio	0.6 to 1.3 x static wheel load
Unit weight	75 to 90 kg's depending on specification
Ambient temp	Min – 45 deg C; Max + 55 deg C
Applications	C130 weight class tracked vehicles

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Hydrostrut

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Hydrostrut is a telescopic hydropneumatic suspension solution. The product combines the proven advantages of a pneumatic spring and hydraulic damper in a lightweight self-contained package that can be readily adapted to both wheeled and tracked vehicles.

The example shown right is from the Singapore Technologies AMX13 upgrade. A similar solution is used on the Bionix IFV family of vehicles. Both these applications are tracked vehicles.

Hydrostrut provides an excellent suspension solution for wheeled vehicles. McPherson, double wish bone and trailing arm arrangements are typically adopted. The picture shows USMC M777 ultra lightweight towed gun which is a leading arm arrangement due to the unique geometry arrangements of this towed vehicle to meet the weight requirement. The suspension can be lowered and this is undertaken to get the gun in and out of action. The picture left shows the suspension in the position prior to firing.

Hydrostrut's can be modified to suit the chassis and suspension mounting arrangement. The one shown (right), from Patria's high performance 8x8 vehicle AMV, has a special bearing for the lower mount and a cup bearing for the upper chassis mount.

Rotary Dampers

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For vehicles with torsion bars, we have a range of high performance rotary dampers. These dampers offer a very high level of damping performance (relative to a linear damper) due to the high internal flow areas and their exceptional heat transfer capacity to the vehicle hull.

The unit shown is from Warrior, which has proved extremely reliable during the 20 year service of the fleet of 800 British Army vehicles. The illustration shows the unit from the rear and without the road wheel arm. The upper tube mounts the torsion bar for the opposite suspension station.

For upgrades and where internal space is at a premium, a lever arm rotary damper can be adopted. Examples of this type are Ulan IFV, Kentaurus and Scorpion.

Rotary dampers use the same proven technology to produce a high level of damping performance in a small volume.

The largest unit we have produced had a nominal damping torque of 37 kNm. The smallest unit is shown right which has a nominal damping torque of 4 kNm.

Variable Height

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A key advantage for a vehicle designer in adopting a hydropneumatic suspension is the ability to include additional suspension components such as variable height geometry. This is undertaken by adjusting the spring force within the spring units by changing the gas volumes. In this way the suspension can not be overloaded (as could occur by changing the oil volume).
	Best performance for cross country mobility, normal ride height for non specific operations.	Maximum protection when operating in land mined zones. Extra ground clearance when operating in deep snow, heavy mud or difficult terrain.	Loading/unloading into aircraft. Best performance for high speed road travel. Reduced silhouette for improved stealth. Reduced threat appearance for public when used for peace- keep roles.

Variable Load

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For vehicles with a significant change in the payload during their duty cycle, we can offer variable load system (VLS) so that the spring characteristic is optimised for either condition.

Examples of vehicles that can benefit from VLS are: ammunition resupply vehicles - FASV, bridgelayers - AVLB, and cargo carriers.

The unit shown is a modification of a Hydrogas unit to vary the load by 30% and also offer a suspension lockout for a heavy bridgelayer application .

Adaptive Systems

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	A fixed suspension damping characteristic is a compromise. Under certain suspension movements, the ride is likely to be under or overdamped. We have done significant work with Adaptive Damping Systems (ADS™) to improve ride performance and to increase operational effectiveness.
Hydrostrut from the Qinetiq 6x6 demonstrator with seven state ADS™ system.		Close up of the G6 Rotary Damper with ADS™, this is a two stage valve which gave an overall improvement of ride of 25% in terms of reduced crew shock acceleration levels.

Track Tensioners

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We have designed a range of track tensioning systems depending of the type of track used and the duty cycle for the vehicle.

The basic system is a grease activated unit using a standard grease gun. The correct tension is achieved by pumping grease into the track tensioner which extends. There is also a pressure relief valve which is set below the maximum tension for the track. In the event of overload, such as can occur when a track is shed, the relief valve opens and dumps grease to allow the tensioner to retract and release tension.

We have also designed and developed a driver controlled system that uses a small hydraulic pump to extend the track tensioner. There is a hand powered backup system used for maintenance and in the event of electrical failure. There is also a safety overload valve which prevents excessive track tension.

The driver can select normal or high tension depending on the expected terrain.

Running Gear

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For AS90, we supplied the complete running gear system. This covered the track (Diehl 640), roadwheels, top rollers & brackets, idler gear & track tensioners plus the Hydrogas wheel stations. By opting for an integrated package, the Prime Contractor - BAE Systems was able to ensure the all the running gear elements worked well together.

By combining supply of the running gear, we can offer attractive package deals for the Prime Contractor as well as insure that the running gear is designed as an integrated system.

The picture to the right shows components form the AS90 running gear package.

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