SubscribeTo gain higher GVW with in-service vehicles one need an integrated solution improving its power pack, power train, suspensions, steering and driving systems.
M113A2IV
The M113A2IV is an Improved Version of the M113A2. It was upgraded to a GVW of 15,300 kg by AOB. A prototype has already been built, tested & approved for serial production for the Israeli Defense Forces (IDF)
Due to the vehicle's increased weight there is a need for the power train upgrading. Several options were considered by AOB and after comprehensive analysis of both technical and operational requirements AOB came with a solution based on a 275 BHP power train, which, along with integration of other systems, classifies this vehicle as M113A2IV.
Power Pack Assembly
The Power-Pack re-powering program is based on the following major components:
- A DDC diesel engine rated at 275 BHP.
- An Allison automatic transmission:
Based on our experience, accumulated during the service of the Allison TX100-1 used in the M113A1/A2 and based on our calculations due to the requirements for higher input power as results from the vehicle higher weight, Allison, the transmission manufacture, developed the TX100-1A transmission which is now installed in the M113A2 IV.
- Improved M113A2 cooling system:
The M113A2IV cooling system is an improved version of the M113A2 based on improved radiator (in the same geometric layout) and higher fan speed.
- Improved braking system:
The system is originally designed for an 11 ton GVW vehicle and does not perform satisfactorily at higher weights, hence can cause serious safety problems, mainly on road operation. The improved braking system was tested under severe conditions of braking and approved for use at GVW of 15.3 ton.
- The solution is based on two major improvements as follows:
Direct: An improved lubrication & cooling of the differential brakes.Indirect: An add-on retarder (engine brake ) for reduction of brake use
- Improved final drives with 4.75:1 gear ratio:
The standard M113A1/A2 final drive with a gear ratio of 3.929:1 is good for vehicles up to GVW of 12,500 kg, for heavier GVW, from 14,000 kg. to 15,300 kg, a final drive with gear ratio of 4.75:1 is more suitable. This final drive has the same original M113A1/A2 housing. This gear ratio will give the upgraded M113 a top speed of 32 MPH and a total performance package which is better than the original vehicle even with the higher GVW.
- Improved drive shafts with 7C size:
Due to the high engine output and higher vehicle weight, the loads transmitted through the U-joints and drive shafts will be too high for the current 6C size units. The components durability will be unacceptable. Based on this, all U-joints and drive shafts are replaced by 7C size ones.
- Improved air intake system:
The combustion air flow required by the 275 BHP engine is higher than the required flow for the 215 BHP one. In order to meet this air flow demand, a new air filter element, of improved media, is used in the air cleaner housing.
- Improved exhaust system:
Due to the high exhaust gases flow, the exhaust system of the 275 BHP engine is equipped with a new muffler and new pipes between the turbocharger outlet and the muffler and between the muffler and the top deck.
Suspension System
A good suspension can compensate for poor performance of power-pack and use the power to its maximum. In many cases the suspension contribution to the mobility is bigger than that of the power-pack. The improved suspension in the M113A2IV was tested and approved for 15.3 Ton vehicles. The kit contains: 4 shock absorbers on each side, new torsion bars of 15.3 ton GVW, steel made road wheels and stronger idler wheel adjuster mounts.
Comparison tests conducted between M113A2IV and M113A3 @ 300 BHP (using standard M113A2/A3 suspension), showed superiority of the system described here. All vehicles had 14 tons GVW. At cross-country terrains the M113A2IV was faster than the M113A3. The subjective feeling of the crew members was much better, compared to the standard suspension. It was mainly reflected in the pitch vibrations.
After the tests, the ground clearance of the vehicles with the improved suspension remained the same while the ground clearance of the vehicles with the standard suspension was reduced in about 20-30 mm.
Driver Controls
The weak point of the M113A1/A2 steering system, mainly from the safety aspect, is the two levers actuating system. The braking of the vehicle by pulling the two levers simultaneously is not stable and any difference in the pulling force can cause to rotation of the vehicle around its vertical axis. The steering control by pulling only one lever is acceptable under normal steering, but steering and braking together create dangerous situations.
AOB driver's control system replaces the steering sticks by a hydraulic power assisted steering wheel and a foot brake pedal.
The M113A1/A2 improved steering and braking system, developed by AOB and tested by the Israeli Defense Forces (IDF), is based on activation of the differential brakes by two separate control systems:
- A steering wheel that activates only one brake at a time at the appropriate side.
- A braking pedal that activates both brakes at the same time and with the equal forces.
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