Manitowoc struts its stuff
AS MOBILE crane designs have developed over the years, one of the major design components – the suspension system on mobile all terrain cranes – has emerged as a major point of difference. The Grove all terrain mobile cranes incorporate an independent suspension system for each wheel. The independent hydraulic suspension cylinder is sealed inside two more cylinders for added protection. Each wheel has its own Mega-Strut which is attached to a floating wheel just above the wheel’s drive line and to the chassis above. It is a different concept to positioning the chassis on a rigid axle system.
One of the noticeable features is the higher ground clearance. The differentials are rigid mounted to the chassis and drive the wheel hub assemblies through live half shafts which means, that as the suspension of the crane is raised, so are the differentials giving the Grove true all terrain capabilities. The main power driveline along the length of the chassis remains aligned at all times whilst there is no side to side wheel interaction. Total vertical movement of the Mega-Strut is 300 mm. The whole suspension system, with a large commonality of parts across the model range, can be controlled from the cab taking it from a lowered position, to a travel height and to a raised position. Compared with conventional suspension systems, the use of independent struts reduces the weight of the suspension system; weight that Grove claims has been able to re-invest to provide a stronger crane with better lift characteristics. The Megatrak system also allows the use of deeper carrier cross sections which improve torsional strength.
Borger Crane Hire is a Sydney-based owner of several Grove all terrain cranes with the Megatrak system. The company finds that when working on sites with full counterweights, the operator does not have to lift any axles, which means better weight distribution over all wheels. “And, on the road it’s better handling, less effort with the steering wheel and a generally more operator-friendly situation,” says Shawn Borger. “More ground clearance, less moving parts, which mean less maintenance for us.”
One of the benefits welcomed by operators is the ability to manoeuvre on sites without having to remove counterweights. A Grove all terrain crane can arrive at a site, fit all of the counterweights and then steer and manoeuvre into position. Another aspect of the system is the all-wheel steerability. Across all of Grove ’s all terrain models, at no stage does an axle have to be raised whilst crab steering the unit on site. And that is with or without all the counterweight fitted. “It can be a significant time saving for our operators and thus a financial benefit for our customers,” says Gibb McKay of Williamstown Crane Hire in Victoria, who is a strong advocate of the system. “With the independent suspension, each wheel does its own thing, riding up and over uneven ground, thus helping maintain a steady level chassis. All axles remain in use at all times and weight is distributed more evenly.”
Another benefit is that the all-wheel crab steer can be achieved with all wheels at the one time – and again this enables the crane to manoeuvre quickly and easily. According to Grove, tyre wear is substantially reduced. The design of the system means there are no tie rods and wheels are far less likely to get out of alignment.
Source: Construction Contractor
5-Mar-2007