Driving factors
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The Drive & Control Company Rexroth Bosch Group

Driving factors | Contents

Contents | Driving factors 3 Comparing drives with variable low speed and high torque The Hägglunds solution The Hydraulic Direct Drive (HDD) Geared solutions The Hydro-Mechanical Drive (HMD) The variable-speed AC Drive (ACD) The variable-speed DC Drive (DCD) 12 Installation Physical considerations Power considerations Control of speed and torque. The need to produce better material at an ever-increasing pace puts industrial drives in the spotlight. For processes to be at their most productive, the control of speed and torque in relation to the process is essential, as it has a strong...

Driving factors | Comparing drives with variable low speed and high torque Comparing drives with variable low speed and high torque A number of different solutions exist for achieving this control, and the best one is chosen according to the requirements of the application and environment. In this booklet, we discuss some of the criteria and evaluate the main contenders. ▶▶ The variable-speed AC Drive (ACD), which is connected to a gear reducer The basic components and characteristics of these drives can be seen in the diagrams on the following pages. ▶▶ The variable-speed DC Drive (DCD),...

Comparing drives with variable low speed and high torque | Driving factors 5

Driving factors | The Hägglunds solution Although still less common than other drive alternatives, the Hydraulic Direct Drive is making steady gains as industrial demands increase. Developed by Hägglunds, the Hydraulic Direct Drive is particularly effective in harsh environments and difficult or demanding operating situations. It is simple, versatile and user-friendly. The Hydraulic Direct Drive (HDD) An HDD is a closed system with a low-speed hydraulic motor at its heart. Notable for its ability to sustain high torque even at minimum speed, the hydraulic motor is Hydraulic motor mounted...

The Hägglunds solution | Driving factors 7 maintain full shaft torque continuously at zero or low speed, and since the electric motor is unaffected, no time restriction applies. (See figure 3.) In addition, an HDD can operate intermittently above its installed power rating with the same limitations that apply to any fixed-speed electric motor with an equivalent service factor. It is the operating torque and the desired service life that determine the size of the hydraulic motor. 100 Among the drive’s key operating advantages is its pre-set pressure-limiting function, which prevents maximum...

Driving factors | Geared solutions Geared solutions The traditional way of thinking when it comes to industrial drives is to use a medium- or high-speed drive motor, which can be either hydromechanical or electro-mechanical. In such a solution, the application speed is achieved by means of a gear reducer, which adds to the drive’s bulk and moment of inertia. The Hydro-Mechanical Drive (HMD) stop, a substantial amount of additional torque is placed on An HMD makes use of a medium- or high-speed hydraulic fatigue within the drive system and application. the driven shaft, which may lead to...

Geared solutions | Driving factors 9 200% overload, a few seconds only An ACD also creates harmonic distortion that can pollute the power distribution grid. This feedback has the potential to overheat transformers, cables and motors, as well as to damage electrical equipment connected to the mains. Though the installation of a low-harmonic converter or external filters can prevent this, both options add complex- Rated power ity and cost while increasing power consumption. Forced cooling A DCD, which combines an AC/DC converter with a DC electric motor, is a less common alternative to an ACD...

Driving factors | Geared solutions selection of a DCD must be based on its continuous torque capacity over the required speed range, its limitations at With a geared drive solution, the electric motor, gear lower speeds lead to over-dimensioning. (For more on reducer and coupling is mechanically connected to the driven shaft, often requiring considerable space around the machine. A direct drive is much more compact. A geared drive solution will also generate high additional torque in case of sudden speed changes caused by heavy shock loads. Failure to compensate for these can lead to...

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Driving factors | Installation Since space is often limited in industrial applications, the physical size and flexibility of an installation are key factors in selecting a drive system. Thought must be given not only to the drive components themselves, but also to the foundations and other accessories that may be required. Physical considerations which means that no foundation has to be built and no When using an HMD, ACD or DCD, all of which require a coupling, and the drive unit can be installed in any conve- gear reducer between the motor and the driven shaft, a good deal of space must...

Installation | Driving factors 13 the converter and the drive motor itself must all be ACDs and DCDs frequently cause harmonic distortion, upgraded to operate at the higher voltage. The alternative which means precautions must be taken to limit the distur- is to install an additional transformer that converts the bances if one of these drive types is chosen. Harmonics can medium/high voltage to low voltage, but both options be reduced either by structural modification within the involve a substantial increase in the drive’s cost. drive system itself, or through the use of external...

Driving factors | Over-dimensioning To handle the demands of high-torque, low-speed applications, HMD, ACD and DCD systems must all be over-dimensioned. This protects them from the peaks associated with starting torque, shock loads and other operating factors, but it also creates built-in losses within the drive system that reduce efficiency. Over-dimensioning of gear reducers Gear reducer losses due to over-dimensioning HMD, ACD and DCD systems all use gear reducers to Gear reducer efficiency is normally expressed at rated achieve the c ombination of high torque and low speed. conditions....