Triple Pump Controls With Speed Sensing Power Management

So far, three is the maximum order of multiple automatic controls of open circuit variabile displacement pumps for mobile applications. Two members of these controls are common to all architectures. Le. the pressure compensator or limiter (PC) and the flow compensator or limiter (Fe). which bound the components of the pump output power. The third member deals with the pump mechanical power and its match with the (diesel) engine. Two implementations are currently found: a) the torque limiter looks at the pump itself and bounds the input torque. It is sometimes extended to. two pumps by means of the symmetric exchange of pressure signals (summing torque limiter) b) the speed limiter (SL) looks at the engine and bounds its minimum speed by acting on the pump. whichever is the cause of the speed droop (pump itself or additional torque) 1. In case of two pumps, one of them works as master unit (with full triple control). and the other (with double control only) shares the same SL signal. In the Simplest configuration (engine plus one or two controlled pumps) the torque and speed limiter have the common advantage of making a pump/engine power ratio greater than one feasible. On the other side they are different in several respects. According to the current qualitative comparison, the torque limiter is said to be faster in response to load changes. operate on a wider range of engine speed. have less power consumption, and require a Simpler and modular hardware. Conversely. the speed sensing is said to use the full engine torque. adjust for altitude or engine deterioration effects. and allow for additional power demands. These pros (and implicit cons). however. miSS the key difference. namely that the torque limiter implies high priority in use of engine power. whereas the speed limiter implies low priority. Such a priority attribute is probably one among the reasons why the torque limiter is much more popular in practical applications. In the same perspective. some problems are also to be seen which will be discussed in this paper.