S45 EPC and Its Fan Drive

In this post, we will introduce Danfoss S45 pump EPC (Electric Proportional Control) and how it works in hydraulic fan drive system.

1 What Is EPC

Overview

The EPC (Electric Proportional Control) consists of a proportional solenoid integrated into a Remote Pressure Compensated control. This control allows the pump to be operated at any pressure limit between the Load Sense and Pressure Compensation settings by varying the current sent to the solenoid. Danfoss EPC has two main types: Normally Closed and Normally Open. NO EPC control has the opposite characteristics to NC EPC, and only NC EPC can be used in fan drive system, so only NC EPC is analyzed in this post.

Structure ViewFrame L&K EPC Control

Frame J&F&E EPC Control

EPC Characteristic – Normally Closed

When an electric current is sent to the Normally Closed configuration control, the pump pressure decreases proportional to an increase in current. When the load in the system changes, the pump will adjust its displacement to maintain the pressure demanded by the controlling current. This control is especially useful for fan-drives, due to the direct relationship between fan-speed and pump pressure.

Due to the nature of Electric Proportional Controls, the relationship between current and pump pressure is unique for each individual PC/LS pressure setting combination. The relationship between different PC settings and different LS settings on the Pressure vs. Current Characteristic curve are shown below. The hydraulic schematic for the Normally Closed Electric Proportional control is shown below as well.

2 How EPC in Fan Drive

The purpose of the fan drive system is to keep the system temperature at a constant level. While the direct drive solution cannot meet this requirement because of the change of engine speed. Hydraulic fan drive system is independent of the engine speed, the fan speed is controlled by the pump outlet pressure.

Danfoss S45 EPC offers this kind of solution for controlling constant system temperature as shown below. This solution consists of S45 EPC pump, L&K motor, HIC valve block and PLUS+1 controller.

The basic formulas for hydraulic fan drive system are related to the fan speed N, fan diameter D, air flow Q, and pump outlet pressure P.

Q = CQ·N·D3 (1)
P = CP·N2·D2 (2)
K = Ck·N3·D5 (3)

N – Fan speed; D – Fan Diameter; Q – Air Flow; P – Pump Outlet Pressure; K – Fan Power; CQ、CP、CK –Coefficient

System temperature is continuously monitored by sensors.
When temperature goes up, it means the cooling system needs more cool air, based on the formula (1), higher fan speed is required. Thus, higher pump outlet pressure is needed based on the calculation of formula (2).
Controller sends signal to EPC control, the max. limited pressure goes up, then pump displacement increases to reach the higher outlet pressure.
Finally, the fan speed increased because of higher delta pressure.
Vice vesa, when temperature goes down.