In 2024, Parker Hannifin announced the launch of a new truck hydraulic pump—the F4 series. This article mainly explains some features of this pump and see if they can be applied to other application areas.
1. What’s special about this pump?
This pump has two main features:
(1) It’s a dual-flow pump, meaning it has two flow paths. How does a fixed-displacement pump achieve dual flow?
(2) It’s a separable pump. What does it separate? Why separate it? How? First, let’s give a basic introduction to this F4 series separable dual-flow pump: It’s a bent-shaft type axial piston fixed-displacement pump with a maximum working pressure of 400 bar. It has two different displacement specifications: 55/52 and 70/36 cm³/rev. (We’ll explain why there are two displacement values later.) The 70/36 model has a maximum flow rate of 125/65 L/min. It uses standard hydraulic oil with a minimum fluid temperature of -40°C and a maximum temperature of 115°C. This pump weighs approximately 29.5 kg and has a maximum operating speed of 2550 rpm. The basic parameters are as follows:
2. Dual-Flow Pump
The image below shows the external shape of the F4 pump. Its inlet and outlet are axial ports, both located on the rear end face of the rear cover. The ports are distributed as one suction port but two outlet ports, port A and port B. This is different from most pumps on the market. Other pumps, whether gear pumps, vane pumps, or piston pumps, mostly have one inlet and one outlet. This pump, however, has two outlet ports. This is likely a design specifically for the unique needs of truck hydraulic systems. Furthermore, the displacement of these two ports is different. How is this achieved?
The functions of this dual-outlet design are:
(1) The pump can simultaneously power two independent operating functions, increasing the speed of the actuators and improving operational accuracy.
(2) Another advantage is flow control. The two actuators can operate under various conditions, such as high flow rate, low flow rate, or equal flow rate. By appropriately constructing the hydraulic system, the dual-flow pump can provide three different flow rates at the same engine speed. My understanding is that if the two outlets are directly connected to the two actuators, the possible operating conditions include:
① Full flow at outlet A, no action at outlet B;
② Full flow at outlet B, no action at outlet A;
③ Both outlet A and outlet B are active, in which case the hydraulic oil preferentially flows to the circuit with lower pressure.
Adding functional valves to the circuit, such as flow divider/combiner valves, can achieve more precise flow control functions.
3. Separable Pump
Having understood the dual-flow design, let’s look at what a separable pump is.
As shown in the diagram, this pump has another unique design: a pneumatically controlled cylinder structure is integrated in the middle of the pump, between the input shaft and the rotating assembly. Only about 5 to 10 bar of pneumatic pressure is needed to move the pneumatic cylinder. The pump’s separation is achieved through a pneumatic switch.
When there is no air input, the engine is connected to the pump’s main shaft, which in turn rotates with the internal rotating assembly.
When pressurized air is input, the rotating assembly is separated from the input shaft. The engine then only drives the main shaft to rotate, while the cylinder, pistons, and other rotating components are disconnected and stop rotating, thus consuming no more energy and achieving energy savings.
The official promotional materials state that the F4 series pump integrates a coupler, enabling dynamic engagement and disengagement of the pump. By pressing a button on the dashboard, the pump can be engaged or disengaged from the diesel engine without shutting it off.
The following is the program control logic for switching off the hydraulic pump: Why is it only allowed to be used when the speed is below 1000 rpm, but there is no signal when the speed is above 1000 rpm? Is this a special requirement for truck applications?
