Case 3550 Crawler Dozer Service Manual

Table of Contents

1. Generalities
2. Engine
3. Transmission
4. Final Drives
5. Brakes and Steering differential
6. Undercarriage
7. Dozer Equipment Hydraulic System
8. Electrical System

Manual Extract: HYDRAULIC STEERING SYSTEM

The steering and the equipment control circuits are within one single hydraulic circuit using the same oil.
The two circuits, although they share some hydraulic components, will be described separately.
The equipment control circuit is described in Section 6 – EQUIPMENT HYDRAULIC SYSTEM.
The two circuits have independent operating pressures: – steering circuit max. press. 350 ± 5 bar – equipment circuit max. press. 200 ± 5 bar.

The steering circuit main components are: – An hydraulic piston pump for steering / equipment circuits (P)
– An hydraulic motor (M)
– A steering / equipment control valve (D) – A steering pilot valves block (Vp)
– A feed valve block (Va)
– Two steering control levers (Ls)
– An oil cooler (S)
– A CONTROL UNIT-Microcontroller (C)

The D350 is equipped with a steering differential that allows a dozer to have continuous power on both tracks when steering, varying track speed without ever stopping it. The speed of a track will increase or decrease equally with respect to the other track, without any power loss in load pushing cycle. This system is particularly profitable also in finish dozing applications, specially in restricted areas.

When the operator shifts the steering levers (Ls), their movement is transformed into an electric signal that is sent through the CONTROL UNIT (C) to the steering pilot valves block (Vp), that will operate piloting directly the steering spool (1) of the control valve (D).

The piston pump (P) driven by the torque converter feeds both the steering and the equipment circuits by means of the control valve. The regulation of pump delivery sharing system operates with steering priority logic, through the Load Sensing signal between control valve and pump.