SECTION HYDRAULIC SYSTEM

Transcription

1 / 1 SECTION GENERAL DESCRIPTION 7 1 This system uses hydraulic power to operate a fan that forces outside air into the radiator located on the left-hand side at the rear of the bus. The cooling effect of this fan allows for the simultaneous temperature reduction of the coolant, hydraulic system oil and engine intake air. On hybrid vehicles, the EV Drive and Dual Power Inverter Module coolant is also cooled by this fan. A dual-action pump activates the fan motor while providing hydraulic fluid and the pressure required for the steering system. Since the cooling system is not linked through a mechanical driveshaft, it provides maximum effectiveness in different operating conditions. OPERATING PRINCIPLE See Figure A pump provides the hydraulic power required for operation of a motor that drives the cooling system fan. This pump is driven by the air compressor's drive through power take-off. The engine's ECU modulates fan speed according to coolant temperature and air intake temperature through a solenoid with electroproportional action, mounted on the radiator fan motor. See Figure 2. The electroproportional valve opens for air intake or when the engine coolant is cold, which allows the oil to bypass the hydraulic motor and thus slow down the fan. When the coolant or intake air gets hot, the valve closes progressively. See Figure 3 for temperature control. This will increase the speed of the hydraulic motor in proportion to the rise in temperature HYDRAULIC MOTOR 2. FAN SIDE PUMP 3. STEERING GEAR HOUSING SIDE PUMP 4. HYDRAULIC TANK 5. HYDRAULIC TANK OIL FILTER 6. HYDRAULIC TANK VIEWING SIGHT GLASS 7. RADIATOR Figure 1 - Diagram of The Hydraulic System Figure 2 - Motor with electroproportional valve

2 CLOSED OPEN 2 / THERMOSTAT OPENING COOLANT TEMPERATURE FAN SPEED* FAN OFF FAN ON AIR INTAKE TEMPERATURE FAN SPEED FAN OFF FAN ON 135 F 150 F 165 F 180 F 190 F 200 F 210 F (57 C 66 C 74 C 82 C 88 C 93 C 99 C) *COOLANT TEMPERATURE ENGINE SPEED FAN SPEED < 180 F < 82 C > 200 F > 93 C Engine Cold Engine Hot Low idle 690 to 760 rpm 150 to 180 rpm Full speed 2200 to 2400 rpm 200 to 240 rpm Low idle 690 to 760 rpm 600 to 800 rpm Full speed 2200 to 2400 rpm 1665 to 1750 rpm Figure 3 - Operating Temperature Diagram OPERATING TEMPERATURE The operating temperature diagram in Figure 3 shows the cooling system s operation. At any temperature under 180 F (82 C), the thermostat is closed. In such conditions, there is no coolant flow in the radiator and the fan operates at a minimum speed. When the thermostat gives a temperature of 180 F (82 C), it starts to open. As the temperature rises, the thermostat opens progressively until it reaches its full opening temperature of 200 F (93 C). Meanwhile, when the coolant temperature reaches 190 F (88 C), the fan begins to accelerate and continues to do so until it reaches its maximum speed at 210 F (99 C). When the temperature exceeds the normal operation cycle interval and reaches 225 F (107 C), a warning light tells the driver that the engine is overheating. If the temperature keeps on rising to 235 F (113 C), the engine then automatically shuts off. On hybrid vehicles, the E V drive coolant oil is not monitored and does not activate the fan for cooling. SYSTEM COMPONENTS See Figure 4. All hydraulic system components, except the steering gear housing, are located at the rear of the bus. See Figures 1, 2, and 4. They are accessible through the ENGINE ACCESS DOOR. The main components of the system include a dual pump, a motor equipped with an electro-proportional piloted control valve, a hydraulic tank and a filtering element with a rating of ISO 16/13/04. See Figure 5. The four types of connectors listed below are used for connecting the various hydraulic system elements: - ORS - SAE 37 - SAE O RWG - NPT piping See section 99: GENERAL PRACTICES for further information on hydraulic lines and connectors.

3 / 3 (ENGINE SIDE) ENGINE COOLANT TEMPERATURE ECU CAC TEMPERATURE MOTOR WITH ELECTRO PROPORTIONAL VALVE OIL COOLER FAN STEERING (SEE SECTION 07) TANK ASM FILTER Figure 4 - Hydraulic Circuit Components The system also contains the following elements: ANTI-CAVITATING CHECK VALVE The anti-cavitating check valve is included in the motor control block assembly, and prevents cavitation that could occur due to the fan s inertia when the engine rapidly decelerates. COOLANT TEMPERATURE SENSOR This sensor is part of the engine assembly. It is located near the thermostat housing on the engine. It is simply an electrical transducer that varies voltage when the intake air temperature is between 190 ºF (88 ºC) and 210 ºF (99 ºC). AIR INTAKE TEMPERATURE SENSOR This sensor is part of the engine assembly. It is located at the engine's air intake. It is simply an electrical transducer that varies voltage when the intake air temperature is between 135 ºF (57 ºC) and 165 ºF (74 ºC).

4 4 / REPLACEMENT Dirty hydraulic systems can quickly clog a new filter element, making cleanliness a vital aspect. It is important to remove any dust from the external surfaces of the filter assembly, and to plug all piping to prevent any dust or dirt from entering the system. Hydraulic fluid should always be filtered through at least an ISO 16/13/04 rated filter before the system is topped with fluid. When the pump, motor, steering gear housing, hydraulic tank, filter or hydraulic lines have been removed or dismantled for replacement or complete maintenance, the hydraulic system should be drained before it goes back into operation. It is then recommended to perform a dialysis. PUMP AND MOTOR A proper dialysis is the only specific adjustment required when these components are replaced and installed on the vehicle. The manufacturer makes all adjustments to follow specifications required for the vehicle's cooling system. Appropriate part numbers are detailed in the Nova Bus Parts Manual. TANK AND FILTER TANK See Figures 5 and 6. The TANK accommodates the needed volume changes associated with the expansion or contraction of hydraulic oil, the flow of the system, and minor leaks. The tank is designed to support maximum volume change when the system is running and it expels air from the fluid flowing in the tank. The tank is not pressurized, and has a breather that enables the flow of air, while keeping dust and dirt out. The tank is accessible through the ENGINE ACCESS DOOR located at the rear of the vehicle. FILTER See Figure 7. A disposable filter element is contained within the tank. The cooling and steering systems share this filter. RADIATOR See section 09: ENGINE COOLING for radiator information. The same oil is used in both the hydraulic and steering systems, and is stored in the same tank. HYDRAULIC PUMP LOCATION HYDRAULIC OIL SAMPLING PORT COVER FILL PORT HYDRAULIC OIL SAMPLING PORT PRESSURE SWITCH BREATHER HYDRAULIC TANK AND FILTER LEVEL INDICATOR Figure 5 - Hydraulic Components Figure 6 - Hydraulic Tank and Filter Assembly

5 / 5 PERIODIC MAINTENANCE HYDRAULIC INSPECTION The system should be periodically checked for oil leaks as well as damaged lines and piping. See Section 99: GENERAL PRACTICES for further information on hydraulic lines and connectors. Make sure all the hardware is properly tightened and in good condition. The hydraulic fluid filter should be replaced at manufacturer recommended intervals. See TANK AND FILTER in this section for the recommended intervals. The oil level can be quickly checked through the sight glass indicator on the hydraulic tank. In addition, an optional LOW LEVEL PROBE WIRE located on the side of the tank will light a tell-tale on the instrument panel and alert the operator when the oil level is low. See section 19: FLUIDS AND LUBRICANTS in this manual to obtain the recommended oil type for the hydraulic system. It is also important to take an oil sample for analysis during inspection. An oil sampling port, located at the rear of the vehicle (see Figures 5 and 6), permits a dialysis of the hydraulic fluid. The samples can be analyzed by the user, or submitted to either Nova Bus or a contractor. Trends or problems that are related to fluid cleanliness will be identified by a sample analysis. Contact your local service representatives for correct test methods and equipment support. HYDRAULIC OIL LEVEL CHECKING TORQUE COVER TO 80 LB/IN (9 N M) FILTER COVER WITH AN O-RING AND A SHIM BREATHER Checking the level of the hydraulic oil can be done while the engine is operating or not. Use the SIGHT GLASS INDICATOR located on the side of the tank to check the level of the oil. See Figure 8. The level of the oil should be approximately at the centerline of the indicator, and not lower than ¼ in. (6 mm) above the red line. If the oil level is outside these limitations, oil must be added or removed accordingly. RETURN INLET HEAD WITH O- RING If the oil level becomes too low, the hydraulic system will begin to take in air. The tank and filter assembly may begin to leak oil, creating a false impression that there is a surplus of oil in the system. FILTER ELEMENT BYPASS TUBE CORRECT OIL LEVEL BYPASS SPRING VALVE RED LINE = VERY LOW OIL LEVEL Figure 7 - Hydraulic Filter Assembly Figure 8 - Sight Glass Indicator

6 6 / FILTER CHANGE See Figure 7. It is recommended to replace the filter element when there are indications that a filter change is needed or at specified intervals, but not to exceed 6 months. Failure to change the element will cause the system to go on bypass. The frequency of filter changes may increase according to operating conditions. Purge the air from the power steering hydraulic circuit after each maintenance procedure. Oil cannot pass through the filter when it is clogged. The oil will be forced into the bypass tube, where it builds pressure. The bypass spring valve opens when the pressure reaches 50 psi (345 kpa). A pressure switch on the filter assembly will light a tell-tale on the engine box when the pressure reaches 35 psi (241 kpa) and closes the switch. CAUTION: To avoid serious damage to the equipment DO NOT re-use old filter elements or run the system without a filter element installed. Filter elements are not reusable and cannot be cleaned. 1. To access the hydraulic tank open the ENGINE ACCESS DOOR at the rear of the vehicle. 2. Disconnect the fitting located on the bottom of the tank (Figure 9) and drain the oil into an appropriate receptacle. 3. Wipe the tank and filter assembly with a dry, clean, and lint-free cloth. 4. Turn the filter cover (Figure 10) counter-clockwise to engage the AUTO-PULL ELEMENT REMOVAL TABS of the cover with those of the filter element. Once the tabs are engaged, pull the cover to lift the filter element out of the tank. 5. Separate the cover from the filter element and rinse the cover in a solvent strong enough to dislodge all accumulated dirt. 6. Lightly lubricate the new o-ring and shim with clean hydraulic oil and replace the o-ring and shim on the cover. 7. Attach a new filter element to the cover, engaging the AUTO-PULL TABS. See the Nova Bus Parts Manual to determine the appropriate filter. 8. Insert the new filter element into the tank and firmly tighten the cover. See Figure 7 and 10 for torque values. The AUTO- PULL TABS will disengage themselves. 9. With pre-filtered fluid, fill the tank using the PRESSURIZED OIL FILL PORT (Figure 6) with the designated oil, and drain the power steering circuit. WARNING: Before starting any work, make sure the vehicle is completely and securely stationary. Disconnect the starting circuit on the control box at the rear of the vehicle and place the battery disconnect switches to the OFF position. CAUTION: The filling oil must be filtered through at least an element rated ISO 16/13/04. FILTER COVER TORQUE TO 80 LB/IN (9 N M) Figure 9 - Tank bottom Figure 10 - Filter Cover

7 / 7 HYDRAULIC OIL CHANGE As a general guideline, it is recommended to change the oil at the suggested intervals. NOTE: See section 19: FLUIDS AND LUBRICANTS of this manual in order to obtain the recommended oil type for the hydraulic system. Remember that more frequent oil changes could be required during certain operating conditions. Monitoring the fluid quality, by using the sample port to easily access test fluid, will help indicate quickly if change is required, encouraging better judgement of change frequency. DRAIN PROCEDURE 1. Remove the drain plug at the bottom of the hydraulic tank. See Figure Allow the hydraulic oil to drain in an appropriate container. 3. Reinstall the drain plug and tighten. 4. Wipe the tank with a dry, clean, and lint-free cloth. FILL PROCEDURE 1. Plug the drum of new oil into the system through the quick connect fitting (oil fill port). See Figure Fill the tank until the fluid level indicator indicates a correct oil level. See Figure Do not disconnect the new fluid line. Start the engine and let it run for 2 minutes at fast idle (1,200 rpm). 4. The fluid level will drop significantly; fill the tank until the level indicates a half full tank. 5. Turn off the engine and disconnect the supply line. 6. Wipe the tank with a dry, clean, and lint-free cloth. TECHNICAL SPECIFICATIONS FILTER Brand... PALL Filter element... 4 in. long Ultra-pleat (ISO 16/13/04) TANK Capacity (full level) l (low level)...7 l Leak test at...5 psi (34.5 kpa) TANDEM GEAR PUMP Brand...PARKER Series...PGP517 Rotation (when viewed on driveshaft)...clockwise Maximum speed... 2,400 RPM PUMP 1 (FAN) Nominal displacement cc/rev Maximum pressure...3,200 psi (22,100 kpa) PUMP 2 (POWER STEERING) Nominal displacement cc/rev Controlled nominal flow /18.9/LPM at 800 RPM pressure adjustment...2,175 psi (15,000 kpa) MOTOR Brand...PARKER Model... PGM511 Nominal displacement cc/rev Pressure limited at psi (20,700 kpa)

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