Escape/Mariner Hybrid SUV

By Glen Beanard technical contributor

The hybrid Escape and Mariner vehicles are full hybrid vehicles. Being a full hybrid means that, at times, the vehicle will run 100% on electric power only. In fact, it is capable of traveling up to 25mph (40kph) without ever starting the engine. At times, the engine may shut off at speeds as high as 40mph (64kph). Plus, when conditions are right, the engine may shut off at stops and not restart until after 25mph. As a result, the advertised fuel economy of a full hybrid vehicle is typically much higher for the city driving conditions than the highway driving conditions. In theory, assuming the person s trip was short enough, a person could drive in slow moving stop and go traffic without using any gasoline at all. How is all of this achieved? And what does it mean to the service technician?

Hybrid Operation Modes

The high voltage electric motor and 4 cylinder engine will trade off between each other while driving, as well as team up at times to propel the vehicle. The electric motor also plays an equally important role during braking and recharging the vehicle s batteries. The PCM decides when to trade one power source for the other and when to team them up.

Startup: When the key is first turned to the start position, the engine will start up. Since there is no conventional electric starter on the vehicle, this action is performed by the 330 volt electric motor located inside the transmission. There is no starter noise that is normally associated with an engine under crank conditions. The only noise is the engine suddenly running. If the high voltage battery has a proper charge, and the climate control demands will allow it, the engine will shut back off after a minute or two.

Electric Drive: The first movements from the vehicle, under light throttle, are silent as only the electric motor propels the vehicle along at slow speeds. It will remain in electric drive mode up to 25mph under light throttle as long as the HV batteries do not run low on charge or too hot, or the climate control needs do not demand the engine to start.

Regenerative Braking: During the deceleration process, the traction motor becomes a voltage generator. This effectively slows the vehicle down in conjunction with the friction brake system. The traction motor is capable of generating up to 397 volts and 78 amps. The high voltage generated from the traction motor is sent to two different locations. One location is the high voltage batteries under the floor of the cargo area, (See high voltage battery pic)

and the other is the DC to DC converter located on the right inner fender. (See DC to DC convert pic)

The DC/DC converter replaces the need for a belt driven alternator. The DC/DC converter steps the high voltage down to 12 volts. During this voltage step down process, the output amperage is multiplied. The DC/DC converter is equal to a 110amp alternator. This serves to power the 12 volt electrical system and recharge the conventional lead/acid 12 volt battery under the hood. The ABS module calculates the amount of braking desired by the driver based on input from the accelerator pedal position sensor, the brake pedal pressure sensor on the master cylinder, and the longitudinal accelerometer. This information is shared with the PCM so that the PCM can control the transmission to generate voltage from the traction motor. Simply letting off of the gas pedal signals for some regenerative braking, applying the brake pedal signals for more.

Electrical Assisted Driving: Normally at highway speed. The gasoline engine is powering the vehicle. However, when more torque is needed (such as when passing), the electric motor will kick in and add it s torque to the driveline as well. As a result, the little 2.3L may now feel more like a 3.0L to the driver. At times, the electric motor may pull the high voltage batteries down to as low as 216 volts, and it may draw as much as 181 amps.

The engine used in the hybrid Escape and Mariner is a 133hp to 155 hp (model year dependent) Atkinson cycle 2.3L engine. An Atkinson cycle engine uses cam lobe profile to hold the intake valve open during a small part of the compression stroke. Doing this lowers the amount of energy used to compress the air/fuel mixture, allowing a 7 to 10 percent increase in fuel economy over a standard Otto cycle design. The transmission in the hybrid Escape/Mariner is an Electronically Controlled Continuously Variable Trans (eCVT). There is no actual shifting occurring in the eCVT because the gear ratios are achieved by a belt-like chain running inside of V shaped pulleys that vary their width as needed to walk the chain higher or lower in them. (See pic CVT1)

Since the engine is not always running on a full hybrid vehicle, some changes are made in regards to the brake system and power steering system as well as some operating differences in the climate control system.

Friction Brake System: Since engine vacuum cannot be relied upon to be present, the power brake system does not have a vacuum brake booster. This vehicle uses an Electro-Hydraulic brake (EHB) system. The EHB master cylinder is also referred to as an Actuation Control Unit (ACU). The bore of the ACU is called a pedal feel emulator and is primarily used simulate normal brake pedal feel for the driver. The pressure generated for the calipers is not, under normal conditions, the direct result of the driver s foot pedal efforts. Normally, this fluid pressure is generated by the ABS HCU and is regulated by the teamed efforts of the ABS and PCM s logic. Under normal conditions, the driver s pedal efforts are displaying to the ABS module as a request for braking. The ABS and PCM then divide the braking effects between the traction motor (for regenerative braking) and the friction brakes as needed. Only in the event that the ABS pump can t function to build pressure does the driver s pedal pressure directly provide the hydraulic pressure for the calipers. There are valves inside the HCU that allow direct passage from the pedal feel emulator chamber of the ACU, through the HCU, and to the wheels. This is called manual mode. In manual mode, there will be no boost so the driver will have a very hard/stiff brake pedal.

The replacement of the friction material is the same as with a conventional system, however, the ABS module does test the brake hydraulic system s integrity by pressurizing it during key-off events such as opening the door or whenever the dome light is activated, and again when the key is switched on. After 4 minutes have passed since the key had been switched off, the accumulator discharges it s stored fluid pressure back into the master cylinder reservoir. Before attempting friction material replacement, you must disconnect the battery to prevent the likely hood of an accumulator discharge event, or a system pressurization, during service. Ford also says to, in addition to battery disconnect, remove fuses 24 (50A) and 31 (50A) in the battery junction box.