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JeepEV: Electric Vehicle Conversion Project
Power Steering

« March 2004 »

     Before the conversion, the Jeep used a typical mechanical power steering pump. The pump was bolted to the Internal Combustion Engine and received mechanical power from the main drive belt, which also drove things like the alternator, water pump, etc. This pump was bulky and I removed it from the Jeep along with the I.C.E.

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The Jeep's old Mechanical power steering pump and reservoir.

     With the mechanical belt-drive of the I.C.E. gone, I had to come up with another way to power a pump. The Jeep's new electric motor does have an accesory driveshaft which I could have used to drive the old mechanical pump. However, doing so would involve rigging up a pulley and belt system, which would have been complicated. Also, using a mechanical pump would have meant that power steering wouldn't function unless the vehicle was moving, since the electric motor does not "idle" like an I.C.E. does.

It was therefore decided that using an electric power steering pump was the best option. However, electric power steering pumps aren't all that common yet, thus few models of vehicles come with an electrical power steering pump from the factory. One car that does use an electric power steering pump is the second generation Toyota MR2. These cars utilize a power steering pump that consists of a 12 volt motor and hydraulic pump head in one self-contained unit. So, I purchased an MR2 power steering pump on the advice of the members of Austin EV. I purchased the pump from a salvage yard.

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The electric power steering pump from a Toyota MR2.

     I decided to mount the new power steering pump under front battery rack #2. This puts it between the vacuum system components and the steering gear box, which is mounted to the driver's side frame rail nearby. The pump already had two pre-threaded holes on the side where the hydraulic lines connect, and one pre-threaded hole in the rear. I used a piece of flat steel and a section of "L" channel welded to the underside of the battery rack to extend down to the hole in the rear. I then used the appropriate metric bolt to secure the pump to it. For support from the front, I welded a small piece of "L" channel to the underside of the battery rack, and bolted a bolt through it and into the threaded hole on the pump.

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The power steering pump is mounted under the front battery rack.

     Also in the power steering system is a small reservoir which holds about a pint of fluid. Another member of AustinEV was kind enough to donate a toyota power steering reservoir to me (it was from a Celica). I decided to mount the power steering reservoir between the controller and the driver's side inner wall of the engine (now motor) compartment.

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The power steering reservoir.

     The power steering reservoir's inlet comes out of the bottom of the reservoir, while the outlet comes out of the side. In order to be able to set the reservoir on the flat surface of the motor compartment fender area I first drilled a hole through the flat surface. I then routed the intake hose from the steering gear box to the reservoir, and installed hose clamps on both ends. Next I attached the output hose to the reservoir, routed it under the controller mount, and connected it to the inlet of the power steering pump. After filling the power steering system with standard Automatic Transmission Fluid, I had power steering which works quite well (oh yeah!).

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The power steering reservoir is hooked up and ATF is added.

     The following is some info about the electrical side of the new power steering system. The MR2 pump head runs off of the 12 volt system. However, it is no small load to the electrical system as it can pull up to 75-80 amps @ 12 volts when the steering wheel is turned close to a stop. It of course pulls less power when the wheel is centered because mechanical load on the pump is reduced. To handle the switching of this load I had to use a heavy duty relay. The relay I ended up using is a 75 amp power relay made by Bosch. this relay is triggered by the ignition switch, so the pump runs anytime the Jeep is on. Also, I used an 80 amp, automatically-resetting circuit breaker as the means of circuit protection for the pump.

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The pump is switched through a power relay and self-resetting circuit breaker.

« June 1st, 2007 »

     I get a lot of questions regarding the specific parts I used to control my electro-hydraulic power steering pump. To clarify, the power steering pump is controlled either full on or off by a power relay and its circuit is protected by a high-current circuit breaker.

The relay I used is pictured above. It is a SPST (Single Pole, Single Throw) relay with 75-Amp rated contacts and a 12-volt coil. The manufacturer is Bosch and the part number is 0 332 002 156. Note that this relay has integral parallel and series diodes to help control the voltage spikes from shutting off the pump motor. A relay without integral diodes could've been used, but would have required the installation of at least one external "freewheeling" diode to prolong the life of the relay.

The circuit breaker is part of the HI-AMP line manufactured by Buss. It is an 80-Amp rated, self-resetting circuit breaker, Buss part number 181080F. I feel that it is important to have a self-resetting breaker in this application because sudden and prolonged loss of power steering could create a safety hazard if you aren't expecting it. The self-resetting breaker helps to avoid this situation because it will attempt to reset even if the output is shorted... and while this could create problems in itself, I belive this would be the lesser of two evils.

« March 2004 »

     As a final convenience I used a small gray type Anderson connector to connect the wires coming out of the pump head to the pump relay. I found this was a smart idea because I can now easily connect/disconnect the pump (of course!)

     As a last note, the MR2 Power steering pump has an extra four-wire wiring harness coming out of it. This harness originally connected to a computer on the MR2 which varied the speed (through Pulse Width Modulation) of the pump in relation to the vehicle speed. This makes sense because the pump really never needs to run at full speed while the vehicle is moving since once the tires are rolling, less force is required to steer. At this time I haven't connected these wires to anything, but in the future I plan to make a PWM controller circuit for the pump.

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